JP2003227936A - Brightness enhancing film, method for manufacturing the same, optical film and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brightness enhancing film which is prepared by laminating a protective film, a cholesteric liquid crystal and a quarter-wave plate via adhesive layers in this order and which has excellent impact resistance and durability. <P>SOLUTION: In the brightness enhancing film where the protective film, a first adhesive layer, the cholesteric liquid crystal layer, a second adhesive layer, and the quarter-wave plate are laminated in this order, the brightness enhancing film has 0.1 to 1.5 MPa dynamic storage shear elasticity of the first adhesive layer placed between the protective film and the cholesteric liquid crystal layer at 25°C. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a brightness enhancement film and a method for manufacturing the same. The present invention also relates to an optical film in which at least one optical film is laminated on the brightness enhancement film. Furthermore, the present invention provides a liquid crystal display device (LC
D), an organic EL display device, and an image display device such as a PDP.

[0002]

2. Description of the Related Art In an image display device such as an LCD, a brightness enhancement film is used for providing a bright display. As the brightness enhancement film, for example, a film in which a protective film, a cholesteric liquid crystal, and a 1/4 wavelength plate are laminated in this order via an adhesive layer is used. Such a brightness enhancement film is required to have various performances. For example, when it is used for an LCD used for a mobile phone, car navigation, etc., it is particularly shock resistant unlike a liquid crystal monitor that is not carried. It becomes an important required characteristic. The portion of the brightness enhancement film having the lowest impact resistance is the portion of the cholesteric liquid crystal layer, and when an impact is applied, cohesive failure occurs in the cholesteric liquid crystal layer.

Among the brightness enhancement films, especially LCDs used for mobile phones and car navigations are left in the car at night or daytime, and are left in a low temperature or a high temperature. Durability at low and high temperatures is an important required property. However, the conventional brightness enhancement film has a problem that cohesive failure occurs in the cholesteric liquid crystal layer when the temperature and the temperature change repeatedly.

[0004]

DISCLOSURE OF THE INVENTION The present invention is a brightness enhancement film comprising a protective film, a cholesteric liquid crystal, and a quarter-wave plate laminated in this order via an adhesive layer, which has good impact resistance and low temperature. It is an object of the present invention to provide a brightness enhancement film that is less likely to cause cohesive failure of a cholesteric liquid crystal layer even under high temperature and a manufacturing method thereof. Furthermore, it aims at providing the optical film using the said brightness | luminance improvement film, and also the image display apparatus using the said brightness improvement film and an optical film.

[0005]

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the above-mentioned object can be achieved by the following brightness enhancement film and its manufacturing method, and completed the present invention. Came to do.

That is, the present invention provides a protective film, a first adhesive layer, a cholesteric liquid crystal layer, a second adhesive layer, a 1/4
In the brightness enhancement film in which the wave plates are laminated in this order, the first film between the protective film and the cholesteric liquid crystal layer is formed.
The dynamic storage shear modulus at 25 ° C. of the adhesive layer is 0.
It relates to a brightness enhancement film having a pressure of 1 to 15 MPa.

The above-mentioned brightness enhancement film of the present invention is largely affected by heat by the protective film, the cholesteric liquid crystal, and the pressure-sensitive adhesive layer interposed between the 1/4 wavelength plate, and the reliability is obtained unless the elastic modulus is to some extent. Is significantly impaired, the dynamic storage shear modulus of elasticity of the first adhesive layer between the protective film and the cholesteric liquid crystal layer is 0.1 to 0.1.
By using a material in the range of 15 MPa, cohesive failure in the cholesteric liquid crystal layer is prevented. First
When the dynamic storage shear modulus of the pressure-sensitive adhesive layer becomes low, the first pressure-sensitive adhesive layer easily flows due to heating, and the cholesteric liquid crystal layer follows the movement of the first pressure-sensitive adhesive layer to cause cohesive failure. From this point of view, the dynamic storage shear modulus is preferably 0.1 MPa or more, and more preferably 0.2 MPa or more. On the other hand, when the dynamic storage shear modulus of the first pressure-sensitive adhesive layer becomes high, the pressure-sensitive adhesive cannot relax the stress when the brightness enhancement film is bent, so that cohesive failure occurs in the cholesteric liquid crystal layer. From this viewpoint, the dynamic storage shear modulus is preferably 15 MPa or less, 13.5 MPa or less, and more preferably 10 MPa or less.

In the brightness enhancement film, triacetyl cellulose is preferably used as the material of the protective film.

In the brightness enhancement film, the cholesteric liquid crystal layer can be formed by an alignment material of a liquid crystal polymer, a polymerization layer of an alignment material of a liquid crystal monomer, or a composite layer thereof.

Further, in the present invention, the cholesteric liquid crystal layer formed and oriented on the alignment substrate is transferred to the protective film via the first pressure-sensitive adhesive layer or to the quarter wavelength plate via the second pressure-sensitive adhesive layer. Then, a first layer is formed on one side of the cholesteric liquid crystal layer.
A 1/4 wavelength plate is placed on the cholesteric liquid crystal layer surface exposed by the transfer via the second adhesive layer so that the adhesive layer is laminated and the second adhesive layer is laminated on the other side, or The present invention relates to the method for manufacturing a brightness enhancement film, wherein a protective film is attached via a first pressure-sensitive adhesive layer.

The present invention also provides the above brightness enhancement film,
Further, the present invention relates to an optical film having at least one optical film laminated thereon.

Furthermore, the present invention relates to an image display device to which the brightness enhancement film or the optical film is applied.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The brightness enhancement film of the present invention will be described below with reference to FIG. As shown in FIG. 1, the brightness enhancement film includes a protective film 1, a first pressure-sensitive adhesive layer a1, a cholesteric liquid crystal layer 2, a second pressure-sensitive adhesive layer a2, and a quarter-wave plate 3 which are laminated in this order. Various materials used for the brightness enhancement film are used as the materials for forming the brightness enhancement film, except that the dynamic storage shear modulus at 25 ° C. of the first pressure-sensitive adhesive layer a1 is 0.1 to 15 MPa. It can be used without particular limitation.

