KR20100004198A - Back light unit and liquid crystal display device having the same - Google Patents

Abstract

PURPOSE: A backlight unit and a liquid crystal display device using the same for increasing the brightness and reducing a bottom half-power angle are provided to reduce a top/bottom half-power angle by condensing the outgoing light of the light guide plate. CONSTITUTION: A light source(104) emits light. A lamp housing(106) protects the light source. A light guide plate(108) of the wedge type changes the incident light of the light source into the surface light source. An optical sheet is installed on the light guide plate. The optical sheet includes the first support film, a light concentration film, a second condensing film and a second support film. The first condensing film has the first pattern and the first refractive index.

Description

Back light unit and Liquid Crystal Display Device having the same}

The present invention relates to a backlight unit and a liquid crystal display device using the same. More particularly, a first light collecting film having a first pattern in which an acid and a valley are alternated, and a second light collecting film having a second pattern filled with a valley of a first pattern are provided. The present invention relates to a backlight unit for improving condensing efficiency by an optical sheet and a liquid crystal display using the same.

CRT (Cathode Ray Tube), one of the commonly used display devices, is mainly used for monitors such as TVs, measuring devices, and information terminal devices.However, due to the weight and size of the CRT itself, the size and size of electronic products are reduced. Could not respond actively. In order to solve the CRT problem, various flat panel display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), an electro luminescent display (ELD), and a vacuum fluorescent display (VFD) have been proposed and utilized.

Among flat panel displays, liquid crystal displays are widely used because they have advantages of miniaturization, light weight, thinness, and low power driving. In particular, the liquid crystal display device using the thin film transistor can realize a high-definition, large-sized, color, and the like of the display screen, and is recently used in various fields as well as notebook PCs and monitors.

A general liquid crystal display device applies a voltage to a specific molecular array of a liquid crystal to convert it into another molecular array, and visually changes optical properties such as birefringence, photoreactivity, dichroism, and light scattering characteristics of the liquid crystal cell emitted by the molecular array. A light-receiving display device that displays information by using modulation of light by a liquid crystal cell, which is converted into a. Since the liquid crystal display device is a light-receiving element, it includes a backlight unit that provides light to represent an image, and the backlight unit is classified into a direct type and an edge type according to the arrangement of the light source. .

The direct type backlight unit is a method in which a plurality of light sources are disposed at regular intervals directly under the liquid crystal display panel to directly irradiate directly under the liquid crystal display panel, and the edge type backlight unit is provided to a light guide plate that converts light emitted from the light source into surface light. This is a method of irradiating light to the liquid crystal display panel. The backlight unit of the liquid crystal display includes optical sheets made of a diffusion plate, a diffusion sheet, a prism sheet, and the like in order to improve optical characteristics of light emitted from a light source, for example, luminance uniformity and front luminance.

1 is a cross-sectional view of a backlight unit according to the prior art, Figure 2 is a schematic diagram of the light path of the backlight unit according to the prior art, Figure 3 is a distribution diagram for the emitted light of the light guide plate according to the prior art.

As shown in FIG. 1, a backlight unit 10 used in a notebook fish is composed of a light guide plate 12 having a reflector 24, an optical sheet 24, and a lamp 22. The optical sheet 24 includes a first diffusion sheet 14, a first prism sheet 16, a second prism sheet 18, and a second diffusion sheet 20. The light guide plate 12 has a pattern formed on an upper surface or a lower surface to emit incident light, and functions to make the light of the lamp 22 as a line light source into a surface light source using the principle of total reflection. The first diffusion sheet 14 functions to conceal the pattern emitted from the light guide plate 12 and to adjust the angle of the emitted light. The first and second prism sheets 16 and 18 function to condense the light passing through the first diffusion sheet 14.

The first and second prism sheets 16 and 18 have vertical and horizontal prism directions, respectively, and are disposed in a vertical form to use the first and second prism sheets 16 and 18 in pairs. The first prism sheet 16 in which the prism direction is vertical condenses left and right lights, and the second prism sheet 18 in which the prism direction is horizontal condenses vertical light. The second diffusion sheet 20 is used as a protective sheet for improving defects of the backlight unit 10 such as unevenness and foreign matters of the second prism sheet 18 that may finally occur. The backlight unit 10 as shown in FIG. 1 used in a notebook fish requires a light guide plate, two or more diffusion sheets, and a prism sheet, respectively. Although the backlight unit 10 as shown in FIG. 1 has excellent image quality, there is a problem in that light collection efficiency is low and thickness is increased.

