JP5017961B2 - Azo compound and polarizing film containing the compound - Google Patents

Description

  The present invention relates to a dye-based polarizing film used for in-vehicle car navigation, a liquid crystal display (LCD) such as a liquid crystal projector, and a flat panel display (FPD) such as a projection television, and an azo compound suitable for the polarizing film.

Liquid crystal display devices (LCD) such as in-vehicle car navigation systems and liquid crystal projectors, and flat panel display devices (FPD) such as projection televisions have come to be used outdoors because of increased light intensity. A polarizing film used in such an apparatus is required to have not only a high degree of polarization but also light resistance such that the transmittance does not decrease even when irradiated with light for a long time at a high temperature.
The polarizing film of the apparatus includes a polarizing film substrate such as a stretched and oriented film of polyvinyl alcohol or a derivative thereof, a polarizing film containing iodine or a dichroic dye as a polarizing material, or a polyvinyl chloride film. An oriented polarizing film produced by producing polyene by dehydration of hydrochloric acid or polyvinyl alcohol film is used.
And in patent document 1, the dye-type polarizing film using the azo compound or its salt represented by a following formula as a polarizing material as a dichroic dye has a high degree of polarization, and also the light resistance in high temperature is excellent. Is disclosed.

JP 2001-240762 A (page 7, formula (Ib))

Recently, with many LCDs and FPDs being used, further improvement in light resistance in polarizing films has been demanded.
An object of the present invention is to provide a polarizing film having a further improved light resistance as well as high polarizing performance and a dye compound for a polarizing film that provides the polarizing film.

（式中、Ａは、スルホ及びカルボキシからなる群から選ばれる少なくとも１種の水溶性基を１〜２個有するフェニル又は該水溶性基を１〜３個有するナフチルを表す。Ｒ¹ 、Ｒ² 、Ｒ³ 、Ｒ⁴ 、Ｒ⁵ 及びＲ⁶ は、同一であっても相異なっていてもよく、水素原子、炭素数１〜４のアルキル又は炭素数１〜４のアルコキシを表す。Ｘは、−Ｎ＝Ｎ−又は−ＮＨＣＯ−を表し、Ｙ^１及びＹ^２は、同一であっても相異なっていてもよく、カルボキシ、スルホ及びヒドロキシルからなる群から選ばれる少なくとも１種の官能基を有する炭化水素基又は水素原子を表す。Ｙ^１及びＹ^２の少なくとも一方は該炭化水素基であり、Ｚは、カルボキシ又はスルホを表す。） The present invention is an azo compound represented by the formula (I) and a polarizing film having the compound.

(In the formula, A represents phenyl having 1-2 water-soluble groups selected from the group consisting of sulfo and carboxy, or naphthyl having 1-3 water-soluble groups. R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ may be the same or different and each represents a hydrogen atom, alkyl having 1 to 4 carbon atoms or alkoxy having 1 to 4 carbon atoms, X being -N = N- or -NHCO-, Y ¹ and Y ² may be the same or different and have at least one functional group selected from the group consisting of carboxy, sulfo and hydroxyl Represents a hydrocarbon group or a hydrogen atom, at least one of Y ¹ and Y ² is the hydrocarbon group, and Z represents carboxy or sulfo.)

  The polarizing film containing the compound of the present invention has a high degree of polarization, and the polarizing film of the present invention does not deteriorate even when irradiated with light for a long time, that is, has excellent light resistance.

Hereinafter, the present invention will be described in detail.
A in the formula (I) represents phenyl having 1 to 2 at least one water-soluble group selected from the group consisting of sulfo and carboxy, or naphthyl having 1 to 3 water-soluble groups. That is, A is phenyl having 1 to 2 sulfo and / or carboxyl bonded thereto, or naphthyl having 1 to 3 sulfo and / or carboxyl bonded thereto.
Examples of the phenyl include monosulfophenyl such as 2-sulfophenyl, 3-sulfophenyl and 4-sulfophenyl, monocarboxyphenyl such as 2-carboxyphenyl, 3-carboxyphenyl and 4-carboxyphenyl, 2,4- Examples include disulfophenyl such as disulfophenyl and 2,5-disulfophenyl, 3,5-dicarboxyphenyl, 2-carboxy-4-sulfophenyl, and 2-carboxy-5-sulfophenyl. Phenyl is preferred because it is readily available.

