JP3422475B2 - Polarized light guide plate and polarized plane light source - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarized light guide plate suitable for forming a backlight of a liquid crystal display device by emitting linearly polarized light with incident light coming from the side surface from one of the front and back surfaces while controlling the vibrating surface. And a polarization plane light source.

[0002]

2. Description of the Related Art Conventionally, as a sidelight type light guide plate which can be used as a backlight of a liquid crystal display device, a light emitting plate made of a translucent resin plate and comprising reflective dots containing a high reflectance pigment such as titanium oxide or barium sulfate. It has been known that a means is provided so that transmitted light due to total reflection inside the plate is emitted from one of the front and back sides of the plate via the light emitting means by scattering or the like. However, the emitted light is natural light that shows almost no polarization characteristics, and it is necessary to convert it into linearly polarized light through a polarizing plate in liquid crystal display. There was a problem that could not exceed 50%.

In view of the above, there has been proposed a system which uses a polarization conversion means which is a combination of a polarization separation plate and a phase difference plate, which obtains linearly polarized light by utilizing Brewster's angle (Japanese Patent Laid-Open No. 6-18873). Japanese Patent Laid-Open No. 6-16084
No. 0, JP-A-6-265892, JP-A-7-
No. 72475, No. 7-261122, No. 7-270792, No. 9-54556, No. 9-105933, No. 9-13.
8406, JP 9-152604 A, JP 9-293406 A, JP 9-326205 A, JP 10-78581 A, etc.). However, in such a backlight, sufficient polarization cannot be obtained and it is difficult to control the polarization direction.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to develop a light guide plate capable of obtaining emitted light composed of linearly polarized light and arbitrarily controlling the polarization direction (vibration plane) thereof.

[0005]

Means for Solving the Problems The present invention provides a laminated body in which a transparent resin plate is provided on one or both sides thereof with a polarizing scattering plate which contains minute birefringent regions dispersed therein and exhibits scattering anisotropy depending on the polarization direction. Which has a specular reflection layer on one surface thereof and at least one layer of a polarization maintaining lens sheet on the other surface of the above-mentioned laminated body, and in the natural light incident from the side surface, due to the above scattering anisotropy, Election
Polarization light guide plate linearly polarized light scattered in択的 characterized by elevation no side or RaIzuru the specular reflective layer, and the polarization, characterized in that it comprises a light source on at least one side surface of the polarization light guide plate A surface light source is provided.

[0006]

According to the present invention, with the above-described structure, natural light is incident from the side surface without forming a special light emitting means such as a reflective dot on the translucent resin plate, and the front and back surface has the specular reflection layers. On the other hand, the linearly polarized light can be efficiently emitted, and the linearly polarized light in the vibration direction corresponding to the linearly polarized light can be obtained through the optical axis of the polarization scattering plate used together. Therefore, the oscillation direction of linearly polarized light can be arbitrarily changed by controlling the optical axis of the polarization scattering plate. In addition, by controlling the optical path of the emitted light through a polarization maintaining lens sheet, linearly polarized light with excellent directivity in the front direction can be obtained, and by arranging the liquid crystal display element with the polarization axis parallel to it, it is more than usual. It is also possible to achieve a brightness of 1.5 times or more.

That is, in the above description, the incident light from the side surface is totally reflected due to the difference in the refractive index from the air interface, is transmitted through the light guide plate and is incident on the polarization scattering plate, and the maximum refraction between the incident light and a minute area is performed. Axial direction (Δn1) showing rate difference (Δn1)
The linearly polarized light having a vibrating surface parallel to the (direction) is selectively and strongly scattered, and a part of the linearly polarized light becomes an angle smaller than the total reflection angle and is emitted from the light guide plate. In that case, the emission is blocked on the side where the specular reflection layer is provided and supplied to the opposite surface, and the emitted light is concentrated on that surface (one of the front and back surfaces of the light guide plate that does not have the specular reflection layer). The optical path of linearly polarized light is controlled from one surface through the lens sheet and is emitted to the front with good directivity.

On the other hand, the light scattered at a large angle due to the scattering in the Δn1 direction, the light that satisfies the Δn1 direction condition but is not scattered, and the light having a vibration direction other than the Δn1 direction are Then, the light is confined in the light guide plate and transmitted while repeating total reflection, the polarization state is also canceled by the birefringence phase difference due to the polarization scattering plate, and the opportunity for emission while satisfying the condition of Δn1 is waited. By repeating the above, the linearly polarized light having the predetermined vibration plane is efficiently emitted from the light guide plate.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The polarized light guide plate according to the present invention is provided with a polarized light scattering plate which contains minute birefringent regions dispersedly and shows scattering anisotropy depending on the polarization direction on one surface or both surfaces of a transparent resin plate. The laminated body has a specular reflection layer on one surface and the other surface of the laminated body has at least one polarization-maintaining lens sheet. the linearly polarized light selectively scattered at isotropic made than those morphism no side or RaIzuru the specular reflection layer. An example thereof is shown in FIG. 1 is a translucent resin plate, 3 is a polarized light scattering plate, 4 is a laminate thereof, 5 is a specular reflection layer, 6 is a lens sheet, 2 is an adhesive layer as necessary, 7 is necessary According to the light diffusion layer. Note that FIG. 1 exemplifies a polarized light source, and 8 is a light source.

The light-transmitting resin plate may be a plate-like member made of an appropriate material that is transparent according to the wavelength range of the light source. Incidentally, in the visible light range, for example, a plate made of an acrylic resin, a polycarbonate resin, a styrene resin, a norbornene resin, or an epoxy resin can be preferably used. A plate made of a resin having a refractive index as small as possible is preferable in terms of light transmittance.

