JP7509851B2 - Azo compound or its salt, and polarizing element, polarizing plate, and display device containing the same - Google Patents

Description

The present invention relates to a novel azo compound or a salt thereof, as well as a polarizing element, a polarizing plate, and a display device that contain the same.

Polarizing plates, which have the function of transmitting and blocking light, are basic components of display devices such as liquid crystal displays (LCDs), along with liquid crystals, which have the function of switching light. Applications of LCDs range from small devices such as early calculators and clocks to notebook computers, word processors, LCD projectors, LCD TVs, car navigation systems, and indoor and outdoor measuring devices. They can also be applied to lenses with polarizing functions, and have been used in sunglasses with improved visibility and, in recent years, polarized glasses compatible with 3D TVs. As the uses of polarizing plates have expanded widely, they are used under a wide range of conditions, from low to high temperatures, low to high humidity, and low to high light levels, so polarizing plates with high polarization performance and high durability are in demand.

Polarizing elements are generally manufactured by adsorbing and orienting iodine or a dichroic dye on a substrate such as a stretched and oriented film of polyvinyl alcohol or its derivatives, or a polyene-based film obtained by dehydrochlorinating a polyvinyl chloride film or dehydrating a polyvinyl alcohol film to generate a polyene and orienting the polyene. A polarizing plate obtained by laminating a protective film made of triacetyl cellulose or the like to this polarizing element via an adhesive layer is used in liquid crystal display devices and the like. A polarizing plate using iodine as a dichroic dye is called an iodine-based polarizing plate, while a polarizing plate using a dichroic dye, such as an azo compound having dichroism, as a dichroic dye is called a dye-based polarizing plate. Among these, dye-based polarizing plates have the characteristics of high heat resistance, high humidity and heat resistance, and high stability, and also high color selectivity due to the dye blend, but have the problem of low transmittance and contrast compared to iodine-based polarizing plates with the same polarization degree. For this reason, a polarizing element that maintains high durability, has diverse color selectivity, and has high transmittance and high polarization characteristics is desired.

Until recently, images were displayed at high brightness on LCD displays to increase their clarity. Demand for longer battery life has arisen for hybrid cars and mobile devices that are equipped with such displays, so LCD display manufacturers have been calling for polarizing plates that can maintain image brightness and color clarity even when the brightness is reduced to reduce power consumption.

However, in a polarizing element in which several dyes are adsorbed and oriented on a polymer film, if there is light leakage (color leakage) of a specific wavelength in the wavelength region of the visible light range when the polarizing element is attached to a liquid crystal panel, the hue of the liquid crystal display may change in the dark state. Therefore, in order to prevent discoloration of the liquid crystal display due to color leakage of a specific wavelength in the dark state when the polarizing element is attached to a liquid crystal display device, the orthogonal transmittance (orthogonal transmittance) in the wavelength region of the visible light range must be uniformly low in a neutral color polarizing element in which several dyes are dyed or contained in a polymer film. In addition, for in-vehicle liquid crystal displays, a polarizing plate that does not change in polarization degree even in harsh environments is required because the inside of a car in summer is a high-temperature and high-humidity environment. In the past, iodine-based polarizing plates that have good polarization performance and exhibit a neutral gray color were used. However, as mentioned above, iodine-based polarizing plates have problems in that they are not sufficiently light-resistant, heat-resistant, and moisture-heat-resistant. To solve this problem, dye-based neutral gray polarizing plates dyed or containing several dichroic dyes have come to be used. Dye-based neutral gray polarizers generally use a combination of dyes in the three primary colors of light: red, blue, and yellow. However, as mentioned above, the polarization performance of dye-based neutral gray polarizers is insufficient. Therefore, it was necessary to develop dichroic dyes with good polarization performance for each of the three primary colors.

As mentioned above, the dye system is characterized by the fact that it contains or dyes the three primary color components of light with independent dyes that correspond to each of them in order to control them. The light sources used in recent LCD panels include cold cathode fluorescent lamps and LEDs, but the wavelength of the light emitted from them varies depending on the system, and even for the same system, it often varies depending on the panel manufacturer. Therefore, when developing dichroic dyes with good polarization performance, it is particularly important to design dichroic dyes with absorption wavelengths that match the wavelength of the light source.

Dyes that can be used in the manufacture of dye-based polarizing elements as described above include water-soluble azo compounds described in, for example, Patent Documents 20, 16, 13, 21, and 22.

