TW201831606A - Azo compound or salt thereof, dye-based polarizing film having the same, and dye-based polarizing plate - Google Patents

Abstract

An object of the present invention is to provide a high performance dye-based polarizing film and dye-based polarizing plate having excellent polarizing performance, in particular, a neutral gray high performance dye type film and dye-based type polarizing plate, and an azo compound or a salt thereof which can produce the same. The present invention provides an azo compound represented by the following formula (1) or a salt thereof. (In the formula, A1 and A2 each independently represent a hydrogen atom or a group represented by the following formula (2), but excluding both A1 and A2 are hydrogen atom.).

Description

 Azo compound or a salt thereof, and a dye-based polarizing film containing a azo compound or a salt thereof, and a dye-based polarizing plate  

The present invention relates to a novel azo compound or a salt thereof, and a dye-based polarizing film containing the azo compound or a salt thereof.

A polarizing plate having a function of transmitting and shielding light is a liquid crystal having a light switching function, and is a basic requirement for forming a display such as a liquid crystal display (LCD). The application fields of this LCD include small devices such as early electronic computers and watches, notebook computers, word processors, liquid crystal projectors, LCD TVs, car navigation systems, and indoor and outdoor information displays and measuring instruments. . Further, it can be applied to a lens having a polarizing function, and has been applied to sunglasses for improving visibility or polarized glasses corresponding to 3D televisions and the like in recent years. Furthermore, it is also applied to practical information terminals including wearable terminals. Since the application of the polarizing plate as described above has been widely spread, and it is also used in a wide range of conditions from low temperature to high temperature, low humidity to high humidity, low light amount to high light quantity, polarized light having high polarization performance and excellent durability is required. board.

Now, the polarizing film is a film of an extended-aligned polyvinyl alcohol or a derivative thereof, or a polyene-based film which is formed by dehydration of a dechlorination or polyvinyl alcohol-based film of a polyvinyl chloride film to form a polyene. The polarizing film substrate is produced by dyeing or containing iodine or a dichroic dye as a dichroic dye. Among these, an iodine-based polarizing film using iodine as a dichroic dye has excellent polarizing performance, is not resistant to water and heat, and has a problem of durability when used for a long period of time in a high-temperature and high-humidity state. In order to improve durability, although a method of treating with formaldehyde or an aqueous solution containing boric acid or a polymer film having a low moisture permeability as a protective film is considered, the effect is not sufficient. On the other hand, when a dichroic dye is used as the dye-based polarizing film of the dichroic dye as compared with the iodine-based polarizing film, although it is excellent in moisture resistance and heat resistance, generally, the polarizing performance is insufficient.

For the dyes used in the production of the dye-based polarizing film, for example, the water-soluble azo compounds described in Patent Documents 1 to 5 are known.

In a polarizing film in which a plurality of dichroic dyes are adsorbed and aligned on a polymer film to form an intermediate color (hereinafter, also referred to as "neutral gray"), the alignment directions of the two polarizing films are made vertical. In the overlapping state (vertical position) of the mode, if there is light leakage (color leakage) of a specific wavelength in the wavelength region of the visible light region, when the polarizing film is mounted on the liquid crystal panel, the color tone of the liquid crystal display is changed in a dark state. Hey. Therefore, when the polarizing film is mounted on a liquid crystal display, in order to prevent discoloration of the liquid crystal display due to color leakage at a specific wavelength in a dark state, a plurality of dichroic dyes are adsorbed and aligned on the polymer film. In the polarizing film of the gray color, the transmittance (vertical transmittance) of the vertical position in the wavelength domain of the visible light region must be uniformly lowered.

Until recently, images were highlighted with high brightness to improve the sharpness of the image of the liquid crystal display. In a hybrid vehicle, an outdoor display (for example, an industrial instrument and a wearable terminal) that has such a display, there is a need to extend the driving time of the battery. Therefore, there has been a polarizer which is required to have a neutral light tone with good polarization performance even if the brightness is lowered in order to reduce the power consumption of the liquid crystal display (hereinafter also referred to as "neutral gray polarizer". "). Further, in a liquid crystal display for a vehicle, a polarizing plate that does not change its polarization degree even in a high-temperature and high-humidity environment in a summer vehicle is required. In the past, an iodine-based polarizing plate having a good polarizing property and a neutral gray color was used for a liquid crystal display for a vehicle. However, as described above, the iodine-based polarizing plate has iodine as a dichroic dye, and thus has problems in that light resistance, heat resistance, and moist heat resistance are insufficient. In order to solve this problem, it has evolved into a neutral gray polarizing plate using a dye-based dichroic dye as a polarizing member. The neutral gray polarizing plate can evenly improve the transmittance and polarization performance in the entire visible light wavelength region, and generally combines the three primary colors (red, green, and blue). Therefore, it is necessary to develop a dichroic dye having good polarizing performance for each of the three primary colors.

At the same time, the light source of each liquid crystal display is not the same. Therefore, in the development of dichroic dyes having good polarizing properties, it is particularly important to design the wavelength of the dye that matches the wavelength of the bright line. Therefore, it is necessary to surely control the light of the respective limited wavelength domains for the dyes of the three primary colors, and to prevent absorption in the wavelength range other than the above, thereby providing excellent polarizing performance.

 [Previous Technical Literature]    [Patent Literature]  

[Patent Document 1] Japanese Patent Laid-Open No. Hei 3-012606

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2001-33627

[Patent Document 3] International Publication No. 2009/154055

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2003-327858

[Patent Document 5] Japanese Patent Laid-Open No. Hei 3-12606

[Patent Document 6] Japanese Patent Laid-Open Publication No. 2005-171231

However, the blue pigment used in the polarizing plate hitherto is a dye having a copper complex structure as described in Patent Document 6, and the absorption in the short-wavelength region is increased by the influence of the copper complex (400 to 500 nm). In the case of the combination of the three primary colors of the present day, there is a disadvantage that the neutral gray color tone cannot be achieved. Therefore, it has been desired to develop a blue coloring matter in such a manner that a neutral gray polarizing plate that suppresses absorption on the short-wavelength side and enhances transmittance and polarization performance in the entire visible light wavelength region can be produced.

Accordingly, an object of the present invention is to provide a high-performance dye-based polarizing film and a dye-based polarizing plate having excellent polarizing properties, particularly a neutral gray high-performance dye-based polarizing film and a dye-based polarizing plate, and can be produced. An azo compound or a salt thereof.

