JP2009180830A - Luminance improving film and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device having a high display grade, a high contrast ratio, and satisfactory appearance for the display surface, and to provide a luminance improving film capable of providing such a device. <P>SOLUTION: The luminance improving film provided with a circularly polarized light separating element and an optically anisotropic element has a diffusion layer between the circularly polarized light separating element and the optically anisotropic element, and the diffusion layer contains inclined refractive index particles, and the liquid crystal display device that has the luminance improving film is provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a brightness enhancement film and a liquid crystal display device.

In a display device such as a liquid crystal display device, it is known to provide an optical element for improving luminance. For example, it has been proposed to provide a brightness enhancement film on the back side of the liquid crystal cell of the liquid crystal display device, that is, on the backlight side. The brightness enhancement film has a characteristic of transmitting linearly polarized light having a predetermined polarization axis or circularly polarized light having a predetermined spiral axis direction and reflecting other light when light is incident from a light source such as a backlight of a liquid crystal display device or the like. Is.
When light incident from a light source such as a backlight enters the brightness enhancement film, light in a predetermined polarization state among the light is transmitted. On the other hand, light other than the predetermined polarization state is reflected without being transmitted and returns to the backlight. The polarization state of the light returning to the backlight is changed by a reflector or the like provided there. When the light whose polarization state is inverted is incident again on the brightness enhancement film, the light in the predetermined polarization state among the light passes through the brightness enhancement film. By repeating this cycle, the amount of light transmitted through the brightness enhancement film and the amount of light that can be used for liquid crystal display devices by supplying polarized light that is not easily absorbed by the polarizing plate can be increased. Can be improved.

  The brightness enhancement film desirably has light diffusibility in order to improve its display quality. As such a brightness enhancement film, for example, Patent Document 1 discloses a brightness enhancement film in which a broadband 1 / 4λ plate made of a specular reflective semi-transmissive reflector and a retardation film is bonded via a light diffusing adhesive layer. Is disclosed. Furthermore, Patent Document 2 discloses a brightness enhancement film in which a light diffusing layer having adhesiveness is provided between a reflective polarizing film and an absorbing polarizing film.

  However, diffusion of light by the light diffusion layer usually results in a change in polarization. For example, when light that consists of only the predetermined circularly polarized light is passed through the light diffusion layer by a layer that selectively transmits only the predetermined circularly polarized light, a part of the circularly polarized light is polarized light such as elliptically polarized light. The light changes in state. When light containing such elliptically polarized light is further passed through a ¼λ plate and a liquid crystal cell, light leaks and passes under operating conditions (black display state, etc.) where light should not be transmitted, and the contrast ratio decreases. Bring. In addition, an unfavorable appearance such as glare may appear on the display surface due to poor control of the polarization state.

JP 2002-323610 A JP 2004-354678 A

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a liquid crystal display device having high display quality, a high contrast ratio, and a good display surface appearance, and such a device. It is to provide a brightness enhancement film that can be provided.

As a result of studies to solve the above problems, the present inventors have found that the above problems can be solved by mixing specific particles in the light diffusion layer, and have completed the present invention.
That is, the present invention provides the following [1] to [5].
[1] A brightness enhancement film comprising a circularly polarized light separating element and an optically anisotropic element, comprising a diffusion layer between the circularly polarized light element and the optically anisotropic element, wherein the diffusion layer is tilted refraction A brightness enhancement film characterized by containing high-rate particles.
[2] The brightness enhancement film obtained by adhering the optically anisotropic element and the circularly polarized light separating element through the diffusion layer.
[3] The brightness enhancement film, wherein the diffusion layer further contains an adhesive resin.
[4] The brightness enhancement film, wherein the circularly polarized light separating element includes a resin layer having a non-liquid crystalline cholesteric regularity formed by polymerizing a liquid crystal composition containing a polymerizable liquid crystal compound.
[5] A liquid crystal display device comprising the brightness enhancement film.

  Since the brightness enhancement film of the present invention includes a material containing gradient refractive index particles as a diffusion layer, the liquid crystal display device of the present invention having the brightness enhancement film of the present invention has a high display quality based on the diffusion of light by the diffusion layer. And a high contrast ratio can be achieved, and the appearance of the display surface is good.

The brightness enhancement film of the present invention includes a circularly polarized light separating element and an optically anisotropic element, and includes a diffusion layer between the circularly polarized light separating element and the optically anisotropic element, and the diffused layer has a gradient refractive index. Contains particles.
FIG. 1 is a partial cross-sectional view showing an example of such a brightness enhancement film. In FIG. 1, the brightness enhancement film 100 includes a circularly polarized light separating element 110, an optically anisotropic element 130, and a diffusion layer 120 between the circularly polarized light separating element 110 and the optically anisotropic element 130. The adhesive resin 121 and the gradient refractive index particles 125 dispersed therein are contained.
Hereinafter, each component of the brightness enhancement film will be sequentially described.

(Circularly polarized light separating element)
The circularly polarized light separating element used in the present invention is an element having a property of selectively transmitting only predetermined circularly polarized light and reflecting other light. Specifically, an element having a resin layer having cholesteric regularity (hereinafter sometimes simply referred to as “cholesteric resin layer”) can be used. The cholesteric resin layer is preferably a non-liquid crystalline layer. More specifically, a resin layer in which molecular orientation having cholesteric regularity is fixed is preferable. Preferable examples of the cholesteric resin layer include those obtained by curing a cholesteric liquid crystal composition containing a rod-like liquid crystal compound.

(Cholesteric liquid crystal composition)
Preferred examples of the cholesteric liquid crystal composition used in the present invention include those containing a rod-like liquid crystal compound having Δn of 0.18 or more and having at least two or more reactive groups in one molecule.

Examples of the rod-like liquid crystalline compound include a compound represented by (Formula 2).
R ³ -C ³ -D ³ -C ⁵ -M C ⁶ -D ⁴ -C ⁴ -R ⁴ (Formula 2)
(Wherein R ³ and R ⁴ are reactive groups, each independently (meth) acryl group, (thio) epoxy group, oxetane group, thietanyl group, aziridinyl group, pyrrole group, vinyl group, allyl group, D ³ and D ⁴ each represent a group selected from the group consisting of a fumarate group, a cinnamoyl group, an oxazoline group, a mercapto group, an iso (thio) cyanate group, an amino group, a hydroxyl group, a carboxyl group, and an alkoxysilyl group. A group selected from the group consisting of a bond, a linear or branched alkyl group having 1 to 20 carbon atoms, and a linear or branched alkylene oxide group having 1 to 20 carbon atoms; C ^{3 to} C ⁶ are a single bond, —O—, —S—, —S—S—, —CO—, —CS—, —OCO—, —CH ₂ —, —OCH ₂ —, —C═. N—N═C—, —NHCO _{, -OCOO -, - CH 2 COO-} , and .M represents a group selected from the group consisting of -CH ₂ OCO- represents a mesogenic group, specifically, have a unsubstituted or substituted group Azomethines, azoxys, phenyls, biphenyls, terphenyls, naphthalenes, anthracenes, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted Two to four skeletons selected from the group of phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles are converted to —O—, —S—, —S—S—, —CO—, —CS. -, - OCO -, - CH 2 -, - OCH 2 -, - C = N-N = C -, - NHCO -, - OCOO -, - C It is formed by bonding with bonding groups such as H ₂ COO— and —CH ₂ OCO—.

Examples of the substituent that the mesogenic group M may have include a halogen atom, an optionally substituted alkyl group having 1 to 10 carbon atoms, a cyano group, a nitro group, —O—R ⁵ , —O—C. (═O) —R ⁵ , —C (═O) —O—R ⁵ , —O—C (═O) —O—R ⁵ , —NR ⁵ —C (═O) —R ⁵ , —C ( ═O) —NR ⁵ or —O—C (═O) —NR ⁵ . Here, R ⁵ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and when it is an alkyl group, the alkyl group includes —O—, —S—, —O—C (═O) —. , —C (═O) —O—, —O—C (═O) —O—, —NR ⁶ —C (═O) —, —C (═O) —NR ⁶ —, —NR ⁶ —, Alternatively, -C (= O)-may be present (except when two or more of -O- and -S- are present adjacent to each other). Wherein, R ⁶ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Examples of the substituent in the “optionally substituted alkyl group having 1 to 10 carbon atoms” include a halogen atom, a hydroxyl group, a carboxyl group, a cyano group, an amino group, and an alkoxy group having 1 to 6 carbon atoms. Group, alkoxyalkoxy group having 2 to 8 carbon atoms, alkoxyalkoxyalkoxy group having 3 to 15 carbon atoms, alkoxycarbonyl group having 2 to 7 carbon atoms, alkylcarbonyloxy having 2 to 7 carbon atoms Group, an alkoxycarbonyloxy group having 2 to 7 carbon atoms, and the like.

