JP2024144086A - Polarizing Film - Google Patents

Abstract

To provide a polarizing film with which it is possible to suppress interference irregularity due to the interface reflection of incident light.SOLUTION: Provided is a polarizing film 1 in which a base material 2, an orientation membrane 3, and a polarizing membrane 4 are laminated in the order stated. The angle formed by the slow axis direction of the base material 2 and the absorption axis direction of the polarizing membrane 4 is 45°±5°. A difference in refractive index for visible light between the polarizing membrane 4 and the orientation membrane 3 satisfies formula (1), and a difference in refractive index for visible light between the orientation membrane 3 and the base material 2 satisfies formula (2) below. Formula (1): |n(polarizing membrane)-n(orientation membrane)|≤0.06; formula (2): |n(orientation membrane)-n(base material)|≤0.06. (In formula (1), the n(polarizing membrane) represents the refractive index of the polarizing membrane in the transmission axis direction).SELECTED DRAWING: Figure 1

Description

This disclosure relates to a polarizing film.

In flat panel displays such as liquid crystal displays and organic EL displays, polarizing films are used for the purpose of optical compensation. Polarizing films are generally made up of a substrate, an alignment film, and a polarizing film laminated in that order.

In recent years, there has been an increasing demand for thinner flat panel displays, which has led to a demand for thinner polarizing films as well. An example of a thin polarizing film is the polarizing film described in Patent Document 1. This conventional polarizing film is made of a composition containing a polymerizable liquid crystal compound and a dichroic dye. Thin polarizing films that have an absorption axis oblique to the longitudinal direction of the polarizing film are also known.

Special Publication No. 2007-510946

In polarizing films like those described above, there was a problem in that interference unevenness became noticeable when the interfacial reflection of incident light between the polarizing film and the alignment film, and between the alignment film and the substrate, became stronger.

This disclosure has been made to solve the above problems, and aims to provide a polarizing film that can suppress interference unevenness caused by interfacial reflection of incident light.

A polarizing film according to one aspect of the present disclosure is a polarizing film having a substrate, an alignment film, and a polarizing film laminated in this order, wherein the angle between the slow axis direction of the substrate and the absorption axis direction of the polarizing film is 45°±5°, the refractive index difference between the polarizing film and the alignment film for visible light satisfies the following formula (1), and the refractive index difference between the alignment film and the substrate for visible light satisfies the following formula (2).
|n (polarizing film) - n (alignment film) | ≦ 0.06 ... (1)
|n (alignment film)-n (substrate)|≦0.06 ... (2)
(In formula (1), n (polarizing film) represents the refractive index in the transmission axis direction of the polarizing film.)

In this polarizing film, by limiting the refractive index difference between the alignment film and the substrate and between the alignment film and the substrate within the above range, it is possible to suppress the interfacial reflection of incident light between the polarizing film and the alignment film and between the alignment film and the substrate. Therefore, in this polarizing film, it is possible to suppress interference unevenness caused by interfacial reflection of incident light.

The thickness of the alignment film is preferably 10 nm to 400 nm. In this case, in a polarizing film with an alignment film thickness in this range, interference unevenness caused by interfacial reflection of incident light can be effectively suppressed.

A hard coat layer may be adjacent to the surface of the substrate opposite the alignment film. When producing a polarizing film, it is conceivable that the substrate may warp due to shrinkage that occurs when the polarizing film is cured, resulting in wrinkles in the resulting polarizing film. By having a hard coat layer adjacent to the surface of the substrate opposite the alignment film, warping of the substrate due to shrinkage that occurs when the polarizing film is cured can be suppressed, and wrinkles can be suppressed from occurring in the resulting polarizing film.

The substrate, alignment film, and polarizing film may be long. In this case, a long polarizing film can be obtained that can suppress interference unevenness caused by interfacial reflection of incident light. By continuously bonding polarizing films cut from a long polarizing film to various display devices, display devices using a polarizing film that suppresses interference unevenness caused by interfacial reflection of incident light can be efficiently manufactured.

The angle between the longitudinal direction and the slow axis direction of the substrate is preferably 0°±5° or 90°±5°. This results in a polarizing film that exhibits high ellipticity.

This disclosure makes it possible to suppress interference unevenness caused by interfacial reflection of incident light.

FIG. 1 is a schematic diagram showing a layer structure of a polarizing film according to an embodiment of the present disclosure. FIG. 2 is a diagram showing layer configurations of polarizing films according to examples and comparative examples. FIG. 1 is a diagram showing evaluation results of polarizing films according to Examples and Comparative Examples.

Below, a preferred embodiment of a polarizing film according to one aspect of the present disclosure will be described in detail with reference to the drawings.

Figure 1 is a schematic diagram showing the layer structure of a polarizing film according to one embodiment of the present disclosure. As shown in Figure 1, the polarizing film 1 is constructed by laminating a substrate 2, an alignment film 3, and a polarizing film 4 in this order. In this embodiment, the substrate 2, the alignment film 3, and the polarizing film 4 are all long, and a long polarizing film 1 is constructed.

The term "long" includes both a state in which the film is wound into a roll and a state in which the film is unwound from a roll. The length of the long polarizing film 1 in the longitudinal direction (the direction in which the polarizing film 1 extends) is, for example, 10 m to 3000 m, and preferably 100 m to 200 m. The length of the long polarizing film 1 in the transverse direction (the direction perpendicular to the direction in which the polarizing film 1 extends) is, for example, 0.1 m to 5 m, and preferably 0.2 m to 2 m.

The long polarizing film 1 is cut to the required size and used in various display devices. Examples of display devices include liquid crystal display devices, organic EL display devices, inorganic EL display devices, electron emission display devices, electronic paper, and piezoelectric ceramic displays. These display devices may display two-dimensional images or three-dimensional images.

The substrate 2 is made of, for example, resin. The substrate 2 is particularly transparent to visible light, with a transmittance of 80% or more for light with wavelengths of 380 nm to 780 nm. Taking into consideration practical handling and processability, the thickness of the substrate 2 is, for example, 5 μm to 300 μm, and preferably 20 μm to 200 μm.

The substrate 2 is, for example, a retardation film that functions as a quarter-wave plate. The substrate 2 as a retardation film is obtained by stretching a long substrate that does not have retardation. The slow axis direction of the substrate 2 varies depending on the stretching method. Stretching methods include uniaxial stretching, biaxial stretching, and oblique stretching. The angle between the longitudinal direction of the polarizing film 1 and the slow axis direction of the substrate 2 is preferably 0°±5° or 90°±5°.

The substrate 2 has optical properties represented by the following formulas (1) and (2). The substrate 2 may also have optical properties represented by the following formulas (3) and (4). In the following formulas (1) to (4), Re(λ) is a front retardation value for light with a wavelength of λ nm.
100nm<Re(550)<160nm...(1)
130nm<Re(550)<150nm...(2)
Re(450)/Re(550)≦1.00…(3)
1.00≦Re(650)/Re(550)…(4)

The front retardation value is determined by the following formula (5). In formula (5), d represents the thickness, and Δn(λ) represents the birefringence at a wavelength of λ nm. In order to obtain a desired front retardation value, d and Δn(λ) may be adjusted. By adjusting the front retardation value, the substrate 2 as a quarter-wave plate can be obtained.
Re(λ)=d×Δn(λ)…(5)

Examples of resin materials constituting the substrate 2 include polyolefins such as polyethylene, polypropylene, and norbornene-based polymers; cyclic olefin-based resins; polyvinyl alcohol; polyethylene terephthalate; polymethacrylic acid esters; polyacrylic acid esters; cellulose esters such as triacetyl cellulose, diacetyl cellulose, and cellulose acetate propionate; polyethylene naphthalate; polycarbonate; polysulfone; polyether sulfone; polyether ketone; polyphenylene sulfide; and polyphenylene oxide. The substrate 2 is preferably a cyclic olefin-based resin, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, polyethylene naphthalate, polymethacrylic acid esters, polyacrylic acid esters, polyethylene, or polypropylene. The substrate 2 is more preferably a cyclic olefin-based resin, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, polymethacrylic acid esters, or polyacrylic acid esters.

The substrate 2 may be subjected to a surface treatment. Examples of surface treatments include corona or plasma treatment from a vacuum atmosphere to an atmospheric pressure atmosphere, laser treatment, ozone treatment, saponification treatment, flame treatment, application of a coupling agent, primer treatment, and treatment using a graft polymerization method in which a reactive monomer or a reactive polymer is attached to the surface and then reacted by irradiating with radiation, plasma, or ultraviolet light.

