KR101995777B1 - Backlight unit and liquid crystal display device including the same - Google Patents

Abstract

The present invention relates to a light guide plate, A light source positioned at one side of the light guide plate; A low refractive index resin layer disposed on the light guide plate and covering the first prism pattern having the first angle and the first prism pattern and a low refractive index resin layer formed on the low refractive index resin layer having a second angle different from the first angle, And a backlight unit including an optical sheet including a prism pattern.

Description

BACKLIGHT UNIT AND LIQUID CRYSTAL DISPLAY DEVICE COMPRISING THE SAME

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly, to a backlight unit and a liquid crystal display including the backlight unit, which can provide light with reduced thickness and high brightness.

A liquid crystal display device (LCD), which is advantageous for moving picture display and has a large contrast ratio and is actively used in TVs and monitors, exhibits optical anisotropy and polarization properties of a liquid crystal, And the like.

Such a liquid crystal display device has a liquid crystal panel in which a liquid crystal panel is interposed between two adjacent substrates through a liquid crystal layer as an essential component and changes the alignment direction of the liquid crystal molecules in an electric field in the liquid crystal panel to realize a difference in transmittance do.

However, since the liquid crystal panel does not have its own light emitting element, a separate light source is required to display the difference in transmittance as an image. To this end, a backlight unit having a light source is disposed on the back of the liquid crystal panel.

The backlight unit can be classified into a direct type and an edge type according to the position of a light source. The double edge type backlight unit has advantages in power consumption, thickness of a liquid crystal display device, and the like.

1, which is a schematic sectional view of a conventional edge type liquid crystal display device, will be described in more detail.

1, the liquid crystal display comprises a liquid crystal panel 10, a backlight unit 20, a main frame 30, a bottom frame 50, and a top frame 40.

The liquid crystal panel 10 is composed of a first substrate 12 and a second substrate 14 which are in contact with each other with a liquid crystal layer (not shown) therebetween.

First and second polarizers 19a and 19b selectively transmitting only specific light are attached to the outer sides of the first and second substrates 12 and 14, respectively.

The backlight unit 20 is positioned on the rear surface of the liquid crystal panel 10 and supplies light to the liquid crystal panel 10.

The backlight unit 20 uses a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp, and a light emitting diode (LED) do.

In particular, LEDs are widely used as light sources for displays, having characteristics such as small size, low power consumption, and high reliability.

The backlight unit 20 includes a light emitting diode (LED) assembly 29 arranged along the longitudinal direction of at least one edge of the main frame 30 and a white or silver reflective plate 25 A light guide plate 23 mounted on the reflection plate 25 and an optical sheet 21 disposed on the light guide plate 23.

The LED assembly 29 is disposed on one side of the light guide plate 23 and includes a plurality of LEDs 29a and an LED printed circuit board PCB 29b on which the LEDs 29a are mounted.

The liquid crystal panel 10 and the backlight unit 20 are composed of a top frame 40 which surrounds the top edge of the liquid crystal panel 10 with its edge surrounded by a main frame 30 having a rectangular frame shape, And the bottom frame 50 covering the backside of the main frame 30 are coupled to each other via the main frame 30 in the front and rear directions.

The light of the LED 29b is incident on the light guide plate 23 and then supplied to the liquid crystal panel 10 through the optical sheet 21. In the liquid crystal display of the above-

Since the light passing through the upper surface of the light guide plate 23 is inclined to the liquid crystal panel 10, it must be adjusted to be perpendicular to the liquid crystal panel 10 while passing through the optical sheet 21.

To this end, the optical sheet 21 includes a plurality of diffusion sheets and a plurality of light condensing sheets.

2, which is a schematic sectional view of a conventional optical sheet, will be described in more detail.

2, the optical sheet 21 includes a first diffusion sheet 21a, a first prism sheet 21b, a second prism sheet 21c, and a second diffusion sheet 21b which are sequentially stacked on a light guide plate (23 in Fig. 1) And a second diffusion sheet 21d.

