TW202033670A - Azo compound or salt thereof, and dye-based polarizing film and dye-based polarizing plate containing the same - Google Patents

Abstract

Provided is an azo compound represented by the following formula (1) or a salt thereof, wherein, in the formula (1), A1 represents a phenyl group which may have a substituent, or a heterocyclic group which may have a substituent, A2, A3 and A4 each independently represent a phenyl group which may have a substituent or a naphthyl group which may have a substituent, R1 represents a hydrogen atom, a hydroxy group, a C1 to 4 alkoxy group, a substituted or unsubstituted amino group, m represents an integer of 0 to 5, M represents a hydrogen atom or ion, a metal ion, or an ammonium ion, n represents 1 or 2, k represents 0 or 1, and hydrogen atoms of ring a and ring b may be substituted with substituent R1 and substituent SO3M.

Description

Azo compound or its salt, and dye-based polarizing film and dye-based polarizing plate containing the compound or its salt

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

Polarizing plates with light transmission and shielding functions are used together with liquid crystals with light switching functions in display devices such as liquid crystal displays (LCD). The applicable fields of this LCD have also gradually expanded from small machines such as electronic calculators and clocks on the market to notebook computers, word processors, liquid crystal projectors, liquid crystal televisions, car navigation, indoor and outdoor information display devices, and measuring machines. Wait. In addition, it can also be applied to lenses with a polarization function, and has been applied to sunglasses with improved visibility, and polarized glasses corresponding to 3D TVs in recent years. In addition, not only for display purposes, but also for applications that improve accuracy in devices for authenticity determination, and applications that increase the signal-to-noise (S/N) ratio by cutting off reflected light in image sensors such as CCD and CMOS. .

General polarizing plates are manufactured by dyeing or containing iodine or dichroic dyes as polarizing elements in a polarizing film substrate. The polarizing film substrate is a film of polyvinyl alcohol or its derivatives that has been stretched and aligned. Or a polyene-based film that is aligned to generate polyene by the dehydrochlorination reaction of a polyvinyl chloride film or dehydration of a polyvinyl alcohol-based film. Among these, the iodine-based polarizing film that uses iodine as a polarizing element has excellent polarization properties, but it is weak to water and heat, and its durability will be problematic when used for a long time under high temperature and high humidity. . On the other hand, a dye-based polarizing film using a dichroic dye as a polarizing element has better moisture resistance and heat resistance than an iodine-based polarizing film, but generally has insufficient polarization performance.

In recent years, in applications such as identification light sources for touch panels, surveillance cameras, sensors, anti-counterfeiting, and communication equipment, it is necessary not only for polarizing plates in the visible wavelength region (visible region), but also in the infrared wavelength region. (Infrared zone) polarizing plate. In order to respond to these requirements, there are the following records: for example, the iodine-based polarizer in Patent Document 1 is an infrared polarizer in which the iodine-based polarizer is polyalkenized, as in Patent Document 2 or 3, an infrared polarizer that uses a wire grid, For example, the infrared polarizer formed by extending glass containing fine particles in Patent Document 4, and the type using cholesteric liquid crystal as in Patent Document 5 or 6. In Patent Document 1, durability, heat resistance, damp heat durability, and light resistance are weak, and practicality is poor. For example, the wire grid type of Patent Document 2 or 3 can be processed into a film type, and at the same time, it is gradually popularized due to its stability as a product. However, if the surface does not have nano-level unevenness, the optical properties cannot be maintained, and the surface cannot be contacted. Therefore, the application is limited, and it is difficult to perform anti-reflection and anti-glare (anti-glare) processing. As described in Patent Document 4, the glass extension type containing fine particles has high durability, and because of its high dichroism, it has good practicality. However, since it is a glass that contains fine particles and extends at the same time, the element itself is fragile and fragile, and because it lacks the flexibility of conventional polarizing plates, it has the problem of difficulty in surface processing and bonding with other substrates. The techniques of Patent Document 5 and Patent Document 6 use the conventionally disclosed circular polarization technology. However, since the color changes depending on the viewing angle and basically belongs to the polarizing plate using reflection, stray light is generated and it is difficult to form absolute polarization. In other words, there is still no such thing as an absorbing polarizer like a normal iodine-based polarizer, which is as flexible as a film type and has high durability corresponding to the infrared region. Light board. This is because the dichroic dyes used in these dyes only absorb in the visible region, but cannot absorb in the infrared region.

As pigments and dyes that absorb in the infrared region, there are diimmonium-based pigments, naphthalocyanine-based pigments, cyanine pigments, etc., but these pigments are weak in durability, and Very few show dichroism. In addition, even though azo dyes have strong durability, there are very few dyes that absorb in the infrared region. As a dye having absorption in the infrared region among azo dyes, for example, the dye described in Patent No. 4244243. However, there is no description about its dichroism. In the examples, N,N-dimethylformamide (hereinafter referred to as DMF) is used as a medium, etc. The importance of the use as a polarizing plate and the solubility in water have not been disclosed, and Absorption of near-infrared light in an aqueous medium.

In particular, it is known that in general water-soluble azo dyes, the absorption wavelength in an aqueous medium is different from that in other media. For example, JP 2007-84803 compound (I-1) exhibits a maximum absorption of 406 nm in an aqueous solution. The wavelength, but in the polyvinyl alcohol film shows 440nm, and it is known that the absorption wavelength varies depending on the medium. That is, it has been found that the absorption wavelength displayed in the state of being dissolved or dispersed in the medium is different from the absorption wavelength displayed in the state of dichroism, that is, the state of exhibiting a polarization function. Accordingly, among water-soluble azo compounds, it is necessary to have dyes that absorb in the infrared region in water or hydrophilic polymers important for polarizing plate applications.

[Prior Technical Literature]

[Patent Literature]

[Patent Document 1] US2,494,686

[Patent Document 2] JP 2016-148871 A

[Patent Document 3] JP 2013-24982 A

[Patent Document 4] JP 2004-86100 A

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

[Patent Document 6] JP 2013-64798 A

[Patent Document 7] Japanese Patent Application Laid-Open No. 2-167791

[Patent Document 8] International Publication No. 2013/035560

[Patent Document 9] JP 63-33477 A

[Non-Patent Literature]

[Non-Patent Document 1] "Dye Chemistry"; by Hosoda Toyoda, Jihodo Publishing Co., Ltd., 1957, p.621

One of the objectives of the present invention is to provide a novel azo compound. Another object of the present invention is to provide a novel dichroic dye azo compound and a polarizing film containing the compound. Another object of the present invention is to provide a water-soluble dichroic dye azo compound having absorption in the infrared region, and a polarizing film that exhibits a polarizing function for infrared light containing the compound.

The inventors of the present invention have discovered a novel azo compound as a result of careful research to accomplish these purposes. It has been discovered more novelly that the film containing the azo compound can function as a polarizing plate by aligning the azo compound. Furthermore, it has been found that, in one aspect of the present invention, a polarizing plate containing a novel azo compound having absorption in the infrared region can act on infrared light.

That is, the present invention relates to the following.

[Invention 1]

An azo compound or a salt thereof, the azo compound is represented by the following formula (1),

式(1)中，

In formula (1),

A ¹ represents a phenyl group which may have a substituent or a heterocyclic group which may have a substituent,

A ² , A ³ , and A ⁴ each independently represent an optionally substituted phenyl group or an optionally substituted naphthyl group,

R ¹ represents a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, a substituted or unsubstituted amino group,

m represents an integer from 0 to 5,

M represents hydrogen atom or ion, metal ion, or ammonium ion,

n means 1 or 2,

k means 0 or 1,

The hydrogen atoms of ring a and ring b may be substituted by the substituent R ¹ and the substituent SO ₃ M.

[Invention 2]

The azo compound or its salt according to Invention 1, wherein A ¹ in the above formula (1) represents a heterocyclic group which may have a substituent.

[Invention 3]

The azo compound or its salt according to Invention 2, wherein the heterocyclic group which may have a substituent is selected from the group consisting of groups represented by the following formulas (2) to (4);

式(2)至(4)中，

In formulas (2) to (4),

X each independently represents a hydrogen atom, a halogen group, a nitro group, a hydroxyl group, a C1 to 4 aliphatic hydrocarbon group, a C1 to 4 alkoxy group, a C1 to 4 aliphatic hydrocarbon group having a sulfonic acid group, and a C1 to 4 aliphatic hydrocarbon group having a hydroxyl group. 4 aliphatic hydrocarbon groups, C1 to 4 aliphatic hydrocarbon groups having carboxyl groups, C1 to 4 alkoxy groups having sulfonic acid groups, C1 to 4 alkoxy groups having hydroxyl groups, C1 to 4 alkoxy groups having carboxyl groups base,

q ¹ represents an integer from 0 to 4, q ² represents an integer from 0 to 6,

M represents hydrogen atom or ion, metal ion, or ammonium ion,

n ¹ and n ² each represent an integer from 0 to 3,

In each formula, * represents the bonding position with the azo bond.

[Invention 4]

The azo compound or its salt according to any one of Inventions 1 to 3, wherein in the above formula (1), A ² , A ³ , and A ⁴ are each independently represented by the following formula (5) or formula (6) ), at least one of A ² , A ³ and A ⁴ is shown in formula (5);

式(5)中，

In formula (5),

R ² represents a hydrogen atom, a hydroxyl group, a C1 to 4 aliphatic hydrocarbon group, a C1 to 4 alkoxy group, a substituted or unsubstituted amine group, or a C1 to 4 alkoxy group having a sulfonic acid group,

m ² represents an integer from 0 to 6,

M represents hydrogen atom or ion, metal ion, or ammonium ion,

n ³ represents an integer from 0 to 2;

式(6)中，

In formula (6),

R ¹¹ and R ¹² each independently represent a hydrogen atom, a C1 to 4 aliphatic hydrocarbon group, a C1 to 4 alkoxy group, a C1 to 4 alkoxy group having a hydroxyl group, or a C1 to 4 alkoxy group having a sulfonic acid group base.

