JP2007017637A - Laminated optical retardation plate, method for producing the same, luminance-improving film, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated optical retardation plate which can be stably produced, without requiring a complicated step such as light irradiation under inert gas atmosphere, excels in orientation retention after liquid crystal orientation fixing and in mechanical strength, and can extensively control phase difference in the thickness direction. <P>SOLUTION: The laminated optical retardation plate is obtained, by stacking and integrating a homeotropically oriented liquid-crystal layer, with the homeotropic orientation fixed and a stretched film having a phase difference function. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laminated retardation plate obtained by laminating and integrating a homeotropic alignment liquid crystal film and a stretched film having a retardation function, and a method for producing the same. The laminated phase difference plate of the present invention is used alone or in combination with another optical film as an optical film such as a quarter-wave film, a viewing angle compensation film, an optical compensation film, an elliptically polarizing film, and a luminance of a liquid crystal display device or the like. Can be used as an enhancement film. Furthermore, the present invention relates to an image display device such as a liquid crystal display device, an organic EL display device, or a PDP using the laminated retardation plate and the brightness enhancement film.

  In an image display device such as a liquid crystal display device, contrast and the like change with a change in viewing angle due to birefringence by liquid crystal or the like. In order to prevent such a contrast change and the like, in a liquid crystal display device or the like, a technique has been proposed in which a retardation plate is disposed in a liquid crystal cell and optical characteristics based on birefringence are compensated to improve viewing angle characteristics. As the compensation retardation plate, a uniaxial or biaxial stretched film is usually used, but it does not have satisfactory viewing angle characteristics for all liquid crystal cells.

  In Patent Document 1, one or two or more heat-shrinkable films are bonded to one or both sides of a long film made of a thermoplastic resin, and the shrinkage force of the heat-shrinkable film is measured while gripping with a tenter. The width direction of the long film is contracted at a magnification A of 0.7 times or more to less than 1.0 times, and the film width excluding the grip holding part after the contraction treatment is defined as 100. 100-magnification (A × 100) × 0.15 or less is disclosed. A continuous production method of a retardation film is disclosed in which the width direction is stretched and widened at a stretching ratio (%) satisfying 100 or less.

  According to the said manufacturing method, since it extends also in the thickness direction, the phase difference plate which has a phase difference also in the thickness direction is obtained. However, in the manufacturing method, when the in-plane main refractive index of the obtained retardation plate is nx, ny, the refractive index in the thickness direction is nz, and nx> ny, Nz = (nx−nz) Nz defined by / (nx−ny) is −1.0 <Nz <0.1, and there is a limit to stretching in the thickness direction, and the retardation in the thickness direction cannot be controlled over a wide range. Moreover, in the said manufacturing method, since the elongate film is heat-shrinked with the heat shrink film and it is extended | stretched in the thickness direction, thickness of the obtained phase difference plate increases rather than a elongate film. That is, the thickness of the retardation plate obtained by the manufacturing method is about 50 to 100 μm, which is not sufficient for the thinning required for a liquid crystal display device or the like.

  As a method for increasing the retardation in the thickness direction, it is considered a shortcut to use homeotropic alignment (vertical alignment) of liquid crystals. Homeotropic alignment of liquid crystal molecules is that the long-axis molecular direction of the liquid crystal is aligned in a direction substantially perpendicular to the substrate. It is well known that homeotropic alignment can be obtained by applying an electric field by putting liquid crystal in two glass substrates as in a liquid crystal display device, but it is very difficult to make this alignment state into a film. However, there are problems with the methods reported in the past. In Patent Document 2 to Patent Document 4, a main chain polymer liquid crystal compound is homeotropically aligned, and then a film is obtained by glass fixation. However, in homeotropic alignment, it is surmised that there is a problem that cracks are likely to occur in the in-plane direction because the polymers are aligned in the film thickness direction, but in these reports, measures such as strengthening the material by crosslinking are taken. Absent. In Patent Document 5, the homeotropic alignment of the side chain polymer liquid crystal compound is fixed by vitrification. However, it is considered that there is a problem in strength as compared with the main chain polymer liquid crystal compound. In Patent Documents 6 to 7, a polymerizable low-molecular liquid crystal compound is added to the side-chain polymer liquid crystal compound. However, since the low-molecular liquid crystal compound is polymerized alone, the strength of the side-chain polymer liquid crystal compound is reinforced. Has its limits. In Patent Document 8, a material in which a radical polymerizable group, or a cationic polymerizable group such as a vinyl ether group or an epoxy group is introduced into a side chain type polymer liquid crystal compound is used. However, since radical polymerization is generally subjected to oxygen inhibition, there is a risk that polymerization may be insufficient, and if equipment is used to remove oxygen, the apparatus becomes large. Vinyl ether groups and epoxy groups are advantageous in this respect because they are not affected by oxygen inhibition, but the ether bond of vinyl ether groups is unstable and easily cleaved, and epoxy groups are complicated to introduce into liquid crystal materials. In addition, it is difficult to obtain a high degree of polymerization when the crosslinking treatment is performed. Furthermore, in order to obtain homeotropic alignment, a large amount of non-liquid crystalline structural units are introduced into the liquid crystal material, and there is a question about the stable liquid crystallinity. In Patent Document 9, a phase difference plate is obtained in which a homeotropic alignment liquid crystal film and a stretched film having a retardation function are laminated and integrated. The method for producing a homeotropic alignment liquid crystal film is the same as in Patent Document 10 and the like. It is a manufacturing method, and it can be said that a problem remains in the manufacture of a conventional homeotropic alignment film, which is insufficient.

JP 2000-304924 A Japanese Patent No. 2853064 Japanese Patent No. 3018120 Japanese Patent No. 3078948 JP 2002-174725 A JP 2002-333524 A JP 2002-333642 A JP 2003-2927 A JP 2003-149441 A JP 2003-2927 A

  The present invention enables stable production without requiring a complicated process such as light irradiation under an inert gas atmosphere, and is excellent in alignment retention ability and mechanical strength after liquid crystal alignment fixation, and has a thickness. It is an object of the present invention to provide a laminated phase difference plate capable of controlling a direction retardation in a wide range and a manufacturing method thereof. Furthermore, it aims at providing the brightness improvement film using the said laminated phase difference plate, and also the image display apparatus using the said laminated phase difference plate and a brightness enhancement film.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the object can be achieved by the laminated retardation plate shown below, and have completed the present invention.

  That is, a first aspect of the present invention relates to a laminated retardation plate characterized by laminating and integrating a homeotropic alignment liquid crystal layer in which homeotropic alignment is fixed and a stretched film having a retardation function.

  According to a second aspect of the present invention, after the homeotropic alignment liquid crystal layer is homeotropically aligned in a liquid crystal state, a liquid crystalline composition containing at least a side chain type liquid crystalline polymer compound having an oxetanyl group is used. The multilayer retardation plate according to the first aspect of the present invention, wherein the homeotropic alignment is fixed by reacting the oxetanyl group.

  According to a third aspect of the present invention, a liquid crystalline composition containing at least a side chain type liquid crystalline polymer compound having an oxetanyl group is homeotropically aligned in a liquid crystal state on an alignment substrate having homeotropic alignment ability. Thereafter, a stretched film having a retardation function is attached to the homeotropic alignment liquid crystal layer on the alignment substrate on which the homeotropic alignment is fixed by reacting the oxetanyl group, using an adhesive or an adhesive means, and then homeotropic The present invention relates to a method for producing a laminated phase difference plate, wherein the alignment liquid crystal layer is peeled off from an alignment substrate, and a homeotropic alignment liquid crystal layer and a stretched film having a retardation function are laminated and integrated.

  According to a fourth aspect of the present invention, there is provided a liquid crystalline composition comprising at least a side chain type liquid crystalline polymer compound having an oxetanyl group on a stretched film substrate having homeotropic alignment ability and retardation function. A stretched film having a retardation function using an adhesive or an adhesive means is laminated and integrated into a laminate obtained by reacting the homeotropic orientation with the oxetanyl group and fixing the homeotropic orientation. The present invention relates to a manufacturing method of a laminated retardation plate.

  5th of this invention is related with the laminated phase difference plate manufactured with the manufacturing method as described in the 3rd or 4th of this invention.