A resin plate having a phase difference in the in-plane direction that is as small as possible is preferable from the viewpoint of maintaining the polarization characteristics of the emitted light. From such a point, orientation birefringence due to distortion or the like during molding of the plate is preferable. A material that does not easily occur, particularly polymethylmetalate or norbornene-based resin, can be preferably used. Such a resin is also excellent in plate formability.

The shape of the translucent resin plate can be appropriately determined according to the size of the liquid crystal cell, the characteristics of the light source, the uniformity of the brightness of the emitted light, etc., and is not particularly limited. A flat plate or a wedge-shaped plate is preferable from the viewpoint of ease of molding. The thickness of the plate can be appropriately determined according to the size of the light source or the liquid crystal cell and is not particularly limited, but it is preferably as thin as possible for the purpose of thinning and lightweight, and especially 10 mm or less, particularly 0.5 to 5 mm. Is preferred.

The transparent resin plate can be formed by, for example, an injection molding method, a cast molding method, an extrusion molding method or a casting molding method.
Appropriate methods such as a rolling molding method, a roll coating molding method, a transfer molding method and a reaction injection molding method (RIM) can be used. Upon formation thereof, if necessary, suitable additives such as a discoloration preventing agent, an antioxidant, an ultraviolet absorber and a release agent can be added.

On the other hand, as the polarized light scattering plate, an appropriate one may be used which contains minute birefringent regions dispersed therein and exhibits scattering anisotropy depending on the polarization direction. By the way, as an example thereof, a transparent film in which microscopic regions having birefringence are dispersed is contained.

The polarized light scattering plate having the above-mentioned scattering anisotropy is formed by subjecting one or more suitable materials having excellent transparency such as polymers and liquid crystals to an appropriate orientation treatment such as stretching treatment. Can be performed by an appropriate method such as a method of obtaining an oriented film by using a combination of forming regions having different birefringence.

Incidentally, examples of the above combination include a combination of polymers and liquid crystals, a combination of isotropic polymers and anisotropic polymers, a combination of anisotropic polymers and the like. From the viewpoint of dispersion distribution in the minute region, a combination of phase separation is preferable, and the dispersion distribution can be controlled by the compatibility of the materials to be combined. The phase separation can be performed by an appropriate method such as a method of dissolving an incompatible material in a solvent or a method of mixing an incompatible material under heating and melting.

When the alignment treatment is carried out by the stretching method in the above combination, the anisotropic polymer is combined at an arbitrary stretching temperature and a stretching ratio in the combination of the polymers and the liquid crystals and the combination of the isotropic polymer and the anisotropic polymer. In the case of a combination of the two, the desired polarizing scattering plate can be formed by appropriately controlling the stretching conditions. Note that anisotropic polymers are classified into positive and negative based on the characteristic of the refractive index change in the stretching direction, but in the present invention, either positive or negative anisotropic polymers can be used, and positive or negative or negative or positive can be used. It can be used in any of the combinations.

Examples of the above-mentioned polymers include ester-based polymers such as polyethylene terephthalate and polyethylene naphthalate, styrene-based polymers such as polystyrene and acrylonitrile / styrene copolymers (AS polymers), polyethylene and polypropylene, cyclo-based polymers. Olefin polymers such as polyolefins and ethylene-propylene copolymers having a norbornene structure, acrylic polymers such as polymethylmethacrylate, cellulosic polymers such as cellulose diacetate and cellulose triacetate, amide polymers such as nylon and aromatic polyamides. Can be given.

Further, carbonate type polymers, vinyl chloride type polymers, imide type polymers and sulfone type polymers,
Polyether sulfone or polyether ether ketone,
Polyphenylene sulfide, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene,
Silicone polymers, urethane polymers, ether polymers, vinyl acetate polymers, blends of the above polymers, or thermosetting types of phenolic, melamine, acrylic, urethane, urethane acrylic, epoxy, silicone, etc. , Or UV-curable polymers are also examples of the above-mentioned transparent polymer.

On the other hand, examples of the liquid crystals include a nematic phase and a smectic phase at room temperature or high temperature such as cyanobiphenyl type, cyanophenylcyclohexane type, cyanophenyl ester type, benzoic acid phenyl ester type, phenylpyrimidine type and their mixtures. Examples thereof include low molecular weight liquid crystals and crosslinkable liquid crystal monomers, and liquid crystal polymers that exhibit a nematic phase or a smectic phase at room temperature or high temperature. The above-mentioned crosslinkable liquid crystal monomer is usually subjected to an alignment treatment and then subjected to a crosslinking treatment by an appropriate method using heat, light or the like to obtain a polymer.

From the viewpoint of obtaining a polarizing scattering plate having excellent heat resistance and durability, the glass transition temperature is 50 ° C. or higher, especially 80 ° C.
Above all, it is preferable to use a combination of polymers having a temperature of 120 ° C. or higher and a crosslinkable liquid crystal monomer or liquid crystal polymer. As the liquid crystal polymer, an appropriate one such as a main chain type or a side chain type can be used, and the type thereof is not particularly limited. A liquid crystal polymer which can be preferably used from the viewpoints of forming property of minute regions excellent in uniformity of particle size distribution, thermal stability, moldability into a film, easiness of orientation treatment, etc., has a degree of polymerization of 8 or more, preferably 10 or less. Above all, especially those of 15 to 5000.