[Invention 5]

The azo compound or its salt according to Invention 1, wherein the above formula (1) is represented by the following formula (7),

式(7)中，

In formula (7),

A ⁵ is the same as A ¹ in the above formula (1),

R ³ and R ⁴ each independently represent a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, a substituted or unsubstituted amino group,

m ³ and m ⁴ each represent an integer from 0 to 5,

M represents hydrogen atom or ion, metal ion, or ammonium ion,

n ⁴ represents 1 or 2.

[Invention 6]

The azo compound or its salt according to Invention 1, wherein the above formula (1) is represented by the following formula (8),

式(8)中，

In formula (8),

A ⁶ is the same as A ¹ in the above formula (1),

R ⁵ , R ⁶ , and R ⁷ each independently represent a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, a substituted or unsubstituted amino group,

m ⁵ to m ⁷ each represent an integer from 0 to 5,

M represents hydrogen atom or ion, metal ion, or ammonium ion,

n ⁵ represents 1 or 2.

[Invention 7]

The azo compound or its salt according to Invention 1, wherein the above formula (1) is represented by the following formula (9),

式(9)中，

In formula (9),

R ⁸ , R ⁹ , and R ¹⁰ each independently represent a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, a substituted or unsubstituted amino group,

m ⁸ to m ¹⁰ each represent an integer from 0 to 5,

M represents a hydrogen atom or ion, a metal ion, or an ammonium ion, and n ⁶ represents 1 or 2.

[Invention 8]

A polarizing film containing at least one of the azo compound or its salt according to any one of Inventions 1 to 7.

[Invention 9]

The polarizing film according to Invention 8, wherein the absorbance ratio Rd (=A _H /A) of the absorbance of the axis showing the highest transmittance for polarized light (A _L ) and the absorbance of the axis showing the lowest transmittance for polarized light (A _H ) _L ) At least 1 of the wavelengths showing a value of 5 or more is 700 to 1500 nm.

[Invention 10]

The polarizing film according to Invention 8 or 9, which contains the azo compound or its salt according to any one of Inventions 1 to 7, and one or more organic dyes other than the azo compound or its salt.

[Invention 11]

The polarizing film according to any one of Inventions 8 to 10, which shows neutral gray.

[Invention 12]

The polarizing film according to any one of Inventions 8 to 11, wherein a film containing polyvinyl alcohol resin or a derivative thereof is used as a substrate.

[Invention 13]

A polarizing plate is provided with a transparent protective layer on at least one side of the polarizing film according to any one of inventions 8 to 12.

[Invention 14]

A display device using the polarizing film according to any one of Inventions 8 to 12 or the polarizing plate according to Invention 13.

[Invention 15]

The display device according to Invention 14 is for vehicles or outdoor display users.

The azo compound or its salt of the present invention can be used as a dye for polarizing film. In one aspect, the azo compound of the present invention or its salt is water-soluble. In one aspect, the azo compound of the present invention or its salt is dichroic. In one aspect, the polarizing film or polarizing plate of the present invention has absorption in the infrared region, and can be processed in the same way as the polarizing film or polarizing plate of light used in the infrared region. In one aspect, the polarizing film or polarizing plate of the present invention has flexibility. In one aspect, the polarizing film or polarizing plate of the present invention is physically stable. In one aspect, since the polarizing film or polarizing plate of the present invention is an absorbing polarizing plate, stray light will not be generated. In one aspect, the polarizing film or polarizing plate of the present invention has high weather resistance (at least one of heat resistance, humidity resistance, and light resistance).

The present invention relates to a novel azo compound or its salt, and its further purpose is to use the dye to dye, stretch and align the film, and to exhibit anisotropic absorption. The infrared region generally refers to 700 to 30000 nm, but the polarizing film containing the compound obtained in the present invention, It has a function as a polarizing film for near-infrared rays, and the wavelength of near-infrared rays refers to a wavelength of 700 to 1500 nm, and becomes a polarizing film that exhibits a polarizing function at this wavelength.

<Azo compound or its salt>

The azo compound of the present invention or its salt is represented by the above formula (1).

In the above formula (1), A ¹ represents an optionally substituted phenyl group or an optionally substituted heterocyclic group, and A ² , A ³ , and A ⁴ each independently represent an optionally substituted phenyl group, or Substituent naphthyl group, R ¹ represents a hydrogen atom, a hydroxyl group, a (C1 to 4) alkoxy group with 1 to 4 carbon atoms, a substituted or unsubstituted amino group, m represents an integer from 0 to 5, and M represents a hydrogen atom Or ion, metal ion, or ammonium ion, n represents 1 or 2, k represents 0 or 1, and the hydrogen atoms of ring a and ring b can be substituted by substituent R ¹ and substituent SO ₃ M.

In the above-mentioned A ^1, may have a substituent group as a substituent of phenyl group is not particularly limited, but examples thereof include: an optionally substituted aliphatic hydrocarbon group of C1 to 4, may have a substituent group of C1 to 4 alkoxy An oxy group, a C1 to 4 alkoxy group that may have a sulfonic acid group, an aryloxy group that may have a substituent, a hydroxyl group, a sulfonic acid group, a carboxyl group, a nitro group, a substituted or unsubstituted amino group, an amide group, etc., Preferably, it is a substituent selected from the group consisting of a C1 to 4 alkoxy group, a sulfonic acid group, a nitro group, and a carboxyl group which may have a substituent.

Examples of the above-mentioned C1 to 4 aliphatic hydrocarbon groups that may have substituents include straight-chain aliphatic hydrocarbon groups such as methyl, ethyl, n-propyl, and n-butyl; isopropyl, secondary butyl, tertiary Branched chain aliphatic hydrocarbon groups such as butyl; cyclic aliphatic hydrocarbon groups such as cyclobutyl.

As the above-mentioned C1 to 4 alkoxy groups which may have substituents, for example, methoxy, ethoxy, n-propoxy, n-butoxy, isopropoxy, secondary butoxy, tertiary Butoxy, cyclobutoxy, etc.

As the above-mentioned C1 to 4 alkoxy group which may have a sulfonic acid group, for example, sulfonic acid methoxy group, sulfonic acid group ethoxy group, 3-sulfonic acid group propoxy group, 4-sulfonic acid group butoxy group can be mentioned. Group, 3-sulfonyl butoxy group, etc.

As said aryloxy group which may have a substituent, a phenoxy group, a naphthoxy group, etc. are mentioned, for example.

As the above-mentioned substituted or unsubstituted amino group, for example, monosubstituted amino groups such as amino group, methylamino group, ethylamino group, n-propylamino group, n-butylamino group, monoanilino group, mononaphthylamino group, etc. Disubstituted amino groups such as methylamino, diethylamino, diphenylamino, N-ethyl-N-methylamino, and N-ethyl-N-anilino. In addition, these substituted amino groups may further have substituents.

The "substituent" in the above-mentioned C1 to 4 aliphatic hydrocarbon groups which may have substituents and C1 to 4 alkoxy groups which may have substituents is not particularly limited, and examples include hydroxyl groups, sulfonic acid groups, and carboxyl groups. , The above-mentioned substituted or unsubstituted amine group, amide group, etc.

The "substituent" in the above-mentioned optionally substituted aryloxy group and the "substituent" that the substituted amino group may further have are not particularly limited, and examples include: C1 to 4 aliphatic hydrocarbon groups that may have substituents .

The phenyl group which may have a substituent in the above A ¹ is more preferably one having a C1 to 4 alkoxy group selected from a sulfonic acid group, a carboxyl group, a C1 to 4 aliphatic hydrocarbon group, and a C1 to 4 alkane group having a sulfonic acid group. Of at least one substituent in the group consisting of an oxy group, a halogen atom, a nitro group, an amino group, a C1 to 4 aliphatic hydrocarbon substituted amino group, and a C1 to 4 aliphatic hydrocarbon substituted aliphatic amino group Phenyl.

When the phenyl group has two or more substituents, at least one of these substituents is a sulfonic acid group, or a nitro group, or a carboxyl group, or a C1 to 4 alkoxy group having a sulfonic acid group, and other Substituents are preferably sulfonic acid groups, nitro groups, C1 to 4 aliphatic hydrocarbon groups, C1 to 4 alkoxy groups, C1 to 4 alkoxy groups with sulfonic acid groups, carboxyl groups, chlorine groups, bromine groups, nitro groups Group, amine group, C1 to 4 aliphatic hydrocarbon substituted amine group, or C1 to 4 aliphatic hydrocarbon substituted amine group. Other substituents are more preferably sulfonic acid, methyl, ethyl, methoxy, ethoxy, carboxy, sulfonic ethoxy, sulfonic propoxy, sulfonic butoxy, and chloro , Nitro group or amino group, especially sulfonic acid group, carboxyl group, nitro group, methyl group, methoxy group, sulfonic acid group ethoxy group, sulfonic acid group propoxy group, or sulfonic acid group butoxy group, especially preferred System sulfonic acid, carboxyl, nitro, methyl, methoxy, sulfonic butoxy.

In the phenyl group that may have a substituent in the above A ¹ , the position of the substituent is not particularly limited, but it is preferably only the 2-position, only the 4-position, the combination of the 2-position and the 6-position, and the combination of the 2-position and the 4-position. , The combination of 3 and 5 positions is preferred, and particularly preferred is only 2 positions, only 4 positions, a combination of 2 and 4 positions, or a combination of 3 and 5 positions. In addition, only the 2-position and the 4-position only indicate that only the 2-position or the 4-position has a substituent other than a hydrogen atom.

As the above-described preferred embodiment of A ^1, when an azo bond at the case, to include having two sulfonic acid group, a nitro group in the 4 position of the phenyl group at 3 and 5 each having a carboxyl group Phenyl.

The above A ¹ preferably represents a heterocyclic group which may have a substituent.

