WO2022075071A1 - Optical laminate and circularly polarizing plate - Google Patents

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

Optical laminate and circular polarizing plate Related application

This application claims the priority of Japanese Patent Application No. 2020-170076 filed on October 7, 2020, and the whole thereof is cited as a part of this application by reference.

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

Various retardation plates are used in thin display devices such as liquid crystal displays (LCDs) and organic light emitting diodes (OLEDs) in order to improve display quality. For example, in an OLED such as an organic EL display device, a broadband circular polarizing plate is used in order to suppress reflection.

As the retardation plate used for the circular polarizing plate, Patent Document 1 (Japanese Unexamined Patent Publication No. 10-68816) describes a 1/4 wave plate in which the phase difference of the birefringent light is 1/4 wavelength and a birefringent light. A phase difference plate characterized in that a 1/2 wave plate having a phase difference of 1/2 wavelength is bonded together with their optical axes crossed is disclosed.

Further, in Patent Document 2 (Japanese Patent No. 4646030), as a phase difference plate of a liquid crystal display device, a first phase difference plate having a phase difference of 1/4 wavelength and a phase difference of 1/2 wavelength are provided. It is described that the second retardation plate is arranged and the Nz coefficient of the second retardation plate is 0 or more and less than 1.

Japanese Unexamined Patent Publication No. 10-68816 Japanese Patent No. 4646030

However, Patent Documents 1 and 2 do not describe the relationship between the Nz coefficients of both the 1/4 wave plate and the 1/2 wave plate, and do not describe the use of different Nz coefficients from each other. As the 1/4 wave plate and the 1/2 wave plate, a stretched film or a film in which a liquid crystal material is oriented on an alignment film is generally used, and such a film has an Nz coefficient of 1 and is optically uniaxial. It is a film of. For example, when an optical uniaxial film is used as both the 1/4 wave plate and the 1/2 wave plate and the laminated circular polarizing plate is mounted on an OLED panel, the reflected light of the electrode is sufficient when observed from the diagonal direction of the panel. There is a problem that the oblique viewing contrast of the OLED panel is lowered.

Further, in Patent Documents 1 and 2, it is necessary to use an adhesive to bond the 1/4 wave plate and the 1/2 wave plate, and the birefringence of the adhesive itself may affect it. ..

Therefore, an object of the present invention is to provide an optical laminate capable of suppressing reflected light even when observed from an oblique direction and suppressing a decrease in oblique viewing contrast.

As a result of diligent research to solve the above problems, the present inventor has identified layers having a phase difference of 1/4 wavelength and layers having a phase difference of 1/2 wavelength, which are laminated adjacent to each other. The present invention has been completed by finding that the optical laminate having the Nz coefficient of can suppress the reflected light even when observed from an oblique direction and can suppress the decrease in the oblique viewing contrast.

That is, the present invention can be configured in the following aspects.
[Aspect 1]
It contains 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. It is an optical laminate,
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 the positive A plate.
One of the first optically anisotropic layer and the second optically anisotropic layer has a phase difference of 1/4 wavelength, and the other layer has a phase difference of 1/2 wavelength. Have an optical laminate.
[Aspect 2]
In the optical laminate according to the first aspect, the slow axis direction of the first optically anisotropic layer and the slow axis direction of the second optically anisotropic layer are non-parallel and non-orthogonal. Optical laminates that intersect at an angle.
[Aspect 3]
In the optical laminate according to the first or second aspect, the first optically anisotropic layer has a phase difference of 1/2 wavelength and has an Nz coefficient of 0 ≦ Nz ≦ 0.5 (preferably). An optical laminate in which 0 <Nz ≦ 0.4, more preferably 0.1 ≦ Nz ≦ 0.3).
[Aspect 4]
In the optical laminate according to the first or second aspect, the first optically anisotropic layer has a phase difference of 1/4 wavelength and has 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.

It should be noted that any combination of the claims and / or at least two components disclosed in the specification is included in the present invention. In particular, any combination of two or more of the claims described in the claims is included in the present invention.

According to the optical laminate of the present invention, the reflected light can be suppressed even when observed from an oblique direction, and the decrease in oblique viewing contrast can be suppressed. By laminating with a linear polarizing plate, a circular polarizing plate can be suppressed. It can be used as.

The present 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 constant scale and are exaggerated to show the principles of the invention. However, embodiments and drawings are for illustration and illustration purposes only and should not be used to define the scope of the invention. The scope of the invention is determined by the appended claims.
It is the schematic cross-sectional view after the film forming process in one Embodiment of the manufacturing method of the optical laminated body of this invention. It is schematic cross-sectional view of the laminated body after a light irradiation step in one Embodiment of the manufacturing method of the optical laminated body of this invention. It is schematic cross-sectional view of the laminated body after the surface orientation process in one Embodiment of the manufacturing method of the optical laminated body of this invention. It is schematic cross-sectional view of the laminated body after the 2nd optical anisotropic layer forming step in one Embodiment of the manufacturing method of the optical laminated body of this invention. It is a figure which shows the viewing angle characteristic of the reflected light of the circular polarizing plate of the structure of Example 1. FIG. It is a spectrum of the reflected light of the circular polarizing plate by the circular polarizing plate of Example 1 and the cyclic polyolefin λ / 4 retardation film single layer. It is a figure which shows the viewing angle characteristic of the reflected light of the circular polarizing plate of the structure of Example 2. FIG. It is a graph which shows the wavelength dependence of the phase difference value of the transmitted light of the circular polarizing plate of Example 2. FIG. It is a figure which shows the viewing angle characteristic of the reflected light of the circular polarizing plate of the structure of the comparative example 1. FIG.

[Optical laminate]
The optical laminate of the present invention comprises 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. Includes an optically anisotropic layer.

In the present invention, the birefringence-inducing material refers to a material capable of inducing birefringence axially selectively by molecular motion due to light irradiation (preferably light irradiation and heat-cooling treatment) and molecular orientation based on the molecular motion. For example, the birefringence-inducing material may contain a side-chain type liquid crystal polymer having a photosensitive group and having a side chain structure capable of forming a liquid crystal structure, and the light of the photosensitive group having the side chain may be contained. It may have a property that molecular orientation is induced by the reaction. Examples of the photoreaction caused by the photosensitive group include a photodimerization reaction, a photoisomerization reaction, and a photofries rearrangement reaction.

As the side chain structure capable of forming a liquid crystal structure, the side chain structure may exhibit liquid crystallinity by having a mesogen group which is a rigid site exhibiting liquid crystallinity, or another polymer or another polymer or It has a structure capable of forming a dimer by hydrogen bonding with other side chains of the same polymer, and may exhibit liquid crystallinity by forming a mesogen structure by dimerization thereof.

A mesogen group or mesogen structure is composed of two or more aromatic or aliphatic rings and a linking group that binds 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 heterocycle (for example, an oxygen-containing heterocycle such as a furan ring and a pyran ring; a nitrogen-containing heterocycle such as a pyrrole ring and an imidazole ring), and examples thereof include an aliphatic ring. Examples include a cyclohexane ring. In addition, these aromatic rings or aliphatic rings may have a substituent, and the substituent may be an alkyl group (for example, a C _1-6 alkyl group, preferably a C _1-4 alkyl group). Alkyloxy group (eg, C _1-6 alkyloxy group, preferably C _1-4 alkyloxy group), alkenyl group (eg, C _2-6 alkenyl group, preferably C _2-4 alkenyl group), alkynyl group (eg, C 2-4 alkenyl group) For example, C _2-6 alkynyl group, preferably C _2-4 alkynyl group), halogen atom and the like can be mentioned.
As a linking group, in the case of a covalent bond, a single bond, -O-, -COO-, -OCO-, -N = N-, -NO = N-, -C = C-, -C≡C-, -CO-C = C-, -CH = N-, alkylene group and the like can be mentioned. In the case of a hydrogen bond, a side chain structure having a carboxy group at the terminal may be mentioned, and in this case, a hydrogen bond is formed between the carboxy groups.