In the present invention, the rod-like liquid crystalline compound preferably has an asymmetric structure. Here, the asymmetric structure is a structure in which R ³ -C ³ -D ³ -C ⁵ -and -C ⁶ -D ⁴ -C ⁴ -R ⁴ are different in the general formula (2) with the mesogenic group M as the center. Say. By using a rod-like liquid crystal compound having an asymmetric structure, alignment uniformity can be further improved.

  In the present invention, the rod-like liquid crystalline compound has a Δn value of preferably 0.18 or more, more preferably 0.22 or more. When a compound having an Δn value of 0.30 or more is used, the absorption edge on the long wavelength side of the ultraviolet absorption spectrum may extend to the visible range, but desired optical performance even when the absorption edge of the spectrum extends to the visible range. It can be used as long as it does not adversely affect By having such a high Δn value, a circularly polarized light separating sheet having high optical performance (for example, circularly polarized light separating characteristics) can be provided.

  In the present invention, the rod-like liquid crystal compound preferably has at least two reactive groups in one molecule. Specific examples of the reactive group include an epoxy group, a thioepoxy group, an oxetane group, a thietanyl group, an aziridinyl group, a pyrrole group, a fumarate group, a cinnamoyl group, an isocyanate group, an isothiocyanate group, an amino group, a hydroxyl group, and a carboxyl group. , Alkoxysilyl groups, oxazoline groups, mercapto groups, vinyl groups, allyl groups, methacryl groups, and acrylic groups. By having these reactive groups, a stable cured product can be obtained when the cholesteric liquid crystal composition used in the present invention is cured. When a compound having one or less reactive group in one molecule is used, when the cholesteric liquid crystal composition is cured, a crosslinked cured product cannot be obtained, so that a film strength that can withstand practical use cannot be obtained. Even when a cross-linking agent described later is used, the film strength is insufficient and practical use is difficult. The film strength that can be practically used is HB or more, preferably H or more, in pencil hardness (JIS K5400). If the film strength is lower than HB, the film is easily scratched and lacks handling properties. The upper limit of preferable pencil hardness is not particularly limited as long as it does not adversely affect the optical performance and durability test.

The cholesteric liquid crystal composition used in the present invention preferably contains a compound represented by the following general formula (1) in addition to the rod-like liquid crystal compound.
R ¹ -A ¹ -BA ² -R ² (1)
Wherein R ¹ and R ² are each independently a linear or branched alkyl group having 1 to 20 carbon atoms, which may be unsubstituted or substituted with one or more halogen atoms. A linear or branched chain group having 1 to 20 carbon atoms, an unsubstituted or optionally substituted alkylene oxide group having one or more halogen atoms; a hydrogen atom; an alkyl group having 1 to 2 carbon atoms; Or a halogen atom, a hydroxyl group, a carboxyl group, a (meth) acryl group, an epoxy group, a mercapto group, an isocyanate group, an amino group, and a cyano group, which may be bonded to an alkylene oxide group. Group,
A ¹ and A ² are each independently unsubstituted or substituted with one or more halogen atoms, hydroxyl groups, carboxyl groups, cyano groups, amino groups, alkyl groups having 1 to 10 carbon atoms, or halogenated alkyl groups. 1,4-phenylene group, 1,4-cyclohexylene group, 1,4-cyclohexenyl group, 4,4′-biphenylene group, 4,4′-bicyclohexylene group, and 2, Represents a group selected from the group consisting of: 6-naphthylene group;
B represents a single bond, —O—, —S—, —S—S—, —CO—, —CS—, —OCO—, —CH ₂ —, —OCH ₂ —, —C═N—N═C—. , -NHCO -, - OCOO -, - CH 2 COO-, and is selected from the group consisting of -CH ₂ OCO-. )

In General Formula (1), R ¹ and R ² are each independently a linear or branched alkyl group having 1 to 20 carbon atoms, or a linear or branched chain having 1 to 20 carbon atoms. And a group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxyl group, a carboxyl group, a (meth) acryl group, an epoxy group, a mercapto group, an isocyanate group, an amino group, and a cyano group. Here, (meth) acryl means acryl and methacryl.

  The alkyl group and alkylene oxide group may be unsubstituted or substituted with one or more halogen atoms. The halogen atom, hydroxyl group, carboxyl group, (meth) acryl group, epoxy group, mercapto group, isocyanate group, amino group, and cyano group are bonded to an alkyl group having 1 to 2 carbon atoms or an alkylene oxide group. May be.

Preferable examples of R ¹ and R ² include a halogen atom, hydroxyl group, carboxyl group, (meth) acryl group, epoxy group, mercapto group, isocyanate group, amino group, and cyano group.

Moreover, it is preferable that at least one of R ¹ and R ² is a reactive group. By having a reactive group as R ¹ and / or R ² , the compound represented by the general formula (1) is fixed in the liquid crystal layer at the time of curing, and a stronger film can be formed. Here, examples of the reactive group include a carboxyl group, a (meth) acryl group, an epoxy group, a mercapto group, an isocyanate group, and an amino group.

In the general formula (1), A ¹ and A ² are each independently 1,4-phenylene group, 1,4-cyclohexylene group, 1,4-cyclohexenyl group, 4,4′-biphenylene group, 4, It represents a group selected from the group consisting of a 4′-bicyclohexylene group and a 2,6-naphthylene group. The 1,4-phenylene group, 1,4-cyclohexylene group, 1,4-cyclohexenyl group, 4,4′-biphenylene group, 4,4′-bicyclohexylene group, and 2,6-naphthylene group are , It may be unsubstituted or substituted with one or more halogen atoms, hydroxyl groups, carboxyl groups, cyano groups, amino groups, alkyl groups having 1 to 10 carbon atoms, or halogenated alkyl groups. In each of A ¹ and A ² , when two or more substituents are present, they may be the same or different.

Particularly preferred examples of A ¹ and A ² include groups selected from the group consisting of 1,4-phenylene group, 4,4′-biphenylene group, and 2,6-naphthylene group. These aromatic ring skeletons are relatively rigid as compared with the alicyclic skeletons, have high affinity with the mesogens of the rod-like liquid crystalline compounds contained in the liquid crystal composition of the present invention, and higher alignment uniformity ability.

In the general formula (1), B represents a single bond, —O—, —S—, —S—S—, —CO—, —CS—, —OCO—, —CH ₂ —, —OCH ₂ —, —C. = N-N = C -, - NHCO -, - OCOO -, - CH 2 COO-, and is selected from the group consisting of -CH ₂ OCO-.

  Particularly preferable examples of B include a single bond, —OCO—, and —C═N—N═C—.

  As for the compound of General formula (1), it is preferable that at least 1 type has liquid crystallinity, and it is preferable to have chirality. The cholesteric liquid crystal composition used in the present invention preferably contains a mixture of a plurality of optical isomers as the compound of the general formula (1). For example, a mixture of plural kinds of enantiomers and / or diastereomers can be contained. At least one of the compounds of the general formula (1) preferably has a melting point in the range of 50 ° C to 150 ° C.

  When the compound of the general formula (1) has liquid crystallinity, a high Δn is preferable. By containing a high Δn liquid crystal, Δn as a cholesteric liquid crystal composition can be improved, and a broadband circularly polarized light separating sheet can be produced. At least one Δn of the compound of the general formula (1) is preferably 0.18 or more, more preferably 0.22 or more.

  Specific examples of particularly preferred compounds of the general formula (1) include the following compounds (A1) to (A3) and (A5) to (A10):

  In the compound (A3), “*” represents a chiral center.