唑基、咪唑基、噻吩基、呋喃基、吡咯基、噻二唑基、吡唑基、吡啶基、哌

基、喹啉基、苯并咪唑基、萘并咪唑基、苯并噻唑基、萘并噻唑基、苯并噻二唑基等，較佳係苯并噻唑基或萘并噻唑基，其中，更佳係選自由後述之上述式(2)至(4)所示之基所構成之群組的基。 Examples of the heterocyclic group which may have a substituent include thiazolyl,

Azolyl, imidazolyl, thienyl, furyl, pyrrolyl, thiadiazolyl, pyrazolyl, pyridyl, piper

Group, quinolinyl, benzimidazolyl, naphthimidazolyl, benzothiazolyl, naphthiazolyl, benzothiadiazolyl, etc., preferably benzothiazolyl or naphththiazolyl, among which, more The preferred series is a base selected from the group consisting of the bases shown in the above formulas (2) to (4) described later.

The "substituent" in the above-mentioned optionally substituted heterocyclic group is not particularly limited, and may be the same as the above-mentioned optionally substituted C1 to 4 aliphatic hydrocarbon group, and preferably has a sulfonic acid Group as a substituent.

In the above formula (1), A ² , A ³ , and A ⁴ each independently represent an optionally substituted phenyl group or an optionally substituted naphthyl group. Phenyl group may have a substituent may be the same as those of the above-mentioned A ^1. In the naphthyl group which may have a substituent, the substituent is not particularly limited, and may be the same as the substituent which may have the above-mentioned C1 to 4 aliphatic hydrocarbon group which may have a substituent. As described later, in the above formula (1), it is preferable that A ² , A ³ , and A ⁴ are each independently represented by the above formula (5) or formula (6), and at least A ² , A ³ , and A ⁴ A system is shown in (5).

In the above formula (1), R ¹ represents a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, and a substituted or unsubstituted amino group.

In the above formula (1), M represents a hydrogen atom or ion, a metal ion, or an ammonium ion. Examples of metal ions include alkali metal ions such as lithium ion, sodium ion, and potassium ion, and alkaline earth metal ions such as calcium ion and magnesium ion. Examples of the ammonium ion include ammonium ion, methylammonium ion, dimethylammonium ion, triethylammonium ion, tetraethylammonium ion, tetra-n-propylammonium ion, tetra-n-butylammonium ion, triethanolammonium ion, etc. . More specifically, for example, in the case of M-based hydrogen atom or ion, it means sulfonic acid (-SO ₃ H), and in the case of M-based sodium ion, it means sodium sulfonate (-SO ₃ Na), In the case of M-based ammonium ion, it means ammonium sulfonate (-SO ₃ NH ₄ ).

The hydrogen atoms of ring a and ring b in the above formula (1) may be substituted by the above substituent (R ¹ ) and the above substituent (-SO ₃ M).

In the above formula (1), ring a and ring b are preferably substituted with a sulfonic acid group either or both. In addition, it is also preferable that the ring b is substituted by a hydroxyl group. Among them, in the case where the azo bonding part of ring a is located at the 1-position, particularly preferred: in the counterclockwise direction, the 2-position is substituted by the hydroxyl group, the 3-position and the 7-position are substituted by the sulfonic acid group, and the 4-position Those substituted with sulfonic acid groups at position 2, hydroxy substituted at positions 4, sulfonic acid groups at position 4, and sulfonic acid groups at position 7.

In the above formulas (2) to (4), X each independently represents a hydrogen atom, a halogen group, a nitro group, a hydroxyl group, a C1 to 4 aliphatic hydrocarbon group, a C1 to 4 alkoxy group, and a C1 having a sulfonic acid group Aliphatic hydrocarbon groups up to 4, C1 to 4 aliphatic hydrocarbon groups having hydroxyl groups, C1 to 4 aliphatic hydrocarbon groups having carboxyl groups, C1 to 4 alkoxy groups having sulfonic acid groups, and C1 to 4 alkyl groups having hydroxyl groups An oxy group or a C1 to 4 alkoxy group having a carboxyl group, q ¹ represents an integer from 0 to 4, q ² represents an integer from 0 to 6, M represents a hydrogen atom or ion, a metal ion, or an ammonium ion, n ¹ , n ² each represents an integer from 0 to 3, in each formula * represents the bonding position with the azo bond, C1 to 4 aliphatic hydrocarbon group, C1 to 4 alkoxy group, C1 to 4 fat with sulfonic acid group The group hydrocarbon group, the C1 to 4 alkoxy group having a sulfonic acid group, and M may be the same as those described above.

As said halogen group, a fluoro group, a chloro group, a bromo group, an iodo group, etc. are mentioned, Preferably it is a chloro group, a bromo group, More preferably, it is a chloro group.

Examples of the above-mentioned C1 to 4 aliphatic hydrocarbon groups having hydroxyl groups include hydroxymethyl, hydroxyethyl, hydroxy-n-propyl, hydroxy-n-butyl, hydroxyisopropyl, hydroxy-second-butyl, and hydroxy -Tertiary butyl, etc.

Examples of the C1 to 4 aliphatic hydrocarbon group having a carboxyl group include: carboxymethyl, carboxyethyl, carboxy-n-propyl, carboxy-n-butyl, carboxyisopropyl, carboxy-second-butyl, carboxyl -Tertiary butyl, etc.

As the above-mentioned C1 to 4 alkoxy group having a hydroxyl group, for example, hydroxymethoxy, hydroxyethoxy, hydroxy-n-propoxy, hydroxy-n-butoxy, hydroxyisopropoxy, hydroxy-dioxy Grade butoxy, hydroxy-tertiary butoxy, etc.

Examples of the C1 to 4 alkoxy group having a carboxyl group include carboxymethoxy, carboxyethoxy, carboxy-n-propoxy, carboxy-n-butoxy, carboxyisopropoxy, carboxy-di Butoxy, carboxy-tertiary butoxy, etc.

In the above formula (1), A ² , A ³ , and A ⁴ each independently represent the above formula (5) or formula (6), and at least one of A ² , A ³ , and A ⁴ is represented by formula (5) , It is preferable because a wide-band polarizing element can be obtained.

In the above formula (5), R ² represents a hydrogen atom, a hydroxyl group, a C1 to 4 aliphatic hydrocarbon group, a C1 to 4 alkoxy group, a substituted or unsubstituted amine group, or a C1 to 4 sulfonic acid group Alkoxy, m ² represents an integer from 0 to 6, M represents a hydrogen atom or ion, metal ion, or ammonium ion, n ³ represents an integer from 0 to 2, C1 to 4 aliphatic hydrocarbon group, C1 to 4 alkoxy A group, a substituted or unsubstituted amine group, a C1 to 4 alkoxy group having a sulfonic acid group, and M may be the same as the above.

In the above formula (5), m ² preferably represents an integer from 0 to 4, more preferably represents an integer from 0 to 2, and particularly preferably represents 0 or 1. R ² preferably represents a hydrogen atom or a hydroxyl group. Preferably, n ³ represents 0 or 1, more preferably ⁶ represents the side of an azo group is 1, A ⁵ in the formula A ^1, of formula (7) (1), the formula (8) A provided in a In this case, the substitution position of R ² is preferably the 2, 3, or 5 position. Particularly preferred is that the 2-position or the 3-position is substituted by a hydrogen atom or a methoxy group, and particularly preferred is that the 3-position is substituted. In the 8-position, it is preferably substituted by a hydrogen atom or a hydroxyl group, and particularly preferably, it is substituted by a hydroxyl group. In the above formula (1), A ³ and A ⁴ preferably have the structure shown in formula (5), because the azo compound of the present invention is used to obtain a polarizing film with a wide frequency band and a high degree of polarization Pigment. Specifically, when k=0, A ³ has the structure of formula (5), and when k=1, A ⁴ has the structure of formula (5).

In the above formula (6), R ¹¹ and R ¹² each independently represent a hydrogen atom, a C1 to 4 aliphatic hydrocarbon group, a C1 to 4 alkoxy group, a C1 to 4 alkoxy group having a hydroxyl group, or a sulfonate C1 to 4 alkoxy groups of acid groups, C1 to 4 aliphatic hydrocarbon groups, C1 to 4 alkoxy groups, C1 to 4 alkoxy groups having hydroxyl groups, C1 to 4 alkoxy groups having sulfonic acid groups Each may be the same as described above.

In the above formula (1), when A ³ and A ⁴ have the structure shown in formula (6), R ¹¹ or R ¹² preferably each independently represents a hydrogen atom or a C1 to 4 alkoxy group, which is due to The azo compound of the present invention is a pigment used to obtain a polarizing film with a wide band and a high degree of polarization, and more preferably each independently represents a methoxy group or an ethoxy group, and particularly preferably, R ¹¹ and R ¹² represent methoxy base. Specifically, when k=0 and A ³ has a structure of formula (6), R ¹¹ and R ¹² preferably represent a methoxy group, and when k=1 and A ⁴ has a structure of formula (6), R ¹¹ and R ¹² particularly preferably represents a methoxy group.

The above formula (1) is preferably represented by the above formula (7). In the above formula (7), A ⁵ is the same as A ¹ in the above formula (1), R ³ and R ⁴ each independently represent a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, substituted or unsubstituted The amino group, m ³ and m ⁴ each represent an integer of 0 to 5. M represents a hydrogen atom or ion, a metal ion, or an ammonium ion, and n ⁴ represents 1 or 2. Each of the C1 to 4 alkoxy group, substituted or unsubstituted amine group, and M may be the same as described above. The above-mentioned formula (1) is preferably as shown in formula (7), because a near-infrared polarizing film with a wider frequency band and a high degree of polarization can be obtained.

The above formula (1) is preferably represented by the above formula (8). In the above formula (8), A ⁶ is the same as A ¹ in the above formula (1), R ⁵ , R ⁶ , and R ⁷ each independently represent a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, a substitution or For unsubstituted amine groups, m ⁵ to m ⁷ each represent an integer of 0 to 5. M represents a hydrogen atom or ion, a metal ion, or an ammonium ion, and n ⁵ represents 1 or 2. Each of the C1 to 4 alkoxy group, substituted or unsubstituted amine group, and M may be the same as described above. The above formula (1) is preferably represented by the formula (8), because a near-infrared polarizing film with a wider frequency band and a high degree of polarization can be obtained.

