JP2002231027A - Lighting apparatus and liquid crystal display unit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve deterioration of brightness caused by variation of polarization component due to the aeolotropy of refraction factor of a diffusion sheet and to suppress emergence of unevenness caused by the non-uniform contact of each sheet. SOLUTION: Out of light from a light source 101 incident on a reflection type polarization plate 104 by way of a reflector 102 or the like, only P-polarized light is transmitted through and S-polarized light is used again by being reflected back to a light guide plate. The light is then outputted after being diffused by a diffusion sheet 105 and P-polarized light is modulated by the aeolotropy of refraction factor of the diffusion sheet 105. Because of this, phase difference of a phase plate 106, set after the diffusion sheet, is controlled so that the component of the polarized light modulated by the diffusion sheet is compensated to linear polarized light. Therefore, the light passed through the phase plate 106 becomes P-polarization component again, converged by a prism sheet 107 and comes into an incident side polarization plate 108 whose axis is adapted to P-polarization light. With this configuration, improvement of the incidence efficiency of the light to a liquid crystal panel 109 and high-luminance display is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device provided for a liquid crystal display device for illuminating the liquid crystal display device from the back or side, and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays,
In particular, liquid crystal display devices using color display elements have become widespread. In a liquid crystal display device, for example, two transparent glass substrates are overlapped at a predetermined interval so that the surfaces on which a pixel electrode made of a transparent conductive thin film and an alignment film are laminated face each other. A liquid crystal display element which is sealed and further provided with a polarizing plate on the outside of both substrates, a backlight which is arranged below the liquid crystal display element and supplies light to the liquid crystal display element, a circuit board which drives the liquid crystal display element, etc. It is comprised including.

FIG. 5 shows a configuration example of a conventional liquid crystal display device. FIG. 5A shows an arrangement of each member, and FIG. 5B shows an example of observation from the display surface side. In a currently mainstream transmissive liquid crystal display device, light from a light source 501 is reflected by a reflector 50.
2 and is guided to the light guide plate 503. Light guide plate 50
In No. 3, the light is emitted from the upper surface as light diffused in a plane by the scattering function at the lower surface. In order to obtain uniformity of light before entering the liquid crystal panel, the light is made incident on the liquid crystal panel 506 via the diffusion sheet 504, where the incident polarizer 505 and the output polarizer 507 are arranged in front and behind.

The diffusion sheet 504 and the incident polarizing plate 505 are arranged in contact with each other. If unevenness occurs in the adhesion, a Newton ring-shaped unevenness as shown in FIG. 5B is observed. This is disclosed in Japanese Patent Application Laid-Open No. 11-133409.

[0005]

In recent years, liquid crystal display devices have been widely used as monitors for PCs. In addition, application development as a liquid crystal TV for displaying a moving image of a movie is also progressing. However, the brightness of the liquid crystal display device is still generally lower than that of a CRT or the like, and a higher brightness than the current state is required. To increase the brightness, it is necessary to increase the output of the light source. At this time, in the configuration of the conventional liquid crystal display element as shown in FIG. 5, half of the light from the light source is absorbed by the incident polarizer 505. As the output of the light source increases, the absorption ratio also increases, so that the polarizing plate 505 loses its uniformity due to heat shrinkage or bending due to the absorbed light, causing a problem such as unevenness in black display.

For this reason, a prism sheet is used to efficiently condense the diffused light of the backlight within the viewing angle to increase the front luminance. Further, before the incident polarizer 505 of the liquid crystal panel, a reflective polarizer for adjusting the polarization direction may be used. This has a function of passing only a specific polarization component such as a P-wave and an S-wave and reflecting the others. The polarized light component reflected by the reflective polarizer is returned to the light guide plate and reflected again, and the polarized light component is modulated and reused by being incident on the reflective polarizer. Therefore, by using this reflective polarizer, the absorption loss of the incident polarizer of the liquid crystal panel can be improved.

[0007] In addition to the above configuration, a diffusion sheet 504 is disposed between the incident polarizer 505 and the light guide plate 503 as shown in FIG. This diffusion sheet is generally produced by adding a light diffusing agent to a transparent resin such as polycarbonate or PET, and is provided with a refractive index anisotropy by a stretching process at the time of producing the sheet. Therefore, when the light whose polarization direction is adjusted by the reflective polarizing plate passes through this diffusion sheet, the polarization direction is modulated, which causes a problem of light absorption by the incident polarizing plate of the liquid crystal panel. Further, problems such as deterioration of display quality due to uneven adhesion between the diffusion sheet and the incident polarizing plate also occur.

