JP2007095624A - Backlight system and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight system using a light-emitting diode in which luminance unevenness and color unevenness are contained to be small and a liquid crystal display device. <P>SOLUTION: The backlight system is provided with a metal core substrate 13 on which an LED unit 15 having two kinds or more of light-emitting diodes which emit light of different main emission wavelength is mounted, a light guide plate for color mixing 14 for mixing emission light of each light-emitting diode, and a main light guide plate 3 which introduces the light from the light guide plate for color mixing 14 and emits to a liquid crystal panel. The light guide plate for color mixing 14 is covered on each light-emitting diode, and the light incident face of the main light guide plate 3 introducing the light from the light guide plate for color mixing 14 and the mounting face of the light-emitting diodes are arranged in parallel. The liquid crystal display device is provided with such backlight system. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a backlight system and a liquid crystal display device, and more particularly to a backlight system using a light emitting diode (LED) and a liquid crystal display device.

The LED does not use mercury like a cold cathode tube, and is small and can be driven with low power. In recent years, the luminous efficiency has been remarkably improved. The conventional LED module has been mainly used in the shape of a shell, but the number of surface mounting types has gradually increased, and the LED module has been downsized, so that its use is widely expected. In recent years, with the rapid spread of liquid crystal televisions and mobile phones and the miniaturization of personal computers, the performance of liquid crystal display devices has been promoted, and the requirement is satisfied by using LEDs as the light source of the backlight. In particular, with regard to color reproducibility, it becomes possible to display colors that could not be reproduced with fluorescent lamps by using LEDs, and display of dark red or dark green is possible. Since the LED is a point light source, in the case of the side light method, even if the light guide plate used in the backlight using the cold cathode fluorescent lamp is used as it is, unevenness in luminance appears, and the backlight has three types of RGB. When the LED is used as a light source and white light is obtained by the three primary colors of light, the three colors of RGB are not mixed and enter the light guide plate, resulting in color unevenness. A light guide plate used in this type of backlight is described in Patent Document 1, for example.
JP-A-11-52370

  As shown in FIG. 2, a backlight system using a sidelight type cold cathode tube for a liquid crystal display device has a cold cathode tube or a hot cathode tube fluorescent lamp on the end face of a light guide plate 3 'made of a transparent material. The light source 1 is arranged, the reflection plate 7 for making the light emitted from the light source 1 incident on the light guide plate 3 ′ without waste is arranged, and the reflection plate 2 for reflecting the light on the lower surface of the light guide plate 3 ′. In order to improve the front luminance of the display device by condensing the diffusion sheet 4 made of a synthetic resin containing a translucent diffusing material for uniforming the luminance on the upper surface and the diffused light emitted from the diffusion sheet 4 The light collecting plate 5 and the light collecting plate 6 are arranged.

  In the conventional backlight system as described above, the light emitted from the light source 1 enters the light guide plate 3 ′, the light guided to the diffusion sheet 4 is diffused by the scattering material, and the light collecting plate 5 and the light collecting plate 6. Pass through. The light source used for the light source 1 is premised on a cold cathode tube or a hot cathode tube having white light.

  When a red LED, a green LED, and a blue LED (hereinafter referred to as RGB-LED) are used as the light source, it is impossible to mix the three colors of RGB with the diffusion sheet 4 alone, and to obtain white light with no color unevenness on the liquid crystal display screen. Is difficult. Further, in the case of LED, since the light emission angle is different from that of a cold cathode tube or a hot cathode tube, the shape of the light guide plate 3 used in the conventional backlight system, the shape of the incident surface thereof, and the reflection plate 7 are used. It is difficult to achieve color mixing at the same time with uniform brightness.

  Accordingly, an object of the present invention is to solve the above-described problems and provide a backlight system and a liquid crystal display device using a light emitting diode in which luminance unevenness and color unevenness are reduced.

