JPH06337413A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve utilization efficiency of light without restricting the visual sense direction by making light incident from a side part of a surface shape light conductor, and arranging a liquid crystal panel outside of a polarization axis rotating unit arranged outside of a polarized light separator on the light emitting surface side. CONSTITUTION:A fluorescent lamp 21 is brought into close contact with one side of a transparent acrylic resin light conductor 24 being a light illuminating surface, and a lamp cover 22 containing a reflector 23 is arranged, and light is introduced in the light conductor 24. A (lambda/4) phase difference plate 25 is arranged on the reverse of the light conductor 24 and on the side surface of the light conductor 24 opposed to a fluorescent lamp installing surface, and a reflecting surface is formed above it, and the light emitting surface side of the light conductor 24 is arranged so that a projecting part faces a polarized light separator 28 by using a lenticular lens array 27. A prism array 29 is arranged outside of this polarized light separator 28 so that an apex angle faces the polarized light separator 28, and a (lambda/2) phase difference plate 30 as a polarization axis rotating unit is arranged outside of it, and a TFT liquid crystal display cell of color display formed by laminating a film having birefringence as a liquid crystal panel 31 is arranged outside of it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat illumination device provided behind a liquid crystal display device using a liquid crystal display system for modulating the polarization state of linearly polarized incident light used in liquid crystal televisions, liquid crystal displays for computers and the like. And a direct-view liquid crystal display device using the same.

[0002]

2. Description of the Related Art In recent years, the technological progress of liquid crystal display devices, especially liquid crystal display devices using color display devices, has been remarkable, and CR
Many displays with display qualities comparable to those of T have come to be seen.

Until a few years ago, a reflection type liquid crystal display device which does not use a backlight, which is a flat lighting device, was the mainstream.
At present, even in black and white display, it is almost replaced by a transmissive liquid crystal display element using a backlight. In addition, laptop computers have entered the popularization stage, and backlight-equipped models have swept the market. A color display liquid crystal display does not serve as a display without a backlight, and the backlight is an essential device in a direct-view liquid crystal display device.

Color liquid crystal display devices are roughly classified into two types: active matrix drive TN liquid crystal display devices using TFTs and multiplex drive STN liquid crystal display devices.
There are two types, a liquid crystal display system that modulates the polarization state of linearly polarized incident light by installing polarizing plates on the light incident side and the light emitting side of an element that holds a liquid crystal layer on a glass substrate. Is to do.

However, since the polarization directions of the incident light of the liquid crystal display element are not uniform and are random polarized light, in the case of both TN type and STN type liquid crystal elements, a polarizing plate mounted on the incident side of the display element causes More than half of the light was absorbed and the light utilization efficiency was low, resulting in a dark display screen. Alternatively, there is a problem that power consumption increases in order to make it bright.

The brightness level required for the backlight varies depending on its application, but especially in a color notebook computer, not only the required brightness but also thinning, weight saving, and power saving (assuming battery driving) are the most important issues. .

There are various methods for producing a flat lighting device, but they are roughly classified into two types. Generally, the most common method is an internal illumination method or a method directly below, in which the light source is inside the illuminated surface. On the other hand, in the edge light type, the light source is arranged outside the illuminated surface, and a fluorescent lamp (often a cold cathode discharge tube) or the like is provided on one or two sides of the light guide body made of a transparent acrylic resin plate or the like which is the illuminated surface. This is a system in which a substantially linear luminous body is brought into close contact and a lamp cover made of a reflector is provided to introduce light into the light guide body. Edge-light type backlights are effective because color notebook computers are required to be thin and lightweight. Necessary functions required for the light guide of the edge light type backlight are a function of sending the light incident from the end portion forward and a function of emitting the sent light to the liquid crystal display element side. The former function depends on the material used and the interface reflection characteristics, and the latter function depends on the shape of the light guide surface that avoids the condition of total internal reflection. Regarding the shape of the light guide surface that avoids this total reflection condition, a method of forming a white diffusion material on the light guide surface and a method of forming a lenticular or prism Fresnel shape on the light guide surface are known.

On the other hand, when the liquid crystal display device is used as a light modulator for a transmissive projector and the tolerance for the depth of the device is large, in order to improve the light utilization efficiency of the light source lamp, A polarization separator that separates non-polarized light into polarized light that is orthogonal to each other is interposed between the lamp and the liquid crystal display device. It has been proposed to use it again as a light source (for example, Japanese Patent Application No.
-184429).

