JP2000329942A - Polarizing light transmission plate and polarization plane light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a light transmission plate from which exiting light of linearly polarized light can be obtd. while the polarizing direction (oscillation plane) of light can be controlled as desired. SOLUTION: This polarizing light transmission plate consists of a laminated body 4, a mirror reflection layer 5 on one surface of the body 4, and at least one light-diffusing layer 6 having maintaining property for polarized light on the other surface of the body 4. The laminated body 4 is produced by forming a scattering plate 3 for polarized light which has birefringent microregions dispersed and which has scattering anisotropy according to the polarization direction on one or both surfaces of a light transmitting resin plate 1. The polarization plane light source consists of the aforementioned polarizing light transmission plate and a light source 7 disposed in at least one side of the light transmission plate. By this constitution, natural light can be used to enter the side face of the transmission plate to efficiently exit as linearly polarized light from one of the front and back faces without requiring formation of a special light-exiting means such as reflective dots on the light transmitting resin plate. The oscillation direction of the linearly polarized light can be controlled as desired by controlling the optical axis of the scattering plate for polarized light, and thereby, a liquid crystal display device having excellent brightness and uniformity can be obtd.

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 from the side surface being controlled from one of the front and back surfaces and the vibrating surface being controlled. And a polarization plane light source.

[0002]

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

[0003] In view of the above, there has been proposed a system in which a polarization converter combining a polarization separation plate and a retardation plate capable of obtaining linearly polarized light by using the Brewster angle is used (Japanese Patent Laid-Open No. Hei 6-18873). Gazette, JP-A-6-16084
0, JP-A-6-265892, JP-A-7-
JP-A-72475, JP-A-7-261122, JP-A-7-270792, JP-A-9-54556, JP-A-9-105933, JP-A-9-13
8406, JP-A-9-152604, JP-A-9-293406, JP-A-9-326205 and JP-A-10-78581. However, such a backlight has a problem in that it is not practically used because sufficient polarization cannot be obtained and it is difficult to control the polarization direction.

[0004]

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

[0005]

According to the present invention, there is provided a laminate comprising a light-transmitting resin plate provided on one or both surfaces thereof with a polarizing and scattering plate which contains a birefringent fine region in a dispersed manner and exhibits scattering anisotropy depending on the polarization direction. A polarizing light guide plate, which has a specular reflection layer on one surface thereof, and at least one polarization maintaining light diffusing layer on the other surface of the laminate, and a light source on at least one side of the polarizing light guide plate. A polarizing plane light source characterized by having

[0006]

According to the present invention, with the above structure, natural light is made to enter from the side surface without forming any special light emitting means such as reflective dots on the translucent resin plate, and the mirror reflection layers on the front and back surfaces are provided. It is possible to efficiently emit linearly polarized light from the other side, and to obtain linearly polarized light in the vibration direction according to the optical axis of the polarization scattering plate used together. Therefore, the oscillation direction of the linearly polarized light can be arbitrarily changed by controlling the optical axis of the polarization scattering plate. In addition, linearly polarized light having excellent diffusivity of emitted light is obtained through the polarization maintaining light diffusion layer, and the liquid crystal display element is arranged with the polarization axis parallel to the liquid crystal display element. It is also possible to achieve nearly twice the brightness.

That is, in the above, the incident light from the side surface is totally reflected by the difference in the refractive index from the air interface and is transmitted through the light guide plate while being incident on the polarization scattering plate. The axial direction (△ n1) indicating the rate difference (△ n1)
The linearly polarized light having the vibration plane parallel to the direction is selectively and strongly scattered, and a part thereof 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 without the specular reflection layer). From one surface, linearly polarized light is dispersed through the light diffusion layer without greatly reducing the degree of polarization, and is emitted with good uniformity.

On the other hand, the light scattered at a large angle in the △ n1 direction, the light that satisfies the △ n1 direction condition but is not scattered, and the light having a vibration direction other than the △ n1 direction Then, the light is confined in the light guide plate and transmitted while repeating total reflection, and the polarization state is canceled by the birefringence phase difference by the polarization scattering plate, and the opportunity to emit light satisfying the Δn1 direction condition is waited. By repeating the above, linearly polarized light having a 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 a birefringent fine region in a dispersed manner and exhibits scattering anisotropy depending on the polarization direction on one or both surfaces of a light transmitting resin plate. The laminate has a specular reflection layer on one side and at least one polarization maintaining light diffusion layer on the other side of the laminate. An example is shown in FIG. 1 is a translucent resin plate, 3 is a polarization scattering plate, 4 is a laminate thereof,
5 is a specular reflection layer, 6 is a light diffusion plate, and 2 is an adhesive layer as required. FIG. 1 illustrates an example in which a polarization plane light source is used, and reference numeral 7 denotes a light source.