  In the cholesteric liquid crystal composition used in the present invention, the weight ratio of (total weight of compound of general formula (1)) / (total weight of rod-like liquid crystal compound) is 0.05 to 1, preferably 0.1 to 0. .65, more preferably 0.15 to 0.45. When the weight ratio is less than 0.05, the alignment uniformity may be insufficient. On the other hand, when the weight ratio is more than 1, the alignment uniformity decreases, the stability of the liquid crystal phase decreases, and the liquid crystal composition As a result, the desired optical performance (for example, circularly polarized light separation characteristics) may not be obtained. The total weight indicates the weight when one kind is used and the total weight when one or more kinds are used.

  In the cholesteric liquid crystal composition used in the present invention, the compound of the general formula (1) preferably has a molecular weight of less than 600, and the rod-like liquid crystal compound has a molecular weight of 600 or more. When the molecular weight of the compound of the general formula (1) is less than 600, the rod-like liquid crystal compound having a molecular weight larger than that can enter the gap, and the alignment uniformity can be improved.

The cholesteric liquid crystal composition used in the present invention can optionally contain a cross-linking agent in order to improve the film strength and durability after curing. As the cross-linking agent, it reacts simultaneously when the liquid crystal layer coated with the liquid crystal composition is cured, or heat treatment is performed after curing to accelerate the reaction, or the reaction proceeds spontaneously by moisture to increase the crosslinking density of the liquid crystal layer. Those that can be enhanced and that do not deteriorate the alignment uniformity can be appropriately selected and used, and those that are cured by ultraviolet rays, heat, moisture, etc. can be suitably used. Specific examples of the crosslinking agent include, for example, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 2- (2-vinyl Polyfunctional acrylate compounds such as loxyethoxy) ethyl acrylate; epoxy compounds such as glycidyl (meth) acrylate, ethylene glycol diglycidyl ether, glycerin triglycidyl ether, pentaerythritol tetraglycidyl ether; 2,2-bishydroxymethylbutanol-tris [ 3- (1-aziridinyl) propionate], 4,4-bis (ethyleneiminocarbonylamino) diphenylmethane, trimethylolpropane-tri-β-aziridinini Aziridine compounds such as lupropionate; Isocyanurate type isocyanates derived from hexamethylene diisocyanate, hexamethylene diisocyanate, isocyanurate type isocyanates, biuret type isocyanates, adduct type isocyanates; polyoxazoline compounds having an oxazoline group in the side chain; vinyltrimethoxysilane; N- (2-aminoethyl) 3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3- (meth) acryloxypropyltrimethoxysilane, N- (1 , 3-dimethylbutylidene) -3- (triethoxysilyl) -1-propanamine and the like alkoxysilane compounds. Moreover, a well-known catalyst can be used according to the reactivity of this crosslinking agent, and productivity can be improved in addition to an improvement in film strength and durability.
The blending ratio of the crosslinking agent is preferably 0.1 to 15% by weight in a cured film obtained by curing the cholesteric liquid crystal composition. When the blending ratio of the crosslinking agent is less than 0.1% by weight, the effect of improving the crosslinking density cannot be obtained. Conversely, when the blending ratio is more than 15% by weight, the stability of the liquid crystal layer is lowered, which is not preferable.

The cholesteric liquid crystal composition used in the present invention can optionally contain a photoinitiator. As the photoinitiator, known compounds that generate radicals or acids by ultraviolet rays or visible rays can be used. Specifically, benzoin, benzylmethyl ketal, benzophenone, biacetyl, acetophenone, Michler's ketone, benzyl, benzylisobutyl ether, tetramethylthiuram mono (di) sulfide, 2,2-azobisisobutyronitrile, 2,2-azobis -2,4-dimethylvaleronitrile, benzoyl peroxide, di-tert-butyl peroxide, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1- (4 -Isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-diethylthioxanthone, methylbenzoyl formate, 2,2-dieto Cyacetophenone, β-ionone, β-bromostyrene, diazoaminobenzene, α-amylcinnac aldehyde, p-dimethylaminoacetophenone, p-dimethylaminopropiophenone, 2-chlorobenzophenone, pp′-dichlorobenzophenone, pp ′ -Bisdiethylaminobenzophenone, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-propyl ether, benzoin n-butyl ether, diphenyl sulfide, bis (2,6-methoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide, 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 2-methyl-1 [ 4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one, anthracenebenzophenone, α-chloroanthraquinone , Diphenyl disulfide, hexachlorobutadiene, pentachlorobutadiene, octachlorobutene, 1-chloromethylnaphthalene, 1,2-octanedione, 1- [4- (phenylthio) -2- (o-benzoyloxime)] and 1- [9-Ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl] ethanone 1- (o-acetyloxime), (4-methylphenyl) [4- (2-methylpropyl) phenyl] iodonium Hexafluorophosphate, 3-methyl-2-butynyltetramethylsulfonate Arm hexafluoroantimonate, diphenyl - (p-phenylthiophenyl) sulfonium hexafluoroantimonate, and the like. In addition, two or more compounds can be mixed depending on the desired physical properties, and if necessary, a known photosensitizer or a tertiary amine compound as a polymerization accelerator is added to control curability. You can also.
The blending ratio of the photoinitiator is preferably 0.03 to 7% by weight in the cholesteric liquid crystal composition. When the blending amount of the photoinitiator is less than 0.03% by weight, the degree of polymerization is lowered and the film strength may be lowered. On the other hand, if it is more than 7% by weight, the alignment of the liquid crystal is inhibited and the liquid crystal phase may become unstable.

  The cholesteric liquid crystal composition used in the present invention can optionally contain a surfactant. As the surfactant, those not inhibiting the orientation can be appropriately selected and used. As the surfactant, specifically, a nonionic surfactant containing siloxane or fluorinated alkyl group in the hydrophobic group portion can be preferably used, and an oligomer having two or more hydrophobic group portions in one molecule. Is particularly preferred. These surfactants are OMNOVA PolyFox PF-151N, PF-636, PF-6320, PF-656, PF-6520, PF-3320, PF-651, PF-652, Neos's Fantgent FTX- 209F, FTX-208G, FTX-204D, Seimi Chemical's Surflon KH-40, and the like can be used. The blending ratio of the surfactant is preferably 0.05% by weight to 3% by weight in the cured film obtained by curing the cholesteric liquid crystal composition. When the blending ratio of the surfactant is less than 0.05% by weight, the orientation regulating force at the air interface is lowered and an orientation defect may occur, which is not preferable. On the other hand, when the amount is more than 3% by weight, it is not preferable because an excessive surfactant may enter between liquid crystal molecules and lower the alignment uniformity.

  The cholesteric liquid crystal composition used in the present invention can further contain other optional components as necessary. Examples of the other optional components include a chiral agent, a solvent, a polymerization inhibitor for improving pot life, an antioxidant for improving durability, an ultraviolet absorber, and a light stabilizer. These optional components can be added as long as the desired optical performance is not deteriorated.

  The method for preparing the cholesteric liquid crystal composition used in the present invention is not particularly limited, and the cholesteric liquid crystal composition can be produced by mixing the above essential components and optional components.

(Preparation of circularly polarized light separating element)
The method for preparing the circularly polarized light separating element used in the present invention is not particularly limited, but the cholesteric liquid crystal composition is applied to a transparent resin substrate to obtain a liquid crystal layer, and then at least one time of light irradiation and / or heating. It can be prepared by curing by treatment.

  The transparent resin substrate is not particularly limited, and a substrate having a thickness of 1 mm and a total light transmittance of 80% or more can be used. Specifically, alicyclic olefin polymers, chain olefin polymers such as polyethylene and polypropylene, triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyethersulfone, modified acrylic polymer, epoxy resin, Examples thereof include a single layer or laminated film made of a synthetic resin such as polystyrene or acrylic resin. Among these, an alicyclic olefin polymer or a chain olefin polymer is preferable, and an alicyclic olefin polymer is particularly preferable from the viewpoint of transparency, low hygroscopicity, dimensional stability, lightness, and the like.

  The transparent resin base material may have an alignment film as necessary. By having the alignment film, the cholesteric liquid crystal composition applied thereon can be aligned in a desired direction. The alignment film is subjected to a corona discharge treatment, if necessary, on the substrate surface, followed by cellulose, silane coupling agent, polyimide, polyamide, polyvinyl alcohol, epoxy acrylate, silanol oligomer, polyacrylonitrile, phenol resin, poly A solution in which oxazole, cyclized polyisoprene or the like is dissolved in water or a solvent is applied using a known method such as reverse gravure coating, direct gravure coating, die coating, bar coating, and the like, and then dried. It can be formed by subjecting to rubbing treatment. The thickness of the alignment film may be any film thickness that provides the desired alignment uniformity of the liquid crystal layer, and is preferably 0.001 to 5 μm, and more preferably 0.01 to 2 μm.