As shown in FIG. 3, the main outgoing light of the light guide plate 12 is distributed between 40 and 80 degrees, and the outgoing light having the highest luminance has an outgoing angle of about 80 degrees. As shown in FIG. 2, in order for the incident light to be refracted in the vertical direction in the first prism sheet 16 made of an ultraviolet resin having a refractive index of 1.58, about 24 to 32 degrees in the prism plane by Snell's law. The first light L1 incident at an angle is required. However, in the light guide plate 12, since the majority of the light is distributed at 40 degrees or more, the fourth light L4 incident beyond 24 to 32 degrees is refracted from the first prism sheet 16 to the fifth light L5. As a result, a side lobe phenomenon, such as A, which occurs from the first prism sheet 16 to the lateral direction and becomes the sixth light L6, occurs, which acts as a factor of rapidly decreasing the emission efficiency. Therefore, the first diffusion sheet 14 is used to change the range of the main outgoing light of the light guide plate 12.

When the first diffusion sheet 14 is used, the distribution of the main outgoing light of the light guide plate 12 is changed from the distribution of 40 to 80 to the distribution of 10 to 45 degrees as shown in FIG. In this case, as shown in FIG. 2, a part of the outgoing light of the light guide plate 12 is included between 24 and 32 degrees, which is the condensing angle of the first prism sheet 16. The first light L1 between 24 and 32 degrees emitted from the light guide plate 12 may have a second light (15 to 20 degrees based on a vertical line of the first prism sheet 16 inside the first prism sheet 16). L2), and the second light L2 leaves the first prism sheet 16 to meet the air and becomes the third light L3 that is vertically refracted. Thus, the vertical luminance of the first prism sheet 16 relative to the light guide plate 12 rises.

However, the outgoing light out of the 24 to 32 degrees emitted from the light guide plate 12 still occurs a side lobe phenomenon such as A. In other words, the light condensing efficiency is low because the main outgoing light of the light guide plate 12 cannot be used. In addition, as shown in FIG. 1, in order to improve the light collecting efficiency, the first diffusion sheet 14 and the first and second prism sheets 16 and 18 should be used. It is necessary to use the first and second diffusion sheets 14 and 20. However, the production cost increases by using four sheets, and the thickness of the backlight unit also increases.

In order to solve the problems of the prior art as described above, the present invention improves the light collecting efficiency by the optical sheet filling the second light collecting film in the valley region of the first light collecting film in the first light condensing film is acid and valley alternate An object of the present invention is to provide a backlight unit and a liquid crystal display device using the same.

A backlight unit according to the present invention for achieving the above object is a light source for emitting light; A light guide plate for converting incident light of the light source into a surface light source; In the optical sheet provided on the light guide plate, the optical sheet is a first support film, a first light collecting film having a first refractive index and a first refractive index of the acid and the valley on the first support film, the first light collecting film And a second support film on the second condensation film having a second pattern and a second refractive index filled in the valley of the second condensation film, wherein the second refractive index is greater than the first refractive index.

It includes a reflecting plate installed under the light guide plate. The light guide plate may be used by selecting one of a flat type, a wedge pit and a prism type.

The difference between the second refractive index and the first refractive index is characterized in that 0.1 to 0.2. In this case, the first refractive index is 1.3 to 1.49, the second refractive index is characterized in that the 1.5 to 1.7.

The acid of the first light collecting film is composed of a vertex angle determined by first and second tilt angles and the first and second tilt angles, and the first and second tilt angles are symmetrical or asymmetrical.

The first light having a first angle of incidence emitted from the light guide plate and incident on the first light converging film is refracted by a second light having a first refractive angle smaller than the first angle of incidence in the first light converging film. The second light incident at the second incident angle at the interface between the first and second light collecting films is refracted by the third light having a second refractive angle smaller than the second incident angle in the second light collecting film, and the third light is The light is incident on the interface between the first and second light collecting films at a third angle of incidence to become a fourth light having a third angle of refraction.

The first and second light collecting films and the first and second supporting films each use a colorless transparent film. The surface of any one of the first and second supporting films, characterized in that to apply a binder containing a bead.

The beads and the binder are characterized in that using a colorless transparent material.