As a result of intensive studies in order to achieve such a result, the present inventors have found that a polarizing film containing a specific azo compound or a salt thereof and a polarizing plate have excellent polarizing performance, and realize a neutral gray hue, thereby achieving the present invention. .

That is, the present invention relates to the following items [1] to [15].

[1] An azo compound or a salt thereof, which is represented by the following formula (1): (wherein A ₁ and A ₂ each independently represent a hydrogen atom or the following formula (2), but excludes both of A ₁ and A ₂ as a hydrogen atom: (wherein, the ring substituted with R ₁ and a sulfo group is a benzothiazole ring in the absence of a ring represented by a broken line, and a naphthylthiazole ring when a ring represented by a broken line is present, and R ₁ is selected from the group consisting of a chlorine atom, a sulfonic acid group, a nitro group, a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms having a sulfonic acid group, and a carbon number having a hydroxyl group An alkyl group of 1 to 4, an alkyl group having 1 to 4 carbon atoms having a carboxyl group, an alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group, an alkoxy group having 1 to 4 carbon atoms having a hydroxyl group, and a carboxyl group having a carboxyl group a group formed by alkoxy groups having 1 to 4 carbon atoms, B is a phenyl or anthracene group which may have a substituent, and the substituent is selected from a chlorine atom, a sulfonic acid group, a nitro group, a hydroxyl group, and a carbon number of 1. An alkyl group to 4, an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms having a sulfonic acid group, an alkyl group having 1 to 4 carbon atoms having a hydroxyl group, and 1 to 4 carbon atoms having a carboxyl group a group formed of an alkyl group, an alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group, an alkoxy group having 1 to 4 carbon atoms having a hydroxyl group, and an alkoxy group having 1 to 4 carbon atoms having a carboxyl group ( When there are multiples, they are independent), m is an integer from 1 to 3), -NH- 2 keys are individually bonded independently represents a or b in the position of substitution).

[2] The azo compound or a salt thereof according to [1], wherein the formula (2) is represented by the following formula (3): (wherein R _1a represents a substituted ring, and R _1a represents the same as R ₁ in the formula (2), and R ₂ and R ₃ are each independently selected from a hydrogen atom, a chlorine atom, a sulfonic acid group. a nitro group, a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms having a sulfonic acid group, and an alkyl group having 1 to 4 carbon atoms having a hydroxyl group. An alkyl group having 1 to 4 carbon atoms of a carboxyl group, an alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group, an alkoxy group having 1 to 4 carbon atoms having a hydroxyl group, and a carbon number of 1 to 4 having a carboxyl group The group formed by the alkoxy group, m ₁ represents the same as m in the formula (2), or the following formula (4) represents: (wherein R _1b represents a substituted ring, and R _1b represents the same as R ₁ in the formula (2), and R ₄ to R ₆ are each independently selected from a hydrogen atom, a chlorine atom, a sulfonic acid group. a nitro group, a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms having a sulfonic acid group, and an alkyl group having 1 to 4 carbon atoms having a hydroxyl group. An alkyl group having 1 to 4 carbon atoms of a carboxyl group, an alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group, an alkoxy group having 1 to 4 carbon atoms having a hydroxyl group, and a carbon number of 1 to 4 having a carboxyl group The group formed by the alkoxy group, m ₂ represents the same as m in the formula (2)).

[3] [2] of the azo compound or a salt thereof, wherein represents A ₁ and A ₂ individually are independently formula (3) or (4).

[4] The azo compound or a salt thereof according to [2], wherein A ₁ is represented by formula (3) or formula (4), and A ₂ is a hydrogen atom.

The azo compound or a salt thereof according to any one of [2], wherein R _1b in the formula (4) is a hydrogen atom, a chlorine atom or an alkyl group having 1 to 4 carbon atoms. Or an alkoxy group having 1 to 4 carbon atoms, and each of R ₄ to R _{6 is} independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms which may have a sulfonic acid group.

The azo compound or a salt thereof according to any one of [2], wherein R _1a in the formula (3) is a hydrogen atom, a chlorine atom or an alkyl group having 1 to 4 carbon atoms. R ₂ and R _{3 are} each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms which may have a sulfonic acid group.

The azo compound or a salt thereof according to any one of the above aspects, wherein the -NH-substitution position in the formula (1) is a.

[8] A dye-based polarizing film comprising the azo compound according to any one of [1] to [7], or a salt thereof, and a polarizing film substrate.

[9] A dye-based polarizing film comprising the azo compound according to any one of [1] to (7) or a salt thereof, and one or more organic dyes other than the above, and a polarizing film substrate.

[10] A dye-based polarizing film comprising the azo compound according to any one of [1] to [7] or a salt thereof, and one or more organic dyes other than the above, and a polarizing film substrate. .

[11] The dye-based polarizing film according to any one of [8], wherein the polarizing film substrate is a film formed of a polyvinyl alcohol resin or a derivative thereof.

[12] A dye-based polarizing plate obtained by laminating a transparent protective layer on at least one surface of the dye-based polarizing film according to any one of [8] to [11].

[13] A liquid crystal display comprising the dye-based polarizing film according to any one of [8] to [11] or the dye-based polarizing plate according to [12].

[14] The dye-based polarizing film according to any one of [8] to [11] which exhibits a neutral gray color.

[15] A display for a vehicle or an outdoor display comprising the dye-based polarizing plate according to [14] or a dye-based polarizing plate obtained by laminating a transparent protective layer on at least one surface of the dye-based polarizing film.

The present invention can provide a high-performance dye-based polarizing film and a dye-based polarizing plate having excellent polarizing properties, in particular, a neutral gray high-performance dye-based film and a dye-based polarizing plate, and an azo compound or a salt thereof capable of producing the same . In one form, the polarizing plate of the present invention has moisture resistance, heat resistance, and/or light resistance.

 <Azo compound or a salt thereof>  

The azo compound of the present invention is represented by the following formula (1): Said.

In the formula (1), the 2-bond of -NH- is independently bonded to the substitution position indicated by a or b.

A ₁ and A ₂ are hydrogen atoms or the following formula (2) represents: . However, it is excluded that both of A ₁ and A ₂ are hydrogen atoms. One of A ₁ and A ₂ is a hydrogen atom, the other is represented by the formula (2), or both of A ₁ and A ₂ are represented by the formula (2). Preferably, both of A ₁ and A ₂ are represented by the formula (2).