A hard coat layer 5 may be adjacent to the surface of the substrate 2 opposite the alignment film 3. The hard coat layer 5 is a cured resin layer that has a higher surface smoothness than the adjacent substrate 2 and can be peeled off from the substrate 2. The hard coat layer 5 can be formed from a material known in the art as long as the desired peel strength can be ensured in the substrate 2. Examples of the hard coat layer 5 include a layer formed from a resin composition containing a water-soluble polymer, and a cured resin layer formed from a resin composition containing an active energy ray-curable or heat-curable resin component.

The resin composition constituting the hard coat layer 5 usually contains a resin component (polymer). Examples of the resin component include (meth)acrylic polymers, urethane polymers, polyester polymers, silicone polymers, polyvinyl ether polymers, polyvinyl alcohol polymers, and other resin components (polymers). These resin components may be used alone or in combination of two or more.

The content of the resin component in the resin composition can be appropriately determined depending on the type of resin component used, etc. The content of the resin component is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and even more preferably 70 parts by mass or more, per 100 parts by mass of the solid content of the resin composition. The content of the resin component is preferably 100 parts by mass or less, more preferably 95 parts by mass or less, and even more preferably 90 parts by mass or less.

The resin composition constituting the hard coat layer 5 may contain a crosslinking agent. As the crosslinking agent, a crosslinking agent normally used in the field can be used. The crosslinking agent can be appropriately selected depending on the resin components constituting the hard coat layer 5, the composition of the layer adjacent to the hard coat layer 5, etc. Examples of the crosslinking agent include methylol compounds, polyfunctional thiol compounds, polyfunctional (meth)acrylates, etc. These may be used alone or in combination of two or more. In addition, the hard coat layer 5 may contain an additive for improving the strength of the substrate 2. Examples of the additive include inorganic fine particles, organic fine particles, or a mixture thereof.

The alignment film 3 is a film that has a regulating force that aligns the dichroic dye in a desired direction. The alignment film 3 aligns the dichroic dye contained in the composition (composition for forming a polarizing film) that forms the polarizing film 4, thereby adjusting the absorption axis direction of the polarizing film 4 to a desired direction. The absorption axis direction of the polarizing film 4 is, for example, the same direction as the regulating force direction of the alignment film 3. The angle between the longitudinal direction of the polarizing film 1 and the regulating force direction of the alignment film 3 is, for example, 45°±5°.

The alignment film 3 is resistant to dissolution when the composition for forming the polarizing film is applied, and is heat resistant to heat treatment for removing the solvent and for orienting the dichroic dye. Examples of the alignment film 3 include a photoalignment film, an alignment film containing an alignable polymer, and a groove alignment film having a concave-convex pattern or multiple grooves on the surface. The thickness of the alignment film 3 is, for example, 10 nm to 1200 nm, preferably 10 to 400 nm, more preferably 10 to 200 nm, and particularly preferably 10 nm to 100 nm, in consideration of sufficient expression of the alignment control force. In this case, in a polarizing film 1 having an alignment film 3 with a thickness in this range, interference unevenness due to interfacial reflection of incident light can be suitably suppressed.

Examples of oriented polymers include polyamides and gelatins having amide bonds in the molecule, polyimides having imide bonds in the molecule, and their hydrolyzates such as polyamic acid, polyvinyl alcohol, alkyl-modified polyvinyl alcohol, polyacrylamide, polyoxazole, polyethyleneimine, polystyrene, polyvinylpyrrolidone, polyacrylic acid, and polyacrylic acid esters. Of these, polyvinyl alcohol is preferred. Oriented polymers can be used alone or in combination of two or more kinds.

The alignment film 3 containing an alignment polymer is usually obtained by applying a composition in which an alignment polymer is dissolved in a solvent (hereinafter also referred to as an "alignment polymer composition") to the substrate 2 and removing the solvent, or by applying an alignment polymer composition to the substrate 2, removing the solvent, and rubbing (rubbing method).

As the solvent, organic solvents are preferred, and examples of the organic solvent include alcohol solvents such as methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, methyl cellosolve, butyl cellosolve, and propylene glycol monomethyl ether; ester solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, γ-butyrolactone, propylene glycol methyl ether acetate, and ethyl lactate; ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, methyl amyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; aromatic hydrocarbon solvents such as toluene and xylene; nitrile solvents such as acetonitrile; ether solvents such as tetrahydrofuran and dimethoxyethane; and chlorinated hydrocarbon solvents such as chloroform and chlorobenzene. The solvents can be used alone or in combination of two or more. The content of the solvent is preferably 100 to 1900 parts by mass, more preferably 150 to 900 parts by mass, and even more preferably 180 to 600 parts by mass, per 100 parts by mass of the orientable polymer composition.

The concentration of the oriented polymer in the oriented polymer composition may be within a range in which the oriented polymer material can be completely dissolved in the solvent, but is preferably 0.1% to 20% in terms of solid content relative to the solution, and more preferably 0.1% to 10%. For the oriented polymer composition, commercially available oriented film materials may be used as is. Examples of commercially available oriented film materials include Sunever (registered trademark, manufactured by Nissan Chemical Industries, Ltd.) and Optomer (registered trademark, manufactured by JSR Corporation).

Methods for applying the oriented polymer composition to the substrate 2 include known methods such as coating methods such as spin coating, extrusion, gravure coating, die coating, bar coating, and applicator methods, and printing methods such as flexography. Methods for removing the solvent contained in the oriented polymer composition include natural drying, ventilation drying, heat drying, and reduced pressure drying.

In order to impart an orientation control force to the orientation film 3, a rubbing treatment can be performed as necessary (rubbing method). One method for imparting an orientation control force by the rubbing method is to apply an orientation polymer composition to the substrate 2 and anneal the composition to bring the orientation polymer film formed on the surface of the substrate 2 into contact with a rubbing roll that is rotating with a rubbing cloth wrapped around it.

The photo-alignment film is usually obtained by applying a composition containing a polymer or monomer having a photoreactive group and a solvent (hereinafter also referred to as a "photo-alignment film forming composition") to the substrate 2 and irradiating it with polarized light (preferably polarized UV). The photo-alignment film is more preferable in that the direction of the alignment control force can be freely controlled by selecting the polarization direction of the polarized light to be irradiated.

The photoreactive group refers to a group that generates liquid crystal alignment ability when irradiated with light. Specific examples include groups involved in photoreactions that are the origin of liquid crystal alignment ability, such as molecular alignment induction or isomerization reaction, dimerization reaction, photocrosslinking reaction, or photodecomposition reaction, which are induced by light irradiation. Among these, groups involved in dimerization reaction or photocrosslinking reaction are preferred in terms of excellent alignment ability. As the photoreactive group, a group having an unsaturated bond, particularly a double bond, is preferred, and a group having at least one selected from the group consisting of a carbon-carbon double bond (C=C bond), a carbon-nitrogen double bond (C=N bond), a nitrogen-nitrogen double bond (N=N bond), and a carbon-oxygen double bond (C=O bond) is particularly preferred.

Examples of photoreactive groups having a C=C bond include vinyl groups, polyene groups, stilbene groups, stilbazolyl groups, stilbazolium groups, chalcone groups, and cinnamoyl groups. Examples of photoreactive groups having a C=N bond include groups having structures such as aromatic Schiff bases and aromatic hydrazones. Examples of photoreactive groups having an N=N bond include azobenzene groups, azonaphthalene groups, aromatic heterocyclic azo groups, bisazo groups, formazan groups, and groups having an azoxybenzene structure. Examples of photoreactive groups having a C=O bond include benzophenone groups, coumarin groups, anthraquinone groups, and maleimide groups. These groups may have substituents such as alkyl groups, alkoxy groups, aryl groups, allyloxy groups, cyano groups, alkoxycarbonyl groups, hydroxyl groups, sulfonic acid groups, and halogenated alkyl groups.

Among these, photoreactive groups involved in photodimerization reactions are preferred, and cinnamoyl and chalcone groups are preferred because they require a relatively small amount of polarized light irradiation for photoalignment and are easy to obtain photoalignment films with excellent thermal and temporal stability. As polymers having photoreactive groups, those having cinnamoyl groups such that the terminals of the polymer side chains have cinnamic acid structures are particularly preferred.

