KR100827380B1 - Planar light source using a light pipe, back light unit and liquid crystal display having the same - Google Patents

Abstract

A surface light source device having a novel structure using a light pipe, a backlight unit having the same, and a liquid crystal display device are disclosed. The surface light source device according to the embodiment of the present invention is structured into a plurality of micro-prism shapes, and includes an inner surface on which light is incident and a smooth outer surface on which light incident on the inner surface is emitted, wherein the outer surface is the liquid crystal. A pair of hollow light pipes that output light input to the panel and include light emitting surfaces disposed substantially parallel to the liquid crystal panel, and disposed on opposite sides of the light pipes, and including a plurality of light emitting diodes. It includes a light source of, wherein the plurality of light emitting diodes are characterized in that arranged in each other in both light source.

Liquid Crystal Display, Backlight Unit, Surface Light Source Device

Description

Surface light source device using a light pipe, a backlight unit and a liquid crystal display device having the same {PLANAR LIGHT SOURCE USING A LIGHT PIPE, BACK LIGHT UNIT AND LIQUID CRYSTAL DISPLAY HAVING THE SAME}

1 is a perspective view illustrating a conventional liquid crystal display device.

2A is an exploded perspective view illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 2B is a cross-sectional view of the liquid crystal display of FIG. 2A.

FIG. 2C is a plan view of the surface light source device of FIG. 2B and illustrates an example in which light emitting diodes are disposed on both sides of a light pipe.

FIG. 2D is a cross-sectional view of the light pipe of FIG. 2B taken along line A-A. FIG.

FIG. 2E is an enlarged partial cross-sectional view of part C of FIG. 2C.

2F is a partial perspective view illustrating a portion of a liquid crystal display according to another exemplary embodiment of the present invention.

3A is a cross-sectional view of a liquid crystal display according to another exemplary embodiment of the present invention.

3B is a cross-sectional view taken along the line B-B of FIG. 3A.

3C and 3D are enlarged partial cross-sectional views of part D of FIG. 3B.

4A to 4C are cross-sectional views illustrating other embodiments of the diffusion layer and the reflector of FIG. 3B of the present invention.

The present invention relates to a surface light source device capable of providing planar light, and more particularly to a surface light source device having a new structure using a light pipe. The present invention also relates to a backlight unit and a liquid crystal display device having such a surface light source device.

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

Liquid crystal display devices have attracted attention as an alternative means of overcoming the shortcomings of the Cathode Ray Tube (CRT), which have been widely used since they have advantages such as miniaturization, light weight, and low power consumption. Is installed in almost all information processing equipment.

Such a liquid crystal display device generally applies an electric field to a liquid crystal layer composed of liquid crystals having a specific molecular arrangement to change the arrangement of the liquid crystals, and the birefringence, photoreactivity, and dichroism of the liquid crystals generated by the change in the molecular arrangement of the liquid crystals. And a change in optical properties such as light scattering specificity to a visual change, and is a display device using modulation of light by liquid crystal.

Meanwhile, a liquid crystal display device, which is a light-receiving element that does not have a self-luminous source, requires a separate light source device capable of illuminating the entire screen of the device from the back side. do.

In the conventional backlight unit, an elongated cylindrical Cold Cathode Fluorescent Lamp (CCFL) is mainly used as a light source for generating light, and according to the method in which the cold cathode fluorescent lamp is disposed, the backlight unit has an edge-lighting method. It is classified into edge-light method and direct lighting method.

The edge-light method is a method in which a light source is disposed on a side of a light guide plate for guiding light generated from a light source, and is applied to a relatively small liquid crystal display device such as a desktop computer or a laptop monitor. On the other hand, the direct method has been developed for use in medium and large display devices of 20 inches or more, and is a method of directly illuminating the front of the liquid crystal panel by arranging a plurality of light sources.

1 is a perspective view illustrating a conventional liquid crystal display device.

Referring to FIG. 1, the liquid crystal display device 30 includes a liquid crystal panel 20 and a backlight unit 10 disposed on a rear surface of the liquid crystal panel.

In understanding and practicing the present invention, the specific structure of the liquid crystal panel 20 is not important. Therefore, the basic structure of the liquid crystal panel 20 will be described within the range necessary for understanding the present invention.

The liquid crystal panel 20 generally includes a pair of transparent substrates, a liquid crystal layer interposed between the transparent substrates, a color filter layer formed on each of the transparent substrates, a black matrix, a pixel electrode, a common electrode, and a TFT array.

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

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

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

The liquid crystal layer is composed of a plurality of liquid crystal molecules, the liquid crystal molecules change the arrangement corresponding to the voltage difference generated between the pixel electrode and the common electrode, whereby the light provided from the backlight unit is the molecular arrangement of the liquid crystal layer The incident on the color filter corresponds to the change of.

The backlight unit 10 includes a light source unit 12, a light guide plate 14, a reflective sheet 16, and an optical sheet 18.

The light source unit 12 includes a light source 12a and a light source reflecting plate 12b.

