JP2001228474A - Light transmission body and back light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means to realize a function of a polarized light separating plate and light transmission body used for enhance the display luminance of a liquid crystal display element by the single light transmission body, by using efficiently an illuminating light ray being made the incident on a light transmission body in a back light. SOLUTION: In the plate-like light transmission body consisting of the transparent solid material composing the back light of the liquid crystal display element, the fine ruggedness having the polarized light separation is formed in a light-emitting surface, and the prism-like ruggedness to reflect the light from a light source is provided in the surface opposed to the light-emitting surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide constituting a backlight of a liquid crystal display device, and more particularly to a lighting technique for improving display characteristics of the liquid crystal display device.

[0002]

2. Description of the Related Art A transmissive liquid crystal display device is frequently used as a monitor for a personal computer, a display device for a portable terminal, a thin TV, or the like. In such a liquid crystal display device, a planar liquid crystal device is usually provided on the back of a liquid crystal element. A lighting device or backlight is provided. This backlight has a function of converting a linear light source such as a cold cathode discharge tube or a linearly arranged point light source such as a light emitting diode array into planar light. Specifically, a typical backlight is a method in which a linear light source is provided at a side end of a liquid crystal element and planar light is obtained using a light guide such as an acrylic plate (side light method).
An optical element formed of a prism array or the like is provided on the light emitting surface to obtain desired optical characteristics. The sidelight method is disclosed in, for example, JP-A-61-99187 and JP-A-63-62104. In order to more effectively bring out the general characteristics of a liquid crystal display device, which is lightweight and thin, it is preferable to use a sidelight method that can make the backlight device thin. Liquid crystal display devices such as portable personal computers in recent years are preferable. , A sidelight type backlight is often used.

The most important performance required for a backlight for a liquid crystal display element is luminance. With the recent improvement in the performance of liquid crystal elements, a demand for higher luminance for the backlight is increasing. For example, in a transmission type full-color liquid crystal element, the definition is advanced, and generally the light transmittance of the display element itself is reduced, so that the luminance required for the backlight is necessarily increased. In addition, since a notebook personal computer or a portable personal computer called a mobile terminal is used with a battery power source, it is necessary to ensure sufficient luminance with low power consumption for its backlight. In order to respond to these demands, in the backlight using the sidelight method, a sheet made of a prism array or the like is frequently used, and the emitted light is effectively used by securing the front luminance by an optical condensing action. Although these methods have been generally used, the frequent use of these materials not only causes a large increase in cost but also causes adverse effects such as narrowing of the viewing angle characteristics. The emergence of a technology for providing a high-brightness backlight has been awaited. The following ideas that meet this requirement are known. That is, this is a method in which light emitted from the backlight is converted into partially polarized light.

A general liquid crystal element has the following restrictions on display luminance due to the principle of using a twisted structure of liquid crystal. In other words, in order for the liquid crystal element to have a function of a minute optical shutter for controlling the amount of light for each display pixel, minute electrodes and color filters are arranged inside the substrate such as glass for enclosing the liquid crystal, and outside the substrate. A polarizing plate is bonded to the polarizing plate.This polarizing plate has the property of transmitting an electric field vibration component in a certain reference plane and absorbing a light component having an electric field vibration plane in a direction perpendicular to the reference plane. The principle is that at least half of the total amount of natural light emitted from the light is absorbed by the polarizing plate.
In order to overcome this limitation, it is effective to use light emitted from the backlight as partially polarized light.

That is, there is known a method in which a polarized light separating plate is disposed between a polarizing plate on a lower substrate of a liquid crystal panel and a light guide plate on a backlight side so that emitted light is partially polarized. The polarized light separating plates have vibration surfaces orthogonal to each other.
One of the two polarized light components (here, P-polarized light and S-polarized light) is provided for direct emission and use, and the other is returned to the backlight side for reuse as light source light. The brightness of the liquid crystal display device can be increased. For example, see the monthly display June 1997 p.
82 discloses a liquid crystal display device as shown in FIG. This liquid crystal display device includes a diffusion plate (not shown) and a lens plate (not shown) on the light emitting side of a light guide 101 of a backlight including a linear light source 104, a reflector 105, a light guide 101, and a reflection plate 106. Not shown) and the polarization separator 10
8, and a liquid crystal display element 110 having a polarizing plate 107 is provided thereon.

