JP5540630B2 - Composition for forming liquid crystal layer, circularly polarized light separating sheet and method for producing the same, brightness enhancement film, and liquid crystal display device - Google Patents

Description

  The present invention relates to a composition for forming a liquid crystal layer useful for preparing an optical material such as a circularly polarized light separating sheet, a circularly polarized light separating sheet prepared from the composition for forming a liquid crystal layer, and a luminance provided with the circularly polarized light separating sheet. The present invention relates to an improvement film and a liquid crystal display device.

  In a display device such as a liquid crystal display device, a birefringent film is used for the purpose of improving the viewing angle and contrast and improving the luminance. As such a birefringent film, a stretched polymer film having positive or negative intrinsic birefringence has been known. However, these stretched films sometimes cause deformation and changes in optical properties at high temperatures.

  Therefore, as a film having improved heat resistance, a film using a compound having liquid crystallinity (hereinafter referred to as “liquid crystalline compound” as appropriate) has been proposed. For example, a film in which a polymer liquid crystalline compound is applied to a substrate and oriented to form a film, or a polymerized liquid crystalline compound is applied to and oriented in a substrate and cured by heat or light to form a film. Films are known. However, in a film obtained by forming these liquid crystalline compounds, the liquid crystalline compounds that can be used are limited due to the low solubility of the liquid crystalline compounds, and it is difficult to obtain sufficient optical characteristics. Moreover, it is difficult to apply a liquid crystalline compound uniformly without defects, and productivity is lacking. Therefore, Patent Documents 1 to 3 propose improvement methods.

International Publication No. 2006/088101 JP-A-10-104615 Special table 2007-502911

  One example of a film obtained by forming a liquid crystal compound is a circularly polarized light separating sheet. This circularly polarized light separating sheet is manufactured by applying, for example, a cholesteric liquid crystal. When the circularly polarized light separating sheet is used as the brightness enhancement film, the circularly polarized light separating sheet preferably has a wide selective reflection band of 300 nm or more in the wavelength range. In order to realize such a wide selective reflection band, it is desired to apply a liquid crystalline compound having a refractive index anisotropy Δn as high as 0.20 or more.

  However, in general, a liquid crystal compound having a higher refractive index anisotropy has a higher crystallinity and poor solubility, and is difficult to apply uniformly without defects. For example, if an attempt is made to form a liquid crystalline compound having a high refractive index anisotropy by the techniques described in Patent Documents 1 to 3, the ink composition for forming a liquid crystal layer described in Patent Document 1 is a poor solvent for the liquid crystalline compound. Since it contains a certain alcohol solvent, there is a possibility that a liquid crystal compound precipitates during the coating and causes defects. The technique described in Patent Document 2 is suitable for a liquid crystal compound having a relatively low Δn, but 2-butanone is a poor solvent for a high Δn liquid crystal compound having a high crystallinity. When applying the compound, precipitation of the liquid crystal compound may occur and become a defect. Further, in the technique described in Patent Document 3, since a large amount of 1,3-dioxolane having a relatively high vapor pressure is used, thickness unevenness is likely to occur, and uniform film formation is difficult.

  The present invention was devised in view of the above problems, a liquid crystal layer forming composition capable of efficiently producing a uniform liquid crystal layer without defects, a circularly polarized light separating sheet using the liquid crystal layer forming composition, and its production It is an object of the present invention to provide a method and a brightness enhancement film and a liquid crystal display device including the circularly polarized light separating sheet.

As a result of intensive studies to solve the above-described problems, the present inventors have found that a mixed solvent in which a solvent having a cyclic ketone structure and a solvent having a cyclic ether structure are combined is a good liquid crystalline compound having a high refractive index anisotropy. Therefore, the present invention was completed by finding that a uniform liquid crystal layer without defects can be efficiently produced.
That is, the gist of the present invention is the following [1] to [8].

[1] It has a liquid crystalline compound having two or more polymerizable functional groups in one molecule and a refractive index anisotropy of 0.20 or more, a solvent having a cyclic ketone structure, and a cyclic ether structure. A composition for forming a liquid crystal layer, comprising a solvent.
[2] The composition for forming a liquid crystal layer according to [1], wherein the solvent having a cyclic ketone structure is cyclopentanone.
[3] The composition for forming a liquid crystal layer according to [1] or [2], wherein the solvent having a cyclic ether structure is 1,3-dioxolane.
[4] For forming a liquid crystal layer according to any one of [1] to [3], wherein the solvent having a cyclic ketone structure and the solvent having a cyclic ether structure are in a weight ratio of 30/70 to 90/10. Composition.
[5] A circularly polarized light separating sheet obtained through a step of applying the composition for forming a liquid crystal layer according to any one of [1] to [4] to a substrate and curing the composition.
[6] Circularly polarized light including a step of applying a composition for forming a liquid crystal layer according to any one of [1] to [4] to a substrate to obtain a liquid crystal layer, and a step of curing the liquid crystal layer A method for producing a separation sheet.
[7] A brightness enhancement film comprising the circularly polarized light separating sheet and the retardation film according to [5].
[8] A liquid crystal display device comprising the brightness enhancement film according to [7] and a liquid crystal panel.

  According to the present invention, a composition for forming a liquid crystal layer capable of efficiently producing a uniform liquid crystal layer without defects, a circularly polarized light separating sheet using the composition for forming a liquid crystal layer, a method for producing the same, and the above circularly polarized light separation A brightness enhancement film including a sheet and a liquid crystal display device can be realized.

  Hereinafter, the present invention will be described in detail with reference to embodiments, examples, etc., but the present invention is not limited to the following embodiments, examples, etc., and can be arbitrarily set within the scope of the present invention. Can be changed and implemented.

[1. Liquid crystal layer forming composition]
The composition for forming a liquid crystal layer of the present invention is a liquid crystal compound having two or more polymerizable functional groups in one molecule and having a refractive index anisotropy of a predetermined value or more (hereinafter referred to as “high Δn polymerizability as appropriate”). Liquid crystal compound ”), a solvent having a cyclic ketone structure (hereinafter referred to as“ cyclic ketone solvent ”as appropriate), and a solvent having a cyclic ether structure (hereinafter referred to as“ cyclic ether solvent ”as appropriate). It is a composition.

[1-1. Liquid crystalline compound
The high Δn polymerizable liquid crystalline compound has two or more polymerizable functional groups in one molecule. The polymerizable functional group is a group that causes a polymerization reaction under appropriate conditions to polymerize a high Δn polymerizable liquid crystalline compound. When the high Δn polymerizable liquid crystalline compound has two or more polymerizable functional groups, when the composition for forming a liquid crystal layer is formed and cured, the high Δn polymerizable liquid crystalline compound is polymerized and cured stably. You can get things. On the contrary, when the composition for forming a liquid crystal layer is cured by forming a film having a polymerizable functional group in one molecule of 1 or less, a crosslinked cured product cannot be obtained. As a result, the film strength that can withstand practical use may not be obtained. Even when a cross-linking agent described later is used, the film strength tends to be insufficient and practical use tends to be 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.

