KR100657330B1 - Back light unit and liquid crystal display apparatus having the same - Google Patents

Abstract

A back light unit and an LCD(Liquid Crystal Display) are provided to maintain uniform luminance over the entire display area and improve the light-emitting efficiency of the back light unit by removing a color filter from the LCD. A back light unit(100) includes a plurality of light-emitting elements(115), an aperture plate(120), a lens sheet(130), a hologram device(140), and a cylindrical lens sheet(151). The plurality of light-emitting elements are arranged in an array on a base substrate and project light forwardly. The aperture plate is located in front of the light-emitting elements and has a plurality of slits(120'). The lens sheet includes a plurality of lens units(131) corresponding to the slits. The lens units are arranged in parallel. Each lens unit includes a collimating lens for converting light emitted through the slits into parallel light, and a prism for refracting the parallel light at a specific projection angle. The hologram device is placed in front of the lens sheet and diffracts red, green and blue components of an incident light at different angles. The cylindrical lens sheet is located before the hologram device and respectively condenses red, green and blue light inputted at different angles to red, green and blue sub-pixel regions.

Description

Back light unit and liquid crystal display apparatus having the same

1 is a cross-sectional view of a conventional liquid crystal display device.

2 is a view illustrating a schematic structure of a backlight unit according to an exemplary embodiment of the present invention.

3 is a view illustrating main parts of the backlight unit illustrated in FIG. 2.

4 is a view showing a schematic structure of a liquid crystal display device according to an exemplary embodiment of the present invention, showing a liquid crystal display device employing the backlight unit of FIG.

<Description of the symbols for the main parts of the drawings>

110: base substrate 111: first reflective surface

115: light emitting diode 120: aperture plate

120`: Slit of aperture plate 121: Second reflection surface

130: lens sheet 131: unit lens unit

133: collimator portion 135: prism portion

140: hologram element 151: cylindrical lens sheet

153: transparent glass substrate

200: liquid crystal panel

The present invention relates to a backlight unit and a liquid crystal display device having the same, and more particularly, a backlight unit having a uniform luminance distribution over the entire display surface and suitable for large area of the display surface, and having improved light emission efficiency and the same. It relates to a liquid crystal display device provided.

A light-receiving flat panel display device such as a liquid crystal display device itself, unlike the self-luminous flat panel display device which emits light to form an image, light is incident from the outside to form an image. Therefore, a back light unit is provided as a lighting device on the back of the light receiving flat panel display device, and a predetermined image is formed by irradiating light to a flat panel display device such as a liquid crystal panel provided with the backlight unit in front. do.

The backlight unit is classified into a direct light type and an edge light type according to the arrangement of the light sources. The direct-emitting type backlight unit has a structure in which a plurality of light sources, for example, light emitting diodes (LEDs), which emit light of Lambertian, is disposed over the entire surface of the panel directly below the liquid crystal panel. The edge emitting type has a structure that transmits light from a light source installed on a sidewall of a light guide panel (LGP) to a liquid crystal panel.

1 is a schematic cross-sectional structure of one embodiment of a conventional liquid crystal display device. As shown in the drawing, the illustrated liquid crystal display device 50 includes a liquid crystal panel 20 and a backlight unit 10 for supplying light to the liquid crystal panel 20. The backlight unit 10 includes a light source 11 installed in the housing 13 and a light guide plate 15 that guides the light incident from the light source 11 toward the liquid crystal panel 20. The hologram pattern 17 is formed on the upper surface of the light guide plate 15, and the light incident on the light guide plate 15 is diffracted by the hologram pattern 17 to be emitted toward the front liquid crystal panel 20. do.

The liquid crystal panel 20 has a liquid crystal layer 21 formed between the transparent glass substrates 25 and 26 disposed on both front and rear sides thereof, and has polarization tendencies perpendicular to each other on the outer surfaces of the transparent glass substrates 25 and 26. Polarizing plates 28 and 29 having are disposed. The light L ′ supplied from the backlight unit 10 becomes gray scale by changing the amount of light according to the alignment structure of the liquid crystal layer 21. A color filter 23 is arranged between the liquid crystal layer 21 and the transparent glass substrates 25 and 26 in which the subpixels of red (R), green (G), and blue (B) are arranged in a matrix form. Light incident from the backlight unit 10 passes through the color filter 23 and is colored with monochromatic light of a specific color, and a combination of these forms a full color image. The light transmittance of the color filter 23 which selectively transmits only monochromatic light of a specific color is very low. The light transmittance representing the ratio of the emitted light to the incident light is only 6.5%, and most of the light is the color filter 23. It is absorbed by and converted into thermal energy or the like. This lowers the driving efficiency of the entire liquid crystal display device 50, thereby increasing the power consumption.

