KR101588900B1 - Liquid crystal display - Google Patents

Abstract

The present invention relates to a liquid crystal display device, and more particularly, to a light guide plate disposed below a liquid crystal display panel. A plurality of light sources facing a side surface of the light guide plate; And a buffer material having a visible light transmittance of 95% or more and a trapezoidal or truncated cross section disposed between the light sources and the light guide plate and becoming thicker toward the light guide plate. The buffer material includes any one of an acrylic copolymer and a silicone resin, and the refractive index thereof is similar to the refractive index of the light emitting portion medium of the light source and the light guide plate. The cushioning material is in contact with the light emitting portion of the light source and is in contact with the side surface of the light guide plate even when the light guide plate is not thermally expanded, and the buffering range of the cushioning material includes the heat distortion range of the light guide plate.

Description

[0001] LIQUID CRYSTAL DISPLAY [0002]

The present invention relates to a liquid crystal display device including an edge type backlight unit.

BACKGROUND ART [0002] Liquid crystal display devices are becoming increasingly widespread due to features such as light weight, thinness, and low power consumption driving. This liquid crystal display device is used as a portable computer such as a notebook PC, an office automation device, an audio / video device, and an indoor / outdoor advertisement display device. A transmissive liquid crystal display device that occupies most of the liquid crystal display device controls an electric field applied to the liquid crystal layer to modulate light incident from the backlight unit to display an image.

The backlight unit is roughly divided into a direct type and an edge type. 1, the edge type backlight unit has a structure in which the light source 1 is disposed so as to face the side surface of the light guide plate 2, and a plurality of optical sheets are disposed between the liquid crystal display panel and the light guide plate. The edge type backlight unit can be realized to be thinner than the direct type backlight unit. The direct-type backlight unit has a structure in which a plurality of optical sheets and a diffusion plate are stacked under a liquid crystal display panel and a plurality of light sources are disposed under the diffusion plate.

The light guide plate 2 of the edge type backlight unit is apt to be thermally expanded due to the heat from the light source 1 because the distance from the light source 1 is short. The size of the light guide plate 2 increases as the display screen of the liquid crystal display device becomes larger, and the size change due to thermal expansion also increases. In order to reduce the mechanical interference between the light source 1 and the light guide plate 2 due to the thermal expansion of the light guide plate 2, the light source 1 and the light guide plate 2 have a predetermined gap d Assembled. However, light loss occurs between the light source 1 and the light guide plate 2 due to the gap d between the light source 1 and the light guide plate 2.

Referring to FIG. 1, when a light emitting diode (LED) package is used as the light source 1, the light emitted from the LED passes vertically through a silicon dome of the LED package And vertically passes through the side surface of the light guide plate 2 via air. Reflection loss occurs between the light source 1 and the light guide plate 2. [ The surface reflection loss (R) reflected from the interface between the medium when light passes vertically through the two media can be defined as shown in Equation (1). The actual light loss between the LED package and the light guide plate 2 is about 4% between the LED package and the air layer and about 8% between the air layer and the light guide plate 2, which is about 4%.

Herein, n1 is the refractive index of the incident light medium, and n2 is the refractive index of the light emitting medium, respectively. The refractive index of silicon is 1.4 to 1.5, and the refractive index of air is approximately 1. The refractive index of the light guide plate medium is about 1.49.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a liquid crystal display device capable of minimizing mechanical interference between a light source and a light guide plate and minimizing light loss between a light source and a light guide plate upon thermal expansion of a light guide plate of an edge type backlight unit, Device.

According to an aspect of the present invention, there is provided a liquid crystal display comprising: a light guide plate disposed below a liquid crystal display panel; A plurality of light sources facing a side surface of the light guide plate; And a buffer material having a visible light transmittance of 95% or more and a trapezoidal or truncated cross section disposed between the light sources and the light guide plate and becoming thicker toward the light guide plate. The buffer material includes any one of an acrylic copolymer and a silicone resin, and the refractive index thereof is similar to the refractive index of the light emitting portion medium of the light source and the light guide plate. The cushioning material is in contact with the light emitting portion of the light source and is in contact with the side surface of the light guide plate even when the light guide plate is not thermally expanded, and the buffering range of the cushioning material includes the heat distortion range of the light guide plate.

