JP5013955B2 - Birefringent film and method for producing the same - Google Patents

Description

  The present invention relates to a thin birefringent film containing at least one polycyclic compound containing a -COOM group and having a refractive index controlled three-dimensionally, a method for producing the same, and use thereof. .

A liquid crystal display device (hereinafter sometimes referred to as an LCD) is an element that displays characters and images using the electro-optical characteristics of liquid crystal molecules, and is widely used in mobile phones, notebook computers, liquid crystal televisions, and the like. . However, LCD uses liquid crystal molecules with optical anisotropy, so even if it shows excellent display characteristics in one direction, the screen becomes dark or unclear in the other direction. There is a problem. In order to improve the viewing angle and the like of the LCD, the LCD is provided with a birefringent film.
As one of the birefringent films, a film in which a refractive index ellipsoid satisfies a relationship of nz> nx = ny is disclosed (for example, see Patent Document 1). In a birefringent film having such a refractive index relationship, a homeotropic alignment side chain type liquid crystal polymer is applied on a substrate, and then the side chain type liquid crystal polymer is homeotropically aligned in a liquid crystal state. It is produced by fixing in a maintained state. However, an even thinner LCD is desired from the market. Therefore, a thinner birefringent film is required.
JP 2006-011369 A

  An object of the present invention is to provide a thin birefringent film whose refractive index is controlled three-dimensionally.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above object can be achieved by the birefringent film shown below, and have completed the present invention.

Birefringent film of the present invention, the refractive index ellipsoid satisfies a relationship of nz> nx = ny, including chromatic also reduce the acenaphtho [1,2-b] quinoxaline derivative represented by the following general formula (I) Do it. However, in formula (I), M represents a counter ion.

  In a preferred embodiment, the birefringence (Δn [590]) in the thickness direction at a wavelength of 590 nm of the birefringent film is −0.05 or less.

  In preferable embodiment, the thickness of the said birefringent film is 0.2 micrometer-2.0 micrometers.

  In a preferred embodiment, the birefringent film has a thickness direction retardation value (Rth [590]) at a wavelength of 590 nm of −300 nm to −10 nm.

  According to another aspect of the present invention, a laminated film is provided. This laminated film includes at least the birefringent film and a substrate.

According to another aspect of the present invention, a method for producing a birefringent film is provided. This manufacturing method includes the following steps (1) to (3).
(1) a step of preparing a solution containing an acenaphtho [1,2-b] quinoxaline derivative represented by the above general formula (I) and a solvent and exhibiting a nematic liquid crystal phase;
(2) a step of preparing a substrate having at least one surface made hydrophilic;
(3) A step of applying and drying the solution prepared in the step (1) on the surface of the base material prepared in the step (2) subjected to the hydrophilic treatment.

  In a preferred embodiment, the hydrophilic treatment is at least one of a corona treatment, a plasma treatment, an alkali treatment, and an anchor coat treatment.

  In a preferred embodiment, the substrate is a glass substrate or a polymer film.

  According to another aspect of the present invention, a polarizing plate is provided. The polarizing plate includes at least the birefringent film and a polarizer.

  In the birefringent film of the present invention, the refractive index ellipsoid satisfies the relationship of nz> nx = ny and has a high birefringence in the thickness direction. The phase difference value can be obtained. In addition, the method for producing a birefringent film of the present invention is a method with excellent productivity that is applied to a substrate and dried, and satisfies the relationship of nz> nx = ny, and produces a thin birefringent film. be able to.

<< 1. Overview of Birefringent Film of the Present Invention >>
In the birefringent film of the present invention, the refractive index ellipsoid satisfies the relationship of nz> nx = ny and contains at least one polycyclic compound containing a —COOM group. Here, M represents a counter ion. The -COOM group represents a carboxylic acid group or a carboxylate.

In the present specification, the “birefringent film” refers to a film showing birefringence in the thickness direction, and includes a film having a birefringence of 1 × 10 ⁻⁴ or more at a wavelength of 590 nm. “Nz> nx = ny” means that the refractive index in the direction that maximizes the refractive index in the plane of the birefringent film (that is, the slow axis direction) is nx, and the direction that is orthogonal to the slow axis direction in the plane (that is, The optical anisotropy of the birefringent film when the refractive index in the fast axis direction is ny and the refractive index in the thickness direction is nz.