Meanwhile, in the case of the edge emission type as illustrated in FIG. 1, the amount of light incident on the liquid crystal panel 20 changes according to the distance from the light source 11, and the front luminance of the backlight unit 10 is positioned. There is a problem of becoming non-uniform. This is due to the structural feature of the edge emitting type in which the light source 11 is concentrated at one end, unlike the direct light emitting type in which the light source is uniformly disposed over the entire display surface. This luminance unevenness prevents the enlargement of the display surface. It will act as a limiting factor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems and other problems, and provides a backlight unit and a liquid crystal display device having the same that maintain uniform luminance regardless of the position of the display surface and are suitable for large area of the display surface. Its purpose is to provide.

Another object of the present invention is to provide a backlight unit having an improved luminous efficiency by removing a color filter restricting light transmittance and a liquid crystal display device having the same.

In order to achieve the other object of the above object, the backlight unit of the present invention,

A backlight unit for supplying surface light to a flat panel display device disposed in front so that a predetermined image is displayed.

A plurality of light emitting elements mounted in an array on a base substrate and emitting light forward;

An aperture plate disposed in front of the light emitting elements and having a plurality of slits formed therein;

A plurality of unit lens units corresponding to the slits are arranged in parallel, and each lens unit is formed on the light incident side and formed on the collimating lens unit and the light exit side to convert divergent light through the slits into parallel light. A lens sheet including a prism portion configured to refract the converted parallel light to a constant exit angle;

A hologram element disposed in front of the lens sheet and diffracting monochromatic components of red (R), green (G), and blue (B) of incident light at different angles; And

The red (R), green (G), and blue (B) monochromatic light beams which are disposed in front of the hologram element and are incident at different angles, respectively, And a cylindrical lens sheet condensing into the pixel region.

In the present invention, preferably, each of the light emitting diodes generating monochromatic light of red (R), green (G), and blue (B) is arranged in a two-dimensional array on the base substrate.

The base substrate and the aperture plate disposed to face each other with the light emitting diodes interposed therebetween are provided as a mixed space of the monochromatic lights.

The mutually opposing surfaces of the base substrate and the aperture plate are reflective surfaces.

In another embodiment of the present invention, a CCFL (Cold Cathode Fluoresent Lamp) for emitting white light having multiple wavelengths as the light emitting device is disposed in parallel in one direction on the base substrate.

In the present invention, preferably, the inclination angle of the exit surface with respect to the incident surface of the prism portion is determined from the incident angle of the hologram element,

The white light inclined at the incidence angle is spectrally divided into green light emitted substantially in front and red light and blue light emitted obliquely left and right with respect to the green light.

On the other hand, the liquid crystal display device according to another aspect of the present invention,

A liquid crystal display device for displaying a predetermined image including a liquid crystal panel and a backlight unit for irradiating light to the liquid crystal panel.

The backlight unit,

A plurality of light emitting elements mounted in an array on a base substrate and emitting light forward;

An aperture plate disposed in front of the light emitting devices, the aperture plate including a plurality of slits;

A plurality of unit lens units corresponding to the slits are arranged in parallel, and each lens unit is formed on the light incident side and formed on the collimating lens unit and the light exit side to convert divergent light through the slits into parallel light. A lens sheet including a prism portion configured to refract the converted parallel light to a constant exit angle;

A hologram element disposed in front of the lens sheet and diffracting monochromatic components of red (R), green (G), and blue (B) of incident light at different angles; And

It is disposed in front of the hologram element, the monochromatic light of red (R), green (G), blue (B) incident at different angles of the corresponding red (R), green (G), blue (B) And a cylindrical lens sheet for condensing each of the subpixel regions.

Hereinafter, a backlight unit and a liquid crystal display device having the same according to an exemplary embodiment of the present invention will be described in detail. 2 is a structural diagram showing a schematic configuration of a backlight unit 100 according to an embodiment of the present invention. The illustrated backlight unit 100 is a direct emission type, and a light emitting diode (LED) 115 through which Lambertian light is emitted may be used as a light source. That is, on the substrate 110, RGB light emitting diodes 115 emitting red (R), green (G), and blue (B) monochromatic light are arranged in an array, and the light emitting diodes 115 form a plurality of lines. As they form, they form a two-dimensional array vertically and horizontally. Red, green, and blue light emitting diodes 115 are alternately arranged in each line, and the RGB single color light emitting diodes 115 may be arranged in the same number or may be arranged in different numbers in consideration of the amount of light for each single color. have. In addition, instead of a light emitting diode that generates a monochromatic light of a certain wavelength band, a white light source for supplying multi-wavelength white light may be used. For example, a light emitting diode in the form of a point light source or a line light source may be provided with electrodes at both ends. Cold Cathode Fluorescent Lamp (CCFL) may be used. However, when such a white light source is used, the reflective surfaces 111 and 121 for mixing RGB monochromatic light are not separately required, as described below.

