Optical laminate and circular polarizing plate

Abstract

Provided is an optical laminate which is capable of suppressing reflected light even when observed from an oblique direction, and is capable of suppressing a decrease in oblique contrast. The optical laminate (100) comprises: a first optically anisotropic layer (30) composed of a birefringence inducing material; and a second optically anisotropic layer (40) composed of a polymerizable liquid crystal material and laminated adjacent to the first optically anisotropic layer (30), wherein the Nz coefficient of the first optically anisotropic layer (30) is -0.5≤Nz≤0.5, the second optically anisotropic layer (40) has an optical characteristic of a positive A plate, one of the first optically anisotropic layer (30) and the second optically anisotropic layer (40) has a phase difference of 1 / 4 wavelength, and the other has a phase difference of 1 / 2 wavelength.

Description

Related Application

[0001] This application claims the priority of Japanese Patent Application No. 2020-170076 filed on October 7, 2020, and the entire disclosure of which is incorporated herein by reference in its entirety and made a part of this application.

Technical Field

[0002] The present invention relates to an optical laminate that can be used as a retardation plate, and a circular polarizing plate including the same.

Background Art

[0003] For thin display devices typified by liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs), various retardation plates are used to improve display quality. For example, in OLEDs such as organic EL display devices, a broadband circular polarizing plate is used to suppress reflection.

[0004] As a retardation plate used for a circular polarizing plate, Patent Document 1 (Japanese Patent Application Laid-Open No. 10-68816) discloses a quarter-wave plate in which the retardation of birefringent light is a quarter wavelength and a half-wave plate in which the retardation of birefringent light is a half wavelength, and a retardation plate characterized in that they are bonded together in a state where their optical axes intersect.

[0005] Further, Patent Document 2 (Japanese Patent No. 4646030) describes that, as a retardation plate for a liquid crystal display device, a first retardation plate having a retardation of a quarter wavelength and a second retardation plate having a retardation of a half wavelength are arranged, and the Nz coefficient of the second retardation plate is 0 or more and less than 1.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, Patent Documents 1 and 2 do not describe the relationship between the Nz coefficients of both the quarter-wave plate and the half-wave plate, nor do they describe using different Nz coefficients. For the quarter-wave plate and the half-wave plate, generally, a stretched film or a film obtained by aligning a liquid crystal material on an alignment film is used, and such a film is an optically uniaxial film with an Nz coefficient of 1. For example, when using optically uniaxial films for both the quarter-wave plate and the half-wave plate and laminating them to form a circular polarizing plate, when attached to an OLED panel, the reflected light from the electrodes cannot be sufficiently suppressed when observed from an oblique direction of the panel, resulting in a problem that the oblique viewing contrast of the OLED panel decreases.

[0008] In addition, in Patent Documents 1 and 2, it is necessary to use an adhesive to bond the quarter-wave plate and the half-wave plate, and the birefringence of the adhesive itself may have an impact.

[0009] Therefore, an object of the present invention is to provide an optical laminate that can suppress reflected light even when observed from an oblique direction and can suppress a decrease in oblique viewing contrast.

Means for Solving the Problems

[0010] As a result of intensive research to solve the above problems, the present inventor has found that an optical laminate having specific Nz coefficients in a layer having a quarter-wave retardation and a layer having a half-wave retardation laminated adjacent to each other can suppress reflected light even when observed from an oblique direction and can suppress a decrease in oblique viewing contrast, thereby completing the present invention.

[0011] That is, the present invention can be configured in the following aspects. 〔Aspect 1〕 An optical laminate including a first optically anisotropic layer made of a birefringence-inducing material and a second optically anisotropic layer made of a polymerizable liquid crystal material and laminated adjacent to the first optically anisotropic layer, wherein the Nz coefficient of the first optically anisotropic layer is -0.5 ≦ Nz ≦ 0.5 (preferably -0.5 ≦ Nz < 0 or 0 < Nz ≦ 0.5, more preferably -0.3 ≦ Nz < 0 or 0 < Nz ≦ 0.3), and the second optically anisotropic layer has the optical characteristics of a positive A plate, An optical laminate in which one of the first optically anisotropic layer and the second optically anisotropic layer has a retardation of 1 / 4 wavelength and the other layer has a retardation of 1 / 2 wavelength. 〔Aspect 2〕 The optical laminate according to Aspect 1, wherein the slow axis direction of the first optically anisotropic layer and the slow axis direction of the second optically anisotropic layer intersect at an angle that is non-parallel and non-orthogonal. 〔Aspect 3〕 The optical laminate according to Aspect 1 or 2, wherein the first optically anisotropic layer has a retardation of 1 / 2 wavelength and an Nz coefficient of 0 ≦ Nz ≦ 0.5 (preferably 0 < Nz ≦ 0.4, more preferably 0.1 ≦ Nz ≦ 0.3). 〔Aspect 4〕 The optical laminate according to Aspect 1 or 2, wherein the first optically anisotropic layer has a retardation of 1 / 4 wavelength and an Nz coefficient of -0.5 ≦ Nz ≦ 0.5 (preferably -0.5 ≦ Nz ≦ 0, more preferably -0.3 ≦ Nz ≦ -0.1). 〔Aspect 5〕 A circular polarizing plate in which the optical laminate according to any one of Aspects 1 to 4 and a linear polarizing plate are laminated.

[0012] In addition, any combination of at least two components disclosed in the claims and / or the specification is included in the present invention. In particular, any combination of two or more claims described in the claims is included in the present invention.

Advantages of the Invention

[0013] According to the optical laminate of the present invention, reflected light can be suppressed even when observed from an oblique direction, it is possible to suppress a decrease in oblique viewing contrast, and it can be used as a circular polarizing plate by laminating it with a linear polarizing plate.

Brief Description of Drawings

[0014] This invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. The drawings are not necessarily shown at a fixed scale and are exaggerated for showing the principle of the present invention. However, the embodiments and the drawings are for illustration and explanation only and should not be used to define the scope of this invention. The scope of this invention is determined by the appended claims.

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0015] [Optical laminate] The optical laminate of the present invention includes a first optically anisotropic layer made of a birefringence - inducing material and a second optically anisotropic layer made of a polymerizable liquid crystal material and laminated adjacent to the first optically anisotropic layer.

[0016] In the present invention, the birefringence - inducing material refers to a material capable of axially selectively inducing birefringence by molecular motion due to light irradiation (preferably light irradiation and heat - cooling treatment) and the molecular orientation based thereon. For example, the birefringence - inducing material may include a side - chain liquid - crystalline polymer having a photosensitive group and a side - chain structure capable of forming a liquid - crystal structure, and may have a property of inducing molecular orientation by a photoreaction of the photosensitive group in the side - chain. Examples of the photoreaction caused by the photosensitive group include a photodimerization reaction, a photo - isomerization reaction, a photo - Fries rearrangement reaction, etc.

[0017] As the side - chain structure capable of forming a liquid - crystal structure, it may exhibit liquid - crystallinity by having a mesogenic group which is a rigid site exhibiting liquid - crystallinity in the side - chain structure, or may have a structure capable of forming a dimer by hydrogen bonding with another polymer or another side - chain of the same polymer, and exhibit liquid - crystallinity by forming a mesogenic structure by dimerization thereof.

[0018] The mesogenic group or mesogenic structure is composed of two or more aromatic rings or aliphatic rings and a linking group connecting them, and the linking group may be a covalent bond or a hydrogen bond. Examples of the aromatic ring include a benzene ring, a naphthalene ring, a heterocyclic ring (for example, an oxygen - containing heterocyclic ring such as a furan ring, a pyran ring; a nitrogen - containing heterocyclic ring such as a pyrrole ring, an imidazole ring), etc., and examples of the aliphatic ring include a cyclohexane ring, etc. Note that these aromatic rings or aliphatic rings may have a substituent, and examples of the substituent include an alkyl group (for example, C 1-6 alkyl group, preferably C 1-4 alkyl group), an alkyloxy group (for example, C 1-6 alkyloxy group, preferably C 1-4(alkyloxy group), alkenyl group (e.g., C 2-6 alkenyl group, preferably C 2-4 alkenyl group), alkynyl group (e.g., C 2-6 alkynyl group, preferably C 2-4 alkynyl group), halogen atom, etc. may be mentioned. As the linking group, when it is a covalent bond, a single bond, -O-, -COO-, -OCO-, -N=N-, -NO=N-, -C=C-, -C≡C-, -CO-C=C-, -CH=N-, an alkylene group, etc. may be mentioned. When it is a hydrogen bond, a side chain structure having a carboxy group at the end, etc. may be mentioned. In this case, hydrogen bonds are formed between carboxy groups.