As the light source 12a, an external electrode fluorescent lamp (EEFL) may be used in addition to the above-described cold cathode fluorescent lamp.

The external electrode fluorescent lamp has a brightness of 400 nit or more, which is more than 60% higher than that of a cold cathode fluorescent lamp, which makes it possible to further spread the application of TFT LCD, such as a TV requiring high brightness, and the cold cathode fluorescent lamp with the electrode inside the lamp. Unlike the electrodes, the electrodes are external and operate in parallel, reducing the voltage deviation between the glass and the lamp, enabling even brightness.

The light source 12a is disposed in parallel with the light guide plate 16 at one side of the light guide plate 16 in a state of being housed inside the light source reflecting plate 12b.

The light source reflecting plate 12b is disposed along the outer circumferential surface of the light source 12a and reflects the light generated from the light source 12a to the side of the light guide plate 14 to improve the efficiency of light incident on the light guide plate 14.

The side surface of the light guide plate 14 disposed adjacent to the light source unit 12 is a light incident surface for light to be incident, and the light incident through the light incident surface is uniformly mixed in the light guide plate 14, Light is emitted toward the liquid crystal panel (not shown) disposed above through the light emitting surface disposed in a substantially perpendicular relationship with the light incident surface.

The reflective sheet 16 reflects the light emitted to the rear surface of the light guide plate 14 back toward the light guide plate 14 to improve light utilization efficiency.

The optical sheet 18 may include a plurality of optical films such as the diffusion sheet 18a, the prism sheet 18b, and the protective sheet 18c.

The light emitted through the light guide plate 14 is incident on the diffusion sheet 18a, and the diffusion sheet 18a diffuses or condenses the incident light to uniform the luminance and widen the viewing angle.

On the other hand, the light passing through the diffusion sheet 18a is sharply lowered in brightness, the prism sheet 18b is used to compensate for this. Since the prism sheet 18b refracts the light emitted from the diffusion sheet 18a and concentrates the light incident at a low angle toward the front side, the prism sheet 18b raises the luminance in the effective viewing angle range.

The protective sheet 18c is located on the prism sheet 18b to prevent scratches of the prism sheet 18b and to re-expand the viewing angle reduced by the prism sheet 18b within a predetermined range.

In the edge-light type backlight unit having the above structure, not only the light efficiency is lowered because only light incident through one side of the light guide plate 14 is used, but also the light loss occurs in the light guide plate 14 itself. have.

Also, a direct backlight unit configured by placing a plurality of light sources, for example, cold cathode fluorescent lamps or external electrode fluorescent lamps, directly below the liquid crystal panel, a diffuser plate on the front side of the light source, and a reflective sheet on the rear side thereof. Likewise, a light loss occurs in an optical plate such as a diffusion plate, and thus has a problem of low light utilization efficiency.

In addition, when a plurality of light sources are disposed adjacent to each other, thermal convection occurs in a limited space of the liquid crystal display, thereby deforming the optical sheet disposed thereon, and also adversely affects the display quality of the liquid crystal display. Is pointed out.

In addition, in such a conventional backlight unit, a plurality of optical films are required in order to obtain uniform luminance, and light loss also occurs considerably in such optical films.

In order to solve this problem, the development of a surface light source device that emits light directly in the form of a plane has been recently developed, and in this regard, a flat fluorescent lamp (FEL), a light emitting diode (LED), Alternatively, a surface light source device using carbon nanotubes (CNT) is disclosed in US Pat. No. 6,771,330, US Patent Application No. 2004-004757, US Pat. No. 6,514,113, and the like.

However, such a conventional surface light source device is difficult to form a partition wall and a discharge cell for forming an electrode, and there are still many issues to be improved in terms of uniformity of luminance and power consumption.

Therefore, in view of these problems of the prior art, the manufacturing is easier than the conventional surface light source device, and there is still a need for development of a surface light source device that is good in terms of optical characteristics and power consumption.

The present invention is to solve the above problems of the prior art, an object of the present invention is to provide a surface light source device that is easier to manufacture than the conventional surface light source device.

In addition, another object of the present invention is to provide a surface light source device that is advantageous in terms of power consumption and heat generation by improving the light use efficiency and using a smaller number of light sources than conventional backlight units.

In addition, another object of the present invention is to provide a surface light source device that can easily cope with an increase in size and thickness of a display device.

Another object of the present invention is to provide a backlight unit and a liquid crystal display device having such a surface light source device.

In order to achieve the objects of the present invention as described above, in one aspect of the present invention, the present invention provides a surface light source device for outputting light provided to the liquid crystal panel on a plane. The surface light source device is structured into a plurality of micro-prism shapes, and includes an inner surface on which light is incident and a smooth outer surface on which light incident on the inner surface is emitted, wherein the outer surface outputs light input to the liquid crystal panel. A hollow light pipe including a light exit surface disposed substantially parallel to the liquid crystal panel and a pair of light sources disposed opposite to each other on both sides of the light pipe and including a plurality of light emitting diodes. In this case, the plurality of light emitting diodes are alternately arranged in both light source units.