The substrate 110 may be provided as a printed circuit board (PCB) for supplying driving power to the light emitting diodes 115, and a first reflective surface 111 is formed on an upper surface of the substrate 110. The light emitted from the light emitting diode 115 to the rear side is reflected to the front side. The reflective surface 111 may be made of a high reflectivity reflective coating layer formed on the substrate 110, for example, an aluminum, silver or gold coating layer, and instead of directly forming a reflective coating layer on the substrate 110, The reflective surface may be obtained by mounting a reflective plate separately provided on 110. In this case, the reflective plate is provided with a plurality of openings into which the light emitting diodes 115 are inserted, which are placed on the substrate 110 on which the light emitting diodes 115 are mounted, so that the light emitting diodes 115 are fitted into each opening. Aligned with respect to substrate 110.

An aperture plate 120 having a plurality of slits 120 ′ formed in parallel is disposed in front of the substrate 110, and a second reflective surface 121 is provided on a rear surface of the aperture plate 120. This reflective surface 121 can be obtained by forming a reflective coating layer on the aperture plate 120, alternatively, by forming the aperture plate itself from a metal sheet of high reflectivity, the reflective surface without a separate coating process This may be obtained.

Monochromatic light emitted forward from each light emitting diode 115 is reflected by the second reflecting surface 121 of the aperture plate 120 to the first reflecting surface 111 on the rear side, and the first reflecting surface 111. The incident light is reflected back to the second reflective surface 121 on the front side again. On the other hand, the monochromatic light emitted rearward from each light emitting diode 115 is reflected by the first reflecting surface 111 formed on the substrate 110 to the second reflecting surface 121 on the front side, and the second reflecting surface ( 121 is reflected back to the first reflective surface 111 on the rear side. The monochromatic light beams of different wavelengths emitted from the light emitting diodes 115 are mixed into white light of multiple wavelength bands while undergoing reflection-rereflection between the first reflective surface 111 and the second reflective surface 121 facing each other. Through this reflection and re-reflection process, a part of the white light is incident on the slit 120 'of the aperture plate 120 and is thereby separated between the reflective surfaces 111 and 121.

The white light emitted through the slit 120 ′ has a wide emission angle distribution to the left and right sides around the slit 120 ′ and is emitted in all directions. A lens sheet 130 in which a plurality of lens units 131 are formed in parallel is disposed in front of the aperture plate 120 in the light exit direction. Each lens unit 131 constituting the lens sheet 130 includes a collimation lens portion 133 on the light incident side and a prism portion 135 on the light exit side facing back and forth through the boundary surface 135a. In addition, each lens unit 131 is aligned in a one-to-one correspondence with the slit 120 'formed on the reflective plate 120. More specifically, the curved point and the slit 120' of the collimator 133, which is the light incident side, are arranged. The centers are aligned back and forth so that they are located on the same extension line, and the pitch Pc between adjacent curved portions is kept at substantially the same interval as the pitch Ps of the slit 120 '.

Referring to FIG. 3, light passing through the slit 120 ′ is incident on the correspondingly formed lens unit 131, and is converted into parallel light while passing through the collimator 133 formed on the light incident side. Here, the parallel light form refers to parallel light traveling in parallel in one direction or near parallel light traveling in parallel, and in this case, the parallel light travels in parallel with or perpendicular to the boundary surface 135a. It means the light to proceed. On the other hand, the light passing through the slit 120` has a wide emission angle distribution and is emitted at a predetermined divergence angle θd with respect to the optical axis, and the collimator 133 having the one-to-one correspondence of the diverging light is emitted. It is preferable that the radius R of the collimator portion is determined in relation to the divergence angle θd so as not to be incident off to another adjacent collimator portion 133. On the contrary, by adjusting the size of the slit 120 ', the divergence angle θd can be regulated within an appropriate range. In particular, when the size of the slit 120' becomes too narrow, the emitted light passing through the collimator part Since the slit 120 ′ may be out of the incident range of 133, the size of the slit 120 ′ is preferably equal to or larger than a sub-micron unit.