[0019] The photosensitive group is not particularly limited as long as it is a functional group capable of causing a photoreaction by light energy. For example, a chalcone group, a coumarin group, a cinnamoyl group, a cinnamic acid group, a cinnamylideneacetic acid group, a biphenylacryloyl group, a furylacryloyl group, a naphthylacryloyl group, an azobenzene group, a benzylideneaniline group or derivatives thereof, etc. may be mentioned. Preferably, a cinnamoyl group may be used.

[0020] The side chain type liquid crystalline polymer may have at least a side chain structure having both a photosensitive group and a structure capable of forming a liquid crystal structure in the repeating unit. The photosensitive group and the mesogen group or mesogen structure may exist independently in the side chain structure or may exist complexly sharing a chemical structure.

[0021] The side chain type liquid crystalline polymer may have at least one side chain structure selected from the group consisting of side chain structures represented by the following formulas (1) and (2) as a side chain structure having both a photosensitive group and a structure capable of forming a liquid crystal structure.

[0022] [Chemical formula]

[0023] In the formula, r is an integer from 1 to 12; s is 0 or 1; t is 0 or 1; X1 represents a single bond, C 1-3 an alkylene group, -C=C-, -C≡C-, -O-, -N=N-, -COO-, or -OCO-; R1 represents a hydrogen atom, an alkyl group (e.g., C 1-6 alkyl group, preferably C 1-4 alkyl group), or a hydroxyalkyl group (e.g., hydroxy C 1-6 alkyl group, preferably hydroxy C 1-4 alkyl group); R2 and R3 are the same or different and represent a hydrogen atom, an alkyl group (e.g., C 1-6 alkyl group, preferably C 1-4 alkyl group), an alkyloxy group (e.g., C 1-6 alkyloxy group, preferably C 1-4 alkyloxy group), a halogen atom or a cyano group. Note that R2 and R3 each represent substituents at four positions on the benzene ring, and may represent the same or different substituents at the four positions.

[0024]

Chemical formula

[0025] In the formula, r' is an integer from 1 to 12; s' is 0 or 1; u is an integer from 1 to 12; X2 represents a single bond, C 1-3 an alkylene group, -C=C-, -C≡C-, -O-, -N=N-, -COO-, or -OCO-; W represents a cinnamoyloxy group, a chalcone group, a biphenylacryloyloxy group, a furylacryloyloxy group, a naphthylacryloyloxy group, or a derivative group thereof; R4 and R5 are the same or different and represent a hydrogen atom, an alkyl group (e.g., C 1-6 alkyl group, preferably C 1-4 alkyl group), an alkyloxy group (e.g., C 1-6 alkyloxy group, preferably C 1-4represents an alkyloxy group, a halogen atom or a cyano group. Note that R4 and R5 each represent substituents at four positions on the benzene ring, and may represent the same or different substituents at the four positions.

[0026] The side-chain type liquid crystalline polymer preferably contains at least the side-chain structure represented by the above formula (1). More preferably, in the above formula (1), t represents 0, and it may contain a side-chain structure having a chemical structure in which R1 represents a hydrogen atom. Such a side-chain structure has a cinnamic acid group which is a photosensitive group at the end. Since the carboxy group in the cinnamic acid group has hydrogen-bonding property, it can form a hydrogen bond with the carboxy group of the benzoic acid group or cinnamic acid group at the end of the side chain of another polymer or the same polymer and dimerize to form a mesogen structure.

[0027] Note that the side-chain structures represented by the above formulas (1) and (2) represent the chemical structures at the ends of the side chains in the repeating unit, and various chemical structures may be included between these side-chain structures and the main-chain structure as long as the effects of the present invention are not impaired.

[0028] The side-chain type liquid crystalline polymer may be a homopolymer composed of the same repeating unit containing the above side-chain structure or a copolymer containing a repeating unit having a side-chain structure different in structure from the repeating unit containing the above side-chain structure. Examples of the main-chain structure include structures formed by polymerizing hydrocarbons, acrylates, methacrylates, siloxanes, maleimides, N-phenylmaleimides, etc.

[0029] When the side-chain type liquid crystalline polymer is a copolymer, it may have a repeating unit having no photosensitive group and / or a structure capable of forming a liquid crystal structure.

[0030] The birefringence-induced material of the present invention may contain a low-molecular compound together with the side-chain liquid crystalline polymer in order to promote the orientation of the side chains of the side-chain liquid crystalline polymer. As the low-molecular compound, those having substituents such as biphenyl, terphenyl, phenyl benzoate, azobenzene, etc. known as mesogenic components, and such substituents and functional groups such as allyl, acrylate, methacrylate, cinnamic acid group (or its derivative group), etc. are preferably used, which have liquid crystallinity bonded via a spacer (for example, an (oxy)alkylene group having 1 to 15 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms)). These low-molecular compounds may be used alone or in combination of two or more.

[0031] In the present invention, the polymerizable liquid crystal material is a composition containing a monofunctional or bifunctional polymerizable liquid crystal compound containing at least a reactive functional group and a mesogenic group, and includes the composition after forming a crosslinked structure by polymerization by light or heat or reaction with a crosslinking agent.

[0032] The polymerizable liquid crystal compound may be a liquid crystal monomer or a liquid crystal polymer. For example, as the polymerizable liquid crystal compound, there may be mentioned a polymerizable liquid crystal monomer and / or a polymerizable liquid crystal polymer having a polymerizable functional group that polymerizes by light or heat, and a crosslinkable liquid crystal monomer and / or a crosslinkable liquid crystal polymer having a crosslinkable functional group capable of introducing a crosslinked structure by reaction with a crosslinking agent, etc.

[0033] The polymerizable liquid crystal compound is a monomer having a mesogenic group or a polymer having a unit composed of a mesogenic group, which can form a liquid crystal structure and is not particularly limited as long as it has polymerizability and / or crosslinkability, and various polymerizable liquid crystal compounds can be used. Examples of the polymerizable liquid crystal compound include Schiff base type, biphenyl type, terphenyl type, ester type, thioester type, stilbene type, trans type, azoxy type, azo type, phenylcyclohexane type, pyrimidine type, cyclohexylcyclohexane type, trimesic acid type, triphenylene type, torquene type, phthalocyanine type, porphyrin type liquid crystal compounds having a molecular skeleton, or mixtures of these compounds, etc. Any compound that exhibits a nematic, cholesteric or smectic liquid crystal phase may be used. As an example, a photopolymerizable nematic liquid crystal monomer may be used as the polymerizable liquid crystal compound.

[0034] The unit composed of the mesogenic group may be in the main chain or the side chain of the liquid crystal polymer. Examples of the main chain type liquid crystal polymer include polyester type, polyamide type, polycarbonate type, polyimide type, polyurethane type, polybenzimidazole type, polybenzoxazole type, polybenzothiazole type, polyazomethine type, polyester amide type, polyester carbonate type, polyester imide type liquid crystal polymers, or mixtures of these. Examples of the side chain type liquid crystal polymer include liquid crystal polymers in which a mesogenic group is bonded as a side chain to a polymer having a linear or cyclic structure backbone chain such as polyacrylate type, polymethacrylate type, polyvinyl type, polysiloxane type, polyether type, polymalonate type, or mixtures of these.

[0035] In addition, when the polymerizable liquid crystal compound has a polymerizable functional group, the polymerizable liquid crystal material may contain a photoinitiator and / or a thermal initiator.

[0036] As the photoinitiator, commercially available photoinitiators such as Irgacure 907, Irgacure 184, Irgacure 651, Irgacure 819, Irgacure 250, Irgacure 369 (all of the above are manufactured by Ciba Japan Co., Ltd.), Seikol BZ, Seikol Z, Seikol BEE (all of the above are manufactured by Seiko Chemical Co., Ltd.), Kayacure BP100 (manufactured by Nippon Kayaku Co., Ltd.), Kayacure UVI-6992 (manufactured by Dow), Adeka Optomer SP-152 or Adeka Optomer SP-170 (all of the above are manufactured by Adeka Corporation), TAZ-A, TAZ-PP (both are manufactured by Nippon Sieber Hegner Co., Ltd.) and TAZ-104 (manufactured by Sanwa Chemical Co., Ltd.) can be used.

[0037] As the thermal initiator, examples include azo compounds such as azobisisobutyronitrile, hydrogen peroxide, persulfates, peroxides such as benzoyl peroxide, etc.

[0038] The content of the polymerization initiator is preferably 0.01 to 20% by weight, more preferably 0.03 to 10% by weight, and even more preferably 0.05 to 8% by weight based on the total weight of the polymerizable liquid crystal material. Within the above range, polymerization can be carried out without disturbing the alignment of the polymerizable liquid crystal compound.