By applying the photo-alignment film forming composition onto the substrate 2, a photo-alignment inducing layer can be formed on the substrate 2. Examples of the solvent contained in the composition include the same solvents as those described in the "alignment polymer composition" section, and can be appropriately selected depending on the solubility of the polymer or monomer having a photoreactive group.

The content of the polymer or monomer having a photoreactive group in the composition for forming a photo-alignment film can be adjusted as appropriate depending on the type of polymer or monomer and the desired thickness of the photo-alignment film, but is preferably at least 0.2% by mass, and more preferably in the range of 0.3 to 10% by mass, relative to the mass of the composition for forming a photo-alignment film. The composition for forming a photo-alignment film may contain a polymer material such as polyvinyl alcohol or polyimide, or a photosensitizer, as long as the properties of the photo-alignment film are not significantly impaired.

The method of applying the photo-alignment film-forming composition to the substrate 2 can be the same as the method of applying the alignment composition to the substrate 2. Methods of removing the solvent from the applied photo-alignment film-forming composition can be, for example, natural drying, ventilation drying, heat drying, and reduced pressure drying.

The method of irradiating polarized light may be a method of directly irradiating polarized UV onto the composition for forming a photo-alignment film coated on the substrate 2 from which the solvent has been removed, or a method of irradiating polarized light from the substrate 2 side and then transmitting the polarized light. It is particularly preferable that the polarized light be substantially parallel light. The wavelength of the irradiated polarized light is preferably in a wavelength range in which the photoreactive group of the polymer or monomer having a photoreactive group can absorb light energy. Specifically, UV (ultraviolet light) with a wavelength in the range of 250 to 400 nm is particularly preferable.

Examples of light sources used for polarized light irradiation include xenon lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, and ultraviolet lasers such as KrF and ArF, with high-pressure mercury lamps, ultra-high-pressure mercury lamps, and metal halide lamps being more preferred. Among these, high-pressure mercury lamps, ultra-high-pressure mercury lamps, and metal halide lamps are preferred because of the high emission intensity of ultraviolet light with a wavelength of 313 nm. Polarized UV can be irradiated by irradiating light from the light source through an appropriate polarizer. Examples of such polarizers include polarizing filters, polarizing prisms such as Glan-Thompson and Glan-Taylor, and wire grid type polarizers. If masking is performed when rubbing or polarized light irradiation is performed, multiple regions (patterns) with different liquid crystal orientation directions can also be formed.

A groove alignment film is a film that has a concave-convex pattern or multiple grooves on the film surface. When a polymerizable liquid crystal compound is applied to a film that has multiple equally spaced linear grooves, the liquid crystal molecules are oriented in the direction along the grooves.

Methods for obtaining a groove alignment film include a method in which the surface of a photosensitive polyimide film is exposed through an exposure mask having slits in the shape of a pattern, followed by development and rinsing to form an uneven pattern; a method in which a layer of uncured UV-cured resin is formed on a plate-shaped master having grooves on its surface, and the formed resin layer is transferred to the substrate 2 and then cured; and a method in which a roll-shaped master having multiple grooves is pressed against an uncured UV-cured resin film formed on the substrate 2 to form unevenness, followed by curing.

The polarizing film 4 is composed of a dichroic dye compound. A dichroic dye compound is a dye compound that has different absorbance in the long axis direction of the molecule and absorbance in the short axis direction of the molecule. The polarizing film 4 composed of the dichroic dye compound has an absorption axis direction in a predetermined direction and a transmission axis direction perpendicular to the absorption axis direction. In addition, the polarizing film 4 composed of the dichroic dye compound has a maximum absorption wavelength in a predetermined wavelength range.

In this embodiment, as described above, the angle between the longitudinal direction of the polarizing film 1 and the direction of the regulating force of the alignment film 3 is 45°±5°, and the absorption axis direction of the polarizing film 4 is parallel to the direction of the regulating force of the alignment film 3. Therefore, the angle between the longitudinal direction of the polarizing film 1 and the absorption axis direction of the polarizing film 4 is 45°±5°. Note that the angle here means the smaller angle between the two axes, that is, an angle of 90° or less. The polarizing film 4 has a maximum absorption wavelength in the range of, for example, 380 nm to 780 nm.

Examples of dichroic dyes include acridine dyes, oxazine dyes, cyanine dyes, naphthalene dyes, azo dyes, and anthraquinone dyes, and among these, azo dyes are preferred. Examples of azo dyes include monoazo dyes, bisazo dyes, trisazo dyes, tetrakisazo dyes, and stilbene azo dyes, and among these, bisazo dyes and trisazo dyes are preferred.

The azo dye includes a compound represented by the following formula (I) (hereinafter sometimes referred to as "compound (I)").
K ¹ (-N=N-K ² ) _p -N=N-K ³ (I)
[In formula (I), K ¹ and K ³ each independently represent a phenyl group which may have a substituent, a naphthyl group which may have a substituent, or a monovalent heterocyclic group which may have a substituent. K ² represents a p-phenylene group which may have a substituent, a naphthalene-1,4-diyl group which may have a substituent, or a divalent heterocyclic group which may have a substituent. p represents an integer of 1 to 4. When p is an integer of 2 or more, multiple K ^2's may be the same or different from each other. -N=N- bonds may be replaced with -C=C-, -COO-, -NHCO-, or -N=CH- bonds within the range in which absorption is exhibited in the visible range.]

Examples of monovalent heterocyclic groups include groups in which one hydrogen atom has been removed from a heterocyclic compound such as quinoline, thiazole, benzothiazole, thienothiazole, imidazole, benzimidazole, oxazole, and benzoxazole. Examples of divalent heterocyclic groups include groups in which two hydrogen atoms have been removed from the above heterocyclic compounds.

Examples of the substituents that the phenyl group, naphthyl group, and monovalent heterocyclic group in K ¹ and K ³ , and the p-phenylene group, naphthalene-1,4-diyl group, and divalent heterocyclic group in K ² may optionally have include alkyl groups having 1 to 4 carbon atoms; alkoxy groups having 1 to 4 carbon atoms such as methoxy, ethoxy, and butoxy groups; fluorinated alkyl groups having 1 to 4 carbon atoms such as trifluoromethyl groups; cyano groups; nitro groups; halogen atoms; and substituted or unsubstituted amino groups such as amino groups, diethylamino groups, and pyrrolidino groups (the substituted amino group means an amino group having one or two alkyl groups having 1 to 6 carbon atoms, or an amino group in which two substituted alkyl groups are bonded to each other to form an alkanediyl group having 2 to 8 carbon atoms. The unsubstituted amino group is -NH _2. ).

Among the compounds (I), a compound represented by any one of formulas (I-1) to (I-8) is preferred, a compound represented by any one of formulas (I-1) to (I-3) is more preferred, and a compound represented by any one of formulas (I-1) and (I-3) is even more preferred.

[In formulas (I-1) to (I-8), B ¹ to B ³⁰ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a cyano group, a nitro group, a substituted or unsubstituted amino group (the definitions of a substituted amino group and an unsubstituted amino group are as described above), a chlorine atom, or a trifluoromethyl group. n1 to n4 each independently represent an integer of 0 to 3. When n1 is 2 or more, multiple B ^2s may be the same or different from each other, when n2 is 2 or more, multiple B ^6s may be the same or different from each other, when n3 is 2 or more, multiple B ^9s may be the same or different from each other, and when n4 is 2 or more, multiple B ^14s may be the same or different from each other.]

The anthraquinone dye is preferably a compound represented by formula (I-9).

[In formula (I-9), R ¹ to R ⁸ each independently represent a hydrogen atom, -R ^x , -NH ₂ , -NHR ^x , -NR ^x ₂ , -SR ^x or a halogen atom. R ^x represents an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 12 carbon atoms.]

The oxazone dye is preferably a compound represented by formula (I-10).

[In formula (I-10), R ⁹ to R ¹⁵ each independently represent a hydrogen atom, -R ^x , -NH ₂ , -NHR ^x , -NR ^x ₂ , -SR ^x or a halogen atom. R ^x represents an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 12 carbon atoms.]

The acridine dye is preferably a compound represented by formula (I-11).

[In formula (I-11), R ¹⁶ to R ²³ each independently represent a hydrogen atom, -R ^x , -NH ₂ , -NHR ^x , -NR ^x ₂ , -SR ^x or a halogen atom. R ^x represents an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 12 carbon atoms.]