  Examples of the polymerizable functional group include a carboxyl group, a (meth) acryl group, an epoxy group, a thioepoxy group, a mercapto group, an isocyanate group, an isothiocyanate group, an oxetane group, a thietanyl group, an aziridinyl group, a pyrrole group, and a vinyl group. , Allyl group, fumarate group, cinnamoyl group, oxazoline group, hydroxyl group, alkoxysilyl group, amino group and the like. In addition, (meth) acryl refers to acryl and methacryl. Moreover, the polymerizable functional group contained in one molecule may be one type or two or more types.

The refractive index anisotropy of the high Δn polymerizable liquid crystalline compound is usually 0.20 or more, preferably 0.21 or more, more preferably 0.23 or more. Due to the high refractive index anisotropy of the high Δn polymerizable liquid crystalline compound, the refractive index anisotropy of the composition for forming a liquid crystal layer containing the high Δn polymerizable liquid crystalline compound is improved, and excellent optical performance ( For example, a circularly polarized light separating sheet having circularly polarized light separating characteristics) can be realized. Further, when the refractive index anisotropy is 0.30 or more, the absorption edge on the long wavelength side of the ultraviolet absorption spectrum may extend to the visible range. It can be used as long as the optical performance is not adversely affected.
The refractive index anisotropy of the compound can be measured by the senalmon method.

Preferred examples of the high Δn polymerizable liquid crystalline compound include rod-shaped liquid crystalline compounds represented by the following general formula (1).
^{R 1 -C 1 -D 1 -C 3} -M-C 4 -D 2 -C 2 -R 2 (1)

In the general formula (1), R ¹ and R ² each independently represent a polymerizable functional group.

In the general formula (1), D ¹ and D ² are each independently a single bond, divalent saturated carbonization such as a linear or branched methylene group having 1 to 20 carbon atoms and an alkylene group. It represents a group selected from the group consisting of a hydrogen group and a linear or branched alkylene oxide group having 1 to 20 carbon atoms.

In the general formula (1), C ^{1 to} C ⁴ are each independently a single bond, —O—, —S—, —S—S—, —CO—, —CS—, —OCO—, —CH. _{2 -, - OCH 2 -,} - CH = N-N = CH -, - NHCO -, - OCOO -, - CH 2 COO-, and represents a group selected from the group consisting of _-CH 2 OCO-.

In the general formula (1), M represents a mesogenic group. Specific examples of M include azomethines, azoxys, phenyls, biphenyls, terphenyls, naphthalenes, anthracenes, benzoic acid esters, cyclohexanecarboxylic acid, which may be unsubstituted or have a substituent. 2-4 skeletons selected from the group of acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, alkenylcyclohexylbenzonitriles, —, —S—, —S—S—, —CO—, —CS—, —OCO—, —CH ₂ —, —OCH ₂ —, —CH═N—N═CH—, —NHCO—, —OCOO _-, - CH 2 _COO-, and a group formed by being linked by linking groups _-CH 2 OCO- or the like.

Examples of the substituent that the mesogenic group M may have include, for example, a halogen atom, an optionally substituted alkyl group having 1 to 10 carbon atoms, a cyano group, a nitro group, —O—R ³ , — O—C (═O) —R ³ , —C (═O) —O—R ³ , —O—C (═O) —O—R ³ , —NR ³ —C (═O) —R ³ , -C (= O) -NR < ³ > R < ⁴ > or -O-C (= O) -NR < ³ > R < ⁴ > is represented.
Here, R ³ and R ⁴ represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. When R ³ and R ⁴ are alkyl groups, the alkyl group includes —O—, —S—, —O—C (═O) —, —C (═O) —O—, —O—C. (═O) —O—, —NR ⁵ —C (═O) —, —C (═O) —NR ⁵ —, —NR ⁵ —, or —C (═O) — may be present. (However, the case where two or more of -O- and -S- are adjacent to each other is excluded). Here, R ⁵ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Examples of the substituent in the above-mentioned “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 1 to 6 carbon atoms. Alkoxy 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, alkylcarbonyl having 2 to 7 carbon atoms Examples thereof include an oxy group and an alkoxycarbonyloxy group having 2 to 7 carbon atoms.

  The composition for forming a liquid crystal layer of the present invention may contain one kind of high Δn polymerizable liquid crystalline compound alone, or two or more kinds of high Δn polymerizable liquid crystalline compounds in combination at any ratio. May be.

  The molecular weight of the high Δn polymerizable liquid crystalline compound is preferably 600 or more. When the composition for forming a liquid crystal layer of the present invention contains a compound represented by the general formula (2) as described later, if the molecular weight of the high Δn polymerizable liquid crystalline compound is increased as described above, the general formula (2 ) Can enter the gaps between the high Δn polymerizable liquid crystalline compounds having a higher molecular weight than that, and the alignment uniformity can be improved.

  In the composition for forming a liquid crystal layer of the present invention, the concentration of the high Δn polymerizable liquid crystal compound is usually 5% by weight or more, preferably 10% by weight or more, more preferably 15% by weight or more, and usually 40% by weight or less. , Preferably 35% by weight or less, more preferably 30% by weight or less. By keeping the concentration of the high Δn polymerizable liquid crystalline compound in such a range, a desired liquid crystal layer can be efficiently formed while suppressing the precipitation of the high Δn polymerizable liquid crystalline compound.

[1-2. solvent〕
The composition for forming a liquid crystal layer of the present invention contains a cyclic ketone solvent and a cyclic ether solvent as solvents. Usually, the composition for forming a liquid crystal layer of the present invention is used in the form of a solution in which other components are dissolved in these solvents. By including these cyclic ketone solvent and cyclic ether solvent, the solubility of the high Δn polymerizable liquid crystalline compound and the controllability of the drying rate of the solvent in the liquid crystal layer forming composition are improved, and there is no defect. Film formation is possible.

  Examples of the cyclic ketone solvent include cyclopropanone, cyclopentanone, cyclohexanone, and the like, among which cyclopentanone is preferable. In addition, a cyclic ketone solvent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Examples of the cyclic ether solvent include tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc. Among them, 1,3-dioxolane is preferable. In addition, a cyclic ether solvent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the liquid crystal layer forming composition of the present invention, the cyclic ketone solvent preferably has a lower vapor pressure than the cyclic ether solvent. From this viewpoint, the weight ratio of the cyclic ketone solvent to the cyclic ether solvent (cyclic ketone solvent / cyclic ether solvent) is usually 30/70 or more, preferably 40/60 or more, more preferably 45/55 or more. 90/10 or less, preferably 80/20 or less, more preferably 70/30 or less. By setting it to be equal to or more than the lower limit of the above range, it is possible to prevent the drying rate of the solvent from becoming excessively high and suppress the occurrence of thickness unevenness. Moreover, by making it below the upper limit of the said range, it can prevent that the drying rate of a solvent becomes slow too much and can suppress that a solvent remains in a liquid crystal layer and a liquid-crystal hardened | cured material layer.