Each of the first and second prism sheets 21b and 21c is formed with prism patterns 62 and 66 on the bases 60 and 64. The prism patterns 62 and 66 are formed on the prisms of the first and second prism sheets 21b and 21c, The patterns 62 and 66 are arranged so as to cross each other at right angles.

According to the optical sheet 21 described above, light emitted from the light guide plate 23 obliquely to the liquid crystal panel 10 is incident on the first and second diffusion sheets 21a and 21d having different refractive indices, And is processed perpendicularly to the liquid crystal panel 10 by the Snell's law in the second prism sheets 21c and 21d and the prism pattern.

However, the optical sheet 21 of the above-described configuration requires two diffusion sheets 21a and 21d and two prisms 21b and 21c, so that the thickness of the backlight unit 20 And as a result, it can not meet the demand for a thin liquid crystal display device.

In the present invention, the thickness of the backlight unit and the liquid crystal display device is increased by the thickness of the optical sheet.

In order to solve the above problems, the present invention provides a light guide plate comprising: a light guide plate; A light source positioned at one side of the light guide plate; A low refractive index resin layer disposed on the light guide plate and covering the first prism pattern having the first angle and the first prism pattern and a low refractive index resin layer formed on the low refractive index resin layer having a second angle different from the first angle, And a backlight unit including an optical sheet including a prism pattern.

In the backlight unit of the present invention, one of the first angle and the second angle is 70 to 85 degrees and the other is 85 to 95 degrees.

In the backlight unit of the present invention, the low refractive index resin layer has a refractive index smaller than that of the first and second prism patterns.

In the backlight unit of the present invention, the refractive index of the low refractive index resin layer is 1.1 to 1.3.

In the backlight unit of the present invention, the refractive indices of the first and second prism patterns are 1.5 to 1.65.

In the backlight unit of the present invention, the low refractive index resin layer completely covers the first prism pattern.

In the backlight unit of the present invention, the first prism pattern may be separated from the lower surface of the second prism pattern by the low refractive index resin layer.

In the backlight unit of the present invention, a diffusion sheet on the light guide plate and a base on the diffusion sheet are provided, and the first prism pattern is formed on the base.

The backlight unit of the present invention is characterized by including a reflector positioned under the light guide plate.

In another aspect, the present invention provides a liquid crystal display comprising: a liquid crystal panel; A light guide plate disposed below the liquid crystal panel; A light source positioned at one side of the light guide plate; A low refractive index resin layer disposed on the light guide plate and covering the first prism pattern having the first angle and the first prism pattern and a low refractive index resin layer formed on the low refractive index resin layer having a second angle different from the first angle, A liquid crystal display device including a backlight unit including an optical sheet including a prism pattern.

In the backlight unit according to the present invention, by using the laminate prism sheet, one diffusion sheet and one prism sheet can be omitted in the conventional optical sheet made of four sheets. Therefore, the thickness of the backlight unit and the liquid crystal display device is reduced.

Further, in the laminate prism sheet, since the first and second prism patterns are laminated with the low refractive index resin interposed therebetween, there is an effect that the problem of staining due to the contact of the prism with the stain due to the air gap is prevented.

In addition, in the laminated prism sheet, by changing the angle of the first and second prism patterns, the backlight unit provides light perpendicular to the liquid crystal panel, thereby improving brightness.

1 is a schematic cross-sectional view of a conventional liquid crystal display device.
2 is a schematic cross-sectional view of a conventional optical sheet.
3 is a schematic exploded perspective view of a liquid crystal display device according to the present invention.
4A and 4B are a schematic perspective view and a sectional view, respectively, of an optical sheet for a backlight unit according to the first embodiment of the present invention.
5 is a view showing a problem of staining in the optical sheet for a backlight unit according to the first embodiment.
6A and 6B are schematic cross-sectional views of an optical sheet for a backlight unit according to a second embodiment of the present invention.
7 is a view for explaining a path of light in an optical sheet for a backlight unit according to a second embodiment of the present invention.