  Examples of naphthyl include 5-sulfo-2-naphthyl, 6-sulfo-2-naphthyl, 7-sulfo-2-naphthyl, 8-sulfo-2-naphthyl, 4-sulfo-1-naphthyl, 5- Monosulfonaphthyl such as sulfo-1-naphthyl, 6-sulfo-1-naphthyl, 7-sulfo-1-naphthyl, 6,8-disulfo-2-naphthyl, 4,8-disulfo-2-naphthyl, 5,7 -Disulfonaphthyl such as disulfo-2-naphthyl, 3,6-disulfo-2-naphthyl, 3,6-disulfo-1-naphthyl, 4,6-disulfo-1-naphthyl, 3,6,8-trisulfo -2-naphthyl, 4,6,8-trisulfo-2-naphthyl, and the like. Among them, disulfonaphthyl is preferable because it is easily available, and disulfo-2-naphthyl is particularly preferable. .

R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ in the formula (I) are the same or different from each other and represent a hydrogen atom, alkyl having 1 to 4 carbon atoms or alkoxy having 1 to 4 carbon atoms. . The alkyl and alkoxy may be linear or branched. Specific examples of alkyl include methyl, ethyl and propyl, and specific examples of alkoxy include methoxy, ethoxy and propoxy.
R ^{1 to} R ⁶ are particularly preferably a hydrogen atom, methyl or methoxy from the viewpoint of the degree of polarization.

  X in the formula (I) represents -N = N- or -NHCO-. Z represents carboxy or sulfo.

Y ¹ and Y ² are the same or different, carboxy, at least one hydrocarbon group functional group is attached are selected from the group consisting of sulfo and hydroxy, or represents a hydrogen atom, the Y ¹ and Y ² At least one is the hydrocarbon group.
Examples of the group of —NY ¹ Y ² include —NHCH ₂ COOH, —NHC ₂ H ₄ COOH,
_{-NHC 3 H 6 COOH, -NHC 4} H 8 COOH, -NHC 2 H 4 OH,
_{-NHC 2 H 4 SO 3 H,} -NHCH (CH 3) COOH,
_{-NH (COOH) CH 2 OH,} -NHCH (COOH) CH (CH 3) 2,
_{-NHCH (COOH) CH 2 CH (} CH 3) 2, -NH (COOH) CH 2 COOH,
_{-NH (COOH) C 2 H 4} COOH, etc. -NH (COOH) CH (OH) CHCH 3 and the like.

（式中、Ｙは、塩素原子、臭素原子などのハロゲン原子を表し、Ｚは前記と同じ意味を表す。） The azo compound (I) or a salt thereof can be produced, for example, by the method described below.
That is, first, the following formula (II-1)

(In the formula, Y represents a halogen atom such as a chlorine atom or a bromine atom, and Z represents the same meaning as described above.)

（式中、Ｙ^１及びＹ^２は前記と同じ意味を表す。） An amine compound represented by the following formula (II-2) in an aqueous solvent:

(In the formula, Y ¹ and Y ² represent the same meaning as described above.)

（式中、Ｙ^１、Ｙ^２、及びＺは前記と同じ意味を表す。）
で示される中間体を得る。ついで、上記（II−3）で得られる中間体を、水性溶媒中、ニトロ基の還元を行い、下式（II−4） With the following formula (II-3)

(In the formula, Y ¹ , Y ² , and Z have the same meaning as described above.)
An intermediate represented by is obtained. Subsequently, the intermediate obtained in the above (II-3) is subjected to reduction of the nitro group in an aqueous solvent, and the following formula (II-4)

（式中、Ｙ^１、Ｙ^２、及びＺは前記と同じ意味を表す。）
で示される芳香族アミン化合物を得る。

(In the formula, Y ¹ , Y ² , and Z have the same meaning as described above.)
The aromatic amine compound shown by is obtained.