In the formula (2), the ring substituted with R ₁ and a sulfonic acid group is a benzothiazole ring when no ring represented by a broken line is present, and a naphthylthiazole ring when a ring represented by a broken line is present. When there is no ring represented by a broken line, that is, when the ring substituted by R ₁ is a benzothiazole ring, the substitution positions of R ₁ and a sulfonic acid group are not particularly limited, but only the 4 position, only the 6 position, 4 The combination of the number and the 6th position and the combination of the 6th and 7th positions are preferred, and the combination of only the 6th position and the 4th and 6th positions is better. When a ring represented by a broken line exists, that is, when the ring substituted by R ₁ is a naphthylthiazole ring, the substitution position of the sulfonic acid group and R ₁ is not particularly limited, but the combination of the 6th position and the 8th position, No. 4 The combination of the position with the 6th and 8th positions, and the combination of the 4th and 7th and 9th positions is preferred, and the combination of the 6th and 8th positions is better.

R ₁ is a hydrogen atom, a chlorine atom, a sulfonic acid group, a nitro group, a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and a carbon number of 1 to 4 having a sulfonic acid group. An alkyl group, an alkyl group having 1 to 4 carbon atoms having a hydroxyl group, an alkyl group having 1 to 4 carbon atoms having a carboxyl group, an alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group, and 1 to 4 carbon atoms having a hydroxyl group A group formed by an alkoxy group and an alkoxy group having a carboxyl group having 1 to 4 carbon atoms. Preferred are a sulfonic acid group and an alkoxy group having 1 to 4 carbon atoms. When R ₁ is plural, these are independently selected independently.

The lower alkoxy group having a hydroxyl group is preferably a linear alkoxy group having an alkoxy group substituted with a hydroxyl group, more preferably a 4-hydroxypropoxy group or a 4-hydroxybutoxy group. The lower alkoxy group having a carboxyl group is preferably a linear alkoxy group having an alkoxy group substituted with a carboxyl group, more preferably a 4-carboxypropoxy group or a 4-carboxybutoxy group. a lower alkoxy group having a sulfonic acid group, preferably a linear alkoxy group substituted with a sulfonic acid group at the alkoxy group, more preferably a 4-sulfonic acid propoxy group or a 4-sulfonic acid butoxy group base.

B is a phenyl or anthracene group which may have a substituent. There is no limitation on the binding position of B to two azo groups. The substituent is selected from the group consisting of a hydrogen atom, a chlorine atom, a sulfonic acid group, a nitro group, a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and a carbon number of 1 to 4 having a sulfonic acid group. An alkyl group, an alkyl group having 1 to 4 carbon atoms having a hydroxyl group, an alkyl group having 1 to 4 carbon atoms having a carboxyl group, an alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group, and 1 to 4 carbon atoms having a hydroxyl group A group formed by an alkoxy group and an alkoxy group having a carboxyl group having 1 to 4 carbon atoms. When the substituents are plural, these are independently selected independently. When B is a phenyl group which may have a substituent, the substitution position is not particularly limited, and a combination of a 2 position and a 5 position and a combination of a 3 position and a 5 position are preferred, and the position is 2 The combination of the 5th position is especially good. When B is a stretching naphthyl group, the substitution position is not particularly limited, and is a combination of only the 2nd position, only the 6th position, only the 7th position, the 2nd position and the 6th position, and the 2nd position. The combination of the bit and the 7th position is preferable, and the combination of only the 2nd position and the 2nd position and the 7th position is preferable.

The formula (2) is preferably the following formula (3): Or formula (4): Said.

In the formula (3), the ring in which R _1a and R _1a are substituted means the same as the ring in which R ₁ and R ₁ in the formula (2) are substituted.

R ₂ and R ₃ represent the same meanings as the substituent which B in the formula (2) may have. Preferred are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group.

m ₁ defines the same as the formula m (2) is intended.

In the formula (4), the ring in which R _1b and R _1b are substituted means the same as the ring in which R ₁ and R ₁ in the formula (2) are substituted.

R ₄ to R ₆ represent the same meanings as the substituent which B in the formula (2) may have. Preferred are a hydrogen atom, a sulfonic acid group, a hydroxyl group, an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms.

m ₂ represents the same meaning as m in the formula (2).

The azo compound represented by the formula (1) may be in a free form or in a salt form. The salt may, for example, be an alkali metal salt such as a lithium salt, a sodium salt or a potassium salt, or an organic salt such as an amine salt or an alkylamine salt. The salt is preferably sodium salt.

Next, specific examples of the azo compound represented by the formula (1) are as follows. Further, the sulfonic acid group, the carboxyl group and the hydroxyl group in the formula are represented by the form of a free acid.

The azo compound represented by the formula (1) or a salt thereof can be subjected to diazotization by, for example, a general dye production method described in Patent Document 3 and Dye Chemistry (Hitata F., 1957, p. 621). Manufactured by coupling.

Specific examples of the production method include the following methods.

The aminothiazole represented by the following formula (A) is diazotized and coupled with the aniline represented by the following formula (B) or the naphthylamine represented by the following formula (C) to obtain the following formula ( D) or a monoazoamine-based compound represented by the following formula (E).

The monoazoamine-based compound (D) or (E) is separately diazotized and coupled to a naphthol of the following formula (F) to obtain an azo compound of the formula (1).

In the formulae (A) to (F), the substitution positions of R ₁ and R ₁ represent the same meanings as in the formula (2), and R ₂ and R ₃ represent the same meanings as in the formula (3), and R ₄ to R ₆ represents the same meaning as in the formula (4), and m represents the same meaning as in the formula (2).

In the above production method, the diazotization step is a normal method of mixing a nitrite such as sodium nitrite with a mineral acid aqueous solution or a suspension of a diazo component such as hydrochloric acid or sulfuric acid, or a neutral or a diazo component. It is preferred to add a nitrite to the weakly alkaline aqueous solution and to carry out the reverse method of mixing with the mineral acid. The temperature of the diazotization is suitably from -10 to 40 °C. Further, the coupling step with the aniline is preferably carried out by mixing an acidic aqueous solution such as hydrochloric acid or acetic acid with the above respective diazonium liquids under acidic conditions at a temperature of -10 to 40 ° C and a pH of 2 to 7.

The monoazo compound of the formula (D) or the formula (E) obtained by coupling may be directly filtered or precipitated by acid precipitation or salting out, filtered, and taken out, or the solution or suspension may be directly subjected to the next step. When the diazonium salt is poorly soluble and forms a suspension, it can be filtered to form a filter cake and used in the next coupling step.