The formation of a polarizing scattering plate using a liquid crystal polymer is carried out, for example, by mixing one or more kinds of polymers with one or more kinds of liquid crystal polymers for forming a micro region, Can be carried out by a method of forming a polymer film containing dispersed and contained in a minute region and subjecting it to an orientation treatment by an appropriate method to form a region having different birefringence.

In view of the controllability of the above-mentioned refractive index differences Δn1 and Δn2 due to the orientation treatment, the glass transition temperature is 50 ° C. or higher and the temperature range is lower than the glass transition temperature of the polymers used in combination. Those exhibiting a nematic liquid crystal phase can be preferably used. Incidentally, specific examples thereof include a side chain type liquid crystal polymer having a monomer unit represented by the following general formula.

General formula:

In the above general formula, X is a skeleton group forming the main chain of the liquid crystal polymer, and may be formed by an appropriate connecting chain such as linear, branched or cyclic. Incidentally, examples thereof include polyacrylates and polymethacrylates, poly-α-haloacrylates and poly-α-cyanoacrylates, polyacrylamides and polyacrylonitriles, polymethacrylonitriles and polyamides, polyesters and Examples thereof include polyurethanes, polyethers, polyimides and polysiloxanes.

Further, Y is a spacer group branched from the main chain, and a spacer group Y which is preferable from the viewpoint of forming a polarizing scattering plate such as refractive index control is, for example, ethylene, propylene, butylene, pentylene, hexylene or octylene. ,
Examples include decylene, undecylene, dodecylene, octadecylene, ethoxyethylene and methoxybutylene.

On the other hand, Z is a mesogenic group which imparts liquid crystal orientation, and examples thereof include the following compounds.

The terminal substituent A in the above compound is, for example, a cyano group, an alkyl group, an alkenyl group, an alkoxy group, an oxaalkyl group or a haloalkyl group or a haloalkoxy group in which one or more hydrogen atoms are substituted with fluorine or chlorine. It may be a suitable one such as a haloalkenyl group.

In the above, the spacer group Y and the mesogen group Z may be bonded via an ether bond, that is, -O-. Further, in the phenyl group in the mesogen group Z, one or two hydrogens may be substituted with halogen, and in that case, chlorine or fluorine is preferable as the halogen.

The nematic side chain type liquid crystal polymer may be any suitable thermoplastic polymer such as a homopolymer or a copolymer having the monomer unit represented by the above general formula. Excellent ones are preferred.

The formation of the polarizing scattering plate using the above-mentioned nematic liquid crystal polymer is carried out by, for example, forming a polymer film and a nematic liquid crystal phase in a temperature range lower than the glass transition temperature of the polymer. A liquid crystal polymer having a glass transition temperature of 50 ° C. or higher, especially 60 ° C. or higher, particularly 70 ° C. or higher is mixed to form a polymer film containing the liquid crystal polymer dispersed in a fine region, and then the fine region is formed. The liquid crystal polymer may be heat-treated to be aligned in a nematic liquid crystal phase, and the alignment state may be fixed by cooling.

The formation of the above-mentioned polymer film containing minute regions dispersed therein, that is, the film to be oriented, is
For example, it can be obtained by an appropriate method such as a casting method, an extrusion molding method, an injection molding method, a roll molding method, or a casting method, and is developed in a monomer state and polymerized by heat treatment or radiation treatment such as ultraviolet ray. It is also possible to use a method of forming a film into a film.

From the viewpoint of obtaining a polarizing scattering plate having excellent even distribution of minute regions, a method of forming a film of a mixed liquid of a forming material through a solvent by a casting method, a casting method or the like is preferable. In that case, the size and distribution of the minute regions can be controlled by the type of solvent, the viscosity of the mixed solution, the drying speed of the mixed solution developing layer, and the like. By the way, in order to reduce the area of the minute region, it is advantageous to reduce the viscosity of the mixed solution and to accelerate the drying speed of the mixed solution developing layer.

The thickness of the film to be subjected to the orientation treatment can be appropriately determined, but it is generally 1 μm in view of the orientation treatment property.
.About.3 mm, especially 5 .mu.m to 1 mm, especially 10 to 500 .mu.m. When forming the film, appropriate additives such as a dispersant, a surfactant, an ultraviolet absorber, a color tone adjusting agent, a flame retardant, a release agent, and an antioxidant can be added.

As described above, the alignment treatment is performed, for example, in the uniaxial or biaxial manner.
Axis, sequential biaxial or Z-axis stretching treatment method or rolling method,
A method of applying an electric field or a magnetic field at a temperature higher than the glass transition temperature or a liquid crystal transition temperature to rapidly cool to fix the alignment, a method of fluidizing alignment during film formation, a self-alignment of liquid crystal based on a slight alignment of an isotropic polymer. It is possible to use one or two or more of suitable methods such as a method of controlling the refractive index by orientation. Therefore, the obtained polarizing scattering plate may be a stretched film or a non-stretched film. When the stretched film is used, a brittle polymer can be used, but a polymer having excellent extensibility can be particularly preferably used.

When the minute regions are composed of the above-mentioned liquid crystal polymer, for example, the liquid crystal polymer dispersed and distributed as minute regions in the polymer film is heated to a temperature at which the liquid crystal polymer exhibits a desired liquid crystal phase such as a nematic phase, and melted. Can also be performed by a method of fixing the orientation state by orienting under the action of the orientation regulating force and quenching. The orientation state of the minute region is preferably in the monodomain state as much as possible from the viewpoint of preventing variations in optical characteristics.