  The amount of the cyclic ketone solvent and the cyclic ether solvent in the composition for forming a liquid crystal layer of the present invention is the total amount of the cyclic ketone solvent and the cyclic ether solvent with respect to 100 parts by weight of the high Δn polymerizable liquid crystalline compound, and usually 100 parts by weight or more. The amount is preferably 150 parts by weight or more, more preferably 200 parts by weight or more, and usually 1900 parts by weight or less, preferably 900 parts by weight or less, more preferably 500 parts by weight or less. By setting it to the lower limit of this range or more, precipitation of the high Δn polymerizable liquid crystalline compound can be stably suppressed, and by setting the upper limit or less of this range, the amount of the solvent becomes excessive, and the liquid crystal layer and the liquid crystal cured product layer are produced. It is possible to prevent the efficiency from decreasing.

[1-3. Other ingredients
The composition for forming a liquid crystal layer of the present invention may contain other components in addition to the components described above as long as the effects of the present invention are not significantly impaired.
For example, the composition for forming a liquid crystal layer of the present invention may contain a compound represented by the following general formula (2).
R < ⁶ > -A < ¹ > -ZA < ² > -R < ⁷ > (2)

In General Formula (2), R ⁶ and R ⁷ are each independently a linear or branched alkyl group having 1 to 20 carbon atoms, a linear or branched chain having 1 to 20 carbon atoms, or A group selected from the group consisting of a branched alkylene oxide group, 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; Represent.

The alkyl group and alkylene oxide group may not be substituted and may be substituted with one or more halogen atoms. Furthermore, when two or more substituents are present in each of the alkyl group and the alkylene oxide group, they may be the same or different.
In addition, the halogen atom, hydroxyl group, carboxyl group, (meth) acryl group, epoxy group, mercapto group, isocyanate group, amino group, and cyano group are alkyl groups and / or alkylene oxides having 1 to 2 carbon atoms. It may be bonded to a group.

Preferred examples of R ⁶ and R ⁷ include 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.

At least one of R ⁶ and R ⁷ is preferably a polymerizable functional group. By having a polymerizable functional group as R ⁶ and / or R ⁷ , the compound represented by the general formula (2) is fixed in the liquid crystal layer at the time of curing to form a liquid crystal cured product layer that is a stronger film can do. Here, examples of the polymerizable functional group include those similar to the high Δn polymerizable liquid crystalline compound, and among them, a carboxyl group, a (meth) acryl group, an epoxy group, a mercapto group, an isocyanate group, and an amino group are preferable. .

In the general formula (2), 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 , 4′-bicyclohexylene group and a group selected from the group consisting of 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 May be unsubstituted, substituted with one or more substituents such as halogen atom, hydroxyl group, carboxyl group, cyano group, amino group, alkyl group having 1 to 10 carbon atoms, halogenated alkyl group, etc. May be. Furthermore, when two or more substituents are present in each of A ¹ and A ² , they may be the same or different.

Particularly preferable examples of A ¹ and A ² include a 1,4-phenylene group, a 4,4′-biphenylene group, and a 2,6-naphthylene group. These aromatic ring skeletons are relatively rigid as compared with the alicyclic skeletons, have a high affinity with the mesogen of the high Δn polymerizable liquid crystalline compound, and have higher alignment uniformity ability.

In the general formula (2), Z represents a single bond, —O—, —S—, —S—S—, —CO—, —CS—, —OCO—, —CH ₂ —, —OCH ₂ —, —CH. = N-N = CH -, - NHCO -, - OCOO -, - CH 2 COO-, and is selected from the group consisting of _-CH 2 OCO-. Particularly preferable examples of Z include a single bond, —OCO—, and —CH═N—N═CH—.

  At least one of the compounds represented by the general formula (2) preferably has liquid crystallinity, and preferably has chirality. Moreover, it is preferable that the composition for liquid crystal layer formation of this invention contains the mixture of a some optical isomer as a compound represented by General formula (2). For example, a mixture of plural kinds of enantiomers and / or diastereomers can be contained. As for at least 1 type of the compound represented by General formula (2), it is preferable that the melting | fusing point exists in the range of 50 to 150 degreeC.

  When the compound represented by the general formula (2) has liquid crystallinity, the refractive index anisotropy is preferably high. Thereby, the refractive index anisotropy of the composition for forming a liquid crystal layer of the present invention can be improved, and a broadband circularly polarized light separating sheet can be produced. At least one refractive index anisotropy of the compound represented by the general formula (2) is preferably 0.18 or more, more preferably 0.22 or more. In addition, some compounds represented by the general formula (2) may satisfy the requirements as a high Δn polymerizable liquid crystalline compound, and such a compound is used as the high Δn polymerizable liquid crystalline compound according to the present invention. Shall be handled.

  In the liquid crystal layer forming composition of the present invention, the compound represented by the general formula (2) preferably has a molecular weight of less than 600. When the molecular weight of the compound represented by the general formula (2) is less than 600, the compound represented by the general formula (2) may enter a gap between the high Δn polymerizable liquid crystal compounds having a higher molecular weight. The alignment uniformity of the liquid crystal compound in the composition for forming a liquid crystal layer of the present invention can be improved.

  Specific examples of particularly preferable compounds represented by the general formula (2) include the following compounds (A1) to (A10). In the compound (A3), “*” represents a chiral center.

  The compounding ratio of the compound represented by the general formula (2) is a weight ratio of (total weight of the compound represented by general formula (2)) / (total weight of the high Δn polymerizable liquid crystalline compound). 05 or more is preferable, 0.1 or more is more preferable, 0.15 or more is particularly preferable, 1 or less is preferable, 0.65 or less is more preferable, and 0.45 or less is particularly preferable. If the weight ratio is too small, the alignment uniformity of the liquid crystal compound in the composition for forming a liquid crystal layer of the present invention may be insufficient. Conversely, if the weight ratio is too large, the liquid crystal in the composition for forming a liquid crystal layer of the present invention may be insufficient. The alignment uniformity of the functional compound is reduced, the stability of the liquid crystal phase of the composition for forming a liquid crystal layer of the present invention is decreased, or the refractive index anisotropy as the liquid crystal composition of the composition for forming a liquid crystal layer of the present invention is reduced. When the film is deposited, 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 indicates the total weight when two or more kinds are used.

  In addition, for example, the composition for forming a liquid crystal layer of the present invention may contain a cross-linking agent in order to improve film strength and durability after curing. The crosslinking agent may react simultaneously when the liquid crystal layer coated with the composition for forming a liquid crystal layer of the present invention is cured, heat treatment may be performed after curing to accelerate the reaction, or the reaction may proceed spontaneously due to moisture. Thus, it is possible to appropriately select and use one that can increase the crosslink density of the liquid crystal cured product layer and does not deteriorate the alignment uniformity. Moreover, what can harden | cure with an ultraviolet-ray, a heat | fever, moisture etc. can be used conveniently, for example.