[0006] Regarding the technology using the above-mentioned concept of reusing the linearly polarized reflected light, many elements having a similar configuration have been proposed for the purpose of improving the polarization separation efficiency or the display characteristics. These are described in JP-A-6-250169, JP-A-6-265892, JP-A-6-337413, JP-A-7-204466, JP-A-7-49496, JP-A-7-64085, and JP-A-7-72475. JP-A-8-271892, JP-A-9-146092, JP-A-9-288274, JP-A-10-20310, JP-A-10-48628, JP-A-10-293212
JP-A-10-319393, JP-A-11-133
409, JP-A-11-142849, JP-A-11-142
No. 149074, JP-A-11-96819, and the like, and monthly display June, 1997, p.
81 discloses a liquid crystal display device as shown in FIG.

This liquid crystal display device is composed of
08 is characterized in that it is a circularly polarized light separating function instead of a linearly polarized light separating function. In the case of this configuration, by providing the quarter-wave plate 109 above the polarization splitting plate 108, it can be converted into elliptically polarized light that is close to linearly polarized light. (Not shown)
By adjusting the major axis of the ellipse to, it is possible to increase the luminance of the liquid crystal display device on the same principle as described above. A number of devices having a similar configuration have been proposed for a technology that uses the concept of reusing circularly polarized reflected light. These are disclosed in JP-A-8-2.
71837, JP-A-9-304770, JP-A-10
-54909, JP-A-10-142407, JP-A-10-197722, JP-A-10-206636,
JP-A-10-232313, JP-A-10-25393
0, JP-A-10-293221, JP-A-10-30
1097, JP-A-10-319235, JP-A-10-319235
-321,025, JP-A-10-321026, JP-A-10-339812, JP-A-11-64841,
JP-A-11-125717, JP-A-11-13323
No. 1, JP-A-11-160539 and the like.

[0008]

However, in the prior arts described above, since the light guide plate itself does not have a polarization separation function, a component having a polarization separation function such as a polarization separation plate (for example, two types having different refractive indexes). In combination with a multilayer film in which transparent materials are alternately laminated. This means that as long as the intention is to reuse reflected polarization,
This means that an increase in the number of parts cannot be avoided, which is contrary to the demand for liquid crystal display devices from the market, which is further reduced in weight, thickness, and cost. The increase in the number of parts has a negative effect on the manufacturing side because it leads to a decrease in display quality.

For example, it is not easy to control the gap between the components, and if the uniformity of the distance between the components is disturbed, display unevenness is caused. As a result, there is a problem that the yield is low. The present invention has been made to solve such problems of the prior art, and an object of the present invention is to efficiently use an illumination light beam incident on a light guide to achieve an improvement in display brightness of a liquid crystal display device. An object of the present invention is to provide the light guide with both functions of polarization separation and light guide emission used for the light guide. If this object is achieved, it is possible to reduce the weight and thickness of the backlight, and it is also possible to improve the yield by facilitating the assembly process.

[0010]

The gist of the present invention is to provide a plate-like light guide made of a transparent solid substance constituting a backlight of a liquid crystal display element, and a light exit surface of the plate-like light guide having a polarization separating function. The light guide is characterized in that the unevenness is formed, and the surface facing the emission surface is provided with prismatic unevenness for reflecting the light from the light source in the direction of the emission surface. Furthermore,
One of the aspects is that the fine unevenness is an aggregate of substantially parallel fine linear ribs formed on the emission surface. Further, the pitch of the linear ribs is 0.1 to 2 μm.
m, the average opening width is 0.05 to 1.5 μm, the rib height is 2 to 8 times the average opening width, and the substance forming the light guide has a refractive index of 1.34 to 1.71, A transparent polymer compound is one of the embodiments. Further, a backlight for a liquid crystal display device, which comprises the light guide of the above-described gist and a light source for supplying light to the light guide, is also included in the gist of the present invention. One.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific examples of the light guide of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing a preferred embodiment of the present invention. On the upper emission surface of the light guide 101, fine unevenness 102 having a polarization separation function is formed. In addition, prism-shaped irregularities 103 that reflect the light incident from the light source in the direction of the emission surface are arranged on the facing surface. In general, when dimensions such as width and depth of fine irregularities are sufficiently large compared to the wavelength of incident light, catadioptric phenomena based on geometrical optics are observed, but these dimensions are equivalent to wavelength. In this case, the reflection and refraction phenomenon based on the geometrical optics is not observed, and the characteristic as the wave of the light appears strongly, and the diffraction phenomenon as a result of the interaction with the medium transmitting the light is observed. In the present invention, the width and depth of the fine irregularities are substantially equal to the wavelength range of visible light, thereby causing the latter diffraction phenomenon and controlling the polarization separation function as a result of superposition of a plurality of diffracted lights. Things. First, the polarization separation function of the fine unevenness 102 formed on the upper emission surface of the light guide will be described with reference to FIG.

