JP2003084283A - Illuminating device and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illuminating device suitable for a direct-view type liquid crystal display element wherein light intensity of a specific direction is intensified while maintaining wide light distribution. SOLUTION: The illuminating device consists of: a planar light guide body 3; a light source 1 disposed so that light is made incident from a side part of the planar light guide body 3; a polarized light separating plane 8 provided on the light emitting side of the planar light guide body 3 and transmitting the p-polarized light component and reflecting at least a portion of the s- polarized light component with respect to a light beam in the direction in the vicinity of prescribed incident direction; and a light reflecting plane 4 provided to be nearly parallel to the light emitting plane on the side opposite to the light emitting plane of the planer light guide body. The principal polarization axis direction of a light beam emitted from the illuminating device and the polarization axis direction of a polarizing plate 9 on the light incident side of the direct-view type liquid crystal display element 12 are made to nearly coincident with each other to dispose the illuminating device in the rear of the liquid crystal display element 12.

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. A typical example of a super twisted nematic element is shown in FIG. FIG. 5 is a diagram showing changes in the contrast ratio on a horizontal line passing through the center of the contrast ratio on the display screen. From this, it can be seen that the viewing angle of the liquid crystal display element spreads 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 luminance of the illumination is set in the viewing direction (most of which is in the vertical direction or in a direction slightly deviated from the vertical direction) that produces the maximum contrast ratio, the illumination efficiency is 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.

[0013]

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.

That is, according to the present invention, 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 exit surface side of the planar light guide are provided. A polarization splitting surface that is provided to transmit a p-polarized component and reflects at least a part of the s-polarized component of a light beam in the vicinity of a predetermined incident direction is provided on the side opposite to the light exit surface of the planar light guide. Provided is a lighting device for a direct-view display element, which comprises an emission surface and a light reflection surface provided substantially parallel to the emission surface.

Further, the polarization splitting surface is composed of a multi-layer structure in which a translucent medium having a relatively large refractive index and a translucent medium having a relatively small refractive index are alternately laminated. An illumination device for the direct-view display device is provided.

Alternatively, the illumination device for a direct-view type display device is characterized in that the polarization splitting surface comprises a transparent support provided with at least one dielectric thin film having a thickness equal to or less than a visible light wavelength. provide.

Alternatively, there is provided the illumination device for a direct-view type display device, wherein the polarization splitting surface is formed by laminating a plurality of types of transparent polymer layers having different refractive indexes.

In addition, the main polarization axis direction of the light beam emitted from the illuminating device and the polarization axis direction of the polarizing plate on the light incident side of the liquid crystal display element are substantially aligned with each other, and the illuminating device is directly viewed. A liquid crystal display device is provided on the back surface of the liquid crystal display device.

In particular, between the polarization splitting surface and the liquid crystal display element, the direction of the light ray having the maximum light intensity in the light distribution direction is
The above liquid crystal display device is provided with a light deflecting means for deflecting the liquid crystal display element in a direction substantially perpendicular to the display surface.

Further, a planar light generating means for generating diffused light containing a first polarized component and a second polarized component having a polarization direction perpendicular to the first polarized component, and an optical path of light generated from the light generating means The first polarized light component is selectively emitted with respect to a light beam in the vicinity of the light distribution direction having the maximum brightness, and at least a part of the second polarized light component is polarized and converted into the first polarized light component. Provided is a lighting device for a direct-view type display device, which has a polarization converting unit for emitting light.

There are various methods for producing a flat lighting device, but they are roughly classified into two types. Generally, the most common method is the internal illumination method or the method directly under,
In this method, the light source is inside the illuminated surface. On the other hand, in the method called edge light type, the light source is placed outside the illuminated surface,
For example, a linear lamp such as a fluorescent lamp (often a cold cathode discharge tube) is attached to one or two sides of a light guide made of a transparent acrylic resin plate, which is the illuminated surface, and a lamp cover made of a reflector is attached. This is a system in which light is introduced 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-polarization component (first polarization component) of the light beam provided on the light exit surface side of the planar light guide and near the predetermined incident direction is transmitted, and the s-polarization component (first polarization component) is transmitted. Two
Polarization component) that reflects at least a part of the polarized light component) and a light reflection surface provided on the side of the planar light guide opposite to the light emission surface and substantially parallel to the light emission 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. Hereinafter, an element having a polarization splitting surface will be referred to as a polarization splitter. However, this does not mean that the polarization separator is required as an element separate from the planar light guide and the like. The planar light guide may also have a polarization separation function.

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, and the s-polarized light is transmitted. The components are reflected into the planar light guide. The reflected s-polarized component is reflected on the surface of the planar light guide,
A phase change occurs that produces a p-polarized component that 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.

