JP2007035463A - Backlight device and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct an angle dependence property of display color provided when an optically-transparent display panel such as a liquid crystal display panel. <P>SOLUTION: A member having a characteristic where transmission and reflection scattering distributions are changed in dependence on incident wavelength is used for a scattering member of a backlight 10 provided for this display device. By providing such a scattering member, the scattering member acts to correct an angle dependence property of display color provided for the display panel 3 side by the transmission and reflection scattering distribution characteristic provided for the scattering member, whereby the angle dependence property of display color provided for the display panel 3 can be eliminated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a backlight device suitable for application to, for example, a backlight of a liquid crystal display device and a display device including the backlight.

  In the liquid crystal display device, since the pixels arranged on the display panel do not emit light, a backlight is arranged on the back of the display panel, and the back is illuminated with the backlight to display an image or the like. . The display area of the display panel is increasing, and the backlight itself is becoming very large.

  As a light source used as a backlight, a light source such as a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) is used. When illuminating, it is necessary to arrange a large number of light sources. For example, when a cold cathode tube is used, a plurality of display tubes are arranged in parallel. Even when light emitting diodes are used, a plurality of light emitting diodes are arranged in a matrix form.

If a backlight device composed of a large number of these light sources is simply placed on the back of the display panel, the light emission brightness is bright at the light source placement positions, and the light emission brightness is dark at the positions between the light sources. As a result, the luminance of the emitted light becomes very uneven when viewed over the entire surface of the backlight. For this reason, in the case of a normal backlight device, light from the light source is scattered by the scattering sheet so that a uniform light emission state is obtained. Patent Document 1 discloses an example of a scattering member used as a backlight.
JP 2004-61604 A

  By the way, in the case of an image display device configured by combining a backlight with a liquid crystal display panel, the color (chromaticity) of the liquid crystal panel differs depending on whether the panel is viewed from the front or obliquely. was there. Specifically, for example, as shown in FIG. 8, when an image displayed on the liquid crystal display panel a is viewed by the user's eye e1 with the light L1 in the front direction (normal direction), The color (chromaticity) changes when the light L2 in the direction with the angle is viewed with the user's eyes e2. The degree to which the chromaticity changes depends on the characteristics of the liquid crystal panel, but when viewing the light L1 in the front direction, the white light appears as it is, but the light in the direction with a certain angle. When L2 is viewed, there is a problem that white light appears to have a magenta color.

  Such a problem of angle dependency is caused by the fact that the spectral transmittance of the liquid crystal layer of the liquid crystal display panel has angle dependency depending on the wavelength of light. That is, when light passes through the liquid crystal layer obliquely, short wavelength light is relatively absorbed. The degree to which the color changes varies slightly depending on the panel configuration, but is a problem that cannot be avoided in principle. FIG. 7 shows an example in which characteristics are measured when the relative transmittance of a certain liquid crystal display panel is compared. The relative value on the vertical axis in this figure is the value obtained by (60 degree transmittance ÷ 0 degree transmittance). As can be seen from the change in wavelength on the horizontal axis, when the wavelength is about 400 nm, the relative value is about 0.4. On the other hand, it is about 0.6 at a wavelength of about 700 nm, and it can be seen that there is angle dependency depending on the color.

  The present invention has been made in view of the above points, and an object of the present invention is to make it possible to correct the angle dependency of display colors when a transmissive display panel such as a liquid crystal display panel is used.

  The present invention is a backlight scattering member provided in a display device, in which transmission and reflection / scattering distributions have different characteristics depending on the incident wavelength.

  By providing such a scattering member, it acts to correct the angle dependency of the display color of the display panel by the transmission and reflection scattering distribution characteristics of the scattering member, and the angle dependency of the display color of the display panel is reduced. It can be lost.

  According to the present invention, it is possible to eliminate the angle dependency of the display color of the display panel by correcting the angle dependency of the display color of the display panel by the transmission and reflection scattering distribution characteristics of the scattering member. become. In this case, the scattering member itself is a member originally provided in the backlight, and the number of constituent members is not increased for realizing the present invention, and the angle dependency of the display color can be corrected with a simple configuration.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. In this example, the present invention is applied to a liquid crystal image display device having a backlight. FIG. 2 is a diagram showing an example of the overall configuration of the liquid crystal image display device 1 of this example. The liquid crystal image display device 1 of this example is a display device configured as a television receiver, and a liquid crystal display panel 3 is arranged on the front surface of the main body 2. A backlight device 10 to be described later is incorporated on the back surface of the liquid crystal display panel 3. Speakers 5 are arranged on the left and right sides of the front frame 4 that holds the liquid crystal display panel 3. The main body 2 is supported by a stand 6, for example. As already described with reference to FIG. 6, the liquid crystal display panel 3 itself is a panel in which the spectral transmittance of the liquid crystal layer has an angle dependency depending on the wavelength of light. It has the characteristic that