The above-mentioned orientation regulating force is, for example, a stretching force by a method of stretching a polymer film at an appropriate ratio, a shearing force at the time of film formation, an electric field or a magnetic field, and an appropriate orientation force. The regulation force can be applied, and the alignment treatment of the liquid crystal polymer can be performed by applying one or more types of the regulation force.

Therefore, the portion other than the minute region in the polarization scattering plate may have birefringence or may be isotropic. Those that exhibit birefringence as a whole of the polarizing scattering plate can be obtained by molecular orientation in the film forming process described above using oriented birefringent polymers for forming a film, and if necessary, for example, stretching Birefringence can be imparted or controlled by adding a known orientation means such as treatment. Further, as the polarizing scattering plate in which the part other than the minute region is isotropic, for example, an isotropic polymer for forming a film is used, and the film is stretched in a temperature region below the glass transition temperature of the polymer. It can be obtained by a method such as.

A polarization scattering plate that can be preferably used is a refractive index difference Δn in each optical axis direction of the minute region between the minute region and the other portion, that is, a portion made of a polymer film.
1, Δn2 and Δn3 are 0.03 or more (Δn1) in the axial direction (Δn1 direction) showing the maximum value, and the remaining two axial directions (Δn2 direction, Δn) orthogonal to the Δn1 direction.
50% or less of the above Δn1 in 3 directions (Δn2, Δ
n3), and those in which Δn2 and Δn3 are equal are more preferable.

By setting the above refractive index difference, Δn1
The linearly polarized light in one direction is strongly scattered and scattered at an angle smaller than the total reflection angle, so that the amount of light emitted from the light guide plate can be increased. Can be locked inside.

In the above description, when the polymer forming the film is optically isotropic, the difference in the refractive index between each optical axis direction of the microscopic region and the portion other than the microscopic region is It means the difference between the refractive index in the axial direction and the average refractive index of the polymer film, and when the polymer forming the film has optical anisotropy, the main optical axis direction of the polymer film and the Since the optical axis direction is usually the same, it means the difference between the respective refractive indexes in the respective axial directions.

From the above-mentioned point of total reflection, it is preferable that the refractive index difference Δn1 in the Δn1 direction is moderately large. In particular, the refractive index difference Δn1 is 0.035 to 1, especially 0.045 to 0.5. Is preferred. The difference in refractive index between the Δn2 direction and the Δn3 direction, Δn2 and Δn3 directions, is preferably appropriately small. Such a difference in refractive index can be controlled by the refractive index of the material used, the above-mentioned orientation operation, and the like.

Since the Δn1 direction is the vibrating surface of the linearly polarized light emitted from the light guide plate, the Δn1 direction is
The direction is preferably parallel to the plane of the polarized light scattering plate. The Δn1 direction in the plane can be an appropriate direction according to the intended liquid crystal cell or the like.

It is preferable that the minute regions in the polarization scattering plate are distributed as evenly as possible in view of the homogeneity of the scattering effect and the like. The size of the minute region, particularly the length in the scattering direction Δn1 is related to backscattering (reflection) and wavelength dependence.

The improvement of light utilization efficiency, prevention of coloration due to wavelength dependency, prevention of visual inhibition of minute areas or prevention of clear display inhibition, and further preferable of minute areas in terms of film-forming property and film strength. The size, particularly the preferable length in the Δn1 direction, is 0.05 to 500 μm, especially 0.1.
˜250 μm, especially 1 to 100 μm. Incidentally, the microscopic region usually exists in the polarization scattering plate in the state of a domain,
There is no particular limitation on the length in the Δn2 direction or the like.

The proportion of the minute area in the polarized light scattering plate is
It can be appropriately determined from the viewpoint of the scattering property in the Δn1 direction,
Generally, it is 0.1 to 70% by weight, especially 0.5 to 50% by weight, and particularly 1 to 30% by weight in consideration of film strength and the like.

The polarized light scattering plate can be formed of a single layer of the above-mentioned film exhibiting the birefringence characteristic, or can be formed by stacking two or more layers of such a film. By stacking the films, a synergistic scattering effect of increasing the thickness or more can be exhibited. The superposed body is
The films may be superposed at an arbitrary arrangement angle such as the Δn1 direction or the Δn2 direction, but from the viewpoint of expansion of the scattering effect, the Δn1 directions are superposed so that the upper and lower layers are in a parallel relationship. Those obtained are preferred. The number of superposed films can be an appropriate number of two or more layers.

The film to be superposed has Δn1 or Δn.
The two and the like may be the same or different. The parallel relationship between the upper and lower layers in the Δn1 direction or the like is preferably as parallel as possible, but deviations due to work errors are allowed. If there are variations in the Δn1 direction, etc., it is based on the average direction.

The film in the superposed body is adhered via an adhesive layer so that the total reflection interface becomes the outermost surface.
For the adhesion, for example, a suitable adhesive such as a hot melt type or an adhesive type can be used. From the viewpoint of suppressing reflection loss, an adhesive layer having a refractive index difference with the film as small as possible is preferable, and the film or a polymer forming a minute region thereof can be used for adhesion.

It is preferable that the scattering polarizing plate has a phase difference in whole or in part of the plate because the polarization state needs to be appropriately canceled in the process of transmitting light in the light guide plate. Basically, since the slow axis of the scattering polarizer and the polarization axis (vibration plane) of linearly polarized light that is difficult to be scattered are orthogonal to each other, polarization conversion due to the phase difference is difficult to occur, but the apparent angle changes due to slight scattering. However, it is considered that polarization conversion occurs.