  In the present invention, “nx = ny” includes not only the case where nx and ny are completely the same, but also the case where they are substantially the same. Note that “when nx = ny is substantially the same” means, for example, that an in-plane retardation value (Re [590]) described later is less than 10 nm.

  The polycyclic compound is an organic compound having two or more aromatic and / or heterocyclic rings in the molecular structure, preferably an organic compound having 3 to 8 aromatic and / or heterocyclic rings, More preferred are organic compounds having 4 to 6 aromatic and / or heterocyclic rings. If such a polycyclic compound is used, a transparent birefringent film having no or small absorption in the visible light region can be obtained.

  Such a birefringent film has a refractive index ellipsoid that satisfies the relationship of nz> nx = ny and exhibits a high birefringence in the thickness direction. The phase difference value can be obtained. According to the estimation by the present inventors, the reason why the birefringent film of the present invention exhibits high birefringence is presumed as follows. That is, since a polycyclic compound containing a —COOM group easily forms an association in a solution, and the order in which the association is formed is high, a film formed from such a solution also has high orientation. It is thought to show. In the present invention, one of the effects of the —COOM group contained in the polycyclic compound on the birefringent film is to improve the solubility of the polycyclic compound in a solvent and to allow film formation by a solvent casting method. The other is to obtain a refractive index ellipsoid satisfying the relationship of nz> nx = ny by controlling the refractive index three-dimensionally.

  The birefringence (Δn [590] = nx−nz) in the thickness direction of the birefringent film of the present invention at a wavelength of 590 nm is preferably −0.05 or less, more preferably −0.2 to −0.08. And particularly preferably from -0.16 to -0.1. Note that Δn [590] can be appropriately adjusted within the above range depending on the molecular structure of the polycyclic compound. According to the present invention, by using a polycyclic compound containing a -COOM group, a birefringent film satisfying such a high birefringence index (absolute value) in the thickness direction could be obtained for the first time.

  The thickness of the birefringent film is preferably 0.2 μm to 2.0 μm, more preferably 0.25 μm to 1.8 μm, and particularly preferably 0.3 μm to 1.7 μm. By using the polycyclic compound, a thin birefringent film as described above can be produced. By using the birefringent film having such a thickness as an optical member of a liquid crystal panel, for example, it can contribute to thinning of the liquid crystal display device.

≪2. Polycyclic compounds >>
Any appropriate polycyclic compound may be used as the polycyclic compound used in the present invention as long as it contains a -COOM group. The polycyclic compound preferably exhibits a liquid crystal phase in a solution state (that is, a lyotropic liquid crystal). The liquid crystal phase is preferably a nematic liquid crystal phase in that it has excellent orientation.

  The birefringent film preferably contains an acenaphtho [1,2-b] quinoxaline derivative represented by the following general formula (I) as a polycyclic compound. In formula (I), M represents a counter ion.

  Such a polycyclic compound can form a stable liquid crystal phase in a solution. By a solvent casting method from a solution containing the polycyclic compound, a transparent birefringent film having a high birefringence in the thickness direction and no or little absorption in the visible light region can be produced.

In the general formula (I), M is a counter ion. The M is preferably a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a metal ion, or a substituted or unsubstituted ammonium ion. Examples of the metal ions include Ni ²⁺ , Fe ³⁺ , Cu ²⁺ , Ag ⁺ , Zn ²⁺ , Al ³⁺ , Pd ²⁺ , Cd ²⁺ , Sn ²⁺ , Co ²⁺ , Mn ²⁺ , and Ce ³⁺ . For example, when the birefringent film of the present invention is formed from an aqueous solution containing the above polycyclic compound and water, the above M initially selects a group that improves the solubility in water and forms a film. Thereafter, in order to increase the water resistance of the film, it can be substituted with a group insoluble or hardly soluble in water.
The acenaphtho [1,2-b] quinoxaline derivative represented by the above general formula (I) comprises a benzene-1,2-diamine carboxy group derivative and acenaphthenequinone as shown in the following reaction formula (a). It can be obtained by condensation polymerization.