In another aspect of the present invention, the present invention provides a backlight unit for illuminating a liquid crystal panel from the rear. The backlight unit is disposed on one side of the surface light source device and the surface light source device for outputting planar light for illuminating the liquid crystal panel, and receives the light output from the surface light source device to condense or uniformize the liquid crystal panel. At least one optical sheet to output to. Here, the surface light source device is structured in a pair of light source units including a plurality of light emitting diodes alternately arranged at a predetermined distance, and a plurality of micro-prism shape, the light provided from the light source unit disposed on each side A hollow outer surface including an incident inner surface and a smooth outer surface on which light incident on the inner surface is emitted, the outer surface outputting light input to the liquid crystal panel and including a light output surface disposed substantially parallel to the liquid crystal panel It includes a light pipe.

On the other hand, in another aspect of the present invention, the present invention, a liquid crystal panel for displaying an image by controlling the amount of light transmitted by changing the arrangement of the liquid crystal molecules of the liquid crystal layer in accordance with an electrical signal applied from the outside and the A liquid crystal display device including a backlight unit configured to provide light input to the liquid crystal panel from a rear of the liquid crystal panel. Here, the backlight unit is disposed on one side of the surface light source device and the surface light source device for outputting the light provided to the liquid crystal panel on a plane, and receives the light output from the surface light source device to focus or uniformize it At least one optical sheet to output to the liquid crystal panel. The surface light source device may include a pair of light source units including a plurality of light emitting diodes alternately arranged at a predetermined distance, and light provided from the light source units disposed on both sides of the pair of light source units. The hollow includes an inner surface of the incident and a smooth outer surface of the light incident on the inner surface, the outer surface outputs light input to the liquid crystal panel and comprises a light output surface disposed substantially parallel to the liquid crystal panel It includes a light pipe.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention. However, the same reference numerals are used for the same or similar parts in the following drawings.

FIG. 2A is an exploded perspective view illustrating a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 2B is a cross-sectional view of the liquid crystal display of FIG. 2A. In addition, FIG. 2C is a plan view of the surface light source device of FIG. 2B, which is a view for explaining an aspect in which light emitting diodes are disposed on both sides of a light pipe.

2A to 2C, the liquid crystal display device 300 according to an exemplary embodiment of the present invention may include a liquid crystal panel 200 displaying a predetermined image according to an electrical signal including display information applied from the outside. The backlight unit 100 is disposed on the rear surface of the liquid crystal panel to illuminate the liquid crystal panel 200.

In understanding and implementing the present invention, the precise structural characteristics of the liquid crystal panel 200 are not important, and the spirit of the present invention may be widely applied to liquid crystal panels having any structure commonly used in liquid crystal display devices. For example, the structure of the liquid crystal panel (20 of FIG. 1) described in detail in the description of the prior art can be employed without limitation to the liquid crystal panel 200 of the present invention. Therefore, the specific structure of the liquid crystal panel 200 will not be specifically described here again.

The backlight unit 100 is located at the rear of the liquid crystal panel 200 and provides light, for example, white light, to the liquid crystal panel 200.

The backlight unit 100 is disposed between the surface light source device 110 and the liquid crystal panel and the surface light source device to provide a planar light sufficient to illuminate the visible surface of the liquid crystal panel 200 to provide light provided by the surface light source device. And an optical sheet 180 that modulates the liquid crystal panel into light suitable for illuminating the liquid crystal panel.

In addition, the surface light source device 110 may be disposed under a pair of the light source unit 120 for generating light provided to the liquid crystal panel 200, the light pipe 140 disposed between the light source units, and a lower portion of the light pipe. Reflective sheet 160.

Each light source unit 120 includes a plurality of light emitting diodes 120a for generating light having a predetermined wavelength, a printed circuit board 120b on which the light emitting diodes are mounted, and a housing 120c for supporting them.

The light emitting diode 120a is more environmentally friendly than cold cathode fluorescent lamps generally employed in conventional backlight units, and has excellent color reproducibility and contrast. There is an advantage in that it is possible.

There is no restriction on the type of the light emitting diode 120a, and a single white light emitting diode or a combination of three light emitting diodes generating colors of red (R), green (G), and blue (B) may be used. It is possible. In addition, the number of light emitting diodes 120a may be appropriately selected according to the size of the liquid crystal panel 200 to be illuminated.

The light emitting diodes 120a are mounted in a predetermined arrangement on the printed circuit board 120b, and external power is electrically connected to the light source 120a through a wiring pattern formed on the printed circuit board 120b.

The housing 120c accommodates the printed circuit board 120b on which the plurality of light emitting diodes 120a are mounted and supports them in the apparatus. The housing 120c may be made of metal or plastic.

In addition, the housing 120c may include a groove into which the printed circuit board 120b may be inserted, as shown in FIG. 2A. In addition, in order to improve light utilization efficiency, the inner wall of the housing 120c is preferably coated with a material capable of reflecting light.