In the above formulas (I-9), (I-10), and (I-11), examples of the alkyl group having 1 to 6 carbon atoms for R ^x include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group, and examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a toluyl group, a xylyl group, and a naphthyl group.

As the cyanine dye, the compounds represented by formula (I-12) and (I-13) are preferred.

In formula (I-12), D ¹ and D ² each independently represent a group represented by any one of formulas (I-12a) to (I-12d).

n5 represents an integer of 1 to 3.

In formula (I-13), ^D3 and ^D4 each independently represent a group represented by any one of formulas (I-13a) to (I-13h).

n6 represents an integer of 1 to 3.

Among these dichroic dyes, azo dyes are preferred from the viewpoint of orientation.

The polarizing film 4 can be formed by applying a polarizing film-forming composition containing a dichroic dye compound onto the alignment film 3 and drying the composition. The application method can be the same as the application method for the photoalignment film-forming composition described above. From the viewpoint of improving the alignment of the dichroic dye, the content of the dichroic dye compound in the polarizing film-forming composition is preferably 0.1 to 30 parts by mass, more preferably 0.1 to 20 parts by mass, even more preferably 0.1 to 10 parts by mass, and particularly preferably 0.1 to 5 parts by mass, relative to 100 parts by mass of the solid content of the polarizing film-forming composition. The solid content here refers to the total amount of components excluding the solvent from the polarizing film-forming composition.

The polarizing film forming composition may contain a polymerizable liquid crystal compound, a solvent, a polymerization initiator, a sensitizer, a polymerization inhibitor, a leveling agent, and a polymerizable non-liquid crystal compound. In the polarizing film 4 containing the polymerizable liquid crystal compound, the strength is improved and color unevenness is reduced. When the polarizing film forming composition contains a polymerizable liquid crystal compound, the polarizing film forming composition may be dried to obtain a dried film, which may be cured. Curing refers to polymerizing the polymerizable liquid crystal compound contained in the dried film. Polymerization methods include heating and light irradiation. The orientation state of the dichroic dye contained in the dried film can be fixed by curing.

A polymerizable liquid crystal compound is a compound that has a polymerizable group and exhibits liquid crystallinity. The polymerizable group means a group involved in a polymerization reaction, and is preferably a photopolymerizable group. The photopolymerizable group is a group that can undergo a polymerization reaction due to an active radical or acid generated from a photopolymerization initiator. Examples of the polymerizable 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, and an oxetanyl group. Examples of compounds that exhibit liquid crystallinity include thermotropic liquid crystals and lyotropic liquid crystals, and thermotropic liquid crystals are preferred because they allow precise film thickness control. The compound that exhibits liquid crystallinity may be a nematic liquid crystal or a smectic liquid crystal in a thermotropic liquid crystal. The polymerizable liquid crystal compound may be a monomer, but may also be an oligomer or a polymer in which the polymerizable group is polymerized.

From the viewpoint of obtaining higher polarization characteristics, the polymerizable liquid crystal compound is preferably a liquid crystal compound that forms a smectic phase. Examples of smectic phases include smectic B phase, smectic D phase, smectic E phase, smectic F phase, smectic G phase, smectic H phase, smectic I phase, smectic J phase, smectic K phase, and smectic L phase. Smectic B phase, smectic F phase, or smectic I phase is preferred, and smectic B phase is more preferred. These smectic phases may be higher-order smectic phases.

When the liquid crystal phase formed by the polymerizable liquid crystal compound is one of these higher-order smectic phases, a polarizing film 4 with higher orientation order can be obtained. In a polarizing film 4 with a high degree of orientation order, a Bragg peak derived from a higher-order structure such as a hexatic phase or a crystalline phase is obtained in X-ray diffraction measurement. The Bragg peak is a peak derived from the periodic structure of the molecular orientation. When the liquid crystal phase formed by the polymerizable liquid crystal compound is one of these higher-order smectic phases, a polarizing film 4 with a periodic interval of the molecular orientation of, for example, 3.0 Å to 6.0 Å can be obtained.

Examples of the polymerizable liquid crystal compound include a compound represented by the following formula (B1) and a polymer of the compound (hereinafter, the compound and the polymer are collectively referred to as "polymerizable liquid crystal compound (B1)").
U ¹ -V ¹ -W ¹ -X ¹ -Y ¹ -X ² -Y ² -X ³ -W ² -V ² -U ² (B1)
[In formula (B1), X ¹ , X ² and X ³ each independently represent a divalent aromatic group or a divalent alicyclic hydrocarbon group. A hydrogen atom contained in the divalent aromatic group or the divalent alicyclic hydrocarbon group may be substituted with a halogen atom, an alkyl group having 1 to 4 carbon atoms, a fluoroalkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a cyano group or a nitro group, and a carbon atom constituting the divalent aromatic group or the divalent alicyclic hydrocarbon group may be substituted with an oxygen atom, a sulfur atom or a nitrogen atom. However, at least one of X ¹ , X ² and X ³ is a 1,4-phenylene group which may have a substituent or a cyclohexane-1,4-diyl group which may have a substituent. Y ¹ and Y ² each independently represent a single bond or a divalent linking group. U ¹ represents a hydrogen atom or a polymerizable group. U ² represents a polymerizable group. W ¹ and W ² are each independently a single bond or a divalent linking group. V ¹ and V ² are each independently an alkanediyl group having 1 to 20 carbon atoms which may have a substituent, and -CH ₂ - constituting the alkanediyl group may be replaced by -O-, -CO-, -S- or NH-.]

In the polymerizable liquid crystal compound (B1), at least one of X ¹ , X ² , and X ³ is a 1,4-phenylene group which may have a substituent, or a cyclohexane-1,4-diyl group which may have a substituent. In particular, X ¹ and X ³ are preferably a cyclohexane-1,4-diyl group which may have a substituent, and the cyclohexane-1,4-diyl group is more preferably a trans-cyclohexane-1,4-diyl group. Examples of the substituent that the 1,4-phenylene group which may have a substituent or the cyclohexane-1,4-diyl group which may have a substituent include an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, and a butyl group, a cyano group, and a halogen atom such as a chlorine atom or a fluorine atom. It is preferably unsubstituted. In addition, when Y ¹ and Y ² have the same structure, it is preferable that at least one of X ¹ , X ² , and X ³ has a different structure. When at least one of X ¹ , X ² and X ³ has a different structure, smectic liquid crystallinity tends to be easily exhibited.

Y ¹ and Y ² are each independently preferably -CH ₂ CH ₂ -, -CH ₂ O-, -CH ₂ CH ₂ O-, -COO-, -OCOO-, a single bond, -N=N-, -CR ^a ≡CR ^b -, -C≡C-, -CR ^a ≡N-, or CO-NR ^a -. ^{R a} and R ^b are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. ^{Y 1} is more preferably -CH ₂ CH ₂ -, -COO-, or a single bond, and Y ² is more preferably -CH ₂ CH ₂ - or CH ₂ O-. In addition, when X ¹ , X ² , and X ³ all have the same structure, it is preferable that Y ¹ and Y ² have structures different from each other. When ^Y1 and ^Y2 have structures different from each other, smectic liquid crystallinity tends to be easily exhibited.

^U2 is a polymerizable group. ^U1 is a hydrogen atom or a polymerizable group, preferably a polymerizable group. It is preferable that both ^U1 and ^U2 are polymerizable groups, and it is preferable that both are photopolymerizable groups. The photopolymerizable group means a group that can be involved in a polymerization reaction by an active radical or an acid generated from a photopolymerization initiator described later.

The photopolymerizable group represented by ^U1 and the polymerizable group represented by ^U2 may be different from each other, but are preferably the same type of group. Examples of the polymerizable 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, and an oxetanyl group. Among them, a radically polymerizable group is preferable, an acryloyloxy group, a methacryloyloxy group, a vinyl group, and a vinyloxy group are more preferable, an acryloyloxy group and a methacryloyloxy group are even more preferable, and an acryloyloxy group is even more preferable.

