JPH10170916A - Illuminator and liquid crystal display device using the illuminator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To practically improve the numerical aperture and the brightness of the liquid crystal display elements having a low numerical aperture by providing a reflection surface having minute unevenness on the light transmission body back surface, maintaining the polarization of the reflected light beams from the non-aperture section of the elements and re- emitting the beams. SOLUTION: A cold cathode fluorescent lamp 52, which has the light emitting section corresponding to the length of two side surfaces of a light transmission body 56 made of transparent acrylic resin, and a lamp cover 51, which covers the lamp 52 and reflects the light beams to the body 56 side, are arranged in the tip section of the device and a reflection plate 54 is arranged on the back surface of the body 56. The cover 51 has a hemi-cylindrical shape and its inner surface is made as a reflection plate. A minute structure 57 of the back surface of the body 56 has a 1.2mm pitch, a height 84 is 50μm, a center tilt angle 83 is 35 degrees and aluminum vapor deposition is made only on a tilt surface 57A. The maximum tilt angle of the surface 57A is approximately 45 degrees and the minimum tilt angle is approximately 25 degrees and the angles are gradually changed. The light beams irradiating the non-aperture section are reflected again to the liquid crystal display elements by the plate 54 located in the back surface of the illuminator while maintaining the polarization and reused.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar illumination device provided on the back of a liquid crystal display device, and more particularly to a planar illumination device with controlled polarization and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art In recent years, the technical progress of liquid crystal display devices, especially color liquid crystal display devices, has been remarkable, and many displays having display quality not inferior to that of CRTs have come to be seen. Further, with the spread of notebook personal computers, a backlight as an illumination device is an essential device in a direct-view color liquid crystal display device.

Color liquid crystal display devices are roughly classified into two types: a twisted nematic (TN) liquid crystal display device driven by active matrix using thin film transistors (TFTs) and a super twisted nematic (STN) liquid crystal display device driven by multiplex. is there. In both cases, polarizing plates are arranged on both sides of an element in which a liquid crystal layer is held by a glass substrate, and display is performed by modulating the polarization state of linearly polarized light.

[0004] The luminance level required for these backlights varies depending on the application. Particularly, in a color notebook type personal computer, not only the required luminance but also a thin, lightweight and low power consumption is the most important proposition. .
In addition, there is a high expectation for a liquid crystal display device as a large-screen display of a computer, and it is required not only to improve brightness but also to have a wide emission characteristic so as to enable a wide viewing angle display.

However, conventionally, since the light emitted from the backlight disposed on the back surface of the liquid crystal display element is unpolarized light, the light is disposed on the incident side of the display element regardless of whether the liquid crystal element is of the TN type or the STN type. According to the polarizing plate, more than half of the incident light is absorbed, so that the light use efficiency is low, and the display becomes dark or the power consumption increases to make the display bright. There was a problem.

Further, there is a problem that the light emitted from the backlight cannot be used sufficiently because the aperture ratio of the liquid crystal display element is low.

[0007]

In order to solve the above problems, for example, as disclosed in Japanese Patent Application Laid-Open No. 6-265892, the outgoing light is applied to the light exit surface side of the surface light guide. The light deflecting means is provided so as to be substantially at right angles to the light, and a polarization separator in which a polarization separation layer is laminated on an array portion of a columnar prism array having a triangular cross section is further disposed thereon, and illumination for emitting polarized light. A device has been proposed.

However, in order to achieve a high-performance polarized light illuminator having a high degree of polarization, high parallelism is required for light incident on the polarization separation layer.

In order to solve this problem, there is proposed an illuminating device in which a thin light guide pipe is arranged adjacently and a light having high parallelism is efficiently emitted by a micro-prism structure (Japanese Patent Laid-Open No. 6-202107). Gazette).

An object of the present invention is to use a liquid crystal display element having a low aperture ratio to reflect reflected light from a non-opening portion again from a backlight to the liquid crystal display element side while maintaining polarization, thereby reducing the amount of light. An object of the present invention is to provide a lighting device that achieves effective use and a substantial improvement in aperture ratio.

Another object of the present invention is to provide a low power consumption liquid crystal display device using the above-mentioned lighting device.

[0012]

The gist of the present invention to achieve the above object is as follows.

[1] A plate-shaped light guide, and a light source disposed close to the periphery of the light guide, and light emitted from the light source propagates through the light guide and from the light exit surface of the light guide. In a lighting device configured to emit light, the light guide includes a plurality of convex, concave, or stepped reflecting surfaces having fine inclined surfaces on the back surface of the light emitting surface of the light guide, and the reflecting surface is at least the reflecting surface. There is a lighting device in which an inclined surface portion is mirror-finished, and a reflection plate is provided on the back surface of the light guide directly or via an air layer.

[2] A pair of transparent substrates, a liquid crystal layer sandwiched between the substrates, and an electrode formed on at least one of the substrates and applying an electric field for driving liquid crystal molecules of the liquid crystal layer. A liquid crystal display comprising: a group; an active element connected to these electrode groups; an alignment film for controlling the alignment of liquid crystal molecules of the liquid crystal layer; and an optical unit for changing optical characteristics according to a molecular alignment state of the liquid crystal layer. A liquid crystal display device comprising a device, a lighting device disposed immediately below the liquid crystal display device, and a means for applying an electric field to an electrode group of the liquid crystal display device, wherein the non-opening portion of the liquid crystal display device has a reflectance. The lighting device is composed of a high material.
3. The liquid crystal display device which is the lighting device described in 1. above.