  The object is to provide a substrate on which two or more types of light emitting diodes emitting light having different main emission wavelengths are mounted, a color mixing light guide plate for mixing light emitted from the light emitting diodes, and light from the color mixing light guide plate. In a backlight system including a leading light plate that enters and emits light to the liquid crystal panel, the light-emitting diode is configured to cover the color mixing light guide plate, and the light guiding plate that receives light from the color mixing light guide plate This is achieved by a backlight system in which the light incident surface and the mounting surface of the light emitting diode are arranged in parallel.

  Here, an optical member having a function of diffusing light may be disposed between the main light guide plate and the color mixing light guide plate. Further, it is preferable that the surface of the color mixing light guide plate with respect to the main light guide plate is subjected to light diffusion processing. The color mixing light guide plate may have a recessed space at a position corresponding to the light emitting diode. The recess shape may be a rectangular parallelepiped shape or a hemispherical shape, and the recess-shaped space may be filled with a transparent resin. Further, the color mixing light guide plate may be formed by connecting a plurality of color mixing light guide plate units. It is preferable that the connection surface between the color mixing light guide plate units is subjected to light diffusion processing.

The color mixing light guide plate has a reflector-shaped portion for directing light from the light-emitting diode toward the main light-guiding plate, and an angle formed by a surface of the light-emitting diode mounting surface and the surface of the reflector-shaped portion from 36 °. It is preferably within the range of 75 °. A reflecting member can be provided on the surface of the reflector-shaped portion. The reflective member can be formed of a reflective sheet or white paint. The material of the main light guide plate and the color mixing light guide plate is preferably the same. Further, when the main light guide plate and the color mixing light guide plate have different thicknesses, the portion of the main light guide plate or the color mixing light guide plate that protrudes from the opposing surface of the main light guide plate and the color mixture light guide plate is larger. It is preferable to arrange a reflecting member on the surface.
A liquid crystal display device according to the present invention includes the above-described backlight system and a liquid crystal panel disposed on an emission surface of the backlight system.

  As described above, the present invention provides a light guide plate (leading light plate) positioned directly under the liquid crystal display screen (liquid crystal panel) and a light guide for mixing colors, which is located outside the range of the liquid crystal display screen and provided next to the leading light plate. A light plate (light guide plate for color mixing) is provided. Here, it is possible to suppress luminance unevenness and perform color mixing by the distance from the LED to the emission surface and the reflector function of the color mixing light guide plate.

Furthermore, the effect can be further improved by providing a diffusion sheet between the main light guide plate and the color mixing light guide plate.
The RGB-LEDs used in the backlight system are arranged so as to fit in a recessed space provided in the color mixing light guide plate, and the recessed space of the color mixing light guide plate is filled with a transparent resin. Thus, the light from the LED can be efficiently incident on the color mixing light guide plate.

  According to the present invention, it is possible to obtain a backlight system and a liquid crystal display device using a light emitting diode in which luminance unevenness and color unevenness are small. In the present invention, the white light necessary for the liquid crystal display is added to the main light guide plate by adding a light guide plate for color mixing with appropriate arrangement of RGB-LEDs and processing of the reflector shape so as to reduce luminance unevenness and color unevenness. A backlight system for obtaining light and a liquid crystal display device can be provided.

  Embodiments of a backlight system and a liquid crystal display device according to the present invention will be described below.

  FIG. 1 is a perspective view showing an example of a backlight system for a liquid crystal display device according to the present invention. As shown in the figure, the backlight system mixes the light emitted from each LED with a metal core substrate 13 on which an LED unit 15 having two or more types of light emitting diodes (LEDs) that emit light having different main emission wavelengths is mounted. And a main light guide plate 3 that receives light from the color mixture light guide plate 14 and emits the light to the liquid crystal panel, and covers the LED unit 15 (LED) with the color mixture light guide plate 14. And the light incident surface of the main light guide plate 3 that receives light from the color mixing light guide plate 14 and the LED mounting surface are arranged in parallel.