However, if this method is simply applied to a direct-view type liquid crystal display device, the thin and compact feature of the direct-view type liquid crystal display device is impaired, which is not preferable.

[0010]

The present inventors have proposed to use a multilayer film polarizing plate as a polarization separator in order to solve the above-mentioned drawbacks (Japanese Patent Application No. 4-298021).
No.).

The polarization separator has such a characteristic that light having a polarization axis in a specific direction is easily transmitted, but light having a polarization axis in a direction perpendicular to the specific direction is easily reflected. . The light reflected by the polarization separator is transmitted through the polarization separator by rotating the polarization axis by 90 ° so as to enter the polarization separator again. As a result, the light that has passed through the polarization separator becomes light with polarized light that is polarized in a specific direction, and the amount of light in the specific direction increases. If the polarization axis transmitted through the polarization separator and the axial direction of the polarizing plate on the polarization separator side of the liquid crystal panel are aligned substantially, the light emitted from the polarization separator is approximately 10
It is possible to use 0%, and the efficiency of using the light from the light source is increased.

FIG. 3 is a typical example of an edge light type backlight using a polarization separator. In the figure, reference numeral 8 indicates a polarization separator using, for example, an interference film. In this case, the polarization axis direction deviated to a specific direction is perpendicular to the fluorescent lamp 1 which is a linear light source. Here, 2 is a lamp cover, 3 is a reflector, 4 is a light guide, 5 is a λ / 4 retardation plate, 6 is a reflecting surface, 7 is a lenticular lens, 9 is a prism array, and 11 is a liquid crystal panel. , 12 are incident side polarization plates,
Reference numeral 13 is an emission side polarizing plate.

In addition to the polarization separator, a multi-layer structure having a structure in which a transparent material layer having a relatively large refractive index and a transparent material layer having a relatively small refractive index are laminated, or a uniform transparent material is used. A structure in which flat bubble layers are dispersed in layers is conceivable. However, even in this case, the polarization axis direction deviated to the specific direction is perpendicular to the fluorescent lamp 1 which is the linear light source.

The drawback of the previous example was that the polarization axis of the light emerging from the polarization separator was determined by the light source located on the side of the planar light guide. For example, in the case of FIG. 3, light polarized in a direction biased in the direction perpendicular to the linear light source is emitted. Therefore, in order to maximize the amount of light used by the liquid crystal panel, the axial direction of the polarizing plate on the polarization separator side of the liquid crystal panel had to be aligned with the polarization axis direction of the light emitted from the polarization separator. . The liquid crystal panel has a high-contrast direction and a low-contrast direction, and is normally designed to maximize the viewing direction. This viewing angle is also affected by the angle of the polarizing plate and the like. When the illuminating device restricts the angle of the polarizing plate on the polarization separator side of the liquid crystal panel, there is a problem in the device design that the viewing angle direction cannot be freely determined.

The present invention is directed to overcoming the aforementioned deficiencies of the prior art.

[0016]

The present invention has been made to solve the above-mentioned problems, and is an illuminating device comprising a light source and a planar light guide arranged in the vicinity of the light source. The illumination device is arranged so that light is incident from the side of the planar light guide, and a polarization separator is installed on the light exit surface side of the planar light guide, and further outside the polarization separator. It is intended to provide a liquid crystal display device including a polarization axis rotator arranged and a liquid crystal panel arranged outside the polarization axis rotator.

In general, it is known that the polarization axis of light can be rotated by transmitting light through a medium having birefringence or transmitting a medium having optical activity. In addition, the polarization axis rotates even if the medium having the birefringence is superposed in multiple layers while rotating the optical axis.

In particular, when linearly polarized light enters a substance having birefringence, elliptically polarized light is obtained as the emitted light. The ellipticity and the major axis direction of the ellipse are determined by the size of the birefringence of the birefringent medium and the optical axis direction. However, when linearly polarized light is incident on a substance having a birefringence that is half the wavelength λ of incident light, the emitted light is always linearly polarized light. Further, when the fast axis direction of the medium having a birefringence of λ / 2 is inclined with respect to the polarization axis direction of the incident linearly polarized light, the outgoing linearly polarized light is relative to the polarization axis direction of the incident linearly polarized light. The light is emitted with an inclination of 2θ.