In the above, a means for parallelizing emitted light is provided between the light source and the light guide. Further, a reflection type polarizing plate is provided on the light emitting surface of the light guide.

Further, a reflection type polarizing plate is provided on the light emitting surface of the light guide, and a retardation plate is provided on one of the front and back surfaces of the light guide. Further, a means for parallelizing emitted light is provided between the light source and the light guide, and a reflective polarizing plate is provided between the parallel light means and the light guide. Further, a reflective polarizing plate is provided on the light guide. A retardation plate may be provided on one of the front and back surfaces of the light guide.

A pair of polarizing plates are used as optical means for changing optical characteristics according to the molecular alignment state of the liquid crystal layer of the liquid crystal display element, and the polarization axis of the incident side polarizing plate is such that the polarization of incident light from the illumination device is changed. Desirably, it is substantially parallel or substantially perpendicular to the axis.

As described above, the light emitted from the light guide is
Most of the light reflected from the non-opening portion of the liquid crystal display element passes through the flat surface on the back surface of the light guide, and is emitted again to the liquid crystal display device while maintaining the polarization state substantially by the reflection plate disposed on the back surface. Is done. Thereby, absorption by the incident-side polarizing plate of the liquid crystal display element is almost eliminated, and light can be used efficiently, so that the brightness of the display can be improved.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Flat lighting devices are roughly classified into two types, a direct type and an edge light type. The direct type is a type in which the light source is inside the illuminated surface, and the edge light type is a type in which the light source is arranged on the outer edge side of the illuminated surface. Then, a columnar light-emitting body such as a fluorescent lamp (a cold cathode discharge tube or a hot cathode discharge tube) is arranged on one or two sides of an illuminating surface made of a light guide made of a transparent acrylic resin or the like, and a lamp made of a reflector is provided. In this method, light is introduced into the light guide by providing a cover outside the cover. An edge light type is effective for a liquid crystal display device which is required to be thin and light.

In a conventional liquid crystal display device, an edge light type backlight is mainly used. In order to obtain in-plane uniformity, the area ratio of the white ink provided on the back surface of the light guide is determined according to the distance from the light source. And changed it. When evaluating the light use efficiency of the backlight of this conventional liquid crystal display device, the value obtained by multiplying the backlight brightness by the transmittance of the liquid crystal display element alone is lower than the actual brightness of the liquid crystal display device. It was confirmed.

As a result of detailed studies, most of the non-opening portions of the liquid crystal display element are made of metal electrodes, and when the aperture ratio is 50%, about half or more of the backlight light is absorbed by the polarizing plate. It was found that 50% was transmitted and the remaining 50% was reflected and returned to the backlight.

The light returned to the backlight is depolarized by the diffusion plate on the light guide or the white ink on the back of the light guide, becomes almost non-polarized light, and enters the liquid crystal display element again. More than half of the light is absorbed by the incident-side polarizing plate, and 50% of the light is transmitted. Since this is repeated, the display efficiency is low and the display is dark.

Therefore, if the polarization state is maintained in the backlight which is an illumination device, the light absorbed by the incident-side polarizing plate of the liquid crystal display element can be greatly reduced, so that the liquid crystal display element having a low aperture ratio can be used. , The effective aperture ratio is improved,
Bright display can be realized.

In order to reflect the reflected light from the non-opening portion of the liquid crystal display element back to the liquid crystal display element side while maintaining the polarization, a diffuser plate which is usually arranged on the upper surface of the light guide, except for the diffusion plate, is provided on the rear surface of the light guide. A fine mirror reflection inclined surface (preferably a metal reflection surface) and a flat mirror surface are provided side by side, and a mirror reflection plate is provided on the back surface of the light guide via an air layer. At this time, the area ratio of the inclined surface is smaller than that of the flat surface.

The inclined surface is a surface for emitting light from the light guide, and the flat surface is for totally reflecting and propagating the light in the light guide. Since the flat surface has a large number of reflections when propagating in the light guide, it is preferable to use total reflection having the highest reflectance.

With this configuration, most of the light reflected from the non-opening portion of the liquid crystal display element passes through the flat surface on the back surface of the light guide, and is again maintained while the polarization state is substantially maintained by the reflector disposed on the back surface. The light is emitted to the liquid crystal display device. Thereby, absorption by the incident-side polarizing plate of the liquid crystal display element is almost eliminated, and light can be efficiently used, so that the brightness can be improved.

Here, the inclined surface of the specular reflection is a convex or concave curved surface. The inclined reflecting surface is a reflecting surface for reflecting the light from the light source toward the liquid crystal display element, and has a curved surface for obtaining the required spread of the outgoing light for the liquid crystal display device. Also at this time, it is preferable to change the ratio of the fine mirror reflection inclined surface in accordance with the distance from the light source similarly to the conventional arrangement of the white ink.

When the light from the light source enters the flat mirror surface on the back surface of the light guide, it is totally reflected and propagates through the light guide. Is emitted.

Here, the incident light from the light source to the light guide is totally reflected when entering the flat mirror surface portion, and is also totally reflected on the upper surface of the light guide. In order to reduce the spread of the light incident on the light guide and improve the in-plane uniformity of the light emitted from the light guide, the light source serves as a parallel light converting means between the light guide and the light source. A parallel light-generating portion was provided that expanded as approaching.

On the surface of the light guide, light having an incident angle equal to or greater than the total reflection angle θc determined by the refractive index of the light guide is totally reflected and propagates through the light guide. Light having an incident angle smaller than the total reflection angle θc is refracted by the upper surface of the light guide and emitted.