As the protective film, those having excellent transparency, mechanical strength, thermal stability, moisture shielding property, isotropy and the like are preferable. Examples of the material of the protective film include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, polystyrene and acrylonitrile-styrene copolymers. (AS
Examples thereof include styrene-based polymers such as resins) and polycarbonate-based polymers. Further, polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymer, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers. , Polyether sulfone-based polymer, polyether ether ketone-based polymer, polyphenylene sulfide-based polymer, vinyl alcohol-based polymer, vinylidene chloride-based polymer, vinyl butyral-based polymer, arylate-based polymer, polyoxymethylene-based polymer, epoxy-based polymer, or the above An example of the polymer forming the protective film is a blend of polymers. In addition, a film made of a thermosetting or ultraviolet curable resin such as an acrylic or urethane type, an acrylic urethane type, an epoxy type or a silicone type may be used. Among these, cellulosic polymers, particularly triacetyl cellulose, are preferable in terms of isotropicity. The thickness of the protective film is generally 500 μm or less, preferably 1 to 300 μm. In particular, the thickness is preferably 5 to 200 μm.

The cholesteric liquid crystal layer may be, for example, one having a property of reflecting either left-handed or right-handed circularly polarized light and transmitting other light. The cholesteric liquid crystal layer can be formed by a polymerized layer of an alignment material of a liquid crystal polymer or an alignment material of a liquid crystal monomer. Further, the cholesteric liquid crystal layer can be formed by these composite layers.

The oriented liquid crystal polymer is obtained by orienting a cholesteric liquid crystal polymer containing an optically active group-containing monomer as a monomer unit. As the cholesteric liquid crystal polymer, polymers having various skeletons of a main chain type, a side chain type or a composite type thereof showing cholesteric liquid crystal alignment can be used without particular limitation. In addition,
A cholesteric liquid crystal polymer can be obtained by incorporating a low molecular weight chiral agent into a nematic liquid crystal polymer or introducing a chiral component into a polymer component.

The polymerized layer of the alignment product of the liquid crystal monomer can be formed by aligning the liquid crystal monomer containing the cholesteric liquid crystal monomer containing an optically active group and further polymerizing the alignment. The liquid crystal monomer is a compound having various skeletons exhibiting liquid crystal alignment, and having at least one unsaturated double bond such as acryloyl group, methacryloyl group, vinyl group or the like or a polymerizable functional group such as epoxy group at the terminal. . In order to improve the durability of the obtained cholesteric liquid crystal layer, it is preferable to use a liquid crystal monomer having two or more polymerizable functional groups and crosslink it with polymerization. When a liquid crystal monomer is used, it usually contains a polymerization initiator. The polymerization initiator is appropriately selected according to the method of polymerizing the liquid crystal monomer. Examples of the method for polymerizing the liquid crystal monomer include ultraviolet polymerization, and in this case, a photopolymerization initiator is used.

The liquid crystal polymer and the liquid crystal monomer are aligned by coating them on the surface (alignment film) having the alignment ability of the substrate having the surface having the alignment ability. As the alignment film, various conventionally known ones can be used, for example, those formed by a method of forming a thin film made of polyimide or polyvinyl alcohol on a transparent substrate and rubbing it, a transparent film. It is possible to use a stretched film obtained by stretching the film, a polymer having a cinnamate skeleton or an azobenzene skeleton, or a polyimide irradiated with polarized ultraviolet light. The transparent substrate used for forming the alignment film is not particularly limited as long as it does not change at the temperature for aligning the mixture, and for example, various single-layer or laminated plastic films, glass plates, metals and the like can be used. The alignment of the liquid crystal polymer and the liquid crystal monomer is usually performed by heat treatment. After completion of the heat treatment, the orientation is fixed by cooling.

In the cholesteric liquid crystal layer, the pitch of the cholesteric liquid crystal changes based on the content of the monomer unit containing an optically active group, so that circular dichroism can be controlled by the content of the monomer unit. The thickness of the cholesteric liquid crystal layer is usually 1 to 50 μm.
Is preferable, and particularly preferably 2 to 20 μm. It should be noted that the cholesteric liquid crystal layer may be blended with a polymer other than the liquid crystal polymer, one or more additives such as a stabilizer, an inorganic compound such as a plasticizer, an organic compound, a metal or a compound thereof, if necessary.

Further, the cholesteric liquid crystal layer has a structure in which two or three or more layers are combined by combining those having different reflection wavelengths to obtain a structure which reflects circularly polarized light in a wide wavelength range such as a visible light region. It is possible to obtain transmitted circularly polarized light in a wide wavelength range based on the above.

In a brightness enhancement film of the type that drops circularly polarized light such as a cholesteric liquid crystal layer, it can be directly incident on a polarizer, but from the viewpoint of suppressing absorption loss, the circularly polarized light is linearly polarized through a retardation plate. It is preferable that the light is incident on the polarizing plate. Circularly polarized light can be converted into linearly polarized light by using a ¼ wavelength plate as the retardation plate.

As the quarter-wave plate, an appropriate retardation plate according to the purpose of use is used. The quarter-wave plate can control optical characteristics such as retardation by laminating two or more kinds of retardation plates. As the retardation plate, polycarbonate, norbornene-based resin (polymer having a norbornene skeleton),
Polyvinyl alcohol, polystyrene, polymethylmethacrylate, polypropylene and other polyolefins, polyarylate, an oriented film made of a liquid crystal material such as a birefringent film or a liquid crystal polymer obtained by stretching a film made of an appropriate polymer such as polyamide,
Examples thereof include those in which an alignment layer of a liquid crystal material is supported by a film. The thickness of the quarter wave plate is usually 20 to 200 μm.
It is preferably m, and particularly preferably 30 to 100 μm.