From the above-mentioned point of polarization conversion, it is preferable that there is an in-plane retardation of 5 nm or more, although it varies depending on the thickness of the scattering polarizing plate. The phase difference is imparted by a method of containing birefringent fine particles or a method of adhering to the surface,
It can be performed by an appropriate method such as a method in which the polymer film has birefringence or a method in which they are used in combination.

The polarized light guide plate according to the present invention uses a laminated body of a translucent resin plate and a polarized light scattering plate. When forming it, the translucent resin plate 1 and the polarized light are used as illustrated in FIG. In order to suppress reflection at the interface with the scattering plate 3 as much as possible, that is, to facilitate the transmission of transmitted light between the translucent resin plate and the polarization scattering plate, the surface of the laminated body composed of those adhered and integrated bodies. In order to achieve total reflection on the back surface, it is preferable that the back surface be bonded with an adhesive having a refractive index as close as possible. The bonding process is
This is more effective than preventing axial misalignment. When forming the polarized light guide plate, the polarized light scattering plates 3 may be provided on both front and back surfaces of the transparent resin plate 1 as illustrated in FIG.

The above-mentioned adhesion treatment is carried out in accordance with the above-mentioned superposition type polarization scattering plate, for example, an appropriate adhesion of a transparent adhesive such as an acrylic type, a silicone type, a polyester type, a polyurethane type, a polyether type or a rubber type. An agent can be used, and there is no particular limitation. From the viewpoint of preventing changes in optical properties, it is preferable that curing and drying do not require a high-temperature process and that curing and drying are not required for a long time. Further, those which do not cause a peeling problem such as floating or peeling under the condition of heating or humidifying are preferable.

From the above points, an alkyl ester of (meth) acrylic acid having an alkyl group having a carbon number of 20 or less such as a methyl group, an ethyl group or a butyl group, and (meth) acrylic acid or (meth) acrylic acid hydroxy. Acrylic monomers consisting of improved components such as ethyl have a glass transition temperature of 0
An acrylic pressure-sensitive adhesive having a weight average molecular weight of 100,000 or more and an acrylic polymer as a base polymer, which is obtained by copolymerization in a combination of not higher than 0 ° C., is preferably used. The acrylic pressure-sensitive adhesive also has advantages such as excellent transparency, weather resistance, and heat resistance.

The adhesive layer may be attached to the transparent resin plate and / or the polarization scattering plate by an appropriate method. As an example thereof, an adhesive component is dissolved or dispersed in a solvent composed of a single solvent or a mixture of appropriate solvents such as toluene and ethyl acetate to prepare an adhesive liquid of about 10 to 40% by weight, which is then poured. A method of directly attaching on a transparent resin plate or a polarization scattering plate by an appropriate development method such as a spreading method or a coating method, or an adhesive layer is formed on a separator in accordance with the above and the transparent resin plate is used. And a method of transferring onto a polarized light scattering plate. The adhesive layer provided may be a superposed layer of different compositions or types.

The thickness of the adhesive layer can be appropriately determined depending on the adhesive strength and the like, and is generally 1 to 500 μm. In the adhesive layer, if necessary, for example, a resin such as a natural or synthetic resin, glass fiber or glass beads, a filler or pigment made of metal powder or other inorganic powder, a coloring agent, an antioxidant, or the like is used. Additives can also be added. Further, a fine particle may be contained to form an adhesive layer having a light diffusing property.

As shown in FIG. 1, the specular reflection layer 5 provided on one surface of the laminated body 4 of the translucent resin plate 1 and the polarization scattering plate 3 polarizes the light emitted from the side where the reflection layer is arranged, through the specular reflection layer. The purpose is to reverse the state without changing the state and concentrate the emitted light on one of the front and back surfaces of the polarization light guide plate to improve the brightness.

The reflective layer is preferably a mirror surface as much as possible from the viewpoint of maintaining the polarization state, and a reflective surface made of a metal is particularly preferred from the viewpoint. As the metal, for example, aluminum, silver, chromium, gold, copper, tin, zinc, indium, palladium, platinum, or an appropriate alloy thereof can be used.

The specular reflection layer can be directly adhered to the laminated body as an additional layer of a metal thin film by a vapor deposition method or the like, but complete reflection is difficult and some absorption by the reflection layer also occurs, and repetition due to total reflection is considered. Then, there is a concern about absorption loss, and from the viewpoint of preventing this, an arrangement method is preferable in which an air layer simply by arranging the reflecting plates can intervene.

From this point of view, therefore, the specular reflection layer is preferably a plate-like one such as a reflection plate having a support substrate provided with a metal thin film by a sputtering method or a vapor deposition method, a metal foil or a rolled sheet of metal. . As the supporting base material of the reflective layer, an appropriate material such as a glass plate or a resin sheet can be used. Among them, those obtained by vapor-depositing silver, aluminum or the like on a resin sheet can be preferably used from the viewpoints of reflectance, tint and handleability. The reflective layer may be arranged on either side of the laminate.

On the other hand, the polarization-maintaining lens sheet provided on the opposite surface of the laminated body, that is, on the surface on which the specular reflection layer is not arranged, allows the scattered outgoing light (linearly polarized light) from the laminated body to have its degree of polarization. The object is to improve the directivity in the front direction, which is advantageous for visual recognition, by controlling the optical path while maintaining the maximum extent, and to set the intensity peak of the scattering emission light in the front direction.

As the lens sheet, the scattered light incident from one surface (rear surface) is controlled so that the scattered light is efficiently emitted from the other surface (front surface) in the direction perpendicular to the sheet surface (front surface) as appropriate. Any material can be used and there is no particular limitation. Therefore, any one having various lens shapes used in the conventional sidelight type light guide plate can be used except for the polarization maintaining property (for example, JP-A-5-169015).

