TW201842076A - Azo compound or salt thereof, and dye-based polarizing film and dye-based polarizing plate containing same - Google Patents

Abstract

An object of the present invention is to provide a high performance polarizing film and polarizing plate that function with light rays having wavelengths in the infrared region, even it is a stretched films using dichroic dyes having absorption in the infrared region, 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. When A1 is a hydrogen atom, R<SP>a</SP> is a hydroxy group, and when A1 is represented by formula (2) or formula (3), R<SP>a</SP> together with R<SP>c</SP> or R<SP>d</SP> forms -O-Cu- O-; When A2 is a hydrogen atom, R<SP>b</SP> is a hydroxy group, and when A2 is represented by formula (2) or formula (3), R<SP>b</SP> together with R<SP>c</SP> or R<SP>d</SP> forms -O-Cu- O-.).

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 formed by containing an azo compound or a salt thereof.

A polarizing plate having a function of transmitting and shielding light can be used together with a liquid crystal having a light switching function on a display such as a liquid crystal display (LCD). The applicable fields of this LCD include small computers such as early electronic computers and watches, notebook computers, word processors, liquid crystal projectors, LCD TVs, car navigators, and information displays and measuring instruments for indoor and outdoor applications. . At the same time, it can also be applied to lenses with polarizing function, and has been applied to enhance the visibility of sunglasses or polarized glasses corresponding to 3D TVs in recent years. In recent years, it has been used not only for display purposes, but also for improving the accuracy of devices for authenticity, or for improving the S/N ratio by cutting reflected light in image sensors such as CCD and CMOS.

A general polarizing film is a film of polyvinyl alcohol or a derivative thereof which has been extended and aligned, or a polyene film which is formed by dehydration of a dechlorination or polyvinyl alcohol 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 polarizing element. Among these, an iodine-based polarizing film using iodine as a polarizing element is excellent in polarizing performance, but 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. On the other hand, compared with the iodine-based polarizing film, a dye-based polarizing film using a dichroic dye as a polarizing element is excellent in moisture resistance and heat resistance, but generally has insufficient polarizing performance.

In recent years, in the use of an identification light source for a touch panel or a monitor camera, an inductor, an anti-counterfeiting, and a communication device, not only a polarizing plate for a visible light region wavelength but also a polarizing plate for use in an infrared region is required. In view of such an expectation, an infrared polarizing plate which polyalkylates an iodine-based polarizing plate, an infrared polarizing plate using a wire grid of Patent Document 2 or 3, and a glass containing fine particles as disclosed in Patent Document 4 have been reported. The extended infrared polarizer or the type of cholesteric liquid crystal as used in Patent Document 5 or 6. The infrared polarizing plate of Patent Document 1 has weak durability, heat resistance, damp heat durability, and light resistance, and is not practical. The wire grid type of Patent Document 2 or 3 can also be processed into a film type, and is gradually popularized as the product is stabilized. However, since there are no nano-scale irregularities on the surface, the optical characteristics cannot be maintained, the contact with the surface cannot be contacted, thus limiting the usable use, and it is difficult to perform anti-reflection (AR) or antiglare processing. The glass-containing glass extending type of Patent Document 4 is practical because it has high durability and high dichroism. However, since it is a glass containing fine particles and extended, the element itself is easily broken and fragile, and has no flexibility like a conventional polarizing plate, so that it is difficult to surface-process or adhere to other substrates. The techniques of Patent Document 5 and Patent Document 6 use the technique of circularly polarized light which has been disclosed previously, but it is difficult to form scattered light or absolute polarization because the color is changed depending on the viewing angle, or since the polarizing plate is basically used for reflection. Light. In other words, there is no dye-based polarizing plate corresponding to an infrared ray wavelength region in which a general iodine-based polarizing plate is an absorption-type polarizing element, a film type, and has flexibility and high durability. This is because conventional dichroic dyes absorb only the visible wavelength region and have no absorption in the infrared wavelength region.