It should be noted that in a wide wavelength range such as a visible light range, it is 1/4.
The retardation plate functioning as a wave plate has a wavelength of 550 n
Obtained by a method in which a retardation layer that functions as a quarter-wave plate and a retardation layer that exhibits other retardation characteristics, such as a retardation layer that functions as a half-wave plate, are superimposed on m light-color light. be able to.

The pressure-sensitive adhesive forming the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer is an acrylic polymer, a silicone-based polymer,
Although various pressure-sensitive adhesives containing various polymers such as polyester, polyurethane, polyamide, polyether and rubber as a base polymer can be used, an acrylic pressure-sensitive adhesive that is colorless and transparent and has good adhesiveness is generally used. In addition,
The pressure-sensitive adhesive forming the first pressure-sensitive adhesive layer is appropriately adjusted so that the dynamic storage shear modulus at 25 ° C. is 0.1 to 15 MPa.

The acrylic pressure-sensitive adhesive has an acrylic polymer having an alkyl (meth) acrylate monomer unit as a main skeleton as a base polymer. In addition, (meth) acrylate refers to acrylate and / or methacrylate, and has the same meaning as (meth) of the present invention. The average carbon number of the alkyl group of the alkyl (meth) acrylate, which constitutes the main skeleton of the acrylic polymer, is 1 to 12
The specific examples of the alkyl (meth) acrylate are methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate,
2-ethylhexyl (meth) acrylate etc. can be illustrated and these can be used individually or in combination. Among these, alkyl having 1 to 8 carbon atoms in the alkyl group (meth)
Acrylate is preferred.

The acrylic polymer is an alkyl (meth)
In addition to the acrylate monomer unit, a monomer unit having a functional group-containing monomer may be contained. Examples of the monomer having a functional group include a carboxyl group-containing monomer and a hydroxyl group-containing monomer.
Specific examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid and the like. Specific examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate and 4-hydroxyethyl (meth) acrylate.
Examples thereof include hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate and N-methylol (meth) acrylamide. In addition, as the monomer having a functional group, an epoxy group-containing monomer such as glycidyl (meth) acrylate, (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N
-N-element-containing monomers such as diethyl (meth) acrylamide, (meth) acryloylmorpholine, (meth) acetonitrile, vinylpyrrolidone, N-cyclohexylmaleimide, itaconimide, N, N-dimethylaminoethyl (meth) acrylamide, and the like. further,
For the acrylic polymer, vinyl acetate, styrene or the like may be used as long as the performance of the pressure-sensitive adhesive is not impaired.

The ratio of the monomer unit (a) having the functional group in the acrylic polymer is not particularly limited, but from the viewpoint of heat resistance, the monomer unit (A) constituting the acrylic polymer (provided that the monomer unit (a (Excluding)) in a weight ratio (a / A) of 0.001 to
It is preferably about 0.12, particularly preferably 0.005 to 0.08.

The average molecular weight of the acrylic polymer is not particularly limited, but the weight average molecular weight is preferably about 300,000 to 2,500,000.

The acrylic polymer can be produced by various known methods, for example, a radical polymerization method such as a bulk polymerization method, a solution polymerization method or a suspension polymerization method can be appropriately selected. As the radical polymerization initiator, various known ones such as azo type and peroxide type can be used, and the reaction temperature is usually 50 to
The reaction time is about 85 ° C and the reaction time is about 1 to 8 hours. Among the above-mentioned production methods, the solution polymerization method is preferable, and a polar solvent such as ethyl acetate or toluene is generally used as the solvent for the acrylic polymer. Solution concentration is usually 20 ~
It is set to about 80% by weight.

Various polyfunctional compounds can be added to the adhesive as a crosslinking agent. Examples of the polyfunctional compound capable of crosslinking with the acrylic polymer include organic crosslinking agents and polyfunctional metal chelates. As the organic cross-linking agent, one having two or more functional groups that react with a functional group such as a carboxyl group and a hydroxyl group such as an epoxy cross-linking agent, an isocyanate cross-linking agent and an imine cross-linking agent in one molecule. can give. As the organic crosslinking agent, an isocyanate crosslinking agent is preferable. The polyfunctional metal chelate is one in which a polyvalent metal is covalently or coordinately bonded to an organic compound. As the polyvalent metal atom, Al, Cr, Zr, C
o, Cu, Fe, Ni, V, Zn, In, Ca, Mg,
Mn, Y, Ce, Sr, Ba, Mo, La, Sn, Ti
Etc. Among these, Al, Zr, Ti
Is preferred. Further, the atom in the organic compound which forms a covalent bond or a coordinate bond includes an oxygen atom and the like, and the organic compound includes an alkyl ester, an alcohol compound, a carboxylic acid compound, an ether compound and a ketone compound.

The mixing ratio of the acrylic polymer and the polyfunctional compound is not particularly limited, and is determined depending on the ratio and kind of the monomer unit having a functional group in the acrylic polymer, the kind of the polyfunctional compound, etc. , 0.01 to 6 parts by weight of polyfunctional compound (solid content), preferably 0.1 to 100 parts by weight of acrylic polymer (solid content).
It is about 1 to 3 parts by weight.

Further, the pressure-sensitive adhesive may contain a tackifier, a plasticizer, glass fibers, glass beads, if necessary.
Metal powder, other fillers such as inorganic powders, pigments, colorants, fillers, antioxidants, ultraviolet absorbers, silane coupling agents, and various additives within the range not departing from the object of the present invention. Can also be used as appropriate. Further, it may be a pressure-sensitive adhesive layer containing fine particles and exhibiting a light diffusing property.