（式中、Ｙ^１、Ｙ^２、及びＺは前記と同じ意味を表す。）
で示されるカルバメート化合物を得る。 Next, the aromatic amine compound obtained in the above (II-4) is reacted with phenyl chlorocarbonate in an aqueous solvent to give the following formula (III)

(In the formula, Y ¹ , Y ² , and Z have the same meaning as described above.)
Is obtained.

（式中、Ａ、Ｘ、Ｒ¹、Ｒ²、Ｒ³、Ｒ⁴、Ｒ⁵及びＲ⁶は、前記と同じ意味を表す。）
で示されるアゾ中間化合物とを、水性溶媒中、２０〜６０℃で反応させることにより、アゾ化合物（I）を得ることができる。 This carbamate compound is then combined with the formula (IV)

(In the formula, A, X, R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ represent the same meaning as described above.)
The azo compound (I) can be obtained by reacting with an azo intermediate compound represented by the formula (2) in an aqueous solvent at 20 to 60 ° C.

  The aqueous solvent is an organic compound that can be arbitrarily mixed with water, or a mixed solvent of the organic compound and water. As the organic compound that can be arbitrarily mixed with water, alcohols having 1 to 3 carbon atoms such as methanol, ethanol, and propanol are usually used.

When an example of the azo compound (I) is represented by a sodium salt, compounds of the formulas (I-1) to (I-10) are exemplified.

  Sulfo and carboxy contained in the azo compound (I) exist as anions together with cations such as alkali metal ions and ammonium ions such as lithium ions, sodium ions and potassium ions, or like ethanolamine and alkylamine. It exists as a sulfonic acid group or a carboxyl group together with other organic amines. When the azo compound (I) is contained in the polarizing film substrate, it is preferably used in the form of an anion together with sodium ions.

The polarizing film of the present invention comprises the azo compound in a polarizing film substrate.
In addition to the azo compound, the polarizing film can contain other organic dyes to correct hue and improve polarization performance. The organic dye used in this case may be any dye as long as it has high dichroism, but a polarizing film suitable for liquid crystal projector applications can be obtained by selecting a dye that is particularly excellent in light resistance. .
In particular, when a dye having a maximum absorption wavelength in the range of 500 to 570 nm is used, the hue can be corrected and the polarization performance can be improved.

Examples of the dye having a maximum absorption wavelength in the range of 500 to 570 nm include compounds represented by the following formula (V).

Here, D in the formula (V) represents phenyl having 1 to 2 sulfo and / or carboxy, or naphthyl having 1 to 3 sulfo. The phenyl or naphthyl of D may be bonded with 1 to 2 alkyls having 1 to 4 carbon atoms and / or alkoxy having 1 to 4 carbon atoms.
Examples of the phenyl of D include monosulfophenyl such as 2-sulfophenyl, 3-sulfophenyl and 4-sulfophenyl; monocarboxyphenyl such as 2-carboxyphenyl, 3-carboxyphenyl and 4-carboxyphenyl; 2,4 Disulfophenyl such as disulfophenyl, 2,5-disulfophenyl; 3,5-dicarboxyphenyl; carboxysulfophenyl such as 2-carboxy-4-sulfophenyl, 2-carboxy-5-sulfophenyl; 2 -Alkylsulfophenyl such as methyl-4-sulfophenyl, 3-methyl-4-sulfophenyl, 2-methyl-4-sulfophenyl, 2,5-dimethyl-4-sulfophenyl; 3-methyl-4-carboxyphenyl , 2,5-dimethyl-4-carboxyphenyl and the like Alkoxysulfophenyl such as 2-methoxy-4-sulfophenyl, 3-methoxy-4-sulfophenyl, 2,5-dimethoxy-4-sulfophenyl; 2-methoxy-4-carboxyphenyl, 3-methoxy And alkoxycarboxyphenyl such as -4-carboxyphenyl and 2,5-dimethoxy-4-carboxyphenyl.
Among them, monosulfophenyl is preferable because it is easily available.