6th of this invention is related with the lamination | stacking phase difference plate as described in 1st, 2nd or 5th of this invention characterized by the said lamination | stacking phase difference plate satisfy | filling the following [1]-[4].
[1] 0 nm ≦ Re1 ≦ 50 nm
[2] −500 nm ≦ Rth1 ≦ −30 nm
[3] 30 nm ≦ Re2 ≦ 500 nm
[4] 30 nm ≦ Rth2 ≦ 300 nm
(Here, Re1 and Re2 mean the in-plane retardation value of the homeotropic alignment liquid crystal layer and the stretched film having a retardation function, respectively, and Rth1 and Rth2 respectively represent the homeotropic alignment liquid crystal layer and the retardation function. The Re1, Re2, Rth1, and Rth2 are Re1 = (Nx1-Ny1) × d1 [nm] and Rth1 = (Nx1-Nz1) × d1 [nm, respectively. ], Re2 = (Nx2-Ny2) * d2 [nm], Rth2 = (Nx2-Nz2) * d2 [nm], where d1 and d2 are respectively a homeotropic alignment liquid crystal layer and a stretch having a retardation function. The film thicknesses, Nx1 and Ny1, are the main refractive indices in the plane of the homeotropic alignment liquid crystal layer, and Nx2 and Ny2 are Respective in-plane main refractive indexes Nz1 and Nz2 of the stretched film having a retardation function are main refractive indexes in the thickness direction of the homeotropic alignment liquid crystal layer and the stretched film having a retardation function, respectively. > Nx1 ≧ Ny1, Nx2> Ny2.)

  A seventh aspect of the present invention is the laminated phase difference plate according to the first, second or fifth aspect of the present invention, wherein the in-plane retardation value (Re2) of the stretched film having a retardation function is in the range of 100 to 170 nm. Further, the present invention relates to a brightness enhancement film, wherein at least one cholesteric liquid crystal film is further laminated.

  An eighth aspect of the present invention relates to an image display device to which the laminated phase difference plate according to the first, second, or fifth aspect of the present invention or the brightness enhancement film according to the seventh aspect of the present invention is applied.

Hereinafter, the present invention will be described in detail.
The laminated retardation plate of the present invention is obtained by laminating and integrating a homeotropic alignment liquid crystal layer and a stretched film having a retardation function. In the present invention, in order to obtain a liquid crystal layer in which the homeotropic alignment of the liquid crystal material is fixed, the selection of the liquid crystal material and the alignment substrate having homeotropic alignment ability is extremely important.

First, the liquid crystal material will be described.
The liquid crystal material used in the present invention contains at least a side chain type liquid crystalline polymer such as poly (meth) acrylate or polysiloxane as a main constituent component. In the present invention, the side chain type liquid crystal polymer has a polymerizable oxetanyl group at the terminal. Therefore, more specifically, it is obtained by homopolymerizing the (meth) acrylic moiety of the (meth) acrylic compound having an oxetanyl group represented by the formula (1) or copolymerizing with another (meth) acrylic compound. A side chain type liquid crystalline polymer substance is preferably used.

In the above formula (1), R ₁ represents hydrogen or a methyl group, R ₂ represents hydrogen, a methyl group or an ethyl group, and L ₁ and L ₂ each independently represent a single bond, —O—, —O. -CO- or -CO-O- is represented, M represents Formula (2), Formula (3) or Formula (4), and n and m each independently represent an integer of 0 to 10.
-P ₁ -L ₃ -P ₂ -L ₄ -P _3- (2)
-P ₁ -L ₃ -P _3- (3)
-P _3- (4)

In Formulas (2) to (4), P ₁ and P ₂ each independently represent a group selected from Formula (5), P ₃ represents a group selected from Formula (6), and L ₃ and L ₄ each independently represents a single bond, —CH═CH—, —C≡C—, —O—, —O—CO— or —CO—O—.

  The method for synthesizing these (meth) acrylic compounds having an oxetanyl group is not particularly limited, and can be synthesized by applying a method used in an ordinary organic chemical synthesis method. For example, by combining a site having an oxetanyl group and a site having a (meth) acrylic group by means such as Williamson's ether synthesis or ester synthesis using a condensing agent, oxetanyl group and (meth) acrylic group 2 A (meth) acrylic compound having an oxetanyl group having two reactive functional groups can be synthesized.

  The (meth) acrylic group having the oxetanyl group represented by the formula (1) is represented by the following formula (7) by homopolymerizing or copolymerizing with another (meth) acrylic compound. A side-chain liquid crystalline polymer substance containing units can be obtained. The polymerization conditions are not particularly limited, and normal radical polymerization or anionic polymerization conditions can be employed.

  As an example of radical polymerization, a (meth) acrylic compound is dissolved in a solvent such as dimethylformamide (DMF), and 2,2′-azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), or the like is used as an initiator. The method of making it react at 60-120 degreeC for several hours is mentioned. Moreover, in order to make the liquid crystal phase appear stably, copper bromide (I) / 2,2′-bipyridyl series, 2,2,6,6-tetramethylpiperidinooxy free radical (TEMPO) series, etc. are used. A method of controlling the molecular weight distribution by conducting living radical polymerization as an initiator is also effective. These radical polymerizations are preferably performed under deoxygenation conditions.

Examples of anionic polymerization include a method in which a (meth) acrylic compound is dissolved in a solvent such as tetrahydrofuran (THF) and reacted with a strong base such as an organic lithium compound, an organic sodium compound, or a Grignard reagent as an initiator. In addition, the molecular weight distribution can be controlled by optimizing the initiator and the reaction temperature for living anionic polymerization. These anionic polymerizations must be performed strictly under dehydration and deoxygenation conditions.
In addition, the (meth) acrylic compound to be copolymerized at this time is not particularly limited and may be anything as long as the synthesized polymer compound exhibits liquid crystallinity, but in order to increase the liquid crystallinity of the synthesized polymer compound, A (meth) acrylic compound having a mesogenic group is preferred. For example, a (meth) acryl compound represented by the following formula (8) can be exemplified as a preferred compound.

In formula (8), R represents hydrogen, a C1-C12 alkyl group, a C1-C12 alkoxy group, or a cyano group.
As the side chain type liquid crystalline polymer substance, those containing 5 to 100 mol% of the unit represented by the formula (7) are preferable, and those containing 10 to 100 mol% are particularly preferable. The side chain type liquid crystalline polymer substance preferably has a weight average molecular weight of 2,000 to 100,000, particularly preferably 5,000 to 50,000.

  The liquid crystal material used in the present invention may contain various compounds that can be mixed without impairing liquid crystallinity, in addition to the side-chain liquid crystalline polymer substance. Examples of compounds that can be contained include compounds having a cationic polymerizable functional group such as an oxetanyl group, an epoxy group, and a vinyl ether group, various polymer substances having film-forming ability, and various low-molecular liquid crystal compounds exhibiting liquid crystallinity. And polymer liquid crystalline compounds. When the side chain liquid crystalline polymer substance is used as a composition, the proportion of the side chain liquid crystalline polymer substance in the entire composition is 10% by mass or more, preferably 30% by mass or more, and more preferably. Is 50 mass% or more. If the content of the side chain type liquid crystalline polymer substance is less than 10% by mass, the concentration of the polymerizable group in the composition becomes low, and the mechanical strength after polymerization becomes insufficient.

  In addition, since the liquid crystal material is subjected to an alignment treatment, the oxetanyl group is cationically polymerized and crosslinked to cross-link the liquid crystal state. Therefore, the liquid crystal material is subjected to cation by external stimulation such as light or heat. It is preferable to contain a photo cation generator and / or a thermal cation generator that generate a cation, and among them, a photo cation generator is more preferable. If necessary, various sensitizers may be used in combination.

The photo cation generator means a compound capable of generating a cation by irradiating with light having an appropriate wavelength, and examples thereof include organic sulfonium salt systems, iodonium salt systems, and phosphonium salt systems. Antimonates, phosphates, borates and the like are preferably used as counter ions of these compounds. Specific examples of the compound include Ar ₃ S ⁺ SbF ₆ ⁻ , Ar ₃ P ⁺ BF ₄ ⁻ and Ar ₂ I ⁺ PF ₆ ⁻ (wherein Ar represents a phenyl group or a substituted phenyl group). In addition, sulfonate esters, triazines, diazomethanes, β-ketosulfone, iminosulfonate, benzoinsulfonate, and the like can also be used.

  The thermal cation generator is a compound capable of generating a cation when heated to an appropriate temperature, for example, benzylsulfonium salts, benzylammonium salts, benzylpyridinium salts, benzylphosphonium salts, hydrazinium salts, carboxylic acid esters, Examples thereof include sulfonic acid esters, amine imides, antimony pentachloride-acetyl chloride complexes, diaryliodonium salts-dibenzyloxycopper, and boron halide-tertiary amine adducts.

  The amount of these cation generators added to the liquid crystal material varies depending on the structure of the mesogenic part and spacer part, the oxetanyl group equivalent, the alignment condition of the liquid crystal, etc. constituting the side chain type liquid crystalline polymer material to be used. Although it cannot be said, it is usually 100 mass ppm to 20 mass%, preferably 1000 mass ppm to 10 mass%, more preferably 0.2 mass% to 7 mass%, most preferably based on the side chain type liquid crystalline polymer substance. Is in the range of 0.5% to 5% by weight. If the amount is less than 100 mass ppm, the amount of cations generated may not be sufficient and polymerization may not proceed. If the amount is more than 20 mass%, the remaining cation generator remains in the liquid crystal film. It is not preferable because there is a risk that the light resistance and the like may deteriorate due to an increase in the number of objects.