 [Previous Technical Literature]    [Patent Literature]  

[Patent Document 1] US Patent No. 2,494,686

[Patent Document 2] Japanese Laid-Open Patent Publication No. 2016-148871

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2013-24982

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2004-86100

[Patent Document 5] International Publication No. 2015/087709

[Patent Document 6] Japanese Patent Publication No. 45-1275

An object of the present invention is to provide a high-performance polarizing film and a polarizing plate which have a function of absorbing a dichroic dye in an infrared region, and which can act as a light source of a wavelength in an infrared region, and can be manufactured. An azo compound or a salt thereof.

As a result of intensive studies to achieve this object, the present inventors have newly discovered a film containing a dye having an absorption in an infrared region, and by aligning the dye in the film, it is possible to achieve an effect on light of an infrared wavelength. The polarizing plate is used to complete the present invention.

That is, the present invention relates to the inventions of the following [1] to [13].

[1] An azo compound or a salt thereof, which is represented by the following formula (1): (wherein A ₁ and A ₂ are each independently a hydrogen atom or represented by the following formula (2) or the following formula (3), but excluding the case where both A ₁ and A ₂ are hydrogen atoms: (wherein, 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, and R ₁ is selected from a chlorine atom, a sulfonate Acid group, nitro group, hydroxyl group, alkyl group having 1 to 4 carbon atoms, alkoxy group having 1 to 4 carbon atoms, alkyl group having 1 to 4 carbon atoms having a sulfonic acid group, and carbon number 1 to 4 having a hydroxyl group An alkyl 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, an alkoxy group having 1 to 4 carbon atoms having a hydroxyl group, and a carbon number 1 having a carboxyl group When alkoxy groups of 4 are grouped, when R ₁ is plural, each of R _{1 is} independently selected from the above group, and R ₂ is selected from the group consisting of a hydrogen atom, a chlorine atom, a sulfonic acid group, a nitro group, and 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, and a carbon having a carboxyl group An alkyl group of 1 to 4, 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. Group, m represents an integer from 1 to 3), (wherein the ring substituted with R ₃ 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 ₃ represents a formula (2) are _identical, R _1, R ₄ and R ₅ individually are independently selected from a hydrogen atom, a chlorine atom alkoxy, sulfo, nitro, hydroxy, alkyl having a carbon number of 1 to 4 1 to 4 a group having 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, and 1 to 4 carbon atoms having a sulfonic acid group; Alkoxy group, alkoxy group having 1 to 4 carbon atoms having a hydroxyl group, and alkoxy group having 1 to 4 carbon atoms having a carboxyl group, n is an integer of 1 to 3), and when A ₁ is a hydrogen atom , R ^a is a hydroxyl group, and when A ₁ is represented by formula (2) or formula (3), R ^a is formed together with R ^c or R ^d to form -O-Cu-O-, and when A ₂ is a hydrogen atom, R ^b is When the hydroxyl group, A ₂ is represented by the formula (2) or the formula (3), R ^b is a 2-bond of -O-Cu-O-, -NH- together with R ^c or R ^d , and each is independently bonded. In the position of substitution indicated by a or b).

[2] The azo compound or a salt thereof according to [1], wherein A ₁ and A ₂ are each independently represented by the formula (2) or the formula (3).

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

[4] The azo compound or a salt thereof according to any one of [1] to [3] wherein the substitution position of -NH- is a.

[5] The azo compound or a salt thereof according to [1], which is represented by the following formula (4): (wherein R ₆ 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 having a sulfonic acid group; An alkyl group of 1 to 4, 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 a carbon having a hydroxyl group The alkoxy group having 1 to 4 groups and the alkoxy group having 1 to 4 carbon atoms having a carboxyl group are grouped, and X represents an integer of 1 to 3).

[6] A dye-based polarizing film comprising the azo compound according to any one of [1] to [5] or a salt thereof, and a polarizing film substrate, and having absorption at least in a near-infrared region.

[7] A dye-based polarizing film comprising the azo compound according to any one of [1] to [5] or a salt thereof, and a polarizing film substrate containing one or more organic dyes other than the above.

[8] A dye-based polarizing film comprising the azo compound according to any one of [1] to [5] or a salt thereof, and one or more organic dyes other than the above, and a polarizing film group. material.

[9] The dye-based polarizing film according to any one of [6] to [8] wherein the polarizing film substrate is a film formed of a polyvinyl alcohol resin or a derivative thereof.

[10] 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 [6] to [9].