The second coupling reaction of the diazo compound of formula (D) or formula (E) with the naphthol of formula (F) is carried out at a temperature of -10 to 40 ° C and a neutrality of pH 7 to 10. It is preferred to carry out under alkaline conditions. After completion of the reaction, it is preferred that the obtained azo compound or salt of the formula (1) is precipitated by salting out, filtered, and taken out. Further, when purification is required, it is only necessary to repeat salting out or to precipitate from water using an organic solvent. The organic solvent to be used for the purification may, for example, be a water-soluble organic solvent such as an alcohol such as methanol or ethanol or a ketone such as acetone.

The aminothiazole compound represented by the formula (A), when the ring represented by a broken line is not present, represents a 2-aminobenzothiazole, and examples thereof include 2-amino-6-sulfonylbenzothiazole and 2-amine. -7-methoxy-6-sulfonic acid benzothiazole, 2-amino-4,6-disulfonic acid benzothiazole and 2-amino-7-methoxy-4,6-di Sulfobenzothiazole. The aminothiazole compound represented by the formula (A), when a ring represented by a broken line, represents a 2-aminonaphthylthiazole, and examples thereof include 2-amino-6,8-disulfonylnaphthylthiazole, 2 -Amino-4,6,8-trisulfonylnaphthylthiazole, 2-amino-4-chloro-6,8-disulfonylnaphthylthiazole, 2-amino-6-sulfonate Oxy-4,8-disulfonic acid naphthylthiazole, 2-amino-6-sulfonic acid propoxy-4,7,8-trisulphonylnaphthylthiazole, 2-amino-6- Methoxy-4,7,8-trisulfonylnaphthylthiazole, 2-amino-7-sulfopropoxy-4,9-disulfonylnaphthylthiazole and 2-amino-4 - sulfonic acid propoxy-5,7,9-trisulphonylnaphthylthiazole, etc., and 2-amino-6-sulfonylnaphthylthiazole, 2-amino-7-methoxy- 6-sulfonylnaphthylthiazole and 2-amino-6,8-disulfonylnaphthylthiazole are preferred.

The aniline of the formula (B) may, for example, be an aniline having a lower alkoxy group having a sulfonic acid group. Examples thereof include 3-(2-amino-4-methylphenoxy)propane-1-sulfonic acid, 3-(2-aminophenoxy)propane-1-sulfonic acid, and 3-(2) -Amino-4-methylphenoxy)butane-1-sulfonic acid and the like. Examples of the anilines other than these include aniline, 2-methylaniline, 3-methylaniline, 2-ethylaniline, 3-ethylaniline, 2,5-dimethylaniline, 2,5- Diethylaniline, 2-methoxyaniline, 3-methoxyaniline, 2-methoxy-5-methylaniline, 2,5-dimethoxyaniline, 3,5-dimethoxyaniline 2,6-dimethylaniline and 3,5-dimethoxyaniline. Preferred are 2-methoxy-5-methylaniline and 2,5-dimethoxyaniline. The amine groups of these anilines are also protected. Examples of the naphthylamines of the formula (C) include 1-naphthylamine, 1-naphthylamine-6-sulfonic acid, 1-naphthylamine-7-sulfonic acid, and 1-amino-2-methoxynaphthalene- 6-sulfonic acid, 1-amino-2-methoxynaphthalene-7-sulfonic acid, 1-amino-2-ethoxynaphthalene-6-sulfonic acid and 1-amino-2-ethoxynaphthalene The -7-sulfonic acid is preferably 1-naphthylamine-7-sulfonic acid and 1-amino-2-methoxynaphthalene-7-sulfonic acid. The amine groups of these naphthylamines can also be protected. The protecting group may, for example, be an ω-methanesulfonic acid group.

The azo compound of the present invention or a salt thereof can be used as a dye for a polarizing film. The azo compound of the present invention or a salt thereof is a blue dye having a maximum absorption wavelength in the vicinity of, for example, 600 to 670 nm. According to the azo compound of the present invention or a salt thereof, a high-performance dye-based polarizing plate having excellent polarizing properties can be produced, and in particular, color leakage in a vertical position in a wavelength region of a visible light region is small, and neutral gray is high. The performance dye is a polarizing plate. In one embodiment, the azo compound of the present invention or a salt thereof can be suitably used for the production of a neutral gray polarizing plate for vehicles or outdoor displays which can be used under high temperature and high humidity conditions.

 <Dye-based polarizing film>  

The dye-based polarizing film contains a dichroic dye and a polarizing film substrate containing at least an azo compound represented by the formula (1) or a salt thereof. The dye-based polarizing film may be any of a color polarizing film and a neutral gray polarizing film, and is preferably a neutral gray polarizing film. Here, "neutral gray" refers to a state in which light leakage (color leakage) at a specific wavelength in a wavelength region of a visible light region is small in a state in which the alignment directions of the two polarizing films are perpendicular to each other.

The dye-based polarizing film contains one or two or more kinds of the azo compound represented by the formula (1) or a salt thereof, and may contain one or more other organic dyes as required. The other organic dye to be used in combination is not particularly limited, and is preferably a dye having absorption characteristics in a wavelength region different from the absorption wavelength region of the azo compound or salt represented by the formula (1), and preferably having high dichroism. The organic dye used in combination may, for example, be CI Direct Yellow 12, CI Direct Yellow 28, CI Direct Yellow 44, CI Direct Orange 26, CI Direct Orange 39, CI Direct Orange 71, CI Direct Orange 107, CI Direct Red 2. The dyes described in CI Direct Red 31, CI Direct Red 79, CI Direct Red 81, CI Direct Red 247, CI Direct Green 80, and CI Direct Green 59, and Patent Documents 1 to 5 are representative examples. These pigments are contained in a dye-based polarizing film as a free acid or as an alkali metal salt (for example, a Na salt, a K salt, a Li salt), an ammonium salt or an amine salt.

When other organic dyes are used in combination, the dye-based polarizing film for the purpose may be a neutral gray polarizing film, a color polarizing film for a liquid crystal projector, or other color polarizing film, and different types of other organic dyes may be blended. The blending ratio of the other organic dyes is not particularly limited, and the total of one or a plurality of organic dyes is in the range of 0.1 to 10 parts by mass based on 100 parts by mass of the azo compound of the formula (1) or a salt thereof. good.

In the neutral gray polarizing film, the type of other organic dyes used in combination and the blending ratio thereof can be adjusted in such a manner that the color leakage of the obtained polarizing film in the wavelength region of the visible light region is reduced.