≪3. Properties of birefringent film >>
The transmittance of the birefringent film at a wavelength of 590 nm is preferably 85% or more, and more preferably 90% or more.

  Rth [590] of the birefringent film can be set to an appropriate value as long as the refractive index ellipsoid satisfies the relationship of nz> nx = ny. The thickness direction retardation value (Rth [590]) of the birefringent film at a wavelength of 590 nm is −300 nm to −10 nm, more preferably −270 nm to −30 nm, and particularly preferably −250 nm to −50 nm. is there. In this specification, the thickness direction retardation value (Rth [λ]) refers to the thickness direction retardation value at 23 ° C. and the wavelength λ (nm). Rth [λ] can be obtained by Rth [λ] = (nx−nz) × d, where d (nm) is the thickness of the film.

  The in-plane retardation value (Re [590]) at a wavelength of 590 nm of the birefringent film is less than 10 nm. In this specification, the in-plane retardation value (Re [λ]) refers to an in-plane retardation value at a wavelength λ (nm) at 23 ° C. Re [λ] can be obtained by Re [λ] = (nx−ny) × d, where d (nm) is the thickness of the film.

The wavelength dispersion value (D) of the birefringent film is preferably 1.01 or more, more preferably 1.02 to 1.1, and most preferably 1.03 to 1.07. In this specification, the chromatic dispersion value (D) is a value calculated from the formula: D = R (40) [450] / R (40) [550]. The R (40) [λ] is a retardation value measured at 23 ° C. at a wavelength λ nm and inclined by 40 ° in a direction perpendicular to the slow axis of the birefringent film.
No conventional birefringent film has been obtained that exhibits such a steep wavelength dependence. In the birefringent film of the present invention, the retardation value measured with short wavelength light is sufficiently larger than the retardation value measured with long wavelength light. Thus, it is also a feature of the birefringent film of the present invention to show the wavelength dependence of the steep retardation.

<< 4. Production method of birefringent film >>
In one embodiment, the birefringent film of the present invention is produced by a method including the following steps (1) to (3).

(1) A step of preparing a solution containing a nematic liquid crystal phase, which contains at least one polycyclic compound (M represents a counter ion) containing a —COOM group and a solvent;
(2) a step of preparing a base material on which at least one surface is hydrophilized,
(3) A step of applying and drying the solution prepared in the step (1) on the hydrophilic surface of the base material prepared in the step (2).

  According to such a production method, a laminated film including at least a birefringent film and a substrate can be obtained.

  As the polycyclic compound containing -COOM group used in the step (1) (M represents a counter ion), an appropriate one can be appropriately selected from the above. As the polycyclic compound, an acenaphtho [1,2-b] quinoxaline derivative represented by the above general formula (I) is preferably used.

  The solvent is used for dissolving the polycyclic compound to develop a nematic liquid crystal phase. Any appropriate solvent can be selected. The solvent may be, for example, an inorganic solvent such as water or an organic solvent. Examples of the organic solvent include alcohols, ketones, ethers, esters, aliphatic and aromatic hydrocarbons, halogenated hydrocarbons, amides, cellosolves and the like. Specifically, examples of the organic solvent include n-butanol, 2-butanol, cyclohexanol, isopropyl alcohol, t-butyl alcohol, glycerin, ethylene glycol, acetone, methyl ethyl ketone, cyclohexanone, cyclopentanone, and 2-pentanone. 2-hexanone, diethyl ether, tetrahydrofuran, dioxane, anisole, ethyl acetate, butyl acetate, methyl lactate, n-hexane, benzene, toluene, xylene, chloroform, dichloromethane, dichloroethane, dimethylformaldehyde, dimethylacetamide, methyl cellosolve, ethyl cellosolve Etc. These solvent can be used individually by 1 type or in mixture of 2 or more types.

  The solvent is particularly preferably water. The electric conductivity of the water is preferably 20 μS / cm or less, more preferably 0.001 μS / cm to 10 μS / cm, and particularly preferably 0.01 μS / cm to 5 μS / cm. The lower limit of the electrical conductivity of the water is 0 μS / cm. By setting the electrical conductivity of water in the above range, a birefringent film having a high birefringence in the thickness direction can be obtained.