The translucent resin plate may be a plate-like material formed of an appropriate material exhibiting transparency according to the wavelength range of the light source. Incidentally, in the visible light region, 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. From the viewpoint of light transmittance, a plate made of a resin having a refractive index as small as possible is preferable.

It is preferable to use a resin plate having as small an in-plane phase difference as possible rather than to maintain the polarization characteristics of the emitted light. Materials that are unlikely to occur, particularly polymethylmetallate and norbornene resins, can be preferably used. Such resins are 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, and the uniformity of the luminance of the emitted light, and is not particularly limited. A flat plate or a wedge-shaped plate is preferred from the viewpoint of ease of molding. The thickness of the plate can also be appropriately determined according to the size of the light source or the liquid crystal cell, etc., and is not particularly limited. However, it is preferably as thin as possible for the purpose of thinning and weight reduction, particularly 10 mm or less, particularly 0.5 to 5 mm. Is preferred.

The transparent resin plate is formed by, for example, an injection molding method, a casting molding method, an extrusion molding method, a casting molding method,
It can be performed by an appropriate method such as a rolling molding method, a roll coating molding method, a transfer molding method, and a reaction injection molding method (RIM). In the formation, appropriate additives such as, for example, a discoloration inhibitor, an antioxidant, an ultraviolet absorber, and a release agent can be added as needed.

On the other hand, as the polarized light scattering plate, an appropriate one which contains a birefringent minute region in a dispersed manner and exhibits scattering anisotropy depending on the polarization direction can be used. Incidentally, examples thereof include those in which a birefringent minute region is dispersed and contained in a transparent film.

The formation of the above-mentioned polarizing scattering plate exhibiting the scattering anisotropy is achieved by, for example, subjecting one or more of suitable materials having excellent transparency, such as polymers and liquid crystals, to an appropriate orientation treatment such as a stretching treatment. The method can be performed by an appropriate method such as a method of obtaining an oriented film by using a combination forming regions having different birefringence.

Incidentally, examples of the above-mentioned combination include a combination of polymers and liquid crystals, a combination of an isotropic polymer and an anisotropic polymer, and a combination of anisotropic polymers. From the viewpoint of the dispersion distribution of the minute region, a combination that separates phases 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 in which an incompatible material is made into a solution with a solvent or a method in which the incompatible material is mixed while being heated and melted.

In the case of performing the orientation treatment by the stretching method in the above-mentioned combination, the combination of the polymer and the liquid crystal and the combination of the isotropic polymer and the anisotropic polymer can be carried out at an arbitrary stretching temperature and stretching ratio. In the combination of the two, the desired polarization scattering plate can be formed by appropriately controlling the stretching conditions. Note that anisotropic polymers are classified into positive and negative based on the characteristics of refractive index change in the stretching direction.In the present invention, any positive or negative anisotropic polymer can be used. It can be used in any of the combinations.

Examples of the above-mentioned polymers include ester polymers such as polyethylene terephthalate and polyethylene naphthalate, styrene polymers such as polystyrene and acrylonitrile-styrene copolymer (AS polymers), polyethylene, polypropylene, cyclo and Polyolefins having a norbornene structure, such as olefin polymers such as ethylene-propylene copolymer, acrylic polymers such as polymethyl methacrylate, cellulose polymers such as cellulose diacetate and cellulose triacetate, and amide polymers such as nylon and aromatic polyamide Is raised.

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

On the other hand, examples of the liquid crystal include nematic phase and 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 mixtures thereof. And a liquid crystal polymer exhibiting 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 such as heat or light to form a polymer.

From the viewpoint of obtaining a polarized light scattering plate having excellent heat resistance and durability, the glass transition temperature is 50 ° C. or more, especially 80 ° C.
As described above, it is particularly 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 in view of the formability and thermal stability of fine regions having excellent uniformity of particle size distribution, the formability into a film, and the ease of alignment treatment, has a degree of polymerization of 8 or more, especially 10 Above, especially those of 15 to 5000.

The formation of the polarized light scattering plate using the liquid crystal polymer is performed, for example, by mixing one or more kinds of polymers and one or more kinds of liquid crystal polymers for forming minute regions, Can be performed by a method of forming a polymer film containing dispersedly in the form of a fine region, orienting the film by an appropriate method, and forming a region having a different birefringence.

