JPH0772475A - Illuminator for direct-view display element and liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain an illuminator having high efficiency of light and to obtain a liquid crystal element using this device. CONSTITUTION:This illuminator is an edge light-type back light in which white ink is applied as a light diffusing material 6 on the back surface of a light guide body 4. An W-shape array with dielectric interference films formed on both surfaces is used as a separating device for polarized light to be disposed on the illuminating side of the light guide body 4. An W-shape array having the cross section as a triangle with 90 deg. apex is used as the W-shape array 8 and arranged in such a manner that the apex faces to the liquid crystal panel 10. The dielectric interference film is a TiO2 film single layer with 640Angstrom thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct view type liquid crystal display device used for a liquid crystal television, a liquid crystal display for a computer and the like.

[0002]

2. Description of the Related Art In recent years, the technical progress of a direct-viewing type liquid crystal display device using a liquid crystal display element, particularly a color display element, has been remarkable, and many displays of display quality not inferior to CRT have come to be seen. In black and white display, until a few years ago, a reflection type liquid crystal display device that does not use a backlight, which is a flat lighting device, has been the mainstream. However, nowadays, even in black and white display, it is almost replaced by a transmissive liquid crystal display device using a backlight. 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.

In recent years, so-called notebook personal computers, which have come into use, are important in portability, and are therefore battery driven. However, at present, the time that can be driven without charging the battery is several hours, which is not enough to continue the work of the day. Extending the continuous use time is extremely important in that sense. In particular, the lighting device is a device that consumes a large amount of power, and reducing the power consumption of the lighting device is extremely significant.

By the way, the liquid crystal display element used in the notebook personal computer shows a specific contrast ratio distribution according to the viewing angle. For example, in the case of a super twisted nematic element, the viewing angle extends substantially 40 ° to 50 ° from the vertical direction, and there is a region with a particularly high contrast ratio near the center.

In practice, the notebook computer is often used with its angle adjusted so that the contrast ratio of the screen seen by the operator is the highest. Therefore, if the maximum brightness of the illumination is set in the viewing direction that produces the maximum contrast ratio (mostly in the vertical direction or in a direction slightly deviated from the vertical direction), the illumination efficiency will be substantially improved.

On the other hand, the viewing angle of a liquid crystal display element used in a notebook computer has substantially expanded to about 40 ° to 50 ° or more, and further studies for widening the viewing angle have been made. Therefore, it is also important to adjust the orientation distribution of the lighting device so that the display can be viewed from a certain angle.

As described above, adapting the brightness distribution of the illuminating device to this contrast ratio distribution is significant as a means for substantially improving brightness.

By the way, the color liquid crystal display device is roughly classified into TN by active matrix driving using TFTs.
There are two methods, a liquid crystal display device and a multiplex drive STN liquid crystal display device. Both have a structure in which polarizing plates are attached to the light incident side and the light emitting side of an element in which a liquid crystal layer is held by a glass substrate, and a liquid crystal display system is performed by modulating the polarization state of linearly polarized incident light. is there.

However, since the polarization direction of the incident light of the conventional liquid crystal display element is usually irregular and randomly polarized, more than half of the incident light is absorbed by the polarizing plate mounted on the incident side of the display element, More than half do not contribute substantially as illumination light.

In the projection type liquid crystal display element, a polarization separation for separating unpolarized light into polarized light orthogonal to each other is provided between the light source lamp and the liquid crystal display device as a structure in which light absorbed by the polarizing plate is reused. It has been proposed that one light is directly emitted from the polarization separator and the other light is focused on the light source lamp and used again as the light source light by interposing a light source (see Japanese Laid-Open Patent Publication No. 4-18429).

However, this method is premised on a projector (projection type), and it is necessary that there is a sufficient distance between the light source and the polarization separator. Further, the light effectively functions as the illumination for the projection type liquid crystal display element only when the light is collimated. Therefore, thinning has become an essential condition, and it is inappropriate to employ it as illumination for a direct-view display device, which should match the brightness distribution of the lighting device with the contrast ratio distribution of the liquid crystal display.