[11] A dye-based polarizing film according to any one of [6] to [9] or a dye-based polarizing plate according to [10].

[12] The dye-based polarizing film according to any one of [6] to [9] which exhibits a neutral gray color.

[13] A vehicle-based display or an outdoor display comprising the dye-based polarizing film according to [12] 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 polarizing film and a polarizing plate which have a function of absorbing a dichroic dye in an infrared region, and which have an effect on the wavelength of the infrared region, and an azo which can be produced. a compound or a salt thereof. The polarizing plate of the present invention is a polarizing plate for light rays in the infrared wavelength region which can be treated in the same manner as the dye-based polarizing plate. In one embodiment, the polarizing plate of the present invention has flexibility and/or physical stability. In one form, since the polarizing plate of the present invention is of an absorption type, no stray light is generated. In one embodiment, the polarizing plate of the present invention has high weather resistance (heat resistance, moist heat resistance, and light resistance).

<Azo compound or a salt thereof>

The azo compound of the present invention is an azo compound represented by the following formula (1) or a salt thereof.

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

In the formula (1), A ₁ and A ₂ are a hydrogen atom or the following formula (2): Or the following formula (3): Said. However, it is the case that both of A ₁ and A ₂ are removed as a hydrogen atom. 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, although the substitution positions of R ₁ and a sulfonic acid group are not limited, only the 4th position and only the 6th position are used. It is better to replace the combination of the 4th and 6th positions and the combination of the 6th and 7th positions, and it is better to use only the combination of the 6th position and the 4th position and the 6th position. When there is a ring represented by a broken line, that is, when the ring substituted by R ₁ is a naphthylthiazole ring, although the substitution position is not limited, the combination of the 6th position and the 8th position, the 4th position and the 6th position The combination with the 8th position and the combination of the 4th and 7th and 9th positions are 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 The alkoxy group and the alkoxy group having a carboxyl group having 1 to 4 carbon atoms are grouped. Preferred are a sulfonic acid group and an alkoxy group having 1 to 4 carbon atoms. When there are a plurality of R ₁ , these are independently selected independently.

The alkoxy group having 1 to 4 carbon atoms having a hydroxyl group is preferably a linear alkoxy group substituted with a hydroxyl group at the alkoxy group, and more preferably a 4-hydroxypropoxy group or a 4-hydroxybutoxy group. The alkoxy group having 1 to 4 carbon atoms of the carboxyl group is preferably a linear alkoxy group substituted with a carboxyl group at the alkoxy group, and more preferably a 4-carboxypropoxy group or a 4-carboxybutoxy group. Alkoxy group having 1 to 4 carbon atoms having a sulfonic acid group, preferably a linear alkoxy group substituted with a sulfonic acid group at the alkoxy group, and 4-sulfonic acid propoxy or 4-sulfonic acid The butyloxy group is more preferred.

R ₂ 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 The alkoxy group and the alkoxy group having a carboxyl group having 1 to 4 carbon atoms are grouped. 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 alkyl group having 1 to 4 carbon atoms having a sulfonic acid group. The substitution position is not particularly limited, and the alignment of R ^C is preferred.

m represents an integer of 1 to 3.

In the formula (3), the ring substituted with R ₃ 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 ₃ is a benzothiazole ring, although the substitution position of R ₃ is not limited, only the 4 position, only the 6 position, the 4th The combination of the bit and the 6th bit 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 more preferable. When there is a ring represented by a broken line, that is, when the ring substituted by R ₃ is a naphthylthiazole ring, although the substitution position is not limited, the combination of the 6th position and the 8th position, the 4th position and the 6th position The combination with the 8th position and the combination of the 4th position and the 7th and 9th positions is preferable, and the combination of the 6th position and the 8th position is better. It is better to use only the combination of the 2nd position, only the 6th position, only the 7th position, the 2nd position and the 6th position, and the combination of the 2nd position and the 7th position, and only the 2nd position and the 2nd position The combination with the 7 position is especially good.

R ₃ represents the same meaning as R ₁ in the formula (2), and can be independently selected from R ₁ .