In view of the above-mentioned controllability of the refractive index differences Δn ¹ and Δn ² by the alignment treatment, the glass transition temperature is 50 ° C. or higher and lower than the glass transition temperature of the polymers used in combination. Those exhibiting a nematic liquid crystal phase in the region 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 skeletal group forming the main chain of the liquid crystal polymer, and may be formed by a suitable 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 include polyurethanes, polyethers, polyimides, and polysiloxanes.

Y is a spacer group branched from the main chain, and a preferable spacer group Y in view of the formability of a polarizing scattering plate such as control of the refractive index is, for example, ethylene, propylene, butylene, pentylene, hexylene or octylene. ,
These include decylene, undecylene, dodecylene, octadecylene, ethoxyethylene, methoxybutylene and the like.

On the other hand, Z is a mesogen group for imparting liquid crystal orientation, and examples thereof include the following compounds.

The terminal substituent A in the compound may be, for example, a cyano group, an alkyl group, an alkenyl group, an alkoxy group, an oxaalkyl group, a haloalkyl group in which at least one of hydrogen is substituted by fluorine or chlorine, a haloalkoxy group, It may be an appropriate 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, ie, —O—. In the phenyl group in the mesogen group Z, one or two hydrogens may be substituted with a halogen. In this case, the halogen is preferably chlorine or fluorine.

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

The formation of the polarizing scattering plate using the liquid crystal polymer having the nematic alignment described above includes, for example, forming a polymer for 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, particularly 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 can be subjected to a heat treatment to align the liquid crystal polymer into a nematic liquid crystal phase, and the alignment state can be fixed by cooling.

The formation of the above-mentioned polymer film containing fine domains dispersed therein, that is, a film to be subjected to an orientation treatment is carried out by
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, a cast molding method, etc., developed in a monomer state, and polymerized by heat treatment or radiation treatment such as ultraviolet rays. It can also be performed by a method of forming a film into a film.

From the viewpoint of obtaining a polarized light scattering plate excellent in uniform distribution of minute regions, a method of forming a mixed solution of a forming material through a solvent by a casting method, a casting method, or the like is preferable. In this case, the size and distribution of the minute region can be controlled by the type of the solvent, the viscosity of the mixed solution, the drying speed of the mixed solution developing layer, and the like. Incidentally, in order to reduce the area of the minute region, it is advantageous to lower the viscosity of the mixed liquid and to increase the drying rate of the mixed liquid developing layer.

The thickness of the film to be subjected to the alignment treatment can be determined as appropriate, but is generally 1 μm
３3 mm, especially 5 μm to 1 mm, especially 10 to 500 μm. In forming the film, for example, appropriate additives such as a dispersant, a surfactant, an ultraviolet absorber, a color tone adjuster, a flame retardant, a release agent, and an antioxidant can be blended.

As described above, the orientation treatment is, for example, a stretching treatment method or a rolling method using uniaxial or biaxial, sequential biaxial or Z-axis, or the like.
Applying an electric or magnetic field at a temperature higher than the glass transition temperature or liquid crystal transition temperature to quench and fix the alignment, or apply a flow alignment at the time of film formation, or self-align the liquid crystal based on the slight alignment of the isotropic polymer. It can be performed using one or two or more of appropriate methods such as a method for controlling the refractive index depending on the orientation. Therefore, the obtained polarized light scattering plate may be a stretched film or a non-stretched film. When a stretched film is used, a brittle polymer may be used, but a polymer having excellent extensibility can be particularly preferably used.

When the fine regions are composed of the liquid crystal polymer described above, for example, the liquid crystal polymer dispersed and distributed as the fine regions in the polymer film is heated and melted to a temperature at which a desired liquid crystal phase such as a nematic phase is exhibited. Can be performed by orienting under the action of an alignment regulating force and quenching to fix the alignment state. It is preferable that the orientation state of the minute region is as mono-domain state as possible from the viewpoint of preventing variation in optical characteristics.

As the above-mentioned alignment regulating force, for example, a stretching force by a method of stretching a polymer film at an appropriate magnification, a sharing force at the time of film formation, an electric field or a magnetic field, etc. A regulating force can be applied, and the alignment treatment of the liquid crystal polymer can be performed by applying one or more kinds of the regulating force.