  That is, in FIG. 1, the LED light unit 3 of the light source provided with the main light board 3, the metal core board | substrate 13, the light-guide plate 14 for color mixing, and the light source is made into the minimum component. The LED unit 15 is mounted on the metal core substrate 13, and the color mixing light guide plate 14 is also disposed on the metal core substrate 13. The color mixing light guide plate 14 is provided with a sealing space for accommodating the LED unit 15. In FIG. 1, the light emitted from the LED unit 15 is mixed by repeating reflection in the light-mixing light guide plate 14, and the light from the LED that is a point light source is diffused, and the light emitted from the light-mixing light guide plate 14 is Uniform brightness. The light emitted from the color mixing light guide plate 14 is incident on the main light guide plate 3 through an optical member having a function of diffusing light, such as the optical sheet 16 interposed between the color mixing light guide plate 14 and the main light guide plate 3. It has become.

  4 is a cross-sectional view of the backlight system shown in FIG. The liquid crystal display device includes the backlight system and a liquid crystal panel 40 disposed on the emission surface thereof. The LED unit 15 of the light source is composed of an RGB-LED and a submount substrate on which the LED is mounted. In this figure, the light incident on the main light guide plate 3 passes through the diffusion member such as the diffusion sheet 4, the light collector plate 5 and the light collector plate 6 by the action of the reflection member such as the reflection sheet 2 and the main light guide plate 3. Light is emitted in the direction of. As shown in the drawing, the light incident surface of the main light guide plate 3 that receives light from the color mixing light guide plate 14 and the mounting surface of the LED unit 15 (LED) on the metal core substrate 13 are parallel to each other. Is efficiently incident on the main light guide plate 3.

  FIG. 3 is a top view of the positional relationship between the RGB-LEDs constituting the LED unit 15 and the submount substrate. Four LEDs are mounted on one submount substrate 8, LED 9 is a red LED, LED 10 and LED 12 are green LEDs, and LED 11 is a blue LED. The light emission of the LEDs 9 to 12 is such that when all the lights are turned on and color mixing is performed, x is 0.27 to 0.31 and y is 0.27 to 0.31 with respect to the chromaticity coordinates (x, y). It is assumed that the current distribution is adjusted.

  FIG. 5 is a diagram in which the submount substrate 8 is disposed in a vertically long positional relationship with respect to the longitudinal direction of the light incident surface of the main light guide plate 3, and four LEDs are mounted on one submount substrate 8. LED 9, LED 10, LED 12, and LED 11 are formed in this order to constitute the LED unit 15 of the light source.

  FIG. 6 is a diagram in which the submount substrate 8 is arranged in a laterally long positional relationship with respect to the longitudinal direction of the light incident surface of the main light guide plate 3, and four LEDs are mounted on one submount substrate 8. LED 9, LED 10, LED 12, and LED 11 in order, and constitutes the LED unit 15 of the light source.

  The light source of the liquid crystal display device of the present invention uses the submount substrate 8 on which the LED shown in FIG. 3, FIG. 5 or FIG. 6 is mounted as the LED unit 15 and uses one or more of the units arranged as a light source.

As shown in FIG. 4, by arranging an optical member (preferably a diffusion sheet) such as the optical sheet 16 between the main light plate 3 and the color mixing light guide plate 14, the color variation of RGB is further reduced to the main light plate 3. It becomes possible to make light mixed with white light incident.
Further, instead of the optical sheet 16, the color mixing light guide plate 14 performs light diffusion processing on the surface facing the main light plate 3 by graining or rubbing glass processing, thereby reducing RGB color variation. It can be an alternative to the sheet 16.