R ₄ and R ₅ 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, and a sulfonic acid group. An alkyl group having 1 to 4 carbon atoms, 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, having The alkoxy group having 1 to 4 carbon atoms of the hydroxyl group and the alkoxy group having 1 to 4 carbon atoms having a carboxyl group are grouped. Further, 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 is preferred. The position of substitution is not particularly limited, and it is preferable to use only the 6th position and only the 7th position.

n represents an integer of 1 to 3.

When A ₁ is a hydrogen atom, R ^a is a hydroxyl group, and when A ₁ is represented by the formula (2) or the formula (3), R ^a forms a -O-Cu-O- together with R ^c or R ^d . When A ₂ is a hydrogen atom, R ^b is a hydroxyl group, and when A ₂ is represented by the formula (2) or the formula (3), R ^b forms a -O-Cu-O- together with R ^c or R ^d .

The azo compound represented by the formula (1) is preferably represented by the formula (4).

In the formula (4), R ₆ is 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, and a sulfonic acid group. An alkyl group having 1 to 4 carbon atoms, 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 having a hydroxyl group The alkoxy group having 1 to 4 carbon atoms and the alkoxy group having 1 to 4 carbon atoms having a carboxyl group are grouped.

x represents an integer from 1 to 3.

The azo compound represented by the formula (1) may be in a free form or in the form of a salt. The salt may be, for example, 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 a 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 produced by diazotization or coupling, for example, according to a method for producing a general dye described in Dye Chemistry (Hosota Hiroshi, published in 1957, p. 621). .

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 respectively coupled to a naphthol of the following formula (F), and a copper salt is added to the obtained azo compound to confuse the copper. Physically, whereby an azo compound of the formula (1) is obtained.

In the formulae (A) to (F), R ₀ and a ring substituted with R ₀ represent the same meanings as those of R ₁ in the formula (2) or R ₃ in the formula (3), and R ₂ represents a formula ( 2) The same meaning as the middle, R ₄ and R ₅ are the same as those in the formula (3), and 1 means the same as m in the formula (2) or n in the formula (3). Rp and Rq are substituents having an oxygen atom of a precursor before copper complexation, and are generally a hydroxyl group or an alkoxy group having 1 to 4 carbon atoms.

In the above production method, the diazotization step is a method in which a nitrite such as sodium nitrite or the like is mixed with an aqueous solution or suspension of a mineral acid such as hydrochloric acid or sulfuric acid as a diazo component, or a neutralization of a diazo component. It is preferred to add a nitrite to the weakly basic aqueous solution and to carry out the reverse reaction with the inorganic 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 after the coupling may be directly filtered, or precipitated by acid precipitation or salting out, and taken out by filtration, or may be directly subjected to a solution or a suspension. 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 secondary 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 to Basic conditions are preferred. After completion of the reaction, it is preferred to precipitate the obtained azo compound or a salt thereof by salting out, and to remove it by filtration. Further, when purification is required, it is only necessary to repeatedly perform salting out or to precipitate from water by using an organic solvent. The organic solvent to be used in 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.

In the copper complexation reaction, a copper salt such as copper sulfate, copper chloride or copper acetate is added to an aqueous solution containing the azo compound or a salt thereof obtained in the above secondary coupling reaction to make it ammonia, single In the presence of an amine such as ethanolamine or diethanolamine, for example, it is reacted at 70 to 100 °C. After completion of the reaction, the obtained azo compound or a salt thereof is preferably precipitated by a salt, filtered, and taken out, whereby an azo compound represented by the formula (1) or a salt thereof can be obtained.

The aminothiazole compound represented by the formula (A) is represented by a 2-aminobenzothiazole in the absence of a ring represented by a broken line, and examples thereof include 2-amino-6-sulfonylbenzothiazole, and 2- Amino-7-methoxy-6-sulfonic acid benzothiazole, 2-amino-4,6-disulfonic acid benzothiazole, 2-amino-7-methoxy-4,6- Disulfonylbenzothiazole. The aminothiazole compound represented by the formula (A) is represented by a 2-alkylnaphthylthiazole in the presence of a ring represented by a broken line, and examples thereof include 2-amino-6,8-disulfonylnaphthylthiazole. 2-Amino-4,6,8-trisulphonylnaphthylthiazole, 2-amino-4-chloro-6,8-disulfonylnaphthylthiazole, 2-amino-6-sulfonate Propoxy-4,8-disulfonylnaphthylthiazole, 2-amino-6-sulfonylpropoxy-4,7,8-trisulphonylnaphthylthiazole, 2-amino-6 -Methoxy-4,7,8-trisulfonylnaphthylthiazole, 2-amino-7-sulfonylpropoxy-4,9-disulfonylnaphthylthiazole, 2-amino- 4-sulfonic acid propoxy-5,7,9-trisulphonylnaphthylthiazole, etc., and 2-amino-6-sulfonylbenzothiazole, 2-amino-7-methoxy -6-sulfonic acid benzothiazole, 2-amino-6,8-disulfonic acid naphthothiazole is preferred.