[0008]

An illumination device according to the present invention includes at least a light source, a polarization direction control unit for emitting light from the light source, a light diffusion unit, and a phase modulation unit, and the phase modulation unit includes the light modulation unit. It is characterized by having a function of modulating light emitted from the diffusion means into substantially linearly polarized light.

Further, the lighting device according to the present invention comprises at least a light source, a polarization direction control means for light emitted from the light source, and a light diffusion means, wherein the light diffusion means has irregularities formed on the surface of an isotropic body. It is characterized by being composed of

Further, the illumination device according to the present invention comprises at least a light source, a polarization direction control means for the light emitted from the light source, a light diffusion means, and a phase modulation means, wherein the phase modulation means is provided by the light diffusion means. It has a function of modulating outgoing light into substantially linearly polarized light, and the light diffusing means is formed of an isotropic body having irregularities formed on its surface.

Further, in the above configuration, it is preferable that the light source includes a point light source.

In the above configuration, it is preferable that the light source includes a linear light source.

In the above configuration, it is preferable that the light source includes a planar light source.

Further, in the above configuration, it is preferable that the light source comprises a combination of a point light source, a linear light source, and a planar light source.

In the above arrangement, it is preferable that the polarization direction control means comprises a reflective polarizing plate.

In the above structure, it is preferable that the reflective polarizing plate has a multilayer structure having different refractive indexes.

In the above configuration, it is preferable that the reflective polarizing plate contains a cholesteric liquid crystal.

In the above arrangement, it is preferable that the phase modulation means has scattering anisotropy.

In the above configuration, it is preferable that the phase modulation means has a phase difference of 100 nm or less.

In the liquid crystal display device according to the present invention, in the liquid crystal display device comprising a combination of a liquid crystal panel having an incident polarizer and an output polarizer attached to the illuminating device, the polarization of the light emitted from the phase modulating means may be improved. The direction is substantially equal to the polarization axis of the incident polarizer.

Further, according to the liquid crystal display device of the present invention, in the liquid crystal display device configured by combining the illumination device with a liquid crystal panel provided with an incident polarizer and an output polarizer, any one of the gaps to the incident polarizer is provided. A transparent material is inserted into the substrate.

In the above structure, it is preferable that the refractive index of the transparent material and the refractive index of each member forming the gap are substantially equal.

In the liquid crystal display device according to the present invention, in the liquid crystal display device configured by combining a liquid crystal panel provided with an incident polarizer and an output polarizer in the illumination device, a light incident surface of the incident polarizer is provided. Characterized in that irregularities are formed on the surface.

In the above structure, it is preferable that unevenness of the surface of the incident polarizer is 100 nm or less.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows a configuration of a lighting apparatus according to Embodiment 1 of the present invention. Light from a light source 101 disposed around the light guide plate 103 is reflected by a reflector 102 and enters the light guide plate 103. The light is scattered by the scattering dots formed on the lower surface of the light guide plate and is emitted from the surface of the light guide plate while repeating reflection inside the light guide plate. The light emitted from the light guide plate 103 enters a reflective polarizing plate 104 as a polarization direction control unit. The reflection type polarizing plate 104 has a function of reflecting S-polarized light and transmitting P-polarized light in the incident light wave. FIG. 3 shows the principle of this reflective polarizing plate. FIG.
FIG. 3A shows a reflection type polarizing plate having a multilayer film structure.
(B) shows a configuration of a reflection type polarizing plate using cholesteric liquid crystal.

As shown in FIG. 3A, a triangular interface is formed, and a multilayer film having a different refractive index is formed on this interface. Since this interface has a function similar to that of the polarizing beam splitter, as shown in the figure, at this interface, P waves are transmitted and S waves are reflected. Reflected S
The waves are reflected again and returned to the entrance side.

In the reflection type polarizing plate having the film structure including the cholesteric liquid crystal shown in FIG. 3B, the right-handed circularly polarized light of the incident light is transmitted and the left-handed polarized light is reflected in accordance with the helical pitch of the cholesteric liquid crystal. . In this case, since the light that has passed through the reflective polarizer is not converted into linearly polarized light, it is used as a reflective polarizer similar to that shown in FIG. Is also possible. Here, description will be made based on the configuration of FIG.

The reflected S-polarized light is reflected by the scattering dots of the light guide plate or a reflecting sheet (not shown) placed thereunder, and is returned to the reflective polarizing plate 104 again. Also,
In the process of being reflected by these scattering dots and reflecting sheet, the polarization direction is also modulated. Therefore, a part of the returned light can pass through the reflective polarizing plate 104. By repeating this process, the light emitted from the light source 101 has its polarization direction adjusted to P-polarized light by the reflective polarizing plate 104.

