KR20120057179A

KR20120057179A - Backlight Unit Having Optical Sheet Including Porous Layer

Info

Publication number: KR20120057179A
Application number: KR1020100118808A
Authority: KR
Inventors: 김보라
Original assignee: 엘지디스플레이 주식회사
Priority date: 2010-11-26
Filing date: 2010-11-26
Publication date: 2012-06-05

Abstract

PURPOSE: A backlight unit with an optical sheet which has a porous layer is provided to pass an optical sheet through a low-refractive area and a high-refractive area, thereby providing a light concentrating function and a light diffusing function by refraction. CONSTITUTION: At least one porous film(PF) is laminated on an optical sheet. A light guide plate is arranged under the optical sheet. A light source is arranged on at least one of a side or a lower side of the light guide plate. A reflecting plate is arranged under the light guide plate. Porous films of the optical sheet are bonded to each other between a first base film(BF1) and a second base film(BF2).

Description

Backlight Unit Having Optical Sheet Including Porous Layer

The present invention relates to a backlight unit of a liquid crystal display device having an optical sheet having a porous layer. In particular, the present invention relates to a backlight unit having an optical film in which a plurality of porous layers are stacked to diffuse and focus the backlight.

BACKGROUND ART Liquid crystal display devices have tended to be gradually widened due to their light weight, thinness, and low power consumption. The liquid crystal display device is used as a portable computer such as a notebook PC, office automation equipment, audio / video equipment, indoor and outdoor advertising display devices, and the like. The transmissive liquid crystal display device, which occupies most of the liquid crystal display device, displays an image by controlling an electric field applied to the liquid crystal layer to modulate the light incident from the backlight unit.

The backlight unit is roughly divided into a direct type and an edge type. The direct type backlight unit has a structure in which a plurality of optical sheets and a diffusion plate are stacked below the liquid crystal display panel and a plurality of light sources are disposed below the diffusion plate. 1A is a diagram illustrating a direct type backlight unit having a thin LED array as a light source.

The direct type backlight unit DBLU includes a light source for directly irradiating light from the lower surface of the liquid crystal display panel LCDP to the liquid crystal display panel LCDP. Although the light source uses a fluorescent lamp, as shown in FIG. 1A, a low power consumption and improved brightness LED array (LEDAR) may be used. The LED array LEDAR is arranged in a matrix manner at the bottom of the case CASE. The case CASE may be mounted on the cover bottom CB again. In some cases, the case CASE may be omitted, and the LED array LEDAR may be directly installed on the cover bottom CB. The diffusion plate DIFF is installed on the LED array LEDAR. The diffusion plate DIFF diffuses the light incident from the LED array LEDAR and evenly distributes the light on the front surface of the light incident surface of the liquid crystal display panel LCDP. Optical sheets OPT are disposed between the diffusion plate DIFF and the liquid crystal display panel LCDP. The optical sheets OPT may include one or more prism sheets, one or more diffusion sheets, and may further include a dual brightness enhancement film (DBEF). The prism sheet condenses the light dispersed by the diffusion plate DIFF to the liquid crystal display panel LCDP to improve luminance. The diffusion sheet serves to diffuse the light condensed by the prism sheet to have an even luminance on the entire LCDP panel. The guide panel GP surrounds the sides of the liquid crystal display panel LCDP and the direct type backlight unit DBLU and supports the liquid crystal display panel LCDP between the liquid crystal display panel LCDP and the optical sheets OPT. The cover bottom CB surrounds the case CASE and the lower surface of the edge type backlight unit. The reflective sheet REF is disposed on the bottom surface of the casing in which the LED array LEDAR is installed, and reflects the light reflected from the diffuser plate DIFF or the optical sheet OPT and sends it to the liquid crystal display panel LCDP. . The top case TP surrounds the top edge of the liquid crystal display panel LCDP and the side surface of the guide panel GP.

Meanwhile, the edge type backlight unit may be implemented to have a thickness thinner than that of the direct type backlight unit. Currently, LCD devices are changing from light source to LED. In particular, an edge type backlight unit for arranging LEDs that can be easily disposed is used.

