JP2006331658A - Optical member for led backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical member for an LED backlight not necessary to install any excessive optical path in order to turn RGB colors of an LED array into white color by mixing it, capable of reducing its size and improving backlight efficiency. <P>SOLUTION: The optical member for the LED backlight 9 is constituted by a light guide plate 3 arranged in proximity to a light source 1 formed by arranging a plurality of LEDs 2R to 2B; a diffraction grating 4 arranged on a surface of the light guide plate 3 facing the LED array; and triangular prisms 5, diffusion patterns, or fine lens faces arranged on an opposite side surface of the light guide plate 3 at intervals. The light from the LED array is diffracted by the diffraction grating 4, and guided in the light guide plate 3 by total reflection, and emitted outside from the triangular prisms 5 or the like arranged on the opposite side surface of the light guide plate 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical member for an LED backlight, and more particularly to a light guide plate and a surface light source device used for a backlight or the like that illuminates a transmissive display device such as a liquid crystal display device using a LED as a light source from the back. is there.

  As a display device, a liquid crystal display device (LCD) is thinner and lighter than an existing CRT display device and is now widely used. Since the LCD is not a self-luminous display device, it is necessary to separately arrange a light source for illuminating the LCD. With increasing demands for lower power consumption and improved display brightness, how to efficiently illuminate the LCD with illumination light from this light source has become a major issue.

  Conventionally, cold cathode fluorescent lamps (CCFLs) have been mainstream as light sources, but light-emitting diodes (LEDs) that are excellent in color reproducibility, miniaturization, and low power consumption have been introduced into the market. It is coming. Currently, LED is mainly used in small LCD applications, but it is considered that LED will be used in medium and large LCDs in the future.

  However, particularly when LEDs of RGB colors are alternately arranged and used as a backlight for an LCD, it is necessary to mix them to whiten them. If this is not done properly, color unevenness and luminance unevenness will occur in the surface. Become.

  Conventionally, in order to perform this color mixture, a space where sufficient color mixing is possible is provided between the LED array and the light guide plate, and in the direct type, a cone-shaped mirror is arranged on the upper part of the LED to diffuse light over a wide range. It was necessary.

  Patent Document 1 discloses a lens that illuminates an LCD as more uniform surface light when an LED that is a point light source is used. In the invention described in Patent Document 1, by installing a funnel-shaped lens on the top of each LED, the light from the LED is first diffused in the horizontal direction and then thoroughly mixed with the light from other LEDs. The LCD is illuminated.

  However, the invention described in Patent Document 1 has a problem that the lens has a complicated shape and is difficult to design and manufacture.

  In addition, since the light once propagated in the horizontal direction is raised in the direction of the LCD, there is a problem that the light use efficiency is lowered.

  In the light guide plate type, as described in Non-Patent Document 1, as a method of mixing colors, a folded portion is provided on the back end portion of the original light guide plate, the LED array is disposed on the back surface, and light from the LEDs is provided. Folds back from the back, enters the light guide plate, and introduces the color mixed in the path between them.

However, with this configuration, the entire backlight becomes thick, which causes a problem in applications such as notebook PCs that are carried around.
JP 2003-8068 A JP-A-11-329030 SID (Society For Information Display) 2003,43.3 "High-efficiency Slim LED Backlight System with Mixing Light Guide"

  The present invention has been made to solve these problems of the prior art, and the purpose thereof is to eliminate the need for providing an extra optical path for whitening by mixing the RGB colors of the LED array, An object of the present invention is to provide an optical member for LED backlight that can be miniaturized and can improve backlight efficiency.

  An optical member for LED backlight according to the present invention that achieves the above object includes a light guide plate disposed in proximity to a light source in which a plurality of LEDs are arranged, and a diffraction grating is provided on a surface of the light guide plate facing the LED array. Protrusions, diffusion patterns, or micro lens surfaces are arranged on the surface of the light guide plate opposite to the diffraction grating, and light from the LED array is diffracted by the diffraction grating to guide the light. Guided by total internal reflection in the optical plate, and out of the surface of the light guide plate opposite to the diffraction grating by the protrusions or micro lens surfaces disposed on the surface of the light guide plate opposite to the diffraction grating. It is characterized by being injected.

  In this case, it is preferable to use a volume hologram as the diffraction grating.