Even in dye-based polarizing plates with diverse color selectivity, the conventional polarizing elements had a problem that when two polarizing elements were stacked so that the absorption axis directions of the two polarizing elements were parallel to each other (hereinafter also referred to as "parallel position") to display white (hereinafter also referred to as "white display" or "light display"), the white color appeared yellowish. In order to improve the problem of the white color appearing yellowish, even in polarizing elements manufactured with reduced yellowness, the conventional polarizing plates had a problem that when two polarizing elements were stacked so that the absorption axis directions were perpendicular to each other (hereinafter also referred to as "orthogonal position") to display black (hereinafter also referred to as "black display" or "dark display"), the black color appeared blue. Therefore, a polarizing plate that displayed achromatic white color when displayed white and black color when displayed black was required. In particular, it was difficult to obtain a polarizing plate that had high-quality white color when displayed white, commonly known as a paper-white polarizing plate. For a polarizing plate to be achromatic, the transmittance for each wavelength in the parallel and perpendicular directions must be approximately constant regardless of wavelength, but until now it has not been possible to obtain such a polarizing plate.

The reason why the hues are different when displaying white and when displaying black is that the wavelength dependency of the transmittance is not the same between the parallel position and the perpendicular position, and in particular, the transmittance of each wavelength is not constant across the visible light range. Furthermore, the fact that the dichroism is not constant across the visible light range is also one of the factors that makes it difficult to realize an achromatic polarizing plate. Taking an iodine-based polarizing plate as an example, an iodine-based polarizing plate that uses polyvinyl alcohol (hereinafter also referred to as "PVA") as a base material and iodine as a dichroic dye generally has absorption centered at 480 nm and 600 nm. It is said that the absorption at 480 nm is due to a complex of polyiodine I ₃ ^- and PVA, and the absorption at 600 nm is due to a complex of polyiodine I ₅ ^- and PVA. The degree of polarization (dichroism) at each wavelength is higher in the polarization degree (dichroism) based on the complex of polyiodine I ₅ ^- and PVA than in the polarization degree (dichroism) based on the complex of polyiodine I ₃ ^- and PVA. In other words, if the transmittance in the orthogonal direction is made constant at each wavelength, the transmittance in the parallel direction is higher at 600 nm than at 480 nm, and the phenomenon of white being colored yellow when white is displayed occurs. Conversely, if the transmittance at each wavelength in the parallel direction is made constant, the transmittance in the orthogonal direction is lower at 600 nm than at 480 nm, and the black is colored blue when black is displayed. When white is yellow when white is displayed, it is generally not preferable because it gives an impression of deterioration. In addition, when the blue color is lost when black is displayed, it gives an impression of lacking a high-class feeling because it is not a clear black. In addition, in the iodine-based polarizing plate, it is difficult to control the hue mainly around 550 nm where the visibility is high, since there is no complex based on that wavelength.

In this way, the degree of polarization (dichroism) at each wavelength is not constant, resulting in wavelength dependency of the degree of polarization. In addition, since there are only two dichroic dyes at 480 nm and 600 nm, which are absorbed by a complex of iodine and PVA, it is not possible to adjust the hue of an iodine-based polarizing plate made of iodine and PVA. Methods for improving the hue of an iodine-based polarizing plate are described in Patent Documents 1 and 2. Patent Document 1 describes a polarizing plate in which the neutral coefficient is calculated and the absolute value is 0 to 3. Patent Document 2 describes a polarizing film in which the transmittance of each wavelength from 410 nm to 750 nm is set within ±30% of the average value, and the color is adjusted by adding a direct dye, reactive dye, or acid dye in addition to iodine. Patent Document 3 also discloses a technology for an achromatic dyed polarizing plate.

JP 2002-169024 A Japanese Patent Application Laid-Open No. 10-133016 Publication No. WO2014/162635 Japanese Patent Application Laid-Open No. 8-291259 JP 2002-275381 A Publication No. WO2015/152026 Japanese Patent Application Laid-Open No. 1-161202 Japanese Patent Application Laid-Open No. 1-172907 Japanese Patent Application Laid-Open No. 1-183602 Japanese Patent Application Laid-Open No. 1-248105 Japanese Patent Application Laid-Open No. 1-265205 Japanese Patent Publication No. 7-92531 JP 2009-132794 A Patent Document 1: WO2006/057214 Japanese Patent Application Laid-Open No. 11-218611 JP 2001-033627 A JP 2004-251962 A Japanese Patent Application Laid-Open No. 8-291259 JP 2008-065222 A Japanese Patent Application Laid-Open No. 3-12606 JP 2001-240762 A JP 2001-108828 A Japanese Patent Application Laid-Open No. 60-156759