The P-polarized light enters the diffusion sheet 105,
The light is scattered uniformly and emitted. Since the diffusion sheet 105 is generally produced by adding a light diffusing agent to a transparent resin such as polycarbonate or PET, a refractive index anisotropy is imparted by a stretching process or the like during sheet production. Therefore, when the light whose polarization direction is adjusted by the reflective polarizing plate 104 passes through the diffusion sheet, the polarization direction is modulated. FIG. 2 shows the relationship between the rotation angle and the transmittance when a polarizing plate whose polarizing axes are orthogonal to each other is arranged before and after the diffusion sheet and the diffusion sheet is rotated. The transmittance changes depending on the rotation angle, and it can be seen that the diffusion sheet has a refractive index anisotropy. When the axis of the diffusion sheet is set to 45 ° or 135 ° as a polarizing plate, it is effective for improving the luminance. However, since the phase component by the diffusion sheet is only arbitrarily set, the modulated polarization component does not become linearly polarized light as emitted from the reflective polarizer 104 only by setting the rotation angle of the diffusion sheet. .

The transmittance 2 in FIG. 2 shows the relationship between the angle (rotation angle in the drawing) between a certain side of the diffusion sheet 105 and a certain side of the phase plate 106 and the transmittance. It can be seen that the phase plate 106 corrects the modulation of the polarization component due to the refractive index anisotropy of the diffusion sheet, and the transmittance at the peak is improved by about 10%. Here, the phase difference of the phase plate is 100 nm.
Something was used. As can be seen from the characteristics of FIG. 2, the modulation amount based on the refractive index anisotropy of the diffusion sheet is not so large as to rotate the polarization direction by 90 ° like a half-wave plate,
It is considered to convert linearly polarized light into elliptically polarized light. Therefore, it is considered that the phase amount is about 1/4 or less with respect to the incident wavelength. Therefore, for a wavelength of 550 nm of visible light, approximately 1
It is estimated to be about 00 nm or less.

Actually, as shown in FIG.
By disposing the phase plate 106 having a phase of about 100 nm, the peak transmittance after passing through the scattering sheet is improved by about 10%. From this, it was found that the polarization from the reflective polarizing plate 104 was modulated by the diffusion sheet 105, whereas the introduction of the phase plate 106 compensated for the modulation of the polarization component and improved the transmittance. .

(Embodiment 2) In the same configuration as in Embodiment 1, isotropic glass is used as the diffusion sheet 104, and irregularities are formed on the surface of the diffusion sheet 104, so that a scattering effect on light incident thereon is obtained. It was configured to have. In order to form irregularities on the surface, sand blasting or the like can be used. It can also be formed by polishing the surface with a file or the like. The thickness of the glass used here is 0.
Those having a size of about 5 mm to 3 mm were used. The size of the illumination device shown in FIG. 1 was about 7 inches. Since the diffusion sheet is made of an isotropic body, the reflection type polarizing plate 1
Modulation due to the refractive index anisotropy as shown in FIG. Phase plate 1 of the first embodiment
06 was compared with the luminance on the emission surface of the lighting device. As a result, an improvement in luminance of about 10% was confirmed.
This has no transmittance anisotropy because it has no refractive index anisotropy.
It is considered that 0% corresponds to the improvement to approximately 100%.

By using glass as the isotropic body, there is no influence of displacement at the time of installation or shrinkage due to heat. As for the use of another isotropic body, a TAC film or the like which is used as an indicator film such as a polarizing plate and has a phase shift of about 10 nm or less due to refractive index anisotropy can be used. It is also possible to provide irregularities on the surface by molding, polishing or the like and use it as a diffusion sheet.

(Embodiment 3) FIG. 4 shows an illuminating device constituted by using several types of light sources. FIG.
(A) shows a point light source 401 such as an LED arranged at the periphery of the light guide plate 103. FIG. 4B shows a direct lighting device in which a linear light source 402 such as a cold cathode tube is disposed between the light guide plate 103 and the reflection sheet 102. FIG. 4C shows an illumination device configured using the planar light source 403.

In a direct-type configuration as shown in FIG. 4B, a lighting device having a diagonal size of the light guide plate 103 of about 10 inches was formed by using one cold cathode tube having an output of about 100 W. . When the luminance after emission from the prism sheet was measured, a high luminance output of about 10000 (cd / mm ² ) was obtained. Further, at this time, even if the light was continuously illuminated for 100 hours or more, non-uniformity of the luminance distribution due to thermal deformation of the prism sheet 106 did not occur. From this, it has been found that stable performance can be obtained even with high luminance in the lighting device based on the present invention.

