KR100750995B1 - Planar light source using a light pipe, back light unit and liquid crystal display having the same - Google Patents

Abstract

A planar light source using a light pipe, a backlight unit and an LCD(Liquid Crystal Display) having the same are provided to facilitate a fabrication method of a planar light source by combining a point light source or a line light source with a light pipe so as to realize a planar light source. A planar light source(110) emits a planar light for illuminating a liquid crystal panel(200). At least one optical sheet(180) is disposed at one side of the planar light source. The optical sheet receives the light emitted from the planar light source, concentrates or uniformizes the light to provide it to the liquid crystal panel. The planar light source includes a light source unit(120) and at least one light pipe(140). The light source unit provides the light to be inputted to the liquid crystal panel and includes a plurality of LEDs(Light Emitting Diodes)(122) arranged such that optical axes of at least some of the LEDs. The light pipe includes an inner surface having a shape of a plurality of micro-prisms and a flat outer surface. The light provided from the light source unit enters the inner surface and then is emitted through the outer surface. The outer surface includes a light emitting surface that emits the light to be inputted to the liquid crystal panel and is disposed substantially parallel to the liquid crystal panel.

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 illustrating the liquid crystal display of FIG. 2A.

FIG. 2C is a cross-sectional view of the light source unit taken along the line A-A of FIG. 2B.

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

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

FIG. 2F is a plan view of the light pipe of FIG. 2B, illustrating a waveguide mode of light in the light pipe. FIG.

FIG. 2G is a cross-sectional view of another embodiment of the light source unit of FIG. 2B.

FIG. 2H is a partial perspective view of another embodiment of the light pipe of FIG. 2B.

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

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

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

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

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 display device which converts a change in optical properties such as light scattering to a visual change and uses 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 in recent years, and in connection with this, a flat fluorescent lamp (FEL), a light emitting diode (LED) Or a surface light source device using carbon nanotubes (CNTs) is disclosed in US Patent No. 6,771,330, US Patent Application No. 2004-004757, US Patent 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.

Another object of the present invention is to provide a surface light source device which is advantageous in terms of power consumption and heat generation by using a smaller number of light sources than conventional backlight units.

Another object of the present invention is to provide a surface light source device having a structure capable of providing more uniform plane light.

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 above object of the present invention, the backlight unit for illuminating the liquid crystal panel according to an embodiment of the present invention, the surface light source device for outputting the plane light for illuminating the liquid crystal panel and the 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 collect or uniformize it and output it to the liquid crystal panel. The surface light source device is configured to provide a light input to the liquid crystal panel, a light source unit including a plurality of light emitting diodes three-dimensionally arranged such that at least some of the optical axes are different, and a plurality of micro-prism shapes. An inner surface to which light provided from the light is incident and a smooth outer surface to which light incident on the inner surface is emitted, the outer surface outputting light input to the liquid crystal panel and having a light exit surface disposed substantially parallel to the liquid crystal panel. At least one hollow light pipe.

In addition, the liquid crystal display device according to an embodiment of 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 And a backlight unit configured to provide light input to the liquid crystal panel from the rear of the liquid crystal panel. 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 in a flat shape, and receives the light output from the surface light source device to condense or uniformize it. At least one optical sheet output to the liquid crystal panel. The surface light source device is configured to provide a light input to the liquid crystal panel, a light source unit including a plurality of light emitting diodes three-dimensionally arranged such that at least some of the optical axes are different, and a plurality of micro-prism shapes. An inner surface to which light provided from the light is incident and a smooth outer surface to which light incident on the inner surface is emitted, wherein the outer surface is configured to output light input to the liquid crystal panel and to be substantially parallel to the liquid crystal panel. At least one hollow light pipe.

In addition, the surface light source device for outputting the light provided to the liquid crystal panel according to an embodiment of the present invention in a planar shape, the light source unit including a plurality of light emitting diodes arranged in three dimensions so that at least some of the optical axis is different, It is structured in the shape of a micro-prism, and includes an inner surface to which the light provided from the light source is incident and a smooth outer surface to which the light incident on the inner surface is emitted, the outer surface outputs light input to the liquid crystal panel and the liquid crystal panel And at least one hollow light pipe, the light exit surface comprising a light exit surface disposed substantially parallel to the.

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 view showing the liquid crystal display 300 according to the exemplary embodiment of the present invention, and FIG. 2B is a combined cross-sectional view illustrating the liquid crystal display 300 of FIG. 2A. FIG. 2C is a cross-sectional view of the light source unit taken along the line A-A of FIG. 2B. 2D is a cross-sectional view of the light pipe cut along the line B-B in FIG. 2B, and FIG. 2E is a partial cross-sectional view showing an enlarged portion C of FIG. 2D. 2F is a plan view of the light pipe of FIG. 2B for explaining the waveguide mode of light in the light pipe.

First, referring to FIGS. 2A to 2C, the liquid crystal display 300 displays a liquid crystal panel 200 and a liquid crystal panel 200 that display a predetermined image according to an electrical signal including display information applied from the outside. It includes a backlight unit 100 disposed on the rear of the liquid crystal panel for illumination.