The pressure-sensitive adhesive layer can be formed by an appropriate method. As an example, the base polymer or its composition is dissolved or dispersed in a solvent composed of a single solvent or a mixture of appropriate solvents such as toluene and ethyl acetate.
A method of preparing a pressure-sensitive adhesive solution of about 0 to 40% by weight and applying it directly onto each substrate by an appropriate development method such as a casting method or a coating method, or an adhesive agent on a separator according to the above. Examples include a method of forming a layer and transferring it to a substrate. The thickness of the first pressure-sensitive adhesive layer is preferably about 1 to 50 μm, more preferably 2 to 30 μm. The thickness of the second pressure-sensitive adhesive layer is preferably about 1 to 50 μm, more preferably 2 to 30 μm.

The brightness enhancement film of the present invention has a protective film, a first pressure-sensitive adhesive layer, a cholesteric liquid crystal layer, a second pressure-sensitive adhesive layer, and a quarter-wave plate, which are laminated in this order. The manufacturing method is not particularly limited, a protective film,
First in either cholesteric liquid crystal layer or quarter wave plate
It is obtained by forming the pressure-sensitive adhesive layer or the second pressure-sensitive adhesive layer and then bonding them together.

As a method for producing the brightness enhancement film, the cholesteric liquid crystal layer formed and oriented on the alignment substrate is attached to the protective film via the first adhesive layer, and then the alignment substrate is peeled off. There is a method (1) of transferring and then bonding a 1/4 wavelength plate to the surface of the cholesteric liquid crystal layer exposed by the transfer via the second adhesive layer. Further, contrary to the method (1), a method of transferring a quarter-wave plate to a cholesteric liquid crystal layer through a second pressure-sensitive adhesive layer and then bonding a protective film through the first pressure-sensitive adhesive layer (2) Can be given.

A polarizing plate is used for an optical film applied to an image display device such as a liquid crystal display device. The obtained brightness enhancement film is used by laminating optical films such as polarizing plates.

The polarizing plate in which the polarizing plate and the brightness enhancement film are bonded together is usually used by being provided on the back side of the liquid crystal cell. The brightness enhancement film has a property of reflecting linearly polarized light of a predetermined polarization axis or circularly polarized light of a predetermined direction when natural light is incident due to reflection from a backlight of a liquid crystal display device or the back side, and transmits other light. A polarizing plate in which a brightness enhancement film is laminated with a polarizing plate allows light from a light source such as a backlight to enter and obtain transmitted light in a predetermined polarization state, and light other than the predetermined polarization state is reflected without being transmitted. It The light reflected by the surface of the brightness enhancement film is inverted through a reflection layer or the like provided on the rear side of the brightness enhancement film to be re-incident on the brightness enhancement film, and part or all of the light is transmitted as light in a predetermined polarization state to achieve brightness. The brightness can be improved by increasing the amount of light transmitted through the improvement film and by supplying polarized light that is difficult to be absorbed by the polarizer to increase the amount of light that can be used for liquid crystal display image display and the like. That is,
When light is input from the back side of the liquid crystal cell through a polarizer without using a brightness enhancement film, almost all light with a polarization direction that does not match the polarization axis of the polarizer is reflected by the polarizer. It is absorbed and does not pass through the polarizer. That is, although depending on the characteristics of the polarizer used, about 50% of light is absorbed by the polarizer, and the amount of light that can be used for displaying the liquid crystal image is reduced accordingly, and the image becomes dark. The brightness enhancement film allows light having a polarization direction that is absorbed by the polarizer to be reflected once by the brightness enhancement film without being incident on the polarizer, and then inverted through a reflection layer or the like provided behind it. The light-increasing film transmits only the polarized light whose polarization direction is such that the light reflected and inverted between the two can pass through the polarizer. Since the light is supplied to the polarizer, light from a backlight or the like can be efficiently used for displaying an image on the liquid crystal display device, and the screen can be brightened.

Brightness enhancing films other than the above-described brightness enhancing films include linearly polarized light having a predetermined polarization axis, such as a multilayer thin film of a dielectric or a multilayer laminate of thin films having different refractive index anisotropies. One that exhibits the property of transmitting other light and reflecting other light. In a brightness enhancement film of a type that transmits linearly polarized light having a predetermined polarization axis, the transmitted light can be efficiently transmitted while suppressing the absorption loss by the polarizing plate by allowing the transmitted light to enter the polarizing plate with the polarization axis aligned. .

The polarizing plate usually has a protective film on one side or both sides of the polarizer. The polarizer is not particularly limited, and various kinds can be used. As a polarizer,
For example, polyvinyl alcohol film, partially formalized polyvinyl alcohol film, ethylene
Polyvinyl acetate copolymer-based partially saponified hydrophilic polymer film, uniaxially stretched by adsorbing dichroic substances such as iodine and dichroic dye, polyvinyl alcohol dehydration products and polyvinyl chloride Examples include polyene-based oriented films such as dehydrochlorinated products. Among these, those obtained by stretching a polyvinyl alcohol film to adsorb and orient a dichroic material (iodine, dye) are preferably used. The thickness of the polarizer is also not particularly limited, but is 5 to 80 μm.
Degree is general.

A polarizer obtained by dyeing a polyvinyl alcohol film with iodine and uniaxially stretching is prepared by, for example, immersing polyvinyl alcohol in an aqueous solution of iodine, dyeing it, and stretching it to 3 to 7 times its original length. You can If necessary, it may be immersed in an aqueous solution of boric acid, potassium iodide, or the like. If necessary, the polyvinyl alcohol film may be immersed in water and washed with water before dyeing. By washing the polyvinyl alcohol-based film with water, it is possible to wash the stains and anti-blocking agents on the surface of the polyvinyl alcohol-based film, and by swelling the polyvinyl alcohol-based film, the effect of preventing unevenness such as uneven dyeing is also obtained. is there. Stretching may be performed after dyeing with iodine, stretching while dyeing, or stretching and then dyeing with iodine. It can be stretched in an aqueous solution of boric acid or potassium iodide, or in a water bath.