Referring to FIG. 1B, the edge type backlight unit EBLU includes a cover bottom CB, a light guide plate LG mounted on a bottom surface in the cover bottom CB, and a side surface and a cover bottom CB of the light guide plate LG. The light source is disposed between the light guide plates LG and emits light toward the side surface of the light guide plate LG. Light sources use fluorescent lamps, but they also use LED arrays (LEDARs) with low power consumption and improved brightness. The light source is disposed on the side of the light guide plate LG using a receiving means such as a housing. The LGP refracts the propagation path of the light incident from the LED array LEDAR at an angle substantially perpendicular to the light incident surface of the liquid crystal display panel LCDP. Optical sheets OPT are disposed between the light guide plate LG and the liquid crystal display panel LCDP. The optical sheets OPT may include at least one prism sheet, at least one diffusion sheet, and the like to diffuse light incident from the light guide plate LG. In order to improve brightness, the optical sheets OPT may further include a dual brightness enhancement film (DBEF). The guide panel GP surrounds the sides of the liquid crystal display panel LCDP and the edge type backlight unit and supports the liquid crystal display panel LCDP between the liquid crystal display panel LCDP and the optical sheets OPT. The reflective sheet REF is disposed between the cover bottom CB and the light guide plate LG, and reflects the light that may be lost from the optical sheet OPT to the lower portion and returned to the liquid crystal display panel LCDP. . The top case TP surrounds the top edge of the liquid crystal display panel LCDP and the side surface of the guide panel GP.

As described above, the liquid crystal display device includes a backlight unit, and the backlight unit includes a diffusion sheet for distributing the backlight evenly over the entire surface of the liquid crystal display panel and a condensing sheet for condensing the backlight in the front direction of the liquid crystal display panel. The same plurality of optical sheets are provided. In particular, DBEF is used to improve luminance, which has a structure in which a plurality of optical films are stacked. An optical sheet in which a plurality of optical films are laminated is a complicated manufacturing process, and is mostly expensive because it uses several sheets of high performance optical films.

In order to apply a liquid crystal display device to a wider variety of fields, it is important to provide inexpensive components having a simpler structure. The optical sheet is also a similar component, and an optical sheet having a diffusion and condensing function at a low price is required.

An object of the present invention is to provide a backlight unit having an optical sheet having a simple structure as an invention devised to solve the problems of the prior art. Another object of the present invention is to provide a backlight unit having an optical sheet having a diffusing and condensing function with a simple structure. Still another object of the present invention is to provide a backlight unit having an optical sheet which simultaneously provides a diffusion and condensing function while having a low manufacturing cost due to its simple structure.

In order to achieve the above object, the backlight unit for a liquid crystal display according to the present invention includes an optical sheet in which at least one porous film is laminated; A light guide plate disposed under the optical sheet; A light source disposed on at least one of side and bottom surfaces of the light guide plate; And a reflector disposed under the light guide plate.

The porous films of the optical sheet are bonded between the first base film and the second base film.

The laminated porous films have the lowest refractive index of the porous film close to the light guide plate, and the porous films having the high refractive index are sequentially stacked.

The porous films are characterized in that it comprises a plurality of pattern holes in the optical film having a high refractive index.

The pattern hole is characterized in that it comprises a shape having a shape isotropy such as circular and regular polygons.

The pattern hole is characterized in that it comprises a shape having anisotropic shape, such as oval and polygon.

The pattern holes of the laminated porous films may be stacked to be staggered with each other.

The backlight unit of the liquid crystal display according to the present invention provides an optical sheet in which randomly stacked optical films interspersed with low and high refractive regions in the same layer. Therefore, the optical sheet according to the present invention simultaneously provides a light condensing function and a diffusing function by refraction while passing through the low and high refractive regions. In addition, the low refractive region is an air layer in which holes are formed in the high refractive optical film, and the manufacturing process is simple. Therefore, it is possible to provide a backlight unit having an optical sheet which simultaneously provides a diffusion and condensing function while having a low manufacturing cost.

1A is a cross-sectional view illustrating a structure of a direct backlight unit of a liquid crystal display device.
1B is a cross-sectional view illustrating a structure of an edge type backlight unit of a liquid crystal display device.
2 is a schematic view showing a structure of an optical sheet having a porous layer according to the present invention.
3 is a cross-sectional view showing the structure of an optical sheet having a porous layer according to the present invention.
4 is a cross-sectional view showing an optical path in an optical sheet having a porous layer according to the present invention.
5a to 5d are views showing various forms of the porous layer according to the present invention.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings and FIGS. 2 to 5D. 2 is a schematic view showing the structure of an optical sheet having a porous layer according to the present invention. 3 is a cross-sectional view showing the structure of an optical sheet having a porous layer according to the present invention.

Referring to FIG. 2, the optical sheet having a porous layer according to the present invention includes a porous film PF interposed between the first base film BF1 and the second base film BF2. In particular, the porous film PF may be formed by applying the adhesive layer AD to the front and rear surfaces thereof, and then forming a hole in the pattern hole H to be bonded to the first base film BF1 and the second base film BF2. Do. The porous film PF is formed by drilling a plurality of pattern holes H in an optical film having a high refractive index. Then, since the pattern hole H corresponds to the air layer, the pattern hole H is formed in the low refractive region. That is, when viewed in cross section, the porous film PF has a shape in which low and high refractive regions are scattered. In FIG. 2, an optical sheet having one porous film PF has been described for convenience of describing the structure of a basic optical sheet.