Examples of the aniline of the formula (B) include 2-methoxyaniline, 2-methoxy-5-methylaniline, 2,5-dimethoxyaniline, and 2,6-dimethoxyaniline. 2-ethoxyaniline, 2-ethoxy-5-methylaniline, 2,5-diethoxyaniline, 2,6-diethoxyaniline, 2-methoxy-5-ethoxy Aniline, 2-ethoxy-5-methoxyaniline or 2-methoxy-5-chloroaniline. Preferably, 2-methoxy-5-methylaniline and 2,5-dimethoxyaniline are mentioned. The amine groups of these anilines are also protected. Examples of the naphthylamines of the formula (C) include 1-amino-2-methoxynaphthalene-6-sulfonic acid, 1-amino-2-methoxynaphthalene-7-sulfonic acid, and 1-amine. Benzyl-2-ethoxynaphthalene-6-sulfonic acid and 1-amino-2-ethoxynaphthalene-7-sulfonic acid. Preferably, 1-amino-2-methoxynaphthalene-6-sulfonic acid is mentioned. 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 has absorption in the near-infrared region. The azo compound of the present invention or a salt thereof can be dyed, stretched and aligned on a film to exhibit anisotropic absorption, and can be used as a dye for a polarizing film. Here, the infrared ray region generally means 700 to 30,000 nm, and the near infrared ray wavelength means a wavelength of 700 to 1,500 nm. According to the azo compound of the present invention or a salt thereof, a high-performance dye-based near-infrared absorbing polarizing plate having a polarizing property in the near-infrared region can be produced. Further, by using a dye having a polarizing property in the visible light region, it is possible to realize a high-performance dye-based polarizing plate which is not only a visible light region but also a neutral gray in the near-infrared region. In one embodiment, the azo compound of the present invention or a salt thereof is suitable for use in the production of a neutral gray polarizing plate for vehicles or outdoor displays which can be used under high temperature and high humidity conditions, or for various sensors required for controlling a near-infrared region. The device uses a near-infrared absorbing polarizer for fabrication.

<Dye-based polarizing film>

The dye-based polarizing film contains a dichroic dye containing at least an azo compound represented by the formula (1) or a salt thereof, and a polarizing film substrate, and has absorption at least in the near-infrared region. The dye-based polarizing film may be any of a color polarizing film, a neutral gray polarizing film, and a near-infrared absorbing polarizing film, and is preferably a near-infrared absorbing polarizing film. Here, in the specification and the patent application of the present application, "neutral gray" refers to a state in which two polarizing films are overlapped in such a manner that their alignment directions are perpendicular to each other (vertical position), and a visible light region and a near-infrared region are reduced. Light leakage at a specific wavelength (color leakage).

The dye-based polarizing film contains one or two or more kinds of azo compounds 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 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. CI Direct Red 31, CI Direct Red 79, CI Direct Red 81, CI Direct Red 247, CI Direct Blue 67, CI Direct Blue 237, CI Direct Blue 273, CI Direct Blue 274, CI Direct Green 80, and CI Direct Green 59 Dyes 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 together, the dye-based polarizing film may be a near-infrared absorbing polarizing film, a neutral gray polarizing film, a color polarizing film for a liquid crystal projector, or other color polarizing films, 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 several organic dyes is preferably 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. .