  FIG. 1 is an exploded view of the liquid crystal display panel 3 and the backlight device 10 disposed on the back surface thereof, and FIG. 3 is a vertical sectional view showing the assembled state. As shown in FIGS. 1 and 3, the backlight device 10 that illuminates the image display area of the liquid crystal display panel 3 from the back has a plurality of light sources 12 arranged in parallel in a light source holding member 11. Here, the light source 12 is an example using a cold cathode tube, and emits white light. On the front surface of the light source holding member 11 on which the light source 12 is disposed, a diffusion plate 17 having a predetermined thickness that functions as a diffusion member that diffuses the light from the light source 12 so that the light intensity is almost uniform at any position. And a diffusion sheet 13 having a predetermined thickness is further arranged on the front surface of the diffusion plate 17. The diffusion sheet 13 also functions as a diffusion member that diffuses the light from the light source 12 so that the light intensity is uniform. The configuration of the diffusion sheet 13 will be described later.

  Optical sheets 14 and 15 that are thinner than the diffusion sheet 13 are disposed on the front surface of the diffusion sheet 13. As the optical sheets 14 and 15, a sheet having a predetermined optical characteristic such as a sheet having a scattering action or a prism sheet is used.

  Here, as shown in a part of the cross section in FIG. 4, the diffusion sheet 13 of the present example has a scattering action by dispersing the scatterers 16 almost uniformly in the diffusion sheet 13. Specifically, for example, an acrylic resin is used as a material constituting the scattering sheet 13, and a small diameter composed of polyethylene terephthalate (PET resin) having a higher light refractive index than the acrylic resin. The scatterers 16 are substantially uniformly dispersed. The scattering sheet 13 configured as described above has a scattering action in which light incident on the scatterer 16 diffuses as indicated by an arrow α to make the light intensity uniform. Then, when this scattering action works, the spectral transmittance has an angle dependency.

  The point having the angle dependency will be described. The scatterer 16, which is a particle having a different refractive index, is placed in the base material constituting the diffusion sheet 13. Here, when the particle size of the particles is set to be approximately the same as the wavelength passing through the sheet, the scattering distribution due to the wavelength can be changed. As a result, the spectral transmittance from the diffusion sheet 13 is given angular dependency. be able to.

  The scattering distribution can be varied depending on the particle size and the difference in refractive index from the substrate. Use the Mie scattering theory for particles of the same wavelength, and the Rayleigh scattering theory for smaller particles. become. For example, since the longer wavelength is a relatively specular scattering distribution, the emission in the normal direction of the diffusion sheet 13 is reddish and can be bluish as it becomes oblique.

As a specific characteristic example, as a light distribution of transmitted light when light of three kinds of wavelengths is incident on the diffusion sheet 13 in which the scattering material (scatterer) 16 shown below is dispersed, The state shown in FIG. 5 is obtained. Each value on the characteristic of FIG. 5 is as follows.
Refractive index of medium (diffusion sheet 13) = 1.49
Refractive index of particles (scattering material) = 1.57
Particle radius = 100 [nm]
Incident light wavelength = 450 [nm] & 550 [nm] & 650 [nm]

  The light distribution diagram of Fig. 5 shows the light distribution from -90 degrees to +90 degrees with the normal direction of the diffusion sheet as 0 degrees, and normalizes the intensity at an angle of 0 degrees at each wavelength. did. FIG. 5 shows that the light distribution is different for each wavelength, and shorter wavelengths tend to be relatively dispersed. That is, the relationship between the dispersities is 450 [nm]> 550 [nm]> 650 [nm]. As a result, the emission in the normal direction becomes reddish and becomes more bluish as it becomes oblique. Such characteristics having different angle dependency for each wavelength are selected so as to correct the angle dependency for each wavelength of the liquid crystal display panel 3. In addition, the scatterer with the particle size of the above-mentioned value has a very small diameter of about 1/10 compared with the scatterer mixed in the conventionally used scattering sheet for backlight. It is.

  The image display device using the diffusion sheet 13 having such a configuration can correct the angle dependency of the light wavelength of the liquid crystal display panel with the light distribution of the diffusion sheet 13. That is, as shown in FIG. 6, for example, as emitted from the backlight device 10, the emitted light L11 in the normal direction tends to have a relatively strong red color, and the emitted light having an oblique angle. L12 tends to have a relatively strong bluish color.