The above formula (1) may also be preferably represented by the above formula (9). In the above formula (9), R ⁸ , R ⁹ , and R ¹⁰ each independently represent a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, a substituted or unsubstituted amino group, and m ⁸ to m ¹⁰ each represent 0 to 5. M represents a hydrogen atom or ion, a metal ion, or an ammonium ion, n ⁶ represents 1 or 2, a C1 to 4 alkoxy group, a substituted or unsubstituted amine group, and M each may be the same as above. The above-mentioned formula (1) is preferably as shown in formula (9), since a near-infrared polarizing film with a wider frequency band and a high degree of polarization can be obtained.

Next, the following series give specific examples of the azo compound represented by the above formula (1) or its salt. In addition, the sulfonic acid group, carboxyl group and hydroxyl group in the formula are represented by the form of free acid.

The azo compound represented by the above formula (1) and formulas (7) to (9) or its salt can be obtained by, for example, following the general azo dye production method described in Patent Document 3 and Non-Patent Document 1. , Diazotization, coupling and manufacturing.

As an example of a specific manufacturing method, the manufacturing method of the above formula (7) will be described below.

Diazotizing the following formula (A) belonging to aminobenzenes or thiazoles, and coupling it with 1-aminonaphthalenes represented by the following formula (B) at one time to obtain the following formula (C) The monoazoamine-based compound shown. The monoazoamine compound (C) is diazotized, and it is coupled with the 1-aminonaphthalene represented by the following formula (D) twice to obtain the double compound represented by the following formula (E) Azoamine-based compounds. The bisazoamine compound (E) is diazotized, and the azo compound of the formula (7) is obtained by three-time coupling with the naphthol of the following formula (F).

In the above manufacturing method, the diazotization step is preferably performed by the so-called cis method in which nitrite such as sodium nitrite is mixed with an aqueous solution or suspension of mineral acids such as hydrochloric acid and sulfuric acid of the diazonium component, or by The so-called reverse method in which nitrite is added to the neutral or weakly alkaline aqueous solution of the diazonium component and mixed with mineral acid is performed. The temperature of diazotization is suitably -10 to 40°C. In addition, the coupling step with anilines is preferably performed by mixing acidic aqueous solutions such as hydrochloric acid and acetic acid with the above-mentioned diazonium liquids under acidic conditions at a temperature of -10 to 40°C and a pH of 2 to 7.

The azo compound of the above formula (C) and formula (E) obtained by coupling can be directly filtered, can be separated out by acid precipitation or salting out and filtered out, or can be directly connected in the state of solution or suspension. Steps down. When the diazonium salt is poorly soluble and in a suspension, it can be filtered and used as a filter cake in the next coupling step.

The third coupling reaction between the diazonium compound of the bisazoamino compound of the above formula (E) and the naphthol represented by the above formula (F) is preferably at a temperature of -10 to 40°C and a pH of 7 to 10 Sexual to alkaline bars Under the piece. After the completion of the reaction, it is preferable to take out the obtained azo compound or salt of formula (7) by salting out to make it precipitate and filter. In addition, when purification is required, the azo compound can be precipitated from water by repeated salting out or using an organic solvent. Examples of organic solvents used for purification include water-soluble organic solvents such as alcohols such as methanol and ethanol, and ketones such as acetone.

The azo compound of the present invention or its salt can be used as a dye for polarizing films. According to the azo compound or its salt of the present invention, it is possible to manufacture a high-performance dye-based near-infrared polarizing plate with polarizing properties in the near-infrared region and moisture resistance/heat resistance/light resistance. In addition, by using dyes with polarizing properties in the visible area, it is possible to realize not only the current visible area, but also a high-performance dye-based polarizer that can control neutral gray in the near-infrared region. Accordingly, the azo compound or its salt of the present invention is suitable for the production of neutral gray polarizing plates for vehicles or outdoor displays used under high temperature and high humidity conditions, and various sensors that must control the near infrared region.

<Dye-based polarizing film>

As the polarizing function, it is usually possible to display the dichroic ratio calculated from the difference in transmittance, the degree of polarization, or the light absorption ratio (absorbance ratio) on the different axis. As one of the indicators of the polarizing function in this application, one with polarization can be cited, but as a preferred form of this application, the transmittance when polarized light is incident on the axis showing the highest transmittance for polarized light Among the absorbance ratios between the absorbance of and the absorbance of the axis showing the lowest transmittance for polarized light, at least one of the wavelengths whose absorbance ratio shows a value of 5 or more is a polarizing film at 700 to 1500 nm. The absorbance ratio is usually called the dichroic ratio, but when the dichroic ratio is 5 or more, it shows the usual absorption anisotropy, that is, it has a polarization function. The dichroic ratio is preferably high, more preferably 10 or more, and particularly preferably 20 or more. When the dichroic ratio is less than 5, although absorption anisotropy is indeed exhibited, the absorption anisotropy, that is, the use as a polarizing function is significantly reduced. In addition, it is preferable that the wavelength at which the dichroic ratio shows the highest value is 700 to 1500 nm, but it is not necessarily limited to this. By using the formula (1) The compound has an absorption anisotropy with a dichroic ratio of 5 or more from 700 to 1500nm, that is, it has a polarizing function, which is the characteristic of this case, and can be obtained from 700 to 1500nm with a higher dichroic ratio of 10 or more. The polarizing film is a feature that has not yet existed. Specifically, it means that when the monomer transmittance is set to 30%, the degree of polarization of the dichroic ratio 5 is 88.2%, that is, the degree of polarization is nearly 90%, and the degree of polarization of the dichroic ratio 10 is 98.3 %, that is, shows a degree of polarization of about 99%.

The dye-based polarizing film of the present invention includes a dichroic dye containing at least the azo compound represented by formula (1) or a salt thereof, and a polarizing film substrate. The dye-based polarizing film of the present invention has a function as a near-infrared polarizing film, and can also be a color polarizing film that functions in the visible area. In particular, it can be produced with a neutral gray polarizing film in the visible area. Here, "neutral gray" refers to the one with less light leakage (color leakage) of a specific wavelength in the visible region and the near-infrared region in a state where two polarizing films are overlapped so that their alignment directions are orthogonal to each other. Specifically, when two polarizing films are superimposed so that their alignment directions are orthogonal to each other so that the hue becomes neutral gray, among the absorption wavelengths of 460nm, 550nm, and 610nm, each wavelength is independently preferably At the same time, it has a transmittance of 3% or less, preferably 1% or less, more preferably 0.3% or less, particularly preferably 0.1% or less, particularly preferably 0.05% or less. At this time, the wavelength of the near infrared region, such as 850nm or 950nm Among them, the transmittance is 3% or less, preferably 1% or less, more preferably 0.3% or less, particularly preferably 0.1% or less, particularly preferably 0.05% or less. Controlling the transmittance of each absorption wavelength of 460nm, 550nm, 610nm is a wavelength that has a strong influence on the perspective. Since the sensitivity of each blue, green, and red is a strong wavelength, the transmittance of each wavelength must be controlled Neutral gray, and preferably can also control the transmittance of the infrared region to almost the same degree of transmittance.

The dye-based polarizing film of the present invention, as a dichroic pigment, contains the azo compound represented by the formula (1) or its salt alone or in plural, and may further contain one or more of the azo compound or its salt as required Of other organic dyes. There are no special restrictions on other organic dyes used in combination, but they are related to the formula (1) The dye having dichroism in the wavelength range different in the absorption wavelength range of the azo compound or salt thereof is preferably one with high dichroism. Examples of organic dyes used in combination include 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 69, CI Direct Blue 78, CI Direct Blue 247, CI Direct Green 80, CI Direct Green 59, etc. as dyes Representative example. These pigments are contained in the dye-based polarizing film as free acid, or alkali metal salt (such as Na salt, K salt, Li salt), ammonium salt, or amine salt.

When the azo compound or its salt represented by formula (1) is used in combination with other organic dyes, the hue of the visible area of the target dye-based polarizing film depends on the neutral gray polarizing film and the color polarizing film for liquid crystal projectors , Other color polarizing films, so that the types of other organic dyes to be blended are different. The blending ratio of other organic dyes is not particularly limited, but based on the mass of the azo compound of formula (1) or its salt, the total of one or more organic dyes is preferably in the range of 0.1 to 10 parts by mass .

In the case of a neutral gray polarizing film with a polarizing function in the near-infrared region, in order to reduce the color leakage of the obtained polarizing film in the visible area, other organic dyes that can be used together with the pigment of formula (1) can be adjusted The types and their proportions.

The near-infrared dye-based polarizing film of the present invention or the dye-based polarizing film having a neutral gray of polarization function in the near-infrared region can be manufactured by the following method: at least containing the azo compound represented by formula (1) or Salts, or dichroic dyes containing other organic dyes as needed, are contained and aligned on a polarizing film substrate (such as a polymer film) by a conventional method, and mixed with liquid crystals, or made by coating methods It is aligned to the polarizing film substrate.

The polarizing film base material is a polymer film, preferably a film obtained by forming a hydrophilic polymer into a film, and more preferably a film composed of a polyvinyl alcohol resin or a derivative thereof. As a pro for polarizing film substrate The water-based polymer is not particularly limited, but refers to a membrane with a high affinity for water. It means, for example, a film containing water or swelling when water is immersed or contacted as a medium. Specifically, polyvinyl alcohol-based resins, amylose-based resins, starch-based resins, cellulose-based resins, polyacrylate-based resins, and derivatives thereof can be used. In a film made of such resins, a dichroic dye that absorbs in the infrared region is contained, and is stretched to align it to obtain a polarizing plate. In consideration of the inclusion of dichroic pigments and cross-linking, the best is a film made of polyvinyl alcohol-based resin. Examples include polyvinyl alcohol or its derivatives, and any of these modified by olefins such as ethylene and propylene, and unsaturated carboxylic acids such as crotonic acid, acrylic acid, methacrylic acid, and maleic acid. . From the viewpoint of dye adsorption and alignment, it is preferable to use a film composed of polyvinyl alcohol or its derivatives as the polarizing film substrate. The thickness of the polarizing film substrate is usually 10 to 100 μm, preferably about 25 to 80 μm.