[0039] In addition, when a photoinitiator is used as the polymerization initiator, a photosensitizer may be used in combination. Examples of the photosensitizer include xanthone compounds such as xanthone and thioxanthone (for example, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, etc.); anthracene compounds such as anthracene and alkoxy group-containing anthracene (for example, dibutoxyanthracene, etc.); phenothiazine; rubrene, etc.

[0040] Furthermore, when the polymerizable liquid crystal compound has a crosslinkable functional group, the polymerizable liquid crystal material may contain an appropriate crosslinking agent. In this case, the polymerizable liquid crystal compound may also be a liquid crystal compound that can be orientation-fixed by means such as crosslinking (thermal crosslinking or photo crosslinking) in the liquid crystal state or in a state cooled below the liquid crystal transition temperature.

[0041] Examples of the crosslinkable functional group include a vinyl group, a vinyloxy group, a 1-chlorovinyl group, an isopropenyl group, a 4-vinylphenyl group, an acryloyloxy group, a methacryloyloxy group, an oxiranyl group, an oxetanyl group, and the like. Among them, an acryloyloxy group, a methacryloyloxy group, a vinyloxy group, an oxiranyl group, and an oxetanyl group are preferable, and an acryloyloxy group is particularly more preferable.

[0042] Examples of the crosslinking agent include polyfunctional compounds having two or more functional groups in the molecule. Examples of the polyfunctional compound include compounds having an isocyanate group, a carbodiimide group, an aziridine group, an azetidine group, an oxazoline group, an epoxy group, an acryloyloxy group, a methacryloyloxy group, a vinyloxy group, and the like. When using a polyisocyanate-based compound, which is a polyfunctional compound having two or more isocyanate groups in the molecule, known polyisocyanate-based compounds can be used. For example, examples of the polyisocyanate-based compound include diisocyanate compounds and triisocyanate compounds. Examples of the diisocyanate compound include phenylenediisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, methylcyclohexylene diisocyanate, bis(isocyanatomethyl)cyclohexane, methylene bis(cyclohexyl isocyanate), isophorone diisocyanate, and a condensation compound of hexamethylene diisocyanate and diol. Examples of the triisocyanate compound include an isocyanurate form of a diisocyanate such as hexamethylene diisocyanate, a biuret form, and an adduct form which is an adduct of a diisocyanate such as hexamethylene diisocyanate and trimethylolpropane.

[0043] The content of the crosslinking agent may be 0.01 to 5% by weight, preferably 0.05 to 3% by weight, more preferably 0.1 to 1.5% by weight, based on the total weight of the polymerizable liquid crystal material, from the viewpoint of suppressing the deterioration of the orientation and optical properties of the second optically anisotropic layer due to the reaction with the liquid crystalline polymer.

[0044] In the optical laminate of the present invention, one of the first optically anisotropic layer and the second optically anisotropic layer has a retardation of 1 / 4 wavelength, and the other layer has a retardation of 1 / 2 wavelength. That is, the optical laminate of the present invention is an optical laminate in which the first optically anisotropic layer has a retardation of 1 / 4 wavelength and the second optically anisotropic layer has a retardation of 1 / 2 wavelength, or an optical laminate in which the first optically anisotropic layer has a retardation of 1 / 2 wavelength and the second optically anisotropic layer has a retardation of 1 / 4 wavelength. The retardation of 1 / 4 wavelength means the case where the in-plane retardation value (Re) is 1 / 4 of the design wavelength. For example, it may be 1 / 4 of the design wavelength - 50 nm to 1 / 4 of the design wavelength + 50 nm. For example, when the design wavelength is 550 nm, the Re of the layer having a retardation of 1 / 4 wavelength may be 88 to 188 nm. The retardation of 1 / 2 wavelength means the case where the in-plane retardation value (Re) is 1 / 2 of the design wavelength. For example, it may be 1 / 2 of the design wavelength - 50 nm to 1 / 2 of the design wavelength + 50 nm. For example, when the design wavelength is 550 nm, the Re of the layer having a retardation of 1 / 2 wavelength may be 225 to 325 nm. Here, the in-plane retardation value (Re) is a parameter defined by the product (ΔNxy × d) of the anisotropy (ΔNxy = |nx - ny|) of the refractive indices (nx, ny) of two orthogonal axes in the film plane and the film thickness d (nm), and is a measure indicating optical isotropy and anisotropy. In the present specification, the in-plane retardation value (Re) may be a measured value for light with a wavelength of 550 nm.

[0045] In the optical laminate of the present invention, the Nz coefficient of the first optically anisotropic layer made of a birefringence-inducing material is -0.5 to 0.5, and the second optically anisotropic layer made of a polymerizable liquid crystal material has the optical characteristics of a positive A plate. In the present invention, it has been found that an optical laminate having specific Nz coefficients in a layer having a quarter-wave retardation and a layer having a half-wave retardation, which are laminated adjacent to each other, can suppress reflected light even when observed from an oblique direction, and can suppress a decrease in oblique viewing contrast. Here, in the present specification, the Nz coefficient is an index of the refractive index component represented by Nz = (nx - nz) / (nx - ny) when the in-plane principal refractive indices are nx (slow axis direction) and ny (fast axis direction), and the refractive index in the thickness direction is nz.

[0046] A positive A plate refers to a positive uniaxial retardation optical element whose refractive index distribution satisfies nx > ny = nz. When having the optical characteristics of a positive A plate, in the present invention, the description "ny = nz" in the positive A plate does not necessarily require the refractive index in the in-plane fast axis direction (ny) and the refractive index in the thickness direction (nz) to exactly match. For example, it may be about Nz = 1 (for example, within the range of the Nz coefficient being 0.95 to 1.05).

[0047] From the viewpoint of further improving the viewing angle characteristics of reflected light, in the optical laminate of the present invention, the Nz coefficient of the first optically anisotropic layer is preferably -0.5 ≦ Nz < 0 or 0 < Nz ≦ 0.5, and more preferably -0.3 ≦ Nz < 0 or 0 < Nz ≦ 0.3.

[0048] From the perspective of further improving the viewing angle characteristics of reflected light, the first optical anisotropic layer of the optical laminate of the present invention preferably has a retardation of 1 / 2 wavelength and an Nz coefficient of 0 ≦ Nz ≦ 0.5, more preferably 0 < Nz ≦ 0.4, and even more preferably 0.1 ≦ Nz ≦ 0.3. That is, the first optical anisotropic layer has a retardation of 1 / 2 wavelength and an Nz coefficient of 0 ≦ Nz ≦ 0.5 (more preferably 0 < Nz ≦ 0.4, and even more preferably 0.1 ≦ Nz ≦ 0.3), and the second optical anisotropic layer has a retardation of 1 / 4 wavelength and has the optical characteristics of a positive A plate (for example, the Nz coefficient is 0.95 ≦ Nz ≦ 1.05), and the optical laminate may be such.

[0049] When the first optical anisotropic layer of the optical laminate of the present invention has a retardation of 1 / 4 wavelength, the Nz coefficient is preferably -0.5 ≦ Nz ≦ 0.5, more preferably -0.5 ≦ Nz ≦ 0, and even more preferably -0.3 ≦ Nz ≦ -0.1. That is, the first optical anisotropic layer has a retardation of 1 / 4 wavelength and an Nz coefficient of -0.5 ≦ Nz ≦ 0.5 (more preferably -0.5 ≦ Nz ≦ 0, and even more preferably -0.3 ≦ Nz ≦ -0.1), and the second optical anisotropic layer has a retardation of 1 / 2 wavelength and has the optical characteristics of a positive A plate (for example, the Nz coefficient is 0.95 ≦ Nz ≦ 1.05), and the optical laminate may be such.

[0050] The thickness of the first optical anisotropic layer can be appropriately adjusted according to the desired in-plane retardation value (Re). For example, it may be 0.1 to 20 μm, preferably 0.3 to 15 μm, and more preferably 0.5 to 10 μm. Also, the thickness of the second optical anisotropic layer can be appropriately adjusted according to the desired in-plane retardation value (Re). It may be 0.1 to 20 μm, preferably 0.3 to 15 μm, and more preferably 0.5 to 10 μm. Also, the ratio of the thickness of the first optical anisotropic layer to the second optical anisotropic layer (first optical anisotropic layer / second optical anisotropic layer) may be 1 / 10 to 10 / 1, preferably 1 / 8 to 8 / 1, and more preferably 1 / 5 to 5 / 1.

[0051] The thickness of the optical laminate of the present invention may be, for example, 1 to 40 μm, preferably 2 to 30 μm, and more preferably 3 to 20 μm.