Examples of the naphthyl of D include, for example, 5-sulfo-2-naphthyl, 6-sulfo-2-naphthyl, 7-sulfo-2-naphthyl, 8-sulfo-2-naphthyl, 4-sulfo-1-naphthyl, Monosulfonaphthyl such as 5-sulfo-1-naphthyl, 6-sulfo-1-naphthyl, 7-sulfo-1-naphthyl; 6,8-disulfo-2-naphthyl, 4,8-disulfo-2-naphthyl, 5 , 7-disulfo-2-naphthyl, 3,6-disulfo-2-naphthyl, 3,6-disulfo-1-naphthyl, 4,6-disulfo-1-naphthyl; 3,6,8- And trisulfonaphthyl such as trisulfo-2-naphthyl and 4,6,8-trisulfo-2-naphthyl.
As naphthyl, disulfonaphthyl is preferable because it is easily available, and disulfo-2-naphthyl is particularly preferable.

R < ⁷ >, R <^8> , R < ⁹ > and R < ¹⁰ > in the formula (V) are the same or different from each other, and represent a hydrogen atom, alkyl having 1 to 4 carbon atoms or alkoxy having 1 to 4 carbon atoms. The alkyl and alkoxy may be linear or branched. Specific examples of alkyl include methyl, ethyl and propyl, and specific examples of alkoxy include methoxy, ethoxy and propoxy.
R ^{7 to} R ¹⁰ are particularly preferably a hydrogen atom, methyl or methoxy from the viewpoint of the degree of polarization.

E represents -NH-, -N = N- or -NHCO-.
F represents phenyl, and 1 to 2 groups selected from the group consisting of hydroxy, amino, alkyl having 1 to 4 carbons, alkoxy having 1 to 4 carbons and sulfo are bonded to phenyl of F. Also good. Here, examples of the alkyl and alkoxy include groups exemplified as R ^{7 to} R ¹⁰ . As F, phenyl, 4-aminophenyl and hydroxyphenyl are preferable because of easy production.
n represents 0 or 1, and particularly when n is 0, it is preferable because production is easy.

When the compound of formula (V) is represented by a sodium salt, formulas (V-1) to (V-7) are exemplified.

  Sulfo and carboxy contained in the compound (V) are present as anions together with cations such as alkali metal ions such as lithium ion, sodium ion and potassium ion, ammonium ions, or like ethanolamine and alkylamine. It exists as a sulfonic acid group or a carboxyl group together with an organic amine. When the compound (V) is contained in the polarizing film substrate, it is preferably used in the form of an anion together with sodium ions.

（式中、ｎ、Ｄ、Ｒ^７〜Ｒ^１０は前記と同じ意味を表す。） The compound represented by the formula (V) can be produced by a method according to the azo compound (I).
Specifically, after the azo compound represented by the following formula is reacted with sodium nitrite at 0 to 40 ° C. in an acidic aqueous solvent,

(In the formula, n, D, and R ^{7 to} R ¹⁰ represent the same meaning as described above.)

（式中、Ｅ及びＦは前記と同じ意味を表す。） Compound (V) can be obtained by reacting a compound represented by the following formula in an aqueous solvent at 0 to 40 ° C. and pH 6 to 11.

(In the formula, E and F have the same meaning as described above.)