It has also been proposed to interpose a prism array between the illumination light source and the display element as means for condensing light in the direction perpendicular to the display surface. However, this is to improve the luminance in the direction perpendicular to the display surface by narrowing the illumination light to a specific range, so that the light distribution of the illumination light becomes narrow. Even with this, the luminance in the direction perpendicular to the display surface is not sufficient. Therefore, the illuminance distribution suitable for the direct-view type liquid crystal display element cannot be obtained.

The present invention provides an illuminating device having an illuminance distribution suitable for a direct-viewing type liquid crystal display element.

[0014]

The present invention focuses on the fact that only polarized light having a certain polarization direction contributes to the improvement of the illuminance of a direct-viewing type liquid crystal display element, and as it is, it improves the illuminance of the liquid crystal display element. Of polarized light that does not contribute, light in a specific direction is selectively polarized. In this way, it becomes possible to increase the light intensity in a specific direction while maintaining a wide light distribution for polarized light having a polarization direction that can contribute to improvement in illuminance, and the illuminance distribution is suitable for a direct-view liquid crystal display element. Will be things.

The present invention has been made to solve the above-mentioned problems, and includes a planar light guide, a light source arranged so that light is incident from a side portion of the planar light guide, and a light guide. The light reflecting means is provided on the surface of the light body opposite to the light emitting surface, and the visible light wavelength is provided on the transparent support having a substantially W-shaped cross section, which is provided on the light emitting surface side of the planar light guide. A polarization separator that is formed by providing at least one or more dielectric thin films having a thickness equal to or less than that of the polarization separator that transmits the p-polarized component and reflects at least a part of the s-polarized component with respect to a ray in the vicinity of a predetermined incident direction. A light deflector provided between the planar light guide and the polarization splitting surface for deflecting light emitted from the planar light guide in a direction perpendicular to the light exit surface of the planar light guide; The present invention provides a lighting device for a direct-view type display device, which comprises:

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.

The light generating means in the present invention is preferably an edge light type comprising a planar light guide and a light source arranged so that light is incident from the side of the planar light guide. This is because the edge light type illumination device is compact and most desirable from the viewpoint of enhancing the portability of the liquid crystal display device.

At this time, the p-polarized component (first polarized component) of the light beam provided on the light exit surface side of the planar light guide near the predetermined incident direction is transmitted, and the s-polarized component (first polarized component) is transmitted. Two
Polarization component) which reflects at least a part of the polarized light component), and a light reflecting surface provided on the side of the planar light guide opposite to the light emitting surface and substantially parallel to the light emitting surface. Is preferably provided. When the light reflecting surface is used in such a configuration, not only can the polarized and separated light be reused,
Since the polarization direction changes during reflection, it functions as a polarization conversion means in cooperation with the above-mentioned polarization separation surface.

With such a configuration, for light whose incident angle on the polarization separator is near a specific angle, the p-polarized component that has passed through the polarization separator passes through the polarizing plate and then enters the liquid crystal display element to produce s-polarized light. The components are reflected into the planar light guide. When the reflected s-polarized light component is reflected on the surface of the planar light guide, a phase change occurs, a p-polarized light component is generated, and can be transmitted through the polarization separator. Therefore, the s-polarized component reflected by the polarization separator also reflects on the surface of the planar light guide to generate a component converted into a p-polarized component, which contributes to the component transmitted to the liquid crystal display element. As a result, a planar illumination device with high illuminance can be obtained in a specific viewing direction.

In order to use this illuminating device as a backlight of a liquid crystal display element, a polarizing plate provided on the light incident side of the liquid crystal display element has a maximum transmittance for the p-polarized light component emitted from the polarization separator. Is preferably arranged so that That is, it is preferable that the average polarization axis direction of the light beam emitted from the planar light guide in the planar illumination device and the polarization axis of the polarizing plate on the light incident side of the liquid crystal display element are substantially aligned with each other.

In the polarized light separator of the present invention, at least one surface of the planar light-transmitting support is preferably 1000 n.
It is possible to use a film in which at least one dielectric film having a thickness of m or less is formed.