The polarization separator of the present invention may be a multi-layer structure or a planar structure in which a translucent medium having a relatively large refractive index and a translucent medium having a relatively small refractive index are alternately laminated. At least one surface of the translucent support, preferably 1000
It is possible to use one in which at least one dielectric film having a thickness of nm or less is formed, or one in which a plurality of types of transparent polymer layers having different refractive indexes are laminated. A polarization separator including a multi-layer structure in which a translucent medium having a relatively large refractive index and a translucent medium having a relatively small refractive index are alternately laminated will be described below.

This multilayer structure has a property that the transmittance and the reflectance of obliquely incident light depend on the polarization of the obliquely incident light. Thereby, it can be used as a non-light-absorption type polarization element. In general, when the incident angle θ _{01 of} light incident from n ₀ to n ₁ is tan θ ₀₁ = n ₁ / n ₀ at an interface between an optical material having a refractive index n _{0 and} an optical material having a refractive index n ₁ , reflection is performed. There is no p-polarized component in the light, it becomes s-polarized light,
It is known that the transmitted light is composed of the remaining s-polarized component and p-polarized component. At this time, the incident angle θ _{01 is referred} to as the Brewster angle θ _B. Therefore, when the optical material layers having the refractive indices n ₀ and n ₁ are alternately laminated, the p-polarized component is transmitted with respect to the incident angle light in the vicinity of the Brewster angle, but the s-polarized component is reflected by a plurality of interfaces and transmitted. The light component is almost gone. Therefore, the light emitted from the above-mentioned multilayer structure has a polarization property.

The multilayer structure may be made of at least two or more light-transmitting materials having different refractive indexes, but the polarization dependence of the reflectance at the interface generally becomes stronger as the refractive index difference increases. Therefore, a combination having a large difference in refractive index is preferable. For example, air (n≈1.0) and transparent resin such as acrylic, polycarbonate, polyurethane, polystyrene and other plastics (n≈1.0)
There is a combination with 1.5). The above combination is
It is also preferable in that a large-area multilayer structure can be easily obtained at low cost.

There is basically no limitation on the thickness of each layer of the multilayer structure. Further, it may have a non-homogeneous structure depending on the place, or may have a structure in which flat bubble layers are dispersed in a layer in a homogeneous plastic. It suffices that the layers in the multilayer structure are arranged substantially in parallel.

A transparent dielectric multilayer film may be used as the material. When the dielectric multilayer film is used as a multi-layer structure, the layer thickness is about 10 times or more compared to the light wavelength order so that the reflected light from each layer interface of the multi-layer structure does not interfere with each other. It is possible to obtain a polarization characteristic with less wavelength dependence. On the other hand, if the thickness of each layer is too thick, the overall thickness of the multi-layer structure becomes thicker and lighter.
It will not fit the thin shape. Therefore, for this purpose 3 μm
A layer thickness of about 1 to 100 μm is suitable. Further, if the film thickness is irregular, coloring due to optical interference can be reduced. Therefore, it may be preferable to make the thicknesses of the layers uneven.

In the case of a structure in which flat bubble layers are dispersed in a layer in a homogeneous plastic, the thickness of the flat bubble layers may be about 3 μm to 100 μm. As another configuration, there is also a multilayer structure in which a transparent thin plate having a thickness of about 3 μm to 100 μm is sprinkled with a gap control material such as beads or glass fibers having a diameter of about several tens μm, and laminated. In this case, as compared with a configuration in which a flat bubble layer is dispersed in a layer in a homogeneous plastic, an incident angle at an interface having different refractive indexes does not vary depending on a place like a flat bubble layer. It is easy to obtain a polarization effect with a high extinction ratio.

Refractive index n _{0 under the} Brewster angle condition
The reflectance R _s of the s-polarized light at the interface between the optical material of ( ₁₎ and the optical material of refractive index n _{1 is} as shown in Formula 1.

[0033]

[Equation 1]

The larger the difference in refractive index, the larger the reflectance R _s . Therefore, it is necessary for 100% of the p-polarized light component and x% of the s-polarized light component of the incident light to the multilayer structure to be transmitted in the approximation not considering the multiple reflection between layers (an approximation that is sufficiently applicable in this case). The number N of layers is calculated by Equation 2.

[0035]

[Equation 2]

Therefore, in the case where the multilayer structure is constituted by the combination of air (n ₁ ≈1.0) and plastic (n ₀ ≈1.5), the Brewster angle θ _B = 56.
3 °, R _s = 14.8%, and the transmittance of the s-polarized component is 2
It can be seen that the number of layers required to be less than or equal to 12 is 12.

That is, in the case of a structure in which flat bubble layers are dispersed in a layer in a homogeneous plastic, if six or more flat bubble layers are formed in the depth direction, the flat bubble layer near the Brewster angle is obtained. With respect to the incident light, the s-polarized component transmittance is 2% or less, and the other 98% or more light is reflected. On the other hand, with the p-polarized component, a transmittance close to 100% can be obtained without loss of light amount.