The present invention minimizes optical loss between a light source and a light guide plate by disposing a cushioning material between the light source and the light guide plate with little difference in refractive index and a high elasticity and absorbs thermal expansion of the light guide plate to prevent mechanical interference between the light guide plate and the light source .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Like reference numerals throughout the specification denote substantially identical components. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 2 to 11B.

2 to 6, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 10, a source driver 12 for driving data lines 14 of the liquid crystal display panel 10, A gate driver 13 for driving the gate lines 15 of the liquid crystal display panel 10, a timing controller 11 for controlling the source driver 12 and the gate driver 13, A backlight unit for irradiating light, and a light source driver 18.

In the liquid crystal display panel 10, a liquid crystal layer is formed between two glass substrates. A plurality of data lines 14 and a plurality of gate lines 15 are intersected with each other on a lower glass substrate of the liquid crystal display panel 10. The liquid crystal cells Clc are arranged in a matrix form in the pixel array by the intersection structure of the data lines 14 and the gate lines 15. [ The liquid crystal cells (TFTs) T1 and T2 connected to the data lines 14, the gate lines 15, the TFTs T1 and T2, and the TFTs T1 and T2 are connected to the lower glass substrate of the liquid crystal display panel 10 Clc), a storage capacitor, and the like are formed. The pixel array may be implemented in various forms as shown in FIGS. The liquid crystal cells Clc are connected to the TFT and driven by the electric field between the pixel electrodes 1 and the common electrode. On the upper glass substrate of the liquid crystal display panel 10, a black matrix, a color filter, and the like are formed. On the upper glass substrate and the lower glass substrate of the liquid crystal display panel 10, a polarizing plate is attached and an alignment film for setting a pre-tilt angle of the liquid crystal is formed.

On the upper glass substrate of the liquid crystal display panel 10, a black matrix, a color filter, and a common electrode are formed. The common electrode is formed on the upper glass substrate in a vertical electric field driving method such as a TN (Twisted Nematic) mode and a VA (Vertical Alignment) mode, and a horizontal electric field such as IPS (In Plane Switching) mode and FFS (Fringe Field Switching) Is formed on the lower glass substrate together with the pixel electrode in the driving method. On the upper glass substrate and the lower glass substrate of the liquid crystal display panel 10, a polarizing plate is attached and an alignment film for forming a pre-tilt angle of the liquid crystal is formed on the inner surface in contact with the liquid crystal.

Figures 3-5 are equivalent circuits illustrating various examples of pixel arrays.

The pixel array of FIG. 3 is a pixel array used in most liquid crystal display devices, and the data lines D1 to D6 and the gate lines G1 to G4 are crossed. In this pixel array, the red subpixel (R), the green subpixel (G), and the blue subpixel (B) are arranged along the column direction. Each of the TFTs applies a data voltage from the data lines D1 to D6 to the pixel electrodes of the liquid crystal cells arranged on the left side (or right side) of the data lines D1 to D6 in response to gate pulses from the gate lines G1 to G4, . In the pixel array shown in Fig. 3, one pixel includes a red subpixel R, a green subpixel G and a blue subpixel B neighboring along the row direction (or the line direction) orthogonal to the column direction . When the resolution of the pixel array shown in Fig. 3 is m x n, m x 3 (where 3 is RGB) data lines and n gate lines are required. Gate pulses of one horizontal period synchronized with the data voltage are sequentially supplied to each of the gate lines of the pixel array.