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. The optical sheet 180 modulates light suitable for illuminating the liquid crystal panel.

In addition, the surface light source device 110 includes a pair of light source units 120 for generating light provided to the liquid crystal panel 200, a pair of housings 130 in which each light source unit is accommodated and supported, and adjacent to the light source units. The light pipe 140 is disposed and the reflective sheet 160 is disposed below the light pipe.

The light source unit 120 includes a plurality of light emitting diodes 122 for generating light, a plurality of printed circuit boards 124a, 124b, and 124c disposed under the light emitting diodes, and heat radiation to which the printed circuit boards are attached. Member 126.

The light emitting diode 122 is not limited, and one white light emitting diode may be used, or a combination of three light emitting diodes generating colors of red (R), green (G), and blue (B) may be used. .

The light emitting diodes 122 are mounted on the printed circuit boards 124a, 124b, and 124c and are electrically connected to an external power source (not shown) through a wiring pattern of the printed circuit board 124a. Here, each printed circuit board (124a, 124b, 124c) can be separated from each other, but electrically connected to each other.

The printed circuit boards 124a, 124b, and 124c are attached to the heat dissipation member 126 through an adhesive means made of a material having high thermal conductivity such as, for example, a thermal conductive resin, and the heat dissipation member 126 is a light emitting diode 122. Heat dissipated to outside.

In addition, the heat dissipation member 126 may include the printed circuit boards 124a, 124b, and 124c so that the light emitting diodes 122 mounted on the printed circuit boards 124a, 124b, and 124c may be three-dimensionally disposed in space. ) Is adhered to the front surface 126 and both side surfaces (126a, 126c) to form a predetermined angle.

That is, the printed circuit boards 124a, 124b, and 124c are attached as shown to the front surface 126b of the heat dissipation member 126 and both side surfaces 126a and 126c at a predetermined angle with the front surface, thereby. The optical axes of the light emitting diodes 122 mounted on one printed circuit board 124a, 124b or 124c are not parallel to the optical axes of the light emitting diodes 122 mounted on the other printed circuit boards 124b, 124c or 124a. Staggered.

The light source unit 120 is optically connected to both ends of the light pipe 140 to be described later in a state in which the light source unit is accommodated in the housing 130 in which a space for accommodating the light source unit is formed. Preferably, as shown in FIG. 2B, the end of the light pipe 140 is disposed in a state of being inserted into the housing 130. Accordingly, the light generated from the light emitting diode 122 travels from both sides of the light pipe 140 to the inside thereof.

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.

In the present embodiment, the light source unit 120 is disposed on the side of the light pipe 140, but because of the excellent light transmission capability of the light pipe 140 and extremely low light loss therein, a cold cathode fluorescent lamp or light emission By arranging a plurality of light sources such as diodes on the rear side of the liquid crystal panel, it is possible to obtain a light efficiency comparable to the conventional direct type backlight unit which directly illuminates the rear side 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 unit 120 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 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 using 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 including the same, and the liquid crystal display device 300 according to the exemplary embodiment will be described with reference to the accompanying drawings.

Referring again to FIG. 2B, when power is applied to the light source unit 120, light is generated from the light emitting diodes 122, and the light is generated inside the light pipe 140 through both sides of the light pipe 140. Is entered.

At this time, as already mentioned, since the plurality of light emitting diodes 122 in the light source unit 120 are three-dimensionally arranged so that the optical axes are crossed with each other, the light is incident in a wide angle range as shown in FIG. 140 is guided inside.

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.

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.

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.

FIG. 2G is a cross-sectional view of another embodiment of the light source unit of FIG. 2B.

Referring to FIG. 2G, the light source unit 220 includes a plurality of light emitting diodes 122 for generating light, a plurality of printed circuit boards 124a, 124b, and 124c on which the light emitting diodes are mounted and electrically connected to each other. And a heat dissipation member 126 having faces 126a, 126b, 126c to which substrates can be attached.

In the above-described embodiment, the angle between the front surface 126b of the heat dissipation member 126 and the both side surfaces 126a and 126c was an acute angle, but in this embodiment, the front surface 126b and the both sides ( The angle formed by 126a and 126c is different in that it is an obtuse angle. However, the optical axes of the light emitting diodes 122 mounted on each printed circuit board 124a, 124b or 124c are staggered from the optical axes of the light emitting diodes 122 mounted on the other printed circuit boards 124b, 124c or 124a. Is the same.

In the printed circuit board 124a, 124b, or 124c, a reflective layer 128 capable of reflecting light may be disposed in a region other than the region where the light emitting diode 122 is mounted. The reflective layer 128 improves light utilization efficiency by reflecting light transmitted from another light source 220 located on the opposite side of the light pipe 140 (FIG. 2B).

On the other hand, since the reflective layer 128 is formed using a metal material having excellent reflectance to light, an insulating material such as, for example, an epoxy resin, is disposed between the reflective layer 128 and the printed circuit board 126 to ensure insulation reliability. An insulating layer 127 formed from may be disposed.