The photosensitive group is not particularly limited as long as it is a functional group capable of causing a photoreaction by light energy. Examples thereof include a frillacryloyl group, a naphthylacryloyl group, an azobenzene group, a benzylideneaniline group or a derivative thereof, and a cinnamoyl group may be preferable.

The side chain type liquid crystal 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, and the photosensitive group is a mesogen. The group or mesogen structure may exist independently in the side chain structure, or may exist in a complex manner by sharing a chemical structure.

The side chain type liquid crystal polymer has a side chain structure 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. It may have at least one side chain structure selected from the group.

In the formula, r is an integer from 1 to 12; s is 0 or 1; t is 0 or 1; X ₁ is a single bond, C _1-3 alkylene group, -C = C-,-. Represents C≡C-, -O-, -N = N-, -COO-, or -OCO-; R ₁ is a hydrogen atom, an alkyl group (eg, C _1-6 alkyl group, preferably C _1- ). Represents a ₄ alkyl group), or a hydroxyalkyl group (eg, a hydroxy C _1-6 alkyl group, preferably a hydroxy C _1-4 alkyl group); R ₂ and R ₃ are the same or different, hydrogen atom, alkyl group. (For example, C _1-6 alkyl group, preferably C _1-4 alkyl group), alkyloxy group (for example, C _1-6 alkyloxy group, preferably C _1-4 alkyloxy group), halogen atom or cyano group. Represents. It should be noted that R ₂ and R ₃ each represent a substituent at four positions on the benzene ring, and may represent the same or different substituents at the four positions.

In the formula, r'is an integer from 1 to 12; s'is 0 or 1; u is an integer from 1 to 12; X ₂ is a single bond, C _1-3 alkylene group, -C = Represents C-, -C≡C-, -O-, -N = N-, -COO-, or -OCO-; W is a cinnamoyloxy group, an alkane group, a biphenylacryloyloxy group, a frillacryloyloxy group. , Naftylacryloyloxy group, or a derivative group thereof; _R4 and R5 are the _same or different, hydrogen atom, alkyl group (eg, C _1-6 alkyl group, preferably C _1-4 alkyl group). , Alkyloxy group (eg, C _1-6 alkyloxy group, preferably C _1-4 alkyloxy group), halogen atom or cyano group. It should be noted that R ₄ and R ₅ each represent a substituent at four positions on the benzene ring, and may represent the same or different substituents at the four positions.

The side chain type liquid crystal polymer preferably contains at least the side chain structure represented by the above formula (1). More preferably, in the above formula (1), a side chain structure having a chemical structure in which t represents 0 and R ₁ represents a hydrogen atom may be contained, and such a side chain structure is photosensitive at the terminal. Since it has a katsura acid group, which is a group, and the carboxy group in the katsura acid group has hydrogen-binding property, the terminal benzoic acid group or katsura skin of the side chain of another polymer or the same polymer. It is possible to form a mesogen structure by forming a hydrogen bond together with the carboxy group of the acid group and dimerizing it.

The side chain structures represented by the above formulas (1) and (2) represent the chemical structure of the end of the side chain in the repeating unit, and these side chain structures are not impaired to the extent that the effect of the present invention is not impaired. Various chemical structures may be contained between the main chain structure and the main chain structure.

The side chain type liquid crystal polymer is a homopolymer composed of the same repeating unit containing the side chain structure or a copolymer containing a repeating unit containing a side chain structure having a different structure in addition to the repeating unit containing the side chain structure. There may be. Examples of the main chain structure include structures formed by polymerizing hydrocarbons, acrylates, methacrylates, siloxanes, maleimides, N-phenylmaleimides and the like.

When the side chain type liquid crystal polymer is a copolymer, it may have a repeating unit that does not have a photosensitive group and / or a structure capable of forming a liquid crystal structure.

The birefringence-inducing material of the present invention may contain a low molecular weight compound together with the side chain type liquid crystal polymer in order to promote the orientation of the side chain of the side chain type liquid crystal polymer. The low molecular weight compound has a substituent such as biphenyl, terphenyl, phenylbenzoate, and azobenzene known as a mesogen component, and such a substituent and an allyl, acrylate, methacrylate, and cinnamic acid group (or a derivative thereof) are included. A liquidity in which a functional group such as (group) is 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)). Those having the above are preferably used. These small molecule compounds may be used alone or in combination of two or more.

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 mesogen group, and is polymerized by light or heat or reacted with a cross-linking agent. Contains the composition after forming a crosslinked structure with.

The polymerizable liquid crystal compound may be a liquid crystal monomer or a liquid crystal polymer. For example, as the polymerizable liquid crystal compound, a polymerizable liquid crystal monomer having a polymerizable functional group that polymerizes by light or heat and / or a polymerizable liquid crystal polymer, or a cross-linking functional group capable of introducing a cross-linked structure by reaction with a cross-linking agent. Examples thereof include a crosslinkable liquid crystal monomer having a crosslinkable liquid crystal monomer and / or a crosslinkable liquid crystal polymer.

The polymerizable liquid crystal compound is a monomer having a mesogen group or a polymer having a unit composed of a mesogen group, and is not particularly limited as long as it can form a liquid crystal structure and has polymerizable and / or crosslinkability. Various polymerizable liquid crystal compounds can be used. Examples of the polymerizable liquid crystal compound include Schiff basic, biphenyl, terphenyl, ester, thioester, stilben, trans, azoxy, azo, phenylcyclohexane, pyrimidine, cyclohexylcyclohexane, and trimesin. Examples thereof include acid-based, triphenylene-based, torquesen-based, phthalocyanine-based, porphyrin-based liquid crystal compounds having a molecular skeleton, or mixtures of these compounds, and any compound exhibiting a nematic, cholesteric, or smectic liquid crystal phase. But it may be. As an example, a photopolymerizable nematic liquid crystal monomer may be used as the polymerizable liquid crystal compound.

The unit composed of the mesogen group may be in the main chain or the side chain of the liquid crystal polymer. As the main chain type liquid crystal polymer, polyester type, polyamide type, polycarbonate type, polyimide type, polyurethane type, polybenzimidazole type, polybenzoxazole type, polybenzthiazole type, polyazomethine type, polyesteramide type, polyester carbonate type, Examples thereof include polyesterimide-based liquid crystal polymers and mixtures thereof. The side chain type liquid crystal polymer is a polymer having a linear or cyclic skeletal chain such as a polyacrylate-based, polymethacrylate-based, polyvinyl-based, polysiloxane-based, polyether-based, or polymalonate-based polymer as a side chain. Examples thereof include a liquid crystal polymer to which a mesogen group is bonded, a mixture thereof, and the like.

Further, the polymerizable liquid crystal material may contain a photopolymerization initiator and / or a thermal polymerization initiator when the polymerizable liquid crystal compound has a polymerizable functional group.

Photopolymerization initiators include Irgacure 907, Irgacure 184, Irgacure 651, Irgacure 819, Irgacure 250, Irgacure 369 (all manufactured by Ciba Japan Co., Ltd.), Sakeol BZ, Sakeall Z, Sakeall BEE (and above). , All manufactured by Seiko Kagaku Co., Ltd., kayacure BP100 (manufactured by Nippon Kayaku Co., Ltd.), Kayacure UVI-6992 (manufactured by Dow), ADEKA PTOMER SP-152 or ADEKA PTOMER SP-170 (above) , All manufactured by ADEKA Corporation), TAZ-A, TAZ-PP (all manufactured by Nippon Sibel Hegner) and TAZ-104 (manufactured by Sanwa Chemical Co., Ltd.) and the like, commercially available photopolymerization initiators can be used.

Examples of the thermal polymerization initiator include azo compounds such as azobisisobutyronitrile, peroxides such as hydrogen peroxide, persulfates, and benzoyl peroxide.