Hereinafter, FIG. 7 will be described. FIG. 7 is a diagram schematically showing a configuration mainly composed of the color mixing light guide plate 20 corresponding to one LED unit of the present invention. Reference numeral 19 denotes a recess-shaped space for accommodating LEDs (hereinafter referred to as a sealing space), 17 denotes a reflecting member such as a reflecting sheet, and 20 denotes a color mixing light guide plate corresponding to one LED unit.
As shown in FIG. 7, the LED unit 15 can be arranged by providing the sealing space 19 that is hollowed out in the concave shape of the color mixing light guide plate 20.
Furthermore, by filling the sealing space 19 with a transparent resin, the refractive index difference generated between the LED and the color mixing light guide plate can be reduced as compared with the case where the sealing space 19 is filled with air, The light extraction efficiency from the LED can be improved.

  In the example shown in FIG. 7, the sealing space 19 is a rectangular parallelepiped. Further, as shown in FIG. 8, it is possible to use a shape in which the sealing space 19 is a hemisphere. In this case, when the sealing space is filled with the transparent resin, it is possible to obtain an effect that it is easy to suppress the generation of bubbles and to fill the corners in the sealing space 19 with the transparent resin.

  As shown in FIG. 7, the color mixing light guide plate 14 can be constituted by a continuous body in which color mixing light guide plate units 20 corresponding to one LED unit 15 are connected, and a plurality of color mixing light guide plates 14 (see FIG. 9). 9 can be configured by connecting the color mixing light guide plate unit 21 corresponding to the LED unit 15, and the entire color mixing light guide plate 14 is integrally formed as shown in FIG. can do.

  When connecting the color mixing light guide plate units, for example, the structure shown in FIG. 10 is obtained. The color mixing light guide plate unit 20 or 21 is connected to the connection surface 23 using an adhesive medium 22 therebetween. The adhesive medium 22 can be a general means such as an adhesive tape, glue or adhesive.

  In addition, when connecting the color mixing light guide plate units, the light diffusion process is performed by diffusing or scattering and reflecting the light by performing light diffusing processing on the connecting surface 23 where the color mixing light guide plate units are in contact with each other by dot processing or grain processing. It can have the effect of reducing.

  FIG. 11 is a diagram illustrating an example of a color mixing light guide plate having a reflector function. FIG. 11 is a perspective view of the color mixing light guide plate unit 20, 17 is a reflecting member such as a reflecting sheet, and 22 is an adhesive medium for attaching the reflecting sheet 17 to the reflector-shaped portion 24. As shown in FIG. 11, the reflector shape 24 is processed by providing an obliquely inclined surface in a shape expanding from the LED mounting surface to the emission surface of the color mixing light guide plate, with the LED mounting portion as the center. As a result, it is possible to further enhance the effect of reducing luminance unevenness and color mixing. This reflector function can also be provided in the same manner for the light guide plate unit 21 for color mixture and the light guide plate 14 for color mixture formed integrally.

  As shown in FIG. 17, when the angle 27 formed by the LED mounting surface and the surface of the reflector-shaped portion 24 of the color mixing light guide plate 20 is defined as the reflector angle θ, the range of the reflector angle θ27 is 36 ° to 75 °. It is desirable to be within the range of °. In the graph shown in FIG. 18, the horizontal axis represents the reflector angle θ, and the left vertical axis represents the light use efficiency until the LED light is transmitted to the emission surface of the color mixing light guide plate. The vertical axis on the right represents an index representing the degree of unevenness in luminance. A graph connected with white circles shows the light use efficiency of the LED, and a graph connected with black circles shows uneven brightness. As indicated by the dotted line in the graph, when the luminance unevenness index value is in an area above the dotted line, the luminance unevenness can be seen with human eyes. Therefore, it is necessary to set the reflector angle θ within the range of 36 ° to 75 ° so that the region is below the dotted line.