Further, it is possible to construct a new lighting device by combining the lighting devices of the respective configurations in FIG. For example, for a direct-type cold-cathode tube disposed behind the light guide plate 103, LEDs having several luminescent colors are arranged above and below the light guide plate to further increase the luminance output, or to increase the emission spectrum of the cold-cathode tube. It is also possible to provide a configuration in which a portion with a small number of colors is supplemented by an LED or the like to improve the color balance.

It is to be noted that the lighting device using various light sources as described above can be used instead of the lighting device (light source, reflector, light guide plate) in the first to third embodiments.

(Embodiment 4) A liquid crystal display device shown in FIG. 1 is constructed by combining a liquid crystal panel with the lighting device constructed in Embodiment 1. An input polarizer 108 and an output polarizer 110 were arranged before and after the liquid crystal panel 109. Reflective polarizing plate 1
The configuration of the polarization axis of the input polarizing plate 04 and that of the incident polarizing plate 108 were the same as those of the diffusion sheet and the front and rear polarizing plates in FIG. With such a configuration, light incident on the incident polarizer is substantially linearly polarized, and the polarization axis of the incident polarizer coincides with the polarization axis of the incident polarizer. Therefore, there is almost no light amount that is absorbed by the incident polarizer and causes loss of heat or the like.
9 can be used more efficiently.

With the above configuration, the light use efficiency can be improved, so that a high-brightness liquid crystal display device which does not cause thermal deterioration due to light absorption even with a light source having a higher output can be realized. It becomes possible.

It is also conceivable that the phase plate 106 has a scattering anisotropic function of scattering only in a specific direction. This is because the optical characteristics such as the viewing angle luminance characteristics change depending on the modulation mode of the liquid crystal used for the liquid crystal panel. In particular, the viewing angle luminance characteristic is highest at the center and decreases toward the both ends. At this time, depending on the liquid crystal mode, there is a case where the luminance increases on the way from the center to both ends. This means that when viewing the image while changing the angle, the brightness suddenly increases in the middle and the user feels uncomfortable. With respect to such viewing angle luminance characteristics, the phase plate 10
When the scattering anisotropy of 6 is set, the light is scattered in that direction, so that the brightness is reduced and the brightness characteristics with respect to the angle are improved. It is preferable to add a scattering anisotropy function to the phase plate 106 in addition to compensating for the polarization component, because it is possible to achieve both an improvement in luminance and an improvement in visibility with respect to a viewing angle.

(Fifth Embodiment) A liquid crystal display device having the same structure as that of the fourth embodiment except for the prism sheet 107 is formed. At this time, the diffusion sheet 105 and the phase plate 10
An optical matching liquid used when assembling a lens or the like as a transparent substance was dropped into the gap between the sixth polarizer and the incident polarizer 108, and the liquid was brought into close contact. The refractive index of this liquid is about 1.5. In this state, observation was performed from a position as shown in FIG. At this time, the entire portion corresponding to the display screen was uniform, and no Newton-ring-like unevenness as shown in FIG. 5B was observed. By filling the gaps between the sheets with a liquid having a refractive index substantially equal to that of the sheet members, it was found that contoured uneven patterns caused by uneven adhesion of the sheets can be eliminated. did.

(Embodiment 6) In a configuration similar to that of Embodiment 5, instead of using an optical matching liquid, a liquid crystal display device is used in which the light incident side surface of the incident polarizing plate 108 is formed with irregularities. Configured. As the incident polarizer, a polarizer having a function of scattering light by providing irregularities on the surface for preventing glare or the like can be used. Also,
It is also possible to produce the surface of a normal polarizing plate by sandblasting, sandpaper polishing, or the like.

If the surface irregularities at this time are larger than about １ ／ wavelength, the phase difference due to the phase plate 106 will be larger than that, and the polarization component will be disturbed at the surface, and the compensation by the phase plate will be reduced. there is a possibility. Therefore, about 1/4 or less of the center wavelength of visible light of 550 nm
Surface unevenness of not more than 00 nm is preferred. Further, if the surface of the polarizing plate has too large irregularities, the roughness due to the irregularities may occur when the panel is observed.

A liquid crystal display device was constructed using a polarizing plate having a roughness of about 50 nm. When the display surface was observed in the same manner as in Embodiment 5, unevenness and roughness such as Newton's rings were not observed, and uniform display quality could be obtained. From this, it has been found that by providing unevenness on the light incident side of the incident polarizing plate in the present invention, it is possible to prevent variations in luminance due to uneven adhesion of each sheet member.