The polarizing film of the present invention contains a azo compound (I), preferably a dye having a maximum absorption wavelength in the range of 500 to 570 nm, such as a compound of formula (V), and other organic dyes as required. The dichroic dye containing can be manufactured by making it contain in a polymeric film-like polarizing film base material by a well-known method.
Examples of the polarizing film substrate used in the polarizing film of the present invention include those made of polyvinyl alcohol resin, polyvinyl acetate resin, ethylene / vinyl acetate (EVA) resin, nylon resin, polyester resin and the like. The polyvinyl alcohol-based resin here includes polyvinyl alcohol itself, which is a part of polyvinyl acetate or a completely saponified product, as well as other copolymerizable monomers such as saponified EVA resin, for example, Saponified copolymers of olefins such as ethylene and propylene, unsaturated carboxylic acids such as crotonic acid, acrylic acid, methacrylic acid and maleic acid, unsaturated sulfonic acids and vinyl ethers, and also polyvinyl alcohol And polyvinyl acetal modified with aldehyde.
As the polarizing film substrate, a polyvinyl alcohol film, particularly a polyvinyl alcohol film, is preferably used from the viewpoint of the adsorptivity and orientation of the dye.

  As a method for incorporating a dichroic dye into the polarizing film substrate, a method of dyeing a polymer film is usually employed. Staining can be performed, for example, as follows. First, a dichroic dye is 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 0.0001 to 10% by weight. Further, if necessary, a dyeing assistant may be used. For example, it is preferable to use 1 to 10% by weight of sodium sulfate in the dye bath. Dyeing is performed by immersing the polymer film in the dye bath thus prepared. The dyeing temperature is preferably 40 to 80 ° C. The orientation of the dichroic dye is performed by stretching a polymer film. As a stretching method, any known method such as a wet method or a dry method may be employed. The polymer film may be stretched before dyeing or after dyeing.

  The polymer film containing the dichroic dye and oriented is subjected to post-treatment such as boric acid treatment by a known method, if necessary. Such post-processing is performed for the purpose of improving the light transmittance, polarization degree, and durability of the polarizing film. The conditions for the boric acid treatment vary depending on the type of polymer film used and the type of dye used, but generally the boric acid concentration in the boric acid aqueous solution is in the range of 1 to 15% by weight, preferably in the range of 5 to 10% by weight. The treatment is usually performed in a temperature range of 30 to 80 ° C, preferably 50 to 80 ° C. Further, if necessary, the fixing treatment may be performed together with an aqueous solution containing a cationic polymer compound.

  The polarizing film thus obtained can be made into a polarizing plate by bonding a protective film excellent in optical transparency and mechanical strength on one or both surfaces thereof. The material for forming the protective film may be those conventionally used. For example, in addition to a cellulose acetate film and an acrylic film, a fluororesin film such as a tetrafluoroethylene / hexafluoropropylene copolymer Polyester film, polyolefin film, polyamide film and the like are used.

The polarizing film containing the azo compound or a salt thereof of the present invention exhibits a high degree of polarization comparable to that of an iodine-based polarizing film, and is excellent in durability and light resistance against long-time exposure.
The polarizing film of the present invention can be suitably used for a large amount of liquid crystal display device such as a car navigation system, a liquid crystal projector, and a projection television because of its excellent characteristics.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples. In the examples, “%” and “parts” are by weight and parts by weight unless otherwise specified.

で示される芳香族ニトロ化合物23.8部を、水100部に加えた後、水酸化ナトリウム５部を加え、その後、β−アラニン178部を加え、90℃で、5時間保温した。 Example 1
Formula (1-1)

After adding 23.8 parts of the aromatic nitro compound represented by the formula (1) to 100 parts of water, 5 parts of sodium hydroxide was added, then 178 parts of β-alanine was added, and the mixture was kept at 90 ° C. for 5 hours.

After confirming the disappearance of the aromatic nitro compound represented by the formula (1-1), the mixture was cooled and the precipitated crystals were filtered to obtain an intermediate represented by the formula (1-2).

Thereafter, the whole amount of the intermediate (1-2) obtained above was subjected to iron powder reduction in water to obtain an intermediate represented by the formula (1-3).