  And it is preferable to use the diffraction grating formed by laminating | stacking several volume type holograms corresponding to each wavelength light-emitted from LED which comprises LED arrangement | sequence as said diffraction grating.

  Further, it is desirable that a reflection layer for reflecting the guided light is provided on the end face of the light guide plate.

  Further, it is desirable that a flat portion is formed in a gap between the protrusions on the surface where the protrusions are arranged on the side opposite to the diffraction grating of the light guide plate.

  In addition, the protrusions disposed on the surface of the light guide plate on the side opposite to the diffraction grating are, for example, a prism having a trapezoidal shape with a triangular cross section or a top portion thereof cut off.

  Further, a diffusing agent may be mixed in at least one of the light guide plate and the protrusion.

  Moreover, the said diffusion pattern arrange | positioned on the surface on the opposite side to the said diffraction grating of the said light-guide plate can be comprised from the fine uneven | corrugated diffusion surface provided in the surface of the said light-guide plate.

  Alternatively, the diffusion pattern disposed on the surface of the light guide plate opposite to the diffraction grating can be formed by applying and curing a resin mixed with fine beads in a pattern on the surface. .

  The present invention provides an optical member for an LED backlight as described above, a light source in which a plurality of LEDs arranged facing a surface on which a diffraction grating of the optical member for LED backlight is arranged, and the LED backlight. The liquid crystal display device includes a transmissive liquid crystal display element disposed in the optical path of illumination light emitted from the surface on which the projection, the diffusion pattern, or the minute lens surface of the light optical member is disposed.

  According to the above-described optical member for LED backlight of the present invention, there is no need to provide an extra optical path for whitening by mixing the RGB colors of the LED array, miniaturization and improved backlight efficiency. The optical member for LED backlight which can be made is realizable.

  The LED backlight optical member of the present invention is an optical member that can be whitened by efficiently mixing the RGB colors of the LED array simply by being inserted between the LED array and the light guide plate or diffusion plate. The optical member is formed by arranging a diffraction grating and a diffusion pattern or a prism shape vertically. Hereinafter, the optical member for LED backlight of this invention is demonstrated in detail based on an Example.

  FIG. 1 is a top view of an essential part of one embodiment of a liquid crystal display device in which the optical member of the present invention is applied to a light guide plate type backlight, and FIG. 2 is a side view of the entire liquid crystal display device having the arrangement of FIG. FIG. In this embodiment, a panel light guide plate 11 is disposed on the back surface of a normal transmissive liquid crystal display element (liquid crystal panel) 20, and illumination light is introduced from one end 12 of the panel light guide plate 11, so that the panel light guide plate is used. 11 is an example in which the optical member of the present invention is used for the light source part of the light guide plate type backlight that illuminates the liquid crystal panel 20 by uniformly emitting illumination light from the front surface 13 of the light source.

  In this embodiment, an LED array 1 in which R light emitting LEDs 2R, G light emitting LEDs 2G, and B light emitting LEDs 2B that respectively emit red light (R), green light (G), and blue light (B) are periodically arranged in one row. The light guide plate 3 is disposed in parallel and close to. A diffraction grating 4 is arranged on the surface of the light guide plate 3 facing the LED array 1, and a large number of fine triangular prisms 5 having an isosceles cross section, for example, are formed on the surface of the light guide plate 3 opposite to the diffraction grating 4. Are spaced apart from each other. In addition, a reflection layer 6 is provided on the end face around the light guide plate 3 to reflect the guided light at the end face for effective use. Thus, the optical member 9 for LED backlight is comprised by arrange | positioning the diffraction grating 4, the triangular prism 5, and the reflective layer 6 in the light-guide plate 3. FIG.

  In the case of this embodiment, the panel light guide plate 11 is disposed in front of the light guide plate 3 on the side where the triangular prism 5 is disposed so that one end 12 of the panel light guide plate 11 faces. A liquid crystal panel 20 is disposed on the front surface of the light guide plate 11 via a prism sheet 21 and another optical member 22.

  Since the optical member 9 for LED backlight according to one embodiment of the present invention has such a configuration, R, G, and B light 10R, 10G, and 10B emitted from the LEDs 2R, 2G, and 2B of the LED array 1, respectively. Enters the diffraction grating 4 of the light guide plate 3 and is diffracted into the light guide plate 3 so as to be at an angle greater than the critical angle with respect to the surface of the light guide plate 3. The diffracted R, G, B light 10R, 10G, 10B is at an angle that exceeds the critical angle with respect to the surface of the light guide plate 3 as described above. It is guided as light guided to the left and right in FIG.