The pixel array shown in FIG. 4 can reduce the number of necessary data lines to 1/2 in the same resolution as compared with the pixel array shown in FIG. 3, and reduce the number of necessary source drive ICs to 1/2. In this pixel array, each of the red subpixel R, the green subpixel G and the blue subpixel B is arranged along the column direction. In the pixel array shown in FIG. 4, one pixel includes red subpixels R, green subpixels G, and blue subpixels G neighboring along the direction of the line orthogonal to the column direction. In the pixel array shown in Fig. 4, the liquid crystal cells neighboring to the left and right share the same data line and continuously charge the data voltage supplied in a time-division manner through the data line. The liquid crystal cells and the TFTs disposed on the left side of the data lines D1 to D4 are defined as the first liquid crystal cell and the first TFTs T1 respectively and the liquid crystal cells and TFTs disposed on the right side of the data lines D1 to D4 The connection relationship of the TFTs defined by the second liquid crystal cell and the second TFT (T2) will be described below. The first TFT T1 supplies a data voltage from the data lines D1 to D4 to the pixel electrodes of the first liquid crystal cell in response to gate pulses from the odd gate lines G1, G3, G5 and G7. The gate electrode of the first TFT T1 is connected to the odd gate lines G1, G3, G5 and G7 and the drain electrode thereof is connected to the data lines D1 to D4. The source electrode of the first TFT (T1) is connected to the pixel electrode of the first liquid crystal cell. The second TFT T2 supplies a data voltage from the data lines D1 to D4 to the pixel electrodes of the second liquid crystal cell in response to gate pulses from the even gate lines G2, G4, G6 and G8. The gate electrode of the second TFT T2 is connected to the even gate lines G2, G4, G6 and G8 and the drain electrode thereof is connected to the data lines D1 to D4. The source electrode of the second TFT (T2) is connected to the pixel electrode of the second liquid crystal cell. When the resolution of the pixel array shown in Fig. 4 is m x n, {m x 3 (where 3 is RGB)} / 2 data lines and 2 n gate lines are required. In each of the gate lines of the pixel array PA, a gate pulse of a half horizontal period synchronized with the data voltage is sequentially supplied.

The pixel array shown in FIG. 5 can reduce the number of data lines required at the same resolution by 1/3 and the number of source drive ICs required can be reduced to 1/3 as compared with the pixel array shown in FIG. In this pixel array, each of the red subpixel R, the green subpixel G and the blue subpixel B is arranged along the line direction. In the pixel array shown in Fig. 5, one pixel includes a red subpixel R, a green subpixel G and a blue subpixel G neighboring along the column direction. Each of the TFTs applies a data voltage from the data lines D1 to D6 to the pixel electrodes of the liquid crystal cells arranged on the left side (or right side) of the data lines D1 to D6 in response to gate pulses from the gate lines G1 to G6, . When the resolution of the pixel array PA shown in Fig. 5 is m x n, m data lines and 3n gate lines are required. In each of the gate lines of the pixel array PA, gate pulses of a 1/3 horizontal period synchronized with the data voltage are sequentially supplied.

The source driver 12 includes a plurality of source drive ICs. The source driver 12 latches the digital video data (RGB) under the control of the timing controller 11. The source driver 12 converts the digital video data RGB to positive / negative polarity analog data voltages using the positive / negative gamma compensation voltages and supplies them to the data lines 14.

The gate driver 13 includes a plurality of gate driver ICs. The gate driver 13 includes a shift register, a level shifter for converting an output signal of the shift register into a swing width suitable for driving the TFT of the liquid crystal cell, and an output buffer. The gate driver 13 sequentially outputs gate pulses (or scan pulses) having a pulse width of about one horizontal period, which are composed of a plurality of gate drive integrated circuits, and supplies the gate pulses to the gate lines 15.

The light source driver 18 generates driving power of the light sources 16 and adjusts the light source driving power in response to the dimming signal DIM input from the timing controller 11 or the external system board.