Referring back to FIG. 11, the reflective performance of the reflector is improved by attaching a reflective member such as the reflective sheet 17 to the reflector-shaped portion 24 of the color mixing light guide plate 20 using the adhesive medium 22. It is possible to increase the efficiency of transmitting emitted light to the exit surface. The adhesive medium 22 can be a general adhesive means such as an adhesive tape, glue, or adhesive. Further, since the reflection sheet 17 has the property of scattering reflection, color mixing in the color mixing light guide plate becomes more advantageous.
As an alternative to the reflection sheet 17, the same effect can be obtained by applying a white coating to the reflector-shaped portion 24.

  Furthermore, as shown in FIG. 12, the light extraction efficiency from the color mixing light guide plate is improved by applying a reflection member such as a reflective sheet or white paint at the position of the region 25 of the color mixing light guide plate to enhance the reflection performance. Is possible.

Returning to FIG. The light emitted from the LED unit 15 is incident on the color mixing light guide plate 14 through the transparent resin filled in the sealing space. Light emitted from the color mixing light guide plate 14 is incident on the main light plate 3 via the diffusion sheet 16. In one of these light transmission paths, as one of the factors that hinder the light transmission, a difference in refractive index generated between the members is raised. Therefore, transmission efficiency can be increased by reducing the difference in refractive index between the members. In particular, by using the same material for the main light guide plate 3 and the color mixing light guide plate 14, the refractive index can be made the same and the light transmission efficiency can be increased.
The material of the main light guide plate 3 and the color mixing light guide plate 14 is preferably a material generally used for a well-known light guide plate, and examples thereof include acrylic resin, methacrylic resin, and polycarbonate.

  13, FIG. 14, FIG. 15, and FIG. 16 are cross-sectional views showing other examples of the backlight system according to the present invention. 4 is an example in which the main light guide plate and the color mixing light guide plate have the same thickness, but those shown in FIGS. 13 to 16 are examples in which the thicknesses of the two are different. FIGS. 13 and 14 are examples in the case where the thickness of the main light guide plate 3 is larger than that of the color mixing light guide plate 14. In this case, the loss of light can be reduced by disposing a reflection member such as the reflection sheet 26 in a portion where the main light plate 3 protrudes from the surface facing the color mixing light guide plate 14. FIG. 15 and FIG. 16 are examples in the case where the thickness of the main light guide plate 3 is smaller than that of the color mixing light guide plate 14. In this case, light loss can be reduced by disposing a reflection member such as the reflection sheet 26 in a portion where the color mixing light guide plate 14 protrudes from the surface facing the main light plate 3.

  The present invention relates to a backlight system and a liquid crystal display device, and more particularly to a backlight system and a liquid crystal display device using a light emitting diode (LED), and has industrial applicability.

