JP4035085B2 - Backlight device for liquid crystal display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a backlight device capable of emitting a polarized light beam consisting only of a specific polarization component used as a light source device of a liquid crystal display device as illumination light, and more specifically, a light source irradiated to the liquid crystal display device. Liquid crystal that can convert the polarized light other than the polarized light effective for operating the liquid crystal display device among the light rays to convert it into effective polarized light and increase the amount of the effective polarized light to improve the luminance. The present invention relates to a backlight device of a display device.
[0002]
[Prior art]
The backlight device that supplies the light beam to the liquid crystal panel (LCD) of the liquid crystal display device has a sidelight system that irradiates the LCD with the light beam from the light source through a light guide plate, etc., and the light beam from the light source directly. There is a direct method to irradiate the LCD. However, due to the recent increase in the size of liquid crystal display devices, a direct method that facilitates high brightness has come to be adopted. This direct-type backlight device includes a light source that illuminates the LCD from behind, and a reflector that is disposed on the opposite side of the LCD from the light source. A long fluorescent tube is mainly used as the light source, and in the case of a large-sized liquid crystal display device, a plurality of fluorescent tubes are arranged in parallel at equal intervals. A reflecting plate is used to uniformly and uniformly lead the LCD, and the reflecting plate is formed to be repeatedly bent according to the number of light sources and the distance between the light sources. (For example, Patent Document 1)
[0003]
On the other hand, in a liquid crystal display device, light from a light source is directly applied to a light valve composed of an LCD, and after modulation corresponding to a display image is performed in the light valve, an image is formed on a projection surface via a projection optical system. It is supposed to be. The liquid crystal light valve for performing modulation corresponding to image information uses only a specific polarization component, and in two linear polarization components whose polarization directions are orthogonal even if the light emitted from the light source is directly irradiated to the LCD Since one polarization component is not used, the light use efficiency is poor and it is difficult to make the projected image brighter.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-156512
[Problems to be solved by the invention]
The present invention is intended to solve such problems, and in a backlight device used in a liquid crystal display device, the backlight device of the liquid crystal display device is designed to improve the use efficiency of light and improve the luminance. Is intended to provide.
[0006]
[Means for Solving the Problems]
The present invention comprises a light source;
Reflecting means for reflecting light rays from the light source toward the liquid crystal panel of the liquid crystal display device;
Polarizing means that is disposed between the liquid crystal panel and the light source and transmits one linearly polarized light of the P component and S component of the light irradiated by the light source and the reflecting means and reflects and separates the other component When,
Wherein disposed between the polarization means and the reflecting means comprises a polarization conversion means for converting the polarized light of the return light reflected by said polarizing means,
The reflecting means has a reflecting concave surface having an arc-shaped cross section, and the light source is disposed on the center line of the arc,
The polarization conversion means is a half-wave plate, and is disposed on the center line so that the optical axis of the half-wave plate is perpendicular to the center line.
The return light incident on one side of the reflecting concave surface across the center line is emitted from the other side after passing through the half-wave plate.
[0007]
According to the present invention, it is possible to improve the luminance by effectively utilizing the return light. Further, it is possible to increase the luminance by increasing the conversion efficiency of the return light. Furthermore, the polarization conversion of the return light by the polarization conversion means can be performed effectively.
[0009]
The second aspect of the present invention, the reflective concave surface of said reflecting means, by a backlight device of a liquid crystal display device according to the first invention is a curved surface or stepped surface, and reflects the returning light, This reflected light can be effectively irradiated and transmitted to the polarization conversion means.
[0010]
In the present invention, focusing on the fact that light other than the actuated polarized light is reflected by the polarization means that separates and transmits the specific polarized light that operates the LCD from the light source, and polarization conversion is performed using the reflected return light. Thus, it is possible to provide a backlight device of a liquid crystal display device in which the return light is converted into working polarized light to improve the light use efficiency and improve the luminance.
[0011]
As the light source used in the present invention, a long cold cathode fluorescent lamp or the like arranged in parallel with the LCD can be used, and one light source may be used, but depending on the size of the LCD, A plurality can be arranged in parallel at equal intervals.
[0012]
As the reflecting means used in the present invention, it is sufficient if it reflects the light emitted from the light source toward the LCD. However, the reflecting means has a reflecting concave surface having a circular arc cross section, and the upper part of the center line of the arc. In addition, it is desirable to have a shape in which the light source is arranged. When a long light source is used as the light source, it is preferable to use a reflection concave surface having an arc cross section extending in parallel with the light source, that is, a semi-cylindrical reflection concave surface. As described above, when using a plurality of light sources arranged in parallel, it is preferable that the reflective concave surface is formed by being repeatedly bent. Such a repeated bending shape can be processed by an appropriate means such as pressing a sheet of aluminum metal or stainless steel. However, a plastic molded substrate is used, and a reflective material is applied to this surface and adhered to reflect. It can also be concave. As the reflective material, there can be used a film made of polyester, polyethylene or polypropylene mixed with a powder of titanium oxide or the like and whitened, or a white polyester film (Toray E-60L).