  Examples of cross-linking agents include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 2- (2-vinyloxyethoxy) Polyfunctional acrylate compounds such as 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-aziridinylpropionate Aziridine compounds such as nates; Isocyanurate type isocyanates derived from hexamethylene diisocyanate, hexamethylene diisocyanate, isocyanurate type isocyanates, biuret type isocyanates, adduct type isocyanates, etc .; Polyoxazoline compounds having an oxazoline group in the side chain; 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; In addition, 1 type may be used for a crosslinking agent and it may use it combining 2 or more types by arbitrary ratios. Further, the composition for forming a liquid crystal layer of the present invention may contain a known catalyst according to the reactivity of the cross-linking agent to improve productivity in addition to improving the film strength and durability.

  The blending ratio of the cross-linking agent is such that the concentration of the cross-linking agent in the liquid crystal cured product layer obtained by curing the liquid crystal layer forming composition of the present invention is 0.1 wt% to 15 wt%. preferable. If the blending ratio of the crosslinking agent is less than 0.1% by weight, the effect of improving the crosslinking density may not be obtained. Conversely, if the blending ratio is more than 15% by weight, the stability of the liquid crystal cured product layer may be lowered. .

For example, the composition for forming a liquid crystal layer of the present invention may contain a polymerization initiator. A thermal polymerization initiator may be used as the polymerization initiator, but a photopolymerization initiator is usually used. As the photopolymerization initiator, for example, a known compound that generates radicals or acids by ultraviolet rays or visible rays can be used.
Examples of photopolymerization initiators include 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-diethoxyacetophenone, β-ionone, β-bromostyrene, diazoaminobenzene, α-amylcinnacaldehyde, 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, Anthracene benzophenone, 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 hexafluoroph Sufeto, 3-methyl-2-butynyl tetramethyl hexafluoroantimonate, diphenyl - (p-phenylthiophenyl) sulfonium hexafluoroantimonate, and the like. Depending on the desired physical properties, one type of polymerization initiator may be used, or two or more types may be used in combination at any ratio. Furthermore, if necessary, the composition for forming a liquid crystal layer of the present invention may contain a known photosensitizer or a tertiary amine compound as a polymerization accelerator to control the curability of the composition for forming a liquid crystal layer. You can also.

  The blending ratio of the polymerization initiator is preferably 0.03% by weight to 7% by weight in the liquid crystal layer forming composition of the present invention. When the blending amount of the polymerization initiator is less than 0.03% by weight, the film strength of the liquid crystal cured product layer that can be obtained may be lowered. On the other hand, if it is more than 7% by weight, the liquid crystal phase may become unstable because the orientation of the liquid crystal compound is inhibited.

For example, the composition for forming a liquid crystal layer of the present invention may contain a surfactant. As the surfactant, those not inhibiting the orientation can be appropriately selected and used.
As examples of the surfactant, a nonionic surfactant containing a siloxane or a fluorinated alkyl group in the hydrophobic group can be preferably used. Of these, oligomers having two or more hydrophobic group moieties in one molecule are particularly suitable. These surfactants include, for example, OM-NOVA PolyFox PF-151N, PF-636, PF-6320, PF-656, PF-6520, PF-3320, PF-651, PF-652; FTX-209F, FTX-208G, FTX-204D; KH-40 of Surflon, Seimi Chemical Co., Ltd. can be used. In addition, 1 type of surfactant may be used and it may use it combining 2 or more types by arbitrary ratios.

  The mixing ratio of the surfactant is such that the concentration of the surfactant in the liquid crystal cured product layer obtained by curing the liquid crystal layer forming composition of the present invention is 0.05 wt% to 3 wt%. Is preferred. When the blending ratio of the surfactant is less than 0.05% by weight, the alignment regulating force at the air interface is lowered and alignment defects may occur. On the other hand, when the amount is more than 3% by weight, an excessive surfactant may enter between the liquid crystal compound molecules to reduce the alignment uniformity.

  For example, the liquid crystal layer forming composition of the present invention may contain a chiral agent. Specific examples of the chiral agent include JP-A-2005-289881, JP-A-2004-115414, JP-A-2003-66214, JP-A-2003-313187, JP-A-2003-342219, JP-A-2003-342219. 2000-290315, JP-A-6-072962, U.S. Pat. No. 6,468,444, WO 98/00428, JP-A 2007-176870, etc. can be used as appropriate. . Specific examples thereof include, for example, LC756, a PASF color produced by BASF. Note that one type of chiral agent may be used, or two or more types may be used in combination at any ratio.

  The blending ratio of the chiral agent is set in a range that does not lower the desired optical performance. A specific blending ratio of the chiral agent is preferably 1% by weight to 60% by weight in the liquid crystal layer forming composition of the present invention.

The composition for forming a liquid crystal layer of the present invention may contain, for example, a polymerization inhibitor for improving pot life, an antioxidant for improving durability, an ultraviolet absorber, a light stabilizer and the like. However, the blending ratio of these other components is within a range that does not deteriorate the desired optical performance.
In addition, 1 type may be used for another component and it may use it combining 2 or more types by arbitrary ratios.

[1-4. Method for producing composition for forming liquid crystal layer, etc.)
The method for producing the composition for forming a liquid crystal layer of the present invention is not particularly limited, and the composition can be produced by mixing the above components.

  The composition for forming a liquid crystal layer of the present invention can suppress the occurrence of defects because the high Δn polymerizable liquid crystalline compound is difficult to precipitate during storage and use. Further, since the evaporation rate of the solvent can be easily controlled, uniform film formation with no thickness unevenness is possible. Furthermore, since the composition for forming a liquid crystal layer of the present invention can make a wider range of high Δn polymerizable liquid crystalline compounds into a stable dissolved state than in the past, various types using a wide range of high Δn polymerizable liquid crystalline compounds. The present invention can be applied to the production of the liquid crystal layer and the liquid crystal cured product layer.

[2. Method for producing circularly polarized light separating sheet]
The composition for forming a liquid crystal layer of the present invention has an excellent advantage that a uniform liquid crystal layer and a liquid crystal cured product layer can be formed without defects as described above. Utilizing this, a circularly polarized light separating sheet can be produced using the composition for forming a liquid crystal layer of the present invention. Hereinafter, a method for producing the circularly polarized light separating sheet will be described.
When producing a circularly polarized light separating sheet using the composition for forming a liquid crystal layer of the present invention, at least a coating step of applying the composition for forming a liquid crystal layer to a substrate to obtain a liquid crystal layer, and the obtained liquid crystal layer And a curing step of obtaining a liquid crystal cured product layer by curing. Further, in addition to the coating process and the curing process, another process may be performed. For example, an alignment treatment process may be performed between the coating process and the curing process.

[2-1. Preparation of substrate
A base material is a member used as the object which apply | coats the composition for liquid crystal layer formation of this invention. Although this base material may be peeled off after forming the liquid crystal cured product layer, it may be used as a part of the circularly polarized light separating sheet together with the liquid crystal cured product layer without being peeled off. When the substrate is used as a part of the circularly polarized light separating sheet, a transparent substrate is usually used as the substrate. Although the specific light transmittance of a transparent base material is not uniform according to the use of a circularly polarized light-separating sheet, for example, a base material having a thickness of 1 mm and a total light transmittance of 80% or more can be used.