On the other hand, the parallel light transmitted through the collimator 133 is subsequently refracted at a predetermined angle with respect to the normal line of the boundary surface 135a by the formed prism portion 135, and this refracted parallel light L is forward at a constant angle of incidence. Is incident on the hologram element 140. The lens sheet 130 including the prism portion 135 may be made of an acrylic transparent resin having a high refractive index (a refractive index of approximately 1.49), and may be integrally formed through injection molding. On the other hand, the exit surface 135b of the prism portion 135 shown in Figure 3 has a downward slope from the right end to the left end, the angle (α) of the exit surface 135b with respect to the incident surface (or boundary surface 135a) ) May be determined in relation to the angle of incidence of the hologram element 140.

The hologram element 140 is disposed in front of the lens sheet 130 in the light exit direction. The hologram element 140 includes diffraction gratings of a triangular wave shape continuously arranged with a constant lattice period P, and functions to spectroscopic multi-wavelength white light L injected at a predetermined angle into monochromatic light according to a wavelength band. do. The shape of the diffraction grating formed on the hologram element 140 may be modified in various ways such as a sine wave or a square wave in addition to the triangular wave shape. The spectroscopic action of the hologram element 140 is due to its diffraction characteristics, that is, the light incident on the hologram element 140 is diffracted at different angles according to the wavelength of the incident light, and thus the white light having a multi wavelength of white light ( L) is spectroscopically emitted at different emission angles [theta] t for each wavelength. This will be described in more detail with reference to Equation 1 below.

(Equation 1)

Where m is the diffraction order, λ is the wavelength of incident light, P is the lattice period of the hologram element, and θ t and θ i are the exit and incident angles for the hologram element, respectively. In addition, n represents the refractive index as a medium property of the hologram pattern. As can be seen from Equation 1, since the emission angle θt from the hologram pattern changes according to the wavelength λ of the incident light, white light having a constant incident angle θi passes through the hologram element 140. It is emitted by separating the color components according to. The multi-wavelength white light L formed by mixing red (R), green (G), and blue (B) monochromatic light is emitted at different diffraction angles for each wavelength band while passing through the hologram element 140. The red, green and blue monochromatic light is incident on the front cylindrical lens sheet 151, respectively.

As shown in FIG. 3, the green light Lg has an exit angle of approximately 0 degrees and is emitted perpendicularly to the incidence plane of the hologram element 140, and the blue light Lb and the red light Lr are emitted vertically. The light is emitted at an angle symmetrically based on the green light (Lg). For example, when the medium refractive index of the hologram element 140 is 1.5 (acrylic transparent resin), the lattice period P of the hologram is 440 nm, and the green light Lg having a wavelength of 540 nm has an emission angle of 0 degrees, The incident angle [theta] i of the hologram element 140 should be regulated to about 60 degrees. In order to obtain the incident angle of the hologram element 140, that is, the exit angle of the lens sheet 130, the angle α of the exit surface 135b with respect to the entrance surface 135a of the prism part 135 is a predetermined value. Can be determined.

Monochromatic lights Lb, Lg, Lr of red (R), green (G), and blue (B) diffracted at different angles by the hologram element 140 are cylindrical lenses disposed in front of the hologram element 140. Through the sheet 151 (FIG. 2), each of the wavelength bands is condensed into different subpixel areas, that is, corresponding subpixel areas of red (R), green (G), and blue (B). That is, the cylindrical lens sheet 151 includes a plurality of cylindrical lenses arranged continuously in the lateral direction, and each cylindrical lens focuses the monochromatic light beams Lb, Lg, and Lr incident through various places of the convex sphere. To condense to the subpixel area of the corresponding RGB. In this way, the three primary color subpixels of R G B are gathered to form one pixel, which is the minimum unit of pixels, and a combination of these realizes a multi-color image. Monochromatic light beams Lb, Lg, and Lr that are focused by color components while passing through the cylindrical lens sheet 151 pass through the transparent glass substrate 153 disposed after the cylindrical lens, and thus the front portion of the transparent glass substrate 153. Focused on and form RGB subpixels according to the color components.

Brightness Enhancement Film (BEF: Brightness Enhancement Film, 155) for improving the straightness of the monochromatic light Lb, Lg, Lr once focused in front of the transparent glass substrate 153 in the outgoing direction so that the light goes straight ahead without being diffused. Is placed. Here, the brightness enhancing film 155 is not limited to a specific structure, according to a known technique, a detailed description thereof will be omitted.