[0052] From the viewpoint of using the optical laminate of the present invention for a circular polarizing plate, the slow axis direction of the first optically anisotropic layer and the slow axis direction of the second optically anisotropic layer may intersect at an angle that is non-parallel and non-orthogonal. For example, the angle formed by the slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer may be 5 to 85°, preferably 8 to 80°, and more preferably 10 to 75°.

[0053] From the viewpoint of arbitrarily setting the angle formed by the slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer, the optical laminate of the present invention is preferably manufactured by the manufacturing method described later. In that case, the first optically anisotropic layer may be composed of an adjacent layer and an internal layer having different slow axes from each other, and the optical laminate in which the adjacent layer is in contact with the second optically anisotropic layer may be used. The adjacent layer may exist only at the interface of the first optically anisotropic layer in contact with the second optically anisotropic layer. For example, the adjacent layer may be formed by subjecting the surface of the first optically anisotropic layer to an alignment treatment so as to apply an orientation different from that of the internal layer. Here, the alignment treatment may be performed by the mode of the surface alignment step in the manufacturing method described later. Since the influence of the alignment in the adjacent layer can be regarded as extremely small, the slow axis of the internal layer of the first optically anisotropic layer may be measured as the slow axis of the entire first optically anisotropic layer, and the angle formed by the slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer may be measured.

[0054] In the optical laminate of the present invention, particularly in the first optically anisotropic layer, it is preferable that the slow axis direction is constant in the plane. In the manufacturing method of the preferred embodiment described later, since the polarization state is not converted (for example, from linearly polarized light to elliptically polarized light) by irradiating the lower layer with polarized light through the alignment layer, it is possible to make the slow axis direction constant without disturbing the molecular orientation.

[0055] The optical laminate of the present invention can be used as a retardation plate and can be used for various optical members (antireflection films, optical compensation films, etc.). The optical laminate of the present invention can be used, for example, as a circularly polarized plate used as an antireflection film for OLEDs such as organic EL display devices by laminating it with a linear polarizer.

[0056] In the circularly polarized plate, the above optical laminate and the linear polarizer are laminated, and the linear polarizer may be laminated on the layer side having a retardation of 1 / 2 wavelength of the optical laminate. The lamination of the linear polarizer and the optical laminate may be performed by directly manufacturing and laminating the optical laminate on the linear polarizer as shown in the manufacturing method described later, that is, a circularly polarized plate in which the linear polarizer and the layer having a retardation of 1 / 2 wavelength of the optical laminate are laminated adjacent to each other may be used. Further, the linear polarizer and the optical laminate may be laminated by bonding them using a known adhesive, adhesive, or the like, that is, a circularly polarized plate laminated via an adhesive or adhesive between the linear polarizer and the layer having a retardation of 1 / 2 wavelength of the optical laminate may be used. Further, a transparent substrate made of an optically isotropic phase such as glass or a triacetyl cellulose film (TAC film) may be included between the linear polarizer and the optical laminate.

[0057] [Manufacturing method of optical laminate] The manufacturing method of the optical laminate of the present invention may include a film forming step of forming a birefringence inducing material layer by forming a birefringence inducing material film, a light irradiation step of irradiating the birefringence inducing material layer with polarized light for developing retardation to form a first optically anisotropic layer, an alignment step of performing alignment treatment to impart a function as an alignment film to the birefringence inducing material layer, and a step of applying a polymerizable liquid crystal material on the surface of the alignment-treated birefringence inducing material layer to form a second optically anisotropic layer.

[0058] In the present invention, although the conditions differ depending on the types of the birefringence inducing material and the polymerizable liquid crystal material, it is possible to control the Nz coefficient and the in-plane retardation value (Re) of each layer by adjusting the orientation of the molecules constituting each layer according to the film forming conditions and the polarized light irradiation conditions.

[0059] The order of the above steps may be changed. For example, a film forming step of forming a birefringence inducing material layer by forming a birefringence inducing material, an alignment step of irradiating polarized light for imparting a function as an alignment film to the birefringence inducing material layer, a step of forming a second optically anisotropic layer by applying a polymerizable liquid crystal material on the surface of the alignment-treated birefringence inducing material layer, and a light irradiation step of irradiating polarized light for developing a phase difference to the birefringence inducing material layer from above the second optically anisotropic layer to form a first optically anisotropic layer. By adjusting the above conditions by a method having these steps in this order, it is possible to manufacture the optical laminate of the present invention.

[0060] In the present invention, from the viewpoint of arbitrarily setting the angle formed by the slow axis of the first optically anisotropic layer and the slow axis of the second optically anisotropic layer, a film forming step of forming a birefringence inducing material layer by forming a birefringence inducing material, a light irradiation step of irradiating polarized light for developing a phase difference on the birefringence inducing material layer to form a first optically anisotropic layer, a surface alignment step of aligning the surface of the first optically anisotropic layer so as to have an orientation different from that inside, and a step of forming a second optically anisotropic layer by applying a polymerizable liquid crystal material on the surface of the aligned first optically anisotropic layer. It is preferable to manufacture an optical laminate by a manufacturing method including By manufacturing an optical laminate by the method of such a preferable embodiment, it is not necessary to cut a plurality of films at a predetermined angle and precisely bond them, etc., so that the crossing angle of the slow axes can be easily adjusted to an arbitrary angle. Further, since it can be manufactured in a long shape, an optical laminate can be efficiently obtained.

[0061] Hereinafter, an embodiment in a manufacturing method of a preferable embodiment will be described with reference to the drawings. FIGS. 1A to 1D are schematic cross-sectional views for explaining an embodiment of a manufacturing method of an optical laminate of the present invention. In FIGS. 1A to 1D, cross-sections of each layer are shown, but these do not show the ratio of actual thicknesses.

[0062] FIG. 1A is a schematic cross-sectional view showing a state after a film-forming step, and shows a laminate of a substrate 10 and a birefringence-inducing material layer 20. FIG. 1B is a schematic cross-sectional view showing a state after a light irradiation step, and shows a laminate of the substrate 10 and a first optically anisotropic layer 30 formed by alignment of molecules of the birefringence-inducing material layer 20 by irradiation with polarized light. FIG. 1C is a schematic cross-sectional view showing a state after a surface alignment step, and shows a laminate of the substrate 10 and the first optically anisotropic layer 30 including an internal layer 31 having the same alignment as the first optically anisotropic layer 30 and an adjacent layer 32 having an alignment different from that of the internal layer 31 by surface alignment treatment on the surface opposite to the substrate 10. FIG. 1D is a schematic cross-sectional view showing a state after a second optically anisotropic layer forming step, and shows an optical laminate 100 of the substrate 10, the first optically anisotropic layer 30 including the internal layer 31 and the adjacent layer 32, and a second optically anisotropic layer 40 formed by applying a polymerizable liquid crystal material.

[0063] By forming a birefringence-inducing material on the substrate 10, a birefringence-inducing material layer 20 can be formed as shown in FIG. 1A. By irradiating polarized light for developing a phase difference on the birefringence-inducing material layer 20 made of a birefringence-inducing material, molecular alignment of the birefringence-inducing material can be induced. As a result, as shown in FIG. 1B, a first optically anisotropic layer 30 having a predetermined slow axis is formed from the birefringence-inducing material layer 20 that is optically isotropic. By adjusting the film-forming conditions of the birefringence-inducing material in the film-forming step and the irradiation conditions of the polarized light in the light irradiation step, the optical characteristics of the first optically anisotropic layer 30 can be controlled. In the light irradiation step, since there is no other layer on the birefringence-inducing material layer 20, it is possible to irradiate the birefringence-inducing material layer 20 with desired polarized light without changing the polarization state of the irradiated polarized light.

[0064] Next, an adjacent layer 32 can be formed on the first optically anisotropic layer 30 by performing an alignment treatment so as to apply an alignment different from the alignment imparted in the light irradiation step on the surface of the first optically anisotropic layer 30 shown in FIG. 1B. As a result, as shown in FIG. 1C, two layers, an internal layer 31 having the alignment originally formed and an adjacent layer 32 having an alignment different from that thereof, are formed in the first optically anisotropic layer 30.

[0065] Then, when a polymerizable liquid crystal material is applied onto the adjacent layer 32 shown in FIG. 1C, the adjacent layer 32 serves as an alignment film, and as shown in FIG. 1D, a second optically anisotropic layer 40 aligned corresponding to the alignment of the adjacent layer 32 can be formed. Thereby, a second optically anisotropic layer 40 having a slow axis different from that of the inner layer 31 is formed on the adjacent layer 32. In the application of the polymerizable liquid crystal material, by adjusting the thickness of the second optically anisotropic layer 40, the in-plane retardation value (Re) can be controlled to have a retardation of 1 / 4 wavelength or 1 / 2 wavelength. Further, in such a manufacturing method, since the alignment of the inner layer 31 and the adjacent layer 32 can be adjusted independently, a desired alignment can be imparted to the second optically anisotropic layer 40 in consideration of the alignment property of the inner layer 31, and they can intersect with each other at a desired slow axis.