Therefore, portions other than the minute regions in the polarized light scattering plate may exhibit birefringence or may be isotropic. The whole of the polarizing scattering plate exhibits birefringence, can be obtained by the molecular orientation in the film forming process described above using a polymer for film formation having an orientation birefringence, if necessary, for example, stretching Birefringence can be imparted or controlled by adding known orientation means such as treatment. In addition, a polarizing scattering plate having an isotropic portion other than the minute region, for example, using an isotropic polymer for forming a film, stretching the film in a temperature region equal to or lower than the glass transition temperature of the polymer. It can be obtained by such a method.

The 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, ie, the portion made of the polymer film.
The remaining two axial directions (△ n2 direction, 以上 n1 direction) that are 0.03 or more (△ n1) in the axial direction (残 る n1 direction) where 1, △ n2, △ n3 show the maximum value, and which are orthogonal to the △ n1 direction. n
50% or less (△ n2, △
n3) is controlled so that they become equal.

By using the refractive index difference, Δn1
The linearly polarized light in the direction is strongly scattered and is 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 trapped inside.

In the above description, the difference in the refractive index between the direction of the optical axis of the minute region and the portion other than the minute region may be different if the polymer forming the film is optically isotropic. The difference between the axial refractive index and the average refractive index of the polymer film.If the polymer forming the film is optically anisotropic, the main optical axis direction of the polymer film and the main Since the direction of the optical axis usually coincides with the direction of the optical axis, it means the difference between the refractive indexes in the respective axial directions.

From the point of total reflection described above, the refractive index difference Δn1 in the Δn1 direction is preferably moderately large, and is preferably 0.035 to 1, especially 0.045 to 0.5. It is preferable that the refractive index differences Δn2 and Δn3 in the Δn2 direction and the Δn3 direction are appropriately small. Such a difference in the refractive index can be controlled by the refractive index of the material to be used, the above-described alignment operation, and the like.

The above-mentioned Δn1 direction is a vibration plane of linearly polarized light emitted from the light guide plate.
The direction is preferably parallel to the plane of the polarized light scattering plate. Note that the Δn1 direction in the plane can be an appropriate direction according to a target liquid crystal cell or the like.

It is preferable that the minute regions in the polarization scattering plate are dispersed and distributed as uniformly as possible from the viewpoint of the homogeneity of the scattering effect and the like. The size of the minute region, particularly the length in the △ n1 direction, which is the scattering direction, is related to backscattering (reflection) and wavelength dependency.

The improvement of light use efficiency, prevention of coloring due to wavelength dependency, prevention of visual inhibition of fine regions or prevention of clear display, and furthermore, micro regions are preferable from the viewpoint of film forming property and film strength. The size, particularly the preferred length in the Δn1 direction, is 0.05 to 500 μm, preferably 0.1 to 500 μm.
２５０250 μm, especially 1 １〜100 μm. Note that the minute region is usually present in the polarization scattering plate in the state of a domain,
The length in the Δn2 direction or the like is not particularly limited.

The ratio of the minute area in the polarization scattering plate is as follows:
Δn1 can be appropriately determined from the viewpoint of scattering properties in the direction,
Generally, the content is 0.1 to 70% by weight, preferably 0.5 to 50% by weight, particularly 1 to 30% by weight in consideration of the film strength and the like.

The polarized light scattering plate can be formed of a single layer of a film exhibiting the above-described birefringence characteristics, or can be formed as a laminate of two or more such films. By superimposing the films, a synergistic scattering effect of increasing the thickness or more can be exerted. The superimposed body is
The film may be superimposed at an arbitrary arrangement angle such as the Δn1 direction or the Δn2 direction, but the film is superimposed so that the Δn1 direction has a parallel relationship between the upper and lower layers from the viewpoint of the expansion of the scattering effect. Are preferred. The number of superimposed films can be an appropriate number of two or more layers.

The film to be superimposed is Δn1 or Δn
2 and the like may be the same or different. The parallel relationship between the upper and lower layers in the Δn1 direction and the like is preferably as parallel as possible, but deviation due to a work error is allowed. If there is variation in the △ n1 direction or the like, it is based on the average direction.

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

The scattering polarizer preferably has a phase difference entirely or partially in the plate, since the polarization state needs to be properly eliminated in the process of transmitting light through the light guide plate. Basically, the slow axis of the scattering polarizer is orthogonal to the polarization axis (vibration plane) of linearly polarized light that is hardly scattered, so polarization conversion due to phase difference is unlikely to occur, but the apparent angle changes due to slight scattering. However, it is considered that polarization conversion occurs.