The light source unit 120 is disposed on both sides of the light pipe 140, and the light generated from the light source unit travels from both sides of the light pipe 140 to the inside thereof.

However, it should be noted that light generated from the light emitting diode 120a has a constant directivity unlike a linear light source such as a cold cathode fluorescent lamp. That is, when the optical axes of the light emitting diodes 120a of the light source unit 120 disposed on both sides of the light pipe 140 coincide with each other, the light will be substantially lost inside the light pipe 140. Therefore, in order to improve light utilization efficiency, it is very important to design the arrangement of the light emitting diodes 120a such that the optical axes of the light emitting diodes 120a disposed opposite to each other on both sides of the light pipe 140 do not coincide with each other. Do.

In one embodiment of the present invention, the light emitting diodes 120a on both sides of the light pipe 140 are alternately arranged left and right as shown in FIG. 2C. Therefore, the optical axes of the light emitting diodes 120a shown in dotted lines do not coincide with each other. As a result, more uniform light is incident on the inside of the light pipe 140, and the loss of light is also significantly reduced.

The light pipe 140 is disposed on the rear surface of the liquid crystal panel 200, and both side surfaces of the light pipe 140 which are adjacent to the light source unit 120 become a light incident surface, and the liquid crystal panel 200 is disposed with the optical sheet 180 interposed therebetween. The opposing face becomes a light exit face from which light is emitted. The light exit surface is preferably equal to or larger than the area of the visible surface of the liquid crystal panel 200 so that light can be uniformly provided to the entire visible surface of the liquid crystal panel 200.

Even if the light source unit 120 is disposed only on the side of the light pipe 140, when the light pipe 140 has excellent light transmission capability and extremely low light loss therein, a plurality of light cathodes such as a cold cathode fluorescent lamp or a light emitting diode may be used. The light source may be disposed on the rear surface of the liquid crystal panel to obtain light efficiency comparable to that of the conventional direct type backlight unit that directly illuminates the rear surface of the liquid crystal panel. In addition, there is an advantage that the number of use of the light emitting diode can be significantly reduced compared to the conventional to obtain a relatively the same brightness.

Meanwhile, in another embodiment of the present invention, the light source unit 120 may be disposed only on one side of the light pipe 140. As such, when the light source unit 120 is disposed only on one side of the light pipe 140, the light source unit 120 includes reflecting means capable of reflecting light on the other side thereof to be radiated from the light source 120a to terminate the light pipe 140. It is desirable to be able to reuse the light transmitted until. In addition, in order to uniformize the light emitted from the light pipe 140, the light pipe may be tapered in a tapered shape such that the cross-sectional area of the light pipe 140 decreases from one end disposed adjacent to the light source 120a to the other end of the opposite side. 140, it is desirable to design. Hereinafter, the structure of the light pipe 140 will be described in more detail with reference to the accompanying drawings.

2D is a cross-sectional view of the light pipe of FIG. 2A taken along line A-A, and FIG. 2E is an enlarged partial cross-sectional view of part C of FIG. 2C.

2D and 2E, the light pipe 140 is a hollow (hollow) optical waveguide filled with a transparent medium, for example air, whose cross section is elliptical or rectangular. The light pipe 140 has a structure suitable for transmitting light input through one or both sides thereof in the longitudinal direction thereof.

In one embodiment of the invention, the inner surface 140b of the light pipe 140 is structured in a microprism shape in which a plurality of microprisms are arranged at a fine pitch along its length direction. The inner surface 140b of the light pipe 140 is a surface on which light input to the light pipe is incident. Each prism preferably has a structure of an isosceles triangle with approximately 90 degrees of vertex as shown in FIG. 2E.

The outer surface 140a of the light pipe 140 is a smooth, unstructured surface, and at least a part of the outer surface is a light exit surface for outputting light input to the light pipe in a direction of a liquid crystal panel (not shown).

On the other hand, depending on the selection, the outer surface 140a of the light pipe 140 may be structured, and the inner surface 140b may not be structured.

The distance between the outer surface 140a and the inner surface 140b may vary depending on the environment of use, but considering the light loss, it is preferable to have a value between 50 and 300 μm.

The material of the light pipe 140 is preferably a thermoplastic resin material having good light transmittance and having a good balance of mechanical properties (particularly impact resistance), heat resistance, and electrical properties. More preferably, the light pipe 140 is composed of, but not limited to, polyethylene terephthalate (PET), polycarbonate (PC) or polymethyl methacrylate (PMMA). Most preferably, the light pipe 140 is composed of polymethyl methacrylate. Polymethyl methacrylate is high in strength and therefore not easily broken and easily deformed. In addition, the visible light transmittance is high, making it suitable as a light source material.

In one embodiment of the invention, the light pipe 140 may be fabricated by conventional plastic molding methods known in the art such as injection or extrusion. Those skilled in the art will be able to manufacture the light pipe 140 of the present invention from the above-mentioned materials using these molding methods without further explanation.