Next, an alignment substrate having homeotropic alignment ability will be described.
As the alignment substrate, a substrate having a smooth plane is preferable, and examples thereof include a film or sheet made of an organic polymer material, a glass plate, and a metal plate. From the viewpoint of cost and continuous productivity, it is preferable to use a material made of an organic polymer. Examples of organic polymer materials include polyvinyl alcohol, polyimide, polyphenylene oxide, polyether ketone, polyether ether ketone, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, Examples include films made of transparent polymers such as polycarbonate polymers and acrylic polymers such as polymethyl methacrylate. Styrene polymers such as polystyrene and acrylonitrile / styrene copolymers, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, olefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, nylon and aromatic polyamides, etc. A film made of a transparent polymer such as an amide polymer may also be mentioned. Furthermore, imide polymers, sulfone polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers Examples thereof include a film made of a transparent polymer such as a polymer, an epoxy-based polymer, and a blend of the above polymers. Among these, the hydrogen bonding property is high, and plastic films such as triacetyl cellulose, polycarbonate, norbornene polyolefin and the like used as an optical film are awarded. Examples of the organic polymer film include ZEONOR (trade name, manufactured by ZEON CORPORATION), ZEONEX (trade name, manufactured by ZEON CORPORATION), Arton (trade name, manufactured by JSR Corporation), etc. A plastic film made of a polymer material having a norbornene structure has excellent optical properties. Moreover, as a metal film, the said film formed from aluminum etc. is mentioned, for example.

  In order to stably obtain homeotropic alignment using the above-mentioned liquid crystal material, the material constituting these substrates has, for example, a long-chain (usually 4 or more carbon atoms, preferably 8 or more) alkyl group. It is preferable to have a layer made of a material having the above-mentioned long chain alkyl group on the surface of these substrates, etc. Among them, polyvinyl alcohol having a long chain alkyl group is most preferable. These organic polymer materials may be used alone as a substrate, or may be formed as a thin film on another substrate. In the field of liquid crystal, it is common to rub the substrate with a cloth or the like, but the homeotropic alignment film of the present invention is an alignment in which in-plane anisotropy does not basically occur. Because of the structure, rubbing is not necessarily required. However, it is more preferable to apply a weak rubbing treatment from the viewpoint of suppressing repelling when a liquid crystal material is applied. An important setting value that defines the rubbing condition is a peripheral speed ratio. This represents the ratio between the movement speed of the cloth and the movement speed of the substrate when the rubbing cloth is wound around a roll and rubbed while the substrate is rubbed. In the present invention, the weak rubbing treatment usually has a peripheral speed ratio of 50 or less, more preferably 25 or less, and particularly preferably 10 or less. When the peripheral speed ratio is greater than 50, the effect of rubbing is too strong, and the liquid crystal material cannot be completely aligned vertically, and there is a possibility that the alignment is tilted in the in-plane direction from the vertical direction.

Next, a manufacturing process of the homeotropic alignment liquid crystal layer (hereinafter also simply referred to as a liquid crystal layer) of the present invention will be described.
Although it does not limit as a manufacturing method of a liquid-crystal layer below, the above-mentioned liquid crystal material is developed on the above-mentioned alignment substrate, and after aligning the said liquid-crystal material, the light irradiation and / or heat-treatment are concerned. It can be manufactured by fixing the orientation state.
The liquid crystal material is spread on the alignment substrate to form the liquid crystal material layer. The liquid crystal material is applied directly on the alignment substrate in a molten state, or the liquid crystal material solution is applied on the alignment substrate, and then the coating film is applied. And drying the solvent to distill off the solvent.

  The solvent used for preparing the solution is not particularly limited as long as it can dissolve the liquid crystal material of the present invention and can be distilled off under suitable conditions. Generally, ketones such as acetone, methyl ethyl ketone, isophorone, and cyclohexanone, butoxyethyl Ethers such as alcohol, hexyloxyethyl alcohol, methoxy-2-propanol, glycol ethers such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether, esters such as ethyl acetate and ethyl lactate, phenols such as phenol and chlorophenol, N Amides such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, halogens such as chloroform, tetrachloroethane, dichlorobenzene, etc. Mixing system is preferably used. Further, in order to form a uniform coating film on the alignment substrate, a surfactant, an antifoaming agent, a leveling agent, or the like may be added to the solution.

Regardless of the method of directly applying the liquid crystal material or the method of applying the solution, the application method is not particularly limited as long as the uniformity of the coating film is ensured, and a known method may be adopted. it can. Examples thereof include spin coating, die coating, curtain coating, dip coating, and roll coating.
In the method of applying a liquid crystal material solution, it is preferable to include a drying step for removing the solvent after the application. As long as the uniformity of a coating film is maintained, this drying process can employ | adopt a well-known method, without being specifically limited. For example, a method such as a heater (furnace) or hot air blowing may be used.

  Although the film thickness of the liquid crystal layer depends on the method of the image display device and various optical parameters, it cannot be generally stated, but is usually 0.2 μm to 10 μm, preferably 0.3 μm to 5 μm, more preferably 0.8 μm. 5 μm to 2 μm. When the film thickness is thinner than 0.2 μm, there is a possibility that a sufficient viewing angle improvement or brightness enhancement effect cannot be obtained. If it exceeds 10 μm, the image display device may be unnecessarily colored.

  Subsequently, the liquid crystal material layer formed on the alignment substrate is formed into a liquid crystal alignment by a method such as heat treatment, and is cured and fixed by light irradiation and / or heat treatment. In the first heat treatment, the liquid crystal is aligned by the self-alignment ability inherent in the liquid crystal material by heating to the liquid crystal phase expression temperature range of the used liquid crystal material. As conditions for the heat treatment, the optimum conditions and limit values differ depending on the liquid crystal phase behavior temperature (transition temperature) of the liquid crystal material to be used, but it cannot be generally stated, but is usually in the range of 10 to 250 ° C., preferably 30 to 180 ° C. The heat treatment is preferably performed at a temperature equal to or higher than the glass transition temperature (Tg) of the liquid crystal material, more preferably at a temperature higher by 10 ° C. than Tg. If the temperature is too low, the liquid crystal alignment may not proceed sufficiently, and if the temperature is high, the cationic polymerizable reactive group in the liquid crystal material and the alignment substrate may be adversely affected. Moreover, about heat processing time, it is 3 seconds-30 minutes normally, Preferably it is the range of 10 seconds-10 minutes. If the heat treatment time is shorter than 3 seconds, the liquid crystal alignment may not be completed sufficiently, and if the heat treatment time exceeds 30 minutes, the productivity is deteriorated.

  After the liquid crystal material layer is formed into a liquid crystal alignment by a method such as heat treatment, the liquid crystal material is cured by a polymerization reaction of oxetanyl groups in the composition while maintaining the liquid crystal alignment state. The curing step is aimed at fixing the liquid crystal alignment state of the completed liquid crystal alignment by a curing (crosslinking) reaction and modifying it into a stronger film.

Since the liquid crystal material of the present invention has a polymerizable oxetanyl group, as described above, it is preferable to use a cationic polymerization initiator (cation generator) for the polymerization (crosslinking) of the reactive group.
When a photo cation generator is used, the liquid crystal material can be obtained by adding the photo cation generator to the heat treatment for aligning the liquid crystal under dark conditions (light blocking conditions that do not cause the photo cation generator to dissociate). The liquid crystal can be aligned with sufficient fluidity without curing until the end of the alignment step. Thereafter, the liquid crystal material layer is cured by generating cations by irradiating light from a light source that emits light of an appropriate wavelength.

As a light irradiation method, a photocation is generated by irradiating light from a light source such as a metal halide lamp, a high pressure mercury lamp, a low pressure mercury lamp, a xenon lamp, an arc lamp, or a laser having a spectrum in the absorption wavelength region of the photocation generator used. Cleave the generator. The dose per square centimeter is usually in the range of 1 to 2000 mJ, preferably 10 to 1000 mJ as the cumulative dose. However, this is not the case when the absorption region of the photocation generator and the spectrum of the light source are significantly different, or when the liquid crystal material itself has the ability to absorb light from the light source. In these cases, it is possible to adopt a method such as using a suitable photosensitizer or a mixture of two or more photocation generators having different absorption wavelengths.
The temperature at the time of light irradiation needs to be within a temperature range in which the liquid crystal material takes liquid crystal alignment. In order to sufficiently improve the curing effect, it is preferable to perform light irradiation at a temperature equal to or higher than Tg of the liquid crystal material.

  The liquid crystal layer produced by the above process is a sufficiently strong film. Specifically, the mesogens are three-dimensionally bonded by the curing reaction, and not only the heat resistance (the upper limit temperature for maintaining the liquid crystal alignment) is improved as compared to before curing, but also scratch resistance, abrasion resistance, crack resistance. The mechanical strength such as property is also greatly improved.