In the present invention, the polarization splitting surface is W-shaped in cross section. By doing so, the polarization separator can be made compact. In particular, it is preferable that the apex angle of the W-shape is around 90 °. Change the maximum luminance direction that is almost perpendicular to the illumination surface by setting the apex angle of the W-shape to about 90 ° and by providing the reflection plate on the back surface of the transparent light guide substantially parallel to the polarization separation surface. Instead, the light reflected by the polarization splitting surface can be reused. W angle is 90 °
± 10 °, preferably 90 ° ± 5 °.

In this case, from the viewpoint of reusing light, it is preferable that the light incident on the polarization splitter has a maximum brightness in a direction substantially perpendicular to the illuminated surface of the light guide. However, it is generally difficult to extract light from the light guide at right angles to its surface.

From the light guide of the edge light type backlight, the shape of the light guide surface is selected so as to avoid the condition of total 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 an uneven shape such as a lenticular or prism on the light guide surface are known. .

However, when forming a white diffusing material,
Light can usually only be extracted at 20 ° to 35 ° with respect to the illuminated surface. In the case of forming a concavo-convex shape, light can usually be extracted only at 60 to 80 with respect to the illuminated surface. Therefore, it is preferable to provide a light deflector on the light emitting surface side of the planar light guide so that the emitted light is substantially perpendicular to the planar light guide.

As the light deflecting means, it is possible to use a structure in which columnar prisms having a triangular section in a plane including the average optical axis of light rays emitted from the planar light guide are arranged in an array. It is preferable that one angle of the triangle facing the planar light guide of the triangular prism of the light deflecting means is 50 ° to 75 °. Further, the surface of the light diffusion plate may be embossed. When the above-mentioned prism array is used, it is possible to obtain a light distribution of light condensed in a specific direction. On the other hand, when the light diffusing plate is used, it is possible to obtain a light distribution of light having a relatively wide angular distribution.

On the other hand, the directivity of the light propagating in the light guide is high, and as a result, the light distribution azimuth distribution of the light emitted from the flat illumination device is concentrated in the vertical direction, and the viewing angle corresponding to the bright display is obtained. The range may be narrow. If the viewing angle is too narrow,
It may be unfavorable as illumination for a direct-view display device. In order to avoid this, it is preferable to dispose a diffusing means such as a diffusing plate that deteriorates directivity between the liquid crystal display element and the deflecting means.

Next, the polarization separator of the present invention will be described.

The polarization separator in which at least one dielectric film having a thickness of preferably 1000 nm or less is formed on at least one surface of the planar light-transmitting support is one which utilizes optical interference. It is described in Japanese Patent Application No. 5-51594. In this case, the interface between the dielectric film and the support serves as the polarization splitting surface. This polarization separator also has a property that its transmittance and reflectance with respect to obliquely incident light depend on the polarization of obliquely incident light, and can be used as a non-light-absorption type polarization element. Here, 1000 nm or less is mainly in the visible light wavelength order or less, preferably 800 n
It is about m or less.

Since the dielectric film having a film thickness on the order of the visible light wavelength of the polarization separator utilizes optical interference, generally, when the number of layers is increased, the degree of polarization of a specific wavelength can be improved, but on the other hand, it depends on the wavelength. The nature becomes large. When the spectrum of the backlight light source to be used is narrow band wavelength light, it is possible to use a multilayer film structure in which the degree of polarization is high in the backlight wavelength range of light. However, if a multi-layer film is used too much, productivity may be impaired.
It is about a layer. On the other hand, when a white backlight is used for color display, it is preferable to use an interference film of 5 layers or less, particularly a single layer in order to suppress the wavelength dependence of the polarization degree and obtain a flat polarization degree in the entire visible range. preferable. A single layer film of TiO ₂ or ZrO ₂ is preferably formed from the viewpoint of easy control of the film thickness.

In the present invention, a translucent support having a substantially W-shaped cross section is used. By doing so, it becomes possible to provide polarization splitting surfaces on both sides of the translucent support, and it becomes possible to obtain a flat and high degree of polarization.