  As the material of the transparent substrate, for example, a transparent resin can be used. Specific examples of the transparent substrate material include alicyclic olefin polymers, chain olefin polymers such as polyethylene and polypropylene, triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyethersulfone, Examples thereof include synthetic resins such as modified acrylic polymers, epoxy resins, polystyrene, and acrylic resins. 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. Further, the transparent substrate may have a single-layer structure consisting of only one layer or a laminated structure having two or more layers.

  An alignment film may be provided on the substrate. By providing the alignment film, the liquid crystal compound in the layer of the composition for forming a liquid crystal layer of the present invention applied thereon can be surely aligned in a desired direction. The alignment film is subjected to corona discharge treatment, if necessary, on the surface of the base material, and then applied with a solution in which the alignment film material is dissolved in water or a solvent, dried, and then rubbed to the dried coating film. Can be formed.

  Examples of the material of the alignment film include cellulose, silane coupling agent, polyimide, polyamide, polyvinyl alcohol, epoxy acrylate, silanol oligomer, polyacrylonitrile, phenol resin, polyoxazole, and cyclized polyisoprene. Polyamide is particularly preferred.

  Examples of the modified polyamide include those obtained by modifying an aromatic polyamide or an aliphatic polyamide. Of these, a modified aliphatic polyamide is preferred. Specific examples include nylon-6, nylon-66, nylon-12, ternary to quaternary copolymer nylon, fatty acid polyamide, or fatty acid block copolymer (eg, polyether ester amide, polyester amide). And the like added. Examples of the modification include terminal amino modification, carboxyl modification, hydroxyl modification and the like, and modification in which a part of the amide group is alkylaminated or N-alkoxyalkylated. Examples of the N-alkoxyalkylated modified polyamide include N-methoxymethylated part of the amide group of copolymer nylon such as nylon-6, nylon-66, or nylon-12. The weight average molecular weight of the modified polyamide is preferably 5000 or more, more preferably 10,000 or more, preferably 500,000 or less, more preferably 200,000 or less.

  The thickness of the alignment film may be any thickness as long as desired alignment uniformity can be obtained in the liquid crystal layer. Specifically, 0.001 μm or more is preferable, 0.01 μm or more is more preferable, 5 μm or less is preferable, and 2 μm or less is more preferable.

[2-2. Application process]
A liquid crystal layer can be obtained by performing a coating process in which the composition for forming a liquid crystal layer of the present invention is applied to a substrate. When the alignment film is formed on the substrate surface, the liquid crystal layer forming composition of the present invention is applied on the alignment film. Usually, after coating, the solvent is dried and removed from the coating film after a certain period of time, and a liquid crystal layer containing a high Δn polymerizable liquid crystalline composition is formed on the substrate. At this time, since the mixed solvent containing the cyclic ketone solvent and the cyclic ether solvent dissolves the high Δn polymerizable liquid crystalline compound well, defects in the liquid crystal layer due to precipitation of the high Δn polymerizable liquid crystalline compound can be prevented. Moreover, since the drying speed of the mixed solvent containing the cyclic ketone solvent and the cyclic ether solvent is not excessively high, the coating film does not cause uneven thickness, and thus prevents the occurrence of uneven thickness in the liquid crystal layer and the liquid crystal cured product layer. it can.

  Although there is no restriction | limiting in the application | coating method of the composition for liquid crystal layer formation of this invention, What is necessary is just to implement by methods, such as an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, a die coating method, a bar coating method, for example.

  The temperature condition at the time of application is usually 10 ° C. or higher, preferably 13 ° C. or higher, more preferably 16 ° C. or higher, and usually 60 ° C. or lower, preferably 45 ° C. or lower, more preferably 35 ° C. or lower. By setting the temperature to be above the lower limit of the above range, it is possible to prevent the drying rate of the solvent from being excessively slowed and lowering the production efficiency. By setting the temperature to be below the upper limit, the drying rate of the solvent is excessively high and the liquid crystal layer It is possible to more stably prevent the occurrence of thickness unevenness.

[2-3. (Orientation treatment process)
After the liquid crystal layer is formed by the coating process, an alignment treatment may be performed as necessary before the curing process. The alignment treatment may be performed, for example, by heating the liquid crystal layer at 50 ° C. to 150 ° C. for 0.5 to 10 minutes. By performing the alignment treatment, the liquid crystalline compound in the liquid crystal layer can be aligned well.

[2-4. Curing process]
After the formation of the liquid crystal layer, a curing step for curing the liquid crystal layer is performed. By performing the curing step, the polymerizable functional group reacts to polymerize the high Δn polymerizable liquid crystalline compound and the like, and the liquid crystal layer is cured to obtain a liquid crystal cured product layer.
The specific content of the treatment to be performed in the curing step is not particularly limited as long as the polymerization of the polymerizable functional group is allowed to proceed. For example, at least one heat treatment and / or light irradiation treatment may be performed. .

  The heating temperature condition in the heat treatment is usually 40 ° C. or higher, preferably 50 ° C. or higher, and is usually 200 ° C. or lower, preferably 140 ° C. or lower. The treatment time in the heat treatment is usually 1 second or longer, preferably 5 seconds or longer, usually 3 minutes or shorter, preferably 120 seconds or shorter.

The light used for the light irradiation treatment includes not only visible light but also ultraviolet rays and other electromagnetic waves. Light irradiation may be performed, for example, by irradiating light having a wavelength of 200 to 500 nm for 0.01 second to 3 minutes. Further, for example, it is also possible to obtain a circularly polarized light separating sheet having a wide reflection band by alternately repeating a weak ultraviolet irradiation of 0.01 to 50 mJ / cm ² and a heating treatment a plurality of times. After the reflection band is expanded by the above-mentioned weak UV irradiation, etc., for example, relatively strong UV light of 50 to 10,000 mJ / cm ² is irradiated to completely polymerize the high Δn polymerizable liquid crystal compound, and the liquid crystal is cured. It can be a physical layer. 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). .

[2-5. Other matters in the method of manufacturing a circularly polarized light separating sheet]
The coating process, the alignment treatment process, and the curing process may be performed only once to form only one liquid crystal cured product layer, or may be repeated twice or more to form two or more liquid crystal cured product layers. You can also. However, even when each of the coating step and the curing step is performed only once, a liquid crystal cured product layer having a sufficient thickness, for example, 5 μm or more, including a polymer of a highly aligned high Δn polymerizable liquid crystalline compound is included. It can be formed easily.

[2-6. Configuration of the circularly polarized light separating sheet obtained]
The liquid crystal cured product layer formed as described above is usually a cholesteric resin layer. In the cholesteric resin layer, the molecular axes are aligned in a certain direction on one plane, but the direction of the molecular axis is slightly shifted in the next plane, and the angle is further shifted in the next plane. It has a structure in which the angle of the molecular axis is shifted (twisted) as it proceeds on a plane in which molecules are arranged in a certain direction. Thus, the structure in which the direction of the molecular axis is twisted becomes an optically chiral structure.