The lens sheet preferably used exhibits a total light transmittance of, for example, 80% or more, especially 85% or more, and particularly 90% or more, and leak light (transmittance) due to depolarization when arranged between crossed Nicols. Is 5% or less, especially 2% or less, and particularly 1% or less, the light transmittance is excellent, and the polarization characteristics of the emitted light are not eliminated as much as possible.

In general, since the depolarization is caused by birefringence or multiple scattering, for example, the lens sheet exhibiting the polarization maintaining property described above should reduce the birefringence as much as possible, and the average reflection (scattering) in the ray trajectory. It can be achieved by reducing the number of times, and specifically, for example, the polymers exemplified in the above-mentioned translucent resin plate and scattering polarizing plate, such as cellulose triacetate resin, polymethyl methacrylate, polycarbonate and norbornene resin. It can be obtained by a method of forming a lens sheet by using one kind or two kinds or more of a resin having a low birefringence (a resin having a good optical isotropy).

As described above, the lens sheet is, for example, a convex lens type in which the refractive index is controlled through a photopolymer or the like on the surface or inside of a transparent resin base material which may contain resins having different refractive indexes. Or a refractive index distribution type (GI type) lens area, in particular, a plurality of minute lens areas formed, or a lens area formed by filling a large number of through holes provided in a transparent resin substrate with a polymer having a different refractive index. It may have an appropriate lens form such as a lens having a plurality of spherical lenses arranged in a single layer and fixed with a thin film, but the point of controlling the optical path through the difference in refractive index. Figure 1 rather than
It is preferable that the sheet 6 has a lens form 61 having a concavo-convex structure on one side or both sides, particularly on one side as illustrated in FIG.

The concavo-convex structure forming the above-mentioned lens form is
It may be any one as long as it has a function of controlling the optical path of the light transmitted through the sheet and condensing the transmitted light in the front direction. For example, a large number of linear grooves or protrusions having a triangular cross section in a stripe shape or a lattice shape. Examples thereof include an array, or an array of a number of pyramidal minute projections having a bottom surface shape such as a triangular pyramid, a quadrangular pyramid, and other polygonal cones and cones. In addition, the linear or dot-shaped concavo-convex structure is used for spherical lenses, aspherical lenses,
It may be a semi-cylindrical lens or the like, and may have an appropriate lens form.

The formation of the lens sheet having the above-mentioned linear or dot-shaped concavo-convex structure is performed, for example, by filling a mold formed so that a predetermined concavo-convex structure is formed with a resin liquid or a monomer for resin formation. An appropriate method such as a method of transferring the uneven structure of the mold by polymerization treatment or a method of transferring the uneven structure by heat-pressing a resin sheet to the mold can be used. The lens sheet may be formed as a superposed layer of two or more resin layers of the same kind or different kinds, such as a lens sheet added to a support sheet.

The lens sheet may be arranged in one layer or two or more layers on the light emitting side of the laminate. When arranging two or more layers, the lens sheets may be the same,
Although they may be different from each other, it is preferable to maintain the polarization maintaining property as a whole. When the lens sheet to be arranged is adjacent to the laminated body, it is preferable that the lens sheet is arranged so that a void is generated in the laminated body as in the case of the above-described specular reflection layer. Further, it is preferable that the void is sufficiently larger than the wavelength of incident light in terms of total reflection.

When the lens shape of the lens sheet has a linear concave-convex structure, the line direction is the optical axis direction of the polarization scattering plate (vibration plane direction of outgoing polarized light) from the viewpoint of optical path control in the front direction. It is preferable to arrange them so as to be in a parallel state or an orthogonal state. In addition, 2 such lens sheet
In the case of arranging more than one layer, it is preferable to arrange them so that the line directions of the upper and lower layers intersect with each other from the viewpoint of efficiency of optical path control.

As shown in FIG. 1, on the light exit side of the laminate 4, the lens sheet 6 and the exit light (linearly polarized light) are diffused while maintaining the degree of polarization as much as necessary to uniformly emit light. For maintaining the polarization of one or more layers between the lens sheet and the laminated body or on the light emitting side of the lens sheet for the purpose of improving visibility by reducing the visual sense of the pattern of the lens sheet, etc. Light diffusing layer 7 can be disposed.

As the light diffusing layer, one having excellent light transmittance and maintaining the polarization characteristics of emitted light as much as possible is preferably used in accordance with the above-mentioned lens sheet. Therefore, for the formation of the light diffusion layer, a resin having a small birefringence exemplified in the above lens sheet is preferably used, for example, a resin layer containing transparent particles dispersed therein, or a resin having a fine concavo-convex structure on the surface. Such a polarization maintaining light diffusion layer can be obtained as a layer or the like.

Examples of the transparent particles dispersedly contained in the resin layer include silica, glass, alumina, and the like.
Titania or zirconia, tin oxide or indium oxide, inorganic fine particles that may be conductive such as cadmium oxide or antimony oxide, or acrylic polymer or polyacrylonitrile, polyester or epoxy resin, melamine resin or urethane resin, Polycarbonate, polystyrene, silicone resin, benzoguanamine, melamine / benzoguanamine condensate, benzoguanamine /
Examples thereof include organic fine particles made of a crosslinked or uncrosslinked polymer such as a formaldehyde condensate.