In the case of a color polarizing film, the obtained polarizing film has a high average light transmittance of a single plate in a specific wavelength range, and an average of two polarizing films when the absorption axis is perpendicular (orthogonal position) is overlapped. The mode in which the light transmittance is lowered is, for example, a method in which the average light transmittance of a single plate having 39% or more in a specific wavelength region and the average light transmittance of a vertical position of 0.4 or less are used together. The type of dye and the adjustment of its blending ratio. Here, the average light transmittance of the single plate refers to one polarizing plate on the polarizing film or a support such as an AR (anti-reflection) layer and a transparent glass plate (hereinafter, the same meaning is used when simply referred to as a polarizing plate). The average of the light transmittance in a specific wavelength region when natural light is incident. The average light transmittance at the vertical position is an average value of the light transmittance in a specific wavelength region when natural light is incident on two polarizing films or polarizing plates arranged in a direction perpendicular to the alignment direction.

Various color dye-based polarizing films or neutral gray dye-based polarizing films containing at least an azo compound represented by formula (1) or a salt thereof, and a dichroic dye of other organic dyes which are required to be contained, The polarizing film substrate (for example, a polymer film) is produced by mixing and aligning it with a liquid crystal by a known method, or by aligning it by a coating method.

The polarizing film substrate is preferably a polymer film, more preferably a film formed of a polyvinyl alcohol resin or a derivative thereof. Specific examples of the polarizing film substrate include a polyvinyl alcohol resin or a derivative thereof, and any of these may be an olefin such as ethylene or propylene, or crotonic acid, acrylic acid, methacrylic acid or maleic acid. A carboxylic acid upgrader, etc. The polarizing film substrate is preferably a film formed of polyvinyl alcohol or a derivative thereof in terms of the adsorptivity and the alignment property of the dye. The thickness of the polarizing film substrate is usually from 30 to 100 μm, preferably from about 50 to 80 μm.

When the polarizing film substrate is a polymer film, when a dichroic dye containing at least the azo compound of the formula (1) or a salt thereof is incorporated, a method of dyeing the polymer film can be usually employed. Dyeing can be carried out, for example, as follows. First, the azo compound of the present invention or a salt thereof, and other organic dyes required for the reaction are dissolved in water to prepare a dyebath. The concentration of the dye in the dyebath is not particularly limited, and is usually selected from the range of about 0.001 to 10% by mass. Further, a dyeing aid may be used depending on the need, for example, Glauber's salt is applied at a concentration of about 0.1 to 10% by mass. The polymer film was immersed in the dye bath thus prepared for dyeing for 1 to 10 minutes. The dyeing temperature is preferably about 40 to 80 °C.

The alignment of the dichroic dye containing the azo compound of the formula (1) or a salt thereof can be carried out by stretching the dyed polymer film. The method of stretching may use any known method such as a wet method, a dry method, or the like. The extension of the polymer film can be carried out before dyeing as the case may be. At this time, the alignment of the water-soluble dye can be performed at the time of dyeing. The water-soluble dye and the aligned polymer film may be subjected to post-treatment such as boric acid treatment by a known method as needed. Such post-treatment is carried out for the purpose of improving the light transmittance and the degree of polarization of the dye-based polarizing film. The conditions of the boric acid treatment may vary depending on the type of the polymer film to be used or the type of the dye to be used. However, it is usually preferable to set the boric acid concentration of the boric acid aqueous solution to 0.1 to 15% by mass, preferably 1 to 10% by mass. For example, a soaking of, for example, 0.5 to 10 minutes is carried out in a temperature range of 30 to 80 ° C, preferably 40 to 75 ° C. Further, it is also possible to perform a side-by-side repair treatment with an aqueous solution containing a cationic polymer compound as needed.

The obtained dye-based polarizing film can be used as a polarizing plate by adding an additional protective film, and a protective layer, an AR layer, a support, and the like can be provided as needed. The use of various color dye-based polarizing plates and neutral gray dye-based polarizing films may, for example, be liquid crystal projectors, electronic computers, watches, notebook computers, word processors, liquid crystal televisions, car navigators, indoor and outdoor measurements. A display such as a car or a car, or a lens or glasses. The dye-based polarizing film has high polarizing performance comparable to that of a polarizing film using iodine, and is excellent in durability. Therefore, it is especially suitable for various liquid crystal displays, liquid crystal projectors, vehicles, and indoor and outdoor displays that require high polarization performance and durability (for example, display applications or wearable applications of industrial measuring instruments).

 <Dye-based polarizing plate>  

The dye-based polarizing plate can be obtained by laminating a transparent protective film on one or both sides of the dye-based polarizing film. The dye-based polarizing plate has excellent polarizing performance because it has the dye-based polarizing film described above. The material for forming the transparent protective film is preferably a material excellent in optical transparency and mechanical strength. For example, in addition to a cellulose acetate film or an acrylic film, a tetrafluoroethylene/hexafluoropropylene system may be used. A film formed of a fluorine-based film such as a copolymer, a polyester resin, a polyolefin resin, or a polyamide resin. The transparent protective film is preferably a triethylenesulfonated cellulose (TAC) film or a cycloolefin film. The thickness of the protective film is usually 40 to 200 μm.

An adhesive used when the polarizing film and the protective film are bonded together may be used, and examples thereof include a polyvinyl alcohol-based adhesive, a polyurethane emulsion-based adhesive, an acrylic adhesive, and a polyester-isocyanate-based adhesive, and polyvinyl alcohol. The adhesive is the best.

A transparent protective layer may be further provided on the surface of the dye-based polarizing plate. The transparent protective layer may, for example, be an acrylic or polyoxyalkylene-based hard coat layer or a polyurethane-based protective layer. Furthermore, in order to further improve the light transmittance of the single board, it is preferable to provide an AR layer on the protective layer. The AR layer can be formed by vapor deposition or sputtering treatment of a substance such as cerium oxide or titanium oxide, or can be formed by applying a thin fluorine-based substance. The dye-based polarizing plate can also be attached to the surface by a phase difference plate to be used as a circular polarizing plate.

The dye-based polarizing plate may be any of a color polarizing plate and a neutral gray polarizing plate for use in combination.

Neutral gray polarizers have excellent polarizing properties. In one form, the neutral gray polarizing plate has less color leakage at a vertical position in the wavelength region of the visible light region. Further, in one form, the neutral gray polarizing plate has a feature of preventing discoloration or a decrease in polarizing performance even in a high-temperature and high-humidity state, and light leakage in a vertical position in the visible light region is small, and is suitable for a vehicle or Outdoor display.