Examples of the alkanediyl group represented by V ¹ and V ² include a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a heptane-1,7-diyl group, an octane-1,8-diyl group, a decane-1,10-diyl group, a tetradecane-1,14-diyl group, and an icosane-1,20-diyl group. V ¹ and V ² are preferably alkanediyl groups having 2 to 12 carbon atoms, more preferably alkanediyl groups having 6 to 12 carbon atoms. Examples of the substituents that the alkanediyl group may have include a cyano group and a halogen atom, but the alkanediyl group is preferably unsubstituted, and more preferably an unsubstituted and linear alkanediyl group. W ¹ and W ² each independently preferably represent a single bond, —O—, —S—, —COO— or OCOO—, and more preferably a single bond or —O—.

Examples of the polymerizable liquid crystal compound (B1) include compounds represented by the following formulae (B-1) to (B-25). When the polymerizable liquid crystal compound (B1) has a cyclohexane-1,4-diyl group, the cyclohexane-1,4-diyl group is preferably a trans isomer.

Among these, at least one selected from the group consisting of compounds represented by formula (B-2), formula (B-3), formula (B-4), formula (B-5), formula (B-6), formula (B-7), formula (B-8), formula (B-13), formula (B-14), formula (B-15), formula (B-16), and formula (B-17) is preferred.

The exemplified polymerizable liquid crystal compounds can be used alone or in combination. When two or more polymerizable liquid crystal compounds are combined, it is preferable that at least one of them is a polymerizable liquid crystal compound, and it is more preferable that two or more of them are polymerizable liquid crystal compounds. By combining them, liquid crystallinity may be temporarily maintained even at temperatures below the liquid crystal-crystal phase transition temperature. When two types of polymerizable liquid crystal compounds are combined, the mixing ratio is usually 1:99 to 50:50, preferably 5:95 to 50:50, and more preferably 10:90 to 50:50.

The polymerizable liquid crystal compound is produced by a known method such as that described in Lub et al. Recl. Trav. Chim. Pays-Bas, 115, 321-328 (1996) and Japanese Patent No. 4719156.

The content of the polymerizable liquid crystal compound in the solid content of the composition for forming an optically absorbing anisotropic film is preferably 50% by mass or more, more preferably 70% by mass or more, and preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less. In this specification, the solid content in the composition for forming an optically absorbing anisotropic film refers to the total amount of components excluding volatile components such as solvents from the composition for forming an optically absorbing anisotropic film.

The solvent may be the same as that described in the "Orientable polymer composition" section, and the content of the solvent is preferably 100 to 1900 parts by mass, more preferably 150 to 900 parts by mass, and even more preferably 180 to 600 parts by mass, per 100 parts by mass of the composition for forming an optically absorptive anisotropic film.

As the polymerization initiator, a photopolymerization initiator is preferred. As the photopolymerization initiator, a photopolymerization initiator that has light absorption at a wavelength of 300 nm to 380 nm is usually used. A photopolymerization initiator is a compound that can initiate the polymerization reaction of a polymerizable liquid crystal compound, and can initiate the polymerization reaction at a lower temperature. Specifically, photopolymerization initiators that can generate active radicals or acids by the action of absorbed light are exemplified, and among them, photopolymerization initiators that generate radicals by the action of light are preferred.

Examples of photopolymerization initiators include benzoin compounds, benzophenone compounds, alkylphenone compounds, acylphosphine oxide compounds, triazine compounds, iodonium salts, and sulfonium salts. These polymerization initiators can be used alone or in combination.

Examples of benzoin compounds include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether.

Examples of benzophenone compounds include benzophenone, o-benzoylmethylbenzoate, 4-phenylbenzophenone, 4-benzoyl-4'-methyldiphenyl sulfide, 3,3',4,4'-tetra(tert-butylperoxycarbonyl)benzophenone, and 2,4,6-trimethylbenzophenone.

Examples of alkylphenone compounds include diethoxyacetophenone, 2-methyl-2-morpholino-1-(4-methylthiophenyl)propan-1-one, 2-dimethylamino-2-benzyl-1-(4-morpholinophenyl)butan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1,2-diphenyl-2,2-dimethoxyethane-1-one, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]propan-1-one, 1-hydroxycyclohexyl phenyl ketone, and oligomers of 2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propan-1-one.

Examples of acylphosphine oxide compounds include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

Examples of triazine compounds include 2,4-bis(trichloromethyl)-6-(4-methoxyphenyl)-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-(4-methoxynaphthyl)-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-(4-methoxystyryl)-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-[2-(5-methylfuran-2-yl)ethenyl] yl]-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-[2-(furan-2-yl)ethenyl]-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-[2-(4-diethylamino-2-methylphenyl)ethenyl]-1,3,5-triazine, and 2,4-bis(trichloromethyl)-6-[2-(3,4-dimethoxyphenyl)ethenyl]-1,3,5-triazine.

Commercially available photopolymerization initiators can be used. Commercially available photopolymerization initiators include "Irgacure (registered trademark) 907", "Irgacure (registered trademark) 184", "Irgacure (registered trademark) 651", "Irgacure (registered trademark) 819", "Irgacure (registered trademark) 250", "Irgacure (registered trademark) 369" (Ciba Japan Co., Ltd.); "Seikuol (registered trademark) BZ", "Seikuol (registered trademark) Z", "Seikuol (registered trademark) 100", "Seikuol (registered trademark) 200", "Seikuol (registered trademark) 1 ... Examples include "BEE (trademark)" (Seiko Chemical Co., Ltd.); "Kayacure (registered trademark) BP100" (Nippon Kayaku Co., Ltd.); "Kayacure (registered trademark) UVI-6992" (Dow Corporation); "ADEKA Optomer SP-152", "ADEKA Optomer SP-170" (ADEKA Corporation); "TAZ-A", "TAZ-PP" (Nippon SiberHegner Co., Ltd.); and "TAZ-104" (Sanwa Chemical Co., Ltd.).

The content of the polymerization initiator can be adjusted appropriately depending on the type and amount of the polymerizable liquid crystal compound contained in the composition for forming an optically absorptive anisotropic film, but is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, relative to 100 parts by mass of the polymerizable liquid crystal compound, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less. When the content of the polymerization initiator is equal to or greater than the above lower limit, the polymerizable liquid crystal compound can be polymerized without disturbing its orientation. When the content of the polymerization initiator is equal to or less than the above upper limit, the long-term storage stability can be improved, and the occurrence of orientation defects in the obtained polarizing film can be more easily suppressed or prevented.

As the sensitizer, a photosensitizer is preferable. Examples of photosensitizers include xanthone compounds such as xanthone and thioxanthone (e.g., 2,4-diethylthioxanthone, 2-isopropylthioxanthone); anthracene compounds such as anthracene and alkoxy group-containing anthracene (e.g., dibutoxyanthracene); phenothiazine and rubrene. The sensitizers can be used alone or in combination of two or more kinds.

When the composition for forming an optically absorptive anisotropic film contains a sensitizer, the polymerization reaction of the polymerizable liquid crystal compound contained in the composition can be further promoted. The amount of the sensitizer used can be appropriately adjusted depending on the type and amount of the polymerization initiator and polymerizable liquid crystal compound, but is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 0.5 to 8 parts by mass, relative to 100 parts by mass of the polymerizable liquid crystal compound.

In order to make the polymerization reaction of the composition for forming an optically absorbing anisotropic film proceed more stably, the composition may contain an appropriate amount of a polymerization inhibitor. This makes it easier to control the degree of progress of the polymerization reaction of the polymerizable liquid crystal compound.

Examples of polymerization inhibitors include radical scavengers such as hydroquinone, alkoxy group-containing hydroquinone, alkoxy group-containing catechol (e.g., butylcatechol, etc.), pyrogallol, and 2,2,6,6-tetramethyl-1-piperidinyloxy radical; thiophenols; β-naphthylamines, and β-naphthols.

When the composition for forming an optically absorptive anisotropic film contains a polymerization inhibitor, the content can be adjusted as appropriate depending on the type and amount of the polymerizable liquid crystal compound, the amount of the sensitizer used, etc., but is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 0.5 to 8 parts by mass, per 100 parts by mass of the polymerizable liquid crystal compound. If the content of the polymerization inhibitor is within this range, the polymerizable liquid crystal compound can be polymerized without disturbing its alignment.

The optically absorptive anisotropic film-forming composition may contain one or more leveling agents. The leveling agent has the function of adjusting the fluidity of the optically absorptive anisotropic film-forming composition and making the coating film obtained by applying the composition flatter, and specifically includes a surfactant. As the leveling agent, at least one selected from the group consisting of leveling agents mainly composed of a polyacrylate compound and leveling agents mainly composed of a fluorine atom-containing compound is preferable.