The timing controller 11 receives digital video data (RGB) and timing signals (Vsync, Hsync, DE, DCLK) input from an external system board on which a video source is mounted. The timing signals Vsync, Hsync, DE and DCLK include a vertical synchronizing signal Vsync, a horizontal synchronizing signal Hsync, a data enable signal DE and a dot clock signal DCLK. The timing controller 11 generates timing control signals DDC and DDC for controlling the operation timings of the source driver 12 and the gate driver 13 based on the timing signals Vsync, Hsync, DE, and DCLK from the system board. GDC). The timing controller 11 inserts an interpolation frame between the frames of the input video signal input at a frame frequency of 60 Hz and multiplies the source timing control signal DDC and the gate timing control signal GDC to obtain 60 × N It is possible to control the operation of the source driver 12 and the gate driver 13 at a frame frequency of Hz.

6, the backlight unit includes a light guide plate 17, light sources 16 for irradiating light to the side surfaces of the light guide plate 17, and a cushioning member 20 disposed between the light sources 16 and the light guide plate 17 do. The light guide plate 17 may be a flat plate or a wedge plate. The backlight unit includes a plurality of optical sheets 26 stacked between the light guide plate 17 and the liquid crystal display panel 10, a reflective sheet 25 disposed under the light guide plate 17, and a liquid crystal display panel 10 A support main 21 for fixing the guide panel 22 and the backlight unit below the guide panel 22, a case top 23 surrounding the guide panel 22, And a cover bottom 24 surrounding the cover bottom 24. The optical sheets 26 include one or more prism sheets and one or more diffusion sheets to diffuse the light incident from the diffuser plate and to guide the light path of the light at an angle substantially perpendicular to the light incident surface of the liquid crystal display panel Refract. The optical sheets 26 may comprise a dual brightness enhancement film (DBEF).

Each of the light sources 16 may be selected as an LED package as shown in Fig. 7, and faces the side surface of the light guide plate 17 with the buffer material 20 therebetween. The LED packages are mounted on FR4 printed circuit boards (PCBs) or metal PCBs. The LED package is mounted on the PCB 76 as shown in FIG. 7 and includes a mold frame 71 made of plastic such as PPA (polypthalamide), an LED chip 72 mounted on the upper groove of the mold frame 71, Cathode lead terminals 74 and 75, and a silicon dome 73 covering the LED chip 72. It should be noted that the LED employed in the present invention is not limited to the LED package shown in FIG. 7 but may be any known LED having any structure.

The cushioning material 20 reduces the surface light loss between the light source 16 and the light guide plate 17 and absorbs the amount of thermal expansion thereof during thermal expansion of the light guide plate medium to prevent mechanical interference between the light source 16 and the light guide plate 17 It plays a role. To this end, the buffer material 20 is a colorless transparent polymer material of an acrylic copolymer or a silicone resin, and contains a urethane group having excellent adhesive strength and elasticity, and has a visible light transmittance of 95% or more. The refractive index of the buffer material 20 is higher than the refractive index of air and is similar to the refractive index of the light emitting portion medium and the light guide plate medium of the light source. In consideration of the refractive index of the cushioning material, the refractive index of the cushioning material 20 may be selected in the range of 1.3 to 1.6. The cushioning material 20 is brought into contact with the light emitting portion of the light source 16 and in contact with the side light incoming portion of the light guide plate 17 even when the light guide plate 17 is not thermally expanded. The cushioning material 20 is adhered to the light emitting portion of the light source 16 and the light incident portion of the light guide plate 17 with its own adhesive force without a separate adhesive.

The amount of deformation due to thermal expansion of the light guide plate 20 can be expressed by a coefficient of linear expansion (cm / DEG C) in a measurement standard such as ASTM D696 and does not exceed 300 mu m / DEG C in the case of a general plastic resin used as a light guide plate material. Considering that the gap between the light source 16 and the light guide plate 17 may vary depending on the set size of the liquid crystal display module and the design specification of the backlight unit, Lt; / RTI > The buffering range of the buffer material 20 should be greater than the maximum thermal deformation amount of the light guide plate 500 占 퐉 / 占 폚. On the other hand, if the buffering range of the cushioning material is smaller than the thermal deformation amount of the light guide plate, mechanical interference occurs between the light source 16 and the light guide plate 17 at the time of thermal expansion of the light guide plate 17. For example, when the light source 16 and the light guide plate 17 are assembled with a gap of 1 mm therebetween and a buffer material having a buffering effect of 10% is filled between the light source 16 and the light guide plate 17, The light guide plate 17 contacts the light source 16 when the light guide plate 17 thermally expands.