[0066] (Film formation step) The birefringence-induced material layer is formed by forming the above-described birefringence-induced material into a film. In FIG. 1A, a birefringence-induced material layer 20 is laminated on a substrate 10, but the substrate 10 may be omitted. When a substrate is used, it may be a substrate made of an optically isotropic material, for example, a transparent substrate made of an optically isotropic phase such as glass or a triacetyl cellulose film (TAC film). Alternatively, as the substrate, for example, a substrate made of a material having low adhesion to the birefringence-induced material layer (first optically anisotropic layer) such as a general-purpose polyester film may be used as a release substrate. When a release substrate is used, since it can be peeled off after the formation of the optical laminate of the present invention, it is not necessary to consider the optical characteristics of the substrate itself, and an opaque substrate may be used. For example, after forming the optical laminate of the present invention on the substrate, it is joined to another optical member (for example, a linear polarizing plate) via an adhesive or the like, and then the release substrate is peeled off and used, so that the optical laminate can be configured without a substrate and can be made into a thin optical member having a thickness substantially consisting only of the film thicknesses of the first optically anisotropic layer and the second optically anisotropic layer.

[0067] The birefringence-inducing material layer may be a cast film formed by dissolving the birefringence-inducing material as described above in a solvent to form a solution, applying this solution onto a substrate, and drying to remove the solvent. When forming a coating film of the birefringence-inducing material, since the Nz coefficient is an index of the refractive index components in the in-plane direction and the thickness direction, as control of the Nz coefficient, it is possible by adjusting the coating conditions and drying conditions that affect the orientation of the molecules (for example, side-chain liquid crystalline polymers) constituting the birefringence-inducing material. Also, since the in-plane retardation value (Re) is a parameter that affects not only the refractive index but also the thickness as described above, as control of the in-plane retardation value (Re), in addition to the above coating conditions and drying conditions, it is possible by adjusting the concentration of the solution during film formation and the like to adjust the thickness of the birefringence-inducing material layer.

[0068] As the solvent for the birefringent organic material, although it affects the Nz coefficient and the in-plane retardation value (Re) due to differences in its solubility and drying properties, it can be appropriately selected according to the type of the birefringence-inducing material. For example, dioxane, dichloroethane, cyclohexanone, toluene, tetrahydrofuran, o-dichlorobenzene, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol derivatives (for example, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether (1,2-dimethoxyethane), diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, etc.), propylene glycol derivatives (for example, propylene glycol monomethyl ether, propylene glycol 1-monomethyl ether 2-acetate, etc.) and the like can be mentioned, and these solvents may be used alone or in combination of two or more.

[0069] The concentration of the solution can be appropriately adjusted in consideration of its influence on the film thickness and the like. For example, it may contain 5 to 50% by weight of the birefringence-inducing material, preferably 8 to 40% by weight, and more preferably 10 to 25% by weight. For coating the solution onto the substrate, known coating methods such as spin coating and roll coating can be used.

[0070] After coating, it is necessary to dry to remove the solvent. Although it varies depending on the solvent used, in order to control the Nz coefficient and the in-plane retardation value (Re), the drying rate may be adjusted by adjusting the drying temperature and time. By slowing down the drying rate, the Nz coefficient tends to decrease, and it is also possible to adjust the drying rate by selecting the solvent. For example, the drying rate can be slowed down by using a high-boiling solvent.

[0071] (Light irradiation step) In the light irradiation step, the birefringence-inducing material layer may be irradiated with polarized light (first polarized light) for developing a retardation. By performing the light irradiation step, a selective photoreaction of molecules occurs not only on the surface but also inside the birefringence-inducing material layer, the molecular orientation is induced, and the first optically anisotropic layer is formed. In the method for manufacturing the optical laminate of the present invention, since the polarized light can be directly irradiated on the birefringence-inducing material layer without passing through another layer, the intended slow axis can be formed by the irradiated polarized light.

[0072] The first polarized light is not particularly limited as long as it is light having a wavelength at which the photosensitive group of the side-chain type liquid crystalline polymer undergoes a photoreaction, such as infrared rays, visible light, ultraviolet rays (for example, near ultraviolet rays, far ultraviolet rays, etc.), X-rays, charged particle beams (for example, electron beams, etc.), and it also varies depending on the type of the side-chain structure of the side-chain type liquid crystalline polymer, but the wavelength of the light may be 200 to 500 nm. The first polarized light may be, for example, linearly polarized ultraviolet light. In this case, for example, an ultraviolet irradiation device such as a high-pressure mercury lamp may be used as a light source, and the polarized light may be converted into linearly polarized light through a Glan-Taylor prism. Also, the irradiation amount of the first polarized light is, from the viewpoints of orienting not only the surface but also the inside of the birefringence-inducing material layer and adjusting the Nz coefficient and the in-plane retardation value (Re), for example, 10 mJ / cm 2 ~10 J / cm 2 and may be preferably 50 mJ / cm 2 ~1 J / cm 2 and more preferably 100 mJ / cm 2 ~500 mJ / cm 2 and may be.

[0073] In the method for manufacturing the optical laminate of the present invention, after the light irradiation step, a heating step of heating the formed first optically anisotropic layer may be provided as necessary. By the heating step, molecular orientation is induced depending on the irradiation direction and vibration direction of the first polarized light irradiated in the light irradiation step, and unoriented molecules also orient following the oriented molecules. Then, subsequent heating enables the side-chain liquid crystalline polymer to perform molecular motion, and the orientation of unoriented molecules can be promoted. After heating, it may be cooled to about room temperature, for example, by leaving it standing.

[0074] The heating temperature in the heating step is not particularly limited as long as the orientation of unoriented molecules is induced along the side chain where the side-chain liquid crystalline polymer has caused a photoreaction by molecular motion, but it is preferably set to be equal to or higher than the liquid crystal phase transition temperature of the birefringence induction material and equal to or lower than the isotropic phase transition temperature (preferably less than the isotropic phase transition temperature). For example, it may be 100 to 200 °C, preferably 110 to 180 °C, and more preferably 120 to 160 °C.

[0075] Also, the heating time is not particularly limited as long as the orientation of unoriented molecules is induced along the side chain where the liquid crystalline polymer has caused a photoreaction by molecular motion, but it can be appropriately set according to the type of the liquid crystalline polymer, the heating temperature, etc. For example, it may be carried out for 1 minute or more, preferably 2 minutes or more, and more preferably 3 minutes or more. The upper limit is not particularly limited, but from the viewpoint of economy, it may be about 60 minutes (preferably about 40 minutes, more preferably about 30 minutes).

[0076] (Surface orientation step) In the surface orientation step, the surface of the first optically anisotropic layer may be subjected to an orientation treatment so as to have an orientation different from that of its internal layer. By performing the surface orientation treatment, an adjacent layer is formed adjacent to the first optically anisotropic layer, and two layers, namely, an internal layer and an adjacent layer, which are composed of the same birefringence induction material but have different orientation states, are formed within the first optically anisotropic layer. Note that the internal layer may indicate a part of the first optically anisotropic layer other than the adjacent layer.

[0077] The method of the alignment treatment is not particularly limited as long as an alignment layer different from its inner layer can be formed on the surface of the first optically anisotropic layer. Examples thereof include a rubbing treatment, an optical alignment treatment by polarized light irradiation, and the like. In the rubbing treatment, the alignment direction can be controlled by rubbing the surface of the first optically anisotropic layer in a certain direction by rotating a roller wrapped with a cloth such as cellulose, nylon, or polyester while pressing it in with a certain pressure, so that an adjacent layer having a desired alignment direction can be formed. However, the method of the alignment treatment is preferably an optical alignment treatment by polarized light irradiation.

[0078] The surface alignment step may be a second light irradiation step of irradiating the surface of the first optically anisotropic layer with a second polarized light having a polarization axis direction different from that of the first polarized light to form an adjacent layer on the first optically anisotropic layer. In the second light irradiation step, even after molecular alignment by the first light irradiation step (the above-described light irradiation step) (preferably, the first light irradiation step and the heating step), by irradiating a second polarized light having a polarization axis direction different from that of the first polarized light, an axis-selective photoreaction selectively occurs in the vicinity of the surface centering on the unreacted birefringence-inducing material of the first optically anisotropic layer, so that an orientation different from that of the inner layer can be imparted to the vicinity of the surface. On the other hand, since the molecules of the inner layer of the first optically anisotropic layer are already highly oriented, the orientation of the inner layer of the first optically anisotropic layer is not converted even after the second light irradiation step.