  Application | coating of the liquid-crystal composition to the said transparent resin base material can be performed by well-known methods, such as reverse gravure coating, direct gravure coating, die coating, and bar coating. The thickness of the coating layer of the liquid crystal composition can be appropriately adjusted so that a desired liquid crystal layer dry film thickness described later can be obtained.

  Before curing the coating layer obtained by the coating, an orientation treatment can be performed as necessary. The alignment treatment can be performed, for example, by heating the coating layer at 50 to 150 ° C. for 0.5 to 10 minutes. By performing the alignment treatment, the cholesteric liquid crystal layer can be aligned well.

After performing an alignment treatment as necessary, the cholesteric liquid crystal composition is cured to obtain a circularly polarized light separating element having a cured layer of the cholesteric liquid crystal composition (hereinafter sometimes simply referred to as “cured liquid crystal layer”). be able to. The curing step can be performed by a combination of one or more light irradiations and a heating treatment. Specifically, the heating condition is, for example, a temperature of 40 to 200 ° C., preferably 50 to 200 ° C., more preferably 50 to 140 ° C., and a time of 1 second to 3 minutes, preferably 5 to 120 seconds. it can. The light used for light irradiation in the present invention includes not only visible light but also ultraviolet rays and other electromagnetic waves. Specifically, the light irradiation can be performed by, for example, irradiating light having a wavelength of 200 to 500 nm for 0.01 second to 3 minutes. Further, for example, a weakly irradiated ultraviolet ray of 0.01 to 50 mJ / cm ² and heating may be alternately repeated a plurality of times to obtain a circularly polarized light separating element having a wide reflection band. After extending the reflection band by the above-mentioned weak ultraviolet irradiation, etc., a relatively strong ultraviolet ray of 50 to 10,000 mJ / cm ² is irradiated to completely polymerize the liquid crystalline compound to form a cured liquid crystal layer. it can. The expansion of the reflection band and the irradiation with strong ultraviolet rays may be performed in the air, or a part or all of the process may be performed in an atmosphere in which the oxygen concentration is controlled (for example, in a nitrogen atmosphere). .

  In the present invention, the step of applying and curing the cholesteric liquid crystal composition on the transparent resin substrate is not limited to one time, and two or more cured liquid crystal layers can be formed by repeating the application and curing a plurality of times. However, in the present invention, a cured liquid crystal layer having a thickness of 5 μm or more that contains a well-oriented rod-like liquid crystalline compound having a Δn of 0.18 or more can be easily formed even by applying and curing the cholesteric liquid crystal composition only once. can do.

  In the circularly polarized light separating element used in the present invention, the dry thickness of the cured liquid crystal layer is preferably 3.0 μm to 10.0 μm, more preferably 3.5 to 8 μm. If the dried film thickness of the cured liquid crystal layer is less than 3.0 μm, the reflectivity decreases, and conversely if it is thicker than 10.0 μm, the cured liquid crystal layer is colored when observed from an oblique direction, Each is not preferred. The dry film thickness refers to the total film thickness of each layer when the cured liquid crystal layer is two or more layers, and the film thickness when the cured liquid crystal layer is one layer.

(Optically anisotropic element)
The brightness enhancement film of the present invention includes an optically anisotropic element in addition to the circularly polarized light separating element.
The optically anisotropic element used in the present invention is an element whose retardation Re in the front direction (hereinafter sometimes abbreviated as “Re”) is approximately ¼ wavelength of transmitted light. Here, the wavelength range of the transmitted light can be a desired range required for the brightness enhancement film of the present invention, and specifically, for example, 400 nm to 700 nm. Further, the retardation Re in the front direction is approximately ¼ wavelength of transmitted light, and the Re value is ± 65 nm from the ¼ value of the center value in the center value of the wavelength range of transmitted light, preferably It means ± 30 nm, more preferably ± 10 nm.

The optically anisotropic element desirably has a thickness direction retardation Rth (hereinafter sometimes abbreviated as “Rth”) of less than 0 nm. The value of retardation Rth in the thickness direction is preferably −30 nm to −1000 nm, more preferably −50 nm to −300 nm, in the central value of the wavelength range of transmitted light. By adopting such an optically anisotropic element having an Re value and Rth, it is possible to reduce color unevenness of emitted light while improving brightness and reducing brightness unevenness.
Here, the retardation Re in the front direction is represented by the formula I: Re = (nx−ny) × d (where nx is a direction perpendicular to the thickness direction (front direction) and gives the maximum refractive index). Ny represents a refractive index in a direction perpendicular to the thickness direction (in-plane direction) and perpendicular to nx, and d represents a film thickness). The direction retardation Rth is expressed by the formula II: Rth = {(nx + ny) / 2−nz} × d (where nx is a direction perpendicular to the thickness direction (in-plane direction) and gives the maximum refractive index) Ny is the refractive index in the direction perpendicular to the thickness direction (in-plane direction) and orthogonal to nx, nz is the refractive index in the thickness direction, and d is the film thickness. ).
In addition, the retardation Re in the front direction and the retardation Rth in the thickness direction are measured using a commercially available phase difference measuring apparatus, and the optically anisotropic elements are spaced 100 mm apart in the longitudinal direction and the width direction (longitudinal or lateral length). If the distance is less than 200 mm, three points are specified at equal intervals in that direction), and measurement is performed in a lattice point shape over the entire surface, and the average value is obtained.

  As the optically anisotropic element used in the present invention, (i) a film-like polymer stretched, or (ii) a liquid crystalline material applied on a transparent resin substrate, oriented, and cured. Can be used. When the optically anisotropic element (ii) is used, a liquid crystalline material is applied on an appropriate base material, oriented, and cured to obtain the optically anisotropic element. On the other hand, preferred examples of the optically anisotropic element obtained by stretching the film-like polymer (i) include the following optically anisotropic elements.

  Although the material which comprises the said optically anisotropic element is not specifically limited, What has the layer which consists of a styrene resin can be used preferably. Here, the styrene-based resin is a polymer resin having a styrene structure as a part or all of the repeating unit, and polystyrene, styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene. , Styrene monomers such as p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, ethylene, propylene, butadiene, isoprene, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, acrylic acid Examples thereof include copolymers with other monomers such as methyl, methyl methacrylate, ethyl acrylate, ethyl methacrylate, acrylic acid, methacrylic acid, maleic anhydride, and vinyl acetate. Among these, polystyrene or a copolymer of styrene and maleic anhydride can be suitably used.

  The molecular weight of the styrenic resin used for the optically anisotropic element is appropriately selected according to the purpose of use, but is the weight average molecular weight (Mw) of polyisoprene measured by gel permeation chromatography using cyclohexane as a solvent. Usually, 10,000 to 300,000, preferably 15,000 to 250,000, and more preferably 20,000 to 200,000.

  The optically anisotropic element preferably has a laminated structure of a layer made of the styrenic resin and a layer containing another thermoplastic resin. By having the laminated structure, it is possible to provide an element that has both the optical characteristics of the styrene resin and the mechanical strength of other thermoplastic resins. Other thermoplastic resins include alicyclic olefin polymers, methacrylic resins, polycarbonates, acrylic ester-vinyl aromatic compound copolymer resins, methacrylic ester-vinyl aromatic compound copolymer resins, polyethersulfone, etc. Can be mentioned. Among these, a resin having an alicyclic structure or a methacrylic resin can be preferably used.

  The alicyclic olefin polymer is an amorphous olefin polymer having a cycloalkane structure or a cycloalkene structure in the main chain and / or side chain. Specifically, (1) norbornene polymer, (2) monocyclic olefin polymer, (3) cyclic conjugated diene polymer, (4) vinyl alicyclic hydrocarbon polymer, and these A hydride etc. are mentioned. Among these, norbornene-based polymers are more preferable from the viewpoints of transparency and moldability. Examples of the resin having these alicyclic structures include those described in JP-A No. 05-310845, JP-A No. 05-097978, and US Pat. No. 6,511,756.