The protective film provided on one side or both sides of the polarizer may be the same as that used for the brightness enhancement film. The thickness of the protective film is generally 500 μm or less, preferably 1 to 300 μm. In particular, the thickness is preferably 5 to 200 μm. The protective film of the brightness enhancement film can also serve as the protective film of the polarizing plate.

As the protective film, a cellulosic polymer such as triacetyl cellulose is preferable from the viewpoint of polarization characteristics and durability. A triacetyl cellulose film is particularly suitable. When protective films are provided on both sides of the polarizer, protective films made of the same polymer material may be used on the front and back sides, or protective films made of different polymer materials may be used. The polarizer and the protective film are usually in close contact with each other via an aqueous pressure-sensitive adhesive or the like. Examples of the water-based adhesive include polyvinyl alcohol-based adhesive, gelatin-based adhesive, vinyl-based latex-based, water-based polyurethane, water-based polyester and the like.

As the protective film, a hard coat layer, anti-reflection treatment, anti-sticking treatment, or treatment for the purpose of diffusion or anti-glare can be used.

The hard coat treatment is carried out for the purpose of preventing scratches on the surface of the polarizing plate. For example, a hardened film excellent in hardness and sliding characteristics made of an appropriate ultraviolet curable resin such as acrylic or silicone is used. It can be formed by a method of adding to the surface of the protective film. The antireflection treatment is carried out for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an antireflection film or the like according to conventional methods. Further, the sticking prevention treatment is performed for the purpose of preventing adhesion with an adjacent layer.

The anti-glare treatment is carried out for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering the visual recognition of the light transmitted through the polarizing plate. For example, a sand blasting method or an embossing method is used. It can be formed by imparting a fine concavo-convex structure to the surface of the protective film by an appropriate method such as a surface-rendering method or a method of blending transparent fine particles. As the fine particles to be contained in the formation of the surface fine uneven structure, for example, silica having an average particle diameter of 0.5 to 50 μm,
Transparent fine particles such as inorganic fine particles which may be conductive, such as alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide, and organic fine particles which are crosslinked or uncrosslinked polymers are used. When the surface fine uneven structure is formed, the amount of the fine particles used is generally about 2 to 50 parts by weight based on 100 parts by weight of the transparent resin forming the surface fine uneven structure.
Parts by weight are preferred. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle enlarging function) for diffusing the light transmitted through the polarizing plate and enlarging the viewing angle.

The antireflection layer, the sticking prevention layer, the diffusion layer, the antiglare layer and the like can be provided on the protective film itself, or can be provided as an optical layer separately from the transparent protective layer. .

The polarizing plate can be used as an elliptically polarizing plate or a circularly polarizing plate in which retardation plates are laminated. The elliptically polarizing plate or circularly polarizing plate will be described. These change linearly polarized light into elliptically polarized light or circularly polarized light, change elliptically polarized light or circularly polarized light into linearly polarized light, or change the polarization direction of linearly polarized light by a retardation plate. In particular, a so-called quarter-wave plate is used as a retardation plate that changes linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light. 1/2
A wave plate is usually used when changing the polarization direction of linearly polarized light.

The elliptically polarizing plate compensates (prevents) coloring (blue or yellow) caused by the birefringence of the liquid crystal layer of a spurts twisted nematic (STN) type liquid crystal display device, and is used for black and white display without the coloring. Used effectively. Further, the one in which the three-dimensional refractive index is controlled is preferable because it can also compensate (prevent) coloring that occurs when the screen of the liquid crystal display device is viewed obliquely. The circularly polarizing plate is effectively used, for example, when adjusting the color tone of an image of a reflective liquid crystal display device in which an image is displayed in color, and also has a function of preventing reflection.

As the retardation plate, for example, various wavelength plates or those for the purpose of compensating for the viewing angle and the like due to birefringence of the liquid crystal layer can be used, and an appropriate retardation depending on the purpose of use can be used. By laminating two or more kinds of retardation plates having the same, optical characteristics such as retardation can be controlled.

The retardation plate is laminated on a polarizing plate as a viewing angle compensation film and used as a wide viewing angle polarizing plate. The viewing angle compensation film is a film for widening the viewing angle so that an image can be seen relatively clearly even when the screen of the liquid crystal display device is viewed from a slightly oblique direction rather than a direction perpendicular to the screen.

As such a viewing angle compensating retarder, a birefringent film that has been biaxially stretched or stretched in two orthogonal directions, or a bidirectionally stretched film such as a tilted oriented film is used. To be Examples of the tilted oriented film include those obtained by adhering a heat-shrinkable film to a polymer film and subjecting the polymer film to stretching treatment and / or shrinking treatment under the action of the shrinkage force caused by heating, and those obtained by obliquely orienting a liquid crystal polymer. Can be mentioned. The viewing angle compensation film can be appropriately combined for the purpose of preventing coloring or the like due to a change in viewing angle due to a phase difference due to a liquid crystal cell, and enlarging a viewing angle for good viewing.

From the viewpoint of achieving a wide viewing angle for good visual recognition, an optically anisotropic layer comprising an alignment layer of a liquid crystal polymer, particularly an inclined alignment layer of a discotic liquid crystal polymer, is supported by a triacetyl cellulose film. A compensation retardation plate can be preferably used.

In addition to the above, the optical layers to be laminated in practical use are not particularly limited, but for example, one or two optical layers which may be used for forming a liquid crystal display device such as a reflecting plate or a semi-transmissive plate. The above can be used. In particular,
A reflection type polarizing plate or a semi-transmission type polarizing plate in which a reflecting plate or a semi-transmissive reflecting plate is further laminated on the elliptically polarizing plate or the circularly polarizing plate is mentioned.