The cholesteric resin layer has a circularly polarized light separation function. That is, it has a function of reflecting left-handed or right-handed circularly polarized light in a specific wavelength region and transmitting other circularly-polarized light. Therefore, the sheet provided with this cholesteric resin layer functions as a circularly polarized light separating sheet.
The cholesteric resin layer is preferably one that exhibits a circularly polarized light separation function over the entire wavelength region of visible light. Specifically, a cholesteric resin layer having a circularly polarized light separation function with respect to light in a wavelength region of 400 nm to 750 nm is preferable. For example, a cholesteric resin layer having a circularly polarized light separation function is preferable for light in any wavelength region of blue (wavelength 410 to 470 nm), green (wavelength 520 to 580 nm), and red (wavelength 600 to 660 nm).

  The wavelength that exhibits the circularly polarized light separation function depends on the pitch of the chiral structure in the cholesteric resin. The pitch of the chiral structure is a distance in the plane normal direction until the angle of the molecular axis in the chiral structure gradually shifts as it advances along the plane and then returns to the original molecular axis direction again. By changing the pitch of this chiral structure, the wavelength at which the circularly polarized light separating function is exhibited can be changed.

  Usually, the cholesteric resin layer obtained as a liquid crystal cured product layer by the above-described production method is a non-liquid crystalline resin layer in which a high Δn polymerizable liquid crystalline compound is polymerized in the curing step and loses liquid crystallinity. A non-liquid crystalline resin layer is preferable because the cholesteric regularity does not change depending on the ambient temperature or electric field.

  In addition, the liquid crystal cured product layer obtained by the manufacturing method described above is usually a cholesteric resin layer in which the pitch of the chiral structure is continuously changed. As a result, the cholesteric resin layer can exhibit a circularly polarized light separation function in a wide range of wavelengths corresponding to a continuously changing pitch size.

Moreover, as another structure of the liquid-crystal hardened | cured material layer obtained, the cholesteric resin layer which changed the magnitude | size of the pitch of a chiral structure in steps is mentioned, for example. A cholesteric resin layer in which the pitch of the chiral structure is changed stepwise includes, for example, a cholesteric resin layer having a chiral structure pitch that exhibits a circularly polarized light separation function with light in the blue wavelength range, and a circle with light in the green wavelength range. It can be obtained by laminating a cholesteric resin layer having a chiral structure pitch that exhibits a polarization separation function and a cholesteric resin layer having a chiral structure pitch that exhibits a circular polarization separation function with light in the red wavelength region. . Further, cholesteric resin layers having a central wavelength of reflected circularly polarized light of 470 nm, 550 nm, 640 nm, and 770 nm are respectively produced, and these cholesteric resin layers are arbitrarily selected, and the order of the central wavelengths of reflected light is 3 to 3 It can be obtained by laminating seven layers. When the cholesteric resin layers having different chiral structure pitches are laminated, it is preferable that the rotation directions of the circularly polarized light reflected by the cholesteric resin layers are the same. In addition, in order to obtain a liquid crystal display device having a wide viewing angle, the stacking order of the cholesteric resin layers having different chiral structure pitches may be ascending or descending in order of the chiral structure pitch. preferable. The lamination of these cholesteric resin layers may be merely overlaid, or may be fixed via an adhesive or an adhesive.
In order to manufacture this type of cholesteric resin layer, for example, a cholesteric resin layer corresponding to each pitch is manufactured and bonded by the above-described manufacturing method, or another pitch is formed on the cholesteric resin layer corresponding to a certain pitch. The cholesteric resin layer corresponding to the above may be stacked and manufactured by the method described above.

  Although there is no restriction | limiting in the thickness of a liquid-crystal hardened | cured material layer, When providing as a cholesteric resin layer in a circularly polarized light separation sheet, the dry film thickness becomes like this. Preferably it is 3.0 micrometers or more, More preferably, it is 3.5 micrometers or more, Preferably It is 10.0 μm or less, more preferably 8 μm or less. When the dry film thickness of the cholesteric resin layer is thinner than 3.0 μm, the reflectance tends to decrease, and conversely, when it is thicker than 10.0 μm, the cholesteric resin layer may be colored when observed from an oblique direction. In addition, the said dry film thickness points out the sum total of the film thickness of each layer, when a liquid-crystal hardened | cured material layer is two or more layers, and points out the film thickness when a liquid-crystal hardened | cured material layer is one layer.

  The circularly polarized light separating sheet may further include another layer as long as it includes at least the liquid crystal cured product layer as a cholesteric resin layer. For example, the transparent substrate, the alignment film, the protective layer, the adhesive layer, and the like described above can be used.

  Since the circularly polarized light separating sheet of the present invention includes a uniform liquid crystal cured product layer having no defects and unevenness in thickness, it can exhibit a uniform circularly polarized light separating function free from defects and variations from place to place. Moreover, according to the method for producing a circularly polarized light separating sheet of the present invention, the above excellent circularly polarized light separating sheet can be efficiently produced.

[3. (Brightness enhancement film)
The brightness enhancement film of the present invention includes at least the above-described circularly polarized light separating sheet and retardation film. The brightness enhancement film is usually provided in a liquid crystal display device or the like so that the circularly polarized light separating sheet and the retardation film are in this order from the light source side. In a liquid crystal display device or the like, when light from a light source such as a backlight passes through a brightness enhancement sheet, only predetermined polarized light is selectively reflected by the circularly polarized light separating sheet, and the remaining light is transmitted. The transmitted light further passes through the retardation film, is converted into predetermined polarized light, and enters the liquid crystal cell. On the other hand, the light reflected by the circularly polarized light separating sheet is reflected by other components of the liquid crystal display device (reflecting plate, etc.) and enters the circularly polarized light separating sheet again while changing the polarization state. The light that has passed through the predetermined polarized light passes through the circularly polarized light separating sheet, is converted into the predetermined polarized light by the retardation film, and enters the liquid crystal cell. As described above, the brightness enhancement sheet can increase the predetermined polarization necessary for display by the liquid crystal cell and supply it to the liquid crystal cell.

  The retardation film is an optical element that causes a phase difference in light incident thereon. Examples of the retardation film include a half-wave plate that generates a phase difference of 180 °, a quarter-wave plate that generates a phase difference of 90 °, and the like. The brightness enhancement film of the present invention usually includes a quarter wave plate as a retardation film.

  The quarter-wave plate may have a retardation Re (hereinafter, abbreviated as “Re” in some cases) in the front direction to be substantially a quarter wavelength of transmitted light. Here, the wavelength range of the transmitted light can be a desired range required for the brightness enhancement film, and specifically, is, 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. By having such a retardation value, the quarter-wave plate can exhibit a polarization conversion function, that is, a function of converting circularly polarized light into linearly polarized light.

  The quarter-wave plate desirably has a retardation Rth in the thickness direction (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 employing such a quarter-wave plate having Re value and Rth, the brightness enhancement film can improve the brightness and reduce the brightness unevenness, while also reducing the color unevenness of the emitted light.