  Specific examples of the norbornene-based polymer include ring-opening polymers of norbornene-based monomers, ring-opening copolymers of norbornene-based monomers and other monomers capable of ring-opening copolymerization, hydrides thereof, and norbornene-based monomers. And addition copolymers with other monomers copolymerizable with norbornene monomers.

  The methacrylic resin is a polymer having a methacrylic acid ester as a main component, and includes a methacrylic acid ester homopolymer and a copolymer of a methacrylic acid ester and other monomers. Usually, alkyl methacrylate is used. In the case of a copolymer, acrylic acid esters, aromatic vinyl compounds, vinylcyan compounds, etc. are used as other monomers copolymerized with methacrylic acid esters.

  As a preferred specific embodiment of the optically anisotropic element used in the present invention, a multilayer film formed by laminating a film (b layer) made of another thermoplastic resin on both surfaces of a film (a layer) made of polystyrene resin. A stretched multilayer film formed by stretching can be mentioned. Hereinafter, this specific embodiment will be described.

  As the polystyrene resin constituting the a layer, the same “styrene resin” as described above can be used.

  The polystyrene resin constituting the a layer preferably has a glass transition temperature of 120 ° C. or higher, more preferably 120 to 200 ° C., and still more preferably 120 to 140 ° C.

  In the present invention, the polystyrene resin and the other thermoplastic resin have Tg (a)> Tg (b) when their glass transition temperatures are Tg (a) (° C.) and Tg (b) (° C.), respectively. ) It is preferable to satisfy the relationship of + 20 ° C. By satisfying such a relationship, optical anisotropy can be effectively given to the a layer made of polystyrene resin when stretched, and a good optical anisotropic element can be obtained.

  The method of laminating the polystyrene resin that is the material of the a layer and the other thermoplastic resin that is the material of the b layer to form a multilayer film is not particularly limited, but is a coextrusion T-die method, coextrusion inflation Known methods such as a method of forming by coextrusion such as a method, a coextrusion lamination method, a film lamination forming method such as dry lamination, and a coating forming method may be appropriately used. Among these, a molding method by coextrusion is preferable from the viewpoints of production efficiency and that volatile components such as a solvent do not remain in the film. The extrusion temperature can be appropriately selected according to the type of the polystyrene resin used and the other thermoplastic resin.

  The multilayer film is formed by laminating the b layer on both surfaces of the a layer. An adhesive layer or a pressure-sensitive adhesive layer can be provided between the a layer and the b layer, but the a layer and the b layer are directly laminated (that is, lamination of a three-layer configuration of b layer / a layer / b layer). Body). In the multilayer film, the thickness of the a layer and the b layer laminated on both sides thereof is not particularly limited, but preferably 10 to 300 μm and 10 to 400 μm, respectively.

The stretched multilayer film is formed by stretching the multilayer film. The stretched multilayer film may include an A layer provided by stretching the a layer and a B layer provided by stretching the b layer. The stretched multilayer film is a stretched film having a three-layer structure of B layer / A layer / B layer formed by stretching a laminate of b layer / a layer / b layer of the multilayer film. It is preferable.
The stretching can be preferably performed by uniaxial stretching or oblique stretching, and more preferably by uniaxial stretching or oblique stretching by a tenter.

  The front direction retardation Re and the thickness direction retardation Rth of the optically anisotropic element can be produced by appropriately adjusting stretching conditions such as a stretching temperature and a stretching ratio. The stretching temperature is preferably Tg (a) -10 ° C to Tg (a) + 20 ° C, and more preferably in the range of Tg (a) -5 ° C to Tg (a) + 15 ° C. The draw ratio is preferably 1.05 to 30 times, and more preferably 1.1 to 10 times. If the stretching temperature and the stretching ratio are out of the above ranges, the orientation may be insufficient and the refractive index anisotropy and thus the retardation may be insufficiently developed, or the laminate may be broken.

  The thickness of the optically anisotropic element is preferably 50 to 1000 μm, more preferably 50 to 600 μm.

(Diffusion layer)
The brightness enhancement film of the present invention includes a diffusion layer provided between the optically anisotropic element and the circularly polarized light separating element. Although other layers may be interposed between the optically anisotropic element and the diffusion layer and between the diffusion layer and the circularly polarized light separating element, preferably, the optically anisotropic element and the circularly polarized light separation are present. The element is adhered through the material of the diffusion layer, and the optically anisotropic element and the circularly polarized light separating element are provided in direct contact with the diffusion layer as shown in the example shown in FIG.
As a material for the diffusion layer, a material exhibiting adhesiveness at normal temperature (20 ± 15 ° C .: JIS standard) is preferable. Here, “adhesive” means that the adhesive has a ball number of 2 or more as measured by a tilting ball tack measurement according to JIS Z0237.

  In the present invention, the diffusion layer contains gradient refractive index particles, and preferably contains gradient refractive index particles and an adhesive resin. As the adhesive resin, a specific adhesive composition described below can be preferably used.

(Adhesive composition)
The pressure-sensitive adhesive composition in the present invention contains at least a main polymer constituting the pressure-sensitive adhesive.
Examples of the main polymer include acrylic polymers and acrylic copolymers, silicone polymers, polyesters, polyurethanes, polyamides, polyvinyl ethers, polyvinyl alcohols, ethylene / vinyl acetate copolymers, ethylene / acrylic ester copolymers, Examples include ethylene / vinyl chloride copolymer, thermoplastic elastomer, epoxy, natural rubber, and synthetic rubber. Among these, a thermoplastic elastomer, an ethylene / vinyl acetate copolymer, and an ethylene / acrylic acid ester copolymer are preferable because they are excellent in transparency, exhibit appropriate wettability and cohesion, and have excellent weather resistance. Thermoplastic elastomer is a resin having rubber elasticity at room temperature without vulcanization treatment. Specifically, styrene-butadiene block copolymer, styrene-ethylene block copolymer, styrene-butadiene- Styrene block copolymer, styrene-isoprene-styrene block copolymer, styrene-ethylenebutylene-styrene block copolymer, styrene-ethylenepropylene-styrene block copolymer, ethylene-propylene copolymer and ethylene-propylene terpolymer , Polyethylene, polypropylene, and those having a carboxyl group or a sulfonyl group introduced thereto. The molecular weight of these main polymers is the weight average molecular weight (Mw) of polyisoprene measured by gel permeation chromatography, and is usually 10,000 to 500,000, preferably 20,000 to 400, 000.

  According to the kind of main polymer, another compounding agent can be mix | blended with the said adhesive composition. Examples of other compounding agents include tackifiers, crosslinking agents or curing agents, antioxidants, antifoaming agents, and stabilizers.

  The tackifier imparts adhesive force to the main polymer that is soft and has a solid surface that is easily wetted. Such tackifiers include rosin and rosin derivatives, polyterpene resins, terpene phenol resins, coumarone-indene resins, petroleum resins, hydrogenated petroleum resins and the like. Among these, petroleum resins, hydrogenated petroleum resins, and terpene phenol resins are preferable because they are excellent in transparency and compatibility with the main polymer. The compounding amount of the tackifier is preferably 2 to 50 parts by weight, more preferably 5 to 20 parts by weight with respect to 100 parts by weight of the main polymer. When the addition amount of the tackifier is less than 2 parts by weight, the effect of the tackifier is not expressed, and conversely, when the addition amount exceeds 50 parts by weight, the adhesive force decreases due to the decrease in the cohesive force of the adhesive. Tend to be.

  Examples of the crosslinking agent or curing agent include polyfunctional isocyanate crosslinking agents such as tolylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, trimethylolpropane tolylene diisocyanate, diphenylmethane triisocyanate; ethylene glycol glycidyl ether, polyethylene glycol di Epoxy crosslinking agents or curing agents such as glycidyl ether, diglycidyl ether, trimethylolpropane triglycidyl ether; vinyltrimethoxysilane, methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 2- (3 , 4-Epoxycyclohexyl) ethyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) A silane crosslinking agent or curing agent such as 3-aminopropyltrimethoxysilane; a melamine resin crosslinking agent; a metal chelate crosslinking agent; an amine crosslinking agent is used. The blending amount of the crosslinking agent or curing agent is preferably 0.001 to 10 parts by weight, more preferably 0.01 to 3 parts by weight with respect to 100 parts by weight of the main polymer. When the addition amount of the crosslinking agent or curing agent is less than 0.001 part by weight, the effect of the crosslinking agent is not exhibited, and foaming and peeling are conspicuous in a weather resistance test or the like. On the contrary, when the addition amount of the crosslinking agent or the curing agent is more than 10 parts by weight, the stress relaxation property of the adhesive is lowered, and warpage becomes conspicuous.