Since a normal light source is non-polarized light, light transmitted through the light guide is also non-polarized light. This means that the intensity of the electric field vibration component in a certain plane of the light and the intensity of the electric field vibration component orthogonal thereto are statistically equal. When the unpolarized light travels upward from below and reaches the fine uneven portion 102 having the polarization separation function, some light is emitted and the remaining light is reflected. In both the emitted light and the reflected light, an intensity difference occurs between an electric field vibration component (hereinafter, P component) in a certain reference plane perpendicular to the emission surface and an electric field vibration component orthogonal to the electric field vibration component (hereinafter, S component). . This difference in intensity depends on conditions such as the wavelength of incident light, the size of fine irregularities, and the refractive index of the medium. Under certain conditions, the P component is strong and the S component is weak, but under other conditions, this intensity difference may be reversed.

In FIG. 2, light is separately shown as a P component and an S component, and the P component represents a state when the S component is emitted strongly and the S component is emitted weakly. That is, as shown in FIG. 2, when the fine unevenness 102 is formed of substantially parallel ribs (linear ribs) having a certain height (a deep groove depth),
The light (P component) of the wave in the direction parallel to the longitudinal direction of the rib is converted into diffracted light emitted from the transparent body having a smooth surface into the air as a result of the interaction with the unevenness, and is perpendicular to the longitudinal direction of the rib. The light (S component) of the wave in the direction is converted into diffracted light which is mostly reflected in the interaction with the unevenness, and the light guide 10
It returns to 1 and the emitted light becomes small.

Therefore, the emitted light is polarized light mainly composed of components in the direction parallel to the longitudinal direction of the ribs forming the fine irregularities 102. The light that has been reflected and returned to the light guide 101 is light that is repeatedly reflected in the light guide due to the prismatic irregularities 103 or the like, or the light that has been emitted from the light guide to the outside and the reflection plate 1
06 or as a result of being reflected by the reflector 105 and entering the light guide again, the light again travels toward the emission surface, and the P wave is emitted light and the S wave is reflected light. This is repeated, and the polarized light becomes the emitted light.

In the above description, the emitted polarized light is described as the P component. However, if the configuration of the rib is changed, light of a wave (S component) in the direction perpendicular to the longitudinal direction of the rib can be used as the emitted light. is there. The form of the fine unevenness 102 is an aggregate of substantially parallel fine linear ribs. This aggregate does not necessarily need to be formed uniformly over the entire exit surface. Further, the rib may have a discontinuous surface. FIG. 3 shows an example of the aggregate. 3A shows an example of parallel continuous ribs, FIG. 3B shows an example of parallel discontinuous ribs, FIG. 3C shows an example of parallel staggered ribs, FIG. 3D shows an example of domain type ribs, and FIG. Others
Depending on the application, the ribs can be arbitrarily designed, such as non-parallel ribs, aggregates with different directions. In addition, the light amount and the polarization wavelength can be adjusted by changing the width of the rib or the width of the groove stepwise, or by changing the height of the rib (depth of the groove) stepwise.