The schematic construction of the polarization separator of the present invention is shown in a perspective view in FIG. Reference numeral 20 is a W-shaped array, and 21 is a dielectric interference film.

Materials used for the translucent support include glass and plastics such as acrylic, polycarbonate, polyurethane and polystyrene. It is desirable that the material is light and the surface is smooth.

The thickness of the light-transmissive support may be an order of visible light wavelength and may give an interference effect to itself, but since it must be held on one side of the planar light guide, it must have a certain degree of rigidity. Is preferred.

In this case, if the apex angle of the W-shaped array of the light-transmitting support, the refractive index, the number of layers of the dielectric film, and the refractive index and the film thickness of each layer satisfy the appropriate conditions. It is possible to increase the ratio of the transmitted light intensity of polarized light vibrating perpendicular to the array direction to the transmitted light intensity of polarized light vibrating parallel to the array direction.

The material of the planar light-transmitting support used for the polarization separator is glass, plastic such as acrylic, polycarbonate, polyurethane, polystyrene and the like. It is desirable that the material is light and the surface is smooth.

The material of the dielectric film is TiO ₂ , Zr.
O ₂ , ZnS, Y ₂ O ₃ , SiO ₂ , MgF ₂ , Na ₃
AlF ₆ , Ta ₂ O _{5 and the} like are considered. The refractive index of these dielectric films is usually about 1.4 to 2.5, and a dielectric having an appropriate refractive index may be selected and formed. The film formation may be performed by a commonly used method such as vapor deposition or sputtering.

The case where the present invention is applied to an edge light type flat lighting device will be described in detail below with reference to FIG.

The light source 1 having a length corresponding to the length of the side surface of the light guide is brought into close contact with one side of the transparent light guide 4, and the lamp cover 2 having the reflector 3 provided therein is provided so that the light emitted from the lamp is emitted. Introduced into the light guide. As the light source 1, a linear light source such as a cold cathode discharge tube or a hot cathode tube is used. As the reflector 3, it is preferable to use a film having a high reflectance made of metal such as aluminum vapor deposition or silver vapor deposition. A material such as acrylic or polycarbonate can be used for the light guide 4.

The directivity (angle distribution) of the light propagating in the light guide is determined by the light distribution characteristics of the light source, the condensing characteristics of the reflector, the propagation characteristics of the light guide plate, and the like. In particular, as described above, the propagation characteristics of the light guide must have both the function of sending the light incident from the end of the light guide forward and the function of emitting the sent light in a predetermined direction. .

The former function is determined by the material used and the interface reflection characteristic, and on the liquid crystal display element 10 side of the light guide 4, the total reflection angle θ _c determined by the refractive index of the light guide 4.
The light with the above incident angle is totally reflected and propagates in the light guide 4,
Light having an incident angle equal to or less than the total reflection angle θ _c is refracted on the surface of the light guide 4 and emitted to the liquid crystal display element 10 side. For example, air (n
= 1.0) and the angle of total reflection θ _{c at} the interface between a transparent resin and a plastic such as acrylic, polycarbonate, polyurethane, polystyrene (n is about 1.5)
Is about sin ⁻¹ (1 / n) = 41.8 °.

That is, incident light having an incident angle of 41.8 ° or less can be emitted from the illumination surface of the light guide 4.

On the other hand, if a reflection surface 5 such as an aluminum reflection surface is formed on the surface of the light guide opposite to the liquid crystal display element, the reflected light is guided as regular reflection light in the light guide. The reflection surface 5 may be a diffuse reflection surface in order to increase the light emitted from the side surface of the liquid crystal display element 10 of the light guide 4.