As the alignment substrate, it is not optically isotropic, or the obtained liquid crystal layer is finally opaque in the intended use wavelength region, or the alignment substrate is too thick, which hinders actual use. When there is a problem such as, a form transferred from a form formed on an alignment substrate to a stretched film having a retardation function may be used. As a transfer method, a known method can be adopted. For example, as described in JP-A-4-57017 and JP-A-5-333313, a liquid crystal film layer is laminated on a substrate different from the alignment substrate via an adhesive or an adhesive, and then if necessary. Examples thereof include a method of transferring a liquid crystal layer by performing a surface curing treatment using an adhesive or an adhesive and peeling the alignment substrate from the laminate.
The pressure-sensitive adhesive or adhesive used for transfer is not particularly limited as long as it is of optical grade, and generally used ones such as acrylic, epoxy, and urethane can be used.

The homeotropic alignment liquid crystal layer obtained as described above can be quantified by measuring the optical phase difference of the liquid crystal layer at an angle inclined from the normal incidence. In the case of a homeotropic alignment liquid crystal layer, this retardation value is symmetric about the vertical incident axis with respect to the tilted angle.
Several methods can be used for measuring the optical phase difference. For example, an automatic birefringence measuring device (manufactured by Oji Scientific Instruments) and a polarizing microscope can be used. This homeotropic alignment liquid crystal layer appears black between the crossed Nicol polarizers. In this way, homeotropic orientation can be evaluated.

  The homeotropic alignment liquid crystal layer thus obtained has a thickness d1 (μm) = 1 to 10 when the in-plane main refractive indexes are Nx1 and Ny1 and the refractive index in the thickness direction is Nz1. For example, according to the materials described in the examples, (Nx1-Ny1) = 0 to 0.0005, and (Nx1-Nz1) = − 0.1800 to −0.2000. In general, Nx1 = 1.53 to 1.55, Ny1 = 1.53 to 1.55, and Nz1 = 1.72 to 1.74.

  In the homeotropic alignment liquid crystal layer of the present invention, when Nz1> Nx1 ≧ Ny1, the in-plane retardation value (Re1 = (Nx1-Ny1) × d1 [nm]) is 0 to 50 nm, and the retardation in the thickness direction. The foundation value (Rth1 = (Nx1-Nz1) × d1 [nm]) is −500 to −30 nm.

  The Re1 and Rth1 values, which are optical parameters of the homeotropic alignment liquid crystal layer, are used as a viewing angle improving film due to differences in applications such as when used as a brightness enhancement film or as a viewing angle improving film of a liquid crystal display device. In some cases, the retardation value (Re1) in the plane of the homeotropic alignment liquid crystal layer is usually 0 nm for monochromatic light of 550 nm because it depends on the method of the liquid crystal display device and various optical parameters. The retardation value (Rth1) in the thickness direction is usually −500 to −30 nm, preferably −400 to −50 nm, more preferably −50 nm, preferably 0 nm to 20 nm, more preferably 0 nm to 5 nm. Preferably, it is controlled to -400 to -100 nm.

  By setting the Re1 value and the Rth1 value in the above ranges, the viewing angle improving film of the liquid crystal display device can widen the viewing angle while correcting the color tone of the liquid crystal display. An improvement effect can be obtained. When the Re1 value is larger than 50 nm, the front characteristics of the liquid crystal display device may be deteriorated due to the large front phase difference value. In addition, when the Rth1 value is larger than −30 nm or smaller than −500 nm, a sufficient viewing angle improvement effect cannot be obtained, or unnecessary coloring may occur when viewed from an oblique direction.

Next, the stretched film having a retardation function will be described.
Examples of the stretched film include a birefringent film obtained by stretching a film made of an appropriate polymer such as polycarbonate, norbornene-based resin, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefins, polyarylate, and polyamide. Or an alignment film made of a liquid crystal material such as a liquid crystal polymer, or a film in which an alignment layer of a liquid crystal material is supported by a film.

  When the in-plane main refractive index is Nx2, Ny2, the refractive index in the thickness direction is Nz2, and Nx2> Ny2, the stretched film has a thickness d2 (μm) = about 25-30 For example, according to the materials described in the examples, materials having (Nx2-Ny2) = 0.040 to 0.0060 and (Nx2-Nz2) = 0.040 to 0.0060 are used. In general, Nx2 is about 1.5930 to 1.5942, Ny2 is about 1.5850 to 1.5887, and Nz2 is about 1.5850 to 1.5883.

  In the stretched film having a retardation function in the present invention, when Nx2> Ny2, the in-plane retardation value (Re2 = (Nx2-Ny2) × d2 [nm]) is 30 to 500 nm, and the retardation in the thickness direction. The foundation value (Rth2 = (Nx2-Nz2) × d2 [nm]) is 30 to 300 nm.

  Re2 value and Rth2 value, which are optical parameters of stretched film with retardation function, are used for viewing angle improving film when used as brightness enhancing film, when used as viewing angle improving film for liquid crystal display device, etc. In this case, since it depends on the method of the liquid crystal display device and various optical parameters, it cannot be said unconditionally, but for the monochromatic light of 550 nm, the in-plane retardation value (Re2) is usually 30 nm to 500 nm, Preferably, it is in the range of 50 nm to 400 nm, more preferably 100 nm to 300 nm, and the retardation value (Rth2) in the thickness direction is usually controlled to 30 to 300 nm, preferably 50 to 200 nm, more preferably 70 to 150 nm. It has been done.

  By setting the Re2 value and the Rth2 value in the above ranges, the viewing angle improving film of the liquid crystal display device can widen the viewing angle while correcting the color tone of the liquid crystal display. An improvement effect can be obtained. When the Re2 value is smaller than 30 nm or larger than 500 nm, a sufficient viewing angle improvement effect cannot be obtained, or unnecessary coloring may occur when viewed from an oblique direction. Further, when the Rth2 value is smaller than 30 nm or larger than 300 nm, a sufficient viewing angle improving effect cannot be obtained, or unnecessary coloring may occur when viewed from an oblique direction.

  The laminated phase difference plate of the present invention can be obtained, for example, by producing a homeotropic alignment liquid crystal layer using a stretched film having homeotropic alignment ability and retardation function as a substrate. Moreover, it obtains by transferring the homeotropic alignment liquid crystal layer produced on the alignment substrate which has homeotropic alignment ability to the stretched film which has a phase difference function through an adhesive layer.

  The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited. For example, an acrylic polymer, a silicone-based polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine-based or rubber-based polymer is appropriately used as a base polymer. Can be selected and used. In particular, an acrylic pressure-sensitive adhesive having excellent optical transparency, moderate wettability, cohesiveness, and adhesive properties, and excellent weather resistance, heat resistance, and the like can be preferably used.

  The pressure-sensitive adhesive layer can be formed by an appropriate method. For example, a pressure sensitive adhesive solution of about 10 to 40% by mass in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of an appropriate solvent alone or a mixture such as toluene and ethyl acetate is prepared. A method of attaching it directly on the liquid crystal layer by an appropriate development method such as casting or coating, or a method of forming an adhesive layer on the separator according to the above and transferring it onto the liquid crystal layer, etc. Is mentioned. The pressure-sensitive adhesive layer includes, for example, natural and synthetic resins, in particular, tackifier resins, fillers made of glass fibers, glass beads, metal powders, other inorganic powders, pigments, coloring Various additives that can be added to the adhesive layer such as an agent and an antioxidant may be contained. Moreover, the adhesive layer etc. which contain microparticles | fine-particles and show light diffusibility may be sufficient.

  When transferring the homeotropic alignment liquid crystal layer to the stretched film having a retardation function via the pressure-sensitive adhesive layer, the surface of the homeotropic alignment liquid crystal layer is surface-treated to improve adhesion with the pressure-sensitive adhesive layer. be able to. The surface treatment means is not particularly limited, and a surface treatment method such as corona discharge treatment, sputtering treatment, low-pressure UV irradiation, or plasma treatment that can maintain the transparency of the liquid crystal layer surface can be suitably employed. Among these surface treatment methods, corona discharge treatment is good.

An optical film such as a polarizing plate can be further laminated on the obtained laminated retardation plate. Hereinafter, what laminated | stacked the optical film on the lamination | stacking phase difference plate is demonstrated.
A polarizing plate is used for an optical film applied to an image display device such as a liquid crystal display device. 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 types can be used. Examples of the polarizer include hydrophilic polymers such as polyvinyl alcohol film, partially formalized polyvinyl alcohol film, and ethylene / vinyl acetate copolymer partially saponified film, and two colors such as iodine and dichroic dye. And polyene-based oriented films such as those obtained by adsorbing a volatile substance and uniaxially stretched, polyvinyl alcohol dehydrated products, polyvinyl chloride dehydrochlorinated products, and the like. Among these, those obtained by stretching a polyvinyl alcohol film and adsorbing and orienting a dichroic material (iodine, dye) are preferably used. The thickness of the polarizer is not particularly limited, but is generally about 5 to 80 μm.