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 (in-plane direction)) and gives the maximum refractive index. Ny represents a refractive index in a direction perpendicular to the thickness direction (in-plane direction) and orthogonal to the nx direction, and d represents a film thickness. Yes, the retardation Rth in the thickness direction is the formula II: Rth = {(nx + ny) / 2−nz} × d (where nx is the direction perpendicular to the thickness direction (in-plane direction) and has the maximum refractive index) Ny is a refractive index in a direction perpendicular to the thickness direction (in-plane direction) and orthogonal to the direction of nx, nz is a refractive index in the thickness direction, and d is It represents a 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 with a quarter-wave plate in the longitudinal direction and the width direction at intervals of 100 mm (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 quarter wavelength plate, for example, a stretched film formed by stretching a film-like polymer can be used. A preferable example is a quarter wavelength plate formed by stretching a resin film including a styrene resin layer. More preferably, the optical anisotropic element described below is mentioned.

  The optically anisotropic element constituting the quarter-wave plate preferably has a layer made of styrene resin. Here, the styrene-based resin is a polymer resin having a styrene structure as a part or all of the repeating units, and among them, 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. In general, it is 10,000 or more, preferably 15,000 or more, more preferably 20,000 or more, and usually 300,000 or less, preferably 250,000 or less, more preferably 200,000 or less.

  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. As the other thermoplastic resin, a resin having an alicyclic structure or a methacrylic resin can be suitably used.

  Examples of the resin having an alicyclic structure include alicyclic olefin polymers. 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.

  The methacrylic resin is a polymer containing methacrylic acid ester as a main component, and examples thereof include a homopolymer of methacrylic acid ester and a copolymer of methacrylic acid ester and other monomers. As the methacrylic acid ester, alkyl methacrylate is usually 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 preferable specific embodiment of the quarter-wave plate, 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 a styrene resin is stretched. A stretched multilayer film is mentioned.

  The method of laminating the styrenic resin that is the material of the a layer and the other thermoplastic resin that is the material of the b layer, and forming it into a multilayer film is not particularly limited. For example, a coextrusion T-die method, Examples include a coextrusion molding method such as a coextrusion inflation method and a coextrusion lamination method, a film lamination molding method such as dry lamination, and a coating molding method. 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 styrenic resin to be 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 can be provided between the a layer and the b layer, but the a layer and the b layer are directly laminated (that is, a laminate having a three-layer structure of b layer / a layer / b layer). Is preferred. 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 stretching can be preferably performed by uniaxial stretching or oblique stretching, and more preferably by uniaxial stretching or oblique stretching by a tenter.

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

  The quarter wavelength plate itself may also have a function as an optical compensation layer, but may additionally have an optical compensation layer in addition to the quarter wavelength plate. As such an optical compensation layer, the same optically anisotropic element as described above can be used, and a homeotropic liquid crystal alignment film obtained by homeotropic alignment of a liquid crystal molecule on a substrate and cured (Japanese Patent No. 399969). And a nematic hybrid liquid crystal alignment film (Japanese Patent Laid-Open No. 2000-66192) obtained by curing a state in which liquid crystal molecules are nematic hybrid aligned on a substrate can be used.

  The brightness enhancement film of the present invention may further include another layer in addition to the above-described circularly polarized light separating sheet and retardation film. For example, a light diffusion sheet that diffuses light incident thereon; a light collecting sheet that condenses light incident thereon; an adhesive layer for adhering optical elements constituting the brightness enhancement film; an antifouling property to the brightness enhancement film; Examples thereof include a protective film imparting functions such as scratch resistance; a hard coat layer; an anti-blocking layer.

  Since the brightness enhancement film of the present invention has a uniform liquid crystal cured product layer free from defects and thickness unevenness, when provided in a liquid crystal display device or the like, the brightness is uniformly increased without defects and brightness unevenness. Can do.

[4. Liquid crystal display device)
The liquid crystal display device of the present invention includes the brightness enhancement film of the present invention and a liquid crystal panel. The liquid crystal panel is not particularly limited, and those used in liquid crystal display devices can be used as appropriate. For example, a TN (Twisted Nematic) type liquid crystal panel, an STN (Super Twisted Nematic) type liquid crystal panel, a HAN (Hybrid Alignment Nematic) type liquid crystal panel, an IPS (In Plane Switching) type liquid crystal panel, and a VA (vertical type liquid crystal panel). Examples thereof include a MVA (Multiple Vertical Alignment type liquid crystal panel) and an OCB (Optical Compensated Bend) type liquid crystal panel.

  The liquid crystal display device of the present invention usually further includes a backlight. In this case, the brightness enhancement film is arranged between the backlight and the liquid crystal panel. More specifically, the brightness enhancement film of the present invention is disposed between the backlight of the liquid crystal display device and the liquid crystal cell so that the layer of the circularly polarized light separating sheet is on the backlight side of the layer of the retardation film. , Brightness improvement can be achieved.

  The liquid crystal display device of the present invention comprises a liquid crystal cured product layer produced using the liquid crystal layer forming composition of the present invention. Since there is no defect in the liquid crystal cured product layer, the liquid crystal display device of the present invention can realize high image quality without defects even in the display image. Moreover, since there is no thickness unevenness in the liquid crystal cured layer, it is possible to suppress the occurrence of uneven brightness in the display image. Furthermore, since a wide variety of high Δn polymerizable liquid crystalline compounds can be used, the degree of freedom in design can be increased.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and can be arbitrarily modified without departing from the gist of the present invention. In the following description, “parts” representing amounts represent “parts by weight” unless otherwise specified. In the structural formula, Me represents a methyl group, and Et represents an ethyl group.

[Examples 1 to 7 and Comparative Examples 1 and 2]
(Preparation of transparent resin substrate having alignment film)
Both surfaces of a film made of an alicyclic olefin polymer (trade name “ZEONOR FILM ZF14-100” manufactured by Optes Co., Ltd.) were subjected to corona discharge treatment. A 5% by weight aqueous polyvinyl alcohol solution was applied to one side of the film using a # 2 wire bar, and the coating film was dried to form an alignment film having a thickness of 0.1 μm. Next, the alignment film was rubbed to prepare a transparent resin substrate having the alignment film.

(Preparation of cholesteric liquid crystal composition)
Cholesteric liquid crystal compositions were prepared as liquid crystal layer forming compositions by mixing the components at the blending ratio (weight ratio) shown in Table 1.
In addition, the detail of each component contained in a cholesteric liquid crystal composition is as follows.

As compound 1, the following compounds were used. This compound 1 is a high Δn polymerizable liquid crystalline compound, and its refractive index anisotropy is 0.22.

As the compound 2, the following compound was used. This compound 2 is a compound having no liquid crystallinity.

As the compound 3, the following compounds were used. This compound 3 is a high Δn polymerizable liquid crystalline compound, and its refractive index anisotropy is 0.23.