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

The dye-based polarizing film contains at least an azo compound represented by the formula (1) or a salt thereof, and can be used for a polarizing film substrate (for example, a polymer film) by a dichroic dye containing other organic dyes as required. The adsorption is aligned by a known method, mixed with a liquid crystal, or aligned 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 polyvinyl alcohol or a derivative thereof, and any of these may be unsaturated with an olefin such as ethylene or propylene, crotonic acid, acrylic acid, methacrylic acid or maleic acid. A carboxylic acid upgrader, etc. The polarizing film substrate is a film formed of polyvinyl alcohol or a derivative thereof in terms of the adsorptivity and alignment 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 can be usually selected from the range of about 0.001 to 10% by mass. Further, the dyeing assistant may be used as needed, for example, the Glauber's salt is applied at a concentration of about 0.1 to 10% by mass. The polymer film is immersed in the dye bath thus prepared for heating 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 condition 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, but the boric acid concentration of the boric acid aqueous solution is usually 0.1 to 15% by mass, and preferably 1 to 10% by mass. The treatment is carried out, for example, at a temperature of, for example, 30 to 80 ° C, preferably 40 to 75 ° C, for example, for 0.5 to 10 minutes. Further, it is also possible to perform a side-by-side fixing 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 a protective film, and a protective layer, an AR (anti-reflection) layer, a support, and the like can be provided as needed.

Color and neutral gray dye-based polarizing film, preferably applicable to, for example, liquid crystal projectors, electronic computers, watches, notebook computers, word processors, LCD TVs, car navigators, indoor and outdoor measuring instruments or vehicles, etc. Display, etc., and lenses or glasses. The infrared ray absorbs the polarizing film and can be applied to an image sensor such as an authenticity determining device or a CCD or CMOS. 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), and high reliability. On the security device.

<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. Since the dye-based polarizing plate has the dye-based polarizing film described above, it has excellent polarizing performance, moisture resistance, heat resistance, and light resistance. 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. Further, examples of the transparent protective layer include 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-depositing or sputtering a substance such as cerium oxide or titanium oxide, or can be formed by coating a fluorine-based substance in a thin layer. 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 the above-described near-infrared absorbing polarizing plate, neutral gray polarizing plate, and color polarizing plate for use in combination.

The neutral gray polarizing plate has characteristics of less color leakage in a vertical position in a visible light region and a near-infrared region, excellent polarization performance, and prevention of discoloration or a decrease in polarizing performance even in a high-temperature and high-humidity state, in a visible light region. There is less light leakage in the vertical position, especially suitable for vehicle or outdoor display, safety equipment requiring high reliability, and the like.

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. Further, it is more preferable to provide an AR layer of a support such as a transparent resin and a polarizing plate of an additional support. The AR layer can be disposed on one or both sides of the polarizing plate. The support body is preferably provided on one surface of the polarizing plate, or may be provided on the polarizing plate through the AR layer or directly disposed. The support is preferably a flat portion for bonding a polarizing plate, 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 the required size.

The near-infrared absorption polarizing plate is excellent in polarizing performance, and does not cause discoloration or a decrease in polarizing performance even in a high-temperature and high-humidity state. Therefore, it is suitable for safety devices requiring high reliability for liquid crystal projectors, vehicles, and outdoor displays. In such a polarizing plate, a protective film is added to the dye-based polarizing film to form a polarizing plate, and a protective layer, an AR layer, a support, and the like may be provided as needed.

The average light transmittance of a single plate refers to a polarizing plate (which is also used in the same manner as the polarizing plate) when natural light is incident on the polarizing film or a support such as an AR layer or a transparent glass plate is not provided. The average value of the light transmittance in a specific wavelength region at that time. The average light transmittance at the vertical position is an average value of light transmittance in a specific wavelength range when natural light is incident on two polarizing films or polarizing plates arranged in a direction perpendicular to the alignment direction.

A color polarizing plate with a support for vehicle or outdoor display can be manufactured by, for example, coating a transparent adhesive on a flat portion of a support, and then applying a dye-based polarizing plate to the coated surface. . At the same time, a transparent adhesive (adhesive) may be applied to the dye-based polarizing plate, and then the support is 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>

A liquid crystal display comprising the above-described dye-based polarizing film or dye-based polarizing plate. A liquid crystal display, such as an electronic computer, a watch, a notebook computer, a word processor, a liquid crystal television, a car navigator, and a display for indoor and outdoor measuring instruments or displays, is particularly suitable 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).