The content of the polymerization initiator is preferably 0.01 to 20% by weight, more preferably 0.03 to 10% by weight, still more preferably 0.05 to 8% by weight, based on the total weight of the polymerizable liquid crystal material. .. Within the above range, the polymerizable liquid crystal compound can be polymerized without disturbing the orientation.

When a photopolymerization initiator 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 (eg, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, etc.); anthracene and anthracene containing an alkoxy group (eg, dibutoxyanthracene, etc.). Compounds; phenothiazine; rubrene and the like can be mentioned.

Further, the polymerizable liquid crystal material may contain an appropriate cross-linking agent when the polymerizable liquid crystal compound has a cross-linking functional group. In this case, the polymerizable liquid crystal compound may be a liquid crystal compound that can be oriented and fixed by means such as crosslinking (thermal crosslinking or photocrosslinking) in a liquid state or in a state of being cooled to a liquid crystal transition temperature or lower.

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 oxylanyl group, an oxetanyl group and the like. Of these, acryloyloxy group, methacryloyloxy group, vinyloxy group, oxylanyl group and oxetanyl group are preferable, and acryloyloxy group is more preferable.

Examples of the cross-linking 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. Among these cross-linking agents, when a polyisocyanate compound which is a polyfunctional compound having two or more isocyanate groups in the molecule is used, known polyisocyanate compounds can be used, for example, polyisocyanate. Examples of the system compound include a diisocyanate compound and a triisocyanate compound. Examples of the diisocyanate compound include phenylenediocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, methylcyclohexylene diisocyanate, bis (isocyanatomethyl) cyclohexane, methylenebis (cyclohexyl isocyanate), isophorone diisocyanate, and hexamethylene diisocyanate. Examples thereof include a condensed compound of diol and diol. Examples of the triisocyanate compound include an isocyanurate compound of diisocyanate such as hexamethylene diisocyanate, a biuret compound, and an adduct compound which is an adduct of diisocyanate such as hexamethylene diisocyanate and trimethylolpropane.

The content of the cross-linking agent is 0. It may be 01 to 5% by weight, preferably 0.05 to 3% by weight, and more preferably 0.1 to 1.5% by weight.

In the optical laminate of the present invention, one of the first optically anisotropic layer and the second optically anisotropic layer has a phase difference of 1/4 wavelength, and the other layer is 1 /. It has a phase difference of two wavelengths. That is, in the optical laminate of the present invention, the first optically anisotropic layer has a phase difference of 1/4 wavelength, and the second optically anisotropic layer has a phase difference of 1/2 wavelength. The body or the first optically anisotropic layer is an optical laminate having a phase difference of 1/2 wavelength, and the second optically anisotropic layer has a phase difference of 1/4 wavelength. The phase difference of 1/4 wavelength means that the in-plane phase difference value (Re) is 1/4 of the design wavelength, and is, for example, from 1 / 4-50 nm of the design wavelength to 1/4 + 50 nm of the design wavelength. There may be. For example, when the design wavelength is 550 nm, the Re of the layer having a phase difference of 1/4 wavelength may be 88 to 188 nm. Further, the phase difference of 1/2 wavelength means a case where the in-plane phase difference value (Re) is 1/2 of the design wavelength, for example, from 1 / 2-50 nm of the design wavelength to 1/1 of the design wavelength. It may be 2 + 50 nm. For example, when the design wavelength is 550 nm, the Re of the layer having a phase difference of 1/2 wavelength may be 225 to 325 nm. Here, the in-plane retardation value (Re) is the anisotropy (ΔNxy = | nx−ny |) of the refractive index (nx, ny) of the orthogonal biaxial axes in the film plane and the film thickness d ( It is a parameter defined by the product (ΔNxy × d) with nm), and is a scale showing optical isotropic and anisotropy. In the present specification, the in-plane phase difference value (Re) may be a measured value for light having a wavelength of 550 nm.

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 material is made of a polymerizable liquid crystal material. The layer has the optical properties of a positive A plate. In the present invention, an optical laminate having a specific Nz coefficient between a layer having a phase difference of 1/4 wavelength and a layer having a phase difference of 1/2 wavelength, which are laminated adjacent to each other, is observed from an oblique direction. However, it has been found that the reflected light can be suppressed and the decrease in the oblique viewing contrast can be suppressed. Here, in the present specification, the Nz coefficient is Nz = (when the main refractive index in the plane is nx (slow phase axis direction) and ny (phase advance axis direction) and the refractive index in the thickness direction is nz. It is an index of the refractive index component represented by nx-nz) / (nx-ny).

The positive A plate refers to a positive uniaxial phase difference optical element whose refractive index distribution satisfies nx> ny = nz. When the positive A plate has the optical characteristics, in the present invention, the description of "ny = nz" in the positive A plate refers to the in-plane refractive index in the phase-advancing axis direction (ny) and the refractive index in the thickness direction (nz). Does not necessarily have to completely match, and may be, for example, about Nz = 1 (for example, the Nz coefficient is in the range of 0.95 to 1.05).

In the optical laminate of the present invention, the Nz coefficient of the first optically anisotropic layer is −0.5 ≦ Nz <0 or 0 <Nz ≦ 0.5 from the viewpoint of further improving the viewing angle characteristics of the reflected light. It is preferably −0.3 ≦ Nz <0 or 0 <Nz ≦ 0.3.

In the optical laminate of the present invention, from the viewpoint of further improving the viewing angle characteristics of reflected light, the first optically anisotropic layer has a phase difference of 1/2 wavelength, and its Nz coefficient is 0 ≦ Nz ≦ 0. It is preferably .5, more preferably the Nz coefficient is 0 <Nz ≦ 0.4, and further preferably the Nz coefficient may be 0.1 ≦ Nz ≦ 0.3. That is, the first optically anisotropic layer has a phase difference of 1/2 wavelength, and the Nz coefficient is 0 ≦ Nz ≦ 0.5 (more preferably 0 <Nz ≦ 0.4, still more preferably 0. 1 ≦ Nz ≦ 0.3), the second optically anisotropic layer has a phase difference of 1/4 wavelength, and has the optical characteristics of a positive A plate (for example, the Nz coefficient is 0.95 ≦). It may be an optical laminate (Nz ≦ 1.05).

When the first optically anisotropic layer has a phase difference of 1/4 wavelength, the optical laminate of the present invention preferably has an Nz coefficient of −0.5 ≦ Nz ≦ 0.5, preferably −0. .5 ≦ Nz ≦ 0 is more preferable, and −0.3 ≦ Nz ≦ −0.1 is even more preferable. That is, the first optically anisotropic layer has a phase difference of 1/4 wavelength, and the Nz coefficient is −0.5 ≦ Nz ≦ 0.5 (more preferably −0.5 ≦ Nz ≦ 0, further. It is preferably −0.3 ≦ Nz ≦ −0.1), the second optically anisotropic layer has a phase difference of 1/2 wavelength, and has the optical characteristics of a positive A plate (for example, Nz). It may be an optical laminate (with a coefficient of 0.95 ≦ Nz ≦ 1.05).

The thickness of the first optically anisotropic layer can be appropriately adjusted according to the desired in-plane retardation value (Re), but may be, for example, 0.1 to 20 μm, which is preferable. May be 0.3 to 15 μm, more preferably 0.5 to 10 μm.
The thickness of the second optically anisotropic layer can be appropriately adjusted according to the desired in-plane retardation value (Re), but may be 0.1 to 20 μm, which is preferable. May be 0.3 to 15 μm, more preferably 0.5 to 10 μm.
The thickness ratio of the first optically anisotropic layer and the second optically anisotropic layer (first optically anisotropic layer / second optically anisotropic layer) is 1/10 to 1/10 or more. It may be 10/1, preferably 1/8 to 8/1, and more preferably 1/5 to 5/1.

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.