As the transparent particles, one kind or two or more kinds can be used, and the particle diameter is preferably 1 to 20 μm from the viewpoints of light diffusivity and uniformity of the diffusion. On the other hand, although the particle shape is arbitrary, a (true) spherical shape or a secondary aggregate thereof is generally used. In particular, from the viewpoint of polarization maintaining property, transparent particles having a refractive index ratio with a resin of 0.9 to 1.1 can be preferably used.

The particle-containing light diffusion layer may be formed, for example, by a method in which transparent particles are mixed with a resin melt and extruded into a sheet or the like, or a solution or monomer of the resin is mixed with transparent particles and cast on a sheet or the like. It can be formed by an appropriate method according to the conventional method such as a method of performing a polymerization treatment, a method of applying a resin liquid containing transparent particles on a predetermined surface or a polarization maintaining film, and the like.

On the other hand, the light diffusing layer having a fine concavo-convex structure on the surface is formed by roughening the surface of the resin sheet by, for example, buffing by sandblasting or embossing. Can be performed by an appropriate method such as a method of forming a layer of a translucent material having However, the method of forming irregularities (protrusions) having a large difference in refractive index with bubbles such as air and a resin such as titanium oxide fine particles is not preferable because polarization can be easily eliminated.

The surface fine uneven structure in the light diffusion layer has a surface roughness of not less than 100 μm and not longer than the wavelength of incident light, and has no periodicity due to unevenness of light diffusion and uniformity of diffusion. Is preferred. In the formation of the transparent particle-containing type or surface fine unevenness type light diffusion layer described above, it is possible to suppress the increase in retardation due to photoelasticity or orientation in the base layer made of the resin as much as possible. It is preferable in terms of polarization maintaining property.

The light diffusing layer may be arranged as an independent layer made of a plate-shaped material or the like, or may be arranged as a subordinate layer which is closely adhered and integrated with the lens sheet. When the light diffusion layer is arranged adjacent to the laminated body, it is preferable that the light diffusion layer is arranged so as to form a void in the laminated body according to the lens sheet described above. When two or more light diffusing layers are arranged, the light diffusing layers may be the same or different, but it is preferable that the entire light diffusing layer retains the polarization maintaining property.

The polarized light guide plate according to the present invention can be preferably used for forming a polarized light source because it exhibits the characteristic that incident light from the side surface is emitted as linearly polarized light from one of the front and back surfaces as described above. The polarized light source can be formed by disposing the light source 8 on at least one side surface of the polarized light guide plate as illustrated in FIG.

The light source may be a polarized light guide plate, especially a (cold, hot) cathode tube which can be arranged on the side surface of the laminate 4.
A linear or planar array body such as a light emitting diode or an appropriate one such as an incandescent bulb may be used. Above all, a cold cathode tube can be preferably used in terms of luminous efficiency, low power consumption, and small diameter. The light sources may be arranged on a plurality of side surfaces such as two side surfaces facing each other of the polarization light guide plate or three side surfaces such as a U-shaped tube in view of brightness and uniformity thereof.

When forming a polarized light source, if necessary, appropriate auxiliary means such as a reflector 81 surrounding the light source 8 is arranged to guide the divergent light from the light source to the side surface of the polarized light guide plate as shown in the figure. You can also For the reflector, a resin sheet or a metal foil provided with a high reflectance metal thin film is generally used. Further, the reflector may be extended to the lower surface of the polarization light guide plate to serve also as the specular reflection layer. The reflector is also useful as a light source fixing means.

Upon formation of the polarized light source, one or two or more kinds of suitable optical layers can be arranged at suitable positions. The optical layer is not particularly limited, and for example, an appropriate layer such as a polarizing plate, a retardation plate, or a liquid crystal cell used for forming a liquid crystal display device can be used. In that case, the lens sheet and the light diffusion layer described above can be brought into close contact with an optical layer arranged on the upper side of the polarization light guide plate via an adhesive layer or the like.
However, in the case of a lens sheet having a concavo-convex structure or a surface fine concavo-convex type light diffusing layer, the above-mentioned arrangement with the voids is preferable.

In the present invention, each layer forming the polarized light guide plate or the polarized light source is, for example, salicylic acid ester compound, benzophenol compound, benzotriazole compound, cyanoacrylate compound, nickel complex salt compound, etc., if necessary. It is possible to add an ultraviolet absorber of 1 to have ultraviolet absorbing ability.

The polarized light guide plate and the polarized light source according to the present invention are
As described above, since the linearly polarized light is provided with its vibrating surface (polarization axis) being controlled, an appropriate device or application that uses the linearly polarized light, such as formation of a liquid crystal display device, based on its characteristics. Can be used for.

[0084]

Example 1 Norbornene-based resin (JSR, Arton, glass transition temperature 182 ° C.) 950 parts (parts by weight, the same applies hereinafter) and a liquid crystal polymer represented by the following formula (glass transition temperature 80 ° C., nematic liquid crystal) A temperature of 100 to 290 ° C.) 50 parts of a 20 wt% dichloromethane solution was dissolved to form a film having a thickness of 100 μm by a casting method.
The film was stretched 3 times at 0 ° C and then rapidly cooled to obtain a polarizing scattering plate.

The above-mentioned polarization scattering plate is a transparent film made of norbornene-based resin in which a liquid crystal polymer is dispersed in domains having substantially the same shape in the state of being long axis in the stretching direction, and the difference in refractive index Δn1 is 0. .23, and Δn2 and Δn3 were 0.029. Further, when the average diameter of the minute region was measured by coloring based on the phase difference by observation with a polarizing microscope, the length in the Δn1 direction was about 5 μm.

