JP2001281654A - Backlight for liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means to realize functions of a polarized light separation plate and a light-transmitting body, used to improve display brightness of a liquid crystal display element, only by the light-transmitting body by efficiently utilizing an illumination light beam incident on the light transmission body in a backlight. SOLUTION: The backlight for the liquid crystal display element is provided with a plate shaped light-transmitting body composed of transparent solid matter and a light source for supplying light to the light-transmitting body, and is characterized by arranging a quarter-wave plate and a reflection plate on the side of the light-transmitting body opposite to the light-emitting surface and by forming fine projecting and recessing parts, having a polarized light separation function on the light-emitting surface of the light-transmitting body.

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.

[0003] 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 such as a prism array is disposed on the light emitting surface to obtain desired optical characteristics. Regarding the sidelight method, see, for example, JP-A-61-9918.
No. 7 and JP-A-63-62104.

In order to more effectively bring out the general features of a liquid crystal display device, such as a light weight and a thin type, it is preferable to use a side light system which can make a backlight device thin. 2. Description of the Related Art Side-light type backlights are often used in liquid crystal display devices. 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, the definition is advanced, and generally the light transmittance of the display element itself is reduced. Therefore, 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 meet these demands, in the backlight of the sidelight type, a sheet made of a prism array or the like is frequently used to secure the front luminance by an optical condensing function, thereby making the emitted light effective. Although it has been generally used, the frequent use of these not only causes a large increase in cost, but also causes adverse effects such as narrowing of the viewing angle characteristics. There has been a long-awaited need for a technique for providing a high-brightness backlight having the following characteristics.

[0007] The following concept that meets this requirement is 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 on the principle that a twisted structure of liquid crystal is used. 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 a 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 on the backlight side to make outgoing light into partially polarized light. The polarized light separating plate directly emits and uses one of two polarized components (here, P-polarized light and S-polarized light) whose vibration planes are orthogonal to each other, and returns the other to the backlight side to use the light source. The liquid crystal display device is provided for reuse as light, so that 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 a polarization separation plate 108, and a liquid crystal display element 110 having a polarization plate 107 is provided thereon.

[0010] Regarding the technology applying the concept of reusing the linearly polarized reflected light, there have been proposed a number of 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, 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 the same as the above-described polarizing beam splitter 1.
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 separation plate 108, it can be converted into elliptically polarized light that is 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 technique using the concept of reusing circularly polarized reflected light. These are disclosed in Japanese Patent Application Laid-Open Nos.
No. 304770, JP-A-10-54909, JP-A-1
0-142407, JP-A-10-197722, JP-A-10-206636, JP-A-10-232313
JP-A-10-253930, JP-A-10-293
No. 211, Japanese Patent Application Laid-Open No. 10-301097, Japanese Patent Application Laid-Open
No. 319235, JP-A-10-321025, JP-A-10-321026, JP-A-10-339812,
JP-A-11-64841, JP-A-11-125717
JP-A-11-133231, JP-A-11-160
No. 539 and the like.

[0013]

However, in any of the above-mentioned prior arts, since the light guide itself does not have a polarization splitting function, a component having a polarization splitting function such as a polarization splitting plate (for example, a component having a different refractive index). It is essential to use them in combination with a multilayer film in which various kinds of transparent materials are alternately laminated.

This means that an increase in the number of components cannot be avoided as long as the purpose of reusing the reflected polarized light is, which is a demand for a liquid crystal display element from the market, which is further reduced in weight and thickness. It was against cost reduction. 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.

[0017]

The gist of the present invention is to provide a backlight for a liquid crystal display device having a plate-shaped light guide made of a transparent solid material and a light source for supplying light to the light guide.
The backlight is characterized in that a quarter-wave plate and a reflection plate are provided on the side opposite to the light exit surface of the light guide, and fine irregularities having a polarization separation function are formed on the light exit surface of the light guide. .

Further, one of the embodiments is that the fine irregularities are 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 and an average opening width of 0.05 to 1.5.
μm, the height of the ribs is 2 to 8 times the average opening width, and the substance forming the light guide is a transparent polymer compound having a refractive index of 1.34 to 1.71. One.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram showing a preferred embodiment of the backlight of the present invention. The unpolarized light emitted from the linear light source 104 disposed at the side end of the light guide 101 is directly or reflected by the reflector 105, enters from the side end of the light guide, and is totally reflected inside the light guide to the side. In the process, a part of the light incident on the reflecting means 103 goes upward and reaches the fine unevenness 102.