  Examples of the antioxidant include phenol-based antioxidants such as tetrakis (methylene-3- (3,5di-t-butyl-4-hydroxyphenyl) propionate) methane, phosphorus-based antioxidants, and thioether-based antioxidants. Is mentioned. The blending amount of the antioxidant is within a range in which the transparency and adhesive strength of the adhesive layer are not lowered.

  The adhesive composition preferably has a shear storage modulus at a temperature of 23 ° C. of 0.1 to 10 MPa. By setting the shear storage elastic modulus in such a range, the pressure-sensitive adhesive composition has an appropriate pressure-sensitive adhesiveness (that is, a property capable of easily holding the adherend to stick the adherend and easily peeled off). obtain.

  The refractive index of the pressure-sensitive adhesive composition is preferably in the range of 1.45 to 1.55. By setting the refractive index within such a range, interface reflection can be prevented in the configuration of the circularly polarized light separating element-diffusion layer-optically anisotropic element.

(Gradient refractive index particles)
In the present invention, the gradient refractive index particles contained in the diffusion layer are particles having a refractive index gradient that changes as the depth from the surface to the center increases. Here, the refractive index gradient may exist in the entire range in the depth direction from the surface of the particle to the center, but exists in a partial range in the depth direction from the surface of the particle to the center. It may be. Specifically, for example, a core having a uniform refractive index and a coating layer covering the core and having a refractive index gradient in the thickness direction can be provided.

  An example of such gradient refractive index particles will be described with reference to FIG. In FIG. 2, the gradient refractive index particle 125 is a spherical particle composed of a nucleus 125C and a coating layer 125D covering the periphery thereof. Since the core 125C has a substantially uniform refractive index, there is no refractive index gradient in its radial direction (ie, the depth direction from the particle surface) 142. On the other hand, the coating layer 125 </ b> D has a refractive index gradient along its thickness direction (that is, a depth direction from the particle surface) 143.

  The gradient of the coating layer may be a gradient close to the nucleus at the interface 125B between the nucleus 125C and the coating layer 125D and close to other materials (such as an adhesive composition) surrounding the periphery at the surface 125S of the particle 125. preferable. For example, in the case where the diffusion layer material includes a binder made of the adhesive composition and a filler made of gradient refractive index particles, and the refractive index of the adhesive composition is smaller than the refractive index of the core 125C, the coating layer 125D The gradient of the refractive index is preferably such that the refractive index increases from the surface 125S toward the interface 125B.

More preferably, the refractive index of the coating layer 125D at the interface 125B, the refractive index of the coating layer 125D at the surface 125S, the refractive index of the core 125C, and the refractive index of the adhesive composition are expressed as n _B , n _S , n _C and n, respectively. _If it is set to _o , it is preferable that these satisfy | fill the relationship of following formula (III)-Formula (VI).
0.05 ≦ | n _B −n _S | (III)
0.05 ≦ | n _C −n _o | ≦ 0.5 (IV)
0 ≦ | n _C −n _B | ≦ 0.1 (V)
0 ≦ | n _S −n _o | ≦ 0.2 (VI)

The absolute value of the difference between n _B and n _S is preferably 0.05 or more, and more preferably 0.1 or more, as in formula (III). It is further preferable to have a gentle refractive index gradient (gradient) between the pressure-sensitive adhesive composition and the core through the coating layer.

n _C and _{n o} is preferably the absolute value of the difference as the formula (IV) is 0.05 or more and 0.5 or less, further still more preferably 0.05 to 0.3. If the absolute value of the difference in refractive index is smaller than 0.05, a sufficient light diffusion effect cannot be obtained, and if it is larger than 0.5, the transparency is deteriorated and the function as an optical film is deteriorated. .

As for n _C and n _B , the absolute value of the difference is preferably 0 or more and 0.1 or less, and more preferably 0 or more and 0.06 or less, as in formula (V). When the absolute value of the difference in refractive index is larger than 0.1, the scattering property inside the particles is increased, and the color unevenness function as an optical film is deteriorated.

n _S and _{n o} is preferably the absolute value of the difference as the formula (VI) is 0 to 0.2, more preferably still at 0 to 0.12. When the absolute value of the difference in refractive index is larger than 0.2, the scattering property inside the diffusion layer is increased, and the color unevenness function as an optical film is lowered, which is not preferable.

  The shape of the gradient refractive index particles is preferably spherical, from the viewpoint that the light diffusion direction can be isotropic, but may be a shape such as an elliptic rotating body deviating from the spherical shape. The particle diameter 141 of the gradient refractive index particles is not particularly limited, but is preferably 0.5 to 20 μm as an average primary particle diameter. In addition, when the diameter here is not a perfect sphere, the diameter of the sphere of the same volume is substituted. The ratio of the radius 142 of the core 125D to the thickness 143 of the coating layer 125D is preferably 2: 3 to 3: 2.

The gradient refractive index particles are not particularly limited as long as they are transparent particles, but fine particles are preferable from the viewpoint of obtaining a more excellent light diffusion effect. The fine particles are not particularly limited as long as they can form a refractive index gradient structure. Examples thereof include organic fine particles and inorganic fine particles.
Examples of the organic fine particles include acrylic fine particles, styrene fine particles, silicone fine particles, styrene-butadiene fine particles, acrylic-acrylic core-shell fine particles, and acrylic-styrene-butadiene core-shell fine particles. In particular, core-shell type fine particles are preferable in forming a gradient refractive index.
As inorganic fine particles, for example, by coating metal alkoxide solutions having different compositions on the surface of fine particles having a high refractive index such as titanium oxide, inorganic fine particles in which the refractive index of the coating layer is continuously or stepwise can be produced. it can.

  The organic fine particles having a gradient refractive index can be prepared using an emulsion polymerization method, a seed polymerization method, a suspension polymerization method, or the like. Specifically, in the initial stage, the monomer (A) whose homopolymer exhibits a high refractive index is polymerized to form a high refractive index at the center of the fine particles. Thereafter, the monomer (B) having a refractive index smaller than that of the homopolymer (A) and having the same refractive index as that of the adhesive resin as a matrix, or smaller than that of the adhesive resin as a matrix (B ) And the mixture of (A) are added to the polymerization system by changing the ratio of (A) and (B), so that the refractive index is continuous as the central part has a high refractive index and goes to the particle coating layer part. Organic fine particles inclined in a target or stepwise manner can be produced.

  A preferable blending ratio of the gradient refractive index particles in the diffusion layer material can be 0.1 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the pressure-sensitive adhesive composition.

  The ratio of the average primary particle diameter (arrow 141 in FIG. 2) d of the gradient refractive index particles contained in the diffusion layer to the thickness l of the diffusion layer is preferably 0.05 ≦ d / l ≦ 0.6, particularly preferably. 0.07 ≦ d / l ≦ 0.3. If it is less than 0.05, the particle size of the particles is too small or the film thickness of the diffusion layer is too thick, so that the required scattering characteristics may not be obtained if the former, but the latter does not require a diffusion layer. There is a possibility of causing a phase difference, and when it exceeds 0.6, a necessary adhesion area cannot be obtained, the adhesive force is insufficient, and the diffusion layer may be peeled off. The thickness l of the diffusion layer is not particularly limited, but can be in the range of 2 to 50 μm. Furthermore, 5-30 micrometers is preferable.

  In the present invention, the diffusion layer contains the above gradient refractive index particles as a diffusing agent for diffusing the light transmitted through the diffusion layer, thereby achieving diffusion while reducing the change in the polarization state of the light. Can do. That is, the light incident on the gradient refractive index particle changes its traveling direction and polarization state as it passes through the layer having the gradient refractive index inside the particle, and the change of the polarization state is caused by the light path at the center of the particle. Maximum when approaching. However, until the light path moves away from the center of the particle and exits from the particle surface again, the change in the polarization state is canceled, and when the light exits, only the light traveling direction changes in the same polarization state as the incident light. Is done.