Leveling agents whose main component is a polyacrylate compound include "BYK-350", "BYK-352", "BYK-353", "BYK-354", "BYK-355", "BYK-358N", "BYK-361N", "BYK-380", "BYK-381" and "BYK-392" [BYK Chemie].

Leveling agents whose main component is a fluorine-containing compound include "Megafac (registered trademark) R-08", "R-30", "R-90", "F-410", "F-411", "F-443", "F-445", "F-470", "F-471", "F-477", "F-479", "F-482" and "F-483" [DIC Corporation]; "Surflon (registered trademark) S-381", "S-3 82", S-383, S-393, SC-101, SC-105, KH-40 and SA-100 [AGC Seimi Chemical Co., Ltd.]; E1830, E5844 [Daikin Fine Chemicals Research Institute Ltd.]; F-top EF301, F-top EF303, F-top EF351 and F-top EF352 [Mitsubishi Materials Electronic Chemicals Co., Ltd.].

When the composition for forming an optically absorptive anisotropic film contains a leveling agent, the content is preferably 0.05 to 5 parts by mass, and more preferably 0.05 to 3 parts by mass, per 100 parts by mass of the polymerizable liquid crystal compound. When the content of the leveling agent is within the above range, the obtained polarizing film tends to be smoother and less prone to unevenness.

<Polarizing film>
The present disclosure includes a polarizing film that is a cured product of the composition for forming a polarizing film. The polarizing film of the present disclosure is a film having a polarizing function, and a dichroic dye is encapsulated in an aligned polymerizable liquid crystal. Since the polarizing film of the present disclosure is formed from the composition for forming a polarizing film, it has little or no alignment defects and has excellent polarizing performance.

The polarizing film of the present disclosure can be produced, for example, by a method including a step (ii) of forming a coating film of the composition for forming a polarizing film, drying and removing the organic solvent from the coating film, and a step (iii) of aligning and curing the polymerizable liquid crystal compound in a smectic liquid crystal phase state.

Step (ii) is a step of forming a coating film by applying the composition for forming a polarizing film onto a substrate, an alignment film, or another layer (e.g., a functional layer) described below, and then drying and removing the organic solvent under conditions in which the polymerizable liquid crystal compound contained in the resulting coating film does not polymerize, to obtain a dry coating film. The polarizing film may be applied directly onto a substrate or another layer (e.g., a functional layer), but it is preferable to apply it onto an alignment film having alignment regularity.

In step (ii), examples of the drying method include natural drying, ventilation drying, heat drying, and reduced pressure drying. When the polymerizable liquid crystal compound is a polymerizable smectic liquid crystal compound, it is preferable to change the liquid crystal state of the polymerizable smectic liquid crystal compound contained in the dried film to a nematic phase (nematic liquid crystal state) and then transition to a smectic phase. In order to form a smectic phase via a nematic phase, for example, a method is used in which the dried film is heated to a temperature at which the polymerizable smectic liquid crystal compound contained in the dried film transitions to a nematic liquid crystal state or higher, and then cooled to a temperature at which the polymerizable smectic liquid crystal compound exhibits a smectic liquid crystal state.

Step (iii) is a step of aligning and curing the polymerizable liquid crystal compound in the dried film in the smectic liquid crystal phase state. Below, a method of photopolymerizing the polymerizable liquid crystal compound while maintaining the smectic liquid crystal state after the liquid crystal state of the polymerizable liquid crystal compound in the dried film is changed to a smectic phase in step (ii) is described. In the photopolymerization, the light irradiated to the dried film is appropriately selected according to the type of photopolymerization initiator contained in the dried film, the type of polymerizable liquid crystal compound (particularly the type of photopolymerizable group possessed by the polymerizable liquid crystal compound) and the amount thereof.

Specific examples of such light include one or more types of light selected from the group consisting of visible light, ultraviolet light, infrared light, X-rays, α-rays, β-rays, and γ-rays, and active electron beams. Among them, ultraviolet light is preferred because it is easy to control the progress of the polymerization reaction and photopolymerization devices that are widely used in this field can be used. It is also preferable to select the type of polymerizable liquid crystal compound and photopolymerization initiator contained in the polymerizable liquid crystal composition so that photopolymerization can be performed by ultraviolet light. In addition, the polymerization temperature can be controlled by irradiating light while cooling the dried film with an appropriate cooling means during polymerization. By adopting such a cooling means, if the polymerization of the polymerizable liquid crystal compound is performed at a lower temperature, a polarizing film can be appropriately formed even if a substrate with relatively low heat resistance is used. During photopolymerization, a patterned polarizing film can also be obtained by masking, developing, etc.

Examples of light sources for the active energy rays include low pressure mercury lamps, medium pressure mercury lamps, high pressure mercury lamps, ultra-high pressure mercury lamps, xenon lamps, halogen lamps, carbon arc lamps, tungsten lamps, gallium lamps, excimer lasers, LED light sources emitting light in the wavelength range of 380 to 440 nm, chemical lamps, black light lamps, microwave excited mercury lamps, metal halide lamps, etc.

The ultraviolet irradiation intensity is usually 10 to 3,000 mW/ ^cm2 . The ultraviolet irradiation intensity is preferably an intensity in a wavelength region effective for activating a photopolymerization initiator. The light irradiation time is usually 0.1 seconds to 10 minutes, preferably 1 second to 5 minutes, more preferably 5 seconds to 3 minutes, and even more preferably 10 seconds to 1 minute. When irradiating once or multiple times with such ultraviolet irradiation intensity, the integrated light amount is 10 to 3,000 mJ/ ^cm2 , preferably 50 to 2,000 mJ/ ^cm2 , and more preferably 100 to 1,000 mJ/ ^cm2 .

By carrying out photopolymerization, the polymerizable liquid crystal compound is polymerized while maintaining the liquid crystal state of the smectic phase, preferably the high-order smectic phase, to form a polarizing film. The polarizing film obtained by polymerizing the polymerizable liquid crystal compound while maintaining the liquid crystal state of the smectic phase has the advantage of having higher polarization performance due to the action of the dichroic dye, compared to conventional host-guest type polarizing films, i.e., polarizing films made of a liquid crystal state of the nematic phase. Furthermore, it has the advantage of being stronger than those coated with only the dichroic dye or lyotropic liquid crystal.

The thickness of the polarizing film can be appropriately selected depending on the display device to which it is applied, and is preferably 0.1 to 5 μm, more preferably 0.3 to 4 μm, and even more preferably 0.5 to 3 μm.

In the polarizing film 1 as described above, the refractive index difference between the polarizing film 4 and the alignment film 3 for visible light satisfies the following formula (6), and the refractive index difference between the alignment film 3 and the substrate 2 for visible light satisfies the following formula (7): In formula (6), n (polarizing film) represents the refractive index in the transmission axis direction of the polarizing film.
|n (polarizing film) - n (alignment film) | ≦ 0.06 ... (6)
|n (alignment film)-n (substrate)|≦0.06 ... (7)

The refractive index difference between the polarizing film 4 and the alignment film 3 for visible light is preferably 0.04 or less, and more preferably 0.02 or less. The refractive index difference between the alignment film 3 and the substrate 2 for visible light is preferably 0.04 or less, and more preferably 0.02 or less.

In such a polarizing film 1, by restricting the refractive index difference between the alignment film 3 and the substrate 2 and the refractive index difference between the alignment film 3 and the substrate 2 within the above range, it is possible to suppress the interfacial reflection of incident light between the polarizing film 4 and the alignment film 3 and between the alignment film 3 and the substrate 2. Therefore, it is possible to suppress interference unevenness due to interfacial reflection of incident light.

In this embodiment, the thickness of the alignment film 3 is 10 nm to 400 nm. In this case, in a polarizing film 1 with an alignment film 3 having a thickness in this range, interference unevenness due to interfacial reflection of incident light can be effectively suppressed.

In this embodiment, the hard coat layer 5 is adjacent to the surface of the substrate 2 opposite the alignment film 3. When producing the polarizing film 1, it is conceivable that the substrate 2 may warp due to shrinkage that occurs when the polarizing film 4 is cured, resulting in wrinkles in the resulting polarizing film 1. In contrast, by having the hard coat layer 5 on the substrate 2, warping of the substrate 2 due to shrinkage that occurs when the polarizing film 1 is cured can be suppressed, and wrinkles can be suppressed from occurring in the resulting polarizing film 1.