  The concentration of the polycyclic compound in the solution can be appropriately adjusted within a range showing a nematic liquid crystal phase depending on the type of the polycyclic compound used. The concentration of the polycyclic compound in the solution is preferably 5% by weight to 30% by weight, more preferably 7% by weight to 20% by weight, and particularly preferably 9% by weight to 15% by weight. . By setting the concentration of the solution in the above range, the solution can form a stable liquid crystal state. The nematic liquid crystal phase can be confirmed and identified by the optical pattern of the liquid crystal phase observed with a polarizing microscope.

  The solution may further contain any suitable additive. Examples of the additive include a surfactant, a plasticizer, a heat stabilizer, a light stabilizer, a lubricant, an antioxidant, an ultraviolet absorber, a flame retardant, a colorant, an antistatic agent, a compatibilizing agent, a crosslinking agent, And thickeners. The amount of the additive is preferably more than 0 and 10 parts by weight or less with respect to 100 parts by weight of the solution.

  The “hydrophilic treatment” in the above step (2) refers to a treatment for reducing the water contact angle of the substrate. The hydrophilization treatment is performed in order to improve the wettability and coating property of the substrate surface on which the polycyclic compound is applied. The hydrophilization treatment is a treatment for reducing the contact angle of water at 23 ° C. of the base material by preferably 10% or more, more preferably a treatment for reducing the contact angle of water by 15% to 80%. The treatment is preferably reduced by 20% to 70%. In addition, the ratio (%) to decrease is obtained by the formula: {(contact angle before treatment−contact angle after treatment) / contact angle before treatment} × 100.

  Furthermore, the hydrophilization treatment is preferably a treatment for reducing the contact angle of water at 23 ° C. of the base material by 5 ° or more, more preferably a treatment for reducing the contact angle of water by 10 ° to 65 °. Particularly preferred is a treatment for lowering by 20 ° to 65 °.

  Further, the hydrophilization treatment is a treatment in which the contact angle of water at 23 ° C. of the substrate is preferably 5 ° to 60 °, more preferably 5 ° to 50 °, and particularly preferably. This is a treatment of 5 ° to 45 °. By setting the water contact angle of the substrate within the above range, a birefringent film having a high birefringence index in the thickness direction and a small thickness variation can be obtained.

  Furthermore, an appropriate method can be adopted for the hydrophilic treatment. As the hydrophilic treatment, for example, a dry treatment or a wet treatment may be used. Examples of the dry treatment include discharge treatment such as corona treatment, plasma treatment, and glow discharge treatment; flame treatment; ozone treatment; UV ozone treatment; ionizing active ray treatment such as ultraviolet treatment and electron beam treatment. Examples of the wet treatment include ultrasonic treatment using a solvent such as water and acetone; alkali treatment; anchor coat treatment. These hydrophilization treatments may be performed alone or in combination of two or more.

  Preferably, the hydrophilization treatment is a corona treatment, a plasma treatment, an alkali treatment, or an anchor coat treatment. With such a hydrophilic treatment, a birefringent film having high orientation and small thickness variation can be obtained. The conditions for the hydrophilization treatment, such as the treatment time and strength, can be appropriately adjusted as appropriate so that the water contact angle of the substrate falls within the above range.

  The corona treatment is typically a treatment for modifying the substrate surface by passing the substrate through corona discharge. The corona discharge is generated by ionizing a dielectric breakdown of the air between the electrodes by applying a high frequency and high voltage between the grounded dielectric roll and the insulated electrodes. The plasma treatment is typically a treatment for modifying the substrate surface by passing the substrate through low-temperature plasma. The low temperature plasma is generated by ionizing a part of gas molecules when glow discharge occurs in an inorganic gas such as a low-pressure inert gas, oxygen, or halogen gas. The above ultrasonic treatment is typically a treatment that removes contaminants on the surface of the base material by immersing the base material in water or an organic solvent and applies ultrasonic waves to improve the wettability of the base material. is there. The alkali treatment is typically a treatment for modifying the substrate surface by immersing the substrate in an alkali treatment solution in which a basic substance is dissolved in water or an organic solvent. The anchor coating treatment is typically a treatment for applying an anchor coating agent to the surface of the substrate.