On the other hand, if the incident angle of light on the light guide 4 is more than the total reflection angle θ _{c in} most cases, the amount of light emitted from the light guide becomes small, so that the condition of total reflection is avoided. However, a function of emitting light to the liquid crystal display element 10 side of the light guide plate 3 is required. As a means therefor, a method of forming a white light diffusing material on the surface of the light guide 4 and a method of forming a lenticular or prism Fresnel shape (microlens array, prism array, etc.) on the surface of the light guide are known. . A Fresnel-shaped film-shaped plate may be placed on the surface of the light guide. When mounting, it is necessary that there be no air layer between the film and the light guide. Therefore, for example, degassing can be performed after laminating, or a film having a refractive index equivalent to that of the film can be used in between. Further, it is desirable that the refractive index of the film is almost the same as that of the light guide.

Since the light emitted from the light guide 4 is used as a surface light source, it is not preferable that the light is uneven depending on the location. Therefore, it is necessary to improve the uniformity of the function of avoiding the total reflection condition. For example, the white light diffusing material 6 is provided on the surface of the light guide 4 while changing the density of the light diffusing material depending on the distance from the light source, the distance in the light source axial direction, or the like.

In order to make the light emitted from the light guide 4 uniform, a diffusion plate is installed on the upper surface of the light guide plate 4.

As described above, in the edge-light type backlight, the directivity of the light propagating through the light guide and exiting is determined in the viewing angle of the observer of the liquid crystal display element, that is, in the direction perpendicular to the surface of the liquid crystal display element. There is no. It is possible to use the above-mentioned light diffusing plate with an embossed surface or to use a prism array to deflect the light distribution of a planar lighting device having a biased light distribution in the direction perpendicular to the illumination surface. Is effective for. Further, as in the present invention, by making the cross section of the polarization separator itself into a W shape, it becomes possible to convert the light distribution of the flat illumination device having a deviated light distribution to the direction perpendicular to the illumination surface to some extent. .

In order to deteriorate the directivity of the light propagating in the light guide body, the reflecting surface 5 formed on the side surface of the light guide body opposite to the liquid crystal display element may be a diffusing surface. Further, the polarization separator itself may have a fine concavo-convex structure so that light scattering may occur at the interface of the structure.

The transparent resin used for the light guide may be polycarbonate, polyurethane, polystyrene, silicone or the like in addition to acrylic.

In order to use this illuminating device as a backlight of a liquid crystal display element, the polarizing plate provided on the light incident side of the liquid crystal display element has the maximum transmittance for the specific polarized light emitted from the illuminating device. That is, it is preferable that the average polarization axis direction of the light beam emitted from the illumination device and the polarization axis of the polarizing plate on the light incident side of the liquid crystal display element are substantially aligned.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Another embodiment of the present invention will be described with reference to FIG.

An edge-light-type back for adhering the light source 1 (cold cathode discharge tube) to one side of the transparent acrylic resin plate light guide 4 and providing the lamp cover 2 including the reflector 3 to introduce light into the light guide. Light was used.

The light source 1 has a length corresponding to the side length (125 mm) of a general-purpose notebook computer and has a tube diameter of 3
A 2 W cold cathode discharge tube having a size of 2 mm was used. Further, the lamp cover 2 is a cylindrical or elliptic cylinder-shaped reflecting mirror that encloses a cold cathode discharge tube, and the light guide 4 is a translucent light guide plate made of acrylic resin (n = 1.49). The size used was 128 mm × 225 mm × 2.8 mm.

Further, white ink was printed on the back side of the light guide 4 as the light diffusion material 6. In order to uniformly distribute the light emitted from the light guide 4, the printing area density of the white ink is changed according to the distance from the light source and the like.

As the W-shaped array 8, a W-shaped array having an isosceles triangular cross-section with an apex angle of 90 ° was used, and was arranged so that the apex angle faces the liquid crystal panel 10. The W-shaped array plate had a thickness of 2 mm and the array pitch was about 30 μm.
Polycarbonate was used as the material for the W-shaped array.

The light emitted from the light guide 4 is further diffused by the diffusion plate 7 and becomes uniform light, which is then incident on the W-shaped array 8. The surface of the diffusion plate 7 is embossed and has the function of deflecting light at the same time.