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

3 is a schematic exploded perspective view of a liquid crystal display device according to the present invention.

3, the liquid crystal display includes liquid crystal panels 110 and 210, backlight units 120 and 220, main frames 130 and 230, top frames 140 and 240, and bottom frames 150 and 250 ).

The liquid crystal panels 110 and 210 serve as a key role in image display and include a first substrate 112 and a second substrate 212 which are bonded to each other with a liquid crystal layer (not shown) therebetween, and a second substrate 114, 214).

Although not shown, a plurality of gate lines and data lines cross each other on the inner surface of a first substrate 112 or 212 called a lower substrate or an array substrate, pixels are defined, and a thin film transistor (TFT) transistor: TFT) are connected in one-to-one correspondence with the transparent pixel electrodes formed in each pixel.

On the inner surfaces of the second substrates 114 and 214 called the upper substrate or the color filter substrate, color filters of red (R), green (G), and blue (B) And a black matrix for covering non-display elements such as a gate line, a data line, and a thin film transistor. In addition, a transparent common electrode covering these elements is provided.

When a signal is applied to the gate line to turn on the thin film transistor, a signal is applied to the pixel electrode through the data line. As a result, an electric field is formed between the pixel electrode and the common electrode, and the liquid crystal molecules of the liquid crystal layer are driven by the electric field.

The gate and data printed circuit boards 117 and 217 are connected to each other through at least one edge of the liquid crystal panel 110 and the connecting member 116 and 216 such as a flexible circuit board, And 230, respectively.

An alignment film (not shown) for determining the initial alignment direction of the liquid crystal is formed at the boundary between the first substrate 112, 212 and the second substrate 114, 214 of the liquid crystal panel 110, And a seal pattern (not shown) is formed along edges of the first and second substrates 112 and 212 and the second substrate 114 and 214 to prevent leakage of the liquid crystal layer filled therebetween. First and second polarizers (not shown) are attached to the outer surfaces of the first and second substrates 112 and 212 and the second substrates 114 and 214, respectively.

The backlight units 120 and 220 are positioned below the liquid crystal panels 110 and 210 to supply light and the liquid crystal molecules of the liquid crystal layer are driven to generate a difference in transmittance, The liquid crystal display device implements the image.

The backlight units 120 and 210 include light guide plates 123 and 223, reflectors 125 and 215, optical sheets 121 and 221, and LED assemblies 129 and 229.

The light guide plates 123 and 223 are positioned below the liquid crystal panels 110 and 210 and the reflection plates 125 and 225 are positioned on the back surfaces of the light guide plates 123 and 223. The optical sheets 121 and 221 are positioned above the light guide plates 123 and 223, that is, between the liquid crystal panels 110 and 210 and the light guide plates 123 and 223.

The LED assemblies 129 and 229 are positioned on one side of the light guide plates 123 and 223 to supply light toward the light guide plates 123 and 223. That is, the light emitted from the LED assemblies 129 and 229 is incident on the light guide plates 123 and 223 and then uniformly spreads within the light guide plates 123 and 223 by total reflection and passes through the optical sheets 121 and 221 And is provided to the liquid crystal panels 110 and 210 as a uniform surface light source.

The light guide plates 123 and 223 may include a pattern (not shown) having a specific shape on the back surface to supply a uniform surface light source. For example, the pattern may be an elliptical shape, a polygon shape, or a hologram pattern.

The reflection plates 125 and 225 reflect light from the back surfaces of the light guide plates 123 and 223 to increase light efficiency. As will be described later, the optical sheets 121 and 221 include a diffusion sheet and a laminate prism sheet.

The LED assemblies 129 and 229 are mounted on the LED printed circuit boards 129a and 229a and the LED printed circuit boards 129a and 229a that are disposed in parallel with the light guide plates 123 and 223, And a plurality of LEDs 129b and 229b that diverge.