By utilizing this property, it is possible to convert the polarization axis of linearly polarized light polarized in an arbitrary direction as it is into linearly polarized light in a specific direction.

The wavelength region required for the liquid crystal display device is all visible light, and the characteristics greatly differ depending on which wavelength is used to set the magnitude of the birefringence of the λ / 2 plate. Normally, it is preferable to use a flat film as the λ / 2 plate, considering the lightness, thinness, cost, and the like. Λ for all visible light
There is no film that satisfies / 2. Therefore 550n
A film satisfying λ / 2 at the wavelength of m is generally used. That is, the film has a birefringence of around 275 nm.

The direction in which the maximum amount of light travels through the polarization axis rotator is not limited to the direction perpendicular to the flat plate of the polarization axis rotator. Therefore, it is assumed that the birefringence magnitude λ / 2 of the polarization axis rotator means the magnitude of the ray trajectory. That is, the size of the birefringence of the film needs to be optimally designed in consideration of the locus of the maximum light amount due to the configuration.

As the material of the film, PVA (polyvinyl alcohol), PC (polycarbonate), PS
(Polystyrene), PMMA (polymethylmethacrylate), etc. are used.

The birefringence of the film is generally obtained by uniaxially stretching to obtain a uniaxial index ellipsoid. A difference between the refractive index in the stretching axis direction and the refractive index in the stretching axis perpendicular direction occurs, and birefringence occurs in the thickness direction.

[0024]

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

A fluorescent lamp 21 (cold cathode discharge tube) is closely attached to one side of a transparent acrylic resin plate light guide 24 which is an illumination surface, and a lamp cover 22 including a reflector 23 is provided to introduce light into the light guide. An edge light type backlight was used.

The fluorescent lamp 21 has a length corresponding to the side length (125 mm) of a general-purpose notebook computer,
A 2 W cold cathode discharge tube having a tube diameter of 3 mm was used. Also,
The lamp cover 22 is a cylindrical or elliptic cylindrical reflecting mirror that wraps the cold cathode discharge tube, and the light guide 24 is a translucent light guide plate made of acrylic resin (n = 1.4).
In 9), a size of 128 mm × 225 mm × 2.8 mm was used.

Further, a λ / 4 retardation plate 25 was provided on the back surface of the light guide 24 and the side surface of the light guide facing the fluorescent lamp installation surface, and a reflection surface 26 made of an Al metal reflection film was formed on the λ / 4 retardation plate 25.

Using the lenticular lens array 27,
The convex portion was arranged so as to face the polarization separator 28. The thickness of the lenticular lens array was 2 mm and the array pitch was about 30 μm. Lenticular lens array 27
The light guide 24 and the light guide 24 are made of the same acrylic resin. An optical adhesive having a refractive index of 1.49, which is the same as that of acrylic resin, is used between the lenticular lens array 27 and the light guide 24.

As the polarization separator 28, titania oxide (TiO 2) is formed on the surface of a homogeneous glass substrate (n = 1.52).
₂ : n = 2.35) was further deposited and mounted on the light emitting surface side of the light guide 23. The Brewster angle of this polarization separator was 72 °. That is, with respect to P-polarized light having an incident angle of 72 °, almost 100% is transmitted and almost no reflection is caused, but S-polarized light is transmitted only about 15% and 85% is reflected.

The polarization of the light emitted from the polarization separator used this time is biased in the direction perpendicular to the linear light source.

Further, as the prism array 29, an isosceles triangular prism array having a vertical cross section of 65 ° is used, and the prism array is arranged so that the vertical angle faces the polarization separator 28. The thickness of the prism array plate was 2 mm, and the pitch of the prism array was about 30 μm. This makes it possible to increase the amount of light in the direction in which the maximum amount of light travels is perpendicular to the light guide plate.

Further, on the outer side thereof, a retardation plate 30 of λ / 2 is provided.
Was installed. The fast axis direction of the λ / 2 retardation plate was set at θ = 45 ° with respect to the light source vertical direction, that is, inclined as shown in FIG. The material is PC (polycarbonate), 55
It had a birefringence of λ / 2 when measured at a wavelength of 0 nm. In FIG. 2, 41 is a fluorescent lamp, 42 is a light guide plate, 43 is a fast axis direction of a λ / 2 plate, 44 is an incident side polarization plate polarization axis, 45 is an emission side polarization plate polarization axis, and 46 is an incidence side. Is a rubbing direction, and 47 is a rubbing direction on the emission side.