Dielectric interference films were formed on both sides of the W-shaped array 8. The dielectric interference film is a single layer of TiO ₂ film and has a thickness of 6
It was 40Å. As a result, the light emitted in the vertical direction from the W-shaped array 8 has a ratio of the emission amount of the light vibrating in the vertical direction to the emission amount of the light vibrating in the parallel direction to the array to 3 Doubled. Almost 75% of the amount of light vibrating in the direction perpendicular to the array is emitted. About 25% of the light vibrating in the direction parallel to the array is emitted, and the remaining about 75% is reflected. The reflected light is diffused again in the diffusion plate 7 and the polarized light is disturbed. The light whose polarization is disturbed is returned to the W-shaped array 8 again, and about 75% of the light vibrating vertically to the array is emitted, and some of the light vibrating parallel to the array is emitted, and most of it is reflected. To be done. The light emitted from the W-shaped array is oscillated perpendicularly to the array by repeating the above operations depending on whether it is oscillating vertically or parallel to the array. Shows a biased distribution of light.

The liquid crystal panel 10 uses TFT liquid crystal display cells for color display. As the incident side polarization plate 9, a normal light absorption type organic polarization plate was used. The polarization axis is perpendicular to the array of W-shaped arrays. Therefore, W-shaped array 8
The most polarized light can be transmitted. The light-emitting side polarizing plate 11 also used a normal light absorption type organic polarizing plate. The polarization axis is parallel to the array.

As compared with the case where there is no W-shaped array, the vertical brightness is increased by about 30% by the presence of the W-shaped array with the dielectric interference film prepared this time.

[0060]

According to the present invention, it is possible to use the polarized light that has been conventionally absorbed by the organic polarizing plate by changing the polarization direction, and a liquid crystal display device with high light utilization efficiency can be obtained.

Further, since the light distribution direction of the light is deflected to the liquid crystal display element in the direction substantially perpendicular to the display surface in advance, the polarized light is separated, so that even in the edge light type liquid crystal display element,
Efficient polarization separation is possible.

Further, by making the polarization separator substantially W-shaped in cross section and providing the reflecting means on the back surface of the light guide, it is possible to efficiently reuse the light.

In the present invention, a translucent support having a substantially W-shaped cross section is used. By doing so, it becomes possible to provide polarization splitting surfaces on both sides of the translucent support, and it becomes possible to obtain a flat and high degree of polarization.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing a polarization separator of the present invention.

[Explanation of symbols]

 1: Light source 2: Lamp cover 3: Reflector 4: Light guide 5: Reflecting surface 6: Light diffusing material 7: Diffusing plate 8: Prism array 9: Incident side polarizing plate 10: Liquid crystal panel 11: Emission side polarizing plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuro Matsumoto 1150, Hazawa-machi, Kanagawa-ku, Kanagawa Prefecture Asahi Glass Co., Ltd. (72) Inventor Yutaka Nakagawa 1150, Hazawa-machi, Kanagawa-ku, Yokohama Asahi Glass Co., Ltd. Central Research Center

Claims (2)

[Claims] 1. A planar light guide, a light source arranged so that light is incident from a side portion of the planar light guide, and a light guide surface provided on a surface opposite to a light exit surface of the light guide. At least one dielectric thin film having a thickness equal to or less than the visible light wavelength is provided on the light reflecting means and on the light emitting surface side of the planar light guide, the transparent support having a substantially W-shaped cross section. Consists of
A polarization separator that transmits a p-polarized light component and reflects at least a part of the s-polarized light component of a light beam in the vicinity of a predetermined incident direction, and a planar light emitting device provided between the planar light guide and the polarized light separation surface. An illumination device for a direct-view display device, comprising: a light deflecting unit that deflects light emitted from the light guide body in a direction perpendicular to a light emitting surface of the planar light guide body. 2. The direct-view type display according to claim 1, wherein an average polarization axis direction of a light beam emitted from the illuminating device and a polarization axis direction of a polarizing plate on a light incident side of the liquid crystal display element are substantially aligned with each other. A liquid crystal display device characterized in that an element lighting device is arranged on the back surface of the liquid crystal display device.