  In the brightness enhancement film of the present invention, the haze of the diffusion layer is preferably 10% to 90%, particularly preferably 30% to 80%. If it is less than 10%, a sharp brightness change caused by the change in the observation angle of the emitted light, that is, a so-called glare, may be visually recognized through the brightness enhancement film. If it exceeds 90%, excessive scattering is caused. Therefore, the expected brightness may not be obtained. As a method for adjusting the haze to the above range, it is possible to appropriately adjust the blending ratio of the gradient refractive index particles. In addition, the measurement of haze is performed using a haze meter (for example, haze guard II (made by Toyo Seiki Co., Ltd.)).

  Although the manufacturing method of the brightness enhancement film of the present invention is not particularly limited, after applying a diffusion layer material for forming a diffusion layer to one or both of the optically anisotropic element and the circularly polarized light separating element The optically anisotropic element and the circularly polarized light separating element can be bonded together, and then the diffusion layer material layer can be cured as necessary.

  The method for coating the diffusion layer material is not particularly limited, and examples thereof include a roll coating method, a gravure coating method, a spin coating method, and a bar coating method. In addition, when the diffusion layer material is directly applied to the circularly polarized light separating element or the optically anisotropic element, in order to improve wettability and adhesion, the coated surface is appropriately subjected to plasma discharge treatment, corona discharge before application. You may use for processes, such as a process, an ultraviolet-ray process, or a flame process.

  The step of curing the layer of the diffusion layer material as necessary after bonding the optically anisotropic element and the circularly polarized light separating element is performed at a temperature range of 40 ° C to 110 ° C, preferably 60 ° C to 100 ° C. It can be performed by heating or the like.

(Liquid crystal display device)
The liquid crystal display device of the present invention includes the brightness enhancement film of the present invention. Specifically, for example, it has a backlight device including a light source, a reflector and a diffuser, the brightness enhancement film of the present invention, and a liquid crystal panel, and light from the backlight device enters the brightness enhancement film and is selected. Thus, a liquid crystal display device that reflects one circularly polarized light and transmits the other circularly polarized light to be supplied to the liquid crystal panel can be obtained. More specifically, the brightness enhancement film of the present invention is disposed such that the surface on the circularly polarized light separating element side faces the light source side and the surface on the optically anisotropic element side faces the liquid crystal panel side. The linearly polarized light emitted from the element can be configured to enter the liquid crystal panel.
The liquid crystal display device of the present invention can further include optional components such as a diffusion sheet and a prism sheet as necessary.

  Hereinafter, the present invention will be described by way of examples. In addition, this invention is not limited by the following examples.

<Production Example 1>
In the following procedure, spherical gradient refractive index particles having the form shown in FIG. 2 were obtained.
A stainless steel reactor equipped with a stirrer was charged with 75 parts by weight of deionized water, 1.0 part by weight of polyvinyl alcohol as a dispersant, and 0.6 parts by weight of benzoyl peroxide as a radical initiator. After nitrogen substitution, 40 parts by weight of α-methylstyrene and 3 parts by weight of divinylbenzene were added and stirred to make an emulsion. The emulsion was transferred to a separately degassed autoclave, and the temperature was raised to 65 ° C. while stirring with a homogenizer, and polymerization was performed for 2 hours.

Next, polymerization liquid A (250 parts by weight of deionized water, 3 parts by weight of polyvinyl alcohol as a dispersing agent, 2.5 parts by weight of benzoyl peroxide as a radical initiator was added, and after substituting with nitrogen by vacuum degassing, α -100 parts by weight of methyl styrene and 10 parts by weight of divinylbenzene emulsified) and 100 parts by weight of a mixed solution of polymerization liquid B (in which the monomer of polymerization liquid A is changed to methyl methacrylate) (polymerization liquid A Was added to the autoclave, and polymerization was carried out for 30 minutes. Next, 100 parts by weight of the second mixed liquid (75 parts by weight of the polymerization liquid A and 25 parts by weight of the polymerization liquid B) was added to the autoclave, and polymerization was performed for 30 minutes. Subsequently, 100 parts by weight of the third liquid mixture (62 parts by weight of the polymer liquid A, 28 parts by weight of the polymer liquid B), 100 parts by weight of the fourth liquid mixture (50 parts by weight of the polymer liquid A, 50 parts by weight) 100 parts by weight of the fifth mixture (40 parts by weight of polymerization liquid A, 60 parts by weight of polymerization liquid B), 100 parts by weight of the sixth mixture (28 parts of polymerization liquid A, polymerization liquid B) Is 72 parts by weight), 100 parts by weight of the seventh mixed solution (20 parts by weight of the polymer solution A, 80 parts by weight of the polymer solution B), and 100 parts by weight of the eighth mixed solution (the polymer solution A is 12 parts by weight, The polymerization liquid B was used in the order of 88 parts by weight), and the same operation as the polymerization with the second liquid mixture was performed. Subsequently, 100 parts by weight of the 9th mixed solution (7 parts by weight of the polymer solution A and 93 parts by weight of the polymer solution B) were added to the autoclave, and the polymerization was completed after cooling for 2 hours. A polymer bead dispersion was obtained.
The obtained polymer bead dispersion was filtered, washed, dried, and sieved (particles of 50 μm or more were removed) to obtain spherical gradient refractive index particles 125 of the embodiment shown in FIG.
The average particle diameter 141 of the obtained gradient refractive index particles 125 is 18.5 μm, the average of the radius 142 of the core 125C is 8.5 μm, and the average of the thickness 143 of the gradient refractive index coating layer 125D is 10. It was 0 μm. The refractive index of the coating layer 125D on the surface 125S of the particle 125 is 1.50, the refractive index of the coating layer 125D at the boundary 125B between the nucleus 125C and the coating layer 125D is 1.67, and the refractive index of the nucleus 125C. Was 1.73. The refractive index distribution was measured using a differential interference microscope (Interphako, manufactured by Carl-Zeiss).

<Production Example 2>
Gradient refractive index particles were obtained in the same manner as in Production Example 1 except that the monomer α-methylstyrene was changed to vinyl naphthalene.
The average particle diameter 141 of the obtained gradient refractive index particles is 15.5 μm, the average of the radius 142 of the core 125C is 7.5 μm, and the average of the thickness 143 of the gradient refractive index coating layer 125D is 8.0 μm. Met. The refractive index of the coating layer 125D at the surface 125S of the particle 125 is 1.42, the refractive index of the coating layer 125D at the boundary 125B between the nucleus 125C and the coating layer 125D is 1.65, and the refractive index of the nucleus 125C. Was 1.68.

<Production Example 3>
A stainless steel reactor equipped with a stirrer was charged with 300 parts by weight of deionized water, 1.0 part by weight of polyvinyl alcohol as a dispersant, and 0.6 parts by weight of benzoyl peroxide as a radical initiator. After nitrogen substitution, 40 parts by weight of α-methylstyrene and 3 parts by weight of divinylbenzene were added and stirred to make an emulsion. The emulsion was transferred to a separately degassed autoclave, and the temperature was raised to 65 ° C. while stirring with a homogenizer, and polymerization was performed for 2 hours.
Next, polymerization liquid A (250 parts by weight of deionized water, 3 parts by weight of polyvinyl alcohol as a dispersing agent, 2.5 parts by weight of benzoyl peroxide as a radical initiator was added, and after substituting with nitrogen by vacuum degassing, α -Emulsified by stirring 60 parts by weight of methylstyrene and 40 parts by weight of divinylbenzene), 100 parts by weight of a mixed solution of Polymer B (in which the monomer of Polymer A is changed to methyl methacrylate) (Polymer A) Was added to the autoclave, and the polymerization was terminated when polymerization was performed for 2 hours to obtain a polymer bead dispersion.
The obtained polymer bead dispersion was filtered, washed and dried, and sieved (particles of 50 μm or more were removed) to obtain particles having a core-shell structure.
The average particle diameter of the obtained particles was 9.5 μm, the average nucleus radius was 4.5 μm, and the average thickness of the coating layer was 5.0 μm. The refractive index of the coating layer on the particle surface was 1.52, the refractive index of the coating layer at the boundary between the nucleus and the coating layer was 1.53, and the refractive index of the nucleus was 1.65.

<Example 1>
A circularly polarized light separating element and an optically anisotropic element were produced as follows.