  A polarizer obtained by dyeing a polyvinyl alcohol film with iodine and uniaxially stretching it can be produced, for example, by dyeing polyvinyl alcohol in an aqueous solution of iodine and stretching it 3 to 7 times the original length. Moreover, it can also be immersed in aqueous solutions, such as a boric acid and potassium iodide, as needed. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing. In addition to washing the polyvinyl alcohol film surface with dirt and anti-blocking agents by washing the polyvinyl alcohol film with water, it also has the effect of preventing unevenness such as uneven coloring by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. The film 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 preferably has excellent transparency, mechanical strength, thermal stability, moisture shielding properties, isotropic properties, and the like. Examples of the material for 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, acrylonitrile and styrene copolymer. Examples thereof include styrene polymers such as coalesced (AS resin), polycarbonate polymers, and the like. Polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Examples of the polymer that forms the protective film include polymer blends. Other examples include films made of thermosetting or ultraviolet curable resins such as acrylic, urethane, acrylic urethane, epoxy, and silicone. Generally the thickness of a protective film is 500 micrometers or less, and 1-300 micrometers is preferable. In particular, the thickness is preferably 5 to 200 μm.

  As the protective film, a cellulose polymer such as triacetyl cellulose is preferable from the viewpoints of polarization characteristics and durability. A triacetyl cellulose film is particularly preferable. In addition, when providing a protective film in the both sides of a polarizer, the protective film which consists of the same polymer material may be used by the front and back, and the protective film which consists of a different polymer material etc. may be used. The polarizer and the protective film are usually in close contact with each other via an aqueous adhesive or the like. Examples of aqueous adhesives include polyvinyl alcohol adhesives, gelatin adhesives, vinyl latexes, aqueous polyurethanes, aqueous polyesters, and the like.

As the protective film, a hard coat layer, an antireflection treatment, an anti-sticking treatment, or a treatment subjected to diffusion or anti-glare treatment can be used.
Hard coat treatment is performed for the purpose of preventing scratches on the surface of the polarizing plate, for example, a protective film with a cured film excellent in hardness, sliding properties, etc. by an appropriate ultraviolet curable resin such as acrylic or silicone. It can be formed by a method of adding to the surface of the film. The antireflection treatment is performed 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 the conventional art. Further, the anti-sticking treatment is performed for the purpose of preventing adhesion with an adjacent layer.

  The anti-glare treatment is performed for the purpose of preventing the outside light from being reflected on the surface of the polarizing plate and obstructing the visibility of the light transmitted through the polarizing plate. For example, a rough surface by a sandblasting method or an embossing method. 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 conversion method or a blending method of transparent fine particles. Examples of the fine particles to be included in the formation of the surface fine concavo-convex structure include a conductive material made of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide, or the like having an average particle diameter of 0.5 to 50 μm. Transparent fine particles such as inorganic fine particles, organic fine particles composed of a crosslinked or uncrosslinked polymer, etc. may be used. When forming a surface fine uneven structure, the amount of fine particles used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, based on 100 parts by weight of the transparent resin forming the surface fine uneven structure. The antiglare layer may also serve as a diffusion layer (viewing angle expanding function or the like) for diffusing the light transmitted through the polarizing plate to expand the viewing angle.

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

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

  The elliptically polarizing plate is effectively used for black-and-white display without coloring by compensating (preventing) the coloring (blue or yellow) caused by the birefringence of the liquid crystal layer of the Spirsist nematic (STN) type liquid crystal display device. It is done. Further, the one in which the three-dimensional refractive index is controlled is preferable because it can compensate (prevent) coloring that occurs when the screen of the liquid crystal display device is viewed from an oblique direction. 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 the image is displayed in color, and also has an antireflection function.

As the retardation plate, for example, various wavelength plates or those for the purpose of compensating for coloring or viewing angle due to birefringence of the liquid crystal layer can be used, and 2 having an appropriate retardation according to the purpose of use. It is possible to control optical characteristics such as retardation by laminating more than one kind of retardation plate. As such a retardation plate, those exemplified above can be used, and the homeotropic alignment liquid crystal film of the present invention can be used alone or in combination with other films.
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 perpendicular to the screen.

  As such a viewing angle compensation retardation plate, a birefringent film such as a uniaxial or biaxial stretching treatment or a stretching treatment in two orthogonal directions, a bi-directional stretched film such as a tilted orientation film, or the like is used. . Examples of the inclined alignment film include a film obtained by bonding a heat shrink film to a polymer film and stretching or / and shrinking the polymer film under the action of the contraction force by heating, or a film obtained by obliquely aligning a liquid crystal polymer. Is 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 based on a phase difference caused by a liquid crystal cell or increasing the viewing angle for good viewing.

In addition, the liquid crystal polymer alignment layer, especially the optically anisotropic layer composed of the tilted alignment layer made of discotic liquid crystal polymer or rod-like liquid crystal polymer, is made of triacetyl cellulose film in order to achieve a wide viewing angle with good visibility. A supported optical compensation phase difference plate can be preferably used.
In addition to the above, the optical layer laminated in practical use is not particularly limited. For example, one or more optical layers that may be used for forming a liquid crystal display device such as a reflective plate or a transflective plate are used. be able to. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which an elliptical polarizing plate or a circular polarizing plate is further laminated with a reflective plate or a semi-transmissive reflective plate can be used.

  A reflective polarizing plate is a polarizing plate provided with a reflective layer, and is used to form a liquid crystal display device or the like that reflects incident light from the viewing side (display side). Such a light source can be omitted, and the liquid crystal display device can be easily thinned. 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, if necessary.

Specific examples of the reflective polarizing plate include those in which a reflective layer is formed by attaching a foil or a vapor-deposited film made of a reflective metal such as aluminum on one side of a protective film matted as necessary. Moreover, what has microparticles | fine-particles contained in the said protective film to make a surface fine concavo-convex structure, and has the reflection layer of a fine concavo-convex structure on it is mentioned. The reflective layer having the fine concavo-convex structure has an advantage that incident light is diffused by irregular reflection to prevent directivity and glaring appearance and to suppress unevenness in brightness and darkness. Moreover, the protective film containing fine particles also has an advantage that incident light and its reflected light are diffused when passing through it and light and dark unevenness can be further suppressed. The reflective layer of the fine concavo-convex structure reflecting the surface fine concavo-convex structure of the protective film is formed by transparent the metal by an appropriate method such as a vapor deposition method such as a vacuum deposition method, an ion plating method, a sputtering method, or a plating method. It can be performed by a method of directly attaching to the surface of the protective layer.
The reflective plate can be used as a reflective sheet in which a reflective layer is provided on an appropriate film according to the transparent film, instead of the method of directly imparting to the protective film of the polarizing plate. Since the reflective layer is usually made of metal, the usage form in which the reflective surface is covered with a protective film, a polarizing plate or the like is used to prevent a decrease in reflectance due to oxidation, and thus the long-term sustainability of the initial reflectance. More preferable is the point of avoiding the additional attachment of the protective layer.

  The semi-transmissive polarizing plate can be obtained by using a semi-transmissive reflective layer such as a half mirror that reflects and transmits light with the reflective layer. A transflective polarizing plate is usually provided on the back side of a liquid crystal cell. When a liquid crystal display device or the like is used in a relatively bright atmosphere, it reflects incident light from the viewing side (display side) to display an image. In a relatively dark atmosphere, a liquid crystal display device that displays an image using a built-in light source such as a backlight built in the back side of the transflective polarizing plate can be formed. In other words, the transflective polarizing plate is useful for forming a liquid crystal display device of a type that can save energy of using a light source such as a backlight in a bright atmosphere and can be used with a built-in light source even in a relatively dark atmosphere. It is.

Moreover, the polarizing plate may consist of what laminated | stacked the polarizing plate and the optical layer of 2 layers or 3 layers or more. Therefore, a reflective elliptical polarizing plate or a semi-transmissive elliptical polarizing plate in which the above-mentioned reflective polarizing plate or transflective polarizing plate and a retardation plate are combined may be used.
The elliptically polarizing plate and the reflective elliptical polarizing plate are obtained by laminating a polarizing plate or a reflective polarizing plate and a retardation plate in an appropriate combination. Such an elliptical polarizing plate can be formed by sequentially laminating them in the manufacturing process of the liquid crystal display device so as to be a combination of a (reflective) polarizing plate and a retardation plate. An optical film such as an elliptically polarizing plate has an advantage that it can improve the production efficiency of a liquid crystal display device and the like because of excellent quality stability and lamination workability.