As the liquid crystal panel 31, a color TFT liquid crystal display cell in which two films having birefringence are laminated is used. As the incident side polarization plate 32, a normal light absorption type organic polarization plate was used. The polarization axis is θ = 90 °. As the emitting side polarizing plate 33, a normal light absorbing type organic polarizing plate was used. The polarization axis is θ = 0 °. The incident side rubbing direction is θ = 90
And the rubbing direction on the emission side is θ = 0 °.

Since the light emitted from the polarization separator is mostly linearly polarized in the direction perpendicular to the light source, when the polarization axis of the polarizing plate on the incident side used this time is 90 degrees, the brightness of the liquid crystal display device is reduced. On the other hand, by using the λ / 2 retardation plate tilted by 45 degrees, the brightness was increased about 3 times and the light utilization efficiency was improved.

Further, the polarization separator of the above-mentioned embodiment and λ /
Instead of them, one layer of titania was formed on the retardation plate of the PC to serve also as the two retardation plates. It was placed between the lenticular lens and the prism array with the interference film side facing the light source side. The retardation plate of PC had a birefringence of λ / 2 when measured at a wavelength of 550 nm with respect to incident light having an incident angle of about 60 degrees. As a result, almost the same result as that of the above-mentioned embodiment was obtained.

[0036]

According to the present invention, it is possible to obtain a liquid crystal display device in which the viewing angle direction is not restricted by the position of the illumination device and the light utilization efficiency is high.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is an optical axis arrangement diagram of an embodiment of the present invention.

FIG. 3 is a sectional view showing a conventional example.

[Explanation of symbols]

 1: Fluorescent lamp 2: Lamp cover 3: Reflector 4: Light guide 5: λ / 4 retardation plate 6: Reflective surface 7: Lenticular lens array 8: Polarization separator 9: Prism array 11: Liquid crystal panel 12: Incident Side polarizing plate 13: Emitting side polarizing plate 21: Fluorescent lamp 22: Lamp cover 23: Reflector 24: Light guide 25: λ / 4 phase difference plate 26: Reflecting surface 27: Lenticular lens array 28: Polarization separator 29: Prism array 30: λ / 2 retardation plate 31: Liquid crystal panel 32: Incident side polarization plate 33: Emission side polarization plate 41: Fluorescent lamp 42: Light guide plate 43: λ / 2 plate fast axis direction 44: Incident side polarization Plate polarization axis 45: Polarizing axis of polarization plate on the output side 46: Rubbing direction on the input side 47: Rubbing direction on the output side

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuro Matsumoto 1160 Matsubara, Hazawa-machi, Kanagawa-ku, Yokohama-shi, Kanagawa AZ Technology Co., Ltd. (72) Yutaka Nakagawa Matsubara, Hazawa-machi, Kanagawa-ku, Yokohama Address 1160, within AG Technology Co., Ltd.

Claims (4)

[Claims] 1. An illumination device comprising a light source and a planar light guide arranged in proximity to the light source, wherein the light source is arranged such that light is incident from a side portion of the planar light guide. , A lighting device in which a polarization separator is installed on the light exit surface side of the planar light guide, a polarization axis rotator arranged further outside the polarization separator, and a further outside the polarization axis rotator A liquid crystal display device including a liquid crystal panel. 2. The polarization axis rotator according to claim 1, which is a retardation plate having a birefringence of approximately ½ of the wavelength, wherein the fast axis or the slow axis of the retardation plate is a polarization splitting device. When the light is emitted at a tilt angle of θ with respect to the main polarization axis direction of the light emitted from the device, the polarization axis of the polarizing plate on the illuminating device side is further outside the retardation plate. 2. A liquid crystal display device, wherein a liquid crystal panel is arranged so as to be tilted by approximately 2θ with respect to the main polarization axis direction of. 3. The liquid crystal display device according to claim 1 or 2, wherein the polarization separator has a structure in which a transparent material layer having a relatively large refractive index and a transparent material layer having a relatively small refractive index are laminated. And a liquid crystal display device having a multilayer structure. 4. The liquid crystal display device according to claim 1 or 2, wherein the polarization separator has at least one layer of a dielectric interference film on a transparent substrate.