JP2001201746A - Light guide body and back light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means to realize the functions of a polarizing separation plate and a light guide body in one single body of a light guide body to efficiently use the illumination rays entering the light guide body in a back light and to improve the display luminance of a liquid crystal display device. SOLUTION: This plate type light guide body consists of a transparent solid material which constitutes the back light of a liquid crystal display device. A fine rugged pattern having a polarization separation function is formed on the face of the body where light exits, and a means to diffuse and reflect the light from a light source is formed on the counter face to the exit face.

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 Monitors for personal computers,
A transmissive liquid crystal display device is frequently used as a display device of a portable terminal, a thin TV, or the like. In such a liquid crystal display device, usually, a planar illumination device, that is, a backlight is provided on a back surface of a liquid crystal element. I have. 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 method is to install a linear light source at a side end of a liquid crystal element and obtain planar light using a light guide such as an acrylic plate (side light method). An optical element such as a prism array is disposed on the surface to obtain desired optical characteristics.

[0003] 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 the liquid crystal display device, which is light and thin, it is preferable to use a sidelight system that can make the backlight device thin, and a liquid crystal display device such as a recent portable personal computer is used. , 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, the demand for improving the luminance of the backlight is increasing.

For example, in a transmission type full-color liquid crystal element, a higher definition is progressed, 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 the 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 a base such as glass for enclosing the liquid crystal, and outside the base. 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, a method is known 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 to make outgoing light into partially polarized light. 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.

[0007] Regarding the technology applying the concept of reusing the linearly polarized reflected light, there have been proposed many devices having a similar configuration 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, and JP-A-11-96819.

[0008] The monthly display June 1997, p. 81 discloses a liquid crystal display device as shown in FIG. This liquid crystal display device is the same as the above-described polarization separation plate 10.
It is characterized in that the function of No. 8 is a circularly polarized light separating function instead of the linearly polarized light separating function. In the case of this configuration, by providing the quarter-wave plate 109 on the upper part of the polarization separation plate 108, it can be converted into elliptically polarized light close to linearly polarized light,
By adjusting the major axis of the ellipse to the polarization plane (not shown) of the polarizing plate 107 under the liquid crystal element, the brightness of the liquid crystal display device can be increased 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-8-271.
No. 837, JP-A-9-304770, JP-A-10-5
4909, JP-A-10-142407, JP-A-10-142407
-197722, JP-A-10-206636, JP-A-10-232313, JP-A-10-253930
JP-A-10-293221, JP-A-10-301
097, JP-A-10-319235, JP-A-10-319
No. 321025, Japanese Unexamined Patent Application Publication No. 10-321026, Japanese Unexamined Patent Application Publication No. 10-339812, Japanese Unexamined Patent Application Publication No. 11-64841, Japanese Unexamined Patent Application Publication No. 11-125717, Japanese Unexamined Patent Application Publication No. 11-133231
And Japanese Patent Application Laid-Open No. H11-160539.

[0009]

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 utilize an illumination light beam incident on a light guide, and to improve the display brightness of a liquid crystal display device. An object of the present invention is to provide a light guide with both functions of polarization separation and light guide emission used to achieve the improvement. 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.

[0011]

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 irregularities are formed, and a means for diffusing and reflecting light from the light source is provided on a surface facing the emission surface. Further, 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 linear ribs have a pitch of 0.1 to 2 μm, an average opening width of 0.05 to 1.5 μm, and a rib height of 2 to 8 of the average opening width.
And the material forming the light guide has a refractive index of 1.34.
The transparent polymer compound having a molecular weight of from 1.71 to 1.71 is also 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.

[0012]

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. A reflecting means 103 for diffusing and reflecting the light incident from the light source is disposed on the facing surface. Typically,
When the dimensions such as the width and depth of the fine irregularities are sufficiently large compared to the wavelength of the incident light, catadioptric phenomena in accordance with geometric optics are observed. The phenomena of reflection and refraction according to the above are not observed, but the characteristics as the wave of light appear 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.