As described above, the polarization function of the multilayer structure works most effectively when the incident angle is the Brewster's angle. Therefore, when arranging the multilayer structure in the flat lighting device including the light source and the planar light guide, the additional optical elements such as the light source, the planar light guide, and the light reflecting means are provided to the multilayer structure. In order to substantially improve the brightness, it is preferable that the incident angle of the incident light has a large component near the Brewster angle.

On the other hand, the reason why the polarization separator using the dielectric film utilizing optical interference exhibits the polarization separation function is considered as follows. 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.

When there is an optical material with a film thickness of the order of visible light having a refractive index n ₁ between the optical material having a refractive index n _{0 and} the optical material having a refractive index n ₂ , light interferes. The incident angle of light entering from n ₀ to n ₁ is θ ₀ , and the outgoing angle is θ ₁ . n ₁ to n
_The incident angle of incidence on ₂ is θ ₁ , and the outgoing angle is θ ₂ . The reflection complex amplitude in consideration of the effect of interference in the optical material n ₁ and the film thickness d ₁ is as shown in Formula 3.

[0041]

[Equation 3]

Here, ρ _a and ρ _b are the refractive indices n ₀ and n, respectively.
₁ shows the amplitude reflectance of Fresnel reflection occurring at the interface between ₁ , ₁ and n ₂ .

The reflection intensity is expressed by ρ ^* as a complex conjugate of ρ.
It becomes like number 4.

[0044]

[Equation 4]

The p-polarized light component is as shown in equation 5.

[0046]

[Equation 5]

The s-polarized light component is as shown in Equation 6.

[0048]

[Equation 6]

Refractive indices n ₀ and n ₂ , refractive index n ₁ and film thickness d
_{When 1} satisfies a certain condition, p is p at a certain incident angle θ _0.
It is known that the ratio of the transmitted light intensity of the polarized component and the transmitted light intensity of the s-polarized component is larger than that in the case where there is no interference. The above-described calculation formula is for the case where the interference film is a single layer, but the same consideration may be applied when the interference film is a multilayer.

As described above, the light emitted from the polarization separator in which at least one dielectric film having a thickness of 1000 nm or less is formed on at least one surface of the planar light-transmitting support has a high polarization property. Will be emitted. Here, 1000 nm or less mainly means that the wavelength is in the visible light wavelength order or less, preferably about 800 nm 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 increases, the degree of polarization of a specific wavelength can be improved, but the wavelength dependence 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. Although a high degree of polarization cannot be obtained, it is possible to obtain a flat degree of polarization in the entire visible range and to easily control the film thickness.
It is preferable to form a monolayer film of ₂ or ZrO ₂ .

The material of the planar light-transmitting support used in the polarization separator is glass, plastic such as acrylic, polycarbonate, polyurethane, polystyrene or 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.

Further, the polarized light separating surface of the present invention may be formed by laminating a plurality of types of transparent polymer layers having different refractive indexes. Also in this case, as in the case of the above-mentioned multilayer structure or dielectric thin film,
It acts as a non-light-absorbing polarization separator.

The polarization separator may have a multi-layer structure in which the degree of polarization is high with respect to the wavelength range of the backlight light. If the film is made of too many layers, productivity may be impaired. Therefore, the number of layers is preferably 30 or more, and more preferably about 100 to 400. The material of the transparent polymer having a different refractive index is preferably suitable for so-called multilayer laminate molding. Further, the larger the difference in the refractive index, the more preferable.

The material of the transparent polymer is preferably at least two kinds selected from plastics such as acrylic, polycarbonate, polyurethane, polystyrene, triacetyl cellulose, polymethylpentene and polyether sulfone. Further, in order to improve efficiency, the difference in the refractive index is preferably 0.03 or more.

The manufacturing method of the polarization separator must be taken into consideration in the selection. As a method for manufacturing a multilayer laminate product, there are a casting method, a multilayer extrusion method, etc.
It is preferable to employ a multilayer extrusion method that allows economical formation of a multilayer film of 0 or more layers.

Its manufacturing method is described in US Pat. No. 3773.
882, U.S. Pat. No. 3,883,606. The polarization separator having a sufficient thickness with a small light interference effect has a large total thickness. Therefore, in order to utilize the coherence of light, the optical thickness of at least one of the polymers having different refractive indexes is 0.05 μm or more and 0.4 or more.
It is preferably 5 μm or less. Also, its thickness is
It is preferable that the difference between the two polymers is substantially equal to that of both polymers, because a so-called pearlescent color due to the thickness variation of each layer is less likely to appear. A hard coat layer such as silicone may be provided on the surface.

FIG. 4 shows a conceptual sectional view of a polarization separator utilizing the coherence of light. The first polymer layer 21 and the second polymer layer 22 are alternately laminated, and at least the second polymer layer 22 is thin enough to cause light interference.