In the case of a set of substantially parallel fine linear ribs, the plane of maximum intensity polarization of emitted light can be determined by the direction in which the ribs extend. It is preferable that the linear rib and the substrate are substantially integral and have no optical interface. That is, the linear ribs are desirably formed directly on the base material. The form of the fine unevenness 102 is an aggregate of substantially parallel fine linear ribs, and the cross section thereof is substantially polygonal. This approximately polygon
The shape is preferably a substantially rectangular or substantially trapezoidal shape, but does not indicate a strict geometric polygon, but also includes a shape having smooth corners without vertices and a shape having curved sides.

FIG. 4 shows an example of the cross-sectional shape. Rectangle (a), triangle (b), trapezoid (c), semicircle (d), rectangle without corners (e), waveform (f), saw blade (g), inverted semicircle (h),
It can be arbitrarily designed such as a step type (i). From the viewpoint of facilitating design and manufacturing, it is preferable that the aggregate of the ribs has the same cross-sectional shape, and the ribs are preferably arranged at a constant period. Since the polarization splitting function strongly depends on this spatial arrangement, some vocabulary is defined here below to illustrate the preferred rib arrangement of the present invention. Pitch 203: one cycle distance of the rib arranged on the base material surface. Groove 202: Space between adjacent ribs. Opening width: The width of the groove in a plane parallel to the substrate surface. In a cross-sectional shape other than the rectangle (a), the opening width changes depending on the height from the substrate surface. Maximum opening width 204: The maximum value of the opening width. In most cases,
The opening width at the top of the groove. Minimum opening width 205: The minimum value of the opening width. In most cases,
The opening width at the bottom of the groove. Rib height 206: the distance from the substrate surface to the top of the rib. Average opening width: A simple average value of the maximum opening width 204 and the minimum opening width 205. Aspect ratio: A value obtained by dividing the rib height 206 by the average opening width.

Hereinafter, a preferred rib arrangement will be described. The pitch 203 is preferably 0.4 to 2 μm,
１1 μm is more preferable. For convenience of rib production, it is preferable that the opening width is larger as it goes upward and smaller as it goes below.
The average opening width is preferably 0.2 to 1.5 μm, and 0.2 μm
m to 0.8 μm is more preferable. The aspect ratio is preferably from 0.5 to 10, preferably from 1.5 to 10, and more preferably from 2.5 to 10. Optimization of these spatial arrangements can be implemented using the following concept. That is, consider a steady state in which an infinite number of electromagnetic waves travel in the transparent solid material and reach the fine irregularities. An infinite number of electromagnetic waves form a specific resonance state due to the structural factors of the micro-concave region.

In order to interpret this state, the state is represented as a superposed (coupled wave) of spatial harmonic waves (plane waves), and is described by Maxwell's equation for electric field vibration. In this equation, diffraction efficiency is a function of the linear solid height, rib width, groove width transparent solid material dimension, transparent solid material refractive index, and incident light wavelength. actually,
Diffraction efficiency can be obtained by solving a simultaneous differential equation set based on the phase matching conditions in the transparent solid material, the fine concave region, the boundary of each region of gas or vacuum with a computer. FIG. 5 shows a calculation example according to this method.

This is because the cross section of the linear rib is rectangular,
The relationship between the rib height / incident light wavelength ratio and the transmittance of the P component and the S component when the pitch is 1.0 μm and the opening width is 0.5 μm is shown. For example, when the rib height is 3.1 times the wavelength, the transmittance of the P wave is about 80% and the transmittance of the S wave is about 30%. The liquid crystal element has a structure in which a polarizing plate is attached to the outside of a substrate such as glass for enclosing liquid crystal, and the polarizing plate transmits an electric field vibration component in a certain reference plane and is an electric field vibration component orthogonal to the reference plane. Therefore, by matching the maximum intensity polarization plane of the light emitted from the light guide with the reference plane of the polarizing plate, at least 50% or more of the total emitted light amount can be guided to the liquid crystal element.