The reflective polarizing plate is a polarizing plate provided with a reflective layer, and is for forming a liquid crystal display device of the type that reflects incident light from the viewing side (display side) for display. Further, there is an advantage that it is possible to omit the incorporation of a light source such as a backlight and to easily reduce the thickness of the liquid crystal display device. The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is attached to one surface of the polarizing plate via a transparent protective layer or the like, if necessary.

Specific examples of the reflection-type polarizing plate include a protective film which is mat-treated if necessary, and a foil or vapor deposition film made of a reflective metal such as aluminum is attached to one surface to form a reflective layer. To be Further, the protective film may contain fine particles to form a finely textured surface structure, and a reflective layer having a finely textured structure formed on the surface.
The reflective layer having the fine concavo-convex structure has the advantage that diffused incident light is diffused to prevent directivity and glare, and uneven brightness can be suppressed. Further, the protective film containing fine particles also has an advantage that incident light and reflected light thereof are diffused when they pass therethrough to further suppress uneven brightness. The formation of the reflective layer having a fine concavo-convex structure reflecting the surface fine concavo-convex structure of the protective film is carried out by transparently protecting the metal by an appropriate method such as a vapor deposition method such as a vacuum vapor deposition method, an ion plating method, a sputtering method or a plating method It can be carried out by a method such as direct attachment to the surface of the layer.

The reflecting plate may be used as a reflecting sheet in which a reflecting layer is provided on a suitable film according to the transparent film, instead of the method of directly applying it to the protective film of the polarizing plate. Since the reflective layer is usually made of a metal, its reflective surface is used in a state of being covered with a protective film, a polarizing plate, etc., to prevent a decrease in reflectance due to oxidation, and in the long term of the initial reflectance. It is more preferable from the standpoint of avoiding the additional provision of the protective layer.

The semi-transmissive polarizing plate can be obtained by using a semi-transmissive reflective layer such as a half mirror which reflects and transmits light by the reflective layer. The semi-transmissive polarizing plate is usually provided on the back side of the liquid crystal cell, and when the liquid crystal display device is used in a relatively bright atmosphere,
An image is displayed by reflecting incident light from the viewing side (display side), and in a relatively dark atmosphere, an image is displayed using a built-in light source such as a backlight built into the back side of the semi-transmissive polarizing plate. It is possible to form a liquid crystal display device of the type that displays That is, the semi-transmissive polarizing plate is useful for forming a liquid crystal display device of a type that can save energy for using a light source such as a backlight in a bright atmosphere and can be used with a built-in light source in a relatively dark atmosphere. Is.

Further, the polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers, like the above-mentioned polarization separation type polarizing plate. Therefore, it may be a reflective elliptical polarizing plate or a semi-transmissive elliptical polarizing plate in which the above reflective polarizing plate or semi-transmissive polarizing plate is combined with a retardation plate.

The above-mentioned elliptically polarizing plate and reflective elliptically polarizing plate are
A polarizing plate or a reflective polarizing plate and a retardation plate are laminated in an appropriate combination. Such elliptically polarizing plates are (reflective type)
A polarizing plate and a retardation plate can be formed by sequentially stacking them separately in the process of manufacturing a liquid crystal display device so as to form a combination, but previously laminated to form an optical film such as an elliptically polarizing plate. Has an advantage that the manufacturing efficiency of a liquid crystal display device and the like can be improved because of excellent quality stability and stacking workability.

An adhesive layer may be further provided on the brightness enhancement film and the optical film of the present invention. The pressure-sensitive adhesive layer can be used for sticking to a liquid crystal cell and also used for laminating optical layers. Upon adhesion of the optical film,
These optical axes can be arranged at appropriate angles according to the intended phase difference characteristics and the like. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited, but the same ones as those exemplified above can be exemplified. Further, it can be provided in the same manner.

The pressure-sensitive adhesive layer can be provided on one side or both sides of the brightness enhancement film or the optical film as a layer in which different compositions or types are laminated. Further, when it is provided on both sides, an adhesive layer having a different composition, type, thickness, etc. can be formed on the front and back of an optical film or the like. The thickness of the pressure-sensitive adhesive layer can be appropriately determined depending on the purpose of use and the adhesive strength, and is generally 1 to 500 μm, preferably 5 to 200 μm, and particularly preferably 10 to 100 μm.

The exposed surface of the pressure-sensitive adhesive layer is temporarily covered with a separator for the purpose of preventing its contamination until it is put into practical use. As a result, it is possible to prevent contact with the adhesive layer in the usual handling state. As the separator, excluding the above thickness conditions, for example, a suitable thin sheet such as a plastic film, a rubber sheet, paper, cloth, non-woven fabric, net, a foamed sheet or a metal foil, or a laminate thereof,
If necessary, a suitable one according to the prior art, such as one coated with a suitable release agent such as silicone-based, long mirror alkyl-based, fluorine-based or molybdenum sulfide, may be used.

In the present invention, each layer such as the above-mentioned brightness enhancement film and optical film, and each layer such as the pressure-sensitive adhesive layer, for example, salicylic acid ester compound, benzophenol compound, benzotriazole compound, cyanoacrylate compound, nickel, etc. It may be one having an ultraviolet absorbing ability by a method such as a method of treating with an ultraviolet absorber such as a complex salt compound.

The brightness enhancement film and optical film of the present invention can be preferably used for forming various devices such as liquid crystal display devices. The liquid crystal display device can be formed in a conventional manner. That is, the liquid crystal display device is generally formed by appropriately assembling the components such as the liquid crystal cell and the optical film, and the illumination system and the like into a drive circuit, but in the present invention, according to the present invention, There is no particular limitation except that a brightness enhancement film or an optical film is used, and the conventional method can be applied. The liquid crystal cell may be of any type such as TN type, STN type, and π type.