As the chiral agent, trade name LC756 (manufactured by BASF) was used.
As a polymerization initiator, trade name Irgacure OXE02 (manufactured by Ciba Japan) was used.
As the surfactant, a fluorine-based surfactant (trade name “Factent 209F” manufactured by Neos) was used.

(Production of circularly polarized light separating sheet)
At a temperature of 23 ° C., the cholesteric liquid crystal composition prepared as described above was applied to the surface having the alignment film of the transparent resin substrate having the alignment film prepared above using a # 10 wire bar. As a result, a liquid crystal layer was formed. A process comprising subjecting this coating film to orientation treatment at 100 ° C. for 5 minutes, and subjecting the coating film to irradiation with weak ultraviolet rays of 0.1 to 45 mJ / cm ² , followed by heating treatment at 100 ° C. for 1 minute. After repeating the above twice, a circularly polarized light separating sheet having a cholesteric resin layer (corresponding to a liquid crystal cured product layer) having a dry film thickness of 5 μm is prepared by irradiating with an ultraviolet ray of 2000 mJ / cm ^{2 in} a nitrogen atmosphere and curing. did.

(Evaluation of circularly polarized light separating sheet)
About the circularly polarized light separating sheet produced above, the circularly polarized light separating sheet is placed on a light box in an environment of a temperature of 23 ° C. and a humidity of 50%, and color defects and point defects derived from crystal precipitation are visually observed through a polarizing plate. did. The evaluation results are shown in Table 1.

As shown in Table 1, in Examples 1 to 7 of the present invention, compared to Comparative Examples 1 and 2, circularly polarized light separating sheets with less color unevenness and defects can be obtained.
Here, comparing Examples 1 and 2 with Example 3, it can be seen that a circularly polarized light separating sheet with particularly little color unevenness can be obtained when cyclopentanone is used as the cyclic ketone solvent. Further, when Examples 1 and 2 are compared with Examples 4 and 5, it is found that when 1,3-dioxolane is used as the cyclic ether solvent, a circularly polarized light separating sheet with particularly little color unevenness can be obtained. Furthermore, when Examples 1 and 2 are compared with Example 6, it can be seen that there is a suitable range for the ratio of the solvent having a cyclic ketone structure and the solvent having a cyclic ether structure.

(Production of 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. The rubber particles have a spherical three-layer structure including an inner core layer, an inner layer, and an outer layer in order from the inside. The inner core layer is a cross-linked polymer of methyl methacrylate and a small amount of allyl methacrylate, and the inner layer is a main component. It is a soft elastic copolymer obtained by crosslinking copolymerization of butyl acrylate, styrene and a small amount of allyl acrylate, 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. This laminated film is a tenter stretching machine so that the slow axis is inclined at 45 ° with respect to the MD direction (machine direction, the film flow direction in the production line, the longitudinal direction of the long film). The film was stretched obliquely at a stretching temperature of 134 ° C. and a draw ratio of 1.8 times to obtain an optically anisotropic element.
The retardation Re in the front direction of the optically anisotropic element was 140 nm, and the retardation Rth 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.

(Preparation of diffusion adhesive layer)
Polyethylene terephthalate separator (trade name “PET50AL”, manufactured by Lintec Corporation), base resin (trade name “SK Dyne 2094”, manufactured by Soken Chemicals Co., Ltd., acrylate copolymer, solid content ratio 25% , Solvent: ethyl acetate / 2-butanone = 93/7)) 400 parts, polyfunctional epoxy crosslinking agent (trade name “E-AX”, manufactured by Soken Chemical Co., Ltd.) 1.1 parts and fine powder (trade name “ A pressure-sensitive adhesive composition having a composition consisting of 4.3 parts of Chemisnow MX300 ”(manufactured by Soken Chemical Co., Ltd.) was applied using a blade having a gap of 200 μm. It dried at 100 degreeC for 2 minutes, the 20-micrometer-thick adhesion layer was formed, and the laminated body which has a layer structure of a separator-diffusion adhesion layer was obtained.

(Production of brightness enhancement film)
The corona discharge treated surface of the optically anisotropic element and the separator-diffusion adhesive layer side surface of the laminate having the layer structure of the diffusion adhesive layer are bonded together to form an optically anisotropic element-diffusion adhesive layer- A laminate A having a separator layer structure was obtained.
The surface of the cholesteric resin layer of the circularly polarized light separating sheet produced as described above was subjected to corona discharge treatment so that the wetting index was 60 mN / m. The separator of the laminate A is peeled off from the diffusion adhesive layer, and the exposed diffusion adhesive layer and the corona discharge treated surface of the circularly polarized light separating sheet are bonded together to form an optically anisotropic element-diffusion adhesive layer-circularly polarized light separating sheet. A brightness enhancement film having the following layer structure was obtained.

(Evaluation of brightness enhancement film)
Disassemble the commercially available liquid crystal television (BRAVIA KDL32J5000 manufactured by Sony Corporation), take out the diffusion sheet and the brightness enhancement film, and instead cut the built-in brightness enhancement film into an appropriate size suitable for the display surface, Reassembled. The obtained television was driven, and the unevenness of the display surface and the visual approval / disapproval of the point defect existing in the circularly polarized light separating sheet were visually observed and evaluated. The results are shown in Table 2.

  From Table 2, it can be seen that if the circularly polarized light separating sheet of the present invention is used, a brightness enhancement film and a liquid crystal display device free from defects on the display surface and free from defects that can be visually recognized can be realized.

The composition for forming a liquid crystal layer of the present invention can be used in any field relating to the production of a liquid crystal layer, and is particularly suitable for use in forming a cholesteric resin layer.
The circularly polarized light separating sheet and the brightness enhancement film of the present invention can be used as an optical element for any application, but are particularly suitable for use in a liquid crystal display device.
The liquid crystal display device of the present invention can be suitably provided in any device as a display device.

Claims (7)

A liquid crystalline compound having two or more polymerizable functional groups in one molecule and having a refractive index anisotropy of 0.20 or more measured by the Senarmon method ;
A solvent having a cyclic ketone structure;
Look containing a solvent having a cyclic ether structure,
A composition for forming a liquid crystal layer , wherein the solvent having a cyclic ketone structure and the solvent having a cyclic ether structure are in a weight ratio of 35/35 or more and 90/10 or less .   The composition for forming a liquid crystal layer according to claim 1, wherein the solvent having a cyclic ketone structure is cyclopentanone.   The composition for forming a liquid crystal layer according to claim 1 or 2, wherein the solvent having a cyclic ether structure is 1,3-dioxolane. The circularly-polarized-light-separation sheet obtained through the process of apply | coating to the base material the composition for liquid crystal layer formation as described in any one of Claims 1-3 , and hardening. The process of apply | coating the composition for liquid crystal layer formation as described in any one of Claims 1-3 to a base material, and obtaining a liquid crystal layer,
And a step of curing the liquid crystal layer. A brightness enhancement film comprising the circularly polarized light separating sheet and the retardation film according to claim 4 . A liquid crystal display device comprising the brightness enhancement film according to claim 6 and a liquid crystal panel.