The optical sheet having a porous layer in the present invention is for use in a backlight unit of a liquid crystal display device. Therefore, the backlight should have a diffusion function to distribute the backlight evenly over the entire area of the liquid crystal display panel. In addition, in order to obtain a desired luminance as the display device, the display device must have a function of condensing the backlight in the front direction without losing the side surface. Therefore, in the backlight unit according to the present invention, it is preferable to use an optical sheet having a plurality of porous layers.

Referring to FIG. 3, an optical sheet having a structure in which a plurality of porous films are stacked according to the present invention will be described. For convenience, the adhesive layer AD is omitted here. The optical sheet according to the present invention includes a first porous film PF1, a second porous film PF2, and a third porous film PF3 laminated between the first substrate film BF1 and the second base film BF2. And fourth porous films PF4.

In particular, each of the porous films PF1, PF2, PF3, and PF4 is preferably formed by drilling a pattern hole H in a film having a high refractive index. Accordingly, each of the porous films PF1, PF2, PF3, and PF4 has a structure in which the film portion F, which is a high refractive index, and the pattern hole H, which is a low refractive index, are scattered. In particular, the size and distribution of the pattern hole H formed in each of the porous films PF1, PF2, PF3, and PF4 may be different from each other. As a result, the cross-sectional shapes of the stacked porous films PF1, PF2, PF3, and PF4 have a structure in which the film part F and the pattern hole H are alternately stacked as shown in FIG. 3.

It looks at how the optical sheet according to the present invention having such a structure simultaneously implements a light condensing function and a diffusion function for the backlight. 4 is a cross-sectional view showing an optical path in an optical sheet having a porous layer according to the present invention. In FIG. 4, for convenience, three porous films PF1, PF2, and PF3 are described as stacked optical sheets.

In FIG. 4, both L1 and L2 indicate that the backlight emitted from the light guide plate is incident on the optical sheet according to the present invention. Even when L1 and L2 are incident in parallel, it can be seen that the optical paths of L1 and L2 proceed differently to emit the optical sheet.

In the condensing light path L1, the light is slightly refracted in the normal direction of the incident surface while passing through the second base film BF2 having a refractive index higher than that of air. That is, the effect which collects to the front part of an optical sheet is acquired. After exiting the second base film BF2, the light is incident on the film part F of the third porous film PF3. If the refractive index of the third porous film PF3 is higher than the refractive index of the second base film BF2, the refractive index of the third porous film PF3 may be slightly refracted. After exiting the third porous film PF3, the film is incident on the film part F of the second porous film PF2. If the refractive index of the second porous film PF2 is higher than the refractive index of the third porous film PF3, it is again slightly refracted in the normal direction of the incident surface. After exiting the second porous film PF2, the second porous film PF2 is incident on the film part F of the first porous film PF1. If the refractive index of the first porous film PF1 is higher than the refractive index of the second porous film PF2, it is again slightly refracted in the normal direction of the incident surface. After exiting the first porous film PF1, the first porous film PF1 is incident to the first base film BF1. If the refractive index of the first base film BF1 is higher than the refractive index of the first porous film PF2, the first base film BF1 is slightly refracted in the normal direction of the incident surface. Thereafter, the first base film BF1 exits into the air. Since air has a lower refractive index than the first base film BF1, the air is refracted away from the normal direction of the exit surface.

As described above, in the case of L1, the second base film BF2, the film part F of the third porous film PF3, the film part F of the second porous film PF2, and the first porous film PF1. It can be seen that while passing through the film portion (F) and the first base film (BF1) of the (), close to the vertical direction of the optical sheet. In this case, it is preferable that the refractive index also be sequentially increased in the order in which the films are laminated.

Meanwhile, in the diffused light path L2, the light is slightly refracted in the normal direction of the incident surface while passing through the second base film BF2 having a refractive index higher than that of air. After exiting the second base film BF2, the second base film BF2 is incident to the pattern hole H of the third porous film PF3. Since the pattern hole H corresponds to an air layer having a low refractive index, it is refracted away from the normal direction of the incident surface. That is, the effect of diffusion is obtained. After exiting the third porous film PF3, the second porous film PF3 enters the pattern hole H of the second porous film PF2. Since it is incident on the same air layer, it is not refracted and proceeds as it is. After exiting the second porous film PF2, the second porous film PF2 is incident to the pattern hole H of the first porous film PF1. Again, since it is incident on the same air layer, it proceeds without refraction. However, while advancing, it enters into the film part F side surface of the 1st porous film PF1. At this time, since the film part F has a higher refractive index than the pattern hole H, the film part F is refracted in the normal direction of the incident surface. Since the entrance plane is a vertical plane, the result is that the plane is bent further in the horizontal direction. That is, the effect is further spread. Thereafter, after exiting the first porous film PF1, the first porous film PF1 is incident to the first base film BF1. If the refractive index of the first base film BF1 is higher than the refractive index of the first porous film PF2, the first base film BF1 is slightly refracted in the normal direction of the incident surface. Thereafter, the first base film BF1 exits into the air. Since air has a lower refractive index than the first base film BF1, the air is refracted away from the normal direction of the exit surface.