  Here, as already described, the liquid crystal display panel 3 itself has an angle dependency for each wavelength, but the angle dependency on the diffusion sheet 13 side is almost opposite to the characteristic on the liquid crystal display panel 3 side. Therefore, as the emitted light from the liquid crystal display panel 3, the light L21 in the front direction (normal direction) is seen with the user's eye e1, and the light L22 in the direction having a predetermined angle. When the user sees the image with the user's eyes e2, there is no change in color (chromaticity), and for example, white light emitted from the backlight appears to be similar in any direction. Therefore, as an image display device, a display device having a good display color in which the hue (chromaticity) does not change depending on the viewing angle can be obtained. In this case, the scattering sheet itself is a member that the backlight originally has, and in realizing the configuration of the present embodiment, the number of components does not increase compared to the conventional backlight, and the manufacturing cost of the device increases. The angle dependency of the display color can be corrected with a simple configuration.

  In the embodiment described so far, the backlight device that illuminates the back surface of the liquid crystal display device is applied to an example using a cold cathode tube as a light source. However, the backlight device using a light emitting diode as a light source is used. It is also applicable to. When a light emitting diode is used as a light source, diodes that emit light of primary colors are arranged in a predetermined order so that the illumination light is mixed color and becomes white light. A display device combined with a backlight device can also be applied to a display device using other transmissive display panels as long as it has the same color angle dependency as the liquid crystal display panel.

  Further, the arrangement position of the scattering sheet (scattering member) constituting the backlight shown in FIG. 1 and the like is also an example. For example, the same applies to any one of the optical sheets 14 and 15. It is good also as a scattering sheet which has an effect | action. Alternatively, the angle dependency of the color is corrected by adding a dedicated member having an angle dependency different from the scattering sheet (member) for making the light intensity of the normal illumination light uniform. You may do it.

  Further, the configuration and each value of the scattering member having the angle dependency are only examples in the above-described embodiment, and similar characteristics may be obtained with another configuration.

It is a disassembled perspective view which shows the structural example by one embodiment of this invention. It is a perspective view which shows the example of whole structure by one embodiment of this invention. It is sectional drawing which shows the example of a cross-sectional structure by one embodiment of this invention. It is sectional drawing of the principal part of the diffusion sheet by one embodiment of this invention. It is a characteristic view which shows the light distribution example of the emitted light by one embodiment of this invention. It is explanatory drawing which shows the example of correction | amendment by one embodiment of this invention. It is a characteristic view for demonstrating the angle dependence of the transmittance | permeability of a liquid crystal display panel. It is explanatory drawing for showing the angle dependence of a liquid crystal display panel.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image display apparatus, 2 ... Main body, 3 ... Liquid crystal display panel, 4 ... Front frame, 5 ... Speaker, 6 ... Stand, 10 ... Backlight apparatus, 11 ... Light source holding member, 12 ... Light source, 13 ... Diffusing sheet, 14, 15 ... Optical sheet, 16 ... Scatterer, 17 ... Diffuser

Claims (6)

A light source that emits light that is arranged in a predetermined state and becomes almost white in a mixed state;
A backlight device comprising: a scattering member that scatters light from the light source and has transmission and reflection scattering distributions having different characteristics depending on an incident wavelength. The backlight device according to claim 1,
The backlight device characterized in that the transmission and reflection scattering distributions of the scattering member differ depending on the incident wavelength such that the scattering rate to the surroundings increases as the wavelength decreases. The backlight device according to claim 2, wherein
In order to obtain a characteristic that the scattering rate to the surroundings increases as the wavelength becomes shorter, particles of a predetermined diameter having a refractive index different from the refractive index of the light of the material are substantially uniform in the material constituting the scattering member. A backlight device characterized in that the backlight device is dispersed. A light source that emits light that is arranged in a predetermined state and becomes almost white in a mixed state;
A scattering member that scatters light from the light source and has transmission and reflection scatter distributions that vary depending on the incident wavelength; and
A display device comprising: a transmissive display panel that transmits light scattered by the scattering member from a back surface. The display device according to claim 4, wherein
The characteristic that the transmission and reflection / scattering distribution of the scattering member differs depending on the incident wavelength is such that the scattering rate to the surroundings becomes higher as the wavelength becomes shorter, and the light transmittance angle dependency at the time of light transmission of the transmissive display panel A display device characterized in that the characteristics are almost opposite to correct the characteristics. The display device according to claim 5, wherein
In order to obtain the property that the scattering rate to the surroundings increases as the wavelength becomes shorter, particles of a predetermined diameter having a refractive index different from the refractive index of the light of the material are substantially uniform in the material constituting the scattering member. A display device characterized by having a configuration in which the display device is dispersed.

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