Part of the light that has reached the fine unevenness 102 is emitted upward as partially polarized light having a plane of maximum intensity polarization, and becomes light that effectively illuminates the liquid crystal element. Other light is light guide 101
It is reflected downward without exiting from. A mode in which this light is returned to the fine unevenness 102 again to effectively illuminate the liquid crystal element 110 will be described below. 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) reflected downward and reaching the lower surface of the light guide 101 travels into the light guide when the reflection means 103 is present at the arrival position. On the other hand, the light reaching the portion without the reflection means 103 exits below the light guide, passes through the quarter-wave plate 109, is reflected by the reflector 106, passes through the wave plate 109 again, and passes through the light guide 101. And reaches the fine unevenness 102 upward. When the polarized light passes through the quarter-wave plate 109, the rotation of the polarization plane occurs. The S-polarized light is converted to left-handed or right-handed elliptically-polarized light, reflected by the reflector 106, and again returned to 1/4.
After passing through the wave plate 109, it is converted into P-polarized light,
When this light reaches the fine irregularities 102 again, the P-polarized light is efficiently emitted from the emission surface.

The quarter-wave plate 109 provides a transparent and uniform optical phase difference. For example, a polycarbonate resin or a polysulfone-based resin formed by a solution casting method is uniaxially stretched and molecularly oriented. And thickness 5
It is a thin transparent plate having a thickness of about 0 to 100 μm. Reflector 1
For example, a mirror plate 06 is formed by depositing silver or aluminum on a metal plate or a synthetic resin plate.

FIG. 1 schematically shows a 、 wavelength plate 10.
While the linearly polarized light (S-polarized light) incident on the plate 9 travels through the plate, its phase in the vibration direction shifts by π / 4 due to the birefringence phenomenon, and is converted into elliptically polarized light whose polarization plane rotates with time. The light exits from the side opposite to 109. The outgoing light of the elliptically polarized light is reflected by the reflecting plate, and is again returned to the 波長 wavelength plate 109.
Return inside.

At this time, the phase is again π / 4 due to the birefringence phenomenon.
As a result, the light is converted into linearly polarized light and is emitted toward the light guide. This polarization plane and the polarization plane of the linearly polarized light that first enters the quarter-wave plate 109 are orthogonal to each other. Therefore, the S-polarized light emitted from the lower surface of the light guide 101 is rotated by 90 degrees for convenience, converted into P-polarized light, and is incident again from the lower surface of the light guide 101. The P-polarized light is emitted upward from the fine irregularities 102 of the light guide 101 and becomes light that effectively illuminates the liquid crystal element.

As described above, the S component polarized light reflected downward by the fine irregularities 102 exits from the lower surface of the light guide, passes through the quarter-wave plate 109 and the reflector 106, enters the light guide 101, and enters the light irregularities. The light that has again reached 102 has an increased P-polarization plane component emitted from the fine irregularities, so that the liquid crystal element 11
It is guided to 0 and contributes to an increase in the amount of light for effective illumination. Again, the light reflected by the fine irregularities 102 proceeds 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 at the fine irregularities 102 is repeated infinitely, the light quantity 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 101, and is approximately 75%. About. Next, 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.

In general, when the dimensions such as the width and depth of the fine irregularities are sufficiently larger than the wavelength of the incident light, a catadioptric phenomenon based on geometrical optics is observed. When the wavelength is equal to the wavelength, the catadioptric phenomenon based on geometrical optics is not observed, and the wave characteristic 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 made substantially equal to the wavelength range of visible light, so that the latter diffraction phenomenon is caused, and as a result of the superposition of a plurality of diffracted lights, the polarization separation function is obtained. Is controlled. 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, a part of the light is emitted and the remaining light is reflected. These emitted light,
In 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 P
Although the component is strong and the S component is weak, the intensity difference may be reversed under other conditions. In FIG. 3, light is separately shown as a P component and an S component, and the P component shows a state when the S component is emitted strongly and the S component is emitted weakly.

That is, as shown in FIG.
2 is composed of substantially parallel ribs (linear ribs) having a certain height (deep groove depth), the wave light (P component) in the direction parallel to the longitudinal direction of the ribs and As a result of this action, the light is converted into diffracted light emitted from the transparent body having a smooth surface into the air, but most of the light (S component) in the direction perpendicular to the longitudinal direction of the rib is reflected in the interaction with the unevenness. The light is converted into diffracted light and returns into the light guide 101, 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. On the other hand, the light reflected back into the light guide 101 becomes polarized light mainly having a component in a direction perpendicular to the longitudinal direction of the rib, and is light that is repeatedly reflected in the light guide by the reflection means 103 of the emitted light. Or after being emitted from the light guide 101 to the outside, reflected by the reflector 106 or the reflector 105 and re-entered into the light guide, the light again travels to the emission surface, and P wave is emitted light, and S wave is reflected light. Become.