[0013]
Further, the reflecting concave surface can be a smooth curved surface, but it can also be a fine curved step surface in order to improve the reflection efficiency.
[0014]
Any polarization means may be used as long as it can selectively transmit P-component or S-component linearly polarized light that operates the LCD and reflect and separate the other component. A flat plate or a sheet-like material can be used.
[0015]
In the present invention, the light beam (returned light) reflected by the polarizing means is converted into linearly polarized light that operates the LCD by transmitting through the polarization converting means. Therefore, the converted linearly polarized light is The LCD emits light together with linearly polarized light that has passed through the polarizing means directly from the light source, so that the brightness can be enhanced. As this polarization conversion means, P component or S component linearly polarized light can be used as S component or P component, respectively. A half-wave plate that can be converted to linearly polarized light can be used. When this polarization conversion means is arranged on the optical axis of the light source arranged above the center line of the reflection concave surface having an arc cross section as described above, the return light is effectively transmitted through the polarization conversion means, and the reflection means Is preferable because it is reflected by the LCD. In particular, when the polarization conversion means is disposed between the light source and the reflection means, it is preferable because the amount of return light converted by the polarization conversion means increases toward the LCD.
[0016]
If the reflection range of the reflection concave surface of the reflection means is set so that the return light whose angle θ formed with the normal plane orthogonal to the polarization plane of the return light polarization means is ± 50 degrees or less can be reflected, the polarization is converted. The return light can be efficiently irradiated onto the LCD.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a backlight device according to the present invention will be described below with reference to the drawings.
Example 1
FIG. 1 is a schematic sectional view of a backlight device according to an embodiment of the present invention. In the figure, 1 is a light source composed of a long cold cathode fluorescent lamp, and 2 is a polarizing plate that transmits S-component linearly polarized light and reflects P-component linearly polarized light. 3 is a half-wave plate for converting the polarized light of the transmitted light beam, 4 is a reflection means, 5 is an LCD, 6 is a diffusion film, and 19 is a brightness enhancement film.
[0018]
The reflecting means 4 includes two semi-cylindrical concave surfaces connected to each other, and a reflective concave surface layer 8 made of a white polyester film is formed on the concave surface of the plastic substrate 7 that is repeatedly bent. The layer 8 is disposed so as to face the polarizing plate 2. In the upper part of the center line of the reflective concave layer 8, the long light source 1 is parallel to the depth direction of the polarizing plate 2 (the vertical direction on the paper surface), and the two light sources 1 are parallel to each other. It is attached as follows. Accordingly, the semi-cylindrical reflective concave surface layer 8 is also arranged so as to be parallel to the light source 1.
[0019]
The half-wave plate 3 is arranged between the light source 1 and the corresponding reflective concave layer 8 so as to coincide with the optical axis 9 of the light source 1.
[0020]
The light beam 10 emitted from the light source 1 is applied to the polarizing plate 2 through the diffusion film 6 and the brightness enhancement film 19, and the irradiated outgoing light beam 10 receives only the S component linearly polarized light by the polarizing plate 2. The S component polarized light that has been transmitted and transmitted through the polarizing plate 2 is applied to the LCD 5 to operate the LCD 5. On the other hand, the P component linearly polarized light which is not transmitted among the light rays 10 emitted from the light source 1 to the polarizing plate 2 is reflected by the polarizing plate 2 and returns to the reflective concave surface layer 8 as return light 12. Emitted.
[0021]
The return light 12 emitted in this way is reflected by the reflective concave layer 8 and passes through the half-wave plate 3, and the P-component polarized light 12 is converted into the S-component polarized light 13 by the half-wave plate 3. Is converted to The S component polarized light 13 thus converted is reflected again by the reflective concave surface layer 8, is applied to the polarizing plate 2, passes through the polarizing plate 2, and is applied to the LCD 5.
[0022]
In this way, not only the S component polarized light of the light emitted from the light source 1 but also the P component polarized light of the return light is converted to S component polarized light and irradiated to the LCD, so that the brightness of the LCD is improved. be able to. In addition, the LCD image screen operated in this way can reduce luminance unevenness and provide good image quality.
[0023]
Of the return light 12 emitted from the light source 1 and irradiated and reflected on the polarizing plate 2, the light having an angle θ of more than ± 50 degrees with the normal perpendicular to the polarization plane 14 of the polarizing plate 2 is P component. Since the content of polarized light is reduced and is not so effective, the reflective concave surface layer 8 is shaped so that the return light having the angle θ within ± 50 degrees is reflected and transmitted through the half-wave plate 3. It is preferable.
[0024]
In this example, the polarizing light 2 and the polarizing plate 2 are separated for the purpose of explaining the polarized lights 11 and 13 transmitted through the polarizing plate 2, but the polarizing plate 2 is in direct contact with the LCD 5. Also good.
[0025]
Furthermore, in this example, two light sources 1 and a reflective concave surface layer 8 corresponding to the light sources 1 are used. However, two or more light sources 1 are provided, and these light sources 1 are arranged in parallel at equal intervals. Corresponding to these light sources 1, the reflective concave surface layer 8 can be repeatedly bent and installed.