  The substrate used in the present invention is used for uniformly casting a solution containing the polycyclic compound and a solvent. Any appropriate substrate can be selected. Examples of the base material include a glass base material, a quartz substrate, a polymer film, a plastic substrate, a metal plate such as aluminum and iron, a ceramic substrate, and a silicon wafer. The substrate is preferably a glass substrate or a polymer film.

  Any appropriate substrate can be selected as the glass substrate. Preferably, the glass substrate is used for a liquid crystal cell. Examples of the glass substrate used in the liquid crystal cell include soda lime (blue plate) glass containing an alkali component, or low alkali borosilicate glass. A commercially available glass substrate may be used as it is. Examples of the commercially available glass substrate include Corning glass code: 1373, Asahi Glass Co., Ltd. glass code: AN635, NH Techno Glass Co., Ltd. glass code: NA-35, and the like.

  Any appropriate resin can be selected as the resin for forming the polymer film. Preferably, the polymer film contains a thermoplastic resin. Examples of the thermoplastic resin include polyolefin resins, cycloolefin resins, polyvinyl chloride resins, cellulose resins, styrene resins, polymethyl methacrylate, polyvinyl acetate, polyvinylidene chloride resins, polyamide resins, and polyacetals. Resin, polycarbonate resin, polybutylene terephthalate resin, polyethylene terephthalate resin, polysulfone resin, polyethersulfone resin, polyetheretherketone resin, polyarylate resin, polyamideimide resin and the like. Said thermoplastic resin is used individually or in combination of 2 or more types. The thermoplastic resin can be used after any appropriate polymer modification. Examples of the polymer modification include modifications such as copolymerization, crosslinking, molecular terminals, and stereoregularity.

  The substrate used in the present invention is preferably a polymer film containing a cellulose resin. This is because it is possible to obtain a birefringent film having excellent wettability of the polycyclic compound, a high birefringence index in the thickness direction, and a small thickness variation.

  Arbitrary appropriate things can be employ | adopted for the said cellulose resin. The cellulose-based resin is preferably a cellulose organic acid ester or a cellulose mixed organic acid ester in which part or all of the hydroxyl groups of cellulose are substituted with an acetyl group, a propionyl group and / or a butyl group. Examples of the cellulose organic acid ester include cellulose acetate, cellulose propionate, and cellulose butyrate. Examples of the cellulose mixed organic acid include cellulose acetate propionate and cellulose acetate butyrate. The cellulose resin can be obtained by, for example, the method described in JP 2001-188128 A [0040] to [0041].

  As the substrate used in the present invention, a commercially available polymer film can be used as it is. Alternatively, a commercially available polymer film that has been subjected to secondary processing such as stretching and / or shrinking can also be used. As a polymer film containing a commercially available cellulose resin, for example, Fujitac series (trade names: ZRF80S, TD80UF, TDY-80UL) manufactured by Fuji Photo Film Co., Ltd., products manufactured by Konica Minolta Opto Co., Ltd. The name “KC8UX2M” and the like can be mentioned.

  The thickness of the base material is preferably 20 μm to 100 μm. By making the thickness of the base material within the above range, the handling property and coating property of the base material are excellent.

  The coating speed of the solution in the step (3) is preferably 50 mm / second or more, and more preferably 100 mm / second or more. By setting the coating speed within the above range, a birefringent film having a high birefringence index in the thickness direction and a small thickness variation can be obtained.

  As a method for applying the solution to the surface of the substrate, a coating method using an appropriate coater may be employed as appropriate. Examples of the coater include a reverse roll coater, a forward rotation roll coater, a gravure roll coater, a knife coater, a rod coater, a slot die coater, a slot orifice coater, a curtain coater, a fountain coater, an air doctor coater, a kiss coater, a dip coater, a bead coater, and a blade. Examples thereof include a coater, a cast coater, a spray coater, a spin coater, an extrusion coater, and a hot melt coater. The coater is preferably a reverse roll coater, a forward rotation roll coater, a gravure coater, a rod coater, a slot die coater, a slot orifice coater, a curtain coater, and a fountain coater.