For the neutral gray polarizing plate for vehicle or outdoor display, in order to further improve the light transmittance of the single plate, it is preferable to provide an AR layer on the polarizing plate formed of the polarizing film and the protective film, and to form a polarizing plate with an additional AR layer. It is more preferable to provide a polarizing plate such as a support such as a transparent resin and an additional AR layer. The AR layer can be disposed on one or both sides of the polarizing plate. The support system is preferably provided on one side of the polarizing plate, or may be disposed on the polarizing plate through the AR layer or directly disposed. The support is preferably a flat portion having a polarizing plate for adhering, and a transparent substrate is preferred for optical use. The transparent substrate can be roughly classified into an inorganic substrate and an organic substrate, and examples thereof include an inorganic substrate such as soda glass, borosilicate glass, a crystal substrate, a sapphire substrate, and a spinel substrate, and acrylic acid, polycarbonate, and polyethylene terephthalate. An organic substrate such as a diester, polyethylene naphthalate or a cycloolefin polymer is preferred as the organic substrate. The thickness or size of the transparent substrate may be a desired size.

The color polarizing plate has excellent polarizing performance. In one embodiment, since the color polarizing plate does not cause discoloration or a decrease in polarizing performance even in a high-temperature and high-humidity state, it is suitable for liquid crystal projectors, vehicles, and outdoor displays. The color polarizing plate can be produced by adding a protective film to the dye-based polarizing film to form a polarizing plate, and providing a protective layer, an AR layer, a support, and the like as needed.

A color polarizing plate with a support for vehicle or outdoor display can be manufactured by, for example, applying a transparent adhesive (adhesive) to a flat portion of the support, and then applying a dye-based polarizing plate to the coated surface. Further, a transparent adhesive (adhesive) may be applied to the dye-based polarizing plate, and then the support may be adhered to the coated surface. The adhesive (adhesive) used herein is preferably, for example, an acrylate. Further, when the dye-based polarizing plate is used as a circularly polarizing plate, the phase difference plate side is usually adhered to the support side, but the polarizing plate side may be adhered to the transparent substrate.

 <liquid crystal display>  

The liquid crystal display includes the above-described dye-based polarizing film or dye-based polarizing plate. Liquid crystal displays are used for displays such as electronic computers, watches, notebook computers, word processors, LCD TVs, car navigators, and indoor and outdoor measuring instruments or displays, especially for applications requiring high polarization performance and durability. For various liquid crystal displays, for example, for vehicle use and outdoor display (for example, industrial measurement type display use or wearable use).

The dye-based polarizing film or the dye-based polarizing plate provided on the liquid crystal display is preferably a neutral gray. By using a neutral gray dye-based polarizing film or a dye-based polarizing plate, discoloration of the liquid crystal display due to color leakage at a specific wavelength in a dark state can be prevented.

In the liquid crystal display, the dye-based polarizing plate may be disposed on either or both sides of the incident side or the exit side of the liquid crystal cell. The dye-based polarizing plate may or may not be in contact with the liquid crystal cell, but in terms of durability, it is preferred that it is not contacted. In the emission side of the liquid crystal cell, when the polarizing plate does not contact the liquid crystal cell, the liquid crystal cell can be made into a support of the dye-based polarizing plate. When the dye-based polarizing plate does not contact the liquid crystal cell, a dye-based polarizing plate using a support other than the liquid crystal cell is preferably used. In addition, in terms of durability, it is preferable that the dye-based polarizing plate is disposed on both the incident side and the output side of the liquid crystal cell, and the polarizing plate surface of the dye-based polarizing plate is disposed on the liquid crystal cell side and the support surface. The configuration is better on the light source side. Further, the incident side of the liquid crystal cell refers to the light source side, and the opposite side is the emission side.

The liquid crystal cell included in the liquid crystal display for a vehicle or an outdoor display is, for example, an active matrix type, and it is preferable to form a liquid crystal between a transparent substrate on which an electrode and a TFT are formed and a transparent substrate on which a counter electrode is formed. Light emitted by a light source such as a cold cathode tube lamp or a white LED passes through a neutral gray polarizing plate, and then passes through a liquid crystal cell, a color filter, and is projected onto a display screen through a neutral gray polarizing plate.

The display for vehicle or outdoor display thus constituted is a neutral gray polarizing plate having brightness and excellent polarizing performance. In another aspect, the display for a vehicle or an outdoor display has durability and light resistance, and therefore has a characteristic that it is less likely to cause discoloration or a decrease in polarizing performance and high reliability even in a high-temperature and high-humidity state inside or outside the vehicle.

[Examples]

In the following, the present invention will be described in more detail by way of examples, but these are merely exemplary, and the invention is not limited thereto. Unless otherwise stated, the % and parts in the examples are quality benchmarks.

 [Example 1]  

36.0 parts of 2-aminonaphthacenethiazole-6,8-disulfonic acid was added to 100 parts of 98% sulfuric acid, and after dissolving at 50 ° C, 12.6 parts of 60% nitric acid was added, at 5 to 10 50 parts of 40% nitrosylsulfuric acid was dropped in ° C for about 10 minutes, and a diazo reaction liquid was obtained after reacting for 1 hour. Next, 15.3 parts of 2,5-dimethoxyaniline was added to an acidic aqueous solution obtained by diluting 10.4 parts of 35% hydrochloric acid with 100 parts of water to dissolve it. The previous diazo reaction was dropped into this aqueous solution over 3 hours and stirred overnight to complete the coupling reaction. Then, filtration was carried out to obtain 41.9 parts of the monoazoamino group compound represented by the following formula (46).

41.9 parts of the obtained monoazoamine-based compound (46) was added to 200 parts of water, and 25% of sodium hydroxide was added thereto to dissolve the monoazoamine-based compound. 13.8 parts of a 40% aqueous solution of sodium nitrite was added thereto, followed by addition of 25.0 parts of 35% hydrochloric acid at 20 to 30 ° C, and stirring at 20 to 30 ° C for 1 hour to obtain a diazotide. On the other hand, 36.9 parts of 6,6'-iminobis(1-hydroxynaphthalene-3-sulfonic acid) is added to 100 parts of water, and a 25% aqueous solution of sodium hydroxide is added thereto to make it weakly alkaline. 6,6'-iminobis(1-hydroxynaphthalene-3-sulfonic acid) was dissolved. The previously obtained diazotide was maintained at pH 8 to 10 and dropped into the solution, and stirred to complete the coupling reaction. Then, after salting out with sodium chloride, it was filtered to obtain 63.7 parts of the compound represented by the formula (5). The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 675 nm.