Examples of preferable combinations of preferable polymers in consideration of the production method include acrylic and polycarbonate, acrylic and polystyrene, and polymethylpentene and polycarbonate.

The liquid crystal display device of the present invention will be described in detail below with reference to FIG.

A fluorescent lamp 1 (cold-cathode discharge tube) having a length corresponding to the length of the side surface of the light guide is closely attached to one side of the transparent light guide 3 (acrylic resin plate) which is an illuminating surface, and is attached to the inner surface. The lamp cover 2 provided with the reflector is provided to introduce the light emitted from the lamp into the light guide 3.

As described above, when the illuminating device is used for the direct-view type liquid crystal display element, the light distribution characteristic of the illumination light is extremely important. The directivity (angle distribution) of light propagating in the light guide 3 is
It is determined by the light distribution characteristics of the fluorescent lamp, the condensing characteristics of the reflector, the propagation characteristics of the light guide plate, and the like. In the propagation characteristics of the light guide, as described above, the function of sending the light incident from the end of the light guide to the inside of the light guide and the function of emitting the sent light in a predetermined direction are important. is there.

The function of sending the light incident from the end of the light guide to the inside of the light guide is determined according to the material used for the light guide and its interface reflection characteristics. That is, the liquid crystal display element 1 of the light guide 3
On the second side, light with an incident angle of a total reflection angle θ _c or more determined by the refractive index of the light guide 3 is totally reflected and propagates in the light guide 3, and light with an incident angle of a total reflection angle θ _c or less is generated. The light is refracted on the surface of the light guide 3 and is emitted to the liquid crystal display element 12 side. For example,
Air (n≈1.0) and transparent resin (for example, n≈1.0).
The total reflection angle θ _{c at} the interface of 5) is as shown in Expression 7, and incident light with an incident angle of 42.2 ° or less can be emitted from the illuminated surface of the light guide 3.

[0065]

[Equation 7]

Preferred transparent resins used for the light guide include acrylic, polycarbonate, polyurethane, polystyrene and silicone.

If a reflecting surface 5 such as an aluminum reflecting surface is formed on the surface of the light guide opposite to the liquid crystal display element, the reflected light is guided through 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 12 of the light guide 3.

On the other hand, if the incident angle of light on the light guide 3 is more than the total reflection angle θ _{c in} most cases, the amount of light emitted from the light guide will be small, so the total reflection condition is avoided. However, it is necessary to have a function of emitting light to the liquid crystal display element 12 side of the light guide plate 3. As means therefor, there are a method of forming a white light diffusing material on the surface of the light guide 3 and a method of forming a lenticular or prism Fresnel shape (microlens array, prism array, etc.) on the surface of the light guide.

In this case, the Fresnel shape may be formed on the surface of the light guide on the liquid crystal display element 12 side or on the opposite side. A Fresnel-shaped film-shaped plate may be placed on the surface of the light guide. When mounting, it is necessary that there is no air layer between the film and the light guide. For this reason, it is preferable to perform degassing after the bonding, or to bond using an adhesive having a refractive index equivalent to that of the film. Further, it is desirable that the refractive index of the film is almost the same as that of the light guide.

The polarization separator used in the present invention exhibits a strong polarization separation function for light having an incident angle (Brewster angle) within a specific range. Therefore, in order to improve the illuminance, it is desirable that the angle of light incident on the polarization separator has a maximum at the Brewster angle of the polarization separator, and that the light amount is concentrated substantially at that angle. Therefore, it is important to control the angle of the light emitted from the light guide.

In order to control the emission angle, the distribution of the white light diffusing material, the Fresnel shape (microlens array, prism array, etc.) of the lenticular or prism formed on the light guide surface can be adjusted. . For example, when the film of the prism array 13 made of the same component as the light guide is placed on the surface of the light guide, the maximum intensity of the light emitted from the light guide is approximately + 40 ° to + 80 ° and −40 °.
Concentrate on a curved range of -80 °.

Specifically, when a multi-layer structure in which flat bubble layers are dispersed in layers as described above is formed as the polarization separator 6, from the equation 1, the interface between the acrylic resin and the bubble layer is calculated. Has a Brewster angle θ _B of 33.7 °. Therefore, the light distribution characteristics of the fluorescent lamp should be set so that the incident light from the acrylic resin side to the multilayer structure is close to 33.7 °.
Only the p-polarized light component is emitted to the liquid crystal display element 12 side by optimizing the condensing characteristics of the reflector and the propagation characteristics of the light guide plate. On the other hand, the s-polarized component propagates in the light guide 3 as if it was totally reflected. The polarization characteristic of the polarization separator 6 has an effect that the incident light is sufficiently expressed even if the incident light deviates slightly from the Brewster angle condition. In this case, a light beam having an incident angle of 40 ° near the incident angle of 20 ° is obtained. On the other hand, although the extinction ratio of the s and p polarized components is slightly deteriorated, the polarized light separating action is remarkable.