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. 4 shows an example of the aggregate. FIG. 4 (a)
Is an example of a parallel continuous rib, (b) is an example of a parallel discontinuous rib, (c) is an example of a parallel staggered rib, (d) is an example of a domain type rib, and (e) is an example of a parallel random rib.

In addition, it is possible to arbitrarily design the ribs according to the application, such as those in which the ribs are not parallel, and those in which the direction of the assembly is different. 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 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. 5 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 expressed as a superposed (coupled wave) of a spatial harmonic wave (plane wave) and described by Maxwell's equation for electric field vibration.

In this equation, diffraction efficiency is a function of the linear rib height, rib width, groove width transparent solid material dimension, transparent solid material refractive index, and incident light wavelength. Actually, the diffraction efficiency can be obtained by solving a simultaneous differential equation set on the basis of the phase matching condition in the transparent solid material, the fine concave region, the boundary of each region of gas or vacuum by a computer.

FIG. 6 shows an example of calculation by this method. This is because the cross section of the linear rib is rectangular, and the pitch is 1.
The relationship between the rib height / incident light wavelength ratio and the transmittance of the P component and the S component when the opening width is 0 μm and the opening width is 0.5 μm is shown. For example, when the rib height is 3.1 times the wavelength,
It can be seen that 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 bonded to the outside of a base such as glass for enclosing liquid crystal.
Since this polarizing plate has a property of transmitting an electric field vibration component in a certain reference plane and absorbing an electric field vibration component orthogonal to the reference plane, the maximum intensity polarization plane of the light emitted from the light guide is set to the reference plane of the polarizing plate. , At least more than 50% of the total emitted light amount can be guided to the liquid crystal element.

Next, the reflection means 103 formed on the surface facing the light exit surface will be described. The reflection unit 103 directs a part of the light that enters the light guide 101 from the linear light source 104 disposed at the light guide 101 side end and is totally reflected and permeates the entire light guide 101 upward. Is formed for.
This includes a method using specular reflection, a method using diffuse reflection, and a method using both simultaneously. In the case of using specular reflection, prismatic irregularities are formed, and in the case of using diffuse reflection, a rough surface portion is formed.

When the former is used, an emission angle distribution with relatively high directivity is obtained, and when the latter is used, a broad emission angle distribution with weak directivity is obtained. In the former case, the intensity of directivity can be controlled by adjusting the surface roughness of the mirror surface. The specular reflection prism-like unevenness is generated by the light source 10
The design is made in consideration of the optimum tilt angle, area and arrangement of the mirror surface obtained from the traveling angle distribution of the light that is incident on and totally reflected at 1.

Regardless of the method of specular reflection by the prismatic irregularities and diffuse reflection by the rough surface portion, the surface density of these reflection means 103 is adjusted to control the uniformity of the amount of light in the emission surface. Examples of the shape of the prismatic irregularities include a linear V-shaped groove or V-shaped convex rib parallel to the light source, a conical mortar or conical mortar, or a pyramidal dent or pyramid-like dot that is independent of each other. Included,
It is not limited to these.

As a method of forming the prismatic irregularities, 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 may be provided with concavities and convexities, or the light guide may be provided with concavities and convexities by chemical etching. However, the present invention is not limited thereto. On the other hand, as a method of forming the rough surface portion, a diffusing agent such as white ink is applied to the surface of the light guide, and the surface is formed. Transfer, the formation of fine roughness by mechanical cutting, the formation of fine roughness by chemical roughening, and the like, but are not limited thereto.

Normally, the light guide 101 of the sidelight type backlight has a light exit surface and an opposing surface in order to penetrate the light from the linear light source 104 entering from the light guide side end into the entire light guide 101. The total reflection phenomenon is used, but the fact that the total reflection phenomenon can be used also in the light guide is supplemented. First, the fine uneven portion 102 having the polarization splitting function on the emission surface exhibits the total reflection phenomenon that is the same as the two-layer structure as shown in FIG.

On the other hand, on the facing surface, a total reflection phenomenon occurs in a portion where the reflection means 103 is not formed. By providing the 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 1.7.
It is preferable to use the transparent polymer compound of No. 2 above. 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

The light guide body 101 may be formed by a method such as precision cutting of a transparent solid material, laser cutting, or press molding, injection molding, or injection compression molding using a precision stamper to which fine irregularities are transferred by photolithography. Can be used, but is not limited thereto. The reflecting plate 106 reflects light emitted from the lower surface of the light guide, and reflects the light from the light guide 1.
Used to return to 01. Therefore, a material having a high reflectance is preferable. Further, the surface is preferably a smooth surface that maintains the polarization plane when reflecting partially polarized light. As a material that satisfies such requirements, for example, a plastic film on which silver or aluminum is deposited is preferably used.