For example, air (refractive index n = 1) and a transparent resin such as acrylic, polycarbonate, polyurethane, or polystyrene (refractive index n = 1.5)
The total reflection angle θc at the interface of (degree) is θc = sin−1
(1 / n) = 42 °.

Here, the light θ incident on the light guide without the collimating portion is-(90 ° -θc) ≦ θ ≦ + (90 ° -θc).
The light is internally reflected and totally reflected at the flat portions on the upper and lower surfaces of the light guide. In order to improve the in-plane uniformity of the light emitted from the light guide by minimizing the spread of the light incident on the light guide from the collimating portion as described above, the light guide and the light source A collimating unit is provided as a collimating means between the light source and the light source.

Further, in order to emit polarized light from the backlight, an SID 92 Di is provided between the parallel light converting portion and the light guide.
gest pp427 and Asia Display 95 Digest pp7
A reflective polarizer shown at 35 is disposed, the incident light to the light guide is polarized light, and the light is emitted while maintaining the polarization by the light guide to obtain polarized light.

Here, the reflective polarizer made of the dielectric multilayer film described in the above SID92 is a reflective polarizer type 1, A
The reflective polarizer using cholesteric characteristic reflection described in sia Display 95 is referred to as reflective polarizer type 2.

When the reflective polarizing plate type 1 is used, a retardation plate for changing the polarization direction by 90 degrees, preferably 1/4
It is preferable that the wavelength plate (1/2 wavelength in the reciprocating direction) is inclined at 45 degrees to the main polarization direction from the reflective polarizing plate and is disposed on the reflective cover of the light source.

Furthermore, even if a reflective polarizer is disposed on the light guide incident side, reflection is repeated many times during propagation through the light guide, and the polarization state is broken because the reflection surface is not a perfect mirror surface. Therefore, it is preferable to dispose the reflective polarizer on the upper surface of the light guide. When the reflective polarizer type 1 is disposed on the upper surface of the light guide, a phase difference plate for changing the polarization direction by 90 degrees on either the upper surface or the lower surface of the light guide, preferably a 波長 wavelength plate (reciprocating). (２ wavelength) is inclined at 45 degrees to the main polarization direction from the reflective polarizer.

The reflective polarizing plate type 1 is a dielectric multilayer film in which dielectric films having different refractive indices are laminated on a prism array having an apex angle of approximately 90 degrees described in the SID 92 described above. The film thickness can be manufactured with high accuracy by dipping or the like. Further, a material obtained by alternately laminating two types of uniaxial refraction media may be used.

Further, the reflective polarizing plate type 2 comprises the above-described Asia.
The cholesteric liquid layer polymer described in Display 95 is laminated with a cholesteric liquid crystal polymer having a different pitch so as to exhibit characteristic reflection in the visible wavelength range, and transmits circularly polarized light around a certain direction and reflects circularly polarized light around the opposite direction. , A quarter-wave plate is laminated thereon, and transmits one-way linearly polarized light.

By arranging the polarization axis of the incident-side polarizing plate of the liquid crystal display element on the illumination device having the above configuration in accordance with the main polarization axis of the light emitted from the illumination device, a bright liquid crystal display with low power consumption is provided. A device can be obtained.

Here, words used in the embodiments are defined. The S-polarized light indicating the polarization state is polarized light perpendicular to the incident surface (the incident surface is a plane formed by the incident light and the incident normal to the boundary surface), and the P-polarized light is polarized light parallel to the incident surface.

In general, when light is incident from the N ₀ medium to the N ₁ medium at the interface between the transparent medium having the refractive index N _{0 and} the transparent medium having the refractive index N ₁ , if the incident angle of the incident light is θ, The tangent of the angle θ is equal to N ₁ / N ₀ (tan θ = N ₁ / N ₀ )
At this time, it is known that there is no P-polarized light reflection component, all reflected light is S-polarized light, and transmitted light is the remaining S-polarized light and P-polarized light. The incident angle θ at this time is called a Brewster angle.

Using this Brewster angle, media having different refractive indices are stacked, and the thickness of the stacked layers is controlled on the wavelength order to control the phase of each polarized light, transmit only P-polarized light, and transmit S-polarized light. Can be produced.

The function of the reflective polarizing plate type 1 is to transmit only the P-polarized light component and reflect the S-polarized light component orthogonal thereto.
When a retardation plate is used as a scattered reflection or depolarizer, the reflected S-polarized light is converted into elliptically polarized light (including linearly polarized light and circularly polarized light) by the retardation plate. Only the S-polarized light component is transmitted, and the S-polarized light component is reflected and returns to the light guide. By repeating this, almost all light is P
The light is converted into polarized light and emitted.

Thus, preferably the reflected S-polarized light is
It is preferable to set a retardation plate that functions as a quarter-wave plate so that all light is converted to P-polarized light so that the wavelength becomes half the wavelength after reciprocal transmission. Thereby, a polarized light illuminating device having high light use efficiency can be achieved.

The function of the reflective polarizing plate type 2 is to transmit only clockwise (or counterclockwise) circularly polarized light, reflect counterclockwise (or clockwise) circularly polarized light, and transmit the circularly polarized light to a quarter wavelength. The plate becomes linearly polarized light in one direction.

On the other hand, the reflected counterclockwise (or clockwise)
Is reflected by the specular reflector, becomes clockwise (or counterclockwise) circularly polarized light, passes through the reflective polarizer type 2 and 1
The light is converted into linearly polarized light in one direction by the 波長 wavelength plate, and all light is converted into linearly polarized light. Even if the reflection plate is not a specular reflection plate, the reflected light becomes elliptically polarized light (including linearly polarized light and circularly polarized light), enters the reflection polarizing plate again, and transmits only clockwise (or counterclockwise) circularly polarized light. The surrounding (or clockwise) circularly polarized light is reflected back to the light guide.