  As a method for drying the solution, an appropriate method can be adopted as appropriate. Drying methods include, for example, an air circulation type constant temperature oven in which hot or cold air circulates, a heater using microwaves or far infrared rays, a roll heated for temperature control, a heat pipe roll, or a metal belt. Can be mentioned.

  The temperature at which the solution is dried is not higher than the isotropic phase transition temperature of the solution, and it is preferable that the temperature is gradually raised from a low temperature to a high temperature to be dried. The drying temperature is preferably 10 ° C to 80 ° C, more preferably 20 ° C to 60 ° C. If it is said temperature range, a birefringent film with small thickness variation can be obtained.

  The time for drying the solution can be appropriately selected depending on the drying temperature and the type of solvent. In order to obtain a birefringent film having a small variation in thickness, the drying time is, for example, 1 minute to 30 minutes, and preferably 1 minute to 10 minutes. By drying the solution, a laminate (laminated film) in which a birefringent film is laminated on the surface of the substrate is obtained.

The method for producing a birefringent film of the present invention preferably further includes a step (4) after the above steps (1) to (3):
(4) The birefringent film obtained in the above step (3) is selected from the group consisting of aluminum salts, barium salts, lead salts, chromium salts, strontium salts, and compounds having two or more amino groups in the molecule. Contacting with a solution comprising at least one compound salt.

  In this invention, the said process (4) is performed in order to make the birefringent film obtained insoluble or hardly soluble with respect to water. Examples of the compound salt include aluminum chloride, barium chloride, lead chloride, chromium chloride, strontium chloride, 4,4′-tetramethyldiaminophenylmethane hydrochloride, 2,2′-dipyridyl hydrochloride, 4,4′- Examples include dipyridyl hydrochloride, melamine hydrochloride, tetraaminopyrimidine hydrochloride and the like. If it is such a compound, the birefringent film excellent in water resistance can be obtained.

  The concentration of the compound salt in the solution containing the above compound salt is preferably 3% by weight to 40% by weight, and particularly preferably 5% by weight to 30% by weight. By bringing the birefringent film into contact with a solution containing a compound salt having a concentration in the above range, a film having excellent durability can be obtained.

  As a method for bringing the birefringent film obtained in the step (3) into contact with the solution containing the compound, any method can be adopted. Examples of the method include (i) a method of coating the surface of the birefringent film with a solution containing the compound salt, and (ii) a method of immersing the birefringent film in a solution containing the compound salt. It is done. When these methods are employed, it is preferable that the obtained birefringent film is washed with a remaining solution (a solution containing a compound salt) with water or an arbitrary solvent. Furthermore, the laminated body excellent in the adhesiveness of the interface of a base material and a birefringent film can be obtained by drying this.

≪5. Applications of birefringent film >>
The use of the birefringent film of the present invention is not particularly limited, but representative examples include λ / 4 plates, λ / 2 plates, wide viewing angle films, antireflection films for flat panel displays, and the like of liquid crystal display devices. It is done. In one embodiment, the birefringent film may be laminated with a polarizer and used as a polarizing plate. Hereinafter, this polarizing plate will be described.

≪6. Polarizing plate of the present invention >>
The polarizing plate of the present invention includes at least the birefringent film and a polarizer. The polarizing plate may include a laminated film including at least a birefringent film and a base material, or may include another birefringent film or an optional protective layer. Practically, any appropriate adhesive layer is provided between the constituent members of the polarizing plate, and the polarizer and each constituent member are adhered.

  Any suitable polarizer may be used as long as it converts natural light or polarized light into linearly polarized light. The polarizer is preferably a stretched film mainly composed of a polyvinyl alcohol resin containing iodine or a dichroic dye. The thickness of the polarizer is usually 5 μm to 50 μm.