[0079] As the second polarized light, the light of various wavelengths described above can be used as the first polarized light. For example, linearly polarized ultraviolet light may be used. Further, the second polarized light may use a different type of light from the first polarized light irradiated in the above-described light irradiation step, or may use the same type of light.

[0080] The second polarization may have a polarization axis direction different from that of the first polarization. For example, the axis angle may be different from that of the polarization axis of the first polarization by 5 to 85°, preferably 10 to 80°, more preferably 20 to 70°. Here, the difference in the axis angle between the polarization axis of the second polarization and the polarization axis of the first polarization is adjusted in consideration of the orientation state (such as the proportion of unreacted birefringence-inducing material) near the surface of the first optical anisotropic layer after the first light irradiation step, so that the slow axis of the second optical anisotropic layer to be formed later can be arbitrarily set.

[0081] From the viewpoint of reorienting the surface of the first optical anisotropic layer that is oriented, the irradiation amount of the second polarization is, for example, 50 mJ / cm 2 ~20 J / cm 2 and may be preferably 100 mJ / cm 2 ~10 J / cm 2 and more preferably 150 mJ / cm 2 ~1 J / cm 2 and may be.

[0082] If necessary, the method for manufacturing the optical laminate of the present invention may further include a surface treatment step of treating the surface of the birefringence-inducing material layer with a solvent after the first light irradiation step. After the surface treatment step, it is preferable to perform a surface orientation step such as second polarization irradiation and rubbing treatment. Further, when a heating step is performed after the first light irradiation step, the surface treatment step may be performed after the heating step.

[0083] In the surface treatment step, by applying a solvent to the surface of the first optical anisotropic layer to dissolve the surface portion, the molecular orientation applied by the first light irradiation step can be relaxed to a random state. For this reason, the orientation of the surface portion of the first optical anisotropic layer once formed by the first polarization can be eliminated, and the orientation of the adjacent layer of the first optical anisotropic layer can be made isotropic. In the surface treatment step, the solvent may be applied to the surface of the first optical anisotropic layer and then dried. The drying method is not particularly limited as long as the applied solvent can be evaporated. For example, it may be left to dry naturally. Only the surface to which the solvent is applied can be made isotropic.

[0084] By making the surface isotropic, in the subsequent second light irradiation step, the light alignment of the surface becomes easier, so that the irradiation amount of the second polarized light can be reduced. When the surface treatment step is performed, the irradiation amount of the second polarized light is, for example, 0.1 mJ / cm 2 ~500 mJ / cm 2 may be sufficient, preferably 0.5 mJ / cm 2 ~400 mJ / cm 2 , more preferably 1 mJ / cm 2 ~300 mJ / cm 2 may also be sufficient. Further, when the surface treatment step is performed, the ratio of the irradiation amount of the first polarized light to the irradiation amount of the second polarized light (first polarized light / second polarized light) may be 1 / 5 to 100 / 1, preferably 1 / 2 to 80 / 1, more preferably 1 / 1.5 to 50 / 1.

[0085] By making the surface isotropic, in the subsequent second light irradiation step, it is not necessary to consider the alignment state of the adjacent layer of the first optically anisotropic layer, so that the axis angle of the polarization axis of the second polarized light can be directly reflected in the slow axis of the second optically anisotropic layer. Therefore, the axis angle of the polarization axis of the second polarized light can be easily selected with respect to the setting of the slow axis of the second optically anisotropic layer formed later.

[0086] The solvent used in the surface treatment step is not particularly limited as long as it can dissolve the birefringence-inducing material constituting the first optically anisotropic layer, and may be a good solvent or a poor solvent for the birefringence-inducing material. The solvent used in the surface treatment step may be, for example, a mixed solvent of a good solvent and a poor solvent of the birefringence-inducing material from the viewpoint of making the surface of the first optically anisotropic layer isotropic and suppressing dissolution to the inside and disturbing its alignment. When a mixed solvent containing a good solvent and a poor solvent of the birefringence-inducing material is used, it can be appropriately adjusted according to the solubility of the solvent used in the birefringence-inducing material. For example, the mixing weight ratio (good solvent / poor solvent) of these may be 1 / 100 to 100 / 1, preferably 1 / 50 to 50 / 1, more preferably 1 / 10 to 10 / 1.

[0087] The solvents used in the surface treatment step include, for example, water; alcohol solvents such as methanol, ethanol, propanol, isopropyl alcohol, pentanol, and hexanol; aliphatic or alicyclic hydrocarbon solvents such as hexane, heptane, octane, and cyclohexane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, isopropyl methyl ketone, methyl isobutyl ketone, and cyclohexanone; ether solvents such as ethyl ether, propyl ether, isopropyl ether, methyl ethyl ether, methyl propyl ether, tetrahydrofuran, and dioxane; nitrile solvents such as acetonitrile and propionitrile; sulfoxide solvents such as dimethyl sulfoxide; amide solvents such as N,N-dimethylformamide; ester solvents such as methyl acetate, ethyl acetate, and butyl acetate; glycol solvents such as ethylene glycol and propylene glycol; glycol ether solvents such as ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol 1-monomethyl ether 2-acetate; halogenated hydrocarbon solvents such as carbon tetrachloride, chloroform, dichloromethane, dichloroethane, and dichlorobenzene; and the like. These solvents may be used alone or in combination of two or more. In addition, since the solubility of these solvents varies depending on the type of the birefringence-inducing material, they can be used after considering whether they are good solvents or poor solvents according to the birefringence-inducing material to be used. In the present invention, a good solvent means a solvent having a solubility of 1% by mass or more in a solute at 25°C, and a poor solvent means a solvent having a solubility of less than 1% by mass in a solute at 25°C.

[0088] For example, as a good solvent for the birefringence-inducing material, dioxane, dichloroethane, cyclohexanone, toluene, tetrahydrofuran, o-dichlorobenzene, dimethoxyethane, etc. may be used, and as a poor solvent for the birefringence-inducing material, ethanol, methanol, n-hexane, etc. may be used. These good solvents and poor solvents may be mixed at the above-described mixing weight ratio and used as a mixed solvent.

[0089] (Second Optically Anisotropic Layer Formation Step) In the second optically anisotropic layer formation step, a polymerizable liquid crystal material may be applied onto the adjacent layer of the aligned first optically anisotropic layer to form a second optically anisotropic layer. By performing the second optically anisotropic layer formation step, since the adjacent layer aligned in the surface alignment step serves as an alignment film, a second optically anisotropic layer aligned using its alignment direction can be formed. As for the control of the in-plane retardation value (Re) of the second optically anisotropic layer, it is possible by adjusting the thickness by adjusting the concentration of the solution, etc. when applying the polymerizable liquid crystal material.

[0090] In the second optically anisotropic layer formation step, the polymerizable liquid crystal material as described above is applied onto the adjacent layer of the first optically anisotropic layer. For the application, it may be performed by dissolving the polymerizable liquid crystal material in a solvent and coating it as a solution by a known coating method such as spin coating or roll coating. The solvent can be appropriately selected according to the type of the polymerizable liquid crystal material. For example, dioxane, dichloroethane, cyclohexanone, toluene, tetrahydrofuran, o-dichlorobenzene, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol derivatives (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, etc.), propylene glycol derivatives (propylene glycol monomethyl ether, propylene glycol 1-monomethyl ether 2-acetate), etc. may be mentioned, and these solvents may be used alone or in combination of two or more.