 [Example 2]  

In addition to 36.9 parts of 6,6'-iminobis(1-hydroxynaphthalene-3-sulfonic acid) substituted with 36.9 parts of 7,7'-iminobis(1-hydroxynaphthalene-3-sulfonic acid) The same operation as in Example 1 was carried out, and 63.7 parts of a compound represented by the formula (6) was obtained. The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 678 nm.

 [Example 3]  

The same operation as in Example 1 was carried out except that 36.0 parts of 2-aminonaphthylthiazole-6,8-disulfonic acid was substituted with 23.0 parts of 2-aminobenzothiazole-6-sulfonic acid to obtain 55.4. A compound represented by the formula (11). The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 647 nm.

 [Example 4]  

Except that 36.0 parts of 2-aminonaphthylthiazole-6,8-disulfonic acid was substituted into 26.0 parts of 2-amino-7-methoxybenzothiazole-6-sulfonic acid, and Example 1 was carried out. In the same operation, 57.3 parts of the compound represented by the formula (14) was obtained. The maximum absorption wavelength in the 20% aqueous pyridine solution was 667 nm.

 [Example 5]  

In the same manner as in Example 1, a diazotide was obtained from 41.9 parts of the compound represented by the above formula (46), and the mixture was dropped into an aqueous solution in which 79.6 parts of the compound represented by the above formula (5) was added and dissolved in 200 parts of water. Maintain at pH 9 to 11 and stir to complete the coupling reaction. Then, after salting out with sodium chloride, it was filtered to obtain 78.4 parts of the compound represented by the formula (16). The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 700 nm.

 [Example 6]  

The same procedure as in Example 5 was carried out except that the compound represented by the above formula (5) was substituted with the compound represented by the above formula (6), and 78.4 parts of the compound represented by the formula (17) was obtained. The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 701 nm.

 [Example 7]  

The same operation as in Example 5 was carried out except that 36.0 parts of 2-aminonaphthylthiazole-6,8-disulfonic acid was substituted with 23.0 parts of 2-aminobenzothiazole-6-sulfonic acid to obtain 65.1. A compound represented by the formula (28). The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 665 nm.

 [Example 8]  

Except that 23.0 parts of 2-aminonaphthylthiazole-6,8-disulfonic acid was substituted into 26.0 parts of 2-amino-7-methoxybenzothiazole-6-sulfonic acid, and Example 1 was carried out. In the same manner as in Example 5, 68.1 parts of a compound represented by the formula (31) was obtained. The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 675 nm.

 [Example 9]  

The same operation as in Example 1 was carried out except that 15.3 parts of 2,5-dimethoxyaniline was substituted with 13.7 parts of 2-methoxy-5-methylaniline, and 40.6 parts of the formula (47) were obtained. Compound.

The same procedure as in Example 5 was carried out except that 41.9 parts of the compound represented by the formula (46) was replaced by 40.6 parts of the compound represented by the formula (47) to obtain 77.6 parts of the compound represented by the formula (32). The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 685 nm.

 [Production Example 1: Polarizing Film]  

A polyvinyl alcohol film having a thickness of 75 μm was immersed for 4 minutes in a dyeing liquid formed of an aqueous solution of the compound of the formula (5) obtained in Example 1 and a solution of 0.03% and thenardite at a concentration of 0.1%. The film was stretched to 5 times in a 3% boric acid aqueous solution at 50 ° C, and after being washed and dried in a tight state, a polarizing film was obtained.

 [Production Examples 2 to 9, Comparative Example 1: Polarizing Film]  

An azo compound substitution formula (5) other than the formulas (6), (11), (14), (16), (17), (28), (31), and (32) obtained in Examples 2 to 9 was used. A polarizing film was obtained in the same manner as in Production Example 1, except for the compound. In addition, a compound of the formula (III-1) described in Example 1 of Patent Document 6 was used as a comparative example, and a polarizing film was obtained in the same manner as in the production example of the present invention.

 (Measurement of the maximum absorption wavelength and polarization ratio of the polarizing film)  

The maximum absorption wavelength and the polarization ratio were measured for the polarizing films obtained in Production Examples 1 to 9 and Comparative Example 1 of the polarizing film. The measurement of the maximum absorption wavelength of the polarizing film and the calculation of the polarization ratio were carried out by measuring the parallel transmittance and the vertical transmittance at the time of incidence of polarized light by a spectrophotometer (manufactured by Hitachi, Ltd.; U-4100). The parallel transmittance (Ky) here refers to the transmittance when the absorption axis of the absolute polarizer is parallel to the absorption axis of the polarizing film; the vertical transmittance (Kz) refers to the absorption axis of the absolute polarizer and the absorption of the polarizing film. Transmittance when the axis is vertical. The parallel transmittance and the vertical transmittance of each wavelength were measured at intervals of 1 nm in 380 to 900 nm. Using the respectively measured values, the polarization ratio of each wavelength was calculated by the following formula (i), and the maximum polarization ratio in 380 to 900 nm and the absorption wavelength (nm) at that time were obtained. The results are shown in Table 1.

Polarization rate (%) = [(Ky-Kz) / (Ky + Kz)] × 100 (i)

As shown in Table 1, a polarizing film made using these compounds has a maximum absorption wavelength on the long wavelength side of a visible light region of about 680 to 740 nm, and both have a high polarization ratio.

 (polarization film color measurement)  

Using the compound of the formula (III-1) described in Example 1 of Patent Document 6, a polarizing film having the same transmittance as that of the polarizing film of Production Example 3 using the compound of the formula (11) is formed. The polarizing film was measured for chromaticity in parallel and perpendicular by the above spectrophotometer. The results are shown in Table 2.

When the b* value is positive, it can be shaken to yellow, and when it is negative, it can be shaken to blue. Originally, as long as the polarizing film having a maximum absorption wavelength near 610 nm has a negative value when the b* value is parallel and perpendicular, the polarizing film of the compound of the formula (11) represents a negative value, and the original blue color is present. . On the other hand, the polarizing film using the compound of the comparative example was a positive value, and it was green even by visual observation. From this result, it can be seen that the use of the polarizing film of the compound of the formula (11) exhibits a sub-absorption in a field other than the maximum absorption wavelength, particularly a region of 500 nm or less, indicating that it is very useful as a blue component of the three primary colors. Sex.