Liquid crystal display device according to the present invention for achieving the above object is a light source for emitting light; A light guide plate for converting incident light of the light source into a surface light source; An optical sheet installed on the light guide plate; A liquid crystal display panel for displaying an image by using the light emitted from the optical sheet, wherein the optical sheet has a first support film, a first pattern having an alternating peak and valley on the first support film, and a first refractive index A light collecting film, a second light collecting film having a second pattern and a second refractive index filled in the valley of the first light collecting film, and a second support film on the second light collecting film, wherein the second refractive index is the first refractive index. It is characterized by being larger than the refractive index.

The backlight unit and the liquid crystal display using the same according to the embodiment of the present invention have the following effects.

In the first light converging film in which mountains and valleys are alternated, an optical sheet filling a second light converging film having a refractive index greater than that of the first light condensing film in the valley region of the first light converging film is configured to condense the output light of the light guide plate vertically. As a result, the upper and lower half-angle angles are reduced to improve luminance.

Since the acid portion of the optical sheet is not exposed to the surface, wear phenomenon due to contact with the light guide plate in contact with the optical sheet is prevented.

The first and second support films are provided on both sides of the first and second light collecting films to prevent deformation of the optical sheet due to different thermal expansion coefficients of the first and second light collecting films, It prevents appearance problems that may occur due to residue on the fingerprint.

The thicknesses of the first and second support films provided on both surfaces of the first and second light collecting films are differently formed to adjust the thermal expansion coefficients of the first and second light collecting films to prevent deformation of the optical sheet.

A binder mixed with beads is applied to the surfaces of any one or both of the first and second supporting films, thereby adjusting the thermal expansion coefficient of any one of the first and second condensing films to prevent deformation of the optical sheet.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each embodiment, the same reference numerals are used for the same components.

4 is an exploded perspective view of a liquid crystal display according to a first embodiment of the present invention, FIG. 5 is a cross-sectional view of a backlight unit according to a first embodiment of the present invention, and FIG. 6 is a first embodiment of the present invention. Progress of the light path of the backlight unit.

As shown in FIG. 4, the liquid crystal display device 100 includes a liquid crystal display panel 102 and a backlight unit 114. The liquid crystal display panel 102 is composed of a color filter substrate (not shown) bonded through an array substrate (not shown) and a liquid crystal layer (not shown). Although not shown in detail in the drawing, an array substrate defines a pixel region by crossing a plurality of gate lines and a plurality of data lines, and a thin film transistor formed at each cross region is connected to a pixel electrode of each pixel region. The color filter substrate includes red, green, and blue color fillers corresponding to each pixel area, and a common electrode is formed on the black matrix, the color filter, and the black mattress in the boundary area of each color filter.

One side of the liquid crystal display panel 102 is electrically connected to a liquid crystal display panel driver (not shown) in which a driving circuit for supplying a driving signal is mounted, and a plurality of gate wires and a plurality of data wires of the liquid crystal display panel 102 are electrically connected. The liquid crystal display panel 102 is driven by supplying a signal to the liquid crystal display panel 102. When the liquid crystal display panel 102 controls the voltage of the data signal applied to the pixel electrode while the voltage is applied to the common electrode, the liquid crystal layer is rotated by dielectric anisotropy according to an electric field between the common electrode and the pixel electrode. The image is displayed by transmitting or blocking light for each pixel area.

The backlight unit 114 includes a light source 104 for emitting light, a lamp housing 106 surrounding the light source 104, a light guide plate 108 for converting incident light from the light source 104 into a surface light source, and a liquid crystal display. An optical sheet 118 positioned between the panel 102 and the light guide plate 108, and a reflective sheet 112 for reflecting light emitted from the rear surface of the light guide plate 108 in the direction of the liquid crystal display panel 102. do. The light guide plate 108 is formed of polymethyl methacrylate (PMMA), and other materials may be used.

The light source 104 may use a variety of light sources, such as a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), or a light emitting diode (LED). have. The lamp housing 106 protects the light source 104 and has a light reflecting material applied therein to minimize the loss of light emitted from the light source 104. Light incident on the light guide plate 108 is uniformly diffused to be emitted toward the optical sheet 118, and part of the light is emitted toward the reflective sheet 112 under the light guide plate 108. The reflective sheet 112 reflects the light emitted from the light guide plate 108 to minimize light loss. The liquid crystal display device 100 may be used between the liquid crystal display panel 102 and the optical sheet 118 through a separate optical sheet as necessary.