Application of Functional Dyes (CMC Publishing Co., Ltd., 1st edition, supervised by Masahiro Irie, pages 98-100) Dye Chemistry; by Yutaka Hosoda, Gihodo Publishing, 1957

One object of the present invention is to provide a high-performance polarizing plate having excellent polarization performance and moisture resistance, heat resistance and light resistance. Another object of the present invention is to provide a high-performance polarizing plate having a neutral gray color formed by adsorbing and aligning two or more kinds of dichroic dyes in a polymer film, which has no color leakage in the orthogonal phase in the visible light wavelength range and has excellent polarization performance and moisture resistance, heat resistance and light resistance.
A further object of the present invention is to provide a dye-based neutral gray polarizing plate for an in-vehicle liquid crystal display, which has good brightness, polarization performance, durability and light resistance.

As can be seen from, for example, Example 1, the polarizing plate of Patent Document 1 has a low neutral coefficient (Np), but the parallel hue calculated from JIS Z 8729 has an a* value of -1.67 and a b* value of 3.51, so that the plate exhibits a yellowish-green color when displayed in white. The orthogonal hue has an a* value of 0.69, but the b* value is -3.40, so that the polarizing plate exhibits a blue color when displayed in black. The polarizing film of Patent Document 2 is obtained by setting the a and b values in the UCS color space measured using only one polarizing film to an absolute value of 2 or less, and is not capable of simultaneously expressing achromatic colors in both hues when displayed in white and when displayed in black when two polarizing films are stacked. The average single transmittance of the polarizing film of Patent Document 2 was 31.95% in Example 1 and 31.41% in Example 2, which were low values. Thus, the polarizing film of Patent Document 2 has low transmittance and therefore does not have sufficient performance in fields that require high transmittance and high contrast, particularly in fields such as liquid crystal display devices and organic electroluminescence. Furthermore, since the polarizing film of Patent Document 2 uses iodine as the main dichroic dye, it has a large color change after durability tests, particularly after moist heat durability tests (for example, in an environment of 85°C and relative humidity of 85%), and has poor durability.

On the other hand, dye-based polarizing plates have excellent durability, but like iodine-based polarizing plates, their wavelength dependency differs between parallel and perpendicular positions. There are almost no azo compounds that exhibit dichroism, which shows the same hue in parallel and perpendicular positions, and even if they do exist, their dichroism (polarization characteristics) is low. Some azo compounds with dichroism have completely different wavelength dependencies in perpendicular and parallel positions, such as white being yellow when white is displayed and black being blue when black is displayed. In addition, since people's sensitivity to color also differs depending on the brightness of light, even if color correction is performed for dye-based polarizing plates, color correction appropriate for each of the brightness and darkness of light generated by controlling the polarization from the perpendicular position to the parallel position is necessary. An achromatic polarizing plate cannot be achieved unless the transmittance is approximately constant at each wavelength in both parallel and perpendicular positions and has no wavelength dependency. Furthermore, to obtain a polarizing element with high transmittance and high contrast, in addition to simultaneously satisfying a certain transmittance in the parallel and orthogonal positions, the degree of polarization (dichroic ratio) for each wavelength must be high and constant. Even when one type of azo compound is applied to a polarizing element, the wavelength dependence of the transmittance differs between the orthogonal and parallel positions. However, in order to achieve a constant transmittance for each wavelength by blending two or more azo compounds, the relationship between the dichroic ratios of the two or more types must be precisely controlled, taking into account the parallel and orthogonal transmittances of each type.

On the other hand, even if the relationship between the parallel and perpendicular transmittances and the dichroic ratios can be precisely controlled and the transmittance of each wavelength can be made constant, it has not yet been possible to achieve high transmittance and high contrast. In other words, the higher the transmittance or the degree of polarization, the more difficult it is to make the color achromatic, and an achromatic polarizing plate with high transmittance or high polarization has not been achieved. It is very difficult to obtain an achromatic polarizing plate with high transmittance and/or high contrast, and it cannot be achieved by simply applying dichroic dyes of the three primary colors. In particular, it is extremely difficult to simultaneously achieve a constant transmittance of each wavelength in the parallel position and high dichroism. White cannot be expressed as high-quality white even if it is only slightly colored. In addition, white in the bright state is particularly important because it has high luminance and high sensitivity. Therefore, a polarizing element that shows achromatic white like high-quality paper when white is displayed and achromatic black when black is displayed, and has a single transmittance of 35% or more after luminosity correction and a high degree of polarization is required. Patent Document 3 also describes a polarizing plate that is achromatic when displaying white and black, but further improvements in performance are desired.