[0091] The solvent for the polymerizable liquid crystal material can be selected according to not only the combination of the birefringence-inducing material and the polymerizable liquid crystal material but also the alignment state of the adjacent layer. For example, when most of the molecules in the adjacent layer are in the desired alignment (for example, when a surface treatment process is performed or when a rubbing treatment is performed as an alignment treatment), from the viewpoint of suppressing the disturbance of the alignment of the first optical anisotropic layer while imparting the alignment of the adjacent layer to the second optical anisotropic layer, the solvent for the polymerizable liquid crystal material is preferably a poor solvent for the birefringence-inducing material. On the other hand, when only a part of the molecules in the adjacent layer is in the desired alignment, the solvent for the polymerizable liquid crystal material is preferably a mixed solvent obtained by mixing a good solvent and a poor solvent for the birefringence-inducing material. Although the mechanism in this case is not clear, when a poor solvent for the birefringence-inducing material is contained as the solvent for the polymerizable liquid crystal material, it is possible to prevent the first optical anisotropic layer from being invaded and suppress the disturbance of its alignment. On the other hand, when a good solvent for the birefringence-inducing material is contained as the solvent for the polymerizable liquid crystal material, the wettability of the solution with respect to the adjacent layer is improved, and the molecules of the polymerizable liquid crystal material can be aligned along the alignment possessed by only a part of the molecules in the adjacent layer. As a result, the second optical anisotropic layer can be aligned. The solvent for the polymerizable liquid crystal material can be appropriately adjusted according to the combination of the birefringence-inducing material and the polymerizable liquid crystal material and the alignment state of the adjacent layer. However, from the viewpoint of maintaining the alignment of the first optical anisotropic layer, it preferably contains a poor solvent for the birefringence-inducing material so as not to invade the adjacent layer. For example, the mixing weight ratio (good solvent / poor solvent) of the good solvent and the poor solvent for the birefringence-inducing material may be 0 / 100 to 100 / 1, preferably 0 / 100 to 50 / 1, and more preferably 0 / 100 to 10 / 1. As the solvent for the polymerizable liquid crystal material, general solvents can be used according to the purpose, and for example, it may contain toluene, tetrahydrofuran, ethylene glycol derivatives, propylene glycol derivatives, and the like.

[0092] A coating film is formed by applying a solution, and if necessary, heated to dry the coating film. At this time, the adjacent layer of the first optical anisotropic layer existing below functions as an alignment film (alignment-imparting film), and the alignment of liquid crystal molecules occurs. As a result, a second optical anisotropic layer in which the liquid crystal is aligned in a predetermined direction is formed.

[0093] In the second optical anisotropic layer forming step, after forming a coating film of the polymerizable liquid crystal material, a heating step and / or a light irradiation step (for example, a non-polarized irradiation step) may be provided as necessary. By forming a coating film, the polymerizable liquid crystal material is already oriented in a predetermined direction corresponding to the orientation of the adjacent layer of the first optical anisotropic layer, and in the subsequent heating step and / or light irradiation step (for example, a non-polarized irradiation step), the polymerizable liquid crystal material polymerizes and / or crosslinks, thereby fixing the orientation. Specifically, when the polymerizable liquid crystal material is made of a thermopolymerizable material, the orientation is fixed by polymerization by heating. When it is made of a photopolymerizable material, polymerization occurs upon irradiation with light, and the orientation is fixed. When it is made of a crosslinkable material, crosslinking occurs upon heating and / or irradiation with light, and the orientation is fixed.

[0094] Further, when the polymerizable liquid crystal material contains a crosslinking agent and the crosslinking agent has a functional group capable of forming a crosslinked bond with the birefringence-inducing material, a crosslinked bond can be formed between the first optical anisotropic layer and the second optical anisotropic layer by applying thermal energy and / or light energy.

[0095] In the heating step in the second optical anisotropic layer forming step, although it is not particularly limited as long as the above polymerization and / or crosslinking reaction proceeds, from the viewpoint of suppressing disturbance of the orientation of the inner layer of the first optical anisotropic layer, it is preferably carried out at a heating temperature equal to or lower than the isotropic phase transition temperature of the birefringence-inducing material (preferably lower than the isotropic phase transition temperature). For example, it may be 70 to 180°C, preferably 70 to 150°C, more preferably 70 to 140°C. Also, the heating time may be, for example, 1 minute or more, preferably 2 minutes or more, more preferably 3 minutes or more. The upper limit is not particularly limited, but from the viewpoint of economy, it may be about 60 minutes (preferably about 40 minutes, more preferably about 30 minutes).

[0096] In the light irradiation step in the second optical anisotropy layer forming step, the polymerization and / or crosslinking reaction is not particularly limited as long as it proceeds. However, non-polarized light is preferably used as the irradiated light. As the non-polarized light, light of various wavelengths described above can be used as the first polarized light or the second polarized light. For example, non-polarized ultraviolet light may be used. The irradiation amount of light may be 10 mJ / cm 2 ~10 J / cm 2 and may preferably be 50 mJ / cm 2 ~1 J / cm 2 , more preferably 100 mJ / cm 2 ~500 mJ / cm 2 .

Examples

[0097] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0098] (Monomer 1) 4-(6-Hydroxyhexyloxy)cinnamic acid was synthesized by heating p-coumaric acid and 6-chloro-1-hexanol under alkaline conditions. Methacrylic acid was added in a large excess to this product in the presence of p-toluenesulfonic acid for an esterification reaction to synthesize Monomer 1 represented by the following chemical formula.

[0099]

Chemical formula

[0100] (Monomer 2) 4-(6-Hydroxyhexyloxy)benzoic acid was synthesized by heating 4-hydroxybenzoic acid and 6-chloro-1-hexanol under alkaline conditions. Then, methacrylic acid was added in a large excess to this product in the presence of p-toluenesulfonic acid for an esterification reaction to synthesize Monomer 2 represented by the following chemical formula.

[0101]

Chemical formula

[0102] (Copolymer 1) Monomer 1, Monomer 2, and 2-hydroxyethyl methacrylate (HEMA) were dissolved in dioxane such that the molar ratio of Monomer 1:Monomer 2:HEMA was 3:7:0.5. AIBN (azobisisobutyronitrile) was added as a polymerization initiator, and polymerization was carried out at 70 °C for 24 hours to obtain Copolymer 1. This Copolymer 1 exhibited liquid crystallinity.

[0103] The following examples Reference Example In the following examples and comparative examples, the optical properties (Nz coefficient, in-plane retardation value Re, etc.) of the obtained optical laminate were measured using a birefringence measurement device (AxoScan manufactured by AXOMETRICS), and the thickness was measured using a film thickness meter (F20 manufactured by FILMETRICS).

[0104] (Example 1) Copolymer 1 was dissolved in 1,2-dimethoxyethane (DME) to a concentration of 15 wt% to prepare a solution. This solution was applied onto a cover glass substrate using a spin coater to a thickness of approximately 3.5 μm, and the coating film was dried at 60 °C for 3 minutes and then at 80 °C for 3 minutes. Thereafter, polarized light (first polarization) converted to linearly polarized light using a Glan-Taylor prism from a high-pressure mercury lamp was irradiated onto the dried coating film for 100 seconds (irradiation dose 100 mJ / cm 2 ). Next, after heating at 130 °C for 3 minutes and then gradually cooling to room temperature, orientation was induced to form Film 1 (first optically anisotropic layer). The optical properties of the obtained Film 1 were such that the Nz coefficient was 0.2 and the in-plane retardation value was 250 nm. Also, the axial direction of the in-plane retardation was 90° with respect to the polarization vibration direction of the irradiated polarized light.

[0105] Subsequently, a mixed solution with a volume ratio of tetrahydrofuran (THF) to ethanol (THF:ethanol) of 1:6 was applied to the obtained film 1 using a spin coater and dried by leaving it standing. Further, ultraviolet light from a high-pressure mercury lamp was converted, using a Glan-Taylor prism, into polarized light (second polarized light) with a linearly polarized vibration direction that is 60° different from the polarized vibration direction of the first polarized light, and the film 1 was irradiated with this polarized light for 300 seconds (irradiation dose 300 mJ / cm 2 ).

[0106] 100 parts by weight of a polymerizable liquid crystal compound (“LC-242”, manufactured by BASF) and 5 parts by weight of a photoinitiator (“Irgacure 907”, manufactured by Ciba Specialty Chemicals) were mixed and dissolved in a mixed solvent with a volume ratio of THF to propylene glycol 1-monomethyl ether 2-acetate (PGMEA) of 1:1 to a concentration of 20% by weight to prepare a solution. This solution was applied onto the surface of the film 1 irradiated with the second polarized light using a spin coater to a thickness of approximately 0.9 μm, heated at 70 °C for 3 minutes, and then cooled to room temperature. Further, non-polarized ultraviolet light was irradiated for 100 seconds (irradiation dose 300 mJ / cm 2 ) to polymerize the polymerizable liquid crystal compound and form a film 2 (second optically anisotropic layer), obtaining a laminate of the film 1 and the film 2. To investigate the optical properties of the obtained laminate, only the film 2 was transferred onto an optically isotropic film with an adhesive, and the optical properties of the film 2 were measured. The optical properties of the film 2 were such that the Nz coefficient was 1 and the in-plane retardation value was 115 nm. Also, the axial direction of the in-plane retardation was 90° with respect to the irradiated polarized vibration direction. As a result, the angle formed by the slow axes of the film 1 and the film 2 was 60°.