  In this embodiment, since the triangular prism 5 is arranged on the surface of the light guide plate 3 opposite to the diffraction grating 4, a part of the light guided in the light guide plate 3 is disposed. Light is emitted from the inclined surface of the triangular prism 5 toward one end 12 of the panel light guide plate 11. Since the triangular prism 5 and the flat portion 7 on the surface of the light guide plate 3 are alternately present on the surface of the light guide plate 3 opposite to the diffraction grating 4, the light is gradually guided in the light guide plate 3. All the light is emitted to the panel light guide plate 11 side.

  All of the above R, G, and B lights 10R, 10G, and 10B act in the same manner, so that they are mixed almost uniformly before being emitted from the light guide plate 3 to become white light 10W. After that, the light can enter the one end 12 of the panel light guide plate 11.

  Here, the type of the diffraction grating 4 is preferably one having angle selectivity. For example, a volume type diffraction grating or a volume type hologram is suitable.

  When the diffraction grating 4 is composed of three volume holograms formed by laminating three volume holograms that selectively diffract the wavelengths of the lights 10R, 10G, and 10B from the LEDs 2R, 2G, and 2B, The lights 10R, 10G, and 10B can be efficiently introduced into the light guide plate 3 as guided light.

  The configuration after the panel light guide plate 11 may be the same as a generally known configuration, but in this embodiment, from the illumination side, the panel light guide plate 11, the prism sheet 21, the other optical member 22, and the liquid crystal The panel light guide plate 11 is arranged in the order of the panels 20, and emits light 10 W incident from one end 12 thereof obliquely from the front surface 13 while being multiple-reflected between the front surface 13 and the rear surface 14 having a wedge shape. The prism sheet 21 is for directing light 10W obliquely emitted from the panel light guide plate 11 in the front direction of the liquid crystal panel 20 as described in Patent Document 2, for example. The optical member 22 is a prism sheet or the like, which is known as a trade name BEF, DBEF (Sumitomo 3M Co., Ltd.) or the like and narrows the angle distribution of illumination light to improve luminance.

  In addition, on the surface opposite to the diffraction grating 4 of the light guide plate 3, as a means for emitting light 10R, 10G, and 10B guided therein gradually toward the panel light guide plate 11, a triangular prism 5 is provided. Instead, a jumping diffusion pattern or a jumping minute lens surface may be used.

  FIG. 3 is a side view of an embodiment in which the LED backlight optical member 9 having the configuration of the above embodiment is applied to a direct type backlight. In this example, the LED backlight optical member 9 is the same as that of FIG. 1, and the liquid crystal panel 20 is directly connected to the front side of the light guide plate 3 on the side where the triangular prism 5 is disposed via the diffusion plate 23. They are arranged almost in parallel. However, in this configuration, as shown in the perspective view of the backlight unit in FIG. 4, the set of the LED array 1 and the LED backlight optical member 9 is not a single row, but covers the display surface of the liquid crystal panel 20. For example, it is desirable to arrange in multiple rows in parallel to cover the entire panel surface.

  As the LED backlight optical member 9 of the present invention, a flying diffusion pattern 8 is formed on the surface of the light guide plate 3 opposite to the diffraction grating 4 instead of the triangular prism 5, as shown in FIG. It may be provided. Here, the diffusion pattern 8 may be configured by providing a fine uneven diffusion surface only in a region corresponding to the diffusion pattern 8 on a plane opposite to the diffraction grating 4 of the light guide plate 3 or obtaining an uneven shape. For this purpose, fine beads having an approximate refractive index may be mixed into the resin, and this may be applied and cured in a region corresponding to the diffusion pattern 8 on the plane opposite to the diffraction grating 4 of the light guide plate 3.

  Furthermore, in order to increase the degree of color mixing of the R, G, B light 10R, 10G, 10B in the LED backlight optical member 9 of the present invention, at least one of the light guide plate 3 and the triangular prism 5 is white. A diffusing agent such as fine particles may be mixed.

  In FIG. 5, in order to adapt the LED backlight optical member 9 to the direct type backlight as shown in FIG. 3, a plurality of pairs of the LED array 1 and the LED backlight optical member 9 are arranged in parallel. It is a perspective view of the backlight part at the time of covering all the panel surfaces.