Subsequently, 13 parts of the intermediate represented by the formula (1-3) was dissolved in 100 parts of water, and then adjusted to pH 7 to 8 with a 15% aqueous sodium carbonate solution at a temperature of 20 to 25 ° C. The portion was added dropwise over 30 minutes. After completion of the dropwise addition, the mixture was stirred at the same temperature and the same pH for 1 hour, and then the precipitated crystals were filtered to obtain an intermediate represented by the formula (1-4).

The total amount of intermediate (1-4) obtained above and formula (2)

7 parts of a disazo intermediate compound represented by formula (1) is added to a mixed solution of 100 parts of water and 100 parts of N-methylpyrrolidone, and stirred for 3 hours at a temperature of 40 to 45 ° C. while adjusting the pH to 8 to 9 with a 15% aqueous sodium carbonate solution. did. After removing insolubles by filtration, 300 parts of ethanol was added to the filtrate to precipitate crystals. After filtering the precipitated crystals, the obtained cake was dissolved again in a mixed solution of 220 parts of water and 80 parts of N-methylpyrrolidone. By adding 30 parts of sodium chloride to this solution and filtering the precipitated crystals, a salt of the disazo compound represented by (I-1) is obtained. This salt has a wavelength of λmax (maximum absorption wavelength) of 406 nm in an aqueous medium. Indicated.

(Production example of polarizing film)
A polyvinyl alcohol film [Kuraray Vinylon # 7500, Kuraray Co., Ltd.] having a thickness of 75 μm was stretched 5 times along a longitudinal axis to obtain a polarizing film substrate. While maintaining this polyvinyl alcohol film in a tensioned state, 0.025% of the salt of the disazo compound represented by the formula (I-1) obtained in Example 1 and 2.0% of mirabilite as a dyeing assistant It was immersed in the 70 degreeC aqueous solution made into the density | concentration. Next, the film was immersed in a 7.5% boric acid aqueous solution at 78 ° C. for 5 minutes, then taken out, washed with 20 ° C. water for 20 seconds, and dried at 50 ° C. to obtain a polarizing film. The obtained polarizing film had a λmax (wavelength at which the transmittance in the stretching direction of the film was minimized) was 440 nm.
When the obtained polarizing film was irradiated with a high-pressure mercury lamp with an illuminance of 520 mW / cm ² (red light) for 48 hours under the condition of 100 ° C., the value of ΔA (%) was 89 (%), Light resistance to long-term exposure at high temperatures was also excellent. ΔA (%) is the absorbance value at 0 hour A (0), and the absorbance value 48 hours later is A (48).
ΔA (%) = (A (48) / A (0)) x 100
Is defined. It shows that it is excellent in light resistance, so that the value of (DELTA) A is large.

(Example 2)
In an aqueous solution at 70 ° C. prepared in the same manner as in Example 1 at a concentration of 0.08% for azo compound (I-1) and 0.005% for compound (V-4) and 2.0% for mirabilite as a dyeing assistant Soaked. Next, the film was immersed in a 7.5% boric acid aqueous solution at 78 ° C. for 5 minutes, then taken out, washed with 20 ° C. water for 20 seconds, and dried at 50 ° C. to obtain a polarizing film. Λmax of the obtained polarizing film was 440 nm.
When the obtained polarizing film was irradiated with a high-pressure mercury lamp with an illuminance of 520 mW / cm ² (red light) for 48 hours under the condition of 100 ° C., the value of ΔA (%) was 86 (%), Light resistance to long-term exposure at high temperatures was also excellent.

(Example 3)
Prepared in the same manner as in Example 1 in an aqueous solution at 70 ° C. having a concentration of 0.08% azo compound (I-1), 0.005% compound (V-2), and 2.0% mirabilite as a dyeing assistant. Soaked. Next, the film was immersed in a 7.5% boric acid aqueous solution at 78 ° C. for 5 minutes, then taken out, washed with 20 ° C. water for 20 seconds, and dried at 50 ° C. to obtain a polarizing film. Λmax of the obtained polarizing film was 440 nm.
When the obtained polarizing film was irradiated with a high-pressure mercury lamp with an illuminance of 520 mW / cm ² (red light) for 48 hours under the condition of 100 ° C., the value of ΔA (%) was 84 (%), Light resistance to long-term exposure at high temperatures was also excellent.