From the point of the above-mentioned polarization conversion, it varies depending on the thickness of the scattering polarizer, but it is generally preferable that there is an in-plane retardation of 5 nm or more. Incidentally, the application of the phase difference is a method of containing birefringent fine particles or a method of attaching to the surface,
The method can be performed by an appropriate method such as a method of making the polymer film birefringent or a method of using them in combination.

The polarizing light guide plate according to the present invention uses a laminate of a light-transmitting resin plate and a polarization scattering plate. When the light-guiding plate is formed, as shown in FIG. In order to suppress reflection at the interface with the scattering plate as much as possible, that is, to facilitate transmission of transmission light between the light-transmitting resin plate and the polarized light scattering plate, the surface of the laminated body composed of a close-adhesive body is easily formed. In order to achieve total reflection on the back surface, it is preferable that the adhesive is bonded with an adhesive having a refractive index as close as possible. The bonding process is
This is more effective than the prevention of misalignment of the shaft relationship. When forming the polarized light guide plate, a polarized light scattering plate 3 may be provided on both front and back surfaces of the translucent resin plate 1 as illustrated in FIG.

The above-mentioned bonding treatment is carried out by appropriately bonding a transparent adhesive such as an acrylic, silicone, polyester, polyurethane, polyether, or rubber based on the above-mentioned superposition type polarizing scattering plate. An agent can be used, and there is no particular limitation. From the viewpoint of preventing a change in optical properties, a material that does not require a high-temperature process for curing and drying and does not require long-time curing or drying treatment is preferable. Further, a material which does not cause a peeling problem such as floating or peeling under heating or humidifying conditions is preferable.

In view of the above, an alkyl ester of (meth) acrylic acid having an alkyl group having 20 or less carbon atoms, such as a methyl group, an ethyl group, or a butyl group, and (meth) acrylic acid or hydroxy (meth) acrylate. An acrylic monomer composed of an improving component such as ethyl was added to a glass transition temperature of 0.
Acrylic pressure-sensitive adhesives having a weight average molecular weight of 100,000 or more and having an acrylic polymer as a base polymer, which is obtained by copolymerization in a combination of not more than ° C, are preferably used. Acrylic pressure-sensitive adhesives also have the advantage of being excellent in transparency, weather resistance, heat resistance, and the like.

The attachment of the adhesive layer to the translucent resin plate and / or the polarization scattering plate can be performed by an appropriate method. Examples thereof include dissolving or dispersing an adhesive component in a solvent consisting of an appropriate solvent alone or a mixture such as toluene or ethyl acetate to prepare an adhesive liquid of about 10 to 40% by weight, A method of directly attaching on a light-transmitting resin plate or a polarizing scattering plate by an appropriate development method such as a rolling method or a coating method, or forming an adhesive layer on a separator according to the above and forming it on a light-transmitting resin plate. And a method of transferring the light onto a polarizing scattering plate. The provided adhesive layer may be a superposed layer of different compositions or types.

The thickness of the adhesive layer can be appropriately determined according to the adhesive strength and the like, and is generally from 1 to 500 μm. The adhesive layer, if necessary, for example, natural or synthetic resins, glass fibers or glass beads, fillers or pigments made of metal powder or other inorganic powder, etc. Additives can also be included. Further, an adhesive layer showing light diffusing properties may be formed by incorporating fine particles.

As shown in FIG. 1, a specular reflection layer 5 provided on one side of a laminated body 4 of a light-transmitting resin plate 1 and a polarization scattering plate 3 serves to polarize light emitted from the side where the reflection layer is disposed via the specular reflection layer. It is an object of the present invention to improve the brightness by inverting the emitted light without changing the state and concentrating the emitted light on one of the front and back surfaces of the polarizing light guide plate.

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

The specular reflection layer can be directly adhered to the laminate as an additional layer of a metal thin film by a vapor deposition method or the like. However, complete reflection is difficult, and a slight absorption by the reflection layer also occurs, and repetition due to total reflection is taken into consideration. Then, there is a concern about absorption loss, and it is preferable to use an arrangement method in which an air layer in which the reflectors are simply stacked is interposed, rather than preventing the loss.

Accordingly, from this point of view, the specular reflection layer may preferably be a plate-like material such as a reflector having a metal thin film attached to a supporting substrate by a sputtering method or a vapor deposition method, or a metal foil or a rolled metal sheet. . An appropriate material such as a glass plate or a resin sheet can be used as the supporting base material of the above-mentioned reflective layer. Above all, silver, aluminum, and the like, which are deposited on a resin sheet, can be preferably used in terms of reflectance, color, handling, and the like. Note that the reflective layer may be disposed on either side of the laminate.