 [Production Example 10: Production Example of Neutral Gray Polarizing Plate]  

The same procedure as in Production Example 1 except that an aqueous solution of a compound of the formula (17), 0.07% of CI Direct Orange 39, 0.02% of CI Direct Red 81, and 0.1% of Glauber's salt at 45 ° C was used as the dyeing liquid. Operation, making a polarizing film. The maximum absorption wavelength of the obtained polarizing film was 555 nm, the average transmittance of the veneer in 380 to 700 nm was 40%, and the average light transmittance in the vertical position was 0.02%, which had a high degree of polarization. In addition, the transmittances of the parallel position and the vertical position in the visible light region are substantially fixed, and are in a neutral gray hue.

A triethylenesulfonated cellulose film (TAC film; manufactured by Fuji Photo Film Co., Ltd.; trade name: TD-80U) was passed through an adhesive of a polyvinyl alcohol aqueous solution, and laminated on both surfaces of the polarizing film. Next, an AR support (manufactured by NOF Corporation; REALEC X 4010) was laminated on one of the TAC films using an adhesive to obtain a neutral gray dye-based polarizing plate to which an AR support was attached. The obtained polarizing plate, like the polarizing film, has a neutral gray hue and a high polarizing ratio.

In addition, although the data is not shown, the obtained polarizing plate exhibits durability even in a state of being exposed to high temperature and high humidity for a long period of time, and further has excellent light resistance for long-term exposure.

Claims (15)

An azo compound or a salt thereof, which is represented by the following formula (1): In the formula, A ₁ and A ₂ are each independently a hydrogen atom or represented by the following formula (2), but excluding that both of A ₁ and A ₂ are hydrogen atoms: In the formula, the ring substituted with R ₁ and a sulfonic acid group is a benzothiazole ring in the absence of a ring represented by a broken line, a naphthylthiazole ring in the presence of a ring represented by a broken line, and R ₁ is selected from a chlorine atom and a sulfonic acid. a group, a nitro group, a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms having a sulfonic acid group, and an alkyl group having 1 to 4 carbon atoms having a hydroxyl group. a group having 1 to 4 carbon atoms having a carboxyl group, an alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group, an alkoxy group having 1 to 4 carbon atoms having a hydroxyl group, and 1 to 4 carbon atoms having a carboxyl group; a group formed by an alkoxy group, B is a phenyl or anthracene group which may have a substituent, and the substituent is an alkyl group selected from a chlorine atom, a sulfonic acid group, a nitro group, a hydroxyl group, and a carbon number of 1 to 4. An alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms having a sulfonic acid group, an alkyl group having 1 to 4 carbon atoms having a hydroxyl group, an alkyl group having 1 to 4 carbon atoms having a carboxyl group, having a group of alkoxy groups having 1 to 4 carbon atoms of a sulfonic acid group, an alkoxy group having 1 to 4 carbon atoms having a hydroxyl group, and an alkoxy group having 1 to 4 carbon atoms having a carboxyl group, in the plural Independent, m is an integer from 1 to 3, and the 2-key of -NH- is unique Bonded to the a or b represents the position of substitution. The azo compound or a salt thereof according to claim 1, wherein the formula (2) is represented by the following formula (3): Wherein R _1a is a substituted ring, and R _1a represents the same as R ₁ in the formula (2), and R ₂ and R ₃ are each independently selected from a hydrogen atom, a chlorine atom, a sulfonic acid group, and a nitrate. a group, a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms having a sulfonic acid group, an alkyl group having 1 to 4 carbon atoms having a hydroxyl group, having An alkyl group having 1 to 4 carbon atoms of a carboxyl group, an alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group, an alkoxy group having 1 to 4 carbon atoms having a hydroxyl group, and an alkoxy group having 1 to 4 carbon atoms having a carboxyl group The group formed by the base, m ₁ represents the same meaning as m in the formula (2); or the following formula (4) represents: Wherein R _1b is a substituted ring, and R _1b represents the same as R ₁ in the formula (2), and R ₄ to R _{6 are} each independently selected from a hydrogen atom, a chlorine atom, a sulfonic acid group, and a nitro group. a hydroxyl group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms having a sulfonic acid group, an alkyl group having 1 to 4 carbon atoms having a hydroxyl group, having a carboxyl group An alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group, an alkoxy group having 1 to 4 carbon atoms having a hydroxyl group, and an alkoxy group having 1 to 4 carbon atoms having a carboxyl group The group formed, m ₂ represents the same meaning as m in the formula (2). The azo compound or a salt thereof according to the second aspect of the invention, wherein A ₁ and A ₂ are each independently represented by formula (3) or formula (4). The azo compound or a salt thereof according to claim 2, wherein A ₁ is represented by formula (3) or formula (4), and A ₂ is a hydrogen atom. The azo compound or a salt thereof according to any one of claims 2 to 4, wherein R _1b in the formula (4) is a hydrogen atom, a chlorine atom, an alkyl group having 1 to 4 carbon atoms or carbon The alkoxy group of 1 to 4, each of R ₄ to R _{6 is} independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms which may have a sulfonic acid group. The azo compound or a salt thereof according to any one of claims 2 to 5, wherein R _1a in the formula (3) is a hydrogen atom, a chlorine atom or an alkyl group having 1 to 4 carbon atoms, R ₂ and R _{3 are} each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms which may have a sulfonic acid group.  The azo compound or a salt thereof according to any one of claims 1 to 6, wherein the -NH-substitution position in the formula (1) is a.    A dye-based polarizing film comprising the azo compound according to any one of claims 1 to 7 or a salt thereof, and a polarizing film substrate.    A dye-based polarizing film comprising the azo compound according to any one of claims 1 to 7 or a salt thereof, and one or more organic dyes other than the above, and a polarizing film substrate.    A dye-based polarizing film, which comprises the azo compound or a salt thereof according to any one of the above claims, and one or more organic dyes other than the above, and a polarizing film substrate.    The dye-based polarizing film according to any one of claims 8 to 11, wherein the polarizing film substrate is a film formed of a polyethyl alcohol resin or a derivative thereof.    A dye-based polarizing plate obtained by laminating a transparent protective layer on at least one surface of the dye-based polarizing film according to any one of claims 8 to 11.    A liquid crystal display comprising the dye-based polarizing film according to any one of claims 8 to 11 or the dye-based polarizing plate according to claim 12 of the patent application.    The dye-based polarizing film according to any one of claims 8 to 11, which exhibits a neutral gray color.    A display for a vehicle or an outdoor display, comprising a dye-based polarizing plate according to claim 14 or a dye-based polarizing plate obtained by laminating a transparent protective layer on at least one surface of the dye-based polarizing film.