In another embodiment of the present invention, the light pipe 140 may also be manufactured by coating a UV curing resin on a polymer base film.

More specifically, first, the surface of the base film is compressed by coating an ultraviolet curing resin (UV curing resin) on the master, and then irradiated with ultraviolet rays to transfer the fine prism pattern to the base film, one side is structured An optical film is produced. Then, with proper heat applied, the optical film is rolled to complete the light pipe 140 of the structure described above with the structured side facing inward.

2A and 2B, the surface light source device 110 according to the exemplary embodiment of the present invention includes the reflective sheet 160 disposed under the light pipe 140. The reflective sheet 160 reflects the light emitted through the bottom of the light pipe 140 and enters the light pipe 140 to improve light utilization efficiency.

In one embodiment of the present invention, the reflective sheet 160 is coated with silver (Ag) on a sheet made of SUS, Brass, aluminum, PET, and the like, even if the heat is generated fine titanium coating to prevent deformation due to endothermic heat for a long time Can be produced. In addition, in another embodiment of the present invention, the reflective sheet 160 may be manufactured by dispersing bubbles for scattering light on a sheet made of synthetic resin such as PET.

An optical sheet 180 is disposed between the liquid crystal panel 200 and the surface light source device 110, and the optical sheet includes a diffusion sheet 180a, a prism sheet 180b, and a protective sheet 180c.

The light emitted through the light exit surface of the light pipe 140 passes through the diffusion sheet 180a, and the diffusion sheet 180a diffuses or condenses the incident light to uniform the luminance and widen the viewing angle.

On the other hand, the light passing through the diffusion sheet 180a is sharply lowered in brightness, the prism sheet 180b is used to compensate for this. Since the prism sheet 180b refracts the light emitted from the diffusion sheet 180a and concentrates the light incident at a low angle toward the front side, the luminance increases in the effective viewing angle range.

The protective sheet 180c is located on the prism sheet 180b to prevent scratches of the prism sheet 180b and to re-expand the viewing angle reduced by the prism sheet 180b within a predetermined range.

In understanding and practicing the present invention, the precise structural and material properties of the optical sheet 180 are not critical, and the backlight unit employing the optical sheet using any structure and material commonly used in the backlight unit is not limited to the present invention. Ideas can be applied broadly.

Hereinafter, operations of the surface light source device 110, the backlight unit 100 and the liquid crystal display device 300 including the same, will be described with reference to the accompanying drawings.

Referring again to FIG. 2B, when power is applied to the light sources 120a, light is generated from the light sources 120a, and the light passes through both sides of the light pipe 140 to the inside of the light pipe 140. Is entered.

When light input into the light pipe 140 is incident at a threshold angle θ c which is determined by a ratio of the refractive indexes between the light pipe 140 and the medium surrounding the light pipe, it is well known in the art. By the total reflection condition according to Snell's Law, the light is reflected and again travels in the longitudinal direction of the light pipe 140 substantially inside the light pipe 140. At this time, since the medium filling the inside of the light pipe 140 is air, light may be guided inside the light pipe 140 with almost no loss.

Meanwhile, light incident at an angle equal to or less than the critical angle θ c is emitted through the outer surface of the light pipe 140. Here, the light emitted to the bottom of the light pipe 140 is reflected by the reflective sheet 160 disposed below the light pipe and is input again to the inside of the light pipe 140. On the other hand, the light emitted through the upper surface of the light pipe 140, that is, the light exit surface is incident on the optical sheet 180 disposed on the light pipe 140.

The light emitted through the light exit surface of the light pipe 140 is incident on the diffusion sheet 180c first, and the diffusion sheet 180c diffuses or condenses the incident light to uniform the luminance and widen the viewing angle.

Light passing through the diffusion sheet 180a is incident on the prism sheet 180b disposed thereon, and the prism sheet 180b refracts the incident light so that light incident at a low angle is visible on the visible surface of the liquid crystal panel 200. To focus.

The light passing through the diffusion sheet 130b is incident on the protective sheet 130a disposed thereon, and the viewing angle reduced by the prism sheet 180b is re-expanded within a predetermined range to enter the liquid crystal panel 200. Done.

The liquid crystal panel 200 implements a predetermined image by changing the molecular arrangement of the liquid crystal layer according to an electrical signal including image information applied from the outside to control light transmittance.

Hereinafter, other embodiments of the present invention will be described.

2F is a partial perspective view illustrating a portion of a liquid crystal display according to another exemplary embodiment of the present invention. However, illustration of the same parts as the above-described embodiments are omitted for convenience of description.

In addition, the above-described embodiment provides a case in which the surface light source device 110 is configured by using one light pipe 140, but according to a selection, the same size as that shown in FIG. 2F is manufactured. It is also possible to configure the surface light source device 110 by arranging the plurality of light pipes 140 close to each other. In this case, since the light pipes 140 have the same size, they can be optically connected by simply placing them in close contact with each other.