4 illustrates a liquid crystal display according to an exemplary embodiment of the present invention. The illustrated liquid crystal display device 500 includes a backlight unit 100 illustrated in FIG. 2 and a liquid crystal panel (or liquid crystal display device 200) disposed in front of the backlight unit 100 in the light emission direction. The liquid crystal panel 200 selectively transmits or blocks each monochromatic light, thereby displaying color image information through gray scale. In general, the liquid crystal panel 200 includes a structure in which polarizers 221 and 223 having polarization tendencies perpendicular to each other with the liquid crystal layer 210 interposed therebetween are disposed in front and rear directions. 210, and changes the polarization direction of the light passing through the liquid crystal director by changing the direction of the liquid crystal director by driving the electric field, thereby enabling gradation expression by changing the amount of light. The liquid crystal panel 200 receives an electric driving signal from a driving circuit unit, which is not shown. For a specific structure or driving method of the liquid crystal panel 200, reference may be made to a known technology, and a detailed description thereof will be omitted. Shall be.

Meanwhile, the liquid crystal display shown in FIG. 4 is only an embodiment of the present invention, and the liquid crystal panel is not limited to the illustrated structure, and various modifications are possible. In particular, in the present embodiment, for convenience of description, the liquid crystal panel and the backlight unit are illustrated as completely separated from the front and rear, but each component may be disposed to overlap each other. For example, the polarizing plate of the liquid crystal panel is a backlight. It may be arranged between the optical elements of the unit.

The backlight unit of the present invention employs a direct light emission method in which light sources are uniformly distributed over the entire display surface, whereby the front luminance is uniformly maintained according to the position of the display surface. In addition, by applying the backlight unit to a liquid crystal display, a display device suitable for large area of the display surface may be provided.

In particular, the present invention provides a color filterless liquid crystal display device without a color filter, which means that the driving efficiency of the liquid crystal display device can be improved by blocking light loss caused by the color filter.

Although the present invention has been described with reference to one embodiment shown in the accompanying drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Could be. Accordingly, the true scope of protection of the invention should be defined by the appended claims.

Claims (5)

A backlight unit for supplying surface light to a flat panel display device disposed in front so that a predetermined image is displayed. A plurality of light emitting elements mounted in an array on a base substrate and emitting light forward; An aperture plate disposed in front of the light emitting elements and having a plurality of slits formed therein; A plurality of unit lens units corresponding to the slits are arranged in parallel, and each lens unit is formed on the light incident side and formed on the collimating lens unit and the light exit side to convert divergent light through the slits into parallel light. A lens sheet including a prism portion configured to refract the converted parallel light to a constant exit angle; A hologram element disposed in front of the lens sheet and diffracting monochromatic components of red (R), green (G), and blue (B) of incident light at different angles; And The red (R), green (G), and blue (B) monochromatic light beams which are disposed in front of the hologram element and are incident at different angles, respectively, And a cylindrical lens sheet for condensing the pixel region. The method of claim 1, On the base substrate, light emitting diodes generating monochromatic light of red (R), green (G), and blue (B) are arranged in a two-dimensional array as the light emitting element. The base substrate and the aperture plate disposed to face each other with the light emitting diodes interposed therebetween are provided as a mixed space of the monochromatic lights. And a surface facing each other between the base substrate and the aperture plate is a reflective surface. The method of claim 1, And a CCFL (Cold Cathode Fluoresent Lamp) for emitting white light having multiple wavelengths as the light emitting element on the base substrate, arranged in parallel in one direction. The method of claim 1, The inclination angle of the exit surface with respect to the incident surface of the prism portion is determined from the incident angle of the hologram element, And white light inclined at the incidence angle is spectrally divided into green light emitted substantially in front and red light and blue light emitted obliquely left and right with respect to the green light. A liquid crystal display device for displaying a predetermined image including a liquid crystal panel and a backlight unit for irradiating light to the liquid crystal panel. The backlight unit, A plurality of light emitting elements mounted in an array on a base substrate and emitting light forward; An aperture plate disposed in front of the light emitting devices, the aperture plate including a plurality of slits; A plurality of unit lens units corresponding to the slits are arranged in parallel, and each lens unit is formed on the light incident side and formed on the collimating lens unit and the light exit side to convert divergent light through the slits into parallel light. A lens sheet including a prism portion configured to refract the converted parallel light to a constant exit angle; A hologram element disposed in front of the lens sheet and diffracting monochromatic components of red (R), green (G), and blue (B) of incident light at different angles; And It is disposed in front of the hologram element, the monochromatic light of red (R), green (G), blue (B) incident at different angles of the corresponding red (R), green (G), blue (B) And a cylindrical lens sheet for condensing each of the subpixel regions.

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