When the polarizing film substrate is a polymer film, when it contains a dichroic dye containing at least the azo compound of formula (1) or its salt, a method of dyeing the polymer film is usually used. Dyeing can be performed as follows, for example. First, the azo compound of the present invention or its salt, and if necessary, organic dyes other than these are dissolved in water to prepare a dye bath. The dye concentration in the dye bath is not particularly limited, but is usually selected from the range of about 0.001 to 10% by mass. In addition, dyeing auxiliary agents can be used as needed, for example, Glauber's salt is suitably used in a concentration of about 0.1 to 10% by mass. In the dye bath prepared in this way, the polymer film is immersed, for example, for 1 to 10 minutes to perform dyeing. The dyeing temperature is preferably about 40 to 80°C.

The alignment of the dichroic dye containing the azo compound of formula (1) or its salt can be performed by stretching a dyed polymer film. As the extension method, any conventional methods such as a wet method and a dry method can be used. The extension of the polymer film can be carried out before dyeing according to the situation. In this case, the dye is aligned at the time of dyeing. The polymer film containing dyes and aligned can be subjected to post-treatments such as boric acid treatment by conventional methods as required. This post-treatment is to improve the light transmission of the dye-based polarizing film Rate and polarization for the purpose. The conditions of boric acid treatment vary depending on the type of polymer film used and the type of dye used, but generally speaking, the boric acid concentration of the boric acid aqueous solution is set to 0.1 to 10% by mass, preferably 0.5 to 7% by mass The range, particularly preferably, is set to 1 to 5 mass%, and the treatment is, for example, in the temperature range of 30 to 80°C, preferably 40 to 75°C, such as immersion for 0.5 to 10 minutes and extending. Furthermore, if necessary, an aqueous solution containing a cationic polymer compound can also be used for the repair treatment. Furthermore, the polarizing film substrate using the pigment of the present invention can be obtained by stretching at pH 4 to 9 in the aqueous solution during immersion in the stretching step, or the step before stretching, or/or the step after further stretching. In the polarizing film of the invention, it is preferable to process the polarizing film at pH 6 to 9 in the stretching step or the post-stretching step. This is because a polarizing film with a wider band and long wavelength in the near infrared region can be obtained. The pH of the aqueous solution during the treatment is particularly a method of adjusting the pH of the boric acid aqueous solution to 6-9, and it is preferable to add alkaline substances such as sodium hydroxide, potassium hydroxide, and borax for treatment. The polymer film, especially when a film composed of polyvinyl alcohol or its derivatives is used, is one of the preferred forms for stretching with borax. In the case of borax, boric acid and borax can be used in combination. As long as the pH of the treatment step is 6 to 9, the wavelength range that can have the polarization function of the polarizing film using the pigment of the present invention is broadened, but it is more preferably 6.5 to 8.5, and particularly preferably 6.5 to 8.0. Better form.

By attaching a protective film, the obtained dye-based polarizing film can be used as a polarizing plate, and a protective layer or an AR (anti-reflection) layer and a support can be provided as needed. As the application of the dye-based polarizing film, for example, liquid crystal projectors, electronic calculators, clocks, notebook computers, word processors, liquid crystal televisions, car navigation, indoor and outdoor measuring instruments or displays, etc., and lenses or glasses, Devices for authenticity determination, image sensors such as CCD or CMOS, etc. Even in the near-infrared region, the dye-based polarizing film has high polarization performance comparable to that of the conventional polarizing film using iodine, and has excellent durability. Therefore, it is especially suitable for High-polarization performance and durability are required for various liquid crystal displays, liquid crystal projectors, vehicles, and outdoor displays (such as display applications and portable applications such as industrial equipment), and security devices that require high reliability.

<Dye-based polarizing plate>

The dye-based polarizing plate can be obtained by laminating a transparent protective film on at least one side of the dye-based polarizing film. The dye-based polarizing plate has excellent polarization performance and moisture resistance/heat resistance/light resistance due to the above-mentioned dye-based polarizing film. As a material for forming a transparent protective film, materials with excellent optical transparency and mechanical strength are preferred. In addition to cellulose acetate films and acrylic films, for example, tetrafluoroethylene/hexafluoropropylene copolymers can be used. Fluorine-based film, a film made of polyester resin, polyolefin resin, or polyamide resin. The transparent protective film is preferably a triacetate cellulose (TAC) film or a cycloolefin-based film. The thickness of the protective film can usually be 10 to 200 μm, preferably 20 to 100 μm.

Examples of adhesives that can be used for bonding the polarizing film and the protective film include: polyvinyl alcohol-based adhesives, urethane emulsion-based adhesives, acrylic-based adhesives, and adhesives composed of polyols and isocyanates Etc., preferably a polyvinyl alcohol-based adhesive.

A transparent protective layer can be provided on the surface of the dye-based polarizing plate. Furthermore, as the transparent protective layer, for example, an acrylic or polysiloxane-based hard coat layer or a urethane-based protective layer can be cited. In addition, since the light transmittance of the veneer can be further improved, it is preferable to provide an AR layer on the protective layer. The AR layer can be formed by, for example, vapor-depositing or sputtering a substance such as silicon dioxide, titanium oxide, and the like, and can be formed by coating a thin fluorine-based substance. The dye-based polarizing plate can also be used as a circular polarizing plate or an elliptical polarizing plate by attaching a phase difference plate to the surface.

The dye-based polarizing plate may be either the above-mentioned near-infrared polarizing plate or a neutral polarizing plate having a polarization function in the near-infrared region due to its application. The neutral gray polarizer of the present invention has the following characteristics: less color leakage in the orthogonal position in the visible area and near-infrared area, excellent polarization performance, and even higher Under high temperature and high humidity, it can also prevent discoloration and degradation of polarization performance, and has less light leakage in the orthogonal position in the visible area; and it is especially suitable for vehicles or outdoor displays that require high-reliability security devices.

A near-infrared polarizer for vehicles or outdoor displays, or a neutral gray polarizer with a polarization function in the near-infrared region. In a polarizer composed of a polarizing film and a protective film, in order to increase the light transmittance of the single plate, It is preferable to provide an AR layer and use it as a polarizer with an AR layer, and it is more preferable to further provide an AR layer with a support such as transparent resin and a polarizer with a support. The AR layer can be set on one side or both sides of the polarizer. The supporting body is preferably arranged on a single side of the polarizing plate, which can be arranged on the polarizing plate through the AR layer or directly. The supporting body preferably has a flat surface for attaching a polarizing plate, and is preferably a transparent substrate for optical purposes. Transparent substrates are roughly divided into inorganic substrates and organic substrates. Examples include inorganic substrates such as soda glass, borosilicate glass, crystal substrates, sapphire substrates, and spinel substrates, as well as acrylic, polycarbonate, and polyterephthalate. Organic substrates such as ethylene glycol, polyethylene naphthalate, and cycloolefin polymers are preferably organic substrates. The thickness and size of the transparent substrate can be desired sizes.

Near-infrared polarizers have excellent polarization performance and will not cause discoloration and degradation of polarization performance even in high temperature and high humidity conditions. Therefore, they are suitable for LCD projectors, vehicles, outdoor displays, and require high reliability. For device. The polarizing film used in these polarizing plates can also be manufactured by the method described in the section of the manufacturing method of the dye-based polarizing film of the present invention. Moreover, the protective film is attached to the polarizing plate, and protection is provided as required Layer, AR layer, support, etc.

Infrared polarizing plate near the support for vehicles or outdoor display, or neutral polarizing plate and color polarizing plate with polarizing function in the near-infrared region, can be achieved by, for example, coating a transparent adhesive (adhesive) on the plane of the support The agent is manufactured by attaching a dye-based polarizing plate to the coated surface. In addition, a transparent adhesive (adhesive) agent may be coated on the dye-based polarizer, and then the support may be attached to the coated surface. The adhesive (adhesive) used here is preferably, for example, an acrylate-based one. Also, the dye-based polarizer is used as an elliptically polarized light When the plate is used, although the phase difference plate side is usually attached to the support side, the polarizing plate side can also be attached to the transparent substrate.

[Example]

Hereinafter, the present invention will be described in more detail based on the examples, but these are exemplary rather than limiting the present inventors. The% and parts in the example, unless otherwise specified, belong to the quality standard.

[Example 1]

(step 1)

After adding 21.8 parts of 2-amino-5-nitrobenzenesulfonic acid to 500 parts of water and dissolving it with 25% sodium hydroxide, 35% hydrochloric acid was added to make the pH 0.2. To the obtained liquid, 17.3 parts of 40% sodium nitrite aqueous solution was added to prepare a diazonium liquid. On the other hand, 22.3 parts of 8-aminonaphthalene-2-sulfonic acid was added to 200 parts of water and dissolved in a 25% aqueous sodium hydroxide solution to become weakly alkaline. In this solution, the previously obtained diazonium solution was dropped to maintain the pH at 4.5 to 6.0, and stirred to complete the coupling reaction. Thereafter, after salting out with sodium chloride, it was filtered to obtain 241 parts of a wet cake of a monoazo compound represented by formula (101).

(Step 2)

241 parts of the obtained wet cake of the monoazo compound (101) was added to 300 parts of water and stirred and suspended. 25% sodium hydroxide was used to make the pH of the aforementioned suspension 9.0, and 34.5 parts of 40% sodium nitrite aqueous solution was added here. The obtained suspension was dropped into a mixed liquid of 200 parts of water and 50 parts of 35% hydrochloric acid to prepare a diazonium liquid. On the other hand, add 22.3 parts of 8-aminonaphthalene-2-sulfonic acid to 200 parts of water and dissolve it with 25% sodium hydroxide in water The liquid dissolves and is weakly alkaline. In this solution, the previously obtained diazonium solution was dropped to maintain the pH at 4.5 to 6.0, and stirred to complete the coupling reaction. Thereafter, after salting out with sodium chloride, it was filtered to obtain 342 parts of a wet cake of the bisazo compound represented by formula (102).