On the other hand, the polarization maintaining light diffusing layer provided on the opposite surface of the laminate, that is, the surface on which the specular reflection layer is not disposed, converts the light emitted from the laminate (linearly polarized light) to the extent possible. The purpose of the present invention is to make the light emission uniform by improving the visibility by improving the visibility while maintaining the light emission.

In the present invention, those having an excellent light transmittance and a degree of diffusion which does not eliminate the polarization characteristics of the emitted light as much as possible are preferably used. Incidentally, the degree of the polarization maintaining property is, for example, that a light diffusing layer is disposed therebetween using a prism polarizer arranged in a crossed Nicols, and the transmittance when fully polarized light is incident thereon is 5% or less. Among them, those having 2% or less, particularly 1% or less are preferable. The light transmittance is preferably 80% or more, especially 85% or more, particularly 90% or more based on the total light transmittance using an integrating sphere.

The light-diffusing layer exhibiting the above-mentioned polarization-maintaining property is generally capable of reducing the birefringence as much as possible because the depolarization is caused by birefringence and multiple scattering. It can be achieved by reducing it. Specifically, for example, a polarized light that is dispersed and contained in an optically isotropic light-transmitting resin layer or an optically isotropic light-transmitting resin layer having a fine uneven structure on its surface. A light-diffusing layer having sustainability can be obtained.

As the above-mentioned optically isotropic translucent resin, an appropriate one such as the above-mentioned translucent resin plate or the polymer exemplified for the scattering polarizer may be used. From the viewpoint, those having a small birefringence such as cellulose triacetate resin, polymethyl methacrylate, polycarbonate and norbornene resin can be preferably used.

On the other hand, examples of the transparent particles dispersed and contained in the light-transmitting resin layer include silica, glass, alumina, titania and zirconia, tin oxide and indium oxide, and the like.
Inorganic fine particles which may be conductive, such as cadmium oxide and antimony oxide, may be used.

Acrylic polymers, polyacrylonitriles, polyesters, epoxy resins, melamine resins, urethane resins, polycarbonates, polystyrene, silicone resins, benzoguanamine, melamine
Organic fine particles such as a crosslinked or uncrosslinked polymer such as a benzoguanamine condensate or a benzoguanamine-formaldehyde condensate are also examples of the transparent particles.

One or more transparent particles can be used, and the particle size is preferably 1 to 20 μm from the viewpoint of light diffusivity and uniformity of the diffusion. On the other hand, the particle shape is arbitrary, but generally a (true) spherical shape or a secondary aggregate thereof is used. In particular, transparent particles having a refractive index ratio of 0.9 to 1.1 with respect to the optically isotropic translucent resin can be preferably used from the viewpoint of the polarization maintaining property.

The light-diffusing layer containing particles is formed by, for example, mixing transparent particles with a resin melt and extruding the mixture into a sheet or the like, or blending the transparent particles with a resin solution or monomer and casting the mixture on a sheet or the like. It can be formed by an appropriate method according to the related art, such as a method of performing a polymerization treatment as needed, or a method of applying a resin liquid containing transparent particles to a predetermined surface or a polarization-maintaining support film.

On the other hand, the light diffusion layer having a fine uneven structure on the surface is formed by, for example, roughening the surface of a sheet made of an optically isotropic translucent resin by buffing by sandblasting or embossing. And a method of forming a layer of a light-transmitting material having protrusions on the surface of the sheet. However, a method of forming unevenness (projections) having a large difference in refractive index from bubbles such as air or a light-transmitting resin such as titanium oxide fine particles is not preferable because polarized light can be easily eliminated.

The fine uneven structure on the surface of the light diffusion layer is formed from irregularities having a surface roughness of not less than the wavelength of incident light and not more than 100 μm and having no periodicity in terms of light diffusivity and uniformity of the diffusion. Are preferred. In addition, when forming the above-described light diffusion layer containing a transparent particle or a surface irregularity type, it is possible to minimize an increase in phase difference due to photoelasticity and orientation, particularly in the base layer made of the translucent resin. This is preferable from the viewpoint of the polarization maintaining property and the like.