Next, the prism-shaped unevenness 103 formed on the surface opposite to the emission surface will be described with reference to FIGS. The prismatic irregularities 103 enter a part of the light guide 101 from the light source 104 disposed at the end of the light guide 101 and partially reflect light that is totally reflected and penetrates the entire light guide 101. Is formed for. As a concept, specular reflection on an optical surface according to geometrical optics is used. Therefore, in designing the uneven shape, it is necessary to consider the optimum tilt angle, area, and arrangement of the mirror surface, which is obtained from the traveling angle distribution of the light that enters the light guide from the light source and is totally reflected. In order to control the light intensity uniformity in the light exit surface, prism-shaped irregularities 103 are used.
Is adjusted.

Referring to FIG. 1, the apex angle θ is 50 to
70 degrees, preferably 55-65 degrees or 110-130
Degrees, preferably about 115 degrees to 125 degrees. The position is at least in the range and area from the vicinity of the linear light source to the end opposite to the light source (the prism-shaped unevenness 10 with respect to the area of the light guide plate).
The area of the lower side where 3 is in contact with the light guide plate) is 50 to 90%, preferably 75 to 80%, of the area of one surface (reflection surface) of the light guide plate. It is preferable to arrange the density close to the light source densely as the distance from the light source increases, and the density is 100%, the central part is 60%, and the density near the light source is 25%.
% Is preferable in order to obtain a uniform light emission amount over the entire surface. Also, the apex angle θ of the prismatic irregularities 103
The angle α facing the light source side of the apex angle bisecting line A bisecting the above is 85 to 90 degrees, preferably about 87 to 89 degrees.

FIG. 8 shows an example of the shape of the prism-shaped unevenness 103.
As shown in (a) to (d), a linear V-shaped groove or a V-shaped convex rib parallel to the light source, a cone-shaped pit or a cone-shaped dot independent of each other, or a pyramid-shaped dent or pyramid-shaped Examples include, but are not limited to, dots. As a method of forming the prismatic irregularities 103, this inverted shape is formed in a mold, and this shape is transferred and formed at the time of molding the light guide 101, by mechanical cutting or sandblasting. The light guide 101 may be provided with irregularities, or the light guide 101 may be provided with irregularities by a chemical etching process. However, the present invention is not limited thereto. Normally, the light guide 101 of the sidelight type backlight has a total reflection at the emission surface and its opposite surface in order to penetrate light from the light source 104 incident from the light guide 101 side end into the entire light guide 101. Although the phenomenon is used, it is supplemented that the total reflection phenomenon can be used in the light guide. First, the fine uneven portion 102 having the polarization splitting function on the emission surface exhibits the total reflection phenomenon equivalent to the two-layer structure as shown in FIG. 7 because the uneven size is the same level as the wavelength of light.

On the other hand, on the opposite surface, the prismatic irregularities 1
A total reflection phenomenon occurs in a portion where 03 is not formed. By providing the prismatic irregularities 103 in a coarse and dense manner, the amount of emitted light can be adjusted. Therefore, the light guide 101 can be suitably used for an ordinary sidelight type backlight. The light guide 101 has a refractive index of 1.34 to 1.71.
Of a transparent polymer compound. As the transparent polymer compound, an acrylic resin obtained by polymerizing from a monomer selected from polyhydric acrylate, polyhydric methacrylate, monoacrylate, and monomethacrylate, or a polycarbonate resin, a polyester resin, or a cyclic polyolefin resin is preferable. Used for As a molding method of the light guide 101, a precision solid cutting of a transparent solid material, a laser cutting, or a transfer method using a precision stamper to which fine irregularities are transferred by photolithography can be used, but the method is not limited thereto.
The present invention can be implemented in a sidelight type backlight form as shown in FIG.

FIG. 6 is a cross-sectional view showing a state in which the light guide according to claims 1 to 4 is incorporated in a backlight. The situation in which light rays entering the light guide are emitted will be described with reference to FIG. Linear light source 104 disposed at the side end of the light guide
The non-polarized light emitted from the light enters from the side end and travels to the side while being totally reflected in the light guide. In the process, the light incident on the prismatic irregularities 103 goes upward and reaches the fine irregularities 102. Part of the light (P-polarized light) that has reached the fine irregularities 102 is transmitted upward and emitted, and the other light is emitted from the light guide 101.
It is reflected downward without exiting from. Both are partially polarized light having a plane of maximum intensity polarization as described above. The maximum intensity polarization plane of the light transmitted and emitted upward is defined as a P polarization plane.
Partially polarized light (mainly S-component polarized light) that is reflected downward and reaches the lower surface of the light guide plate 101 is reflected under an angle condition that allows total reflection within the light guide when the prismatic irregularities 103 are present at the arrival position. .