Next, the polarizing scattering plate was placed on one side of an acrylic resin plate (made by Mitsubishi Rayon Co., Ltd.) having a thickness of 2 mm so that the Δn1 direction has an angle of intersection of 45 degrees with the end face, and an acrylic adhesive layer was interposed therebetween. A laminated body is formed by adhering, a PET sheet is provided with a specular reflection sheet having silver vapor deposited on the lower surface, and a lens sheet is arranged on the upper surface to obtain a polarized light guide plate, and a cold cathode tube is provided on one side surface of the laminated body. A polarized surface light source was obtained by fixing with a lamp reflector made of a matte-treated PET-based reflection sheet.

The lens sheet has a lens shape having linear projections of a 90 ° apex angle and a height of 180 μm and having a triangular cross section in a stripe shape at intervals of 350 μm. The cellulose acetate resin film was provided on one side, and the lens form side was placed as the upper side and the stripe direction was arranged in parallel with the Δn2 direction. Such a lens sheet has a transmittance (amount of leaked light due to depolarization, the same applies hereinafter) of 1.0% of all incident light when placed between crossed Nicols and excellent in polarization maintaining property. Is.

Example 2 30 parts of silicone particles having an average particle size of 4 μm were added to 70 parts of an ultraviolet curable epoxy resin, stirred and mixed for defoaming, and then 30 μm on one side of a cellulose triacetate film having a thickness of 80 μm.
With a thickness of 10 mm, and apply light with a high pressure mercury lamp at an integrated light intensity of 10
A polarized light guide plate and a polarized surface light source were obtained in the same manner as in Example 1 except that the light diffusing plate obtained by irradiation with 00 mj / cm ² and curing treatment was arranged between the laminate and the lens sheet. The amount of leaked light due to depolarization of the light diffusion plate was 0.7% of all incident light.

Comparative Example 1 Reflective ink mixed with titanium white was printed in dots on one surface of an acrylic resin plate having a thickness of 2 mm, and foamed PET was formed on one surface thereof.
A surface light source was obtained in the same manner as in Example 1 except that a light guide plate formed by disposing a white reflector was formed.

Comparative Example 2 The amount of leaked light due to depolarization using a polyester film in place of the cellulose triacetate film was 6.2 of the total incident light.
%, A polarized light guide plate and a polarized surface light source were obtained in the same manner as in Example 1.

Evaluation Test Regarding the (polarized) surface light sources obtained in Examples and Comparative Examples, the brightness in the front direction at the central portion and the transmittance of 44 on the surface light source.
%, A commercially available absorption type polarizing plate with a polarization degree of 99% has a transmission axis of 45
The brightness in the front direction when arranged so as to have a degree was measured with a brightness meter (BM-7, manufactured by Topcon Corp.), and the ratio was examined with reference to the case without a polarizing plate of Comparative Example 1. The results are shown in the table below.

No front brightness polarizing plate With polarizing plate Example 1 95 76 Example 2 98 77 Comparative Example 1 100 44 Comparative Example 2 95 48

From the table, it can be seen from the table that the linearly polarized light is emitted in the embodiment and the brightness is drastically improved when passing through the polarizing plate, and in comparison with the comparative example 2, the lens sheet eliminates the polarized state. In some cases, it can be seen that the advantage of emitting linearly polarized light cannot be utilized. From the above, it can be seen that by using the polarized surface light source according to the present invention as a backlight of a liquid crystal display device, a brightness which is 1.5 times or more that of a normal case (Comparative Example 1) can be achieved and a very bright display can be achieved. In addition, in Example 2 in which the light diffusion plate was added, the visual sense of the linear pattern on the lens sheet was alleviated, and the visibility was improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of a polarized surface light source.

FIG. 2 is a sectional view of another example of a polarized light guide plate.

[Explanation of symbols]

4: Laminated body 1: translucent resin plate 2: adhesive layer 3: polarized light scattering plate 5: Specular reflection layer 6: Lens sheet 7: Light diffusion layer 8: Light source

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI G02B 5/30 G02B 5/30 G02F 1/13357 G02F 1/1335 530 (56) Reference JP-A-9-134607 (JP, A, JP ) JP-A-9-274108 (JP, A)

Claims (7)

(57) [Claims] 1. A specular reflection on one surface of a laminate comprising a transparent resin plate, on one or both sides of which a polarizing scattering plate having dispersed birefringent microscopic regions and exhibiting scattering anisotropy depending on the polarization direction is provided. The layered product has at least one layer of a polarization-maintaining lens sheet on the other surface of the laminated body, and is selectively scattered by the above-mentioned scattering anisotropy in natural light incident from the side surface. polarization light guide plate, characterized in that the elevation does not have side or RaIzuru the specular reflection layer linearly polarized light is. 2. The polarized light guide plate according to claim 1, wherein the lens sheet is made of one or more resins having low birefringence. 3. The polarized light guide plate according to claim 1, wherein the lens sheet is made of cellulose triacetate-based resin, polymethyl methacrylate, polycarbonate or norbornene-based resin. 4. The polarized light guide plate according to claim 1, wherein the lens sheet has a linear or dot-shaped concavo-convex structure on one surface. 5. The polarized light guide plate according to claim 4, wherein the lens sheet has a linear concavo-convex structure, and the line direction is parallel or orthogonal to the optical axis direction of the polarization scattering plate. 6. The polarized light guide plate according to claim 1, further comprising at least one polarization-maintaining light diffusing layer between the lens sheet and the laminated body or on the light emitting side of the lens sheet. 7. A polarized light source having a light source on at least one side surface of the polarized light guide plate according to claim 1.