As shown in FIG. 5, the backlight unit 114 includes a light source 104, a lamp housing 106, a light guide plate 108, and an optical sheet 118. The optical sheet 118 positioned on the light guide plate 108 collects and diffuses the light emitted from the light guide plate 108 and supplies the light to the liquid crystal display panel 102. The optical sheet 118 has a valley pattern of the first condensing film 124 and the first condensing film 124 having a first pattern in which an acid and a valley on the first support film 122 and the first support film 122 are alternated. Four films including a second light collecting film 126 having a second pattern filled in, and a second support film 134 on the second light collecting film 126.

The thermal expansion coefficients of the first and second light collecting films 124 and 126 are different from each other, and the first refractive index of the first light collecting film 124 is lower than the second refractive index of the second light collecting film 126. The first and second support films 122 and 134 and the first and second condensing films 124 and 126 basically use acrylic resins, which are PET and UV curing resins, which can form patterns, respectively. The first and second refractive indices are different from each other. The first refractive index has a low refractive index compared to the second refractive index, and the second refractive index has a high refractive index compared to the first refractive index. The first and second light collecting films 124 and 126 add different additives to the acrylic resin to vary the first and second refractive indices. The first light collecting film 124 has a first refractive index of 1.3 to 1.9, and the second light collecting film 126 has a second refractive index of 1.4 to 2.0. Preferably the first refractive index is 1.3 to 1.49 and the second refractive index is 1.5 to 1.7. The difference between the first refractive index and the second refractive index is preferably 0.1 to 0.2.

In the liquid crystal display device 100, the light emitted from the light guide plate 108 passes through the first support film 122 in the air layer to be incident on the first light collecting film 124, and is incident from the first light collecting film 124. Light is emitted through the second light collecting film 126 and passed through the second support film 134 to be provided to the liquid crystal display panel 102. Since the air layer between the light guide plate 108 and the optical sheet 118 has a refractive index of 1, the light emitted from the light guide plate 108 has an air layer having a higher refractive index, the first light collecting film 124, and the second light collecting film ( 126).

The optical sheet 118 according to the first embodiment is composed of the first and second condensing films 124 and 126 whose refractive indices are increased in accordance with the traveling direction of the light to condense the light, and the first to the mountain and the valley alternately. The light condensing may be maximized by changing the path of light by the second light collecting film 126 having the second pattern filled in the valley pattern of the first light collecting film 124 having the pattern. In addition, it is possible to improve the light efficiency as compared to the prism sheet or the inverted prism sheet of the prior art, as well as to prevent the light guiding plate from being broken by the prism acid.

The first and second support films 122 and 134 may be polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, It is formed from synthetic resins such as cellulose acetate, weather-resistant vinyl chloride, and the like. In addition, since the first and second support films 122 and 134 must pass the light emitted from the light guide plate 108, a colorless transparent film is preferable.

The thickness of the first and second support films 122 and 134 may be selected from one of 100 μm, 125 μm, 188 μm, and 250 μm, and a pattern may be formed on the first support film 122. The ultraviolet curable resin is applied, and a mold is used to form a first light condensing film 124 composed of a first pattern in which an acid and a valley are alternately cured to UV light, and ultraviolet light is cured on a bone region of the first light condensing film 124. The second light collecting film 126 of the second pattern filled with resin is cured with ultraviolet rays, and the second support film 134 is attached onto the second light collecting film 126 by a lamination method.

In the first embodiment of the present invention, the first and second support films 122 and 134 are formed of a material having a thermal expansion rate of a value obtained by averaging the thermal expansion rates of the first and second light collecting films 124 and 126. The calculation of the average coefficient of thermal expansion takes into account the volume of each of the first and second light collecting films 124 and 126 and the pitch between the acid and the acid. In order to prevent deformation due to different thermal expansion, the first boundary of the first support film 122 and the first condensing film 124 and the second boundary of the second support film 134 and the second condensing film 126. The coefficient of thermal expansion at is the same.

The first and second supporting films 122 and 134 may use a material that is equal to the average thermal expansion average of the respective thermal expansion rates of the first and second light collecting films 124 and 126. The first and second support films 122 and 134 may function as supports of the first and second light collecting films 124 and 126 to prevent wrinkles and warpage. When the first and second support films 122 and 134 are formed to have a larger thickness than the first and second light collecting films 124 and 126, the warpage phenomenon due to thermal expansion of the first and second light collecting films 124 and 126 may be prevented. .