In the optical laminate of the present invention, the slow-phase axial direction of the first optically anisotropic layer and the slow-phase axial direction of the second optically anisotropic layer are non-parallel from the viewpoint of being used for a circular polarizing plate. They may intersect at angles that are 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 °. More preferably, it may be 10 to 75 °.

The optical laminate of the present invention is produced by the manufacturing method described later 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. It is preferably manufactured, in which case the first optically anisotropic layer is composed of an adjacent layer and an inner layer having different slow axes, and the adjacent layer and the second optically anisotropic layer are formed. It may be an optical laminate in contact with. The adjacent layer may be present 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 orienting the surface of the first optically anisotropic layer so as to give an orientation different from that of the inner layer. Here, the alignment treatment may be performed according to the aspect of the surface alignment step in the manufacturing method described later. Since the influence of orientation in the adjacent layer can be considered to be negligible, the slow axis of the inner layer of the first optically anisotropic layer is measured as the slow axis of the entire first optically anisotropic layer. , 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.

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

The optical laminate of the present invention can be used as a retardation plate, and can be used for various optical members (antireflection film, optical compensation film, etc.). The optical laminate of the present invention can be used as a circular polarizing plate used as an antireflection film in an OLED such as an organic EL display device by laminating it with a linear polarizing plate, for example.

The circular polarizing plate may be obtained by laminating the above optical laminated body and the linear polarizing plate, and the linear polarizing plate may be laminated on the layer side having a phase difference of 1/2 wavelength of the optical laminated body. As for the lamination of the linear polarizing plate and the optical laminate, the optical laminate may be directly manufactured and laminated on the linear polarizing plate as shown in the manufacturing method described later, that is, 1 of the linear polarizing plate and the optical laminate. It may be a circular polarizing plate in which layers having a phase difference of / 2 wavelengths are laminated adjacent to each other. Further, the linear polarizing plate and the optical laminate may be laminated by bonding them together using a known adhesive, adhesive, or the like, that is, the phase difference of 1/2 wavelength between the linear polarizing plate and the optical laminate. It may be a circular polarizing plate laminated with an adhesive or a pressure-sensitive adhesive between the layers. Further, a transparent substrate made of glass or an optically isotropic phase such as a triacetyl cellulose film (TAC film) may be contained between the linear polarizing plate and the optical laminate.

[Manufacturing method of optical laminate]
The method for producing an optical laminate of the present invention includes a film forming step of forming a birefringence-inducing material to form a birefringence-inducing material layer, and a polarization for expressing a phase difference on the birefringence-inducing material layer. A light irradiation step of forming a first optically anisotropic layer by irradiating with water, an alignment step of orienting the birefringence-inducing material layer in order to impart a function as an alignment film, and a birefringence-induced birefringence. A step of applying a polymerizable liquid crystal material to form a second optically anisotropic layer may be provided on the surface of the material layer.

In the present invention, the conditions differ depending on the types of the birefringence-inducing material and the polymerizable liquid crystal material, but the Nz coefficient of each layer and the Nz coefficient of each layer are adjusted by adjusting the orientation of the molecules constituting each layer according to the film forming conditions and the irradiation conditions of polarization. It is possible to control the in-plane phase difference value (Re).

The order of each of the above steps may be changed, for example, a film forming step of forming a birefringence-inducing material to form a birefringence-inducing material layer, and imparting a function as an alignment film to the birefringence-inducing material layer. The second step of forming a second optically anisotropic layer by applying a polymerizable liquid crystal material on the surface of the birefringence-induced birefringence-induced material layer that has been subjected to the alignment treatment. A method comprising, in this order, a light irradiation step of irradiating a birefringence-induced material layer from above the optically anisotropic layer with polarization for expressing a phase difference to form a first optically anisotropic layer. By adjusting each of the above conditions, it is possible to manufacture the optical laminate of the present invention.

In the present invention, a birefringence-inducing material is formed 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 for forming the birefringence-induced material layer, and a light irradiation step for forming the first optically anisotropic layer by irradiating the birefringence-induced material layer with polarized light for expressing a phase difference. A surface alignment step of orienting the surface of the first optically anisotropic layer so as to give an orientation different from the inside thereof, and a polymerizable property on the surface of the first optically anisotropic layer subjected to the orientation treatment. It is preferable to manufacture the optical laminate by a manufacturing method including a step of applying a liquid crystal material to form a second optically anisotropic layer.
By manufacturing the 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 to each other. It can be adjusted to the angle. Further, since it can be manufactured in a long shape, an optical laminate can be efficiently obtained.

Hereinafter, one embodiment of the preferred embodiment of the manufacturing method will be described with reference to the drawings. 1A to 1D are schematic cross-sectional views for explaining an embodiment of the method for manufacturing an optical laminate of the present invention. FIGS. 1A-1D show cross sections of each layer, but they do not show the actual thickness ratio.

FIG. 1A is a schematic cross-sectional view showing a state after the film forming process and showing a laminate of the base material 10 and the birefringence-induced material layer 20. FIG. 1B shows a state after the light irradiation step, which is a laminate of the base material 10 and the first optically anisotropic layer 30 formed by orienting the molecules of the birefringence-induced material layer 20 by irradiation with polarization. It is a schematic cross-sectional view which shows. FIG. 1C shows the state after the surface alignment step, in which the base material 10, the inner layer 31 having the same orientation as the first optically anisotropic layer 30, and the surface opposite to the base material 10 are oriented. It is a schematic cross-sectional view which shows the laminated body with the 1st optical anisotropic layer 30 which consists of the adjacent layer 32 which was given the orientation different from the inner layer 31. FIG. 1D shows a state after the second optically anisotropic layer forming step, in which a base material 10, a first optically anisotropic layer 30 composed of an inner layer 31 and an adjacent layer 32, and a polymerizable liquid crystal material are provided. It is a schematic cross-sectional view which shows the optical laminated body 100 with the 2nd optically anisotropic layer 40 formed by applying.

By forming a birefringence-inducing material on the base material 10, the birefringence-inducing material layer 20 can be formed as shown in FIG. 1A. By irradiating the birefringence-inducing material layer 20 made of the birefringence-inducing material with polarization for developing a phase difference, the molecular orientation of the birefringence-inducing material can be induced. As a result, as shown in FIG. 1B, a first optically anisotropic layer 30 oriented so as to have a predetermined delayed phase axis is formed from the optically isotropic birefringence-induced material layer 20. The optical characteristics of the first optically anisotropic layer 30 can be controlled by adjusting the film forming conditions of the birefringence-inducing material in the film forming step and the polarization irradiation conditions in the light irradiation step. In the light irradiation step, since there is no other layer on the birefringence-induced material layer 20, the birefringence-induced material layer 20 is irradiated with the desired polarization without changing the polarization state of the irradiated polarization. Is possible.

Next, the surface of the first optically anisotropic layer 30 shown in FIG. 1B is oriented so as to have an orientation different from the orientation given in the light irradiation step, so that the first optically anisotropic layer 30 is oriented. The adjacent layer 32 can be formed on the surface. As a result, as shown in FIG. 1C, the first optically anisotropic layer 30 is formed with two layers, an inner layer 31 having the originally formed orientation and an adjacent layer 32 having a different orientation. Will be done.

Then, when the polymerizable liquid crystal material was applied on the adjacent layer 32 shown in FIG. 1C, the adjacent layer 32 served as an alignment film and was oriented corresponding to the orientation of the adjacent layer 32 as shown in FIG. 1D. The second optically anisotropic layer 40 can be formed. As a result, a second optically anisotropic layer 40 oriented so as to have a slow phase 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) is changed to the phase difference of 1/4 wavelength or the position of 1/2 wavelength. It can be controlled to have a phase difference. Further, in such a manufacturing method, the orientation of the inner layer 31 and the adjacent layer 32 can be adjusted independently, so that the second optically anisotropic layer 40 is considered in consideration of the relationship with the orientation of the inner layer 31. Can be imparted with the desired orientation and can intersect each other on the desired slow axis.