By repeating this, almost all the light is converted into only clockwise (or counterclockwise) circularly polarized light, and thereafter, is output as linear polarized light in one direction by a quarter-wave plate.

Since there is considerable light absorption in the reflector, the reflected counterclockwise (or clockwise) circularly polarized light is completely converted into clockwise (or counterclockwise) circularly polarized light. It is preferable that the mirror reflection plate is a simple mirror reflection plate.

A liquid crystal display device using the above illuminating device has a polarization axis of an incident side polarizing plate of a liquid crystal element for displaying by controlling a polarization state of a TN type or an STN type, and a polarization axis of the illuminating device. It is the structure which combined. Thus, light from the lighting device can be efficiently used, and a bright and low power consumption liquid crystal display device can be obtained.

FIG. 1 shows an example of a liquid crystal display device suitable for the present invention.
It is shown in FIG. FIGS. 12A and 12B are schematic cross-sectional views (a) and (b) of a lateral electric field type active matrix type liquid crystal display device, and schematic plan views (c) and (d), in which (a) and (c) are omitted. (B) and (d) show the orientation states of the liquid crystal molecules in the electric field applied state, respectively.

Further, the illumination device of the present invention has a light guide back surface structure without using a scattering member, and can broaden or narrow the distribution of the emission characteristics, and is applicable to a liquid crystal display device having a wide viewing angle. it can.

[0052]

【Example】

[Embodiment 1] Figs. 1 and 2 are schematic side sectional views of a lighting device according to the present invention. This embodiment is an edge-light type flat illuminating device, in which a cold cathode fluorescent lamp 52 having a light emitting portion corresponding to the length of two sides of a light guide 56 made of a transparent acrylic resin.
And a lamp cover 51 that covers it and reflects light toward the light guide 56 at the end, and a reflector 5 on the back surface of the light guide 56.
4 was arranged. As the light source 52, a cold cathode fluorescent lamp having a diameter of 3 mm and a length of about 290 mm was used.

The lamp cover 51 has a semi-cylindrical shape (or an elliptical cylindrical shape), and has an inner surface serving as a reflection plate. The light guide 56 made of acrylic resin has a refractive index of 1.49 and 290 mm × 22.
Those having a size of 4 mm × 4.5 mm were used. The fine structure 57 on the back surface of the light guide 56 has a pitch of 1.2 mm and a height (84) of 5
Aluminum was vapor-deposited only on the inclined surface 57A with a central inclination angle (83) of 35 degrees. This inclined surface 57A is
The gradient was gradually changed at a maximum inclination of about 45 degrees and a minimum inclination of about 25 degrees.

Further, the parallel light converting portion 53 at the incident portion to the light guide is provided.
Has a thickness of 4 mm on the light source 52 side and a thickness of 4 mm on the light guide 56 side.
5 mm, the length 81 was about 10 mm, and the inclination angle 80 was about 1.4 degrees. Each surface of the light guide 56 and the parallel light conversion unit 60 was subjected to an optical mirror surface treatment.

A 64 nm-thick ZrO ₂ film is placed between the light guide 56 and the parallel light converting portion 53 on a prism-shaped array made of polycarbonate (refractive index: 1.586) having a vertex angle of 90 ° and a pitch of about 30 μm. (Refractive index 2.05), film thickness 64n
A reflective polarizing plate 60 of type 1 in which five MgF ₂ layers (refractive index: 1.38) were alternately laminated was arranged such that the stripes formed by the prism-shaped grooves were in the vertical direction in the drawing. As the reflective polarizing plate 60, a type 2 reflective polarizing plate can also be used.

As the liquid crystal display element 10, a 13.3 inch diagonal super TFT-LC announced by SID96 was used.
D (opening ratio: about 40%) was used.

As a result of the above configuration, the outgoing light 70 from the light source 52 enters the parallel light converting section 53 within about ± 42 degrees,
The light is converted into light within approximately ± 36 degrees by the parallel light conversion unit, and is incident on the reflective polarizing plate 60.

Here, the unpolarized light 70 incident on the reflective polarizing plate 60 transmits the P-polarized light in the direction perpendicular to the plane of the paper, reflects the S-polarized light parallel to the plane of the paper, returns to the light source side, breaks the polarized light, and again. Repetition of incidence on the reflective polarizing plate 60 and transmission of only the P-polarized component is repeated, and most of the unpolarized light from the light source 52 is converted into P-polarized light and is incident on the light guide 56.

As for the polarized light 71 that has entered the light guide 56, only the light that has reached the inclined surface 57A is emitted from the upper surface of the light guide 56, and the flat light of the fine structure 57 and the upper surface of the light guide 56 are formed. The collected light is totally reflected at the interface due to a difference in refractive index, propagates in the light guide 56, reaches the inclined surface 57A, and is emitted from the upper surface of the light guide 56.

With this effect, it was possible to achieve substantially uniform outgoing light on the upper surface of the light guide 56. With the above configuration, in-plane uniformity of 80% or more (minimum luminance ratio to maximum luminance) was achieved.

The spread of the emitted light was measured in an angle range where the brightness was １ ／ of the front luminance. As a result, the direction parallel to the light source 52 was about ± 50 degrees, and the direction perpendicular to the light source 52 was about ± 50 degrees. It was 40 degrees, and sufficient emission characteristics could be obtained for application to a liquid crystal display device having a wide viewing angle.