On the other hand, the light that has reached the portion without the prismatic irregularities 103 exits below the light guide, is reflected by the reflector 106, reenters the light guide 101, and travels upward. The polarization plane rotation behavior of the reflected light depends on the reflection surface composition and shape. For example, in the case of the reflection plate 106 having a silver vapor-deposited surface, the polarization plane rotates by a certain angle, but when the reflection plate 106 is formed of foamed polyethylene terephthalate, it rotates almost completely randomly. Therefore, the light reflected by the fine irregularities 102 passes through the lower surface of the light guide 101 again and then returns to the fine irregularities 10.
When it reaches No. 2, it is unpolarized light or partial polarized light whose maximum intensity polarization plane has changed. Therefore, since this light has an increased P-polarized plane component transmitted through the fine unevenness 102, it is guided to the liquid crystal element and contributes to an increase in the amount of light for effective illumination.

On the other hand, the light reflected by the fine irregularities 102 again travels to the lower surface of the light guide, but by repeating the same reflection and rotation of the polarization plane as described above, contributes to an increase in the P-polarization plane component of the emitted light. When the reflection on the fine irregularities 102 is repeated infinitely many times, the light amount utilization rate converges to a certain value, but this is because there is a loss of incidence and incidence on the lower surface of the light guide plate 101,
It is about 75%. It is desirable that the in-plane luminance distribution of the backlight is small. In the related art, fine adjustment has been performed while checking the arrangement of the diffuse reflection means formed by printing white ink or the like on the actual product. In the backlight, similar effects can be obtained by finely adjusting the arrangement of the prismatic irregularities.

[0028]

The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the present invention. Example 1 A 3 mm thick cast plate of polymethyl methacrylate manufactured by Mitsubishi Rayon Co., Ltd. was degreased with methanol and dried. A nickel stamper with fine irregularities formed on the upper surface side of the cast plate, a stainless steel stamper with prism-shaped concave portions formed on the lower surface side, and sandwiched between both stampers, 230 ° C
And set in a press machine. After pressure bonding for 2 seconds at a pressure of 2 MPa, cooling at 90 ° C. for 3 minutes with the pressure returned to zero, the two stampers were peeled off, and the plate was cooled in a room temperature atmosphere to obtain a plate-shaped light guide.

The nickel fine concave / convex stamper was manufactured by transferring an electroformed method from a glass substrate master made by photolithography. The shape was such that a pattern in which grooves having a pitch of 1 μm and an average opening width of 0.5 μm were arranged in parallel within 10 mm square was formed on the entire surface of the stamper, and the groove depth was set to 0.9 μm. As a result of the transfer, the groove of the stamper forms a rib on the cast plate, and the shape is a pitch of 1 μm.
m, average opening width 0.5 μm, and groove depth 0.8 μm. On the other hand, the stainless stamper in which the prism-shaped concave portions are formed is arranged so as to be denser as the distance from the linear light source increases, and the plane portion thereof has a tilt of approximately 30 degrees (vertical angle is approximately 12 degrees).
A V-shaped groove-shaped depression which is a slope of 0 °) formed by machine cutting in a direction parallel to the linear light source was used. The V-shaped dent of the stamper was transferred as a V-shaped convex rib, and it was confirmed that the plane portion thereof was approximately 30 degrees. In order to evaluate the polarization separation function of the obtained light guide plate, diffuse unpolarized light having a wavelength intensity peak at about 550 nm from the lower surface side was converted to V
The angle dependency of the polarization intensity of the straight-out light was measured while avoiding the letter-shaped convex rib. As a result, the ratio between the maximum intensity and the minimum intensity was 2.3 times.