The directivity of the light emitted from the polarization separator is not necessarily distributed 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. Rather, in the configuration as shown in FIG. 1, the outgoing direction of the light incident on the polarization separator at an incident angle near the Brewster's angle is usually concentrated in the splayed viewing angle range. For example, in a plane including the optical axis of light propagating in the light guide, −40 ° to −70 ° and 40 ° to 70 ° with respect to the vertical direction of the liquid crystal display element surface.
Only a small amount of light concentrates in the range of and reaches the viewing angle range of the observer. Therefore, this cannot be said to be a bright display.

For example, in FIG. 1, when the incident light from the acrylic resin side to the multilayer structure is 33.7 °, the exit angle of the multilayer structure is sin ^-1 ((sin 33.7 °) / n).
= 56.3 °. As described above, in order to convert the light distribution of the flat lighting device having the light distribution in the deviated viewing angle range (± 40 ° to ± 70 °) into the vertical direction of the illumination surface, the light exit side of the polarization splitter is included. In addition, it is effective to further provide an optical deflector. As the optical deflector, a microlens array or prism array having a lenticular shape or a Fresnel shape on the surface can be used.

In FIG. 1, a prism array 7 having a Fresnel shape on the surface is provided between the light guide body 3 in which the polarization separator 6 is laminated and the light incident side polarization plate 9 of the liquid crystal display element 12.
The case where the prism surfaces are arranged in parallel in the traveling direction of the light propagating inside is shown. That is, the prism array 7 is a columnar prism, and the cross section of the surface including the average optical axis of the light rays emitted in the planar light guide 3 is triangular. Depending on the shape and arrangement of the prism array 7 (whether the prism apex angle is on the light incident side or the light emitting side), only the refraction occurs on the incident surface and the exit surface of the prism and the case where total reflection occurs. Therefore, it is possible to control the orientation distribution direction of the emitted light. The optimum shape and arrangement may be determined from the finally required light distribution distribution direction and the light distribution distribution direction of the light emitted from the polarization separator.

For example, the cross-sectional shape has an apex angle of about 60 °.
The prism array 7 having an isosceles triangle is used and is arranged so that the apex angle faces the plane of the polarization separator. Thus, the light transmitted from the polarization separator at an emission angle of about 60 ° is incident from the side surface of the prism and is totally reflected on the other side surface, and then is emitted from the bottom surface of the prism to the liquid crystal display element side in the vertical incident direction. It Therefore, the light distribution azimuth of the light emitted from the polarization separator at an exit angle of about 60 ° can be converted into the light distribution azimuth perpendicular to the liquid crystal display element surface.

In this way, a linearly polarized plane illumination device for illuminating the liquid crystal display element in the vertical light distribution direction can be obtained. If the directivity of the light propagating in the light guide is high, the light distribution azimuth distribution of the light emitted from the flat lighting device will be concentrated in the vertical direction, and the range of the viewing angle corresponding to bright display will be narrowed. It may be too much. In such a case, an optical element such as a diffuser plate 8 which deteriorates directivity can be arranged between the liquid crystal display element and the deflecting means such as the prism array described above.

Further, in order to deteriorate the directivity of the light propagating in the light guide, the reflecting surface 5 formed on the side of the light guide 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. As described above, in the case of a polarization separator having a structure in which flat bubble layers are dispersed in a layer in a homogeneous plastic, the interface shape of the bubble layers is random and a fine uneven structure is likely to occur, so light diffusion The effect is easily exhibited at the same time.

Although FIG. 1 shows the case where the multi-layer structure is formed on the surface of the light guide, it does not necessarily have to be formed on the surface of the light guide and may be located inside the light guide.

In the present invention, in order to efficiently obtain the linearly polarized light from the planar illuminating device, the s-polarized light reflected by the multilayer structure and pulled back into the light guide is efficiently p-polarized while propagating in the light guide. It is important to convert it into light containing components and reuse it. Although there are various methods for converting s-polarized light into light containing a p-polarized component, representative examples will be described below.

It is generally known that when linearly polarized light is obliquely incident on a metal surface and reflected, the linearly polarized light becomes elliptically polarized light according to the optical physical constants (refractive index n, absorption coefficient k) of the metal. ing. That is, even if the s-polarized light is incident, the p-polarized component is generated in the reflected light. Therefore, in the present invention, when the reflecting surface 5 formed on the surface of the light guide 3 on the side opposite to the liquid crystal display element 12 is a metal such as aluminum, a part of the s-polarized light is reflected every time the reflecting surface 5 is reflected. Are converted into p-polarized light.