(Comparative Example 1)
Instead of the polarizing film dye containing the azo compound (I-1), a polarizing film was obtained in the same manner as in Example 2 using the compound represented by the formula (1b) on page 7 of Patent Document 1. . Λmax of the obtained polarizing film was 440 nm. When the value of light resistance ΔA was determined in the same manner as in Example 1, the value of ΔA (%) was only 76 (%), and the light resistance was inferior to the polarizing film of the present invention.

  The polarizing film of the present invention is excellent in light resistance in addition to high polarization performance, so it is suitable for use in liquid crystal display devices (LCD) such as car navigation and liquid crystal projectors, flat panel display devices (FPD) such as projection televisions, etc. can do.

Claims (13)

An azo compound represented by the formula (I).

(In the formula, A represents phenyl having 1-2 water-soluble groups selected from the group consisting of sulfo and carboxy, or naphthyl having 1-3 water-soluble groups. R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ may be the same or different and each represents a hydrogen atom, alkyl having 1 to 4 carbon atoms or alkoxy having 1 to 4 carbon atoms, X being -N = N- or -NHCO-, Y ¹ and Y ² may be the same or different and have at least one functional group selected from the group consisting of carboxy, sulfo and hydroxyl Represents a hydrocarbon group or a hydrogen atom, at least one of Y ¹ and Y ² is the hydrocarbon group, and Z represents carboxy or sulfo.)   The azo compound according to claim 1, wherein the sulfo and carboxy contained in the azo compound (I) are present as an anion together with a cation, or are present as a sulfonic acid group or a carboxyl group together with an organic amine.   The azo compound according to claim 1 or 2, wherein A is monosulfophenyl or disulfonaphthyl. The azo compound according to claim 1, wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are each independently a hydrogen atom, methyl or methoxy. Azo compounds according to claim 1 one of Y ¹ and Y ² are hydrogen atoms.   A polarizing film comprising the polarizing film substrate containing the azo compound according to claim 1.   A polarizing film comprising the polarizing film substrate containing the azo compound according to claim 1 and a dye having a maximum absorption wavelength in the range of 500 to 570 nm. The polarizing film according to claim 7, wherein the dye having a maximum absorption wavelength in the range of 500 to 570 nm is a compound represented by the following formula (V).

(In the formula, D represents phenyl having 1 to 2 water-soluble groups selected from the group consisting of sulfo and carboxyl, or naphthyl having 1 to 3 water-soluble groups. The naphthyl may have 1 to 2 alkyls having 1 to 4 carbon atoms and / or alkoxy having 1 to 4 carbon atoms, and R ⁷ , R ⁸ , R ⁹ and R ¹⁰ may be the same or different from each other. Differently, a hydrogen atom, alkyl having 1 to 4 carbon atoms or alkoxy having 1 to 4 carbon atoms, E represents —NH—, —N═N— or —NHCO—, F represents phenyl, 1 to 2 groups selected from the group consisting of hydroxy, amino, alkyl having 1 to 4 carbon atoms, alkoxy having 1 to 4 carbon atoms and sulfo may be bonded to phenyl, and n is 0 or 1. To express.) The polarizing film according to claim 8, wherein R ⁷ , R ⁸ , R ⁹ and R ^{10 in the} compound (V) are each independently a hydrogen atom, methyl or methoxy.   The polarizing film according to claim 8 or 9, wherein F in the compound (V) is phenyl having hydroxy or amino.   The polarizing film according to claim 8, wherein D is monosulfophenyl or disulfonaphthyl.   The polarizing film according to any one of claims 6 to 11, wherein the polarizing film substrate is polyvinyl alcohol.   The liquid crystal display device which has a polarizing film in any one of Claims 6-12.