For a liquid crystal display for a vehicle or an outdoor use, it is preferable to have a neutral gray polarizing film or a polarizing plate. Since the neutral gray polarizing film or polarizing plate has brightness, excellent polarizing performance, durability, and light resistance, it is less likely to cause discoloration or a decrease in polarizing performance even in a high-temperature and high-humidity state inside or outside the vehicle. A highly reliable vehicle or outdoor display.

 [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, % and share 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 when it was dissolved 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 10.4 parts of hydrochloric acid and dissolved in 100 parts of an aqueous acidic solution diluted with water to dissolve. 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 monoazoamine group compound represented by the following formula (45).

The obtained 41.9 parts of the monoazo compound (45) was added to 200 parts of water, and 25% sodium hydroxide was added thereto to dissolve the monoazoamine compound (45). 13.8 parts of a 40% aqueous solution of sodium nitrite was added, 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 (46).

After 63.7 parts of the obtained diazonium-based compound (46) was added to 200 parts of water to dissolve, 19.2 parts of copper sulfate pentahydrate and 39.0 parts of monoethanolamine were added, and the mixture was reacted at 95 ° C for 3 hours. After completion of the reaction, it was cooled and then salted out with sodium chloride, and filtered to obtain 53.5 parts of the compound of the above formula (8). The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 752 nm.

[Embodiment 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 53.5 parts of the compound represented by the formula (9) was obtained. The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 756 nm.

[Example 3]

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, 46.7 parts of the compound represented by the formula (15) were obtained. The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 692 nm.

[Example 4]

In the same manner as in Example 1, 41.9 parts of the compound represented by the above formula (45) was diazotized, kept at pH 9 to 11, and dropped to 200 parts of water to be dissolved and dissolved in 79.6 parts of the above formula (46). The synthesized dissolved aqueous solution is stirred to complete the coupling reaction. Then, it was salted out with sodium chloride, and then filtered to obtain 78.4 parts of a compound represented by the formula (47).

After the obtained 78.4 parts of the tetradiazepine compound (47) was added to 200 parts of water to dissolve, 30.7 parts of copper sulfate pentahydrate and 31.2 parts of monoethanolamine were added, and the mixture was reacted at 95 ° C for 3 hours. After completion of the reaction, the mixture was cooled and then salted with sodium chloride. After filtration, 66.6 parts of the compound of the above formula (17) was obtained. The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 802 nm.

[Example 5]

The same procedure as in Example 4 was carried out except that the compound represented by the above formula (8) was substituted with the compound represented by the above formula (9), and 66.6 parts of the compound represented by the formula (18) was obtained. The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 806 nm.

[Embodiment 6]

The same procedures as in Example 1 and Example 4 were 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. Operation, 55.9 parts of the compound represented by the formula (27) were obtained. The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 706 nm.

[Embodiment 7]

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 manner as in Example 4, 55.9 parts of the compound represented by the formula (29) was obtained. The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 723 nm.

[Embodiment 8]

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 to obtain 40.6 parts of the formula (48). Compound.

The same procedure as in Example 4 was carried out except that 41.9 parts of the compound represented by the formula (45) was replaced by 40.6 parts of the compound represented by the formula (48) to obtain 65.9 parts of the compound represented by the formula (35). The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 794 nm.

[Embodiment 9]

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 46.7. The compound represented by the formula (13). The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 652 nm.

[Production Example 1: Polarizing Film]

A polyvinyl alcohol 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 (8) obtained in Example 1 in an aqueous solution of 0.03% and a Glauber's salt at a concentration of 0.1%. The film was stretched to 5 times in a 3% boric acid aqueous solution at 50 ° C, kept in a tight state, washed with water, and dried to obtain a polarizing film.

[Production Examples 2 to 8: Polarizing Film]

In addition to using the azo compounds of the formulae (9), (15), (17), (18), (27), (29), and (35) obtained in Examples 2 to 8 in place of the compound of the formula (8) The same operation as in Production Example 1 was carried out to obtain a polarizing film.