In this way, it is also possible to actively cope with the enlargement of the display device. That is, the surface light source device 110 having a large area can be simply arranged by arranging the light pipes 140 vertically and horizontally according to the size of the liquid crystal display (not shown) and arranging light sources (120 of FIG. 2B) on both sides thereof. Can be implemented.

3A is a cross-sectional view of a liquid crystal display according to another exemplary embodiment of the present invention. 3B is a cross-sectional view taken along the line B-B of FIG. 3A, and FIGS. 3C and 3D are enlarged partial cross-sectional views of part D of FIG. 3B. Meanwhile, in describing the present embodiment, detailed description of the same configuration as the above-described embodiments will be omitted.

Referring to FIGS. 3A and 3B, the liquid crystal display device 400 may include a liquid crystal panel 200 displaying a predetermined image according to an electrical signal applied from the outside and a rear surface of the liquid crystal panel to illuminate the liquid crystal panel. It includes a backlight unit 100 disposed.

The backlight unit 100 is disposed between the surface light source device 110 and the liquid crystal panel and the surface light source device that provide plane light sufficient to illuminate the visible surface of the liquid crystal panel 200, and the light provided from the surface light source device. It includes an optical sheet 180 for modulating the light into a light suitable for illuminating the liquid crystal panel.

The surface light source device 110 may include a light source unit 120 for generating light provided to the liquid crystal panel 200, a light pipe 140 disposed adjacent to the light source unit, and a diffusion layer 142 disposed on an outer surface of the light pipe. And a reflector 144 disposed inside the light pipe.

The light source unit 120 includes a plurality of light emitting diodes 120a for generating light having a predetermined wavelength, a printed circuit board 120b on which the light emitting diodes are mounted, and a housing 120c for storing them.

Light sources 120 are disposed on both sides of the light pipe 140, and the arrangement relationship of the light emitting diodes 120a is the same as in the above-described embodiment. Therefore, the optical axes of the light emitting diodes 120a disposed opposite to both sides of the light pipe 140 do not coincide with each other.

The light pipe 140 is disposed adjacent to the light source unit 120 at the rear side of the liquid crystal panel 200, and both sides of the light pipe unit 140 adjacent to the light source unit 120 serve as light incident surfaces, and the optical sheet 180 is interposed therebetween. On the other hand, the surface facing the liquid crystal panel 200 becomes a light exit surface from which light is emitted.

In this embodiment, the inner surface of the light pipe 140 is a structured surface in which a plurality of linear prisms are disposed adjacent to each other, whereas the outer surface is not structured. On the other hand, in another embodiment of the present invention, the outer surface of the light pipe 140 may be structured, the inner surface may not be structured.

A diffusion layer 142 is disposed on an outer surface of the light pipe 140, and the diffusion layer emits light incident through the light pipe 140 to the outside and simultaneously scatters the light output through the light pipe 140. Equalize.

Referring to FIGS. 3C and 3D, the diffusion layer 142 includes a resin base material 142b and a plurality of beads 142a dispersed and disposed on the base material.

As the base material 142b, it is preferable to use an acrylic resin such as polyacrylate or polymethyl methacrylate (PMMA) that is transparent and has excellent heat resistance and mechanical properties.

The bead 142a may be made of the same type or different types of resin as the base material 142b.

Meanwhile, the beads 142a may be included in an amount of 25 wt% to 35 wt% with respect to the base material 142 b. More preferably, the weight ratio of the beads to the base material is 30wt%.

In one embodiment of the present invention, the size and distribution of the beads 142a are random as shown in FIG. 3C. Since beads of various sizes 142a are irregularly distributed in the base material 142b, the haze effect increases, so that defects such as scratches generated in the base material 142b due to physical contact may be caused by the liquid crystal panel 200 (see FIG. 3A). It is effective to prevent the projection as it is.

In another embodiment of the present invention, the plurality of beads 142b have substantially the same size and are distributed substantially uniformly in the base material 132a as shown in FIG. 3D. As such, when the beads 142a having substantially the same size are uniformly distributed in the base material 142b, the haze effect is reduced, but the luminance is increased. That is, as the beads 142a are regularly distributed in the base material 142b, the haze effect decreases but the luminance increases.

The diffusion layer 142 having the above-described structure may be obtained through various methods known in the art.

For example, the diffusion layer 142 may be obtained by compressing the film obtained by dispersing the beads in a liquid resin and solidifying the film solidified on the outer surface of the light pipe 140 in a state where the film is heated to an appropriate temperature. In addition, the liquid resin in which the beads are dispersed may be obtained by coating the outer surface of the light pipe 140 to a predetermined thickness.

Referring again to FIGS. 3A and 3B, a reflector 144 is disposed inside the light pipe 140.

The reflector 144 is disposed on a structured surface inside the light pipe 140, and reflects the light incident directly from the light source 120a or reflected from the light pipe 140 so that the light reflects the light pipe 140. The light utilization efficiency is improved by preventing the emission from the bottom surface of the backplane).