  As described above, according to the present invention, it is not necessary to provide an extra optical path for whitening by mixing the RGB colors of the LED array, and the LED can be downsized and the backlight efficiency can be improved. An optical member for backlight can be realized.

  In the above description, the triangular prism 5 is used as a projecting member that emits light guided in the light guide plate 3 by being disposed on the surface of the light guide plate 3 opposite to the diffraction grating 4. However, other protrusions such as a protrusion having a trapezoidal cross section, a cone shape, a pyramid shape, or a truncated cone shape, a truncated pyramid shape, or a roof shape can be used.

  Next, specific examples of the optical member for LED backlight of the present invention will be described.

[Example 1]
In the first embodiment, a volume hologram is disposed on the lower surface of the color mixing light guide plate, and a prism array is disposed on the upper surface.

The specifications of the hologram and prism array are shown below.
(hologram)
Hologram recording optical system: Two parallel light beams having incident angles of 0 ° and 50 ° (incident angle in a medium having a refractive index n = 1.50) are incident on the surface of the hologram recording medium (photopolymer). Interfered.
Refractive index modulation Δn: The refractive index modulation Δn of the interference fringes recorded in the hologram recording medium was 0.04.
Sensitive material thickness: The thickness of the hologram recording medium was 5 μm.
Recording wavelength: The wavelength of two parallel light beams for interference fringe recording was 532 nm.
(Prism array)
Side inclination angle: The inclination angle of the slope of the prism with respect to the upper surface of the light guide plate was 82 °.
Prism pitch: The prism pitch was 0.25 mm.
Prism height: The top of the triangular prism having an isosceles triangle shape was cut into a trapezoid, and the height of the trapezoid was 0.125 mm.
-Length of the bottom of the prism: The length of the bottom of the trapezoidal prism was 0.125 mm. Therefore, the length of the flat portion between the prisms was also 0.125 mm.

  A 1.0 mm thick plate made of acrylic resin was used as the light guide plate.

  An ultraviolet curable resin is applied to the acrylic plate, the mold on which the prism array is formed is pressed against the ultraviolet curable resin, and ultraviolet rays are irradiated from the back side of the acrylic plate to cure the ultraviolet curable resin. Then, the mold was peeled off to shape the prism array shape.

  As for the hologram, the hologram produced under the above conditions was bonded to the opposite side of the prism molding surface of the acrylic plate using an ultraviolet curable resin, and the LED backlight optical member of this example was completed.

  In FIG. 6, light having a wavelength of 550 nm emitted from the LED 2 disposed in front of the cross section of the optical member 9 for LED backlight and the surface on the hologram (diffraction grating) 4 side is guided into the light guide plate 3 and guided. A state in which all light is gradually emitted from the inclined surface of the following prism 5 guided in the light guide plate 3 is shown. In this case, the angle of the central ray from the LED 2 in the light guide plate 3 is 51 ° (angle relative to the surface of the light guide plate 3), and the exit angle from the prism 5 into the air is 20 °. In this case, the optical path is based on ray tracing.

  The peak wavelengths of the R, G, and B LEDs in the LED array were those having peaks at approximately 625 nm, 540 nm, and 460 nm, respectively. The diffraction angles at the respective wavelengths were 41.5 °, 51.0 °, and 64.2 ° (in the medium).

  When this LED backlight optical member 9 is arranged immediately above an LED array in which LEDs of R, G, and B colors are independently arranged, the colors are mixed almost uniformly and whitened to provide the prism 5. It was confirmed that the light was emitted with substantially uniform brightness.

  By using the LED backlight optical member 9 of this embodiment, it becomes possible to whiten the light from the LEDs of each color of RGB without using an unnecessarily long optical path and to make a backlight.

[Example 2]
In the second embodiment, the same hologram and light guide plate as those in the first embodiment are used, and a diffusion pattern is formed instead of the prism array on the upper surface.

  In order to pattern the diffusion layer on the upper surface of the acrylic plate, a dot pattern was printed using a screen printing method. As the ink for printing, an ultraviolet curable resin mixed with diffusion beads was used. The dot pattern had a diameter of 0.2 mm, and the area ratio of the dot pattern to the entire area of the upper surface of the light guide plate was 50%.