As shown in FIG. 6, in the backlight unit of the first exemplary embodiment, the optical sheet 118 has a second shape of the second light collecting film 126 positioned on the first light collecting film 124 than the first refractive index of the first light collecting film 124. Since the refractive index is large, the light emitted from the light guide plate 108 is refracted at least three times to be provided in the direction of the liquid crystal display panel 102. Each acid in the first light collecting film 124 is a vertex angle c and a first inclination angle determined by a first inclination angle a, a second inclination angle b, and first and second inclination angles a and b. It is composed of a first inclined surface 140 extending from), and a second inclined surface 142 extending from the second inclination angle (b). The first and second inclination angles a and b are each formed in the range of 60 to 89 degrees, and may be formed symmetrically or asymmetrically. The first light collecting film 124 has a first refractive index of 1.48, the second light collecting film 126 has a second refractive index of 1.61, the first inclination angle a is 69 degrees, and the second inclination angle ( In the case where b) is 67 degrees, the optical path will be described in detail as follows.

The first light L1 having the first incident angle θi1 from the light guide plate 108 is the second light L2 having the first refraction angle θr1 smaller than the first incident angle θi1 at the first light collecting film 124. The second light L2, which is refracted by the second inclined plane 142 and is incident at a second incident angle θ i2 at the interface between the first and second light collecting films 124 and 126 of the second inclined surface 142, is the second light collecting film 126. Is refracted by the third light L3 having a second refractive angle θr2 smaller than the second incident angle θi2, and the third light L3 is the first and second light collecting films 124 of the first inclined surface 140. , 126 becomes the fourth light L4 incident at the third incident angle θi3 and refracted at the third refractive angle θr3. The fourth light L4 travels in the vertical direction under the liquid crystal display panel 102.

The first incident angle θi1 emitted from the light guide plate 108 peaks at 72 degrees from the lower portion of the first light condensing film 124 with respect to the vertical extension line, and according to Snell's law, the first refractive angle θi1. Is 40 degrees based on the vertical extension line, the second incident angle θ i2 is 27 degrees based on the normal of the second inclined surface 142, and the second refractive angle θ r2 is based on the normal of the second inclined surface 124. 24 degrees, the third incident angle θ i3 is 68 degrees based on the normal of the first inclined surface 140, and the third refractive angle θ r3 is 68 degrees based on the normal of the first inclined surface 140. The fourth light L4 is refracted vertically by total reflection.

The first inclination angle (a) and the second inclination angle (b) of the first light collecting sheet 124 correspond to the room of the fourth light L4 emitted to the liquid crystal display panel 102 according to the incidence angle of the first light L1. The square can be adjusted. Snell's law is n 2 / n 1 = sin θ 2 / sin θ 1, n 1 is the first refractive index of the first light collecting film 124, and n 2 is the second refractive index of the second light collecting film 126. According to Snell's law, the light is condensed because the dispersion becomes smaller as the refractive index progresses from the medium having the smaller refractive index to the larger medium. In the first exemplary embodiment according to the present invention, in order to overcome the limitation caused by the refraction according to the prior art, as shown in FIG. 6, the light emitted from the light guide plate 108 is focused using the principle of total reflection. Such induction of vertical light by total reflection has a high condensing efficiency because most of the light emitted from the light guide plate 108 is used.

FIG. 7 is a contour chart of measuring an optical profile of a backlight unit of the prior art as shown in FIG. 1, and FIG. 8 is a contour chart of measuring an optical profile of a backlight unit according to a first embodiment of the present invention as shown in FIG. 9 is a graph showing the vertical distribution of the optical profiles of FIGS. 7 and 8.

As shown in FIG. 7, as a result of measuring the light emitted from the backlight unit of the prior art, the light distribution has a peak of 1902 nits, and as shown in FIG. 8, the distribution of light emitted from the backlight unit according to the first embodiment of the present invention has a peak. With 2440 nits, it can be seen that the peak distribution of the emitted light in the backlight unit of the first embodiment of the present invention is improved by about 28% compared with the prior art. In addition, in the first embodiment of the present invention, the peak distribution of the emitted light is improved by reducing the upper and lower half-angle angles while the emitted light of the light guide plate 108 is vertically focused. Half angle means an inclination angle in which the front luminance is maintained at 50% or more. As shown in Fig. 9, in the first embodiment of the present invention, the half-value angle is located in the range of -20 to +20 degrees, but in the prior art, the half-value angle is located in the range of -40 to +40 degrees. Thus, the first embodiment of the present invention improves luminance while reducing the half-angle angle.