The embodiments of the present invention are not limited to those described here, and it is needless to say that these improved and modified configurations can be used.

[0047]

As described above, according to the present invention, the modulation of the polarization component by the diffusion sheet is corrected, the light use efficiency in the liquid crystal panel is improved, and the display due to the non-uniform adhesion between the sheets is achieved. Unevenness and the like on the screen can be eliminated. Therefore, the liquid crystal image display device has a great value because it can contribute to high brightness, power saving and high image quality.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a liquid crystal display device configured according to the present invention.

FIG. 2 is a diagram showing an example of characteristics of a diffusion sheet used in the present invention.

FIG. 3 is a diagram showing an example of a reflective polarizing plate used in the present invention.

FIG. 4 is a diagram showing an example of a lighting device configured according to the present invention.

FIG. 5 is a diagram showing an example of a conventional liquid crystal display element.

[Explanation of symbols]

 Reference Signs List 101 light source 102 reflector 103 light guide plate 104 reflective polarizer 105 diffusion sheet 106 phase plate 107 prism sheet 108 incident polarizer 109 liquid crystal panel 110 emission polarizer 301, 302 reflective polarizer 401 point light source 402 linear light source 403 planar light source 404 Reflection sheet 405 Light guide plate 406 Diffusion sheet 407 Reflection type polarization plate 408 Prism sheet 501 Light source 502 Reflector 503 Light guide plate 504 Diffusion sheet 505 Incident polarizer 506 Liquid crystal panel 507 Emission polarizer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/00 336 G09F 9/00 336J // F21Y 101: 02 F21Y 101: 02 103: 00 103: 00 105 : 00 105: 00 (72) Inventor Kazunori Komori 1006 Kadoma, Kazuma, Osaka Pref.F-term (reference) in Matsushita Electric Industrial Co., Ltd. GG23 GG24 GG25 GG26 HH04 KK07

Claims (17)

[Claims] An illumination device comprising a light source, a polarization direction control means for light emitted from the light source, a light diffusion means, and a phase modulation means, wherein the phase modulation means substantially converts the light emitted from the light diffusion means. An illumination device having a function of modulating linearly polarized light. 2. An illuminating device comprising a light source, a polarization direction controlling means for light emitted from the light source, and a light diffusing means, wherein the light diffusing means comprises an isotropic body having irregularities formed on its surface. A lighting device characterized by being performed. 3. The lighting device according to claim 1, wherein the light diffusing means has an uneven surface formed on an isotropic body. 4. The lighting device according to claim 1, wherein the light source includes a point light source. 5. The lighting device according to claim 1, wherein the light source includes a linear light source. 6. The lighting device according to claim 1, wherein the light source includes a planar light source. 7. The lighting device according to claim 1, wherein the light source comprises a combination of the light sources according to any one of claims 4 to 6. . 8. The apparatus according to claim 1, wherein said polarization direction control means comprises a reflection type polarizing plate.
The lighting device according to any one of the preceding claims. 9. The illumination device according to claim 8, wherein said reflective polarizing plate has a multilayer structure having different refractive indexes. 10. The lighting device according to claim 8, wherein said reflective polarizing plate includes a cholesteric liquid crystal. 11. The apparatus according to claim 1, wherein said phase modulation means has scattering anisotropy.
The lighting device according to any one of the preceding claims. 12. The lighting device according to claim 11, wherein said phase modulation means has a phase difference of 100 nm or less. 13. A liquid crystal display device comprising the illumination device according to claim 1 and a liquid crystal panel provided with an incident polarizer and an output polarizer, wherein said phase modulating means is provided. A polarization direction of light emitted from the liquid crystal display is substantially equal to a polarization axis of the incident polarizer. 14. A liquid crystal display device comprising the lighting device according to claim 1 and a liquid crystal panel provided with an incident polarizer and an output polarizer. For the control means, a light diffusing means, a phase modulation means, and the incident polarizer are sequentially provided in a light emitting direction, and a transparent substance is inserted into at least one of the gaps from the light diffusing means to the incident polarizer. A liquid crystal display device characterized by the above-mentioned. 15. The liquid crystal display device according to claim 14, wherein the refractive index of the transparent substance is substantially equal to the refractive index of the member forming the gap. 16. A liquid crystal display device comprising a combination of the illumination device according to claim 1 and a liquid crystal panel provided with an incident polarizer and an output polarizer, wherein irregularities are formed on the light incident side surface of the incident polarizer. A liquid crystal display device characterized by being formed. 17. The unevenness on the surface of the incident polarizer is 100n.
17. The liquid crystal display device according to claim 16, wherein m is equal to or less than m.