The main frames 130 and 230 surround the side surfaces of the liquid crystal panels 110 and 210 and the backlight units 120 and 220. The bottom frames 150 and 250 surround the backlight units 120 and 220, . The top frames 140 and 240 cover the front edges of the liquid crystal panels 110 and 210 and are coupled with the main frames 130 and 230 and the bottom frames 140 and 240, .

Hereinafter, the configuration of the optical sheet will be described in more detail with reference to the drawings.

4A and 4B are a schematic perspective view and a sectional view, respectively, of an optical sheet for a backlight unit according to the first embodiment of the present invention.

As shown in FIG. 4A, the optical sheet 121 according to the first embodiment of the present invention includes a diffusion sheet 121a and a laminate prism sheet 121b. The diffusion sheet 121a is disposed on the light guide plate 123 and the laminate prism sheet 121b is laminated on the diffusion plate 121a.

The laminate prism sheet 121b includes a first prism sheet 164 composed of a first base 160 and a first prism pattern 162 and a second prism sheet 164 composed of a second base 170 and a second prism pattern 172, And a prism sheet 174. At this time, the first and second prism patterns 162 and 172 are arranged to cross each other.

Referring to FIG. 4B, the first prism sheet 164 and the second prism sheet 174 are attached to each other to form the laminate prism sheet 121b. The first and second prism sheets 164 and 174 are bonded together so that the first prism pattern 162 of the first prism sheet 164 contacts the second base 170 of the second prism sheet 174 do.

As described above, the light emitted from the light guide plate 123 is inclined to the liquid crystal panel 110 surface. The light passes through the laminate prism sheet 121b composed of the first and second prism sheets 164 and 174 and is processed into a light perpendicular to the surface of the liquid crystal panel 110. [

Therefore, as compared with the conventional optical sheet structure including two diffusion sheets and two prism sheets, one sheet of diffusion sheet and one sheet of prism sheet can be omitted. Therefore, the backlight and the liquid crystal display device The thickness is reduced. It also has advantages in terms of manufacturing cost.

However, some problems occur in the liquid crystal display device including the optical sheet according to the first embodiment of the present invention.

Referring to FIG. 5, since the first and second prism sheets 164 and 174 are not completely joined together, the gap between the first and second prism sheets 164 and 174 may be uneven, There is a wavy pattern called Newton's ring.

Air is present between the first prism pattern 162 and the second base 170 when the first and second prism sheets 164 and 174 are attached together to form the laminate prism sheet 121b, The aforementioned problem of staining occurs in the air gap. That is, the first prism pattern 162 and the second base 170 must be bonded together, but because the area of the bonding surface is insufficient, the bonding may not be partially performed, resulting in a gap difference. Accordingly, a difference occurs in the path of light, and Newton rings are generated due to optical interference due to the phase difference of light.

In addition, light is scattered at a point where the first prism pattern 162 and the second base 170 are in contact with each other, resulting in dot-shaped white spots on the screen or white spots.

An optical sheet for solving the problems of the first embodiment described above will be described.

6A and 6B, which are schematic sectional views of an optical sheet for a backlight unit according to a second embodiment of the present invention,

The optical sheet 221 according to the second embodiment of the present invention comprises a diffusion sheet 221a and a laminate prism sheet 221b. The diffusion sheet 221a is disposed on the light guide plate 223 and the laminate prism sheet 221b is laminated on the diffusion plate 221a.

The laminate prism sheet 221b includes a base 260, a first prism pattern 262, a low refractive index resin layer 266, and a second prism pattern 264. At this time, the first and second prism patterns 262 and 264 are arranged to cross each other.

The first prism pattern 262 is formed on the base 260 and the low refraction resin layer 266 covers the first prism pattern 262 and the second prism pattern 264 covers the first prism pattern 262, Is formed on the refractive resin layer 266.