FIG. 2H is a partial perspective view of another embodiment of the light pipe of FIG. 2B.

Although the above-described embodiments provide a case in which the surface light source device 110 is configured using one light pipe 140, according to a selection, as shown in FIG. It is also possible to configure the surface light source device 110 by arranging light pipes 140 in close contact with 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 implemented by arranging the light pipes 140 vertically and horizontally according to the size of the liquid crystal display (not shown) and arranging the light sources 120 and 220 on both sides thereof. Can be.

3A is a cross-sectional view illustrating a liquid crystal display according to another exemplary embodiment of the present invention. 3B is a cross-sectional view taken along the line C-C 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 housing 130 in which the light source unit is inserted and supported, a light pipe 140 disposed adjacent to the light source unit, The diffusion layer 142 is disposed on an outer surface of the light pipe and a reflector 144 is disposed inside the light pipe.

The light source unit 120 includes a plurality of light emitting diodes 122 generating light having a predetermined wavelength, a plurality of printed circuit boards 124 on which the light source is mounted, and a heat radiating member 126 to which the printed circuit boards are attached. Include.

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 unit 120 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 unit 122 disposed on both sides of the light pipe 140 is input into the light pipe 140 through both sides of the light pipe 140. At this time, since the plurality of light emitting diodes 122 in the light source unit 122 are arranged three-dimensionally so that the optical axes are crossed with each other, light is input to the light pipe 140 at a wider range of angles.

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 to completely surround the outer surface of the light pipe 140, and 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 that the reflector 144 is disposed at the bottom 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 in which a light pipe is combined with a point light source or a linear light source, the surface light source device can be manufactured more easily than in the related art.

In addition, the present invention can obtain an advantageous surface light source device in terms of power consumption by using a smaller number of light sources than conventional backlight units.

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. Because of this, thermal deformation of the optical sheet can be alleviated.

In addition, since at least a portion of the plurality of light emitting diodes disposed in the light source unit are arranged such that optical axes thereof are staggered from each other, light is input and guided into the light pipe in a wider range. Therefore, light is smoothly mixed inside the light pipe, and more uniform light is output to the light output surface of the light pipe.

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

Claims (20)

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 light source unit providing light input to the liquid crystal panel and including a plurality of light emitting diodes three-dimensionally arranged such that at least some optical axes are different from each other; And An inner surface structured into a plurality of micro-prism shapes, into which light provided from the light source 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 exit surface disposed substantially parallel to the liquid crystal panel. Backlight unit comprising a light pipe. The method of claim 1, wherein the light source unit, A plurality of printed circuit boards on which the plurality of light emitting diodes are mounted to electrically connect an external power source and the plurality of light emitting diodes; And And a heat dissipation member having a plurality of surfaces for attaching the plurality of printed circuit boards. The method of claim 2, wherein the light source unit, An insulating layer formed on a surface on which the light emitting diode is mounted; And And a reflective layer formed on the insulating layer. The method of claim 1, The surface light source device, And a housing configured to receive and support the light source unit. The backlight unit according to claim 4, wherein the surface light source device is disposed such that an end of the light pipe is inserted into the housing. 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 6, 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 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 light source unit providing light input to the liquid crystal panel and including a plurality of light emitting diodes three-dimensionally arranged such that at least some optical axes are different from each other; And An inner surface structured into a plurality of micro-prism shapes, into which light provided from the light source 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 exit surface disposed substantially parallel to the liquid crystal panel. And a light pipe of the liquid crystal display device. The method of claim 8, wherein the light source unit, A plurality of printed circuit boards on which the plurality of light emitting diodes are mounted to electrically connect an external power source and the plurality of light emitting diodes; And And a heat dissipation member having a plurality of surfaces for attaching the plurality of printed circuit boards. The method of claim 9, wherein the light source unit, An insulating layer formed on a surface on which the light emitting diode is mounted; And And a reflective layer formed on the insulating layer. The surface light source device of claim 10, And a housing accommodating and supporting the light source unit. 12. The liquid crystal display device according to claim 11, wherein the surface light source device is arranged such that an end of the light pipe is inserted into the housing. The method of claim 8, 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 13, 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, A light source unit including a plurality of light emitting diodes three-dimensionally arranged such that at least some of the optical axes are different; And An inner surface structured into a plurality of micro-prism shapes, into which light provided from the light source 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 exit surface disposed substantially parallel to the liquid crystal panel. Surface light source device comprising a light pipe. The method of claim 15, wherein the light source unit, A plurality of printed circuit boards on which the plurality of light emitting diodes are mounted to electrically connect an external power source and the plurality of light emitting diodes; And And a heat dissipation member having a plurality of surfaces for attaching the plurality of printed circuit boards. The method of claim 16, wherein the light source unit, An insulating layer formed on a surface on which the light emitting diode is mounted; And The surface light source device further comprises a reflective layer formed on the insulating layer. The method of claim 17, The surface light source device, And a housing for accommodating and supporting the light source unit. 19. The surface light source device according to claim 18, wherein an end of the light pipe is inserted into the housing. The method of claim 15, 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.

Images