(Film formation process)
The birefringence-inducing material layer is formed by forming a film of the above-mentioned birefringence-inducing material. In FIG. 1A, the birefringence-induced material layer 20 is laminated on the base material 10, but the base material 10 may be omitted. When a base material is used, it may be a base material made of an optically isotropic material, and may be a transparent base material made of an optically isotropic phase such as glass or a triacetyl cellulose film (TAC film). good. Alternatively, as the base material, a base material made of a material having low adhesion to the birefringence-inducing material layer (first optically anisotropic layer), such as a general-purpose polyester film, is used as the mold release base material. May be. When a release base material is used, it can be peeled off after forming the optical laminate of the present invention, so that the optical characteristics of the base material itself need not be considered, and an opaque base material may be used. For example, after forming the optical laminate of the present invention on a substrate, it is bonded 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. By doing so, the optical laminate is configured to have no base material, and the thickness is substantially only the thickness of the first optically anisotropic layer and the second optically anisotropic layer. It can be a member.

The birefringence-inducing material layer is a cast film formed by dissolving the birefringence-inducing material as described above in a solvent to prepare a solution, applying this solution on a substrate, and drying to remove the solvent. There may be. When forming a coating film of a birefringence-inducing material, the Nz coefficient is an index of the refractive index component in the in-plane direction and the thickness direction. It is possible by adjusting the coating conditions and the drying conditions that affect the orientation of the type liquid crystal polymer). Further, as described above, the in-plane phase difference value (Re) is a parameter that affects not only the refractive index but also the thickness. Therefore, as the control of the in-plane phase difference value (Re), the above coating is performed. In addition to the conditions and drying conditions, it is possible by adjusting the concentration of the solution and the like at the time of film formation to adjust the thickness of the birefringence-induced material layer.

The solvent of the double refraction organic material affects the Nz coefficient and the in-plane retardation value (Re) due to the difference in its solubility and dryness, but can be appropriately selected depending on the type of the double refraction-inducing material. For example, dioxane, dichloroethane, cyclohexanone, toluene, tetrahydrofuran, o-dichlorobenzene, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol derivatives (eg, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether (1,2-dimethoxyethane), diethylene glycol monoethyl). Examples include ethers, diethylene glycol dimethyl ethers, etc.), propylene glycol derivatives (eg, propylene glycol monomethyl ethers, propylene glycol 1-monomethyl ether 2-acetate, etc.), and these solvents may be used alone or in combination of two or more. May be good.

The concentration of the solution can be appropriately adjusted in consideration of the influence on the film thickness and the like, and may contain, for example, 5 to 50% by weight of the birefringence-inducing material, preferably 8 to 40% by weight. , More preferably 10 to 25% by weight. A known coating method such as spin coating or roll coating can be used for applying the solution to the substrate.

After coating, it needs to be dried to remove the solvent. Although it depends on the solvent used, the drying rate may be adjusted by adjusting the drying temperature and time in order to control the Nz coefficient and the in-plane retardation value (Re). The Nz coefficient tends to decrease by slowing down the drying rate, and the drying rate can also be adjusted by selecting a solvent. For example, the drying rate can be slowed down by using a high boiling point solvent.

(Light irradiation process)
In the light irradiation step, the birefringence-induced material layer may be irradiated with polarization (first polarization) for developing a phase difference. By performing the light irradiation step, a selective photoreaction of molecules occurs not only on the surface of the birefringence-induced material layer but also inside, the orientation of the molecules is induced, and the first optically anisotropic layer is formed. Will be done. In the method for producing an optical laminate of the present invention, it is possible to directly irradiate the birefringence-induced material layer with polarized light without interposing another layer, so that the intended slow-phase axis can be formed by the irradiated polarized light. can.

The first polarization is a photosensitive group of a side chain type liquid crystal polymer such as infrared rays, visible rays, ultraviolet rays (for example, near ultraviolet rays, far ultraviolet rays, etc.), X rays, charged particle rays (for example, electron beams, etc.). The wavelength of the light is not particularly limited as long as it is light having a wavelength that causes a photoreaction, and varies depending on the type of side chain structure of the side chain type liquid crystal polymer, but the wavelength of the light may be 200 to 500 nm. The first polarization may be, for example, linear polarization of ultraviolet rays, and in this case, for example, even if an ultraviolet irradiation device such as a high-pressure mercury lamp is used as a light source and the polarization is converted to linear polarization via a Grantailer prism. good.
Further, the irradiation amount of the first polarization is, for example, 10 mJ / cm ² from the viewpoint of aligning not only the surface of the birefringence-induced material layer but also the inside, and from the viewpoint of adjusting the Nz coefficient and the in-plane retardation value (Re). It may be up to 10 J / cm ² , preferably 50 mJ / cm ² to 1 J / cm ² , and more preferably 100 mJ / cm ² to 500 mJ / cm ² .

The method for producing an optical laminate of the present invention may include a heating step for heating the formed first optically anisotropic layer, if necessary, after the light irradiation step. The heating step induces molecular orientation depending on the irradiation direction and vibration direction of the first polarized light irradiated in the light irradiation step, and the unaligned molecules are also oriented according to the oriented molecules, but the side chains are further heated. The type liquid crystal polymer can perform molecular movement and can promote the orientation of unaligned molecules. After heating, it may be cooled to about room temperature by, for example, leaving it to stand.

The heating temperature in the heating step is not particularly limited as long as the orientation of the unoriented molecule is induced along the side chain in which the side chain liquid crystal polymer causes a photoreaction by molecular motion, but the liquid crystal of the birefringence-inducing material is liquid crystal. It is preferable to set the temperature to be equal to or higher than the phase transition temperature and lower than or equal to 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.

The heating time is not particularly limited as long as the orientation of the unoriented molecule is induced along the side chain in which the liquid crystal polymer causes a photoreaction by molecular motion, but the type of the liquid crystal polymer, the heating temperature, etc. It may be appropriately set according to the above, and may be carried out for, for example, 1 minute or longer, preferably 2 minutes or longer, and more preferably 3 minutes or longer. The upper limit is not particularly limited, but from the viewpoint of economic efficiency, it may be about 60 minutes (preferably about 40 minutes, more preferably about 30 minutes).

(Surface orientation process)
In the surface orientation step, the surface of the first optically anisotropic layer may be oriented so as to be oriented differently from the inner layer thereof. By performing the surface orientation treatment, an adjacent layer is formed on the first optically anisotropic layer, and the two layers of the inner layer and the adjacent layer, which are composed of the same birefringence-inducing materials but have different orientation states, are formed. It is formed in the first optically anisotropic layer. The inner layer may indicate a portion of the first optically anisotropic layer other than the adjacent layer.

The method of alignment treatment is not particularly limited as long as the surface of the first optically anisotropic layer can form an alignment layer different from the inner layer thereof, and examples thereof include rubbing treatment and photoalignment treatment by polarization irradiation. In the rubbing process, the orientation direction can be controlled by rubbing the surface of the first optically anisotropic layer in a fixed direction by rotating a roller wrapped with a cloth such as cellulose, nylon, or polyester while pushing it at a constant pressure. Therefore, an adjacent layer in a desired orientation direction can be formed, but the orientation treatment method is preferably photoalignment treatment by polarization irradiation.

In the surface orientation step, the surface of the first optically anisotropic layer is irradiated with a second polarization having a polarization axis direction different from that of the first polarization, and the layer adjacent to the first optically anisotropic layer is formed. It may be the second light irradiation step to form. In the second light irradiation step, even after the molecular orientation by the first light irradiation step (the above-mentioned light irradiation step) (preferably, the first light irradiation step and the heating step), the first polarization is applied. By irradiating the second polarization with different polarization axis directions, an axis-selective optical reaction is selectively generated in the vicinity of the surface centering on the unreacted birefringence-inducing material of the first optically anisotropic layer. Perhaps because of this, it is possible to impart a different orientation to the vicinity of the surface than the inner layer. On the other hand, probably because the molecules in the inner layer of the first optically anisotropic layer are already oriented with a high degree of orientation, the inside of the first optically anisotropic layer even after the second light irradiation step. The layer orientation itself is not transformed.