It is a perspective view which shows an example of the backlight system for liquid crystal display devices which concerns on this invention. It is sectional drawing of the backlight system part of the liquid crystal display device which uses the fluorescent lamp as a light source. It is the figure which looked at the positional relationship of RGB-LED which comprises LED unit 15, and a submount board | substrate from the top. It is sectional drawing of the backlight system of FIG. FIG. 4 is a diagram in which four sub-mount substrates are arranged in a vertically long positional relationship with respect to the longitudinal direction of the light incident surface of the main light guide plate, and four LEDs are mounted on one sub-mount substrate. FIG. 4 is a diagram in which four sub-mount substrates are arranged in a horizontally long positional relationship with respect to the longitudinal direction of the light incident surface of the main light guide plate, and four LEDs are mounted on one sub-mount substrate. It is a figure which shows an example of the light-guide plate unit for color mixing corresponding to one LED unit. It is a figure which shows the other example of the light-guide plate unit for color mixing corresponding to one LED unit. It is a figure which shows an example of the light-guide plate unit for color mixing corresponding to multiple LED units. It is a figure for demonstrating the connection of the light-guide plate units for color mixing. It is a figure which shows an example of the color mixing light-guide plate which comprised the reflector function. It is a figure which shows an example of the color mixing light-guide plate which gave the reflection member. It is sectional drawing which shows the other example of the backlight system for liquid crystal display devices which concerns on this invention. It is sectional drawing which shows the other example of the backlight system for liquid crystal display devices which concerns on this invention. It is sectional drawing which shows the other example of the backlight system for liquid crystal display devices which concerns on this invention. It is sectional drawing which shows the other example of the backlight system for liquid crystal display devices which concerns on this invention. It is a figure for demonstrating an example of the color mixing light-guide plate which comprised the reflector function. It is a graph which shows the relationship between reflector angle | corner (theta), the utilization efficiency of LED light, and the nonuniformity of a brightness | luminance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cold cathode fluorescent lamp, 2 ... Reflecting plate, 3 ... Leading light plate, 4 ... Diffusing sheet, 5 ... 1st light collecting plate, 6 ... 2nd light collecting plate, 7 ... Reflecting plate, 8 ... Submount, 9 ... Red LED Bare chip, 10 ... first green LED bare chip, 11 ... blue LED bare chip, 12 ... second green LED bare chip, 13 ... metal core substrate, 14 ... light guide plate for color mixing, 15 ... LED unit, 16 ... diffusion sheet, 17 ... reflector, DESCRIPTION OF SYMBOLS 19 ... Sealing space, 20 ... 1 unit color mixing light guide plate, 21 ... 3 unit color mixing light guide plate, 22 ... Adhesive medium, 23 ... Adhesive surface, 24 ... Reflector shape part, 25 ... Reflecting member provision area | region, 26 ... reflective sheet, 27 ... reflector angle θ

Claims (14)

  A substrate on which two or more types of light emitting diodes that emit light having different main emission wavelengths are mounted, a color mixing light guide plate for mixing light emitted from the light emitting diodes, and a liquid crystal that receives light from the color mixing light guide plate In a backlight system including a main light plate that emits light to a panel, the light-emitting diode is configured to cover the color mixing light guide plate, and a light incident surface of the main light plate that receives light from the color mixing light guide plate; A backlight system, wherein the light emitting diode is disposed so that the mounting surface thereof is parallel to the light emitting diode.   2. The backlight system according to claim 1, wherein an optical member having a function of diffusing light is arranged between the main light guide plate and the color mixing light guide plate.   2. The backlight system according to claim 1, wherein a surface of the color mixing light guide plate with respect to the main light guide plate is subjected to light diffusion processing.   The backlight system according to claim 1, wherein the color mixing light guide plate has a recessed space at a position corresponding to the light emitting diode.   The backlight system according to claim 4, wherein the concave shape is a rectangular parallelepiped shape or a hemispherical shape.   6. The backlight system according to claim 4 or 5, wherein the recess-shaped space is filled with a transparent resin.   The backlight system according to claim 1, wherein the color mixing light guide plate is formed by connecting a plurality of color mixing light guide plate units.   The backlight system according to claim 7, wherein a connecting surface between the color mixing light guide plate units is subjected to light diffusion processing.   The color mixing light guide plate has a reflector-shaped portion for directing light from the light-emitting diode to the main light-guiding plate, and an angle formed by a mounting surface of the light-emitting diode and a surface of the reflector-shaped portion is 36 ° to 75 °. The backlight system according to any one of claims 1 to 8, wherein the backlight system is within the range.   The backlight system according to claim 9, wherein a reflecting member is provided on a surface of the reflector-shaped portion.   The backlight system according to claim 10, wherein the reflecting member is formed of a reflecting sheet or white paint.   The backlight system according to claim 1, wherein a material of the main light guide plate and the color mixing light guide plate is the same.   When the thickness of the main light guide plate and the color mixing light guide plate is different, reflection is performed on a portion of the main light guide plate or the color mixing light guide plate that is larger than the opposite surface of the main light guide plate and the color mixing light guide plate. The backlight system according to claim 1, wherein a member is disposed.   A liquid crystal display device comprising: the backlight system according to claim 1; and a liquid crystal panel disposed on an emission surface of the backlight system.

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