  Any appropriate adhesive can be selected as long as the above-described adhesives are bonded to each other with a practically sufficient adhesive force and adhesion time. Examples of the material for forming the adhesive layer include an adhesive, a pressure-sensitive adhesive, and an anchor coating agent. The adhesive layer may have a multilayer structure in which an anchor coat agent layer is formed on the surface of an adherend and an adhesive layer or a pressure-sensitive adhesive layer is formed thereon. Alternatively, the adhesive layer may be a thin layer (also referred to as a hairline) that cannot be recognized with the naked eye. In the polarizing plate, the adhesive layer arranged on one side of the polarizer and the adhesive layer arranged on the other side may be the same or different.

The present invention will be further described using examples and comparative examples. In addition, this invention is not limited only to these Examples. In addition, each analysis method used in the Example is as follows.
(1) Measuring method of thickness:
When the thickness was less than 10 μm, measurement was performed using a spectrophotometer for thin film [manufactured by Otsuka Electronics Co., Ltd., “instant multi measurement system MCPD-2000”]. When the thickness was 10 μm or more, measurement was performed using an Anritsu digital micrometer “KC-351C type”.
(2) Transmittance (T [590]), birefringence in the thickness direction (Δn [590]), retardation values (Re [λ], Rth [λ]), chromatic dispersion value (D) (R (40 ) [450] / R (40) [550]) measurement method:
Measurement was performed at 23 ° C. using a trade name “KOBRA21-ADH” manufactured by Oji Scientific Instruments. In addition, the value measured using the Abbe refractometer [Atago Co., Ltd. product name "DR-M4"] was used for the average refractive index.
(3) Electrical conductivity measurement method:
A 1 cm ³ container connected to the electrode after washing the electrode of a solution conductivity meter [manufactured by Kyoto Electronics Industry Co., Ltd., product name “CM-117”] with an aqueous solution prepared to a concentration of 0.05% by weight When the sample was observed, the displayed electric conductivity showed a constant value, which was taken as the measured value.
(4) Method for measuring water contact angle:
Using a solid-liquid interface analyzer [product name “Drop Master 300” manufactured by Kyowa Interface Science Co., Ltd.], the contact angle after 5 seconds had elapsed after the liquid was dropped onto the substrate. The measurement condition is static contact angle measurement. As the water, ultrapure water was used, and the droplets were 0.5 μl. About each base material, the average value of 10 repetitions was made into the measured value.

[Synthesis Example 1]
<Synthesis of acenaphtho [1,2-b] quinoxaline-9-carboxylic acid>
500 mL of dimethylformaldehyde was added to a mixture of purified 10 g acenaphthenequinone and 84 g 3,4-diaminobenzoic acid. The reaction was kept stirring at room temperature for 21 hours. The precipitate was filtered to obtain a crude composition. This crude composition was dissolved in hot dimethylformamide, filtered again, and purified by washing with dimethylformamide and water.

[Synthesis Example 2]
<Synthesis of acenaphtho [1,2-b] quinoxaline-9-carboxylate ammonium>
As shown in the reaction route (b) below, the purified acenaphtho [1,2-b] quinoxaline-9-carboxylic acid is dissolved in 2 liters of pure water (electric conductivity: 1.7 μS / cm). Further, ammonium hydroxide was added, and the acid was neutralized with ammonium hydroxide. The obtained aqueous solution was put into a supply tank and purified using a triple flat membrane evaluation apparatus equipped with a reverse osmosis membrane filter [trade name “NTR-7430”] manufactured by Nitto Denko Corporation. Next, this purified aqueous solution was adjusted using a rotary evaporator so that the concentration of the polycyclic compound in the aqueous solution was 13.3% by weight. When the aqueous solution obtained here was observed with a polarizing microscope, it exhibited a nematic liquid crystal phase at 23 ° C.

[Example 1]
A polymer film (trade name “ZRF80S” manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 80 μm as a main component is immersed in an aqueous solution in which sodium hydroxide is dissolved, and an alkali treatment (saponification treatment) is performed on the surface. (Also called). The contact angle of water at 23 ° C. of the polymer film was 64.6 ° before the treatment and 26.5 ° after the treatment. Next, the aqueous solution obtained in Synthesis Example 2 is applied to the surface of the polymer film which has been subjected to alkali treatment using a bar coater [trade name “mayer rot HS1.5” manufactured by BUSCHMAN Co., Ltd.]. Coating was performed so that the thickness was 0.35 μm. The coated film was dried while blowing air on the coated surface in a constant temperature room at 23 ° C., and further dried in an air circulation drying oven at 40 ° C. for 3 minutes. As a result, a birefringent film A having a refractive index ellipsoid showing a relationship of nz> nx = ny was formed on the surface of a polymer film containing triacetyl cellulose as a main component. The characteristics of this birefringent film A are shown in Table 1.