In the configuration shown in FIG. 1, the brightness in which the polarization axis of the incident-side polarizing plate 12 of the liquid crystal display element 10 and the main polarization axis of the light emitted from the illumination device 50 are almost matched, and the brightness of the illumination device 50
As a result of comparing the brightness obtained by dividing only the polarizing plate on the liquid crystal display element 10 with the aperture ratio of 40%, the former was about 5%.
It turned out that it was about 0% bright.

This is because the light irradiated on the non-opening 13 is
This is a result of being reflected again by the liquid crystal display element 10 while maintaining the polarization by the reflector 54 on the back surface of the illumination device 50, and being able to be reused. Therefore, by using the illumination device of this embodiment, even if a liquid crystal display element having a low aperture ratio is used, if the non-opening portion is a metal electrode or the like having a high reflectance, it can be reused while maintaining polarization. Therefore, brightness equivalent to that of a liquid crystal display device having an aperture ratio of 1.5 can be achieved.

[Embodiment 2] FIGS. 3 and 4 are schematic side sectional views of a lighting device of this embodiment and a liquid crystal display device using the same. The configuration is the same as that of the first embodiment, except for the microstructure 58 on the back surface of the light guide 56 and the parallel light portion 53. here,
Only differences from the configuration of the first embodiment will be described.

The fine structure 58 on the back surface of the light guide 56 has a pitch of 0.1 mm on the light source 52 side, a height (84) of about 5 μm, a pitch of 0.05 mm at the center, and an average inclination angle (8
3) was set to 40 degrees, and aluminum was deposited only on the inclined surface 58A. The inclined surface 58A is configured to gradually change at a maximum inclination of about 45 degrees and a minimum inclination of about 35 degrees.

The inclined surface 58A has a constant depth direction in the drawing. In addition, the parallel light converting portion 53 which is an incident portion to the light guide 56 has a thickness of 3 mm on the light source 53 side, a thickness of 4.5 mm on the light guide 56 side, and a length (81) of about 10 mm, and is inclined. Angle 80 was about 4 degrees. In addition, the respective surfaces of the light guide 56 and the parallel light forming portion 53 were subjected to an optical polishing process.

The type 2 reflective polarizing plate 60 in which a cholesteric polymer liquid crystal and a 波長 wavelength plate are laminated between the light guide 56 and the parallel light converting portion 53 is so arranged that the polarization direction is the depth direction of the drawing. Was placed. In addition, the reflective polarizing plate of the type 1 may be used.

The liquid crystal display element 10 includes a 13.3 inch diagonal super TFT-LCD announced by SID96.
(An aperture ratio of about 40%) was used.

As a result of the above configuration, the outgoing light 70 from the light source 52 enters the parallel light converting section 53 within about ± 42 degrees and is converted into light within about ± 22 degrees by the parallel light converting section. The light enters the reflective polarizing plate 60.

With the above configuration, the light emitted from the light guide 56 achieves an in-plane uniformity of 80% or more. The spread of the emitted light was measured in an angle range where the brightness was １ ／ of the front luminance. As a result, the direction parallel to the light source 52 was approximately ± 50.
The direction perpendicular to the light source 52 (the horizontal direction in the drawing) is approximately ± 35.
And the emission characteristics sufficient to be applied to a liquid crystal display device having a wide viewing angle could be obtained.

In the configuration shown in FIG. 3, the brightness in which the polarization axis of the incident-side polarizing plate 12 of the liquid crystal display element 10 and the main polarization axis of the light emitted from the illumination device 50 are substantially matched, and the brightness of the illumination device 50
As a result of comparing the brightness obtained by dividing only the polarizing plate on the liquid crystal display element 10 with the aperture ratio of 40%, the former was about 5%.
It turned out that it was about 0% bright.

This is because the light irradiated on the non-opening portion 13 is
This is a result of being reflected again by the liquid crystal display element 10 while maintaining the polarization by the reflector 54 on the back surface of the illumination device 50, and being able to be reused. Therefore, by using the illumination device of this embodiment, even if a liquid crystal display element having a low aperture ratio is used, if the non-opening portion is a metal electrode or the like having a high reflectance, it can be reused while maintaining polarization. Therefore, brightness equivalent to that of a liquid crystal display device having an aperture ratio of 1.5 can be achieved.

The brightness at this time was improved by about 15% as compared with the first embodiment. This is because light returning to the light source 52 is reduced by improving the structure of the light guide 56 so that the center portion is made thinner, and light use efficiency is improved.

[Embodiment 3] FIGS. 5 and 6 are schematic side sectional views of a lighting device of the present embodiment and a liquid crystal display device using the same. The configuration is the same as that of the first and second embodiments, except for the microstructure 58 on the back surface of the light guide 56 and the parallel light portion 53. Here, only differences from the configuration of the first embodiment will be described.

The fine structure 58 on the back surface of the light guide 56 has a pitch of 0.1 mm and a height (84) of about 10 μm on the light source 52 side.
The center portion was pitch 0.05 mm, the average inclination angle (83) was 35 degrees, and aluminum was vapor-deposited only on the fine structure 58. This fine structure 58 has a maximum inclination of about 40 degrees,
It gradually changed at the minimum inclination of about 30 degrees. This fine structure 58 has a constant depth direction in the drawing. Also,
The parallel light converting portion 53, which is an incident portion to the light guide, has a thickness of 4.5 mm on the light source 52 side, a thickness of 4.5 mm on the light guide 56 side, a length (81) of about 10 mm, and a tilt angle. (809 was set to about 0 degrees. Each surface of the light guide 56 and the parallel light forming part 53 was subjected to an optical polishing treatment.