  A hologram was bonded to the light guide plate in the same manner as in Example 1 to complete the optical member for LED backlight of this example.

  When this optical member for LED backlight is arranged immediately above an LED array in which LEDs of R, G, and B colors are independently arranged, each color is mixed almost uniformly, whitened and provided with a diffusion pattern It was confirmed that the light was emitted with substantially uniform brightness.

  By using the optical member for LED backlight of this embodiment, it becomes possible to whiten light from LEDs of each color of RGB without using an unnecessarily long optical path, and to make a backlight.

It is a top view of the principal part of one Example of the liquid crystal display device which applied the optical member of this invention to the light-guide plate type backlight. It is the side view which looked at the whole liquid crystal display device of arrangement of Drawing 1 from the side. It is a side view of an Example at the time of applying the optical member for LED backlight of the structure of the Example of FIG. 1 to a direct type | mold backlight. It is a perspective view of the backlight part of the Example of FIG. FIG. 5 is a view similar to FIG. 4 when a flying diffusion pattern is provided instead of the triangular prism. It is a figure which shows the cross section of the optical member for LED backlights of Example 1 of this invention, and the mode of the light introduce | transduced and inject | emitted in it.

Explanation of symbols

1 ... LED array 2 ... LED
2R ... R light emitting LED
2G ... G light emitting LED
2B ... B light emitting LED
DESCRIPTION OF SYMBOLS 3 ... Light guide plate 4 ... Diffraction grating 5 ... Triangular prism 6 ... Reflective layer 7 ... Flat part 8 ... Diffusion pattern 9 ... LED backlight optical member 10R ... R light 10G ... G light 10B ... B light 10W ... White Light 11 ... Panel light guide plate 12 ... One end 13 of the panel light guide plate ... Front face 14 of the panel light guide plate ... Back face 20 of the panel light guide plate ... Transmission type liquid crystal display element (liquid crystal panel)
21 ... Prism sea 22 ... Other optical member 23 ... Diffusion plate

Claims (10)

A light guide plate arranged close to a light source arranged with a plurality of LEDs, a diffraction grating arranged on a surface of the light guide plate facing the LED array, and a surface of the light guide plate opposite to the diffraction grating Are provided with protrusions, diffusion patterns, or micro lens surfaces, and light from the LED array is diffracted by the diffraction grating and guided by total reflection in the light guide plate, and the diffraction of the light guide plate. An optical member for LED backlight, which is emitted from a surface opposite to the diffraction grating of the light guide plate by the protrusions or micro lens surfaces arranged on the surface opposite to the grating. 2. The optical member for LED backlight according to claim 1, wherein a volume hologram is used as the diffraction grating. The LED backlight according to claim 2, wherein a diffraction grating formed by laminating a plurality of volume holograms corresponding to respective wavelengths emitted from the LEDs constituting the LED array is used as the diffraction grating. Optical member. The optical member for LED backlight according to any one of claims 1 to 3, wherein a reflection layer that reflects guided light is provided on an end face of the light guide plate. 5. The flat portion is formed in a gap between the protrusions on the surface of the light guide plate on which the protrusions are disposed on the side opposite to the diffraction grating. 5. Item 2. An optical member for LED backlight according to the item. 6. The projection according to claim 1, wherein the protrusion disposed on the surface of the light guide plate opposite to the diffraction grating is a prism having a triangular shape or a trapezoidal shape with a top portion thereof cut off. The optical member for LED backlight according to 1. The optical member for LED backlight according to any one of claims 1 to 6, wherein a diffusing agent is mixed in at least one of the light guide plate and the protrusion. 5. The diffusion pattern disposed on the surface of the light guide plate opposite to the diffraction grating is a fine uneven diffusion surface provided on the surface of the light guide plate. The optical member for LED backlight according to 1. The diffusion pattern disposed on the surface of the light guide plate opposite to the diffraction grating is formed by applying and curing a resin mixed with fine beads in a pattern on the surface. Item 5. The optical member for LED backlight according to any one of Items 1 to 4. An optical member for LED backlight according to any one of claims 1 to 9, and a light source in which a plurality of LEDs arranged facing the surface on which the diffraction grating of the optical member for LED backlight is arranged, And a transmissive liquid crystal display element disposed in the optical path of the illumination light emitted from the surface on which the projection, diffusion pattern, or micro lens surface of the LED backlight optical member is disposed. Display device.

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