Next, a brightness enhancement film in which a cholesteric liquid crystal film is laminated on the laminated retardation plate of the present invention will be described.
The brightness enhancement film of the present invention includes a polarizing element, a laminated retardation film obtained by laminating a stretched film having a retardation function in which Re2 is in the range of 100 to 170 nm, a homeotropic alignment liquid crystal layer, and a cholesteric liquid crystal film. This is a linearly polarizing plate having a significant brightness enhancement function.

As the cholesteric liquid crystal film, various films used for conventional brightness enhancement films can be used without particular limitation. A cholesteric liquid crystal film is a characteristic that reflects either left-handed or right-handed circularly polarized light and transmits other light, such as an oriented film of a cholesteric liquid-crystal polymer or a film substrate on which the oriented liquid-crystal layer is supported. And the like showing. As the cholesteric liquid crystal film, for example, a film exhibiting circular dichroism in at least a partial band of visible light or a film exhibiting circular dichroism in a band of 200 nm or more of visible light is used. The cholesteric liquid crystal film can be formed of a cholesteric liquid crystal polymer containing an optically active group-containing monomer as a monomer unit. Since the pitch of the cholesteric liquid crystal changes based on the content of the monomer unit containing the optically active group, the circular dichroism can be controlled by the content of the monomer unit. The thickness of the cholesteric liquid crystal film is usually preferably from 0.5 to 30 μm, particularly preferably from 2 to 15 μm. The cholesteric liquid crystal film can be blended with one or more additives such as polymers other than the liquid crystal polymer, inorganic compounds such as stabilizers and plasticizers, organic compounds, metals and compounds thereof, as necessary.
A cholesteric liquid crystal film can be obtained by reflecting circularly polarized light in a wide wavelength range such as a visible light region by combining two or more layers with different reflection wavelengths in combination. Based on this, transmitted circularly polarized light in a wide wavelength range can be obtained.

  A polarizing plate in which a polarizing element and a brightness enhancement film are laminated is usually provided on the back side of a liquid crystal cell. The brightness enhancement film reflects a linearly polarized light with a predetermined polarization axis or a circularly polarized light in a predetermined direction when natural light is incident due to a backlight such as a liquid crystal display device or reflection from the back side, and transmits other light. In addition, a polarizing plate in which a brightness enhancement film is laminated with a polarizing element allows light from a light source such as a backlight to enter to obtain transmitted light in a predetermined polarization state, and reflects light without transmitting the light other than the predetermined polarization state. The The light reflected on the surface of the brightness enhancement film is further inverted through a reflective layer or the like provided behind the brightness enhancement film and re-incident on the brightness enhancement film, and part or all of the light is transmitted as light having a predetermined polarization state. Luminance can be improved by increasing the amount of light transmitted through the enhancement film and increasing the amount of light that can be used for liquid crystal display image display or the like by supplying polarized light that is difficult to be absorbed by the polarizer.

  That is, when light is incident through the polarizer from the back side of the liquid crystal cell without using a brightness enhancement film, light having a polarization direction that does not coincide with the polarization axis of the polarizer is almost polarized. It is absorbed by the polarizer and does not pass through the polarizer. That is, although depending on the characteristics of the polarizer used, approximately 50% of the light is absorbed by the polarizer, and the amount of light that can be used for liquid crystal image display or the like is reduced accordingly, resulting in a dark image. 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 further inverted through a reflective layer provided on the rear side thereof. Repeatedly re-enter the brightness enhancement film, and the brightness enhancement film transmits only polarized light whose polarization direction is such that the polarization direction of light reflected and inverted between the two can pass through the polarizer. Therefore, light such as a backlight can be efficiently used for displaying an image on the liquid crystal display device, and the screen can be brightened.

An adhesive layer can also be provided in the laminated phase difference plate and the brightness enhancement film of the present invention. The pressure-sensitive adhesive layer can be used for adhering to a liquid crystal cell, and can also be used for laminating other optical films such as the above-described retardation plate and stretched film. When adhering the optical films, their optical axes can be set at an appropriate arrangement angle in accordance with the target retardation characteristics.
Although the adhesive which forms an adhesive layer is not restrict | limited in particular, The thing similar to what was used for bonding of the said homeotropic alignment liquid crystal layer and a translucent film can be illustrated. Moreover, it can provide by the same system.
The pressure-sensitive adhesive layer can also be provided on one side or both sides of a polarizing plate or an optical film as a superimposed layer of different compositions or types. Moreover, when providing in both surfaces, it can also be set as the adhesion layers of a different composition, a kind, thickness, etc. in the front and back of a polarizing plate or an optical film. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 to 500 μm, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  On the exposed surface of the adhesive layer, a separator is temporarily attached and covered for the purpose of preventing contamination until it is put to practical use. Thereby, it can prevent contacting an adhesion layer in the usual handling state. As the separator, except for the above thickness conditions, for example, an appropriate thin leaf body such as a plastic film, rubber sheet, paper, cloth, non-woven fabric, net, foamed sheet, metal foil, laminate thereof, and the like, if necessary In addition, an appropriate one according to the prior art, such as those coated with an appropriate release agent such as a long-chain alkyl, fluorine-based, or molybdenum sulfide, can be used.

  In the present invention, the polarizer, transparent protective film, optical film, and the like that form the polarizing plate described above, and each layer such as an adhesive layer include, for example, salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, cyano compounds, and the like. Those having an ultraviolet absorbing ability by a method such as a method of treating with an ultraviolet absorber such as an acrylate compound or a nickel complex salt compound may be used.

The laminated phase difference plate and the brightness enhancement film of the present invention can be preferably used for forming various devices such as a liquid crystal display device, and are particularly preferably used as a viewing angle improving film for a liquid crystal display device. The liquid crystal display device can be formed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, an optical film, and, if necessary, a lighting system and incorporating a drive circuit. There is no limitation in particular except the point which uses a board and a brightness enhancement film, and it can apply according to the former.
Although there is no restriction | limiting in particular as a liquid crystal display device, Various liquid crystal display devices of a transmissive type, a reflective type, and a semi-transmissive type can be mentioned. Examples of modes by liquid crystal alignment in a liquid crystal cell include TN type, STN type, VA (vertical alignment) type, MVA (multi-domain vertical alignment) type, OCB (optically compensated bend) type, ECB (electrically controlled biriefringence). Type, HAN (hybrid-aligned nematic) type, IPS (in-plane switching) type, bistable nematic (Bistable Nematic) type, ASM (Axially Symmetric Aligned Microcell) type, halftone grayscale type, ferroelectric liquid crystal, anti-strong A display method using dielectric liquid crystal can be used.

  The liquid crystal alignment may have a single direction in the plane of the cell, or may be used for a liquid crystal display device in which the alignment is divided. Further, in terms of a method of applying a voltage to the liquid crystal cell, for example, a liquid crystal display device driven by a passive method using an ITO electrode or the like, an active method using a TFT (thin film transistor) electrode, a TFD (thin film diode) electrode, or the like. be able to.

  An appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate or an optical film is disposed on one side or both sides of a liquid crystal cell, or a backlight or a reflector used in an illumination system can be formed. In that case, the optical film can be installed on one side or both sides of the liquid crystal cell. When providing a polarizing plate and an optical film on both sides, they may be the same or different. Further, when forming a liquid crystal display device, for example, a single layer of an appropriate part such as a diffusion plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusion plate, and a backlight at an appropriate position. Alternatively, 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 emitter (organic electroluminescent light emitter). 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 and 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 laminate of such a light emitting layer and an electron injection layer composed of a perylene derivative or the like, or a laminate of these hole injection layer, light emitting layer, and electron injection layer is known. It has been.

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

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

  In the organic EL display device having such a configuration, the organic light emitting layer is formed of a very 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, light that is incident from the surface of the transparent substrate at the time of non-light emission, passes through the transparent electrode and the organic light emitting layer, and is reflected by the metal electrode is again emitted to the surface side of the transparent substrate. The display surface of the organic EL display device looks like a mirror surface.

In an organic EL display device comprising an organic electroluminescent light emitting device comprising a transparent electrode on the surface side of an organic light emitting layer that emits light upon application of a voltage and a metal electrode on the back side of the organic light emitting layer, the surface of the transparent electrode While providing a polarizing plate on the side, 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 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 by the polarization action. In particular, the mirror surface of the metal electrode can be completely shielded by configuring the retardation plate with a quarter-wave plate and adjusting the angle formed by the polarization direction of the polarizing plate and the retardation plate to π / 4. .
That is, only the linearly polarized light component of the external light incident on the organic EL display device is transmitted by the polarizing plate. This linearly polarized light becomes generally elliptically polarized light by the phase difference plate, but becomes circularly polarized light particularly when the phase difference plate is a quarter wavelength plate and the angle formed by the polarization direction of the polarizing plate and the phase difference plate is π / 4. .
This circularly polarized light is transmitted through the transparent substrate, the transparent electrode, and the organic thin film, is reflected by the metal electrode, is again transmitted through the organic thin film, the transparent electrode, and the transparent substrate, and becomes linearly polarized light again on the retardation plate. And since this linearly polarized light is orthogonal to the polarization direction of a polarizing plate, it cannot permeate | transmit a polarizing plate. As a result, the mirror surface of the metal electrode can be completely shielded.