As the second polarization, light of various wavelengths described above can be used as the first polarization, and for example, linear polarization of ultraviolet rays may be used. Further, as the second polarization, light of a different type from that of the first polarization irradiated in the light irradiation step may be used, or light of the same type may be used.

The second polarization may have a polarization axis direction different from that of the first polarization, for example, the axis angle may differ from the polarization axis of the first polarization by 5 to 85 °, preferably 10. It may differ by -80 °, more preferably 20-70 °. Here, the difference in the axis angle between the polarization axis of the second polarization and the polarization axis of the first polarization is the orientation state near the surface of the first optically anisotropic layer after the first light irradiation step (not yet). The slow axis of the second optically anisotropic layer to be formed later can be arbitrarily set by adjusting in consideration of the abundance ratio of the birefringence-inducing material in the reaction.

The irradiation amount of the second polarization may be, for example, 50 mJ / cm ² to 20 J / cm ² , preferably 100 mJ / cm, from the viewpoint of reorienting the surface of the first optically anisotropic layer to be oriented. It may be cm ² to 10 J / cm ² , more preferably 150 mJ / cm ² to 1 J / cm ² .

If necessary, the method for producing an optical laminate of the present invention may further include a surface treatment step of treating the surface of the birefringence-induced 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 a second polarization irradiation and a rubbing treatment. Further, when the heating step is performed after the first light irradiation step, the surface treatment step may be performed after the heating step.

In the surface treatment step, a solvent is applied to the surface of the first optically anisotropic layer to dissolve the surface portion, whereby the molecular orientation applied by the first light irradiation step can be relaxed and a random state can be obtained. Perhaps because of this, the orientation of the surface portion of the first optically anisotropic layer once formed by the first polarization can be eliminated, and the orientation of the adjacent layer of the first optically anisotropic layer becomes isotropic. can do. In the surface treatment step, the solvent may be applied to the surface of the first optically anisotropic layer and then dried. The drying method is not particularly limited as long as the applied solvent can be evaporated, but for example, it may be left to dry naturally. Only the surface to which the solvent is applied can be isotropic.

Since the surface becomes isotropic, the light orientation of the surface becomes easy in the subsequent second light irradiation step, so that the irradiation amount of the second polarization can be reduced. When the surface treatment step is performed, the irradiation amount of the second polarization may be, for example, 0.1 mJ / cm ² to 500 mJ / cm ² , preferably 0.5 mJ / cm ² to 400 mJ / cm ² . More preferably, it may be 1 mJ / cm ² to 300 mJ / cm ² .
Further, when the surface treatment step is performed, the ratio of the irradiation amount of the first polarization to the irradiation amount of the second polarization (first polarization / second polarization) is 1/5 to 100/1. It may be preferably 1/2 to 80/1, more preferably 1 / 1.5 to 50/1.

Since the surface is isotropic, it is not necessary to consider the orientation state of the adjacent layer of the first optically anisotropic layer in the subsequent second light irradiation step, so that the polarization axis of the second polarization can be used. The axis angle can be directly reflected on the slow axis of the second optically anisotropic layer. Therefore, the axis angle of the polarization axis of the second polarization can be easily selected with respect to the setting of the slow phase axis of the second optically anisotropic layer to be formed later.

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 is a good solvent for the birefringence-inducing material. It may be a poor solvent. The solvent used in the surface treatment step is, for example, a good birefringence-inducing material from the viewpoint of making the surface of the first optically anisotropic layer isotropic and suppressing the dissolution to the inside to disturb the orientation. It may be a mixed solvent in which a solvent and a poor solvent are mixed. When a mixed solvent containing a good solvent and a poor solvent of the compound refraction-inducing material is used, it can be appropriately adjusted depending on the solubility of the solvent used in the compound refraction-inducing material. / Poor solvent) may be 1/100 to 100/1, preferably 1/50 to 50/1, and more preferably 1/10 to 10/1.

The solvent used in the surface treatment step is, for example, water; an alcohol solvent such as methanol, ethanol, propanol, isopropyl alcohol, pentanol, hexanol; an aliphatic or alicyclic solvent such as hexane, heptane, octane, 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; ethyl ether and propyl Ether solvents such as ether, isopropyl ether, methyl ethyl ether, methyl propyl ether, tetrahydrofuran, dioxane; nitrile solvents such as acetonitrile and propionitrile; sulfoxide solvents such as dimethyl sulfoxide; amides such as N, N-dimethylformamide System solvent; Ester solvent such as methyl acetate, ethyl acetate, butyl acetate; Glycol solvent such as ethylene glycol and propylene glycol; Glycol monoethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol 1-monomethyl ether 2 -Glycol ether solvent such as acetate; halogenated hydrocarbon solvent such as carbon tetrachloride, chloroform, dichloromethane, dichloroethane, dichlorobenzene; and the like. These solvents may be used alone or in combination of two or more. Since these solvents have different solubility depending on the type of birefringence-inducing material, it is necessary to consider whether the solvent is a good solvent or a poor solvent depending on the birefringence-inducing material used. can.
In the present invention, a good solvent means a solvent having a solubility in a solute of 1% by mass or more at 25 ° C., and a poor solvent means a solvent having a solubility in a solute of less than 1% by mass at 25 ° C.

For example, dioxane, dichloroethane, cyclohexanone, toluene, tetrahydrofuran, o-dichlorobenzene, dimethoxyethane and the like may be used as a good solvent for the birefringence-inducing material, and ethanol, methanol, n- as a poor solvent for the birefringence-inducing material. You may use hexane or the like. These good solvents and poor solvents may be mixed at the above-mentioned mixed weight ratio and used as a mixed solvent.

(Second optically anisotropic layer forming step)
In the second optically anisotropic layer forming step, even if a polymerizable liquid crystal material is applied on the adjacent layer of the first optically anisotropic layer that has been oriented, the second optically anisotropic layer is formed. good. By performing the second optical anisotropy layer forming step, the adjacent layer oriented in the surface orientation step acts as an alignment film, and therefore the second optical anisotropy oriented using the orientation direction. Layers can be formed. The in-plane retardation value (Re) of the second optically anisotropic layer can be controlled by adjusting the concentration of the solution or the like at the time of applying the polymerizable liquid crystal material to adjust the thickness.

In the second optically anisotropic layer forming step, the above-mentioned polymerizable liquid crystal material is applied on the adjacent layer of the first optically anisotropic layer. The application may be carried out by dissolving the polymerizable liquid crystal material in a solvent and applying it as a solution by a known coating method such as spin coating or roll coating. The solvent can be appropriately selected depending on 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 derivative (for example, 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.), etc., these solvents may be used alone or in two. You may use it in combination of more than seeds.