(Step 3)

34.2 parts of the obtained wet cake of the bisazo compound (102) was added to 200 parts of water and stirred and suspended. Use 25% sodium hydroxide to make the pH of the aforementioned suspension 9.0, and add 6.9 parts of 40% sodium nitrite aqueous solution here. The obtained suspension was dropped into a mixed liquid of 100 parts of water and 20 parts of 35% hydrochloric acid to prepare a diazonium liquid. On the other hand, 10.0 parts of 1,5-dihydroxynaphthalene-2,6-disulfonic acid was added to 200 parts of water, and dissolved in a 25% aqueous sodium hydroxide solution to be weakly alkaline. In this solution, the previously obtained diazonium solution was dropped to maintain the pH at 6.5 to 8.0, and stirred to complete the coupling reaction. Then, after salting out with sodium chloride, 14.0 parts of azo compounds represented by formula (10) were obtained by filtration and drying.

<Production of polarizing film and polarizing plate>

A polyvinyl alcohol film (VF-PS #7500 manufactured by Kuraray Corporation) with a saponification degree of 99% or more and an average degree of polymerization of 2400 was immersed in warm water at 45°C for 3 minutes, and a swelling treatment was applied to increase the stretch ratio to 1.30 times. In a 45°C dyeing solution containing 1500 parts by mass of water, 1.5 parts by mass of anhydrous sodium sulfate, and 0.30 parts by mass of azo compound (10), The swollen film was immersed for 10 minutes, and the azo compound was contained in the film. The obtained film was immersed in an aqueous solution containing 20 g/l of boric acid (manufactured by Societa Chimica Larderello s.p.a.) at 40°C for 1 minute. While stretching the immersed film 5.0 times, it is stretched for 5 minutes in an aqueous solution containing 15.0 g/l of boric acid and 15.0 g/l of borax at 50°C. The obtained film was kept in its tension state, and was immersed in water at 25° C. for 20 seconds to perform washing treatment. The cleaned film was dried at 70°C for 9 minutes to obtain a polarizing film. For this polarizing film, polyvinyl alcohol (NH-26 manufactured by Vam & Poval, Japan) was dissolved in water at 4% as an adhesive, and an alkali-treated cellulose triacetate film (TD manufactured by Fuji Film Co., Ltd.) -80) Laminate to obtain a polarizing plate. The obtained polarizing plate maintains the optical properties of the above-mentioned polarizing film, especially the transmittance and the degree of polarization. This polarizing plate was used as the measurement sample of Example 1.

[Example 2]

68.4 parts of the wet cake of the bisazo compound (102) obtained in Example 1 was added to 400 parts of water and stirred and suspended. 25% sodium hydroxide was used to make the pH of the aforementioned suspension 9.0, and 13.8 parts of 40% sodium nitrite aqueous solution was added here. The obtained suspension was dropped into a mixed liquid of 100 parts of water and 40 parts of 35% hydrochloric acid to prepare a diazonium liquid. On the other hand, 4.5 parts of 8-aminonaphthalene-2-sulfonic acid was added to 150 parts of water, and it was dissolved in a 25% aqueous sodium hydroxide solution to become weakly alkaline. In this liquid, the previously obtained diazonium liquid was dropped to maintain the pH at 4.5 to 6.0, and stirred to complete the coupling reaction. Thereafter, after salting out with sodium chloride, filtration was performed to obtain 100 parts of a wet cake of the trisazo compound represented by the formula (103).

50 parts of the obtained wet cake of the trisazo compound (103) was added to 200 parts of water, and stirred and suspended. Use 25% sodium hydroxide to make the pH of the aforementioned suspension 9.0, and add 6.9 parts of 40% sodium nitrite aqueous solution here. The obtained suspension was dropped into a mixed liquid of 100 parts of water and 25 parts of 35% hydrochloric acid to prepare a diazonium liquid. On the other hand, 10.0 parts of 1,5-dihydroxynaphthalene-2,6-disulfonic acid was added to 100 parts of water and dissolved in a 25% aqueous sodium hydroxide solution to be weakly alkaline. In this solution, the previously obtained diazonium solution was dropped to maintain the pH at 6.5 to 8.0, and stirred to complete the coupling reaction. Thereafter, after salting out with sodium chloride, 5.0 parts of the azo compound represented by formula (14) was obtained by filtration and drying.

<Production of polarizing film and polarizing plate>

The above compound (14) was used instead of the compound (10) used in the preparation of the polarizing film in Example 1, and in the stretching treatment, the stretching treatment was applied for 5 minutes in an aqueous solution containing 30.0 g/l of boric acid at 50°C, and A polarizing plate was produced in the same manner as in Example 1 except that an aqueous solution of pH 7.5 added with sodium hydroxide was applied for 30 seconds in the water washing treatment after stretching, and used as the measurement sample of Example 2.

[Example 3]

50 parts of the wet cake of the trisazo compound (103) obtained in Example 2 was added to 200 parts of water, and stirred and suspended. Use 25% sodium hydroxide to make the pH of the aforementioned suspension 9.0, and add 6.9 parts of 40% sodium nitrite aqueous solution here. The obtained suspension was dropped into a mixed liquid of 100 parts of water and 25 parts of 35% hydrochloric acid to prepare a diazonium liquid. On the other hand, 4.5 parts of 8-aminonaphthalene-2-sulfonic acid was added to 100 parts of water, and it was dissolved in a 25% aqueous sodium hydroxide solution to become weakly alkaline. In this solution, drop the previously obtained diazonium solution to keep the pH at 4.5 To 6.0, and stir to complete the coupling reaction. Thereafter, after salting out with sodium chloride, filtration was performed to obtain 80 parts of a wet cake of the tetrasazo compound represented by formula (104).

80 parts of the obtained wet cake of the tetrasazo compound (104) was added to 300 parts of water and stirred to suspend it. The pH was maintained at 4.0 to 4.5 using 35% hydrochloric acid and stirred at 70 to 75°C for 3 days. Then, after salting out with sodium chloride, 5.0 parts of azo compounds represented by formula (16) were obtained by filtration and drying.

<Production of polarizing film and polarizing plate>

Except having used the above-mentioned compound (16) instead of the compound (10) used in the preparation of the polarizing film in Example 1, a polarizing plate was produced in the same manner as in Example 1, and used as a measurement sample of Example 3.

[Example 4]

(step 1)

18.1 parts of 5-aminoisophthalic acid and 75 parts of 35% hydrochloric acid were added to 100 parts of water and suspended. To the obtained liquid, 18.1 parts of a 40% sodium nitrite aqueous solution was added to prepare a diazonium liquid. On the other hand, 24.7 parts of 8-amino-4-hydroxynaphthalene-2-sulfonic acid was added to 200 parts of water and dissolved in a 25% aqueous sodium hydroxide solution to become weakly alkaline. In this liquid, the previously obtained diazonium liquid was dropped to maintain the pH at 4.5 to 6.0, and stirred to complete the coupling reaction. Thereafter, after salting out with sodium chloride, filtration was performed to obtain 150 parts of a wet cake of the monoazo compound represented by formula (105).

(Step 2)

150 parts of the obtained wet cake of the monoazo compound (105) was added to 300 parts of water, and stirred and suspended. 25% sodium hydroxide was used to make the pH of the aforementioned suspension 9.0, and 18.1 parts of 40% sodium nitrite aqueous solution was added here. The obtained liquid was dropped into a mixed liquid of 100 parts of water and 60 parts of 35% hydrochloric acid to prepare a diazonium liquid. On the other hand, 22.3 parts of 8-aminonaphthalene-2-sulfonic acid and 300 parts of N-methyl-2-pyrrolidone were added to 300 parts of water and dissolved in a 25% aqueous sodium hydroxide solution to become weakly alkaline. In this liquid, the previously obtained diazonium liquid was dropped to maintain the pH at 4.5 to 6.0, and stirred to complete the coupling reaction. Thereafter, after salting out with sodium chloride, filtration was performed to obtain 130 parts of a wet cake of the disazo compound represented by the formula (106).

(Step 3)

130 parts of the obtained wet cake of the bisazo compound (106) was added to 300 parts of water, and stirred and suspended. 25% sodium hydroxide was used to make the pH of the aforementioned suspension 9.0, and 17.3 parts of 40% sodium nitrite aqueous solution was added here. The obtained suspension was dropped into a mixed liquid of 100 parts of water and 30 parts of 35% hydrochloric acid to prepare a diazonium liquid. On the other hand, 24.7 parts of 8-amino-4-hydroxynaphthalene-2-sulfonic acid and 300 parts of N-methyl-2-pyrrolidone were added to 300 parts of water and dissolved in 25% sodium hydroxide aqueous solution. Weakly alkaline. In this solution, the previously obtained diazonium solution was dropped to maintain the pH at 4.5 to 6.0, and stirred to complete the coupling reaction. Use 25% sodium hydroxide to obtain The pH of the reaction liquid became 9.0, and after salting out with sodium chloride, filtration was performed to obtain 50 parts of a wet cake of the trisazo compound represented by formula (107).

(Step 4)

80 parts of the obtained wet cake of the trisazo compound (107) was added to 300 parts of water and stirred to suspend it. The pH was maintained at 4.0 to 4.5 using 35% hydrochloric acid and stirred at 50 to 60°C for 5 days. Then, after salting out with sodium chloride, 3.0 parts of azo compounds represented by formula (108) were obtained by filtration and drying.

<Production of polarizing film and polarizing plate>

The above-mentioned compound (108) was used in place of the compound (10) used in the preparation of the polarizing film in Example 1, and in the extension treatment, except that the extension treatment was applied for 5 minutes in an aqueous solution containing 30.0 g/l of boric acid at 50°C A polarizing plate was produced in the same manner as in Example 1, and used as a measurement sample of Example 4.