Another method is to use a retardation plate made of a translucent polymer material. For example, by disposing this retardation plate 4 having an appropriate film thickness between the reflection surface 5 of the light guide 3 and the polarization separator 6, the s-polarized light reflected by the polarization separator becomes elliptically polarized light. It is possible to convert a part of it into p-polarized light. FIG. 1 shows a configuration example in which the retardation plate 4 is brought into close contact with the reflection surface 5 provided on the light guide 3 to efficiently perform polarization conversion. Further, the retardation plate 4 may be arranged between the polarization separator 6 and the light guide plate 3.

In FIG. 2, as the polarization separator, a polarization separator in which one layer of a dielectric film is formed on one surface of the planar light-transmitting support is used to avoid the total reflection condition of the light guide. This is an example using a prism array 13 for emitting light to the liquid crystal display element side. Reference numeral 6a is a planar translucent support, and 6b is a dielectric film. Since other configurations are almost the same as those in FIG. 1, the same parts as those in FIG. 1 are denoted by the same reference numerals in FIG. 2, and the description thereof will be omitted.

As described above, the polarization separator may have a structure different from that of the light guide, but may have a single structure.
For example, a polarization separation layer such as a dielectric interference film is formed on the surface of the light guide. The interfaces between the light guide, the outside of the light guide, and the dielectric interference film exhibit the same effect as that of the polarization separator. In order to increase or equalize the amount of light emitted from the light guide,
When the structure of the light guide is a prism array or the like, a dielectric interference film may be formed on the surface of the prism array.

FIG. 3 shows such an example. A prism array shape is formed on the surface of the light guide 3, and a dielectric film 6c is further formed. A polarized light separating function is exhibited at the interface between the light guide and the dielectric film. Since other configurations are almost the same as those in FIG. 1, the same parts as those in FIG. 1 are denoted by the same reference numerals in FIG. 3, and the description thereof will be omitted.

[0086]

EXAMPLES [Examples 1 to 3] Examples of the present invention will be described with reference to FIG. An edge light in which a fluorescent lamp 1 (cold-cathode discharge tube) is closely attached to one side of a transparent acrylic resin plate light guide 3 which is an illuminated surface, and a lamp cover 2 made of a reflector is provided to introduce light into the light guide. The polarization separator 6 composed of a multilayer structure was combined in the mold backlight.

As the fluorescent lamp 1, cold cathode discharge tubes of 10 W and 16 W having a length corresponding to the side length (152 mm) of the 10-inch liquid crystal display surface and having a small tube diameter were used. Further, as the lamp cover 2, a cylindrical or elliptic cylinder-shaped reflecting mirror that surrounds the cold cathode discharge tube is used.
Is a translucent light guide plate made of acrylic resin (n = 1.4
In 9), the size used was 160 mm × 220 mm × 5 mm.

Further, the retardation plate 4 was provided on the side surface of the light guide facing the back surface of the light guide 3 and the fluorescent lamp installation surface, and the reflection surface made of an Al metal reflection film was formed thereon. The multilayer structure of the polarization separator 6 has a height in the thickness direction of 10 μm in a homogeneous transparent plastic plate (n≈1.5).
A structure in which flat bubble layers having a radius of about several mm are dispersed in a layered form of about 5 layers is mounted on the light emitting surface side of the light guide 3.

As the prism array 7, an isosceles triangular prism array having a vertical cross section of 58 ° is used.
The apex angle was arranged so as to face the polarization separator 6. The thickness of the prism array plate was 2 mm and the pitch of the prism array was about 1 mm. Further, a diffusion plate 8 was used on the light emitting surface side of the prism array 7 to widen the viewing angle.

The liquid crystal cell 11 is a TFT driven TN.
As the liquid crystal, an RGB color TFT drive TN liquid crystal display cell having a VGA compatible pixel number was used.

As the incident side polarizing plate 9, a usual light absorbing type organic polarizing plate was used. If the required contrast ratio is about 10: 1, the polarizing plate may not be used, and only the multilayer structure may be sufficient. However, in this case, since the extinction ratio of polarized light is low (about 10: 1, for example, about 1000: 1 for a light-absorption type organic polarizing plate), a TFT drive requiring a contrast ratio of 100: 1 or more is required. A liquid crystal TV requires an incident side polarization plate. At this time, the polarization axis of the light-absorbing organic polarizing plate is set so that the p-polarized light emitted from the multilayer structure has the maximum transmittance and the polarization axis of the emitted light of the polarization separator 6 and the polarization axis of the polarizing plate 9 are the same. Matched.

A light-absorption type organic polarizing plate was similarly used for the emitting side polarizing plate 10. The direction of the polarization axis is appropriately selected depending on the display mode (normally white, normally black),
In this embodiment, normally white display is performed, and the polarization axis of the polarizing plate 10 on the exit side is set in the direction in which the polarization axis is rotated by 90 ° with respect to the polarization axis of the polarizing plate 9 on the entrance side.

The characteristics of the light source and the light guide are changed variously to adjust the power consumption of the lamp and the brightness of the vertical visual field.
~ 3 was done. Table 1 shows a comparison between this and the conventional example.