In addition, the reflector 144 reflects the light generated from the light source 120a to be emitted to the outside through the light exit surface of the light pipe 140. That is, the reflector 144 serves to allow the reflected light to re-inject into the light pipe 140 at a critical angle θc or less to be emitted to the outside of the light pipe 140.

The reflector 144 is made of a highly reflective material. For example, the reflector 144 may be obtained by coating a metal material having excellent reflectivity such as aluminum (Al) or silver (Ag) on the resin surface.

An optical sheet 180 composed of a diffusion sheet 180a, a prism sheet 180b, and a protective sheet 180c is disposed between the liquid crystal panel 200 and the surface light source device 110.

Hereinafter, the operation of the liquid crystal display device 400 according to the embodiment of the present invention will be described with reference to the drawings. However, the case where the refractive index of the light pipe 140 is larger than the refractive index of the diffusion layer 142 disposed on the outer surface will be described by way of example.

Referring again to FIG. 3A, light generated from the light source 120a disposed at both sides of the light pipe 140 is input into the light pipe 140 through both sides of the light pipe 140.

When light input to the inside of the light pipe 140 is incident on the interface between the light pipe 140 and the diffusion layer 142 at a critical angle θ c or more predetermined by the ratio of the refractive indexes of the optical film and the diffusion layer, total reflection When the condition is satisfied, the light is totally reflected and again propagates substantially in the longitudinal direction inside the light pipe 140. At this time, since the medium inside the light pipe 140 is air, light may be guided inside the light pipe 140 with almost no loss.

A portion of the light propagated into the light pipe 140 is reflected at the surface of the reflector 144 and is incident on the interface between the light pipe 140 and the diffusion layer 142, where the incident angle is the critical angle θ c. Below, light is output to the outside of the light pipe 140 and input to the diffusion layer 142.

Here, the light input to the diffusion layer 142 is uniformized while being scattered by the beads (142a of FIGS. 3A and 3B) dispersed in the diffusion layer 142 and input to the optical sheet 180 disposed thereon. .

Light passing through the diffusion layer 142 is first input to the diffusion sheet 180a, which diffuses or condenses the light to make the luminance uniform and widen the viewing angle.

The light passing through the diffusion sheet 180a is incident on the prism sheet 180b disposed thereon, and the prism sheet 180b refracts the incident light so that light incident at a low angle is visible on the visible surface of the liquid crystal panel 200. To focus.

Light passing through the prism sheet 130b is incident on the protective sheet 130a disposed thereon, and the viewing angle reduced by the prism sheet 180b is re-expanded within a predetermined range and is incident on the liquid crystal panel 200. Done.

The liquid crystal panel 200 implements a predetermined image by controlling the light transmittance in each pixel by adjusting the molecular arrangement of the liquid crystal layer of each pixel according to an electrical signal including image information applied from the outside.

In the above-described embodiment, the diffusion layer 142 is disposed so as to completely surround the outer surface of the light pipe 140, the reflector 144 has a structure disposed inside the light pipe 140, but the diffusion layer 142 and The structure of the reflector 144 may be variously modified by those skilled in the art. Hereinafter, some modified examples of the structures of the diffusion layer 142 and the reflector 144 will be described with reference to the drawings.

4A to 4C are cross-sectional views illustrating other embodiments of the diffusion layer and the reflector of FIG. 3B of the present invention. However, the following description will focus on the structural differences between the diffusion layer 142 and the reflector 144 illustrated in FIG. 3B.

Referring to FIG. 4A, in another embodiment of the present invention, the diffusion layer 142 is disposed to completely surround the outer surface of the light pipe 140, and the reflector 144 is disposed on the bottom surface of the diffusion layer 142, as shown. Can be arranged.

Referring to FIG. 4B, in another embodiment of the present invention, both the diffusion layer 142 and the reflector 144 may be disposed only at some portion of the outer surface of the light pipe 140. In this case, the diffusion layer 142 for diffusing the light emitted through the light pipe 140 is disposed toward the liquid crystal panel (not shown), and reflects the light emitted through the light pipe 140 to re-inject. It is important for the reflector 144 to be disposed on the bottom surface of the light pipe 140 to face the diffusion layer 142.

Referring to FIG. 4C, in another embodiment of the present invention, the diffusion layer 142 may be disposed to completely surround the outer surface of the light pipe 140, and the reflector 144 may be disposed inside the light pipe 140. have. In this case, however, there is no structure such as a fine prism in a part of the inner surface of the light pipe 140 where the reflector 144 is disposed.

Preferred embodiments of the present invention described above are merely disclosed for purposes of illustration, and those skilled in the art having various ordinary knowledge of the present invention will be able to make various modifications, changes, additions within the spirit and scope of the present invention. And additions should be considered to be within the scope of the following claims.

Since the surface light source device can be implemented in a relatively simple structure using a light pipe, the present invention has an advantage that the surface light source device can be more easily manufactured than in the related art.

In addition, when the light source unit is configured according to the present invention, the light utilization efficiency is increased, and thus, a smaller number of light emitting diodes can be used than the conventional backlight unit. Therefore, there is an advantage that a surface light source device advantageous in terms of power consumption can be obtained.