In this embodiment, the substrate 2, the alignment film 3, and the polarizing film 4 are long. That is, in this embodiment, the polarizing film 1 is a long polarizing film 1 that can suppress interference unevenness due to interfacial reflection of incident light. By continuously bonding polarizing films 1 cut from the long polarizing film 1 to various display devices, display devices using the polarizing film 1 that suppresses interference unevenness due to interfacial reflection of incident light can be efficiently manufactured.

In this embodiment, the angle between the longitudinal direction and the slow axis direction of the substrate 2 is 0°±5° or 90°±5°, and the angle between the slow axis direction of the substrate 2 and the absorption axis direction of the polarizing film 4 is 45°±5°. This results in a polarizing film 1 that exhibits high ellipticity.

[Example]
The present disclosure will be described in more detail below with reference to examples. In the following examples, "%" and "parts" are "mass%" and "parts by mass" unless otherwise specified. The configurations and evaluation results of the polarizing films in each example and comparative example are summarized in FIG. 2 and FIG. 3.

[Preparation of composition for forming photo-alignment film]
The following components were mixed, and the resulting mixture was stirred at 80° C. for 1 hour to obtain a composition for forming a photoalignment film (1).
Photo-alignable polymer: 2 parts

(Polymer described in JP 2013-033249 A, number average molecular weight: about 28,200, Mw/Mn: 1.82)
Solvent: o-xylene 98 parts

（Ａ２）
・二色性色素：アゾ色素Ａ ２．５部

・二色性色素：アゾ色素Ｂ ２．５部

・二色性色素：アゾ色素Ｃ ２．５部

・光重合開始剤：２－ジメチルアミノ－２－ベンジル－１－（４－モルホリノフェニル）ブタン－１－オン（イルガキュア３６９；チバ・スペシャルティ・ケミカルズ株式会社製） ６部
・レベリング剤：ポリアクリレート化合物（ＢＹＫ－３６１Ｎ；ＢＹＫ－Ｃｈｅｍｉｅ社製） １．２部
・溶剤：メチルエチルケトン ４００部 [Preparation of composition for forming polarizing film]
The following components were mixed and stirred for 1 hour at 80° C. to obtain a composition for forming a polarizing film (1). The dichroic dye used was an azo dye described in the examples of JP-A-2013-101328.
・Polymerizable liquid crystal compound: A1 90 parts

(A1)
・Polymerizable liquid crystal compound: A2 10 parts

(A2)
・Dichroic dye: Azo dye A 2.5 parts

・Dichroic dye: Azo dye B 2.5 parts

・Dichroic dye: Azo dye C 2.5 parts

Photopolymerization initiator: 2-dimethylamino-2-benzyl-1-(4-morpholinophenyl)butan-1-one (Irgacure 369; manufactured by Ciba Specialty Chemicals Co., Ltd.) 6 parts Leveling agent: polyacrylate compound (BYK-361N; manufactured by BYK-Chemie Co., Ltd.) 1.2 parts Solvent: methyl ethyl ketone 400 parts

[Preparation of substrate]
A protective film of a cyclic olefin resin (ZEON Corporation, ZEONORFILM ZM series (registered trademark)) was used as the substrate for the polarized film in Examples 1, 3 to 5, and 7. A protective film of a cyclic olefin resin (ZEON Corporation, ZEONORFILM ZT series (registered trademark)) was used as the substrate for the polarized film in Example 2.

A protective film of cyclic olefin resin (ZEONORFILM ZD series (registered trademark), manufactured by ZEON Corporation) was used as the substrate for the polarizing film of Example 6. For the polarizing film of Comparative Example 1, a uniaxially stretched film WRF-S (modified polycarbonate resin) was used as the substrate. The thickness of the obtained substrate was 50 μm, and the in-plane retardation value at a wavelength of 550 nm was 144.6 nm.

[Preparation of hard coat layer forming composition]
The following components were mixed and stirred at 50° C. for 4 hours to obtain a resin composition (1) for forming a hard coat layer.
- Polyfunctional acrylate compound having the following structure: 50 parts (dipentaerythritol hexaacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., "NK Ester A-DPH"), the number of atoms in the chain connecting the branch point closest to the acryloyl group in the branched structure to the acryloyl group is 2.)

Urethane acrylate polymer: urethane acrylate (Daicel Allnex Corporation's "Ebecryl 4858", functional group number 2, weight average molecular weight Mw 450, functional group number per unit molecular weight 44.4 × 10-4) 50 parts Radical polymerization initiator: 2-[4-(methylthio)benzoyl]-2-(4-morpholinyl)propane (BASF Corporation's "Irgacure 907") 3 parts Solvent: methyl ethyl ketone 10 parts

[Formation of hard coat layer]
The composition for forming a hard coat layer (1) was applied to a substrate by a bar coating method (#2 30 mm/s). The obtained coating film of the composition for forming a hard coat layer (1) was irradiated with ultraviolet light at an exposure dose of 500 mJ/cm ² (based on 365 nm) using a UV irradiation device (SPOT CURE SP-7; manufactured by Ushio Inc.), to obtain a substrate with a hard coat layer. When measured with a laser microscope (OLS3000 manufactured by Olympus Corporation), the thickness of the hard coat layer was 1.5 μm.

[Preparation of Polarizing Film]
After subjecting the substrate surface of the substrate with a hard coat layer to a corona treatment, the photo-alignment film-forming composition (1) was applied by a bar coating method, and the composition was dried at 120°C to obtain a dried coating film. Next, the dried coating film was irradiated with polarized UV to form a photo-alignment film, and a laminate having a hard coat layer/substrate/photo-alignment film in this order was obtained. When measured with a laser microscope (OLS3000 manufactured by Olympus Corporation), the thickness of the photo-alignment film was 100 nm in Examples 1 to 3, 6, and 7, and the thickness of the photo-alignment film was 200 nm in Example 4. In addition, the thickness of the photo-alignment film was 400 nm in Example 5. The polarized UV treatment was performed using a UV irradiation device (SPOT CURE SP-7; manufactured by Ushio Inc.) under the condition of a measurement intensity of 100 mJ at a wavelength of 365 nm.

The polarizing film-forming composition (1) was applied to the surface of the photo-alignment film in the obtained laminate by a bar coating method, and the polymerizable liquid crystal compound was phase-transitioned to a liquid phase by heating and drying in a drying oven at 120° C. for 1 minute, and then cooled to room temperature to cause the polymerizable liquid crystal compound to phase-transition to a smectic liquid crystal state. Next, using a UV irradiation device (SPOT CURE SP-7; manufactured by Ushio Inc.), ultraviolet rays with an exposure dose of 1000 mJ/cm ² (based on 365 nm) were irradiated onto the coating film formed by the polarizing film-forming composition (1). As a result, the polymerizable liquid crystal compound contained in the dried coating film was polymerized while maintaining the smectic liquid crystal state of the polymerizable liquid crystal compound, and a polarizing film having a hard coat layer/substrate/photo-alignment film/polarizing film in this order was obtained. When measured with a laser microscope (OLS3000 manufactured by Olympus Corporation), the thickness of the polarizing film was 2.3 μm.

[Preparation of Long Polarizing Film]
The long polarizing film according to each Example and Comparative Example was continuously produced by a roll to roll method. The long substrate according to each Example and Comparative Example was continuously unwound, and the surface of the substrate was subjected to plasma treatment. Then, the composition for forming a photo-alignment film (1) was discharged to the center of the substrate using a slot die coater to form a first coating film. Furthermore, the substrate on which the first coating film was formed was transported in a ventilated drying oven set at 100° C. for 2 minutes to remove the solvent, and a first dry film was formed. The substrate on which the first dry film was formed was irradiated with polarized UV light in a predetermined direction at an intensity of 20 mJ/cm ² (based on 313 nm) in the longitudinal direction, and an alignment regulating force was imparted to the first dry film, thereby forming a long photo-alignment film.

Next, a composition for forming a polarizing film was discharged onto the center of the obtained long-length photo-alignment film using a slot die coater, forming a second coating film. The substrate on which the second coating film was formed was then transported through a ventilated drying oven set at 110°C for 2 minutes to remove the solvent, forming a second dry film. The substrate on which the second dry film was formed was irradiated with UV light at 1000 mJ/cm ² (based on 365 nm) to cure the polymerizable liquid crystal compound contained in the second dry film, forming a long-length polarizing film.