[Example 5]

Except that 22.3 parts of 8-aminonaphthalene-2-sulfonic acid was used in place of 24.7 parts of 8-amino-4-hydroxynaphthalene-2-sulfonic acid in step 1 of Example 4, the same procedure as in Example 4 was carried out to obtain the formula ( 109) 4.0 parts of the azo compound shown in.

<Production of polarizing film and polarizing plate>

Except having used the above-mentioned compound (109) instead of the compound (10) used in the preparation of the polarizing film in Example 1, a polarizing plate was produced in the same manner as in Example 1, and used as a measurement sample of Example 5.

[Example 6]

Except that 18.1 parts of 5-aminoisophthalic acid was used to replace 21.8 parts of 2-amino-5-nitrobenzenesulfonic acid in step 1 of Example 1, the same operation as in Example 1 was carried out to obtain the couple represented by formula (110). 9.0 parts of nitrogen compounds.

<Production of polarizing film and polarizing plate>

Except having used the above-mentioned compound (110) instead of the compound (10) used in the preparation of the polarizing film in Example 1, a polarizing plate was produced in the same manner as in Example 1, and used as a measurement sample of Example 6.

[Example 7]

Except that 18.1 parts of 5-aminoisophthalic acid were used to replace 21.8 parts of 2-amino-5-nitrobenzenesulfonic acid in step 1 of Example 1, and 10.0 parts of 1,5-dihydroxynaphthalene-2-sulfonic acid were used instead Except 10.0 parts of 1,5-dihydroxynaphthalene-2,6-disulfonic acid in Step 3, the same procedure as in Example 1 was carried out to obtain 4.0 parts of the azo compound represented by the formula (111).

<Production of polarizing film and polarizing plate>

Except that the compound (111) was used instead of the compound (10) used in the preparation of the polarizing film in Example 1, a polarizing plate was produced in the same manner as in Example 1, and used as a measurement sample of Example 7.

[Example 8]

In step 3 of Example 4, except that 22.3 parts of 8-aminonaphthalene-2-sulfonic acid was used to replace 24.7 parts of 8-amino-4-hydroxynaphthalene-2-sulfonic acid, it was obtained in the same manner as in Example 4 4.0 parts of the azo compound represented by formula (112).

<Production of polarizing film and polarizing plate>

Except having used the above-mentioned compound (112) instead of the compound (10) used in the preparation of the polarizing film in Example 1, a polarizing plate was produced in the same manner as in Example 1, and used as a measurement sample of Example 8.

[Example 9]

(step 1)

Suspend 23.0 parts of 2-aminobenzothiazole-6-sulfonic acid in 130 parts of 50% sulfuric acid. Under stirring, 34.0 parts of 40% nitrososulfuric acid was dropped in about 20 minutes at 5 to 10°C to obtain Diazonium reaction solution. On the other hand, 22.3 parts of 8-aminonaphthalene-2-sulfonic acid was added to 200 parts of water and dissolved in a 25% aqueous sodium hydroxide solution to become weakly alkaline. In this solution, the previously obtained diazonium solution was dropped to maintain the pH at 4.5 to 6.0, and stirred to complete the coupling reaction. Thereafter, after salting out with sodium chloride, filtration was performed to obtain 241 parts of a wet cake of the monoazo compound represented by the formula (113).

(Step 2)

241 parts of the obtained wet cake of the monoazo compound (113) was added to 300 parts of water, and stirred and suspended. 25% sodium hydroxide was used to make the pH of the aforementioned suspension 9.0, and 34.5 parts of 40% sodium nitrite aqueous solution was added here. The obtained suspension was dropped into a mixed liquid of 200 parts of water and 50 parts of 35% hydrochloric acid to prepare a diazonium liquid. On the other hand, 22.3 parts of 8-aminonaphthalene-2-sulfonic acid was added to 200 parts of water and dissolved in a 25% aqueous sodium hydroxide solution to become weakly alkaline. In this solution, the previously obtained diazonium solution was dropped to maintain the pH at 4.5 to 6.0, and stirred to complete the coupling reaction. Thereafter, after salting out with sodium chloride, filtration was performed to obtain 342 parts of a wet cake of the disazo compound represented by the formula (114).

(Step 3)

34.2 parts of the obtained wet cake of the bisazo compound (114) was added to 200 parts of water, and stirred and suspended. Use 25% sodium hydroxide to make the pH of the aforementioned suspension 9.0, and add 6.9 parts of 40% sodium nitrite aqueous solution here. The obtained suspension was dropped into a mixed liquid of 100 parts of water and 20 parts of 35% hydrochloric acid to prepare a diazonium liquid. On the other hand, 10.0 parts of 1,5-dihydroxynaphthalene-2,6-disulfonic acid was added to 200 parts of water, and dissolved in a 25% aqueous sodium hydroxide solution to be weakly alkaline. In this solution, the previously obtained diazonium solution was dropped to maintain the pH at 6.5 to 8.0, and stirred to complete the coupling reaction. Then, after salting out with sodium chloride, 14.0 parts of azo compounds represented by formula (30) were obtained by filtration and drying.

<Production of polarizing film and polarizing plate>

Except having used the above-mentioned compound (30) instead of the compound (10) used in the preparation of the polarizing film in Example 1, a polarizing plate was produced in the same manner as in Example 1, and used as a measurement sample of Example 9.

[Comparative Example 1]

14 parts of 4-((4-aminophenyl)diazenyl)benzenesulfonic acid was added to 200 parts of water, and stirred and suspended. 25% sodium hydroxide was used to make the pH of the aforementioned suspension 9.0, and 9.1 parts of 40% sodium nitrite aqueous solution was added here. The obtained suspension was dropped into a mixed liquid of 100 parts of water and 20 parts of 35% hydrochloric acid to prepare a diazonium liquid. On the other hand, 16.0 parts of 1,5-dihydroxynaphthalene was added to 200 parts of water and dissolved in a 25% sodium hydroxide aqueous solution to become weakly alkaline. In this solution, the previously obtained diazonium solution was dropped to maintain the pH at 6.5 to 8.0, and stirred to complete the coupling reaction. Then, after salting out with sodium chloride, 10.0 parts of azo compounds represented by formula (115) were obtained by filtration and drying.

<Production of polarizing film and polarizing plate>

Except having used the above-mentioned compound (115) instead of the compound (10) used in the production of the polarizing film in Example 1, a polarizing plate was produced in the same manner as in Example 1, and used as a measurement sample of Comparative Example 1.

[Comparative Example 2]

In step 1 of Example 1, except that 21.8 parts of 2-amino-5-nitrobenzenesulfonic acid were replaced with 47.3 parts of 8-amino-8-toluenesulfonyloxynaphthalene-3 and 6-disulfonic acid Other than that, the same operations as in step 1 and step 2 of Example 1 were carried out to obtain 300 parts of a wet cake of the azo compound represented by formula (116).

Add 300 parts of the obtained wet cake of the bisazo compound (116) to 800 parts of water and stir to suspend it. Use 25% sodium hydroxide aqueous solution to maintain the pH at 10.5 to 11.0, and stir at 70 to 90°C 2 hours. Then, after salting out with sodium chloride, 30.0 parts of azo compounds represented by formula (117) were obtained by filtration and drying.

<Production of polarizing film and polarizing plate>

Except that the compound (117) was used instead of the compound (10) used in the preparation of the polarizing film in Example 1, a polarizing plate was produced in the same manner as in Example 1, and used as a measurement sample of Comparative Example 2.

[Comparative Example 3]

<Production of polarizing film and polarizing plate>

It was produced in the same manner as in Example 1, except that the following compound (118) described in Example 2 in JP 2003-64276 A was used instead of the compound (10) used in the preparation of the polarizing film in Example 1. A polarizing plate was used as a measurement sample of Comparative Example 3.

[Comparative Example 4]

<Production of polarizing film and polarizing plate>

It was produced in the same manner as in Example 1, except that the following compound (119) described in Example 2 in Japanese Patent Publication No. 60-168743 was used instead of the compound (10) used in the preparation of the polarizing film in Example 1. Polarizing plate was used as the measurement sample of Comparative Example 4.

[Comparative Example 5]

<Production of polarizing film and polarizing plate>

Except that the following compound (120) described in Compound Example No. 1 in JP 2001-56412 A was used instead of the compound (10) used in the preparation of the polarizing film in Example 1, the same operation was performed as in Example 1 A polarizing plate was produced and used as a measurement sample of Comparative Example 5.

[Comparative Example 6]

<Production of polarizing film and polarizing plate>

Except that the following compound (121) described in Japanese Patent Application Laid-Open No. 11-269136 was used instead of the compound (10) used in the preparation of the polarizing film in Example 1, a polarizing plate was produced in the same manner as in Example 1, and used as The measurement sample of Comparative Example 6. However, the following compound (121) is not only insoluble in water, but also not contained in the polyvinyl alcohol film, that is, it has no function as a polarizing film.

(Measurement of polarizing plate's maximum absorption wavelength, its transmittance and degree of polarization)

For the polarizing plates obtained in Examples 1 to 9 and Comparative Examples 1 to 6, the maximum absorption wavelength, the monomer transmittance (%) of the wavelength, and the degree of polarization (%) were measured. In the measurement of the maximum absorption wavelength (nm, λmax) of the polarizer and the calculation of the degree of polarization, the parallel transmittance (Ky,%) and the orthogonal transmittance (Kz,%) when polarized light is incident are measured by a spectrophotometer (Hitachi U-4100 manufactured by Seisakusho) measurement. Here, the parallel transmittance (Ky) means: the transmittance when the absorption axis of the absolute polarizer used in the measurement is parallel to the absorption axis of the polarizer; the orthogonal transmittance (Kz) means: the absolute polarization used in the measurement The transmittance when the absorption axis of the sheet is orthogonal to the absorption axis of the polarizer. The parallel transmittance and orthogonal transmittance of each wavelength are measured at intervals of 5 nm from 380 to 1200 nm. Using the respective measured values, the monomer transmittance of each wavelength is calculated by the following formula (i), and the polarization degree of each wavelength is calculated by the following formula (ii) to obtain the highest value in the range of 380 to 1200 nm The degree of polarization, its maximum absorption wavelength ( λ max), and monomer transmittance. In addition, convert Ky and Kz into absorbance (A _L =log(1/(Ky/100)), A _H =log(1/(Kz/100)), thereby calculating the dichroic ratio Rd(=A _H /A _L =log(Kz/100)/log(Ky/100)). In addition, it was confirmed that the two-color ratio system shows a wavelength range of 5 or more, and the two-color ratio system shows a wavelength range of 10 or more. The results are shown in Table 1. In addition, since the measurement sample of Comparative Example 6 did not show a polarization function, it was not described in Table 1.