[0013] Since a normal light source is unpolarized light, light transmitted through the light guide is also unpolarized 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 unevenness 102. The light that has been reflected and returned to the light guide 101 is converted into light in various directions by the reflection / scattering means 103 and the like, and returns to the emission surface. 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, the wavelength of the light, and the like are changed, light (S component) in the direction perpendicular to the longitudinal direction of the rib may be used as the emitted light. It is possible. 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 a parallel continuous rib, FIG. 3B shows an example of a parallel discontinuous rib, FIG. 3C shows an example of a parallel alternate rib, FIG. 3D shows an example of a domain type rib, and FIG. In addition, it is possible to arbitrarily design, for example, a rib having non-parallel ribs or a rib having a different direction according to the application. Others
By changing the width of the rib and the width of the groove stepwise, or by changing the height of the rib (depth of the groove) stepwise,
The polarization wavelength can also be adjusted. In the case of a set of substantially parallel fine linear ribs, the plane of maximum polarization of the 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. The substantially polygonal shape is preferably a substantially rectangular shape or a 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. 6 shows an example of the cross-sectional shape. Rectangle (a), triangle (b), trapezoid (c), semicircle (d), rectangle without corners (e), waveform (f), saw blade shape (g), inverted semicircle (h), step shape (I) and the like can be arbitrarily designed.

From the viewpoint of convenience in design and manufacture, it is preferable that the aggregate of the ribs has the same sectional shape.
Further, the ribs are preferably arranged at a constant period. Since the polarization separation function strongly depends on this spatial arrangement,
Here, some vocabulary is defined as follows 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 function of the diffuse reflection means 13 formed on the surface facing the emission surface will be described with reference to FIG. The diffuse reflection means 103 includes the light source 1 disposed at the light guide 101 side end.
The light guide 101 enters the light guide 101 from the light guide 104 and is totally reflected.
The traveling direction of light that permeates the whole is randomly reflected, that is, diffusely reflected.

This function directs a portion of the light upward.
By adjusting the existing surface density of the diffuse reflection means 103, it is possible to control the uniformity of the amount of light in the emission surface. An even more important function of the diffuse reflection means 103 is that when the light travels inside the light guide 101 and is reflected by the diffusion reflection means 103 on the surface facing the emission surface, the electric field vibration surface of the reflected light rotates randomly. That is, when polarized light enters the diffuse reflection means 103, the reflected light does not have a specific electric field vibration surface, that is, becomes unpolarized light. Therefore, the partially polarized light reflected downward in the light guide by the above-mentioned minute uneven portion 102 is converted into non-polarized light by the diffuse reflection means 103 and returned to the minute uneven portion 102 again. Contributes to the lighting of the element.

The method for forming the diffuse reflection means 103 is as follows.
Applying a diffusing agent such as white ink on the surface of the light guide,
At the time of forming the light guide 101, fine irregularities are formed in a mold, and the irregularities are transferred and formed. Fine irregularities are formed by mechanical cutting, and fine irregularities are formed by chemical roughening. There are irregularities and the like, but the present invention is not limited to these. 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 facing surface, the diffuse reflection means 10
A total reflection phenomenon occurs in a portion where 3 is not formed. By providing the diffuse reflection means 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 1.35 to 1.72,
It is preferably formed of a transparent polymer compound. As the transparent polymer compound, polyacrylate, polymethacrylate, monoacrylate, acrylic resin obtained by polymerization from a monomer selected from monomethacrylate, or polycarbonate resin, polyester resin,
Alternatively, a cyclic polyolefin resin is preferably used.