  Uses a liquid crystal material containing a side-chain liquid crystalline polymer obtained by polymerizing a (meth) acrylic compound having a novel oxetanyl group, and has excellent heat resistance by fixing the alignment state of the liquid crystal material. A phase difference plate obtained by laminating and integrating a homeotropic alignment film having high hardness and excellent mechanical strength and a stretched film having a retardation function is obtained. For various liquid crystal display devices, organic EL display devices, PDPs, etc. It is useful as an optical film for an image display apparatus.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In addition, each analysis method used in the Example is as follows.
⁽¹⁾ Measurement compound of 1 H-NMR was dissolved in deuterated chloroform and measured by ¹ H-NMR of 400 MHz (Variant Co. INOVA-400).
(2) Measurement of GPC The compound was dissolved in tetrahydrofuran, and TSK-GEL SuperH1000, SuperH2000, SuperH3000, and SuperH4000 were connected in series with a Tosoh 8020GPC system and measured using tetrahydrofuran as an eluent. Polystyrene standards were used for molecular weight calibration.
(3) Microscope observation The alignment state of the liquid crystal was observed with an Olympus BH2 polarizing microscope.
(4) Parameter measurement of liquid crystal film An automatic birefringence meter KOBRA21ADH manufactured by Oji Scientific Instruments was used.

[Example 1]
A liquid crystal material solution was prepared as follows.
First, a liquid crystalline polymer of the following formula (9) was synthesized. The molecular weight was Mn = 8000 and Mw = 15000 in terms of polystyrene. In addition, although Formula (9) is described with the structure of a block polymer for convenience, the number represents the molar composition ratio of a monomer.
After dissolving 1.0 g of the polymer of the formula (9) in 9 ml of cyclohexanone and adding 0.1 g of a triallylsulfonium hexafluoroantimonate 50% propylene carbonate solution (manufactured by Aldrich) in the dark, A solution of liquid crystal material was prepared by filtering insoluble matter with a 0.45 μm polytetrafluoroethylene filter.

An alignment substrate was prepared as follows.
A 38 μm thick polyethylene terephthalate film (manufactured by Toray Industries, Inc.) was cut into a 15 cm square, and a 5 mass% solution of alkyl-modified polyvinyl alcohol (manufactured by Kuraray Co., Ltd., MP-203 (PVA)) (the solvent was water and isopropyl. (A mixed solvent of alcohol in a weight ratio of 1: 1) was applied by spin coating, dried on a hot plate at 50 ° C. for 30 minutes, and then heated in an oven at 120 ° C. for 10 minutes. Subsequently, it was rubbed with a rayon rubbing cloth. The film thickness of the obtained PVA layer was 1.2 μm. The peripheral speed ratio during rubbing (moving speed of rubbing cloth / moving speed of substrate film) was 4.

The liquid crystal material solution was applied to the alignment substrate thus obtained by spin coating. Next, the film was dried on a hot plate at 60 ° C. for 10 minutes, and heat-treated in an oven at 150 ° C. for 2 minutes to align the liquid crystal material. Next, the sample is placed in close contact with an aluminum plate heated to 60 ° C., and then irradiated with ultraviolet light of 600 mJ / cm ² (however, measured at 365 nm) with a high-pressure mercury lamp lamp, a liquid crystal material (homeotropic) The thickness of the alignment liquid crystal layer was 0.8 μm.
Since the polyethylene terephthalate film used as a substrate has a large birefringence and is not preferable as an optical film, the liquid crystal layer on the obtained alignment substrate is transferred to a triacetyl cellulose (TAC) film via an ultraviolet curable adhesive. did. That is, an adhesive was applied to a thickness of 5 μm on the cured liquid crystal material layer on the polyethylene terephthalate film, laminated with a TAC film, and irradiated with ultraviolet rays from the TAC film side to cure the adhesive. Thereafter, the polyethylene terephthalate film was peeled off.

When the obtained laminated film (PVA layer / liquid crystal layer / adhesive layer / TAC film) is observed under a polarizing microscope having a crossed Nicols, there is no disclination and the monodomain has a uniform orientation. It was found that the homeotropic alignment has a uniaxial refractive index structure. When this film was tilted and light was incident from an oblique direction and observed in the same manner with crossed Nicols, light transmission was observed. Moreover, the optical phase difference of the film was measured by an automatic birefringence measuring apparatus KOBRA21ADH. The measurement light was incident on the sample surface vertically or obliquely, and the homeotropic alignment was confirmed from the chart of the optical phase difference and the incident angle of the measurement light. In homeotropic alignment, the phase difference (front phase difference) in the direction perpendicular to the sample surface is almost zero. Regarding this sample, when the phase difference was measured obliquely in the slow axis direction of the liquid crystal layer, it was determined that the homeotropic alignment was obtained because the phase difference value increased as the incident angle of the measurement light increased. did it. From the above, it was judged that the homeotropic orientation was good.
In addition, Nx1 of the homeotropic alignment liquid crystal film was 1.54, Ny1 was 1.54, and Nz1 was 1.73.
Further, only the liquid crystal material portion of the laminated film was scraped, and Tg was measured using a differential calorimetry (DSC). The Tg was 100 ° C. Moreover, the pencil hardness of the liquid crystal layer surface of the film was about 2H, and a sufficiently strong film was obtained.

The obtained liquid crystal layer on the alignment substrate is a stretched polycarbonate retardation film having a retardation of 140 nm in the in-plane direction via an ultraviolet curable adhesive (Sumitomo Chemical Co., Ltd., thickness 40 μm, Nx2: 1.5930, Ny2: 1.5887, Nz2: 1.5883). That is, after applying an adhesive on a cured liquid crystal layer on a polyethylene terephthalate film, laminating with a polycarbonate film, and curing the adhesive by irradiating 400 mJ / cm ² ultraviolet light from the polycarbonate film side. Then, the PVA layer and the polyethylene terephthalate film were peeled to obtain a laminated retardation plate of the present invention in which a homeotropic alignment liquid crystal layer and a polycarbonate stretched film were laminated.
The obtained laminated retardation plate (homeotropic alignment liquid crystal film / adhesive layer / polycarbonate film) had an in-plane retardation (Re3) of 140 nm and biaxiality.
With respect to a commercially available IPS type liquid crystal television arranged in the order of a backlight, a lower polarizing plate, an IPS type liquid crystal cell, and an upper polarizing plate using one laminated retardation plate thus obtained, FIG. As shown in FIG. 4, a laminated retardation plate was disposed between the upper polarizing plate and the liquid crystal cell. As a result, it was found that the viewing angle was widened compared to the case where the present film was not used, and a good image was obtained even when viewed from an oblique direction.

[Example 2]
An alignment substrate was prepared as follows.
Polycarbonate stretched film retardation plate having a thickness of 40 μm and a retardation of 140 nm in the in-plane direction (Sumitomo Chemical Co., Ltd., thickness 40 μm, Nx2: 1.5930, Ny2: 1.5887, Nz2: 1. 5883) was cut into 15 cm square, and a 5% by mass solution of alkyl-modified polyvinyl alcohol (manufactured by Kuraray Co., Ltd., MP-203 (PVA)) (the solvent was a mixed solvent of water and isopropyl alcohol in a weight ratio of 1: 1). It was applied by a spin coating method, dried on a hot plate at 50 ° C. for 30 minutes, and then heated in an oven at 120 ° C. for 10 minutes. Subsequently, it was rubbed with a rayon rubbing cloth. The film thickness of the obtained PVA layer was 1.2 μm. The peripheral speed ratio during rubbing (moving speed of rubbing cloth / moving speed of substrate film) was 4.

The liquid crystal material solution prepared in Example 1 was applied to the alignment substrate thus obtained by spin coating. Next, it was dried on a hot plate at 60 ° C. for 10 minutes and heat-treated in an oven at 150 ° C. for 2 minutes to align the liquid crystal material. Next, the sample is placed in close contact with an aluminum plate heated to 60 ° C., and then irradiated with ultraviolet light of 600 mJ / cm ² (however, measured at 365 nm) with a high-pressure mercury lamp, a liquid crystal material (homeotropic) By curing the alignment liquid crystal layer having a thickness of 0.8 μm, a laminated phase difference plate of the present invention in which a homeotropic alignment liquid crystal layer and a polycarbonate stretched film were laminated was obtained.

  In order to confirm whether or not the obtained liquid crystal layer forms a good homeotropic alignment, the liquid crystal layer on the obtained liquid crystal layer / PVA layer / polycarbonate stretched film is subjected to TAC via an ultraviolet curable adhesive. Transferred to film. That is, on the liquid crystal layer cured on the PVA layer, an adhesive is applied to have a thickness of 5 μm, laminated with a TAC film, and irradiated with ultraviolet rays from the TAC film side to cure the adhesive, The stretched PVA / polycarbonate film was peeled off.