[0107] The laminate thus produced was bonded to a linear polarizer using an adhesive to produce a circular polarizer. The component order of the circular polarizer was laminated in the order of the linear polarizer, the film 1, and the film 2, and the bonding angle was such that the slow axis of the film 1 was 15° and the slow axis of the film 2 was 75° with respect to the transmission axis of the linear polarizer. The viewing angle characteristics of the reflected light of this circular polarizing plate were confirmed by calculation using simulation software ("LCDMaster", manufactured by Syntec), and the reflection characteristics of the circular polarizing plate are shown in Fig. 2. Comparing with Fig. 6 of Comparative Example 1 described later, it can be estimated from the calculation that the range with high contrast (the range where the color in the figure is dark) is much wider and the viewing angle characteristics of the reflected light are improved. In addition, when visually checking the reflection characteristics at an oblique view, it was confirmed that the reflected light could be suppressed as compared with the circular polarizing plate of Comparative Example 1. In addition, this circular polarizing plate was placed on a mirror surface and the spectrum of the reflected light was measured (Fig. 3). It was confirmed that the spectrum of the reflected light has broadband antireflection characteristics as compared with a single layer product of a uniaxially stretched cyclic polyolefin λ / 4 retardation film.

[0108] ( Reference Example 2) Copolymer 1 was dissolved in a mixed solvent with a volume ratio of DME, THF and cyclohexanone (DME: THF: cyclohexanone) of 7:5:5 to a concentration of 15% by weight to prepare a solution. This solution was applied onto a cover glass substrate using a spin coater to a thickness of about 2 μm, and the coating film was allowed to stand at room temperature for 10 minutes and then dried at 80 °C for 3 minutes. Then, ultraviolet light from a high-pressure mercury lamp was irradiated onto the dried coating film for 100 seconds (irradiation dose 100 mJ / cm 2 ) with polarized light (first polarization) converted to linear polarization using a Glan-Taylor prism. Next, after heating at 130 °C for 3 minutes and then gradually cooling to room temperature, orientation was induced to form Film 1 (first optically anisotropic layer). The optical properties of the obtained Film 1 were that the Nz coefficient was -0.1 and the in-plane retardation value was 110 nm. Also, the axial direction of the in-plane retardation was 90° with respect to the polarization vibration direction of the irradiated polarized light.

[0109] Subsequently, a mixed solution with a volume ratio of THF and ethanol (THF: ethanol) of 1:6 was applied to the obtained Film 1 using a spin coater and dried by leaving it standing. Further, ultraviolet light from a high-pressure mercury lamp was irradiated onto Film 1 for 300 seconds (irradiation dose 300 mJ / cm 2)。

[0110] 100 parts by weight of a nematic liquid crystal compound (“LC-242”, manufactured by BASF) and 5 parts by weight of a photoinitiator (“Irgacure 907”, manufactured by Ciba Specialty Chemicals) were mixed and dissolved in a mixed solvent having a volume ratio of THF to PGMEA (THF:PGMEA) of 1:1 to a concentration of 20% by weight to prepare a solution. This solution was applied onto the surface of Film 1 irradiated with the second polarized light using a spin coater to a thickness of about 2.3 μm, heated at 70° C. for 3 minutes, and then cooled to room temperature. Further, non-polarized ultraviolet light was irradiated for 100 seconds (irradiation dose: 300 mJ / cm 2 ), polymerizing the nematic liquid crystal compound to form Film 2 (the second optically anisotropic layer), and obtaining a laminate of Film 1 and Film 2. In order to investigate the optical properties of the obtained laminate, only Film 2 was transferred onto an optically isotropic film with an adhesive, and the optical properties of Film 2 were measured. The optical properties of Film 2 were such that the Nz coefficient was 1 and the in-plane retardation value was 250 nm. Also, the axial direction of the in-plane retardation was 90° with respect to the polarization vibration direction of the irradiated polarized light. As a result, the angle formed by the slow axes of Film 1 and Film 2 was 60°.

[0111] The laminate thus produced was bonded to a linear polarizing plate using an adhesive to produce a circular polarizing plate. The component order of the circular polarizing plate was laminated in the order of the linear polarizing plate, Film 2, and Film 1, and the bonding angles were such that the slow axis of Film 2 was 15° and the slow axis of Film 1 was 75° with respect to the transmission axis of the linear polarizing plate. The viewing angle characteristics of the reflected light of this circular polarizing plate were confirmed by calculation using simulation software (“LCDMaster”, manufactured by Syntec), and FIG. 4 shows the reflection characteristics of the circular polarizing plate. Comparing with FIG. 6 of Comparative Example 1 described later, it can be estimated from the calculation that the range with high contrast (the range where the color in the figure is dark) is wide and the viewing angle characteristics of the reflected light are improved. Also, when the circular polarizing plate was placed on a mirror surface and the reflection characteristics at an oblique view were visually confirmed, it was confirmed that the reflected light could be suppressed as compared with the circular polarizing plate of Comparative Example 1. Using this circular polarizing plate, the wavelength dependence of the retardation value of the transmitted light (linear polarizing plate on the incident side, Film 1 and substrate on the exit side) was measured (FIG. 5). It was confirmed that the retardation wavelength dependence exhibited inverse wavelength dispersion.

[0112] (Comparative Example 1) Using a uniaxially stretched cyclic polyolefin λ / 2 retardation film (Nz coefficient is 1) and a uniaxially stretched cyclic polyolefin λ / 4 retardation film (Nz coefficient is 1), they were laminated to a linear polarizing plate via an adhesive to produce a circular polarizing plate. The lamination order of the circular polarizing plate is laminated in the order of a linear polarizing plate, a λ / 2 retardation film, and a λ / 4 retardation film. The lamination angle was set such that the slow axis of the λ / 2 retardation film is 15° and the slow axis of the λ / 4 retardation film is 75° with respect to the transmission axis of the linear polarizing plate. It was confirmed that this circular polarizing plate also shows inverse wavelength dispersion in the retardation wavelength dependency. However, the reflection characteristics of this circular polarizing plate are estimated from calculations to be inferior in the viewing angle characteristics of the reflected light compared with those of Example 1 and Reference Example 2 (Fig. 6). Actually, when the circular polarizing plate was placed on a mirror surface and the reflection characteristics at an oblique view were visually confirmed, it was confirmed that the reflected light could not be suppressed compared with the circular polarizing plates of Example 1 and Reference Example 2.

Industrial Applicability

[0113] The optical laminate of the present invention can be used as a retardation plate and can be used in applications such as polarizing plates and optical compensation films used in liquid crystal display devices and organic EL display devices. In particular, it can be used as a circular polarizing plate used in an organic EL display device by laminating it with a linear polarizing plate.

[0114] As described above, the preferred embodiments of the present invention have been described with reference to the drawings. However, those skilled in the art will easily assume various changes and modifications within an obvious range by looking at this specification. Therefore, such changes and modifications are construed as being within the scope of the invention determined from the claims.

Explanation of Reference Numerals

[0115] 10 ··· Substrate 20 ··· Birefringence-inducing material layer 30 ··· First optically anisotropic layer 31 ··· Inner layer 32 ··· Adjacent layer 40 ··· Second optically anisotropic layer 100 ··· Optical laminate

Claims

1. An optical laminate including a first optically anisotropic layer made of a birefringence-inducing material and a second optically anisotropic layer made of a polymerizable liquid crystal material and laminated adjacent to the first optically anisotropic layer, wherein the Nz coefficient of the first optically anisotropic layer satisfies 0.2 ≤ Nz ≤ 0.3, and the second optically anisotropic layer has the optical characteristics of a positive A plate, wherein one of the first optically anisotropic layer and the second optically anisotropic layer has a retardation of 1 / 4 wavelength, and the other has a retardation of 1 / 2 wavelength, and the birefringence-inducing material includes a side-chain liquid crystalline polymer having a photosensitive group and a side-chain structure capable of forming a liquid crystal structure. The optical laminate.

2. The optical laminate according to Claim 1, wherein the slow axis direction of the first optically anisotropic layer and the slow axis direction of the second optically anisotropic layer intersect at an angle that is non-parallel and non-orthogonal. The optical laminate.

3. The optical laminate according to Claim 1 or 2, wherein the first optically anisotropic layer has a retardation of 1 / 2 wavelength, and the second optically anisotropic layer has a retardation of 1 / 4 wavelength. The optical laminate.

4. The optical laminate according to Claim 1 or 2, wherein the first optically anisotropic layer has a retardation of 1 / 4 wavelength, and the second optically anisotropic layer has a retardation of 1 / 2 wavelength. The optical laminate.

5. A circular polarizing plate in which the optical laminate according to any one of Claims 1 to 4 and a linear polarizing plate are laminated.

Images