That is, it was confirmed that the outgoing light of this light guide plate was 70% of the S component and 30% of the P component with respect to the incident light of the non-polarized light. Next, an embodiment of a backlight using the light guide plate will be described. A cold cathode tube as a light source, a reflector for collecting the light of the cold cathode tube on the end face of the light guide plate, the light guide plate, and a light guide plate provided on the lower surface side and around the light guide plate for returning light emitted from the light guide plate to the light guide plate again. A backlight was assembled by arranging a silver-evaporated film reflector. The luminance at the center of the emission surface was measured in two cases, with and without a polarizing plate. The optical axis of the latter polarizing plate was measured in accordance with the maximum polarization intensity plane of the backlight. As a result of measuring the tube current of the cold cathode fluorescent lamp at 5 mA, the luminance without the polarizing plate was 1090 at the maximum.
cd / m ² , brightness with polarizer is 550 cd / max.
m ² .

Comparative Example 1 For comparison, a backlight was manufactured by replacing only the light guide plate having the above-described structure with a light guide plate having no polarization-separated fine unevenness, and the luminance was measured under the same conditions as in the example. As a result, the luminance without the polarizer is 1 at the maximum.
160 cd / m ² , with a polarizing plate, the maximum luminance is 49
It was 0 cd / m ² .

[0032]

As described above, the present invention makes it possible to efficiently utilize the illuminating light rays incident on the light guide in the backlight, and to improve the polarization separation plate and the light guide used for improving the display brightness of the liquid crystal display element. The purpose of the present invention is to provide a means for realizing the function with a single light guide. If the light guide plate of the present invention is used for a backlight, the display element can be reduced in weight and thickness, and further,
The yield can be improved by facilitating the assembly process of the backlight.

[Brief description of the drawings]

FIG. 1 is a side view and a partially enlarged perspective view of an example of a light guide of the present invention.

FIG. 2 is a conceptual diagram illustrating a polarization separation function of the light guide of the present invention.

FIG. 3 is an explanatory view of a pattern of polarization separation unevenness of the light guide of the present invention.

FIG. 4 is an explanatory view of a rib cross-sectional shape of the polarization separation unevenness of the light guide of the present invention.

FIG. 5 is a graph showing the wavelength and transmittance of the light guide of the present invention.

FIG. 6 is a diagram illustrating an example of a backlight according to the present invention.

FIG. 7 is an explanatory diagram of an optical configuration of a light guide according to the present invention.

FIG. 8 is an explanatory view of an example of the shape of the prismatic irregularities 103;

FIG. 9 is a schematic view showing an example of a conventional liquid crystal display element.

FIG. 10 is a schematic view showing an example of a conventional liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Light guide 102 Fine unevenness 103 Prism-shaped unevenness 104 Linear light source 105 Reflector 106 Reflection plate 107 Polarization plate 108 Polarization separation plate 109 Quarter wavelength plate 110 Liquid crystal element 201 Rib 202 Groove 203 Pitch 204 Maximum aperture width 205 Minimum aperture Width 206 rib height

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Liu Tongki 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama Research Laboratory F-term (reference) 2H038 AA55 BA06 2H042 AA02 AA04 AA26 BA04 BA20 DD01 DE04 2H091 FA02Y FA08X FA08Z FA14Z FA23Z FA41Z LA12 LA16

Claims (5)

[Claims] 1. A plate-shaped light guide made of a transparent solid substance constituting a backlight of a liquid crystal display element, wherein a fine unevenness having a polarization separation function is formed on a light emission surface thereof, and faces a light emission surface. A light guide, wherein the surface is provided with prismatic irregularities for reflecting light from a light source. 2. The light guide according to claim 1, wherein the fine unevenness is an aggregate of substantially parallel fine linear ribs formed on the emission surface. 3. The linear rib has a pitch of 0.1 to 0.1.
3. The light guide according to claim 2, wherein the light guide has a thickness of 2 μm, an average opening width of 0.05 to 1.5 μm, and a rib height of 2 to 8 times the average opening width. 4. The substance constituting the light guide has a refractive index of 1.34 or more.
The light guide according to any one of claims 1 to 3, wherein the light guide is a transparent polymer compound of 1.71. 5. A backlight for a liquid crystal display element,
A backlight comprising a light guide according to any one of claims 1 to 4 and a light source for supplying light to the light guide.