It is possible to form an appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate and an optical film are arranged on one side or both sides of a liquid crystal cell, or a backlight system or a reflection plate is used for an illumination system. In that case, the optical film can be installed on one side or both sides of the liquid crystal cell. When a polarizing plate and an optical film are provided on both sides, they may be the same or different. Further, when forming the liquid crystal display device, for example, a diffusion plate, an anti-glare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusion plate, a backlight, and other appropriate components are provided at appropriate positions in a single layer or Two or more layers can be arranged.

Next, an organic electroluminescence device (organic EL display device) will be described. Generally, in an organic EL display device, a transparent electrode, an organic light emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light emitting body (organic electroluminescent light emitting body). Here, the organic light emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative or the like and a light emitting layer made of a fluorescent organic solid such as anthracene, Alternatively, a structure having various combinations such as a laminated body of such a light emitting layer and an electron injection layer formed of a perylene derivative, or a laminated body of these hole injection layer, light emitting layer, and electron injection layer is known. Has been.

In the organic EL display device, holes and electrons are injected into the organic light emitting layer by applying a voltage to the transparent electrode and the metal electrode, and energy generated by the recombination of these holes and electrons is fluorescent. It emits light based on the principle that a substance is excited and the excited fluorescent substance emits light when returning to the ground state. The mechanism of recombination in the middle is similar to that of a general diode, and as can be expected from this, the current and the emission intensity show a strong nonlinearity with rectification with respect to the applied voltage.

In the organic EL display device, at least one of the electrodes must be transparent in order to extract light emitted from the organic light emitting layer. In general, indium tin oxide (IT) is used.
A transparent electrode formed of a transparent conductor such as O) is used as an anode. On the other hand, it is important to use a substance having a small work function for the cathode in order to facilitate electron injection and increase the luminous efficiency, and a metal electrode such as Mg-Ag or Al-Li is usually used.

In the organic EL display device having such a structure, the organic light emitting layer is formed of an extremely thin film having a thickness of about 10 nm. For this reason, the organic light emitting layer transmits light almost completely like the transparent electrode. As a result, when entering from the surface of the transparent substrate during non-light emission, the light transmitted through the transparent electrode and the organic light emitting layer and reflected by the metal electrode goes out to the surface side of the transparent substrate again, when viewed from the outside, The display surface of the organic EL display device looks like a mirror surface.

In an organic EL display device including an organic electroluminescent light-emitting body having a transparent electrode on the front surface side of an organic light-emitting layer that emits light when a voltage is applied and a metal electrode on the back surface side of the organic light-emitting layer, A polarizing plate can be provided on the surface side of the electrode, and a retardation plate can be provided between the transparent electrode and the polarizing plate.

Since the retardation plate and the polarizing plate have a function of polarizing the light incident from the outside and reflected by the metal electrode, there is an effect that the mirror surface of the metal electrode is not visually recognized from the outside by the polarization action. Especially, the phase difference plate is 1/4.
The mirror surface of the metal electrode can be completely shielded by using a wave plate and adjusting the angle between the polarization directions of the polarizing plate and the retardation plate to π / 4.

That is, as for the external light incident on the organic EL display device, only the linearly polarized light component is transmitted by the polarizing plate. This linearly polarized light is generally elliptically polarized by the retardation plate, but it is circularly polarized when the retardation plate is a 1/4 wavelength plate and the polarization direction between the polarizing plate and the retardation plate is π / 4. .

This circularly polarized light passes through the transparent substrate, the transparent electrode and the organic thin film, is reflected by the metal electrode, passes through the organic thin film, the transparent electrode and the transparent substrate again, and becomes linearly polarized light again on the retardation plate. . Since this linearly polarized light is orthogonal to the polarization direction of the polarizing plate, it cannot pass through the polarizing plate. as a result,
The mirror surface of the metal electrode can be completely shielded.

[0074]

EXAMPLES One embodiment of the present invention will be described below with reference to examples, but it goes without saying that the present invention is not limited to the examples. Parts and% in each example are based on weight.

Example 1 (Preparation of pressure-sensitive adhesive for first pressure-sensitive adhesive layer) As a base polymer, a copolymer of butyl acrylate: acrylic acid: 2-hydroxyethyl acrylate = 100: 5: 0.1 (weight ratio) was used. A solution (solid content: 25%) containing an acrylic polymer having a weight average molecular weight of 2,000,000 was used. To the above-mentioned acrylic polymer solution, 2 parts of Coronate L manufactured by Nippon Polyurethane Co., Ltd., which is an isocyanate-based polyfunctional compound, was added 2 parts to 100 parts of the polymer solid content, and 200 parts of a solvent (toluene) for viscosity adjustment was added to prepare an adhesive solution ( Solid content 3
0%) was prepared.

(Measurement of Dynamic Storage Shear Modulus) In order to evaluate the elastic modulus of the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive prepared above, the pressure-sensitive adhesive solution was poured into a disposable cup, and then at 24 ° C. at 24 ° C. The sample was placed in a dryer for 1 hour at 110 ° C. for 1 hour to remove water, and a thickness of 1 mm was punched out with a punch having a diameter of 8 mm to obtain a sample. This sample is called ARES (AnestiWata Corporation).
(Viscoelasticity measuring device manufactured by ation) (frequency 1 Hz). The dynamic storage shear elastic modulus of the pressure-sensitive adhesive layer (first pressure-sensitive adhesive layer) formed by this pressure-sensitive adhesive is 0.
It was 2 MPa.

(Preparation of brightness enhancement film) On a polyethylene terephthalate (PET) film subjected to orientation treatment,
A cholesteric liquid crystal polymer having selective reflection center wavelengths of 450 nm, 550 nm, and 610 nm and sequentially formed and oriented with each layer having a thickness of 2 μm is used. This cholesteric liquid crystal surface and a triacetyl cellulose film (40 μm) Formed by 10μ
m first adhesive layer (dynamic storage shear modulus 0.2MP
After bonding via a), only the PET film was gently peeled off to transfer the cholesteric liquid crystal layer to the triacetyl cellulose film. Then, on the cholesteric liquid crystal layer side exposed by the transfer, a 1/4 wavelength plate (polycarbonate film) is formed through a second pressure-sensitive adhesive layer (dynamic storage shear elastic modulus 0.1 MPa) with a thickness of 25 μm formed separately by an acrylic pressure-sensitive adhesive. Stretched oriented material, 40 μm)
Were bonded together to produce a brightness enhancement film.