As a method for forming the light guide 101, there can be used a precision cutting of a transparent solid material, laser cutting, or a transfer method using a precision stamper in which fine irregularities are transferred by photolithography, but are not limited thereto. is not. The present invention can be implemented in a sidelight type backlight form as shown in FIG. FIG.
FIG. 4 is a cross-sectional view illustrating a state where light guides of Nos. To 4 are incorporated in a backlight, and a situation in which a light ray entering the light guide is emitted will be described with reference to FIG. Although unpolarized light emitted from the linear light source 104 disposed at the side end of the light guide enters from the side end and proceeds to the side while being totally reflected in the light guide,
In the process, a part of the light incident on the reflection means 103 reaches the fine unevenness 102 upward. Part of the light (P component polarized light) that has reached the fine irregularities 102 is transmitted upward and emitted, and the other light is reflected downward without exiting the light guide 101.

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 goes upward when the diffuse reflection means 103 is present at the arrival position, and the polarization plane rotates randomly (diffuse). This light can be considered as unpolarized light. On the other hand, the light that reaches the portion without the reflection means 103 is emitted downward from the light guide, reflected by the reflection plate 106 and re-enters the light guide 101, and goes upward if there is no diffuse reflection means 103 at that position. . 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, when the light reflected by the fine irregularities 102 reaches the fine irregularities 102 again via the lower surface of the light guide 101, the light 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 contributes to an increase in the P-polarization plane component of the emitted light by repeating the same reflection and rotation of the polarization plane as described above. Fine irregularities 102
When the reflection at the light guide plate is repeated infinitely, the light amount utilization rate converges to a certain value. This is because there is a loss of the incident light on the lower surface of the light guide plate 101, and 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 confirming the arrangement of the diffuse reflection means by matching the actual object, but this method is also effective in the backlight.

[0026]

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 a diffuse reflection concave portion 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 irregularity stamper was manufactured by transferring from a glass substrate master made by photolithography by electroforming. The shape is such that a groove having a pitch of 1 μm, an average opening width of 0.5 μm, and
Patterns arranged in parallel in a square of mm were 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 its shape is pitch 1 μm, average opening width 0.5 μm,
A groove depth of 0.8 μm was confirmed.

On the other hand, a stainless stamper having a diffuse reflection recess formed therein was formed by etching an elliptical recess arranged so as to become denser as the distance from the linear light source increased. The top of the elliptical dent has fine irregularities. In order to evaluate the polarization separation function of the obtained light guide plate, diffuse non-polarized light having a wavelength intensity peak at about 550 nm from the lower surface side is incident avoiding the diffuse reflection convex portion, and the polarization intensity of the light emitted straight ahead is obtained. Was measured for angle dependence. 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 for installing the light guide plate on the lower surface side and around the light guide plate for returning the light emitted from the light guide plate to the light guide plate A backlight was assembled by disposing a foamed polyester reflector, a prism sheet made by Mitsubishi Rayon installed on the upper surface side and correcting the emission direction upward. 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 current of the cold cathode fluorescent lamp at 5 mA, the luminance without the polarizer was 910 cd / m2 at the maximum, and the luminance with the polarizer was 43 at the maximum.
It was 0 cd / m ² .

[0028]

Comparative Example 1 For comparison, only the light guide plate having the above-described configuration was used.
A backlight was manufactured by replacing the light guide plate with no polarization separating fine unevenness, and the luminance was measured under the same conditions as in the example. As a result, the luminance without the polarizer is 930 cd / m at maximum.
2. The luminance with a polarizing plate was 390 cd / m ² at the maximum.

[0029]

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 a diffuse reflection means of the light guide according to the present invention.

FIG. 4 is an explanatory view of a rib cross-sectional shape of the diffuse reflection means of the light guide according to 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 a schematic view showing an example of a conventional liquid crystal display device.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Light guide 102 Fine unevenness 103 Diffuse reflection means 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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 6/00 331 G02F 1/1335 530 (72) Inventor Tatsuki Liu 1000 Kamoshidacho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Address Mitsubishi Chemical Corporation Yokohama Research Laboratory F-term (reference) 2H038 AA55 BA06 2H042 BA03 BA11 BA13 BA15 BA16 2H049 BA02 BA45 BB61 BC01 BC22 2H091 FA23Z FA31Z FA41Z FC10 FC19 LA11 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 a means for diffusing and reflecting light from a light source is provided on the surface. 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.