The solvent of the polymerizable liquid crystal material can be selected not only according to the combination of the types of the birefringence-inducing material and the polymerizable liquid crystal material, but also according to the orientation state of the adjacent layer. For example, if the majority of the molecules in the adjacent layer are in the desired orientation (eg, when a surface treatment step is performed, or when a rubbing treatment is performed as an alignment treatment), the orientation of the adjacent layer is second. The solvent of the polymerizable liquid crystal material is preferably a poor solvent of the birefringence-inducing material from the viewpoint of suppressing the orientation of the first optically anisotropic layer from being disturbed while imparting it to the optically anisotropic layer. On the other hand, when only a part of the molecules of the adjacent layer has a desired orientation, the solvent of the polymerizable liquid crystal material is preferably a mixed solvent in which a good solvent and a poor solvent of the birefringence-inducing material are mixed. Although the mechanism in this case is not clear, when a poor solvent of the birefringence-inducing material is contained as the solvent of the polymerizable liquid crystal material, the first optically anisotropic layer is not invaded and the orientation is suppressed from being disturbed. can do. On the other hand, if a good solvent of the birefringence-inducing material is contained as the solvent of the polymerizable liquid crystal material, the wettability of the solution with respect to the adjacent layer is improved, or it is polymerizable with respect to the orientation of only a part of the molecules of the adjacent layer. The molecules of the liquid crystal material can be aligned, and as a result, the second optically anisotropic layer can be oriented. The solvent of the polymerizable liquid crystal material can be appropriately adjusted according to the combination of the types of the birefringence-inducing material and the polymerizable liquid crystal material and the orientation state of the adjacent layer, but the orientation of the first optically anisotropic layer is maintained. From this point of view, it is preferable to contain a poor solvent for the birefringence-inducing material so as not to invade the adjacent layer. May be 0/100 to 100/1, preferably 0/100 to 50/1, and more preferably 0/100 to 10/1. As the solvent of the polymerizable liquid crystal material, a general solvent can be used depending on the purpose, but for example, toluene, tetrahydrofuran, ethylene glycol derivative, propylene glycol derivative and the like may be contained.

A coating film is formed by applying the solution, and if necessary, it is heated to dry the coating film. At that time, the adjacent layer of the first optically anisotropic layer existing at the lower part functions as an alignment film (orientation-imparting film), and the alignment of the liquid crystal molecules occurs. As a result, a second optically anisotropic layer in which the liquid crystal is oriented in a predetermined direction is formed.

The second optically anisotropic layer forming step may include a heating step and / or a light irradiation step (for example, a non-polarized irradiation step), if necessary, after forming the coating film of the polymerizable liquid crystal material. The polymerizable liquid crystal material is already oriented in a predetermined direction corresponding to the orientation of the adjacent layer of the first optically anisotropic layer by forming a coating film, and is subsequently heated and / or irradiated with light. The orientation is fixed by the polymerization and / or cross-linking of the polymerizable liquid crystal material in the step (eg, unpolarized irradiation step).
Specifically, when the polymerizable liquid crystal material is made of a heat-polymerizable material, the orientation is fixed by polymerization by heating. When it is made of a photopolymerizable material, polymerization occurs when it is irradiated with light, and the orientation is fixed. When made of a crosslinkable material, crosslinkage occurs during heating and / or irradiation with light, and the orientation is fixed.

Further, when the polymerizable liquid crystal material contains a cross-linking agent and the cross-linking agent has a functional group capable of forming a cross-linking bond with the birefringence-inducing material, the first optical difference is obtained by applying thermal energy and / or light energy. Crosslinks can be formed between the layers of the square layer and the second optically anisotropic layer.

The heating step in the second optically anisotropic layer forming step is not particularly limited as long as the above-mentioned polymerization and / or cross-linking reaction proceeds, but suppresses disturbing the orientation of the inner layer of the first optically anisotropic layer. From the viewpoint, it is preferable to carry out the heating at a heating temperature equal to or lower than the isotropic phase transition temperature (preferably less than the isotropic phase transition temperature) of the birefringence-inducing material. For example, it may be 70 to 180 ° C., preferably 70 to 150 ° C., and more preferably 70 to 140 ° C. The heating time may be, for example, 1 minute or longer, preferably 2 minutes or longer, and more preferably 3 minutes or longer. The upper limit is not particularly limited, but from the viewpoint of economic efficiency, it may be about 60 minutes (preferably about 40 minutes, more preferably about 30 minutes).

The light irradiation step in the second optically anisotropic layer forming step is not particularly limited as long as the above-mentioned polymerization and / or crosslinking reaction proceeds, but non-polarized light is preferable as the light to be irradiated. As the unpolarized light, light having various wavelengths described above can be used as the first polarized light or the second polarized light, and for example, unpolarized ultraviolet rays may be used. The irradiation amount of light may be 10 mJ / cm ² to 10 J / cm ² , preferably 50 mJ / cm ² to 1 J / cm ² , and more preferably 100 mJ / cm ² to 500 mJ / cm ² . ..

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the present Examples.

(Monomer 1)
4- (6-Hydroxyhexyloxy) cinnamic acid was synthesized by heating p-coumaric acid and 6-chloro-1-hexanol under alkaline conditions. A large excess of methacrylic acid was added to this product in the presence of p-toluenesulfonic acid to cause an esterification reaction, and Monomer 1 represented by the following chemical formula was synthesized.

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

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

In the following examples and comparative examples, the optical characteristics (Nz coefficient, in-plane retardation value Re, etc.) of the obtained optical laminate are obtained by using a birefringence measuring device (AXOMETRICS, AxoScan), and the thickness is the film thickness. The measurement was performed using a meter (F20 manufactured by FILMETRIS).

(Example 1)
Copolymer 1 was dissolved in 1,2-dimethoxyethane (DME) in an amount of 15% by weight to prepare a solution. This solution was applied onto a cover glass substrate to a thickness of about 3.5 μm using a spin coater, and the coating film was dried at 60 ° C. for 3 minutes and then at 80 ° C. for 3 minutes. Then, the ultraviolet rays from the high-pressure mercury lamp were converted into linearly polarized light using a Grantailer prism (first polarization), and the dried coating film was irradiated with the dried coating film for 100 seconds (irradiation amount 100 mJ / cm ² ). Next, the film 1 (first optically anisotropic layer) was formed by inducing orientation by heating at 130 ° C. for 3 minutes and then slowly cooling to room temperature. The optical characteristics of the obtained film 1 were an Nz coefficient of 0.2 and an in-plane retardation value of 250 nm. The axial direction of the in-plane phase difference was 90 ° with respect to the irradiated polarization vibration direction.

Subsequently, a mixed solution having a volume ratio of tetrahydrofuran (THF) and ethanol (THF: ethanol) of 1: 6 was applied to the obtained membrane 1 with a spin coater, and dried by leaving it to stand. Further, using a Grantailer prism, the ultraviolet rays from the high-pressure mercury lamp are converted into a linear polarization whose polarization vibration direction is 60 ° different from the polarization vibration direction of the first polarization, and the polarization (second polarization) is applied to the film 1. It was irradiated for 300 seconds (irradiation amount 300 mJ / cm ² ).

Mix 100 parts by weight of a polymerizable liquid crystal compound (“LC-242”, manufactured by BASF) and 5 parts by weight of a photopolymerization initiator (“Irgacure 907”, manufactured by Ciba Specialty Chemicals), and mix THF and propylene glycol 1-monomethyl. A solution was prepared by dissolving the ether 2-acetate (PGMEA) in a mixed solvent having a volume ratio (THF: PGMEA) of 1: 1 so as to be 20% by weight. This solution was applied onto the surface of the membrane 1 irradiated with the second polarization to a thickness of about 0.9 μm using a spin coater, heated at 70 ° C. for 3 minutes, and then cooled to room temperature. Further, a non-polarizing ultraviolet ray is irradiated for 100 seconds (irradiation amount 300 mJ / cm ² ) to polymerize the polymerizable liquid crystal compound to form a film 2 (second optically anisotropic layer), and the film 1 and the film 2 are formed. Was obtained. In order to investigate the optical properties of the obtained laminate, only the film 2 was transferred to an optically isotropic film with an adhesive, and the optical properties of the film 2 were measured. The optical characteristics of the film 2 were an Nz coefficient of 1 and an in-plane retardation value of 115 nm. The axial direction of the in-plane phase difference was 90 ° with respect to the irradiated polarization vibration direction. As a result, the angle formed by the slow axis of the film 1 and the film 2 was 60 °.