The first prism pattern 262 has a first angle? 1 and the second prism pattern 264 has a second angle? 2 different from the first angle? 1. For example, the first angle? 1 may be smaller than the second angle? 2. The second angle? 2 may be about 85 to 95 degrees, and the first angle? 1 may be about 70 to 85 degrees. Alternatively, the first angle? 1 may be greater than the second angle? 2. That is, in the present invention, as long as the first and second prism patterns 262 and 264 are configured to have different angles, the relative magnitude of the angle is not limited.

The base film 260 is made of a material having a refractive index of about 1.5 to 1.6. For example, the base film 260 may be made of polyethylene terephthalate (PET) or polycarbonate (PC).

The first prism pattern 262 and the second prism pattern 264 are made of a material having a refractive index of about 1.5 to 1.65. For example, the first prism pattern 262 may be formed of a material having a refractive index smaller than that of the material forming the base 260 and having a refractive index of about 1.55. Also, the second prism pattern 264 may be made of a material having a refractive index of about 1.59. The first and second prism patterns 262 and 264 may be made of acrylic resin.

The low refractive index resin layer 266 is made of a material having a refractive index of about 1.1 to 1.3. The low refractive index resin layer 266 has an adhesive property and may include a fluorine compound such as polytetrafluoroethylene (PTFE) or may be made of a porous material such as silica.

Each of the base 260, the first prism pattern 262, the low refractive index resin layer 266 and the second prism pattern 264 has first through fourth thicknesses t1, t2, t3, t4 ).

The refractive index of the material constituting each of the base 260, the first prism pattern 262, the low refractive index resin layer 266 and the second prism pattern 264 is based on a liquid phase.

The third thickness t3 of the low refractive resin layer 266 is smaller than the first thickness t1 of the base 260 and larger than the second thickness t2 of the first prism pattern 262. [ Therefore, the low refractive index resin layer 266 completely covers the first prism pattern 262. The second thickness t2 of the first prism pattern 262 is greater than the fourth thickness t4 of the second prism pattern 264.

Alternatively, when the first angle [theta] 1 of the first prism pattern 262 is larger than the second angle [theta] 2 of the second prism pattern 264, The thickness t2 is smaller than the fourth thickness t4 of the second prism pattern 264. [

For example, the first thickness t1 of the base 260 is about 22-27 μm and the second thickness t2 of the first prism pattern 262 is about 13-16 μm. The third thickness t3 of the low refractive resin layer 266 is about 15 to 22 占 퐉 and the fourth thickness t4 of the second prism pattern 264 is about 10 to 12 占 퐉. Accordingly, the low refractive index resin layer 266 between the first prism pattern 262 and the second prism pattern 264 has a thickness of about 2 to 7 μm. In other words, the first prism pattern 262 is spaced from the bottom surface of the second prism pattern 264 by a distance of about 2 to 7 mu m.

A path of light will be described with reference to FIG. 7, which is a view for explaining the path of light in the optical sheet for a backlight unit according to the second embodiment of the present invention.

The light emitted from the LED (229a in FIG. 3) passes through the light guide plate (223 in FIG. 3) and the diffusion sheet 221a and is incident on the base 260. At this time, the light incident on the base 260 has a third angle? 3 with respect to an imaginary line L parallel to the surface of the liquid crystal panel 210 (see FIG. 3).

The light emitted from the light guide plate 223 is inclined to an imaginary line L and processed through the diffusion sheet 221a to have a third angle? .

The light incident on the base 260 is refracted by the Snell's law and processed to have a fourth angle? 4 with respect to the imaginary line L. The base 260 and the first prism pattern 262 And has a fifth angle [theta] 5 with respect to the virtual line L. [

Further, the first prism pattern 262 is refracted again at the interface between the first prism pattern 262 and the low refractive index resin layer 266 to have a sixth angle 6 with respect to the hypothetical line L, 266 and the second prism pattern 265 to have a seventh angle 7 with respect to the virtual line L. [

 The second prism pattern 264 is refracted at the interface between the air layer and the upper part of the second prism pattern 264 and is supplied to the liquid crystal panel 210 at an eighth angle? 8 with respect to the line L of the imaginary line.