The type 2 reflective polarizing plate 60 in which a cholesteric polymer liquid crystal and a 波長 wavelength plate are laminated between the light guide 56 and the parallel light converting portion 53 is used. It was arranged as follows. Note that a reflective polarizing plate of the type 1 may be used.

As the liquid crystal display element 10, the one having the same aperture ratio of about 40% as in the first embodiment was used.

As a result of the above configuration, the outgoing light 70 from the light source 52 enters the collimating section 53 within about ± 42 degrees,
The light is totally reflected by the parallel light conversion unit in a range of about ± 42 degrees, and enters the reflective polarizing plate 60.

With the above configuration, the light emitted from the light guide 56 achieves an in-plane uniformity of 80% or more. The spread of the emitted light was measured in an angle range where the brightness was １ ／ of the front luminance. As a result, the direction parallel to the light source 52 (the depth direction of the paper) was approximately ± 55 degrees, and The direction (horizontal direction of the paper) was about ± 45 degrees, and sufficient emission characteristics could be obtained for application to a wide viewing angle liquid crystal display device.

In the configuration shown in FIG. 5, the brightness in which the polarization axis of the incident-side polarizing plate 12 of the liquid crystal display element 10 and the main polarization axis of the light emitted from the illumination device 50 are almost matched, and the illumination device 50 of the invention described above. As a result of comparing the brightness obtained by dividing only the aperture ratio of the liquid crystal display element 10 by arranging only the polarizing plate on the upper side, it was found that the former was about 50% brighter.

This is because the light irradiated on the non-opening 13 is
This is a result of being reflected again by the liquid crystal display element 10 while maintaining the polarization by the back reflector 54 of the illuminating device 50 and being reused. Therefore, by using the lighting device of the present embodiment,
Even if a liquid crystal display element having a low aperture ratio is used, if the non-opening portion is a metal electrode or the like having a high reflectance, the non-opening portion can be reused while maintaining the polarization, so that the aperture ratio is 1.5 times. Brightness equivalent to that of a liquid crystal display element can be achieved.

At this time, the brightness was reduced by about 10% as compared with the first embodiment. This is due to the fact that the range of the emitted light is widened, and not that the light amount is reduced.

[Embodiment 4] Next, FIGS. 7 and 8 show an example of the reflective polarizing plate 60. FIG. FIG. 7 illustrates a dielectric multilayer film type 1 reflective polarizer. This is made of polycarbonate (refractive index 1.586), a vertex angle of 90 degrees and a pitch of about
ZrO ₂ (refractive index 2 on the array of prismatic shape 0 .mu.m.
05) and MgF ₂ (refractive index: 1.38).

Thus, the incident light 70, which is non-polarized light,
Is transmitted only P-polarized light to become emission light 71, and S-polarized light 75 is reflected. Therefore, if a polarizing plate having no absorption loss can be manufactured, and the reflected S-polarized light can be reused, improvement in light use efficiency can be realized.

As the dielectric multilayer material, TiO ₂ , Z
rO ₂ , ZnS, Y ₂ O ₃ , SiO ₂ , MgF ₂ , Na ₃ , A
lF _6, Ta ₂ O ₅ or the like can be used. The refractive index is usually 1.
The film is formed so as to satisfy the Brewster condition at about 4 to 2.5.

The film formation method includes vapor deposition, sputtering, dipping,
Known methods such as coating can be used.

The type 1 reflective polarizing plate of the dielectric multilayer type can be produced by laminating a uniaxial anisotropic medium, for example, by laminating polycarbonate, polyvinyl alcohol, polystyrene or the like.

FIG. 8 shows the use of characteristic reflection using a cholesteric liquid crystal polymer. In the cholesteric liquid crystal polymer 65, layers having different pitches are laminated so that characteristic reflection is exhibited in the visible region.

It has been experimentally confirmed that at least two layers are required. There is no problem as long as the pitch of the cholesteric liquid crystal polymer can be changed in one layer even in one layer and Δn (refractive index anisotropy) is sufficiently large.

Further, on the cholesteric liquid crystal polymer 65, a retardation plate 64 acting as a quarter-wave plate was arranged.
As a result, the incident light 70, which is non-polarized light, reflects circularly polarized light around the same direction as the cholesteric liquid crystal polymer 65, and is reflected by the cholesteric liquid crystal polymer 65.
Then, the circularly polarized light in the opposite direction is transmitted and becomes linearly polarized light by the phase difference plate 64 and is emitted. Therefore, a polarizing plate having no absorption loss can be manufactured, and the reflected circularly polarized light can be re-used as, for example, circularly polarized light in the opposite direction by metal reflection to improve the light use efficiency.

[Embodiment 5] With respect to the basic structure of the present invention, three embodiments and the embodiment of the reflective polarizing plate used therein have been described.

In the first to third embodiments, the lighting device 50
It was confirmed that the polarization characteristics of the light emitted from the light guide were lower than when the light guide was incident.

Therefore, a description will be given with reference to FIGS. 9 and 10 in order to enhance the polarization characteristics of the light emitted from the illumination device 50. FIG. By arranging the reflective polarizing plate 60 on the lighting device 50, the degree of polarization of light emitted from the lighting device 50 can be improved. Here, a dielectric multilayer film-type reflective polarizing plate shown in FIG. 7 was used. Further, a phase difference plate 69 (a 波長 wavelength plate is arranged at an angle of 45 ° in the polarization direction) is arranged on the lower surface of the light guide 56.