[0094]

[Table 1]

In Example 1, the brightness is 1.5 as compared with the conventional example.
Not only has it doubled, but the viewing angle range has not been limited. In Example 2, the brightness and the viewing angle were almost the same as those of the conventional example, but the lamp power consumption was reduced to 2/3 and the battery drive time was extended. In Example 3, the power consumption of the lamp and the vertical brightness were the same as those of the conventional example, but the viewing angle was widened.

As described above, various light distributions can be obtained according to the contrast ratio curve of the liquid crystal display element used. In particular, it is possible to selectively increase the brightness of the vertical visual field.

[Embodiments 4 to 6] Another embodiment of the present invention will be described with reference to FIG. A fluorescent lamp 1 (cold cathode discharge tube) is closely attached to one side of a transparent acrylic resin plate light guide 3 which is an illumination surface, and a lamp cover 2 made of a reflector
An edge light type backlight was used in which light was introduced into the light guide body.

As the fluorescent lamp 1, 2 W and 4 W cold cathode discharge tubes having a tube diameter (3 mm) and a length corresponding to the side length (120 mm) of a general-purpose notebook computer were 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 3 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, the retardation plate 4 was provided on the side surface of the light guide facing the back surface of the light guide 3 and the fluorescent lamp installation surface, and the reflection surface made of an aluminum metal reflection film was formed thereon. The retardation plate was a quarter-wave plate.

As the prism array 13, an isosceles triangular prism array having an apex angle of 160 ° was used, and the prism array was arranged so that the apex angle faces the polarization separator 6. The prism array plate is 2 mm thick and the prism array pitch is about 1 m.
m. The prism array 13 and the light guide 3 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, was used between the prism array 13 and the light guide 3.

As the polarization separator 6, titania oxide (TiO 2) was formed on the surface of a homogeneous glass substrate (n = 1.52) 6 b.
₂ : n = 2.35) A further film 6a was formed and mounted on the light emitting surface side of the light guide 3. The separation angle of this polarization separator is 72 °
Became.

As the prism array 7, an isosceles triangular prism array having an apex angle of 60 ° is used, and the apex angle is arranged so as to face the polarization separator 6. The thickness of the prism array plate is 2 mm and the pitch of the prism array is about 1
mm. Further, a diffusion plate 8 was used on the light emitting surface side of the prism array 7 to widen the viewing angle.

As the liquid crystal display element 12, a monochrome display STN liquid crystal display cell in which films having birefringence are laminated is used. The twist angle is 240 °.

As the incident side polarization plate 9, a usual light absorption type organic polarization plate was used. At this time, the polarization axis of the light-absorbing organic polarizing plate and the polarization axis of the polarizing plate 9 are set so that the p-polarized light emitted from the polarization separator has maximum transmittance. Matched.

A light-absorption type organic polarizing plate was similarly used for the emitting side polarizing plate 10. Although the orientation of the polarization axis is appropriately selected, in this embodiment, the polarization axis of the polarizing plate 10 on the exit side surface is set in the direction in which the polarization axis is rotated by 85 ° with respect to the polarization axis of the incident polarizing plate 9.

The characteristics of the light source and the light guide are variously changed to adjust the power consumption of the lamp and the brightness of the vertical visual field.
~ 6 was done. Table 2 shows a comparison between this and a conventional example having no polarization separator.

[0107]

[Table 2]

In Example 4, the brightness is 1.5 compared with the conventional example.
Not only is it doubled, but the viewing angle range is not tight. In Example 5, the brightness and the viewing angle were almost the same as the conventional example, but the lamp power consumption was reduced to 2/3 and the battery drive time was extended. In Example 6, the power consumption of the lamp and the brightness in the vertical direction were the same as those in the conventional example, but the viewing angle was widened.

As described above, it is possible to obtain various light distributions according to the contrast ratio curve of the liquid crystal display element used. In particular, it is possible to selectively increase the brightness of the vertical visual field.

[Embodiment 7] Description will be given with reference to FIG. The surface shape of the light guide 3 is a prism array. Thin films of ZrO ₂ and SiO ₂ were alternately formed on the surface in three layers. Specifically, on the light guide, ZrO ₂ , SiO
₂ and ZrO ₂ are formed in this order, and the polarization degree at the separation angle is 5
The maximum value was set near 30 nm. The light guide and the dielectric interference film are integrated. The vertical angle of the prism array of the light guide 3 was set to 160 °. At this time, the direction of the light emitted from the dielectric interference film has a spread with respect to the direction perpendicular to the surface of the light guide, so that the apex angle is further directed in the direction opposite to the light guide. The prism array was installed. The configuration other than that described above is the same as that of the fourth embodiment. At this time, Example 1
The brightness was slightly higher than that of. It is considered that this is because the interface in Example 7 was reduced and the interface reflection was reduced. Further, the integral molding enables the thickness to be reduced as compared with the fourth embodiment. It also has the advantage of lower costs in mass production.