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

The polarizing film obtained in Production Examples 1 to 9 of the polarizing film was measured for the maximum absorption wavelength and the polarizing ratio. 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 1,100 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 1,100 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, the polarizing film formed using these compounds all had an absorption wavelength in the near-infrared region and a high polarization ratio.

[Production Example 9: Neutral Gray Polarizer]

An aqueous solution of 0.2%, a direct orange 39 of 0.07%, a CI direct red 81 of 0.02%, a CI direct blue 274 of 0.03%, and a Glauber's salt of 0.1% at 45 ° C was used as the dyeing liquid. The same operation as in Production Example 1 was carried out to prepare a polarizing film. The obtained polarizing film had a single plate average transmittance of 38% in 380 to 850 nm, an average light transmittance of 0.02% in the vertical position, and a high degree of polarization in the wide band. In addition, the parallel position and the vertical position have a substantially constant transmittance in the visible light region, and have 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 one by one. 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.

Further, 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 (13)

An azo compound or a salt thereof 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) or (3), but excluding the case where both 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; When alkoxy groups are grouped, when R ₁ has a plurality, R _{1 is} independently selected from the above group, and R ₂ is 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, an alkyl group having 1 to 4 carbon atoms having a hydroxyl group, and a carbon number having a carboxyl group a group of 1 to 4 alkyl groups, alkoxy groups having 1 to 4 carbon atoms having a sulfonic acid group, alkoxy groups having 1 to 4 carbon atoms having a hydroxyl group, and alkoxy groups having 1 to 4 carbon atoms having a carboxyl group Group, m represents an integer from 1 to 3, In the formula, the ring substituted with R ₃ 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 ₃ represents a compound in the formula (2) It is the same as R _1, R ₄ and R ₅ individually are independently selected from hydrogen atom, chlorine atom, an alkoxy group, a sulfonic acid group, nitro, hydroxy, alkyl having a carbon number of 1 to 4 1 to 4 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, and 1 to 4 carbon atoms having a sulfonic acid group. An alkoxy 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, n represents an integer of 1 to 3, and when A ₁ is a hydrogen atom, R ^a is a hydroxyl group, and when A ₁ is represented by formula (2) or formula (3), R ^a forms -O-Cu-O- together with R ^c or R ^d , and when A ₂ is a hydrogen atom, R ^b is a hydroxyl group. When A ₂ is represented by formula (2) or formula (3), R ^b is taken together with R ^c or R ^d to form -O-Cu-O-, and 2-bond of -NH- is independently bonded to each other at a or b indicates the position of substitution. The azo compound or a salt thereof according to claim 1, wherein A ₁ and A ₂ are each independently represented by the formula (2) or the formula (3). The azo compound or a salt thereof according to claim 1, wherein A ₁ is represented by formula (2) or formula (3), and A ₂ is a hydrogen atom.  The azo compound or a salt thereof according to any one of claims 1 to 3, wherein the substitution position of -NH- is a.   The azo compound or a salt thereof as described in claim 1 is represented by the following formula (4): In the formula, R ₆ 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 1 having a sulfonic acid group. An alkyl group having 4 to 4, 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 a carbon number having a hydroxyl group The alkoxy group of 1 to 4 and the alkoxy group having 1 to 4 carbon atoms having a carboxyl group are grouped, and x represents an integer of 1 to 3.  A dye-based polarizing film comprising the azo compound or a salt thereof according to any one of claims 1 to 5, and a polarizing film substrate, and having absorption at least in a near-infrared region.    A dye-based polarizing film comprising the azo compound or a salt thereof according to any one of claims 1 to 5, and a polarizing film substrate containing one or more organic dyes other than the above.    The dye-based polarizing film is an azo compound or a salt thereof according to any one of the above-mentioned items 1 to 5, 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 6 to 8, wherein the polarizing film substrate is a film formed of a polyvinyl 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 6 to 9.    A liquid crystal display comprising the dye-based polarizing film according to any one of claims 6 to 9 or the dye-based polarizing plate according to claim 10 of the patent application.    The dye-based polarizing film according to any one of claims 6 to 9 is a neutral gray.    A display for a vehicle or an outdoor display, comprising the dye-based polarizing film according to claim 12, or a dye-based polarizing plate obtained by laminating a transparent protective layer on at least one surface of the dye-based polarizing film.