One or more light diffusion layers can be arranged on the light emission side of the laminate. When two or more layers are arranged, the light diffusion layers may be the same or different, but it is preferable that the above-described polarization maintaining properties be maintained as a whole. It is preferable that the light diffusion layer is also arranged such that a gap is formed in the laminate according to the above-mentioned mirror reflection layer. Preferably, the gap is sufficiently larger than the wavelength of the incident light than the point of total reflection.

The polarized light guide plate according to the present invention can be preferably used for forming a polarized surface 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 polarization plane light source can be formed by arranging the light source 7 on at least one side of the polarization light guide plate as illustrated in FIG.

The light source may be a polarized light guide plate, for example, a (cold, hot) cathode tube,
Appropriate devices such as a linear or planar array body such as a light emitting diode and an incandescent bulb can be used. In particular, a cold cathode tube can be preferably used in terms of luminous efficiency, low power consumption, small diameter, and the like. The light source may be arranged on a plurality of side surfaces such as two opposing side surfaces of the polarizing light guide plate or three side surfaces of a U-shaped tube or the like in view of brightness and uniformity thereof.

In forming the polarization plane light source, if necessary, appropriate auxiliary means such as a reflector 71 surrounding the light source 7 are arranged to guide divergent light from the light source to the side surface of the polarization light guide plate as shown in the figure. You can also. For the reflector, a resin sheet or a metal foil provided with a metal thin film having a high reflectance is generally used. In addition, a reflector may be provided on the lower surface of the polarization light guide plate to serve also as a mirror reflection layer. The reflector is also useful as a light source fixing means or the like.

In forming the polarization plane light source, one or more appropriate optical layers can be arranged at appropriate positions. The optical layer is not particularly limited, and for example, an appropriate material 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 this case, the above-mentioned light diffusion layer can be adhered to an optical layer disposed above the polarizing light guide plate via an adhesive layer or the like. However, in the case of a light diffusion layer having a fine surface irregularity, the above-described arrangement in which the gap is provided is preferable.

In the present invention, if necessary, each layer forming the polarizing light guide plate or the polarizing surface light source may include, for example, a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, a nickel complex salt compound, etc. The ultraviolet absorbing agent can be blended to have an ultraviolet absorbing ability.

The polarized light guide plate and the polarized plane light source according to the present invention
Since the linearly polarized light is provided in a state where the vibration plane (polarization axis) is controlled as described above, an appropriate device or application utilizing the linearly polarized light, such as formation of a liquid crystal display device, based on its features. Can be used.

[0078]

EXAMPLES Example 1 A norbornene resin having a glass transition temperature of 182 ° C. (JS
A 20% by weight dichloromethane solution obtained by dissolving 950 parts (parts by weight, hereinafter the same) of Arton, and 50 parts of a liquid crystal polymer having a glass transition temperature of 80 ° C. and a nematic liquid crystalization temperature of 100 to 290 ° C. Was used to form a polymer film having a thickness of 100 μm by a casting method, which was stretched three times at 180 ° C., and then rapidly cooled to obtain a polarization scattering plate.

The above-mentioned polarization scattering plate is obtained by dispersing a liquid crystal polymer in a domain having substantially the same shape having a long axis in the stretching direction in a transparent film made of a norbornene resin.
The refractive index difference Δn1 is 0.23, and Δn2 and Δn3 are 0.0
29. Further, when the average diameter of the fine region was measured by coloring based on a phase difference by observation with a polarizing microscope, the length in the Δn1 direction was about 5 μm.

Next, an acrylic resin plate (manufactured by Mitsubishi Rayon Co., Ltd.) having a thickness of 2 mm is provided on one side of the polarizing scattering plate with an acrylic adhesive layer interposed therebetween so that the Δn1 direction has a crossing angle of 45 ° with the end face. A laminated body is obtained by bonding, and a mirror-reflective sheet obtained by depositing silver on a PET sheet is disposed on the lower surface of the laminate, and a light diffusing plate is disposed on the upper surface to obtain a polarized light guide plate. Was fixed with a lamp reflector made of a PET-based reflective sheet subjected to a mat treatment to obtain a polarized surface light source.

In the light diffusion plate, 30 parts of silicone particles having an average particle size of 4 μm were coated with an ultraviolet-curable epoxy resin 7.
0 parts, stirred, mixed and defoamed, then applied to one side of an 80 μm-thick cellulose triacetate film with a thickness of 30 μm, and cured by irradiating 1000 mj / cm ² of integrated light with a high-pressure mercury lamp. The refractive index ratio between the silicone particles and the cured epoxy resin is 0.95. The amount of light leaked by depolarization when placed between crossed Nicol polarizers (the same applies hereinafter) is 0.7% of the total incident light.
Met.