[Embodiment 8] A laminate of 400 layers of acrylic and polycarbonate was used as a polarization separator in the same form as in FIG. The brightness in the vertical direction is improved by about 1.5 times as compared with the case where the polarization separator is not used.

[0112]

According to the present invention, it is possible to obtain an illuminating device for a direct-view type display element in which the illuminance is particularly high in a specific high contrast ratio region. In particular, in the present invention, unlike the case where the prism array or the like is used alone, of the light in the desired viewing direction, by polarization-converting the light that does not substantially contribute as the illumination light of the display device as it is, Improving the illuminance for a desired viewing direction. Therefore, it is possible to obtain an illumination device having a high illuminance in a specific direction while maintaining a wide illuminance distribution. This is an optimal illuminating device for a direct-viewing type display element having a wide viewing angle.

Furthermore, by using a so-called edge light type light source as the light generating means, it is possible to easily obtain diffused light suitable as illumination light for a direct-view type display element. In addition, in particular, the polarization converting means is used in combination with the polarization splitting surface provided on the light emitting surface side of the light guide of the edge light and the light reflecting surface provided on the side opposite to the light emitting surface of the planar light guide. If configured to work, the light guide for the edge light will also be used as a space for polarization separation. Therefore,
It is even more desirable to have a very compact configuration.

Further, the illuminating device of the present invention is arranged on the back surface of the liquid crystal display element so that the polarization axis direction of the light beam emitted from the illuminating device and the polarization axis direction of the light incident side of the liquid crystal display element are substantially aligned with each other. It is possible to obtain a direct-viewing liquid crystal display device with a practical viewing angle, high illuminance, and low power consumption.

[Brief description of drawings]

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

FIG. 2 is a sectional view showing another embodiment of the present invention.

FIG. 3 is a sectional view showing another embodiment of the present invention.

FIG. 4 is a sectional view showing the configuration of a polarization separator used in the present invention.

FIG. 5 is a graph showing a contrast ratio curve of an STN liquid crystal display device.

[Explanation of symbols]

1: Fluorescent lamp 2: Lamp cover 3: Light guide 4: Retardation plate 5: Reflective surface 6: Polarization separator 7: Prism array 8: Diffuser 12: Liquid crystal display element

Continued front page    (72) Inventor Masao Ozeki             1150 Hazawa-machi, Kanagawa-ku, Yokohama-shi, Kanagawa             Asahi Glass Co., Ltd. Central Research Laboratory (72) Inventor Hiroaki Ito             3-474 Tsukakoshi 3-chome, Kawasaki City, Kanagawa Prefecture               Asahi Glass Co., Ltd. Tamagawa branch room F-term (reference) 2H091 FA07X FA07Z FA21Z FA29Z                       FA41Z FB02 FB06 KA01                       KA10 LA12 LA16 LA17 LA30

Claims (7)

[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 exit surface side of the planar light guide, A polarization splitting surface 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 light exit surface on the side opposite to the light exit surface of the planar light guide is substantially An illumination device for a direct-view display element, comprising: a light-reflecting surface provided in parallel. 2. The illumination device according to claim 1, wherein the polarization splitting surface is a multilayer structure in which a translucent medium having a relatively large refractive index and a translucent medium having a relatively small refractive index are alternately laminated. A lighting device for a direct-view type display device, which comprises a body. 3. The direct-view type illumination device according to claim 1, wherein the polarization splitting surface is formed by providing at least one dielectric thin film having a thickness equal to or less than a visible light wavelength on a transparent support. Lighting device for display device. 4. The illumination device for a direct-view type display device according to claim 1, wherein one or more dielectric films each having a polarization separation surface with a thickness of 1000 nm or less are formed. . 5. A main polarization axis direction of a light beam emitted from the illuminating device and a polarization axis direction of a polarizing plate on the light incident side of the liquid crystal display device are substantially aligned with each other, and the polarization axis direction of the polarizing plate is substantially the same. A liquid crystal display device, wherein an illuminating device is arranged on the back surface of a direct-viewing type liquid crystal display element. 6. A light deflecting means for deflecting a direction of a light ray having a maximum light intensity in a light distribution direction between the polarization splitting surface and the liquid crystal display element in a direction substantially perpendicular to the display surface of the liquid crystal display element. The liquid crystal display device according to claim 5, further comprising: 7. A planar light generating means for generating diffused light containing a first polarized light component and a second polarized light component having a polarization direction perpendicular to the first polarized light component, and an optical path of light generated from the light generating means. The first polarized light component is selectively emitted with respect to a light beam in the vicinity of the light distribution direction having the maximum brightness, and at least a part of the second polarized light component is polarized and converted into the first polarized light component. An illumination device for a direct-view type display device, comprising: a polarization conversion unit that emits light.