Example 2 In (Preparation of pressure-sensitive adhesive for first pressure-sensitive adhesive layer) of Example 1,
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the acrylic polymer was changed to polyether polyurethane. A brightness enhancement film was prepared in the same manner as in Example 1. The dynamic storage shear modulus of the first adhesive layer is 1.3M
It was Pa.

Example 3 (Preparation of pressure-sensitive adhesive for first pressure-sensitive adhesive layer) in Example 1
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the acrylic polymer was changed to the polyester polymer. A brightness enhancement film was prepared in the same manner as in Example 1.
The dynamic storage shear modulus of the first adhesive layer is 10.0 MPa
Met.

Example 4 (Preparation of pressure-sensitive adhesive for first pressure-sensitive adhesive layer) in Example 1
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the compounding amount of the isocyanate-based polyfunctional compound was changed to 0.5 part. A brightness enhancement film was prepared in the same manner as in Example 1. The dynamic storage shear modulus of the first adhesive layer is 0.1M
It was Pa.

Example 5 (Preparation of pressure-sensitive adhesive for first pressure-sensitive adhesive layer) in Example 1
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the acrylic polymer was changed to polyester polyurethane. A brightness enhancement film was prepared in the same manner as in Example 1. The dynamic storage shear modulus of the first adhesive layer is 13.5.
It was MPa.

Comparative Example 1 (Preparation of pressure-sensitive adhesive for first pressure-sensitive adhesive layer) in Example 1
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the compounding amount of the isocyanate-based polyfunctional compound was changed to 0.1 part. A brightness enhancement film was prepared in the same manner as in Example 1. The dynamic storage shear modulus of the first adhesive layer is 0.08.
It was MPa.

Comparative Example 2 (Preparation of pressure-sensitive adhesive for first pressure-sensitive adhesive layer) in Example 1
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the acrylic polymer was changed to a urethane polymer and the isocyanate polyfunctional compound was changed to an epoxy compound.
A brightness enhancement film was prepared in the same manner as in Example 1. The dynamic storage shear modulus of the first adhesive layer is 30.0M
It was Pa.

The following tests were conducted on the brightness enhancement films obtained in Examples and Comparative Examples. The results are shown in Table 1.

(Cohesive failure test) At room temperature (25 ° C.), the protective film side of the brightness enhancement film was placed on a glass plate,
It was fixed by sticking with an adhesive. After that, the brightness enhancement film was triggered, and when the brightness enhancement film was peeled off, the state of cohesive failure of the cholesteric layer was visually observed and evaluated according to the following criteria.

[0086] ◯: No cohesive failure. Δ: Cohesive failure occurs partially. X: There is cohesive failure on the entire surface.

(Cold-heat shock test) The state of cohesive failure of the cholesteric layer was visually observed after 200 times of operation of changing the temperature environment of the brightness enhancement film to −35 ° C. and 85 ° C. every 30 minutes. The following criteria were evaluated.

[0088] ◯: No cohesive failure. Δ: Cohesive failure occurs partially. X: There is cohesive failure on the entire surface.

[0089]

[Table 1]

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a brightness enhancement film.

[Explanation of sign]

1 protective film 2 Cholesteric liquid crystal layer 3 1/4 wave plate a1 First adhesive layer a2 Second adhesive layer

Continued front page    (72) Inventor Naoki Takahashi             1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto             Electric Works Co., Ltd. (72) Inventor Satoshi Kawahara             1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto             Electric Works Co., Ltd. F-term (reference) 2H049 BA06 BA47 BB03 BB33 BB51                       BB62 BC14 BC22                 2H091 FA11 FB02 FC30 FD10 FD14                       GA07 GA16 GA17 HA11 JA02                       LA03 LA11 LA12 LA13 LA16                 4F100 AH03 AJ06A AJ06K AK01A                       AK01C AK25 AK45 AR00E                       AS00C BA05 BA07 BA10A                       BA10E CB05B CB05D EC04                       EC20 GB41 JK07B JN21                       YY00B

Claims (6)

[Claims] 1. In a brightness enhancement film in which a protective film, a first adhesive layer, a cholesteric liquid crystal layer, a second adhesive layer, and a quarter-wave plate are laminated in this order, between the protective film and the cholesteric liquid crystal layer. 25 ℃ of the first adhesive layer of
2. The brightness enhancement film having a dynamic storage shear elastic modulus of 0.1 to 15 MPa. 2. The brightness enhancement film according to claim 1, wherein the material of the protective film is triacetyl cellulose. 3. The brightness enhancement film according to claim 1, wherein the cholesteric liquid crystal layer is formed by a liquid crystal polymer alignment material, a liquid crystal monomer alignment material polymerization layer, or a composite layer thereof. 4. A cholesteric liquid crystal layer formed and oriented on an orientation substrate, to a protective film via a first adhesive layer,
Alternatively, after transferring to the quarter-wave plate via the second adhesive layer, the first adhesive layer may be laminated on one surface of the cholesteric liquid crystal layer and the second adhesive layer may be laminated on the other surface of the cholesteric liquid crystal layer. The cholesteric liquid crystal layer surface exposed by the transfer is laminated with a quarter-wave plate via the second adhesive layer or a protective film via the first adhesive layer. 4. The method for manufacturing the brightness enhancement film according to any one of 3 above. 5. An optical film, wherein the brightness enhancement film according to any one of claims 1 to 3 is further laminated with at least one optical film. 6. An image display device to which the brightness enhancement film according to claim 1 or the optical film according to claim 5 is applied.