As a result, although the reflected light 78 from the reflective polarizing plate 60 is S-polarized light, it acts as a half-wave plate by reciprocatingly passing through the retardation plate 69, and becomes P-polarized light. The light passes through and irradiates the liquid crystal display element 10.

With the configuration shown in FIG. 9, the polarization characteristics of the light emitted from the illumination device 50 can be improved, and the brightness can be improved. Here, the retardation plate 69 is arranged on the back surface of the light guide 56, but the same effect can be obtained even if it is arranged on the top surface.

The structure shown in FIG. 9 can be applied to the first to third embodiments.
However, in this case, the phase difference plate 69 is not required.

FIG. 9 shows a configuration in which the light sources are arranged on both sides of the light guide 56, but the same effect can be realized in the case of only one side. In this case, the fine structure on the back surface is at a distance from the light source. It is necessary to change according to.

In the above embodiment, the TN liquid crystal display device of the horizontal electric field type has been described as an example. However, if the display mode is to control the polarization, a normal vertical electric field type liquid crystal display device is used.

[Embodiment 6] FIG. 11 is a schematic side sectional view of a lighting device of this embodiment and a liquid crystal display device using the same. This embodiment is an edge-light type planar illumination device, in which a light source 52 and a lamp cover 51 are provided on one side of a light guide 56 made of a transparent acrylic resin, and a light guide 5 is provided.
6 is characterized in that a reflecting plate 54 is arranged on the back surface via an air layer 100.

The light source 52 is 3 mm in diameter × 290 mm in length.
A cold cathode fluorescent lamp (in the depth direction of the paper) was used. The fine structure 57 on the back surface of the light guide 56 has a pitch of 50 μm and a height of 20 μm, and the end face of the light guide has a pitch of 30 μm and a height of 1 μm.
The distance was changed to 0 μm as the distance from the light source 52 increased.
The inclination angle of the microstructure 57 was about 36 degrees at the center, and was curved so that the maximum inclination was 41 degrees and the minimum inclination was 31 degrees.

Further, as the liquid crystal display element 10, the one having the same aperture ratio of about 40% as in Example 1 was used.

As a result of the above configuration, of the incident light from the light source 52 to the light guide 56, the fine structure 57 on the back surface of the light guide 56
The light that has entered the inclined portion becomes outgoing light 72 and enters the liquid crystal display element 10. Here, the non-opening portion 1 made of a metal film
The light incident on 3 is reflected, and while maintaining the polarization state,
Again, the light is reflected by the reflection plate 54 on the back surface of the light guide 56, emitted from the opening, and becomes emitted light 74.

Of the light incident on the light guide 56 from the lamp,
The light incident on the flat portion of the fine structure 57 on the back surface of the light guide 56 is guided in the light guide 56 in a direction away from the light source 52, and the light incident on the inclined portion of the fine structure 57 is directed to the liquid crystal display element 10. Incident.

The light that has entered the opening is emitted from the liquid crystal display element 10, the light that has entered the non-opening is reflected, and is again reflected by the reflector 54 on the back surface of the light guide 56 while maintaining the polarization state. The light emitted from the opening becomes the emitted light 74. As described above, the brightness is improved by reusing the reflected light from the non-opening portion while maintaining the polarization.

The brightness is improved 1.3 times as compared with the conventional backlight. Further, in this embodiment, as shown in FIG. 1, a reflective polarizing plate 60 is provided on the light guide incident side, and a reflective polarizer 60 is provided between the light guide 56 and the liquid crystal display element 10 as shown in FIG.
Can be introduced, whereby the light use efficiency can be further improved.

[0106]

According to the present invention, a reflection surface made of minute irregularities is provided on the back surface of the light guide, and the polarization of the reflected light from the non-opening portion of the liquid crystal display element is maintained and emitted again, so that the liquid crystal display element having a low aperture ratio is obtained. In this case, the aperture ratio can be substantially improved, and the brightness can be improved.

Further, a reflective polarizing plate is provided at the light guide incident portion,
A bright lighting device with low power consumption for irradiating polarized light can be obtained. Further, the illumination device having a wide emission characteristic and a wide viewing angle can be obtained by the minute reflection curved surface on the back surface of the light guide.

[Brief description of the drawings]

FIG. 1 is a schematic side sectional view showing one embodiment of a liquid crystal display device using the lighting device of the present invention.

FIG. 2 is a schematic side sectional view showing one embodiment of the lighting device of the present invention.

FIG. 3 is a schematic side sectional view showing one embodiment of a liquid crystal display device using the lighting device of the present invention.

FIG. 4 is a schematic side sectional view showing one embodiment of the lighting device of the present invention.

FIG. 5 is a schematic side sectional view showing one embodiment of a liquid crystal display device using the lighting device of the present invention.

FIG. 6 is a schematic side sectional view showing one embodiment of a lighting device of the present invention.

FIG. 7 is a schematic side sectional view of one embodiment of a reflective polarizing plate used in the present invention.

FIG. 8 is a schematic side sectional view of one embodiment of a reflective polarizing plate used in the present invention.

FIG. 9 is a schematic side sectional view showing one embodiment of a liquid crystal display device using the lighting device of the present invention.

FIG. 10 is a schematic side sectional view showing one embodiment of a lighting device of the present invention.

FIG. 11 is a schematic side sectional view showing one embodiment of a liquid crystal display device using the lighting device of the present invention.