Transmittance (%)=(Ky+Kz)/2 (i)

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

[Table 1]

As shown in Table 1, the polarizing plates obtained in Examples 1 to 9 have high polarization performance in the maximum absorption wavelength ( λ max), and any one of them has a dichroic ratio (Rd) of 5 or more in the near infrared region. The absorption anisotropy, that is, has the function of polarization. In addition, even at 900nm or more, it exhibits a dichroic ratio of 10 or more, that is, it has a high degree of polarization in a wide frequency band.

On the other hand, in Comparative Examples 1 to 5, the frequency bands showing a dichroic ratio of 5 or more are all limited to the wavelength range of less than 700 nm. It is found that the compounds of Comparative Examples 1 to 3 and 5, as described in Japanese Patent Application Laid-Open No. 11-269136, even if they have at least one -OH group at the p-position of the diazenyl group, there is almost no With polarizing function. In particular, in Comparative Example 2, since there is no wavelength range where the dichroic ratio is 5 or more, it is found that the polarization function is significantly low. Furthermore, it is known that the λ max of Comparative Example 1, which is similar to the dye represented by the structural formula (III) in JP 11-269136 A, is 540 nm, and a compound similar to the dye represented by the structural formula (X) is used The λ max of Comparative Example 2 is 590 nm, and none of them has a maximum absorption wavelength in the near infrared region in the state of the polarizing plate.

[Production example of neutral gray polarizer]

As the dyeing solution, except for using the compound (14) obtained in Example 2 at a concentration of 0.2%, CI Direct Orange 39 0.07%, CI Direct Red 81 0.02%, and Glauber's salt 0.1% concentration of 45 ℃ aqueous solution, and implementation The manufacturing method of the polarizing film of Example 1 is the same to manufacture the polarizing film. The obtained polarizing film has an average single-plate transmittance of 38% in the range of 380 to 1200 nm, an average light transmittance of 0.02% in the orthogonal position, and a high degree of polarization of more than 10 in the dichroic ratio across the wide band. Moreover, both the parallel position and the orthogonal position show a neutral gray hue in the hue in the visible area. Each sheet of cellulose triacetate film (TAC film; manufactured by Fujifilm Co., Ltd.; trade name TD-80U) is laminated on both sides of the polarizing film via an adhesive of polyvinyl alcohol aqueous solution. Secondly, an AR support (manufactured by NOF Corporation; ReaLook X4010) was laminated on a single-sided TAC film with an adhesive to obtain a neutral gray dye-based polarizer with AR support. The obtained polarizing plate has a neutral gray hue like the polarizing film, and has a high degree of polarization from the visible region to the near-infrared region. The obtained polarizing plate shows long-term durability even in a high-temperature and high-humidity state, and is excellent in light resistance to long-term exposure.

[Industrial availability]

The polarizing film and polarizing plate obtained by using the azo compound represented by formula (1) or its salt can have a high degree of polarization in the infrared region, or the visible region to the infrared region. The obtained polarizing plate exhibits long-term durability even under high temperature and high humidity conditions. Furthermore, it has excellent light resistance to long-term exposure and is extremely useful. Therefore, the polarizing plate obtained by using the azo compound represented by formula (1) or its salt can be applied to sensors, lenses, switching elements, isolators, cameras, and indoor and outdoor measuring instruments that require high degree of polarization. Or in-vehicle devices such as driver perception modules. In addition, it can be better used in infrared-sensing machines, such as infrared panels, spatial infrared touch modules, etc., and by using conventional displays, such as computing Not only visual displays, but also modules that use infrared light can also be provided such as monitors, clocks, notebook computers, word processors, LCD TVs, polarized lenses, polarized glasses, and car navigation.

Claims (15)

An azo compound or a salt thereof, the azo compound is represented by the following formula (1),

In formula (1), A ¹ represents a phenyl group which may have a substituent or a heterocyclic group which may have a substituent, A ² , A ³ , and A ⁴ each independently represent an optionally substituted phenyl group or an optionally substituted naphthyl group, R ¹ represents a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, a substituted or unsubstituted amino group, m represents an integer from 0 to 5, M represents hydrogen atom or ion, metal ion, or ammonium ion, n means 1 or 2, k means 0 or 1, The hydrogen atoms of ring a and ring b may be substituted by the substituent R ¹ and the substituent SO ₃ M. The azo compound or its salt according to the first item of the patent application, wherein A ¹ in the above formula (1) represents a heterocyclic group which may have a substituent. The azo compound or its salt according to the second item of the patent application, wherein the heterocyclic group which may have a substituent is selected from the group consisting of the groups represented by the following formulas (2) to (4) ；

In formulas (2) to (4), X each independently represents a hydrogen atom, a halogen group, a nitro group, a hydroxyl group, a C1 to 4 aliphatic hydrocarbon group, a C1 to 4 alkoxy group, a C1 to 4 aliphatic hydrocarbon group having a sulfonic acid group, and a C1 to 4 aliphatic hydrocarbon group having a hydroxyl group. 4 aliphatic hydrocarbon groups, C1 to 4 aliphatic hydrocarbon groups having carboxyl groups, C1 to 4 alkoxy groups having sulfonic acid groups, C1 to 4 alkoxy groups having hydroxyl groups, C1 to 4 alkoxy groups having carboxyl groups base, q ¹ represents an integer from 0 to 4, q ² represents an integer from 0 to 6, M represents hydrogen atom or ion, metal ion, or ammonium ion, n ¹ and n ² each represent an integer from 0 to 3, In each formula, * represents the bonding position with the azo bond. The azo compound or its salt according to any one of the 1st to 3rd items of the patent application, wherein, in the above formula (1), A ² , A ³ , and A ⁴ are each independently represented by the following formula (5) Or as shown in formula (6), at least one of A ² , A ³ , and A ⁴ is as shown in formula (5);

In formula (5), R ² represents a hydrogen atom, a hydroxyl group, a C1 to 4 aliphatic hydrocarbon group, a C1 to 4 alkoxy group, a substituted or unsubstituted amine group, or a C1 to 4 alkoxy group having a sulfonic acid group, m ² represents an integer from 0 to 6, M represents hydrogen atom or ion, metal ion, or ammonium ion, n ³ represents an integer from 0 to 2;

In formula (6), R ¹¹ and R ¹² each independently represent a hydrogen atom, a C1 to 4 aliphatic hydrocarbon group, a C1 to 4 alkoxy group, a C1 to 4 alkoxy group having a hydroxyl group, or a C1 to 4 alkoxy group having a sulfonic acid group base. The azo compound or its salt described in the first item of the scope of patent application, wherein the above formula (1) is represented by the following formula (7),

In formula (7), A ⁵ is the same as A ¹ in the above formula (1), R ³ and R ⁴ each independently represent a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, a substituted or unsubstituted amino group, m ³ and m ⁴ each represent an integer from 0 to 5, M represents hydrogen atom or ion, metal ion, or ammonium ion, n ⁴ represents 1 or 2. The azo compound or its salt described in item 1 of the patent application, wherein the above formula (1) is represented by the following formula (8),

In formula (8), A ⁶ is the same as A ¹ in the above formula (1), R ⁵ , R ⁶ , and R ⁷ each independently represent a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, a substituted or unsubstituted amino group, m ⁵ to m ⁷ each represent an integer from 0 to 5, M represents hydrogen atom or ion, metal ion, or ammonium ion, n ⁵ represents 1 or 2. The azo compound or its salt described in item 1 of the patent application, wherein the above formula (1) is represented by the following formula (9),

In formula (9), R ⁸ , R ⁹ , and R ¹⁰ each independently represent a hydrogen atom, a hydroxyl group, a C1 to 4 alkoxy group, a substituted or unsubstituted amino group, m ⁸ to m ¹⁰ each represent an integer from 0 to 5, M represents hydrogen atom or ion, metal ion, or ammonium ion, n ⁶ represents 1 or 2. A polarizing film containing at least one of the azo compound or its salt as described in any one of items 1 to 7 in the scope of the patent application. The polarizing film described in item 8 of the scope of patent application, wherein the ratio of the absorbance of the axis showing the highest transmittance to polarized light (A _L ) to the absorbance of the axis showing the lowest transmittance to polarized light (A _H ) is Rd(= A _H /A _L ) At least one of the wavelengths showing a value of 5 or more is 700 to 1500 nm. The polarizing film as described in item 8 or 9 of the scope of patent application, which contains the azo compound or salt thereof as described in any one of items 1 to 7 in the scope of patent application, and one or more kinds of the azo compound or Organic dyes other than its salt. The polarizing film described in any one of items 8 to 10 in the scope of patent application shows neutral gray. The polarizing film according to any one of items 8 to 11 in the scope of the patent application, wherein a film containing polyvinyl alcohol resin or a derivative thereof is used as a substrate. A polarizing plate is provided with a transparent protective layer on at least one side of the polarizing film as described in any one of items 8 to 12 in the scope of patent application. A display device that uses the polarizing film described in any one of the 8th to 12th patent application scope or the polarizing plate described in the 13th patent application scope. For example, the display device described in item 14 of the scope of patent application is for vehicles or outdoor display users.