[0026]
(Example 2)
FIG. 2 shows a basic schematic configuration diagram in which the LCD 5, the diffusion film 6 and the like of another embodiment according to the present invention are omitted. Basically, it is the same as the backlight device of Example 1, but the cross-sectional shape of the reflective concave layer 8 of the reflecting means 4 is changed, and only the central portion 15 of the reflective concave layer 8 has a circular arc shape. The outer peripheral portion 16 is a reflecting surface having a linear cross section opened from the arcuate surface of the central portion 15. By setting the reflection surface in such a shape, there is an advantage that the amount of return light transmitted through the half-wave plate 3 can be increased.
[0027]
(Example 3)
FIG. 3 shows a basic schematic configuration diagram in which the LCD 5 and the diffusion film 6 of another embodiment are omitted.
[0028]
In this embodiment, an example in which one light source 1 is used is shown. When the LCD 5 has a small area, the reflective concave surface layer 8 of the reflecting means 4 is provided so that sufficient luminance can be obtained even with one light source 1. The cross-sectional shape is formed in a circular arc shape at the central portion 15, an arc shape slightly wider than the arc-shaped surface of the central portion 15 at the intermediate portion 17, and an arc shape narrower than the arc-shaped surface of the intermediate portion 17 at the outer peripheral portion 16. The light quantity of the light source 1 is to be used as effectively as possible.
[0029]
Example 4
In this embodiment, a plurality of half-wave plates 3 (3 and 3 ′, or 3 and 3 ′ and 3 ″) are used for the light source 1, and the light source corresponding to one reflective concave surface layer 8 is used. By making the number of 1 plural (1 and 1 ') and the shape of the reflective concave surface layer 8 of the reflecting means 4 to be a stepped circular arc surface 19, the conversion efficiency of the return light 12 is further increased. The light source 1 is increased to increase the amount of light so as to improve the luminance.
[0030]
In the backlight device according to the present invention, means for improving other functions such as a brightness enhancement film can be added in addition to the diffusion film 6 that diffuses light rays and effectively irradiates the LCD 5.
[0031]
Furthermore, in addition to the liquid crystal display device having the transmission mode described in the above embodiment, the upper polarizing plate is disposed on the upper part of the LCD, so that it can be effectively used for a liquid crystal display device that can share a reflection mode using external light as a light source. be able to.
[0032]
Further, the reflecting concave surface of the reflecting means according to the present invention is not limited to the form of the above-described embodiment, but may be a polygonal cross-sectional shape, etc. Further, depending on the arrangement relationship of the polarizing means 2, the light source 1, and the half-wave plate 3. The opening angle of the reflective concave surface can be set as appropriate.
[0033]
【The invention's effect】
As described above, in the present invention, the light source, the reflection means for reflecting the light from the light source toward the LCD of the liquid crystal display device, and disposed between the LCD and the light source, the light source and the reflection means A liquid crystal display comprising: polarizing means for polarizing light irradiated by the light source; and a polarization converting means disposed between the polarizing means and the reflecting means for converting the polarized light of the return light from the polarizing means. By using the backlight device of the apparatus, the return light can be effectively used to improve the luminance.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a backlight device according to an embodiment of the present invention.
FIG. 2 is a basic schematic configuration diagram of a backlight device in which an LCD 5 and a diffusion film 6 according to another embodiment of the present invention are omitted.
FIG. 3 is a basic schematic configuration diagram of a backlight device in which the LCD 5 and the diffusion film 6 of another embodiment are omitted.
4 is a basic schematic configuration diagram of a backlight device in which an LCD, a diffusion film, and the like according to a fourth embodiment to which the present invention is applied are omitted. FIG.
[Explanation of symbols]
1, 1 ′ light source 2 polarizing plate 3, 3 ′, 3 ″ half-wave plate 4 reflecting means 5 LCD
8 Reflective concave surface layer 9 Optical axis 10 Light source outgoing light 11 Transmitted polarized light 12 Returned light 13 Converted light 18 Stepped circular arc surface

Claims (2)

A light source;
Reflecting means for reflecting light rays from the light source toward the liquid crystal panel of the liquid crystal display device;
Polarizing means that is disposed between the liquid crystal panel and the light source and transmits one linearly polarized light of the P component and S component of the light irradiated by the light source and the reflecting means and reflects and separates the other component When,
Wherein disposed between the polarization means and the reflecting means comprises a polarization conversion means for converting the polarized light of the return light reflected by said polarizing means,
The reflecting means has a reflecting concave surface having an arc-shaped cross section, and the light source is disposed on the center line of the arc,
The polarization conversion means is a half-wave plate, and is disposed on the center line so that the optical axis of the half-wave plate is perpendicular to the center line.
The return light incident on one side of the reflective concave surface across the center line is emitted from the other side after passing through the half-wave plate. Device backlight device. The backlight device of the liquid crystal display device according to claim 1 , wherein the reflecting concave surface of the reflecting means is a curved surface or a stepped surface .

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