The reflector 106 is used for collecting the light of the linear light source at the end face of the light guide. The reflective surface is preferably made of a material having a high reflectivity. For example, a mirror-finished aluminum or silver-deposited plastic sheet is preferably used.

[0052]

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 cold cathode tube having a diameter of 2 mm as a linear light source, a reflector made of aluminum, a reflecting plate made of a silver-evaporated polyester film, and a quarter-wave plate made of a phase difference film (trade name “Sumilite”) manufactured by Sumitomo Chemical Co., Ltd. A backlight was assembled by disposing the light guides described below and as shown in FIG.

The light guide was manufactured in the following procedure. 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, sandwiched by both stampers, set in a press machine in a state heated to 230 ° C did.

After pressing for 2 seconds at a pressure of 2 MPa, cooling at 90 ° C. for 3 minutes in a state where the pressure was returned to zero, the two stampers were peeled off, and the plate-shaped light guide was cooled in a room temperature atmosphere. Obtained. The nickel fine irregularity stamper was manufactured by transferring from a glass substrate master made by photolithography by electroforming.

The stamper has a pattern in which grooves having a pitch of 1 μm and an average opening width of 0.5 μm are arranged in parallel within a 10 mm square on the entire surface of the stamper.
It was set to 9 μm. As a result of the transfer, the groove of the stamper formed a rib on the cast plate, and the shape was confirmed to be 1 μm in pitch, 0.5 μm in average opening width, and 0.8 μm in groove depth.

On the other hand, the stainless stamper in which the prism-shaped concave portions are formed is arranged so as to become denser as the distance from the linear light source increases, and the flat portion thereof is formed by machining a V-shaped concave which is an inclined surface having an inclination of approximately 30 °. The formed one was used. It was confirmed that the V-shaped dent of the stamper was transferred as a V-shaped convex rib, and the plane portion thereof was approximately 30 °.

The luminance at the center of the exit 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 tube at 5 mA, the maximum luminance without the polarizing plate was 1040 cd / m2, and the maximum luminance with the polarizing plate was 590 cd / m2.

[0058]

Comparative Example 1 For comparison, only the light guide having the above-described configuration was used.
A backlight was manufactured by substituting a light guide having no polarization separation fine unevenness, and the luminance was measured under the same conditions as in the example. As a result, the luminance without the polarizer is 1110 cd / max.
m2, brightness with polarizer is 470 cd / m2 at maximum
Met.

[0059]

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 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 schematic view showing an example of a backlight according to the present invention.

FIG. 2 is a side view and a partially enlarged perspective view of an example of a light guide constituting the backlight of the present invention.

FIG. 3 is a conceptual diagram illustrating a polarization separation function of a light guide constituting a backlight according to the present invention.

FIG. 4 is an explanatory view of a pattern of polarization separation unevenness of the light guide constituting the backlight of the present invention.

FIG. 5 is an explanatory view of a rib cross-sectional shape of the polarization separating unevenness of the light guide constituting the backlight of the present invention.

FIG. 6 is a graph showing wavelength and transmittance of a light guide constituting the backlight of 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 device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Light guide 102 Fine unevenness 103 Reflecting means 104 Linear light source 105 Reflector 106 Reflecting plate 107 Polarizing plate 108 Polarization separating plate 109 Quarter-wave plate 110 Liquid crystal element 201 Rib 202 Groove 203 Pitch 204 Maximum opening width 205 Minimum opening width 206 rib height

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13363 G09F 9/00 324 G09F 9/00 324 G02F 1/1335 530 F-term (reference) 2H038 AA55 BA06 2H091 FA08X FA08Z FA11Z FA14Z FA21X FA23Z FA41Z FB02 FC14 LA12 LA30 5G435 AA03 BB12 FF03 FF05 FF08 GG08LL

Claims (4)

[Claims] 1. A backlight for a liquid crystal display device having a plate-shaped light guide made of a transparent solid material and a light source for supplying light to the light guide, the backlight being opposite to the light exit surface of the light guide. 1 /
A backlight comprising a four-wavelength plate and a reflection plate, and fine irregularities having a polarization separation function formed on a light exit surface of a light guide. 2. The backlight 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 backlight according to claim 2, wherein the average opening width is 0.05 to 1.5 [mu] m, and the rib height is 2 to 8 times the average opening width. 4. The backlight according to claim 1, wherein the substance constituting the light guide is a transparent polymer compound having a refractive index of 1.34 to 1.71.