FIG. 12 is a schematic view of a horizontal electric field type liquid crystal display device suitable for the lighting device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Common electrode (common electrode), 2 ... Gate insulating film, 3 ...
Signal electrode (drain electrode), 4 pixel electrode (source electrode), 5 alignment film, 6 liquid crystal molecules, 7 substrate, 8 polarizing plate, 9 electric field direction, 10 liquid crystal display element, 11 emission side Polarizing plate, 12: incident side polarizing plate, 13: non-opening, 14:
Opening, 50: lighting device, 51: cover, 52: light source,
53: parallel light converting portion, 54: reflecting plate, 55: mirror-surface curved reflecting surface, 56: light guide, 57: microstructure, 57A: mirror-surface curved reflecting surface, 58: microstructure, 58A: mirror-surface curved reflecting surface, 6
0: reflective polarizing plate, 60A: reflective polarizing plate type 1, 60B
... Reflective polarizing plate type 2, 61, 62 ... Reflective polarizing plate support member, 63 ... dielectric multilayer film, 64 ... 1/4 wavelength plate, 65 ...
Cholesteric polymer liquid crystal layer, 69 ... retardation plate, 70 ...
Non-polarized light from the light source, 71 ... outgoing light from the parallelizing unit,
72: light emitted from a mirrored curved reflecting surface, 73: light reflected from a non-opening portion, 74: light emitted from a light guide, 75: reflected light from a reflective polarizing plate, 76: reflected light from a reflective polarizing plate , 7
7: light emitted from the light guide, 78: reflected light from the reflective polarizing plate, 79: emitted light after passing through the phase difference plate, 80: inclination angle of the parallel light converting portion, 81: length of the parallel light converting portion , 82: incident angle of the parallel light conversion unit, 83: center inclination angle of the mirrored curved reflecting surface, 84
... Height of the mirror-surface curved reflecting surface, 90, 91... Light emitted from the reflective polarizing plate, 100.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Mori 3300 Hayano Mobara-shi, Chiba Pref. Electronic Device Division, Hitachi, Ltd. (72) Inventor Shuji Yano 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Inside the corporation

Claims (15)

[Claims] 1. A light guide having a plate-shaped light guide and a light source disposed close to the periphery thereof, and light emitted from the light source propagates through the light guide and is emitted from a light emitting surface of the light guide. The light guide is configured to have a plurality of convex, concave or stepped reflecting surfaces having fine inclined surfaces on the back surface of the light emitting surface of the light guide, and the reflecting surfaces are at least the inclined surfaces. An illumination device, wherein a surface portion is mirror-finished, and a reflecting plate is provided directly or via an air layer on the back surface of the light guide. 2. The illuminating device according to claim 1, further comprising means for parallelizing emitted light between the light source and the light guide. 3. The lighting device according to claim 2, wherein a reflection type polarizing plate is provided on a light exit surface of the light guide. 4. The lighting device according to claim 2, wherein a reflection type polarizing plate is provided on a light exit surface of the light guide, and a retardation plate is provided on one of the front and back surfaces of the light guide. 5. The light-emitting device according to claim 1, further comprising: means for parallelizing emitted light between the light source and the light guide; and a reflective polarizing plate between the parallel light means and the light guide. Lighting equipment. 6. The lighting device according to claim 5, wherein a reflective polarizing plate is provided on the light guide. 7. The lighting device according to claim 6, wherein a retardation plate is provided on one of the front and back surfaces of the light guide. 8. A pair of transparent substrates, a liquid crystal layer sandwiched between the substrates, and an electrode group formed on at least one of the substrates and applying an electric field for driving liquid crystal molecules of the liquid crystal layer. A liquid crystal display element comprising: an active element connected to these electrode groups; an alignment film that regulates the alignment of liquid crystal molecules in the liquid crystal layer; and an optical unit that changes optical characteristics according to the molecular alignment state of the liquid crystal layer. And a lighting device disposed immediately below the liquid crystal display element, and a liquid crystal display device including means for applying an electric field to an electrode group of the liquid crystal display element, wherein the non-opening portion of the liquid crystal display element has a high reflectance. The illumination device has a plate-shaped light guide and a light source disposed close to the periphery of the light guide, and light emitted from the light source propagates through the light guide to form the light guide. From the light exit surface of A light-emitting surface of the light guide, the light-emitting surface of which has a plurality of convex, concave, or stepped reflecting surfaces having fine inclined surfaces, and at least the inclined surface portions are mirror-finished. And a reflector provided on the back surface of the light guide directly or via an air layer. 9. The liquid crystal display device according to claim 8, wherein means for parallelizing emitted light is provided between the light source and the light guide of the lighting device. 10. The liquid crystal display device according to claim 9, wherein a reflection type polarizing plate is provided on a light emitting surface of a light guide of the lighting device. 11. The liquid crystal display device according to claim 9, wherein a reflection type polarizing plate is provided on a light emitting surface of the light guide of the lighting device, and a retardation plate is provided on one of the front and back surfaces of the light guide. 12. The illumination device according to claim 8, further comprising means for parallelizing emitted light between the light source of the lighting device and the light guide, and a reflective polarizing plate between the parallel light means and the light guide. 3. The liquid crystal display device according to 1. 13. The liquid crystal display device according to claim 12, wherein a reflective polarizing plate is provided on the light guide of the lighting device. 14. The liquid crystal display device according to claim 13, wherein a retardation plate is provided on one of the front and back surfaces of the light guide of the lighting device. 15. An optical means for changing optical characteristics according to a molecular orientation state of the liquid crystal layer of the liquid crystal display element is a pair of polarizing plates, and a polarization axis of an incident side polarizing plate is provided so that incident light from the lighting device is incident. The liquid crystal display device according to any one of claims 8 to 14, wherein the liquid crystal display device is substantially parallel or substantially perpendicular to the polarization axis.