Various types of light guide plates 108 are used in the liquid crystal display device 100. 10 to 12 are cross-sectional views of light guide plates of the flat type, wedge type, and prism type according to the first embodiment of the present invention. It is divided into a flat type as shown in FIG. 10, a wedge type as shown in FIG. 11, and a prism type as shown in FIG. In the light guide plate 208 of the flat type, as shown in FIG. 10, the thicknesses of both ends are constant, and the first and second light sources 204a and 204b are provided at both sides of the light guide plate 208, respectively. The first and second light sources 204a and 204b are provided with first and second lamp housings 206a and 206b respectively surrounding the first and second light sources 204a and 204b. In addition, a plurality of printed patterns 250 are installed at upper and lower portions of the light guide plate 212 to block leakage light.

The wedge type light guide plate 308 of FIG. 11 has a first side surface 360 adjacent to the light source 304 and a second side surface 362 facing the first side surface 360, and at the first side surface 360. The thickness is reduced to the second side 362. One light source 304 is installed on the first side surface 360, and a lamp housing 306 surrounding the light source 304 is installed. The upper portion of the light guide plate 308 is kept flat, and the lower portion is formed as an inclined surface. A plurality of printed patterns 350 are installed on upper and lower portions of the light guide plate 308 to block leakage light.

As shown in FIG. 12, the prism type light guide plate 408 has a constant thickness at both ends, and first and second light sources 404a and 404b are provided at both sides of the light guide plate 408, respectively. The first and second light sources 404a and 404b are provided with first and second lamp housings 406a and 406b respectively surrounding the first and second light sources 404a and 404b. A prism pattern 452 is formed on the light guide plate 408, and a plurality of printed patterns 450 are provided below the light guide plate 408 to block leakage light. In addition, the light guide plate 408 may be formed in a wedge type as illustrated in FIG. 11. The light guide plates 208, 308, and 408 of the flat type, wedge type, and prism type may be made of a polymer material such as polymethyl methacrylate (PMMA) or cyclic olefin polymer (COP). Form.

In addition, in order to reduce the thickness of the optical sheet 118 in the first embodiment, a second embodiment in which the first and second support films 122 and 134 are formed in an asymmetric thickness is proposed. 13 and 14 are cross-sectional views of an optical sheet according to a second embodiment of the present invention. 13 and 14, the thicknesses of the first and second support films 122 and 134 formed on both surfaces of the first and second light collecting films 124 and 126 are different from each other.

FIG. 13 forms a thinner second support film 134 on the optical sheet 118 than the first support film 122 on the lower side. The reason why the second support film 134 is formed thinner than the first support film 122 is that when the first and second support films 122 and 134 are formed to have the same thickness, the second support film 134 is formed to be first. The coefficient of thermal expansion is greater than that of the support film 122, and at this time, a hat-shaped warpage phenomenon occurs in which both ends of the light collecting sheet 128 are rolled downward. In order to prevent a hat-shaped warpage phenomenon, the first support film 122 is formed thicker than the second support film 134.

FIG. 14 forms a thicker second support film 134 on the optical sheet 118 than the first support film 122 on the lower side. The reason why the second support film 134 is formed thicker than the first support film 122 is that when the first and second support films 122 and 134 are formed to have the same thickness, the second support film 134 is formed to have the first thickness. This is a case where the coefficient of thermal expansion is smaller than that of the support film 122, and at this time, a cup-like warpage phenomenon occurs in which both ends of the optical sheet 118 are rolled up. Therefore, in order to prevent the cup-shaped warpage phenomenon, the second support film 134 is formed thicker than the first support film 122.

Then, one or both of the first and second support films 122 and 134 are coated with a binder mixed with beads, and the binder and the first and second support films 132 and 134 are bonded to each other. A third embodiment for preventing warpage is proposed. 15 is a sectional view of an optical sheet according to a third embodiment of the present invention.