Example 2 Silica particles 10 having an average particle size of 1.8 μm were used as a light diffusing plate.
Part, UV-curable acrylic urethane oligomer 10
0 parts and 3 parts of benzophenone were stirred at a high speed with ethyl acetate to form a mixed dispersion having a solid content of 50% by weight, which was applied to one surface of a cellulose triacetate film having a thickness of 80 μm with a wire bar and dried to a thickness of 4 μm. A polarizing light guide plate and a polarizing surface according to Example 1, except that the material was irradiated with a light of 150 mj / cm ² at a cumulative light amount using a high-pressure mercury lamp and cured to obtain a fine uneven surface. Light source was obtained.

The refractive index ratio between the silica particles and the cured resin in the light diffusion plate was 0.93, and the amount of leaked light due to depolarization was 1.0% of the total incident light. The surface roughness Rz (10-point average roughness based on JIS B0601) measured by a surface roughness meter was 1.5 μm.

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 printed on one surface.
A surface light source was obtained in the same manner as in Example 1 except that a light guide plate provided with a white reflecting plate was used.

Comparative Example 2 The amount of leakage light due to depolarization using a polyester film instead of the cellulose triacetate film was 5.2 of the total incident light.
%, A polarizing light guide plate and a polarizing plane light source were obtained in the same manner as in Example 2 except that a light diffusion plate was used.

Comparative Example 3 A polarized light guide plate and a polarized plane light source were obtained in the same manner as in Example 1 except that no light diffusing plate was provided.

Evaluation Test For the (polarized) surface light sources obtained in the examples and comparative examples, the luminance in the front direction at the center and the uniformity of the luminance on the surface were measured with a luminance meter (BM-7, manufactured by Topcon Corporation). The ratio was measured and the ratio was determined based on Comparative Example 1. The results are shown in the following table. In the table, the ratio of the luminance to the reference when the polarizing plate is arranged on the surface light source so that the transmission axis is 45 degrees is shown in parentheses.

Front Brightness (Polarizing Plate Arrangement) Uniformity Example 1 110 (100) Good Example 2 90 (80) Good Comparative Example 1 100 (40) Good Comparative Example 2 90 (50) Good Comparative Example 3 60 (50) Bad

From the comparison with Comparative Example 3 shown in the table, it can be seen that the front luminance is remarkably improved by the arrangement of the light diffusion layer, and the luminance uniformity on the surface is also improved. Further, as compared with the example and the comparative example 1, in the example, linearly polarized light was emitted and the luminance when passing through the polarizing plate was dramatically improved. It can be seen that the advantage of emitting linearly polarized light cannot be utilized in the case of solving the above problem. From the above, it can be seen that the use of the polarizing plane light source according to the present invention as a backlight of a liquid crystal display device achieves a luminance twice or more that of a normal case (Comparative Example 1), thereby achieving a very bright display with excellent uniformity. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a polarization plane light source.

FIG. 2 is a cross-sectional view of another example of the 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: Light diffusion layer 7: Light source

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13357 G02F 1/1335 530 F-term (Reference) 2H038 AA55 BA06 2H042 BA02 BA03 BA15 BA20 2H049 BA02 BA42 BB23 BB25 BB28 BB34 BB43 BB44 BB45 BB46 BB47 BB48 BB49 BB50 BB51 BB63 BC03 BC06 BC10 BC14 BC22 2H091 FA07Z FA23Z FB02 FD01 GA06 KA01 LA18

Claims (4)

[Claims] 1. A specular reflection on one surface of a laminate comprising a light-transmitting resin plate provided on one or both surfaces thereof with a polarizing and scattering plate exhibiting scattering anisotropy depending on the polarization direction by dispersing and containing microscopic birefringent regions. A polarizing light guide plate comprising a layer and at least one polarization maintaining light diffusion layer on the other surface of the laminate. 2. The method according to claim 1, wherein the light diffusion layer contains transparent particles having a refractive index ratio of 0.9 to 1.1 dispersed in the optically isotropic light-transmitting resin layer. Alternatively, a polarized light guide plate comprising an optically isotropic translucent resin layer having a fine uneven structure on the surface. 3. The polarized light guide plate according to claim 2, wherein the optically isotropic light-transmitting resin is a cellulose triacetate resin, polymethyl methacrylate, polycarbonate, or norbornene resin. 4. A polarization plane light source, comprising a light source on at least one side of the polarization light guide plate according to claim 1.