Therefore, one of the objects of the present invention is to provide a high-performance achromatic polarizing element that has high transmittance and a high degree of polarization, is achromatic in both white and black display modes, and exhibits high-quality white color in particular when displaying white, as well as an achromatic polarizing plate and a liquid crystal display device using the same.

As a result of intensive research conducted by the inventors to achieve this objective, they discovered that polarizing elements and polarizing plates containing specific azo compounds or salts thereof have excellent polarizing performance, moisture resistance, heat resistance, light resistance, etc., and thus completed the present invention.

The inventors have further discovered that by combining the azo compounds of formula (5), formula (6), and formula (1), it is possible to produce a polarizing element whose dichroism is not wavelength dependent, which is achromatic in both the parallel and perpendicular positions, and which has a higher degree of polarization than ever before. The inventors have discovered for the first time that it is possible to achieve wavelength independence in the visible light range even with high transmittance, and have developed a polarizing element with a higher degree of polarization that can achieve a white color with the same quality as high-quality paper, commonly known as paper white.

That is, the present invention relates to the following Inventions 1 to 35, but is not limited thereto.
Invention 1
An azo compound represented by formula (1) or a salt thereof:

In the formula, _Ay1 and _Ay2 each independently represent a naphthyl group which may have a substituent, or a phenyl group which may have a substituent; s and t each independently represent 0 or 1, and either s or t is 1; and _Ry1 to _Ry8 each independently represent a hydrogen atom or a substituent.
Invention 2
2. The azo compound or a salt thereof according to claim 1, wherein at least one of _Ay1 and _Ay2 is a phenyl group which may have a substituent.
Invention 3
The azo compound or a salt thereof according to Invention 2, wherein the phenyl group which may have a substituent has at least one or more substituents selected from the group consisting of a sulfo group, a carboxy group, an alkoxy group having 1 to 4 carbon atoms and a sulfo group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a halogen atom, a nitro group, an amino group, an alkyl-substituted amino group having 1 to 4 carbon atoms, and an alkyl-substituted acylamino group having 1 to 4 carbon atoms.
Invention 4
The azo compound or a salt thereof according to Invention 3, wherein the phenyl group which may have a substituent has at least one substituent selected from the group consisting of a sulfo group, a carboxy group, and an alkoxy group having 1 to 4 carbon atoms and a sulfo group.
Invention 5
The azo compound or a salt thereof according to any one of Inventions 2 to 4, wherein the phenyl group which may have a substituent is represented by the following formula (2):

In the formula, either _Ry9 or _Ry10 is a sulfo group, a carboxy group, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group, and the other is a hydrogen atom, a sulfo group, a carboxy group, an alkoxy group having 1 to 4 carbon atoms and a sulfo group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a halogen atom, a nitro group, an amino group, an alkyl-substituted amino group having 1 to 4 carbon atoms, or an alkyl-substituted acylamino group having 1 to 4 carbon atoms, and * in the formula indicates the bonding position with the NH moiety of the terminal amide group in formula (1) above.
Invention 6
6. The azo compound or a salt thereof according to invention 5, wherein one of _Ry9 and _Ry10 is a sulfo group or a carboxy group, and the other is a hydrogen atom, a sulfo group, a carboxy group, a methyl group, or a methoxy group.
Invention 7
7. The azo compound or a salt thereof according to any one of Inventions 2 to 6, wherein _Ay1 and _Ay2 each independently represent a phenyl group which may have a substituent.
Invention 8
8. The azo compound or a salt thereof according to claim 7, except that _Ay1 and _Ay2 are a phenyl group having one each of a carboxy group, a sulfo group and a hydroxy group as a substituent and a phenyl group having a triazole group as a substituent, respectively.
Invention 9
7. The azo compound or a salt thereof according to any one of Inventions 1 to 6, wherein at least one of Ay ₁ and Ay ₂ is a naphthyl group which may have a substituent.
Invention 10
The azo compound or a salt thereof according to Invention 9, wherein the naphthyl group which may have a substituent is a naphthyl group which may have a substituent selected from the group consisting of a hydroxy group, an alkoxy group having 1 to 4 carbon atoms and having a sulfo group, and a sulfo group.
Invention 11
The azo compound or a salt thereof according to Invention 10, wherein _Ay1 and _Ay2 are each independently a naphthyl group which may have a substituent selected from the group consisting of a hydroxy group, an alkoxy group having 1 to 4 carbon atoms and having a sulfo group, and a sulfo group.
Invention 12
The azo compound or a salt thereof according to any one of Inventions 9 to 11, wherein the naphthyl group which may have a substituent is represented by the following formula (3):