When the obtained laminated film (liquid crystal layer / adhesive layer / TAC film) is observed under a polarizing microscope with crossed Nicols, there is no disclination and the monodomain is uniformly oriented, and positive uniaxial refraction from conoscopic observation It was found that the homeotropic orientation has a refractive index structure. When this film was tilted and light was incident from an oblique direction and observed in the same manner with crossed Nicols, light transmission was observed. Moreover, the optical phase difference of the film was measured by an automatic birefringence measuring apparatus KOBRA21ADH. The measurement light was incident on the sample surface vertically or obliquely, and the homeotropic alignment was confirmed from the chart of the optical phase difference and the incident angle of the measurement light. In homeotropic alignment, the phase difference (front phase difference) in the direction perpendicular to the sample surface is almost zero. Regarding this sample, when the phase difference was measured obliquely in the slow axis direction of the liquid crystal layer, it was determined that the homeotropic alignment was obtained because the phase difference value increased as the incident angle of the measurement light increased. did it. From the above, it was judged that a good homeotropic alignment liquid crystal layer was formed.
In addition, Nx1 of the homeotropic alignment liquid crystal film was 1.54, Ny1 was 1.54, and Nz1 was 1.73.
Further, only the liquid crystal material portion of the laminated film was scraped, and Tg was measured using DSC. The Tg was 100 ° C. Moreover, the pencil hardness of the liquid crystal layer surface of the film was about 2H, and a sufficiently strong film was obtained.

The obtained laminated retardation plate (homeotropic alignment liquid crystal layer / PVA layer / polycarbonate film) had an in-plane retardation (Re3) of 140 nm and biaxiality.
With respect to a commercially available IPS type liquid crystal television arranged in the order of a backlight, a lower polarizing plate, an IPS type liquid crystal cell, and an upper polarizing plate using one laminated retardation plate thus obtained, FIG. As shown in FIG. 4, a laminated retardation plate was disposed between the upper polarizing plate and the liquid crystal cell. As a result, as in the case of Example 1, it was found that the viewing angle was enlarged compared to the case where the present laminated retardation plate was not used, and a good image was obtained even when viewed from an oblique direction.

[Example 3]
Using a TAC film (thickness 80 μm) on which a cholesteric liquid crystal layer 5 μm exhibiting circular dichroism in a band of 400 to 700 nm is formed, the homeotropic alignment liquid crystal obtained in Example 1 is used on the liquid crystal layer. Luminance of the present invention is improved by laminating a retardation plate 50 μm in which a film and a polycarbonate stretched film retardation plate (front retardation 140 nm) are laminated via an adhesive layer (25 μm) formed of an acrylic adhesive. A film was prepared.
Using the commercially available liquid crystal display in which the brightness enhancement film thus obtained is arranged in the order of the backlight, the lower polarizing plate, the liquid crystal cell, and the upper polarizing plate, as shown in FIG. It arrange | positioned between polarizing plates. As a result, it was found that a bright image having a luminance improvement rate of 30% was obtained as compared with the case where no luminance enhancement film was used.

[Comparative Example 1]
A side chain type liquid crystal polymer represented by the following formula (10) (for convenience, it is indicated by a block body, and the number in the formula represents mol% of the monomer unit. Weight average molecular weight: 5000) 5 parts by weight, Cyclohexanone 75 containing 20 parts by weight of a photopolymerizable liquid crystal compound (BASF, Paliocolor LC242) and a photopolymerization initiator (Ciba Specialty Chemicals, Irgacure 907) (ratio to the photopolymerizable liquid crystal compound) showing a nematic liquid crystal layer. The insoluble matter was filtered from the solution dissolved in parts by weight using a polytetrafluoroethylene filter having a pore size of 0.45 μm to prepare a liquid crystal material solution.
The liquid crystal material solution described above was applied to the alignment substrate obtained in the same manner as in Example 1 by spin coating. Subsequently, the liquid crystal material layer was homeotropically aligned by heating at 80 ° C. for 2 minutes and then cooled to room temperature, and the homeotropic alignment liquid crystal layer was fixed by vitrification while maintaining the alignment. Furthermore, a homeotropic alignment liquid crystal film (thickness: 1.0 μm) was formed by irradiating the fixed homeotropic alignment liquid crystal layer with ultraviolet rays.
Only the liquid crystal material portion of the obtained homeotropically aligned liquid crystal film was scraped, and Tg was measured using DSC. The Tg was 80 ° C. Further, it was found that the film had a low hardness of about 2B on the surface of the liquid crystal material layer of the film.

1 is a conceptual diagram of a liquid crystal display used in Example 1. FIG. 6 is a conceptual diagram of a liquid crystal display used in Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper polarizing plate 2 Homeotropic alignment liquid crystal layer 3 Polycarbonate film 4 IPS type liquid crystal cell 5 Lower polarizing plate 6 Backlight 7 Upper polarizing plate 8 Liquid crystal cell 9 Lower polarizing plate 10 1/4 wavelength plate 11 Homeotropic alignment liquid crystal film 12 Cholesteric Liquid crystal film 13 Brightness enhancement film 14 Diffusion plate 15 Condensing sheet 16 Condensing sheet
17 Diffuser 18 Light guide 19 Reflector 20 Lamp 21 Backlight

Claims (8)

  A laminated phase difference plate, wherein a homeotropic alignment liquid crystal layer in which homeotropic alignment is fixed and a stretched film having a retardation function are laminated and integrated.   The homeotropic alignment liquid crystal layer is homeotropically aligned in a liquid crystal state with a liquid crystalline composition containing at least a side chain type liquid crystalline polymer compound having an oxetanyl group, and then reacted with the oxetanyl group. The laminated phase difference plate according to claim 1, wherein the homeotropic orientation is fixed.   A liquid crystalline composition containing at least a side chain type liquid crystalline polymer compound having an oxetanyl group is aligned homeotropically in a liquid crystal state on an alignment substrate having homeotropic alignment ability, and then the oxetanyl group is reacted. At least, the homeotropic alignment liquid crystal layer on the alignment substrate on which the homeotropic alignment is fixed is stuck to a stretched film having a retardation function using an adhesive or an adhesive means, and the homeotropic alignment liquid crystal layer is removed from the alignment substrate. A method for producing a laminated retardation plate, comprising peeling and integrating a homeotropic alignment liquid crystal layer and a stretched film having a retardation function.   After a homeotropic alignment in a liquid crystal state of a liquid crystalline composition containing at least a side chain type liquid crystalline polymer compound having an oxetanyl group on a stretched film substrate having homeotropic alignment ability and retardation function A laminated phase difference plate comprising: a laminate obtained by reacting the oxetanyl group and fixing the homeotropic orientation; and a stretched film having a retardation function is laminated and integrated using an adhesive or an adhesive means. Manufacturing method.   The laminated phase difference plate manufactured with the manufacturing method of Claim 3 or 4. The laminated phase difference plate according to claim 1, 2, or 5, wherein the laminated phase difference plate satisfies the following [1] to [4].
[1] 0 nm ≦ Re1 ≦ 50 nm
[2] −500 nm ≦ Rth1 ≦ −30 nm
[3] 30 nm ≦ Re2 ≦ 500 nm
[4] 30 nm ≦ Rth2 ≦ 300 nm
(Here, Re1 and Re2 mean the in-plane retardation value of the homeotropic alignment liquid crystal layer and the stretched film having a retardation function, respectively, and Rth1 and Rth2 respectively represent the homeotropic alignment liquid crystal layer and the retardation function. The Re1, Re2, Rth1, and Rth2 are Re1 = (Nx1-Ny1) × d1 [nm] and Rth1 = (Nx1-Nz1) × d1 [nm, respectively. ], Re2 = (Nx2-Ny2) * d2 [nm], Rth2 = (Nx2-Nz2) * d2 [nm], where d1 and d2 are respectively a homeotropic alignment liquid crystal layer and a stretch having a retardation function. The film thicknesses, Nx1 and Ny1, are the main refractive indices in the plane of the homeotropic alignment liquid crystal layer, and Nx2 and Ny2 are Respective in-plane main refractive indexes Nz1 and Nz2 of the stretched film having a retardation function are main refractive indexes in the thickness direction of the homeotropic alignment liquid crystal layer and the stretched film having a retardation function, respectively. > Nx1 ≧ Ny1, Nx2> Ny2.)   The in-plane retardation value (Re2) of the stretched film having a retardation function is in the range of 100 to 170 nm, and at least one cholesteric liquid crystal film is further laminated on the laminated retardation plate according to claim 1, 2 or 5. A brightness enhancement film characterized by being made.   An image display device to which the laminated phase difference plate according to claim 1, or the brightness enhancement film according to claim 7 is applied.

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