As shown in FIG. 15, beads 162 are mixed and applied to the binder 160 to one or both of the first and second support films 132 and 134 formed on both surfaces of the first and second light collecting films 124 and 126. . The binder 160 functions to fix the beads 162 to the surfaces of the first and second support films 122 and 134. The bead 162 has a function of concealing the emitted light of the optical sheet 118 so as not to be affected by foreign matter, and a function of softening the outgoing light in appearance.

As the binder 160, an acrylic resin, polyurethane, polyester, fluorine-based resin, silicon-based resin, polyamide, and epoxy resin Use a polymer such as). Since the binder 160 must pass incident light of the first or second light collecting films 124 and 126, a colorless transparent material is preferable.

The beads 162 are spherical in shape, and include acrylic resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide, and the like. use. Since the beads 162 must pass incident light of the first or second light collecting films 124 and 126, similarly to the binder 160, a colorless transparent material is preferable.

1 is a cross-sectional view of a backlight unit according to the prior art

Figure 2 is a schematic diagram of the optical path of the backlight unit according to the prior art

Figure 3 is a distribution diagram for the light emitted from the light guide plate according to the prior art

4 is an exploded perspective view of a liquid crystal display according to a first embodiment of the present invention;

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

6 is a progress view of an optical path of the backlight unit according to the first embodiment of the present invention;

7 is a contour chart of measuring an optical profile of a backlight unit of the related art as shown in FIG.

FIG. 8 is a contour chart of measuring an optical profile of a backlight unit according to a first embodiment of the present invention as shown in FIG. 5.

9 is a graph showing the vertical distribution of the optical profile of FIGS. 7 and 8

10 to 12 are cross-sectional views of the light guide plate of the flat type, wedge type, and prism type according to the first embodiment of the present invention.

13 and 14 are cross-sectional views of an optical sheet according to a second embodiment of the present invention.

15 is a sectional view of an optical sheet according to a third embodiment of the present invention \

Claims (11)

A light source for emitting light; A wedge type light guide plate for converting incident light from the light source into a surface light source; An optical sheet installed on the light guide plate; A liquid crystal display panel for displaying an image by using the light emitted from the optical sheet, wherein the optical sheet has a first support film, a first pattern having an alternating peak and valley on the first support film, and a first refractive index A light collecting film, a second light collecting film having a second pattern and a second refractive index filled in the valley of the first light collecting film, and a second support film on the second light collecting film, wherein the second refractive index is the first refractive index. A liquid crystal display device, characterized in that greater than the refractive index. The method of claim 1, And a reflective plate disposed under the light guide plate. The method of claim 1, The light guide plate includes a plurality of printing patterns disposed at an upper portion or a lower portion thereof, and the light guide plate has a first side surface and a second side surface facing the first side surface, and has a thickness from the first side surface to the second side surface. A liquid crystal display device characterized in that it becomes smaller. The method of claim 1, And the difference between the second refractive index and the first refractive index is 0.1 to 0.2. The method of claim 1, Wherein the first refractive index is 1.3 to 1.49 and the second refractive index is 1.5 to 1.7. The method of claim 1, Wherein the acid of the first light converging film includes a vertex angle determined by first and second inclination angles and the first and second inclination angles, and the first and second inclination angles are symmetrical or asymmetrical. . The method of claim 6, The first light having a first angle of incidence emitted from the light guide plate and incident on the first light collecting film is refracted by a second light having a first refractive angle smaller than the first angle of incidence in the first light collecting film. The second light incident at the second incident angle at the interface of the second light collecting film is refracted to third light having a second refractive angle smaller than the second incident angle in the second light collecting film, and the third light is the first light. And a fourth light having a third angle of refraction, incident at a third angle of incidence at an interface of the second light collecting film. The method of claim 1, The first and second light collecting film and the first and second support film, respectively, characterized in that using a colorless transparent film. The method of claim 1, A liquid crystal display device comprising applying a binder including a bead to the surface of any one of the first and second supporting films. The method of claim 9, The bead and the binder is a liquid crystal display, characterized in that using a colorless transparent material. A light source for emitting light; A light guide plate for converting incident light of the light source into a surface light source; In the optical sheet provided on the light guide plate, The optical sheet may include a first support film, a first light collecting film having a first pattern in which acid and a valley are alternated, and a first refractive film having a first refractive index, and a second pattern and a second filling material in the valleys of the first light collecting film. And a second support film on the second light collecting film, wherein the second refractive index is greater than the first refractive index.

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