In the formula, Ry ₁₁ is a hydrogen atom, a hydroxyl group, an alkoxy group having 1 to 4 carbon atoms and a sulfo group, or a sulfo group, k is an integer of 1 to 3, and * in the formula indicates the bonding position with the NH moiety of the terminal amide group in the above formula (1). Note that the substitution positions of Ry ₁₁ and the sulfo group can be any positions on the naphthalene ring, as long as they are other than the positions where the bonding position with the NH moiety of the terminal amide group in the above formula (1) is substituted.
13. The azo compound or a salt thereof according to claim 12, wherein, in the above formula (3), Ry ₁₁ is a hydrogen atom and k is 2.
Invention 14
14. The azo compound or a salt thereof according to any one of claims ₁ to ₁₃ , wherein _Ry1 , _Ry2 , _Ry7 , and _Ry8 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, and Ry3 to Ry6 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group.
Invention 15
15. The azo compound or a salt thereof according to invention 14, wherein Ry ₃ to Ry ₆ are each independently a group selected from the group consisting of a hydrogen atom, a methyl group, an ethyl group, a methoxy group and a 3-sulfopropoxy group.
Invention 16
The azo compound or a salt thereof according to any one of Inventions 1 to 15, wherein the formula (1) is represented by the following formula (4):

In the formula, Ay ₁ , Ay ₂ , Ry ₁ to Ry ₈ , s and t each have the same meaning as in the above formula (1).
Invention 17
17. A polarizing element comprising the azo compound or a salt thereof according to any one of claims 1 to 16.
Invention 18
18. The polarizing element according to claim 17, further comprising one or more organic dyes having a structure other than that represented by formula (1).
Invention 19
19. The polarizing element according to claim 18, comprising an azo compound represented by formula (5) or a salt thereof and/or an azo compound represented by formula (6) or a salt thereof.

In the formula, Ar ₁ represents a phenyl group having a substituent or a naphthyl group having a substituent, Rr ₁ to Rr ₄ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group, Dr ₁ represents an azo group or an amido group, j represents 0 or 1, Xr ₁ represents an amino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent, a benzoyl group which may have a substituent, or a benzoylamino group which may have a substituent;

In the formula, _Ag1 represents a phenyl group having a substituent or a naphthyl group having a substituent, Bg and Cg are each independently represented by the following formula (7) or formula (8), either one of which is represented by formula (7), and _Xg1 represents an amino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent, a benzoyl group which may have a substituent, or a benzoylamino group which may have a substituent:

In the formula, _Rg1 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group, _p1 represents an integer of 0 to 2;

In the formula, _Rg2 and _Rg3 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group.
Invention 20
20. The polarizing element according to claim 19, comprising both an azo compound represented by the formula (5) or a salt thereof and an azo compound represented by the formula (6) or a salt thereof.
Invention 21
21. The polarizing element according to claim 19, wherein Cg in formula (6) is represented by formula (7).
Invention 22
The polarizing element according to the twenty-first aspect of the present invention, wherein the azo compound represented by the formula (6) or a salt thereof is an azo compound represented by the following formula (9) or a salt thereof:

In the formula, Ag ₂ represents a phenyl group having a substituent or a naphthyl group having a substituent; Rg ₄ and Rg ₅ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group; Xg ₂ represents an amino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent, a benzoyl group which may have a substituent, or a benzoylamino group which may have a substituent; and p ₂ and p ₃ each independently represent an integer of 0 to 2.
Invention 23
23. The polarizing element according to claim 22, wherein _p2 and _p3 in the formula (9) are each 1 or 2.
Invention 24
24. The polarizing element according to any one of claims 19 to 23, wherein Xr ₁ in the formula (5) is a phenylamino group which may have a substituent.
Invention 25
The polarizing element according to any one of inventions 19 to 24, wherein Xg ₁ in formula (6) or Xg ₂ in formula (8) is a phenylamino group which may have a substituent.
Invention 26
The polarizing element according to any one of Inventions 17 to 25, wherein the difference between the average transmittance at each wavelength of 420 nm to 480 nm and the average transmittance at each wavelength of 520 nm to 590 nm, which are determined by stacking two of the polarizing elements so that the absorption axis directions of the two elements are parallel to each other, is 2.5% or less in absolute value, and the difference between the average transmittance at each wavelength of 520 nm to 590 nm and the average transmittance at each wavelength of 600 nm to 640 nm is 3.0% or less in absolute value.
Invention 27
In accordance with JIS Z 8781-4:2013, the absolute values of the a* value and the b* value obtained when measuring the transmittance of natural light are
Each of the polarizing elements alone is equal to or less than 1.0 (-1.0≦a*-s≦1.0, -1.0≦b*-s≦1.0),
When the two polarizing elements are stacked and arranged so that the absorption axis directions of the two polarizing elements are parallel to each other, both of the polarizing elements have a value of 2.0 or less (-2.0≦a*-p≦2.0, -2.0≦b*-p≦2.0).
A polarizing element according to any one of Inventions 17 to 26 (wherein a*-s indicates the a* value when the element is a single component, b*-s indicates the b* value when the element is a single component, a*-p indicates the a* value in the parallel position, and b*-p indicates the b* value in the parallel position).
Invention 28
The polarizing element has a single transmittance after visibility correction of 35% to 45%,
The average transmittance of each wavelength from 520 nm to 590 nm obtained when the two polarizing elements are stacked so that the absorption axes of the two polarizing elements are parallel to each other is 28% to 45%.
28. A polarizing element according to any one of claims 17 to 27.
Invention 29
In the transmittance obtained when the two polarizing elements are stacked and arranged so that the absorption axis directions of the polarizing elements are perpendicular to each other,
A polarizing element according to any one of Inventions 17 to 28, wherein the difference between the average transmittance at each wavelength of 420 nm to 480 nm and the average transmittance at each wavelength of 520 nm to 590 nm is 1.0% or less as an absolute value, and the difference between the average transmittance at each wavelength of 520 nm to 590 nm and the average transmittance at each wavelength of 600 nm to 640 nm is 1.0% or less as an absolute value.
Invention 30
30. The polarizing element according to any one of claims 17 to 29, wherein the cross-phase transmittance at each wavelength in the wavelength bands of 420 nm to 480 nm, 520 nm to 590 nm, and 600 nm to 640 nm is 1% or less, or the degree of polarization is 97% or more.
Invention 31
The polarizing element according to any one of Inventions 17 to 30, wherein the absolute values of a* and b* values obtained when measuring the transmittance of natural light according to JIS Z 8781-4:2013 in a state where two of the polarizing elements are stacked so that the absorption axis directions of the respective polarizing elements are perpendicular to each other, are both 2.0 or less (-2.0≦a*-c≦2.0, -2.0≦b*-c≦2.0) (a*-c indicates the a* value in the orthogonal position, and b*-c indicates the b* value in the orthogonal position).
Invention 32
32. The polarizing element according to any one of claims 17 to 31, wherein the polarizing element comprises a polyvinyl alcohol-based resin film as a substrate.
Invention 33
A polarizing plate comprising the polarizing element according to any one of Inventions 17 to 32, and a transparent protective layer provided on one or both sides of the polarizing element.
Invention 34
A neutral gray polarizing plate comprising the polarizing element according to any one of Inventions 17 to 32 or the polarizing plate according to Invention 33.
Invention 35
A display device comprising the polarizing element according to any one of Inventions 17 to 32 or the polarizing plate according to Inventions 33 or 34.

The azo compounds or salts thereof of the present invention are useful as dyes for polarizing elements. Polarizing elements containing these compounds have high polarization performance comparable to polarizing elements using iodine, and also have excellent durability. Therefore, they are suitable for use in various liquid crystal displays and liquid crystal projectors, as well as in-vehicle applications that require high polarization performance and durability, and for display applications in industrial instruments used in various environments.