[Example 2]
Birefringence showing the relationship of nz> nx = ny in the same manner as in Example 1 except that the aqueous solution obtained in Synthesis Example 2 was coated so that the thickness after drying was 0.45 μm. Film B was obtained. The characteristics of this birefringent film B are shown in Table 1.

[Example 3]
Birefringence showing the relationship of nz> nx = ny in the same manner as in Example 1 except that the aqueous solution obtained in Synthesis Example 2 was coated so that the thickness after drying was 0.61 μm. Film C was obtained. The characteristics of the birefringent film C are shown in Table 1.

[Example 4]
Birefringence showing the relationship of nz> nx = ny in the same manner as in Example 1 except that the aqueous solution obtained in Synthesis Example 2 was coated so that the thickness after drying was 0.85 μm. Film D was obtained. The characteristics of the birefringent film D are shown in Table 1.

[Example 5]
Birefringence showing the relationship of nz> nx = ny in the same manner as in Example 1 except that the aqueous solution obtained in Synthesis Example 2 was coated so that the thickness after drying was 1.5 μm. Film E was obtained. The characteristics of the birefringent film E are shown in Table 1.

[Example 6]
Birefringence showing a relationship of nz> nx = ny in the same manner as in Example 1 except that the aqueous solution obtained in Synthesis Example 2 was applied so that the thickness after drying was 1.6 μm. Film F was obtained. The characteristics of this birefringent film F are shown in Table 1.

[Evaluation]
As shown in Examples 1 to 5, by applying a solution containing at least a polycyclic compound containing a —COOM group and a solvent to the substrate surface, the refractive index ellipsoid becomes nz> nx = A birefringent film satisfying the ny relationship and showing a high birefringence in the thickness direction could be obtained. These birefringent films can obtain a predetermined retardation value with a thinner thickness than conventional birefringent films.

  As described above, the birefringent film of the present invention satisfies the relationship of nz> nx = ny and exhibits a high birefringence in the thickness direction, so that the birefringent film of the present invention has a high birefringence in the thickness direction. This can greatly contribute to improvement of display characteristics and thinning.

Claims (9)

The refractive index ellipsoid satisfies the relationship of nz> nx = ny and is an acenaphtho [1,2-b] quinoxaline derivative represented by the following general formula (I) (in the formula (I), M represents a counter ion. ) comprising a containing also a small, birefringent film.

  The birefringent film according to claim 1, wherein the birefringence (Δn [590]) in the thickness direction at a wavelength of 590 nm of the birefringent film is −0.05 or less.   The birefringent film according to claim 1 or 2, wherein the birefringent film has a thickness of 0.2 µm to 2.0 µm.   The birefringent film according to any one of claims 1 to 3, wherein a retardation value (Rth [590]) in a thickness direction at a wavelength of 590 nm of the birefringent film is -300 nm to -10 nm.   A laminated film comprising at least the birefringent film according to claim 1 and a substrate. A method for producing a birefringent film including the following steps (1) to (3):
(1) An acenaphtho [1,2-b] quinoxaline derivative represented by the following general formula (I) (wherein M represents a counter ion in formula (I)) and a solvent, and a nematic liquid crystal phase Preparing the indicated solution;
(2) a step of preparing a substrate on which at least one surface has been subjected to a hydrophilic treatment,
(3) A step of applying and drying the solution prepared in the step (1) on the hydrophilic-treated surface of the substrate prepared in the step (2).

  The method for producing a birefringent film according to claim 6, wherein the hydrophilization treatment is a corona treatment, a plasma treatment, an alkali treatment, or an anchor coat treatment.   The method for producing a birefringent film according to claim 6 or 7, wherein the substrate is a glass substrate or a polymer film.   A polarizing plate comprising at least the birefringent film according to claim 1 and a polarizer.