As described above, in the case of L2, the second hole film BF2, the pattern hole H of the third porous film PF3, the pattern hole H of the second porous film PF2, and the first porous film It can be seen that while passing through the pattern hole H, the film portion F, and the first base film BF1 of the PF1, the optical sheet is refracted close to the horizontal direction.

In FIG. 4, two extreme optical paths have been described for clear contrast. However, the backlight actually entered into the optical sheet according to the present invention has a more diverse light path. That is, since the high and low refractive regions are randomly stacked, condensing and diffusing phenomena alternately or continuously occur to form various optical paths. As a result, the optical sheet according to the present invention condenses and diffuses the backlight, thereby exhibiting excellent optical sheet performance in the backlight unit of the liquid crystal display device. In particular, the manufacturing method and structure is simple, the manufacturing cost is low.

As described above, in the optical sheet according to the present invention, it is preferable that the low refractive index region and the high refractive index region are scattered irregularly. To this end, it is more preferable that the stacked porous layers have pattern holes of different shapes, and the pattern holes have different arrangements. Hereinafter, various cases of the porous layer applied to the optical sheet according to the present invention will be described. 5a to 5d are views showing various forms of the porous layer according to the present invention.

5A illustrates a case in which the pattern holes H are arranged in a spaced manner so as to have a circular shape and have the same distance in the horizontal and vertical directions. When the porous layers having such a structure are stacked on each other, it is preferable to stack the pattern holes H so that they are alternately arranged. That is, the shape of the pattern holes (H) may be formed such that the shape isotropic (Shape Isotropy), such as circular, square, regular hexagon, square octagon.

5B illustrates a case in which the pattern holes H have an elliptical shape and are arranged in the horizontal direction. Even if the separation distance is the same in the horizontal direction, since the pattern hole H has a shape anisotropy, the separation distance in the horizontal direction and the vertical direction is not the same. In addition, the elliptical pattern holes H may be arranged in the vertical direction. That is, the shape of the pattern holes (H) may be formed to have a shape anisotropy (shape anisotropy), such as oval, rectangular, right triangle, pentagon.

5C illustrates a case where a circular pattern hole and an oval pattern hole are mixed. 5D illustrates a case where a square pattern hole and a rectangular pattern hole are mixed.

In addition, although not shown in the drawings, the shape of the pattern hole H may be formed in various ways, and the arrangement interval may be variously changed so that the pattern holes H are irregularly arranged. In addition, by stacking the porous films in which the various pattern holes H are formed to cross each other, an optical sheet having various stacking structures may be formed.

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.

BF1: first base film BF2: second base film
PF1: first porous film PF1: second porous film
PF3: third porous film PF4: fourth porous film
F: Film part H: Pattern hole
TC: Top Case GP: Guide Panel
LCDP: Liquid Crystal Display Panel OPT: Optical Sheet
REF: reflector DIFF: diffuser
CB: Cover Bottom LG: Light Guide Plate
DBLU: Direct type backlight unit EBLU: Edge type backlight unit
PR: Prism Sheet
L1: Condensing Light Path L2: Diffusing Light Path

Claims

An optical sheet having at least one porous film laminated thereon;
A light guide plate disposed under the optical sheet;
A light source disposed on at least one of side and bottom surfaces of the light guide plate; And
And a reflector disposed under the light guide plate.

The method of claim 1,
And the porous films of the optical sheet are bonded between the first base film and the second base film.

The method of claim 1,
The laminated porous films have the lowest refractive index of the porous film close to the light guide plate, and the backlight unit according to claim 1, wherein the porous films having a high refractive index are sequentially stacked.

The method of claim 1,
The porous film is a backlight unit, characterized in that it comprises a plurality of pattern holes in the optical film having a high refractive index.

The method of claim 4, wherein
The pattern hole is a backlight unit, characterized in that it comprises a shape having a shape isotropy such as circular and regular polygons.

The method of claim 4, wherein
The pattern hole is a back light unit, characterized in that it comprises a shape having anisotropy, such as shape and polygon.

The method of claim 4, wherein
And the pattern holes of the laminated porous films are alternately stacked with each other.