(Circularly polarized light separating element)
One side of a film (manufactured by Optes Co., Ltd.) made of an alicyclic olefin polymer having a thickness of 100 μm, a width of 50 mm, and a length of 200 mm was subjected to corona discharge treatment so that the wetting index of the surface was 56 dyne / cm. This was used as a substrate film.
5% modified polyamide (FR105 / CM4000 70/30 mixture, FR105: methoxymethylated nylon manufactured by Lead City Co., Ltd. CM4000: Toray on the surface of the base film subjected to the corona discharge treatment. An aqueous solution of a copolymerized polyamide) was applied. After coating, the film was dried at 120 ° C. for 5 minutes to produce a dry film having a thickness of 0.1 μm.

  The dry film was rubbed in one direction to obtain an alignment film. On the prepared alignment film, a coating solution having the following composition was applied using a wire bar # 6, dried at 100 ° C. for 5 minutes, and subjected to orientation aging.

[Coating liquid composition for forming cholesteric resin layer]
Solid content: 40% by weight
Rod-like liquid crystalline compound (rod-like liquid crystalline compound having Δn (= ne-no) = 0.18) 29.0 parts by weight A1 compound (compound represented by (A1); melting point 66 ° C.) 7.5 parts Light Polymerization initiator (IRG907 manufactured by Ciba Specialty Chemicals) 1.2 parts by weight Surfactant (KH-40 manufactured by Seimi Chemical Co., Ltd.) 0.04 parts by weight Chiral agent (LC756 manufactured by BASF) 2.3 parts by weight Methyl ethyl ketone (SP value: 9.3) 60 parts by weight

The coating film was irradiated with ultraviolet rays of 70 mJ / cm ² (UV-A), held at 100 ° C. for 1 to 5 minutes, then irradiated with ultraviolet rays to cure the coating film, and a cholesteric resin layer having a thickness of 3 μm ( A circularly polarized light separating sheet 1 having an optical functional layer) was obtained. This cholesteric resin layer has an average value of light transmittance from 400 nm to 570 nm of about 55%, and it was found that the remaining 45% including interface reflection is reflected.

In the production of the circularly polarized light separating sheet 1, the same procedure was performed except that 29.0 parts by weight of the polymerizable liquid crystalline compound was changed to 29.4 parts by weight and 2.3 parts by weight of the chiral agent was changed to 1.9 parts by weight. A circularly polarized light separating sheet 2 was obtained. This cholesteric resin layer had an average light transmittance of about 55% from 560 to 730 nm, and it was found that the remaining 45% including the interface reflection was reflected.
The cholesteric resin layer side of the produced circularly polarized light separating sheet 2 is bonded and fixed to the base film side of the circularly polarized light separating sheet 1 through an adhesive (manufactured by Sumitomo 3M, “8142”), and the circularly polarized light separating element Got.

(Optically anisotropic element)
A monomer composition composed of 97.8% by weight of methyl methacrylate and 2.2% by weight of methyl acrylate was polymerized by a bulk polymerization method to obtain resin pellets.

  Rubber particles were produced according to Example 3 of JP-B-55-27576. This rubber particle has a spherical three-layer structure, the core inner layer is a crosslinked polymer of methyl methacrylate and a small amount of allyl methacrylate, and the inner layer is composed of butyl acrylate and styrene as main components and a small amount of acrylic acid. It is a soft elastic copolymer obtained by crosslinking and copolymerizing allyl, and the outer layer is a hard polymer of methyl methacrylate and a small amount of ethyl acrylate. The average particle size of the inner layer was 0.19 μm, and the particle size including the outer layer was 0.22 μm.

  70 parts by weight of the resin pellets and 30 parts by weight of the rubber particles were mixed and melt kneaded with a twin screw extruder to obtain a methacrylic acid ester polymer composition A (glass transition temperature 105 ° C.).

  By coextruding the methacrylic ester polymer composition A (b layer) and the styrene maleic anhydride copolymer (glass transition temperature 130 ° C.) (a layer) at a temperature of 280 ° C., a b layer / a layer A multilayer film having an average thickness of 45/70/45 (μm) with a three-layer structure of / b layers was obtained. The laminated film was obliquely stretched with a tenter stretching machine at a stretching temperature of 134 ° C. and a stretching ratio of 1.8 times so that the slow axis was inclined at 45 degrees with respect to the MD direction. Got.

  The retardation in the front direction of the optically anisotropic element was 140 nm, and the retardation in the thickness direction was −85 nm (each numerical value is a measured value after oblique stretching). Further, one side of the optically anisotropic layer was subjected to corona discharge treatment so that the wetting index was 56 dyne / cm.

(Production and evaluation of brightness enhancement film)
Next, the circularly polarized light separating element and the optically anisotropic element were bonded and integrated with an adhesive diffusion layer material to produce a brightness enhancement film.

  The gradient refractive index particles obtained in Production Example 1 were mixed with an acrylic emulsion-based pressure-sensitive adhesive (manufactured by Daido Kasei; Vinizol E-5301, refractive index 1.53) to obtain a diffusion layer material. The blending ratio of the gradient refractive index particles in the adhesive composition was 3 parts by weight with respect to 100 parts by weight of the adhesive. This diffusion layer material is laminated on the cholesteric resin layer of the circularly polarized light separating element so that the average thickness is 25 μm, and this layer and the corona-treated surface of the optically anisotropic layer are laminated using a laminator, At 80 ° C., bonding was performed at a nip pressure of 2 kgf / 50 mm to obtain a brightness enhancement film.

  A commercially available liquid crystal display device (manufactured by Sharp, AQUIS, LC-37BE1W) was disassembled, and the brightness enhancement film obtained above was incorporated as a brightness enhancement film and reassembled. A commercially available liquid crystal display device is composed of a light source, a diffusion plate, a diffusion sheet, a prism sheet, a brightness enhancement film, and a liquid crystal panel in this order. The parts of the apparatus were used as they were for gripping the film. When the brightness enhancement film was incorporated, the optically anisotropic element was arranged on the liquid crystal panel side. The liquid crystal display device is whitely displayed by reassembling, and the front luminance at that time is measured using Ergoscope (manufactured by Autronic-MELCHERS), and the front luminance is set to 1 as the measurement result of Example 1, and other examples and comparative examples The measurement results were expressed as relative values. Further, the glare and color unevenness of the display surface were visually evaluated, and the glare was judged as ◯ when the steep luminance change when changing the observation angle was eliminated, and as x when it was not eliminated. The case where color unevenness was not observed was marked with ◯, the case where it was observed but mild, Δ, and the case where it was observed and the display quality was remarkably deteriorated was marked with ×. The results are shown in Table 1.

<Example 2>
A brightness enhancement film was obtained and evaluated in the same manner as in Example 1 except that the blending ratio of the gradient refractive index particles was 10 parts by weight. The results are shown in Table 1.

<Example 3>
A brightness enhancement film was obtained and evaluated in the same manner as in Example 1 except that the gradient refractive index particles used were those obtained in Production Example 2 instead of those obtained in Production Example 1. The results are shown in Table 1.

<Comparative Example 1>
A brightness enhancement film was obtained and evaluated in the same manner as in Example 1 except that the particles obtained in Production Example 3 were used instead of the gradient refractive index particles obtained in Production Example 1. The results are shown in Table 1.

It is a fragmentary sectional view which shows an example of the brightness enhancement film of this invention. It is sectional drawing which shows roughly an example of the gradient refractive index particle | grains in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Brightness enhancement film 110 Circularly polarized light separation element 120 Diffusion layer 125 Gradient refractive index particle | grain 130 Optically anisotropic element

Claims (5)

A brightness enhancement film comprising a circularly polarized light separating element and an optically anisotropic element,
A diffusion layer is provided between the circularly polarized light separating element and the optically anisotropic element,
The brightness enhancement film, wherein the diffusion layer contains gradient refractive index particles.   The brightness enhancement film according to claim 1, wherein the optically anisotropic element and the circularly polarized light separating element are adhered through the diffusion layer.   The brightness enhancement film according to claim 1, wherein the diffusion layer further contains an adhesive resin.   The said circularly polarized light separation element is an element which has a resin layer which has a non-liquid crystalline cholesteric regularity formed by superposing | polymerizing the liquid crystal composition containing a polymeric liquid crystal compound. Brightness enhancement film.   The liquid crystal display device provided with the brightness improvement film of any one of Claims 1-4.

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