When the first prism pattern 262 and the second prism pattern 264 have angles of 80 degrees and 90 degrees in the backlight unit 220 including the light guide plate 221 as described above, The results are shown in Table 2 below.

  Diffusion sheet -> base    Base -> 1st prism The first prism -> low refraction
Resin layer angle of incidence 36.00 58.98 58.54 Refractive index 1.00 1.57 1.57 1.55 1.55 1.27 Outgoing angle 58.98 58.54 66.60

  Low refraction resin layer-> second prism       Second prism -> air angle of incidence 66.60 71.50 Refractive index 1.27 1.59 1.59 1.00 Outgoing angle 71.50 90.20

As shown in Table 1 and Table 2, light incident on the optical sheet 221 at an angle of about 36 degrees is emitted at an angle of about 90 degrees while passing through the diffusion sheet 221a and the laminate prism sheet 221b. That is, light perpendicular to the surface of the liquid crystal panel is provided. Therefore, the luminance of the liquid crystal display device is improved.

When the angle of emergence from the diffusion sheet 221a is about 30 to 40 degrees, the angle of the second prism pattern 264 is fixed at 90 degrees and the angle of the first prism pattern 262 is adjusted to about 74 to 84 degrees The light finally emitted from the optical sheet 221 becomes perpendicular to the surface of the liquid crystal panel.

In the optical sheet 221 having the above-described configuration, the low refractive index resin layer 266 completely covers the first prism pattern 262 and the second prism pattern 264 covers the low refractive index resin layer 266 The first and second prism patterns 262 and 264 are completely adhered by the low refractive index resin layer 266 and the air between the first and second prism patterns 262 and 264 Gap does not occur. Therefore, the problem of the Newton ring does not occur as in the first embodiment.

Also, because the first prism pattern 262 does not contact the second prism pattern 264 or the second base (170 of FIG. 4B), a problem of staining due to light scattering is also prevented.

That is, the backlight and the liquid crystal display device including the optical sheet according to the second embodiment of the present invention are reduced in thickness by omitting one diffusion sheet and one prism sheet without causing problems such as stains.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. It can be understood that

110, 210: liquid crystal panel 120, 220: backlight unit
123 and 223: a light guide plate 125, 225:
121 and 221: optical sheets 121a and 221a: diffusion sheet
121b, 221b: Laminate prism sheet 160, 170, 260: Base
162, 172, 262, 264: prism pattern 266: low refractive index resin layer

Claims (12)

A light guide plate;
A light source positioned at one side of the light guide plate;
And a second prism pattern disposed on the light guide plate and having a first prism pattern having a first angle and a low refractive index resin layer covering the first prism pattern and a second prism pattern having a second angle formed on the low refractive index resin layer, An optical sheet,
Wherein the first angle is less than the second angle,
Wherein the first prism pattern is formed on the base, and the second prism pattern is formed directly on the low refractive index resin layer without the base.
The method according to claim 1,
Wherein the first angle is 70-85 degrees and the second angle is 85-95 degrees.
3. The method of claim 2,
Wherein the low refractive index resin layer has a smaller refractive index than the first and second prism patterns.
The method of claim 3,
Wherein the refractive index of the low refractive index resin layer is 1.1 to 1.3.
The method of claim 3,
Wherein a refractive index of the first and second prism patterns is 1.5 to 1.65.
3. The method of claim 2,
Wherein the low refractive resin layer completely covers the first prism pattern.
The method according to claim 6,
Wherein the first prism pattern is spaced apart from the lower surface of the second prism pattern by the low refractive index resin layer.
delete The method according to claim 1,
And a reflective plate positioned below the light guide plate.
A liquid crystal panel;
The backlight unit according to any one of claims 1 to 7, 9,
And the liquid crystal display device.
The method according to claim 1,
Wherein the low refractive index resin layer is smaller than the base and has a thickness greater than that of the first prism pattern.
The method according to claim 1,
Wherein the first prism pattern and the second prism pattern are arranged to cross each other.

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