The film was then continuously wound up into a roll to obtain 200 m of long polarizing film for each Example and Comparative Example. The angle between the longitudinal direction of the long polarizing film and the slow axis direction of the substrate was 0° in Examples 1, 3 to 5, and 7 and Comparative Example 1, 90° in Example 2, and 45° in Example 6. The angle between the longitudinal direction of the long polarizing film and the absorption axis direction of the polarizing film was 45° in Examples 1, 3 to 5, and Comparative Example 1, 45° in Example 2, 0° in Example 6, and 46° in Example 7.

[Measurement of refractive index]
The refractive indexes of the substrate, the photo-alignment film, and the hard coat layer (average refractive index at a wavelength of 589 nm) were measured using a refractometer (Multi-wavelength Abbe Refractometer DR-M4 manufactured by Atago Co., Ltd.). The refractive index of the substrate in Examples 1 to 7 was 1.53. The refractive index of the substrate in Comparative Example 1 was 1.62. The refractive index of the photo-alignment film in Examples 1 to 7 and Comparative Example 1 was 1.55. The refractive index of the hard coat layer in Example 3 was 1.53.

Regarding the refractive index in the transmission axis direction of the polarizing film, polarizing film samples for refractive index evaluation were prepared for each Example and Comparative Example as follows. First, a composition for forming a polarizing film for refractive index evaluation was prepared with a composition excluding the dye. For the substrate, a protective film of an unstretched cyclic olefin resin with a thickness of 23 μm and an in-plane retardation value of 0 (ZEONORFILM (registered trademark), manufactured by Zeon Corporation) was used. Other than these, polarizing film samples for refractive index evaluation were formed for each Example and Comparative Example using the same procedure as in the above Example.

For the polarizing film sample for refractive index evaluation, an automatic birefringence meter KOBRA-WPR manufactured by Oji Scientific Instruments was used to measure the front phase difference value and the phase difference value when tilted 40° from the fast axis center by changing the incident angle of light on the sample. The average refractive index at each wavelength was measured using an ellipsometer M-220 manufactured by JASCO Corporation. The film thickness of the polarizing film was measured using an optical nanogauge film thickness meter C12562-01 manufactured by Hamamatsu Photonics K.K. Based on the obtained front phase difference value, phase difference value when tilted 40° from the fast axis center, average refractive index, and film thickness values, the three-dimensional refractive index was calculated by referring to the Oji Scientific Instruments technical documentation (http://www.oji-keisoku.co.jp/products/kobra/reference.html).

The refractive index in the transmission axis direction of the polarizing film in Examples 1 to 7 and Comparative Example 1 was 1.53. As a result, in Examples 1 to 7 and Comparative Example 1, |n(polarizing film) - n(alignment film)| was 0.02 in all cases. In addition, in Examples 1 to 7, |n(alignment film) - n(substrate)| was 0.02 in all cases, but in Comparative Example 1, |n(alignment film) - n(substrate)| was 0.07.

[Appearance inspection]
Each of the long polarizing films produced in the Examples and Comparative Examples was cut into a 70 mm x 150 mm square, a λ/4 wavelength plate was attached to the polarizing film side via a pressure-sensitive adhesive, and an aluminum plate was further attached to the λ/4 wavelength plate side via a pressure-sensitive adhesive to obtain a sample for appearance inspection according to each of the Examples and Comparative Examples. The obtained samples for appearance inspection were visually inspected for the presence or absence of interference unevenness from a position inclined 20° from the front vertical direction.

In the visual inspection, the area where the interference unevenness was visible was less than 2% of the sample area, was rated as "A", the area where the interference unevenness was visible was 2% or more but less than 5% of the sample area, was rated as "B", the area where the interference unevenness was visible was 5% or more but less than 15% of the sample area, was rated as "C", and the area where the interference unevenness was visible was 15% or more of the sample area, was rated as "D".

In Examples 1 to 3, 6, and 7, it was "A," in Example 4, it was "B," in Example 5, it was "C," and in Comparative Example 1, it was "D." From these results, it was confirmed that by suppressing the refractive index difference between the alignment film and the substrate and the refractive index difference between the alignment film and the substrate to 0.06 or less, it is possible to suppress the interfacial reflection of incident light between the polarizing film and the alignment film and between the alignment film and the substrate, and to suppress interference unevenness due to interfacial reflection of incident light in the polarizing film.

[Curl evaluation]
Each of the long polarizing films produced in the Examples and Comparative Examples was cut into a 70 mm x 150 mm square, and a λ/4 wavelength plate was attached to the polarizing film side with a pressure-sensitive adhesive using a laminator to obtain a curl evaluation sample for each of the Examples and Comparative Examples. The shape of the obtained curl evaluation sample was visually observed.

In the curl evaluation, a gently convex shape on the substrate side was rated "A" because it improves workability when attaching to a panel, and a flat shape was rated "B." Example 3, in which a hard coat layer is adjacent to the surface opposite the orientation surface of the substrate, was rated "A," while Examples 1, 2, 4 to 7 and Comparative Example 1, which do not have a hard coat layer, were rated "B."

[Curling test]
Each of the long polarizing films produced in the Examples and Comparative Examples was cut to a width of 50 mm and a length of 300 mm (longitudinal direction), and the film was wrapped around an iron bar with a diameter of 6 mm in the longitudinal direction, and then placed in an oven at 140° C. and left to stand for 3 minutes. Each film was taken out to a room temperature environment, the iron bar was removed, and the curling tendency of each film was confirmed.

The curl test is a test that assumes that a roll of long polarizing film is stored in a high-temperature environment for a long period of time. From the viewpoint of long-term storage stability, in the curl test, films that have a curl such that the central axis in the width direction of the film is parallel to the long sides of the film were rated "A", and films that have a curl such that the central axis in the width direction of the film is not parallel to the long sides of the film were rated "B". As a result, Examples 1 to 5, 7 and Comparative Example 1 were rated "A", and Example 6 was rated "B".

The gist of the present disclosure is as follows: [1] to [5]
[1] A polarizing film comprising a substrate, an alignment film, and a polarizing film laminated in this order, wherein an angle between a slow axis direction of the substrate and an absorption axis direction of the polarizing film is 45°±5°, a refractive index difference between the polarizing film and the alignment film for visible light satisfies the following formula (1), and a refractive index difference between the alignment film and the substrate for visible light satisfies the following formula (2):
|n (polarizing film) - n (alignment film) | ≦ 0.06 ... (1)
|n (alignment film)-n (substrate)|≦0.06 ... (2)
(In formula (1), n (polarizing film) represents the refractive index in the transmission axis direction of the polarizing film.)
[2] The polarizing film according to [1], wherein the thickness of the alignment film is 10 nm to 400 nm.
[3] The polarizing film according to [1] or [2], wherein a hard coat layer is adjacent to the surface of the substrate opposite to the alignment film.
[4] The polarizing film according to any one of [1] to [3], wherein the substrate, the alignment film, and the polarizing film are long.
[5] The polarizing film according to [4], wherein the angle between the longitudinal direction and the slow axis direction of the substrate is 0°±5° or 90°±5°.

1...polarizing film, 2...substrate, 3...alignment film, 4...polarizing film, 5...hard coat layer.

Claims (5)

A polarizing film having a substrate, an alignment film, and a polarizing film laminated in this order,
an angle between a slow axis direction of the substrate and an absorption axis direction of the polarizing film is 45°±5°;
A polarizing film, wherein a refractive index difference between the polarizing film and the alignment film for visible light satisfies the following formula (1), and a refractive index difference between the alignment film and the substrate for visible light satisfies the following formula (2):
|n (polarizing film) - n (alignment film) | ≦ 0.06 ... (1)
|n (alignment film)-n (substrate)|≦0.06 ... (2)
(In formula (1), n (polarizing film) represents the refractive index in the transmission axis direction of the polarizing film.) The polarizing film of claim 1, wherein the thickness of the alignment film is 10 nm to 400 nm. The polarizing film according to claim 1, wherein a hard coat layer is adjacent to the surface of the substrate opposite the alignment film. The polarizing film according to any one of claims 1 to 3, wherein the substrate, the alignment film, and the polarizing film are long. The polarizing film according to claim 4, wherein the angle between the longitudinal direction and the slow axis direction of the substrate is 0°±5° or 90°±5°.

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