In addition, in the present invention, since the heat generating light source is housed inside the light pipe, the heat generated from the light source only convections inside the light pipe, so that the heat generated from the light source is suppressed to the optical sheet as much as possible. Since there is an advantage that thermal deformation of the optical sheet can be alleviated.

In addition, the light pipe of the present invention can easily change the size according to the environment used, there is an advantage that can actively respond to the increase in size and thickness of the display device.

Claims (14)

A backlight unit for illuminating a liquid crystal panel from the rear, A surface light source device for outputting planar light for illuminating the liquid crystal panel; And At least one optical sheet disposed on one side of the surface light source device, and receives the light output from the surface light source device to condense or equalize it and output the light to the liquid crystal panel, The surface light source device, A pair of light source units including a plurality of light emitting diodes alternately arranged at a predetermined distance; And An inner surface structured into a plurality of micro-prism shapes, from which light provided from light source units disposed on both sides is incident; And a smooth outer surface on which light incident on the inner surface is emitted, wherein the outer surface outputs light input to the liquid crystal panel and includes a hollow light pipe including a light output surface disposed substantially parallel to the liquid crystal panel. Backlight unit comprising a. The method of claim 1, wherein the light source unit, At least one printed circuit board on which the light emitting diode is mounted and electrically connecting an external power source to the light emitting diode; And And a housing accommodating and supporting the printed circuit board on which the light emitting diode is mounted. The surface light source device of claim 1, further comprising a reflection sheet disposed under the light pipe, reflecting light emitted through the bottom surface of the light pipe, and inputting the light back into the light pipe. Backlight unit. The method of claim 1, The surface light source device, A base material disposed on an outer surface of the light pipe, the light emitted from the light exit surface of the light pipe being input, and made of a resin which may transmit light; And And a diffuser layer disposed on the base material and including a plurality of beads capable of scattering light input to the base material. The method of claim 1, The surface light source device, And a reflector having a surface capable of reflecting light. A liquid crystal panel for displaying an image by controlling a transmission amount of light input by changing an arrangement of liquid crystal molecules of the liquid crystal layer according to an electrical signal applied from the outside; And It includes a backlight unit for providing light input to the liquid crystal panel from the rear of the liquid crystal panel, The backlight unit, A surface light source device for outputting light provided to the liquid crystal panel on a plane; And It is disposed on one side of the surface light source device, and includes at least one optical sheet for receiving the light output from the surface light source device to condense or uniformize the output to the liquid crystal panel, The surface light source device, A pair of light source units including a plurality of light emitting diodes alternately arranged at a predetermined distance; And An inner surface structured into a plurality of micro-prism shapes and having incident light provided from the light source units disposed on both sides thereof; And a smooth outer surface on which light incident on the inner surface is emitted, wherein the outer surface outputs light input to the liquid crystal panel and includes a hollow light pipe including a light output surface disposed substantially parallel to the liquid crystal panel. Liquid crystal display device comprising a. The semiconductor device of claim 6, further comprising: a printed circuit board on which the light emitting diode is mounted and electrically connecting an external power supply to the light emitting diode; And And a housing accommodating and supporting the printed circuit board on which the light emitting diode is mounted. The light source apparatus of claim 6, wherein the surface light source device further comprises a reflective sheet disposed under the light pipe to reflect light emitted through the bottom surface of the light pipe and input the light back into the light pipe. Liquid crystal display device. The method of claim 6, The surface light source device, A base material disposed on an outer surface of the light pipe and inputting light emitted from the light exit surface of the light pipe, wherein the base material is made of a resin that can transmit light; And And a diffusion layer disposed on the base material and including a plurality of beads capable of scattering light input to the base material. The method of claim 6, The surface light source device, The liquid crystal display device further comprising a reflector having a surface capable of reflecting light. In the surface light source device for outputting the light provided to the liquid crystal panel on a plane, The inner surface is structured in a plurality of micro-prism shape, the light is incident; And a smooth outer surface on which light incident on the inner surface is emitted, wherein the outer surface outputs light input to the liquid crystal panel and includes a light output surface disposed substantially parallel to the liquid crystal panel; And A pair of light sources disposed opposite to each other on both sides of the light pipe and including a plurality of light emitting diodes, And the plurality of light emitting diodes are alternately disposed in both light source units. The display device of claim 11, further comprising: a printed circuit board on which the light emitting diode is mounted and electrically connecting the external power supply to the light emitting diode; And And a housing for receiving and supporting the printed circuit board on which the light emitting diode is mounted. The method of claim 11, The surface light source device, A base material disposed on an outer surface of the light pipe and inputting light emitted from the light exit surface of the light pipe, wherein the base material is made of a resin that can transmit light; And And a diffuser layer disposed on the base material and including a plurality of beads capable of scattering light input to the base material. The method of claim 11, The surface light source device, And a reflector having a surface capable of reflecting light.

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