The laminate thus prepared was bonded to a linear polarizing plate using an adhesive to prepare a circular polarizing plate. The composition order of the circular polarizing plate is that the linear polarizing plate, the film 1, and the film 2 are laminated in this order, and the bonding angle is 15 ° with respect to the transmission axis of the linear polarizing plate, the slow axis of the film 1 is 15 °, and the film 2 is formed. The slow axis of was set to 75 °.
The viewing angle characteristics of the reflected light of this circularly polarizing plate are confirmed by calculation using simulation software (“LCDMaster”, manufactured by Shintech), and FIG. 2 shows the reflection characteristics of the circularly polarizing plate. Compared with FIG. 6 of Comparative Example 1 described later, it can be estimated from the calculation that the high contrast range (the dark color range in the figure) is much wider and the viewing angle characteristic of the reflected light is improved. Further, when the reflection characteristics in 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.
Further, this circular polarizing plate was placed on a mirror surface and the spectrum of reflected light was measured (FIG. 3). It was confirmed that the spectrum of the reflected light had wide-wavelength antireflection characteristics as compared with the single-layer product of the uniaxially stretched cyclic polyolefin λ / 4 retardation film.

(Example 2)
Copolymer 1 was dissolved in a mixed solvent having a volume ratio of DME, THF and cyclohexanone (DME: THF: cyclohexanone) of 7: 5: 5 so as to be 15% by weight to prepare a solution. This solution was applied onto a cover glass substrate to a thickness of about 2 μm using a spin coater, and the coating film was allowed to stand at room temperature for 10 minutes and then dried at 80 ° C. for 3 minutes. Then, the ultraviolet rays from the high-pressure mercury lamp were converted into linearly polarized light using a Grantailer prism (first polarization), and the dried coating film was irradiated with the dried coating film for 100 seconds (irradiation amount 100 mJ / cm ² ). Next, the film 1 (first optically anisotropic layer) was formed by inducing orientation by heating at 130 ° C. for 3 minutes and then slowly cooling to room temperature. The optical characteristics of the obtained film 1 were that the Nz coefficient was −0.1 and the in-plane retardation value was 110 nm. The axial direction of the in-plane phase difference was 90 ° with respect to the irradiated polarization vibration direction.

Subsequently, a mixed solution having a volume ratio of THF and ethanol (THF: ethanol) of 1: 6 was applied to the obtained membrane 1 with a spin coater, and dried by leaving it to stand. Further, using a Grantailer prism, the ultraviolet rays from the high-pressure mercury lamp are converted into a linear polarization whose polarization vibration direction is 60 ° different from the polarization vibration direction of the first polarization, and the polarization (second polarization) is applied to the film 1. It was irradiated for 300 seconds (irradiation amount 300 mJ / cm ² ).

Mix 100 parts by weight of a polymerizable liquid crystal compound (“LC-242”, manufactured by BASF) and 5 parts by weight of a photopolymerization initiator (“Irgacure 907”, manufactured by Ciba Specialty Chemicals), and the volume ratio of THF and PGMEA. (THF: PGMEA) was dissolved in a 1: 1 mixed solvent in an amount of 20% by weight to prepare a solution. This solution was applied onto the surface of the membrane 1 irradiated with the second polarization to a thickness of about 2.3 μm using a spin coater, heated at 70 ° C. for 3 minutes, and then cooled to room temperature. Further, a non-polarizing ultraviolet ray is irradiated for 100 seconds (irradiation amount 300 mJ / cm ² ) to polymerize the polymerizable liquid crystal compound to form a film 2 (second optically anisotropic layer), and the film 1 and the film 2 are formed. Was obtained. In order to investigate the optical properties of the obtained laminate, only the film 2 was transferred to an optically isotropic film with an adhesive, and the optical properties of the film 2 were measured. The optical characteristics of the film 2 were an Nz coefficient of 1 and an in-plane retardation value of 250 nm. The axial direction of the in-plane phase difference was 90 ° with respect to the irradiated polarization vibration direction. As a result, the angle formed by the slow axis of the film 1 and the film 2 was 60 °.

The laminate thus prepared was bonded to a linear polarizing plate using an adhesive to prepare a circular polarizing plate. The composition order of the circular polarizing plate is that the linear polarizing plate, the film 2, and the film 1 are laminated in this order, and the bonding angle is 15 ° with respect to the transmission axis of the linear polarizing plate, the slow axis of the film 2 is 15 °, and the film 1 is formed. The slow axis of was set to 75 °.
The viewing angle characteristics of the reflected light of this circularly polarizing plate are confirmed by calculation using simulation software (“LCDMaster”, manufactured by Shintech), and FIG. 4 shows the reflection characteristics of the circularly polarizing plate. Compared 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 characteristic of the reflected light is improved. Further, when the circularly polarizing plate was arranged on the mirror surface and the reflection characteristics in oblique view were visually confirmed, it was confirmed that the reflected light could be suppressed as compared with the circularly polarizing plate of Comparative Example 1.
Using this circular polarizing plate, the wavelength dependence of the phase difference value of the transmitted light (straight polarizing plate on the incident side, film 1 on the emitting side, substrate) was measured (FIG. 5). It was confirmed that the phase difference wavelength dependence indicates the inverse wavelength dispersibility.

(Comparative Example 1)
Using a uniaxially stretched cyclic polyolefin λ / 2 retardation film (Nz coefficient 1) and a uniaxially stretched cyclic polyolefin λ / 4 retardation film (Nz coefficient 1), a linear polarizing plate is used via an adhesive. To prepare a circular polarizing plate. The composition order of the circular polarizing plate is that the linear polarizing plate, the λ / 2 retardation film, and the λ / 4 retardation film are laminated in this order, and the bonding angle is λ / 2 with respect to the transmission axis of the linear polarizing plate. The slow axis of the retardation film was set to 15 °, and the slow axis of the λ / 4 polarizing film was set to 75 °.
It was confirmed that even with this circularly polarizing plate, the phase difference wavelength dependence shows the inverse wavelength dispersibility. However, it can be estimated from the calculation that the reflection characteristics of this circular polarizing plate are inferior in the viewing angle characteristics of the reflected light as compared with Examples 1 and 2 (FIG. 6). Actually, when the circularly polarizing plate was arranged on the mirror surface and the reflection characteristics in oblique view were visually confirmed, the reflected light could not be suppressed as compared with the circularly polarizing plates of Examples 1 and 2. Was confirmed.

The optical laminate of the present invention can be used as a retardation plate, and can be used in applications such as a polarizing plate used in a liquid crystal display device and an organic EL display device, and an optical compensation film. 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.

As described above, a preferred embodiment of the present invention has been described with reference to the drawings, but those skilled in the art can easily assume various changes and modifications within a trivial range by looking at the present specification. There will be. Therefore, such changes and amendments are construed as being within the scope of the invention as defined by the claims.

10 ... Substrate 20 ... Birefringence-induced material layer 30 ... First optical anisotropy layer 31 ... Internal layer 32 ... Adjacent layer 40 ... Second optical anisotropy Layer 100 ... Optical laminate

Claims (5)

1. It contains 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. It is an optical laminate,
   The Nz coefficient of the first optically anisotropic layer is −0.5 ≦ Nz ≦ 0.5, and the second optically anisotropic layer has the optical characteristics of the positive A plate.
   One of the first optically anisotropic layer and the second optically anisotropic layer has a phase difference of 1/4 wavelength, and the other layer has a phase difference of 1/2 wavelength. Have an 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 are non-parallel and non-orthogonal. Optical laminates that intersect at an angle.
3. The optical laminate according to claim 1 or 2, wherein the first optically anisotropic layer has a phase difference of 1/2 wavelength and has an Nz coefficient of 0 ≦ Nz ≦ 0.5. , Optical laminate.
4. The optical laminate according to claim 1 or 2, wherein the first optically anisotropic layer has a phase difference of 1/4 wavelength and has an Nz coefficient of −0.5 ≦ Nz ≦ 0. An optical laminate of 5.
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.

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