The present invention is characterized in that a cushioning material 20 having little difference in refractive index from that of the light source 16 and the light guide plate 17 and having high elasticity is disposed to minimize light loss between the light source 16 and the light guide plate 17 It is possible to absorb the thermal expansion of the light guide plate 17 and to prevent the mechanical interference between the light guide plate 17 and the light source 16.

Figs. 9A to 9E are views showing various arrangements of the cushioning material 20 and the light source 16. Fig.

9A to 9E, the light source 16 may be disposed so as to face at least one of four sides including the upper and lower sides, the left and right sides of the light guide plate 17, and the like. The cushioning material 20 is adhered to the light emitting portion of the light source 16 and the light incoming portion of the light guide plate 17 between the light source 16 and the side surface of the light guide plate 17, It can be adhered only to the side surface. Thus, the cushioning material 20 may include one or more cushioning materials, and may be adhered to at least one of the four sides of the light guide plate 17.

Figs. 10A to 10D are views showing various structural modifications of the cushioning material 20. Fig.

10A to 10D, the cushioning material 20 has a rectangular cross section, a trapezoidal shape, a trumpet shape, or the like in which the corners are rounded at the corners close to the light source. The cushioning material 20 may become thicker from the light emitting portion of the light source 16 to the light incident portion of the light guide plate 17. [

Figs. 11A and 11B are views showing examples of independent arrangement and common arrangement of the cushioning materials 20. Fig.

11A and 11B, the cushioning material 20 may be commonly adhered as a single piece between a plurality of light sources 16 and the light guide plate 17, and may be adhered with the light sources 16 in a ratio of 1: 1 .

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. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

1 is a view showing a gap between a light source and a light guide plate in an edge light guide plate.

2 is a block diagram showing a liquid crystal display device according to an embodiment of the present invention;

Figs. 3 to 5 are views showing various pixel array examples of the liquid crystal display panel shown in Fig.

6 is a cross-sectional view illustrating an assembled state of an edge type backlight unit and a liquid crystal display panel according to an embodiment of the present invention.

7 is a cross-sectional view showing an example of an LED package.

8 is a diagram comparing light loss of an edge type backlight unit according to the related art and the present invention.

9A to 9E are views showing various arrangements of a cushioning material and a light source.

10A to 10D are views showing various structural modifications of the cushioning material.

Figs. 11A and 11B are views showing independent arrangements and common arrangements of cushioning materials. Fig.

Description of the Related Art

201: light guide plate 201a: lenticular lens array

202: Light source array

Claims (6)

A liquid crystal display panel; A light guide plate disposed below the liquid crystal display panel; A plurality of light sources facing a side surface of the light guide plate; And And a cushioning material having a visible light transmittance of 95% or more and a trapezoidal or truncated cross-section disposed between the light sources and the light guide plate and becoming thicker toward the light guide plate, Wherein the cushioning material comprises a colorless transparent polymeric material selected from the group consisting of an acrylic copolymer and a silicone resin and the refractive index thereof is similar to the refractive index of the light emitting portion medium of the light source and the light guide plate, Wherein the cushioning material is in contact with a light emitting portion of the light source and is in contact with a light emitting portion of the light source even when the light guiding plate is not thermally expanded, and the buffering range of the cushioning material includes a heat distortion range of the light guiding plate. The method according to claim 1, Wherein the cushioning material comprises a urethane group. delete The method according to claim 1, And the refractive index of the buffer material has a refractive index between 1.3 and 1.6. The method according to claim 1, Wherein the cushioning material is adhered to a light emitting portion of the light source and a side surface of the light guide plate. delete

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