In one aspect, the present invention provides a high-performance achromatic polarizing element that has high transmittance and a high degree of polarization and exhibits high-quality white color when displaying white. In particular, the polarizing element is achromatic in both white and black display modes, and an achromatic polarizing plate and display device using the same can be provided.

In the present specification and claims, unless it clearly represents a free form, "azo compound or a salt thereof" may be referred to simply as "azo compound."

In the present specification and claims, the term "lower" in lower alkyl, lower alkoxy, and lower alkylamino groups refers to groups having 1 to 4 carbon atoms, preferably 1 to 3 carbon atoms. In the present specification, "substituent" includes hydrogen atoms for convenience. "May have a substituent" means that the group does not have a substituent. For example, "a phenyl group which may have a substituent" includes a simple unsubstituted phenyl group and a phenyl group which has a substituent.

Examples of "lower aliphatic hydrocarbon groups (having 1 to 4 carbon atoms)" include straight-chain alkyl groups such as methyl, ethyl, n-propyl, and n-butyl, branched-chain alkyl groups such as sec-butyl and tert-butyl, and unsaturated hydrocarbon groups such as vinyl.

Examples of "lower alkoxy groups (having 1 to 4 carbon atoms)" include methoxy groups, ethoxy groups, propoxy groups, n-butoxy groups, sec-butoxy groups, and tert-butoxy groups.

Examples of "aryloxy groups" include phenoxy groups and naphthoxy groups.

<Azo compounds>
The azo compound of the present invention is represented by the above formula (1).

The above formula (1) will now be described. In the above formula (1), _Ay1 and _Ay2 each independently represent a naphthyl group which may have a substituent, or a phenyl group which may have a substituent, s and t each independently represent 0 or 1, and either s or t is 1, and _Ry1 to _Ry8 each independently represent a hydrogen atom or a substituent.

In one embodiment, either _Ay1 or _Ay2 is a naphthyl group which may have a substituent.

In one embodiment, _Ay1 and _Ay2 are each independently a naphthyl group which may have a substituent, and preferably each independently a naphthyl group which may have a substituent selected from the group consisting of a hydroxy group, an alkoxy group having 1 to 4 carbon atoms and having a sulfo group, and a sulfo group.

In one embodiment, _Ay1 and _Ay2 each independently represent a phenyl group which may have a substituent.

In one embodiment, the azo compound or a salt thereof of the present invention is such that _Ay1 and _Ay2 are a phenyl group having one each of a carboxy group, a sulfo group and a hydroxy group as a substituent and a phenyl group having a triazole group as a substituent, respectively.

The substituents in the phenyl group which may have a substituent are not particularly limited, but examples include an aliphatic hydrocarbon group having 1 to 4 carbon atoms which may have a substituent, an alkoxy group having 1 to 4 carbon atoms which may have a substituent, an aryloxy group which may have a substituent, a hydroxy group, a sulfo group, a carboxy group, a substituted or unsubstituted amino group, an amide group, etc., and the substituents selected from the group consisting of an alkoxy group having 1 to 4 carbon atoms which may have a substituent, a sulfo group, and a carboxy group are preferred.

Examples of the "substituted or unsubstituted amino group" include mono-substituted amino groups such as amino group, methylamino group, ethylamino group, n-propylamino group, n-butylamino group, monophenylamino group, and mononaphthylamino group, and di-substituted amino groups such as dimethylamino group, diethylamino group, and diphenylamino group. These substituted amino groups may further have a substituent.

The "substituents" in the aliphatic hydrocarbon group having 1 to 4 carbon atoms which may have a substituent and the alkoxy group having 1 to 4 carbon atoms which may have a substituent are not particularly limited, and examples thereof include a hydroxy group, a sulfo group, a carboxy group, a substituted or unsubstituted amino group, an amide group, etc. The "substituents" in the aryloxy group which may have a substituent, and the "substituents" which the substituted amino group may further have are not particularly limited, and examples thereof include an aliphatic hydrocarbon group having 1 to 4 carbon atoms which may have a substituent.

_Ay1 and _Ay2 in the above formula (1) are more preferably phenyl groups having one or more substituents selected from the group consisting of a sulfo group, a carboxy group, a lower alkoxy group having a sulfo group, a lower alkyl group, a lower alkoxy group, a halogen atom, a nitro group, an amino group, a lower alkyl-substituted amino group, and a lower alkyl-substituted acylamino group.

One or both of _Ay1 and _Ay2 in the above formula (1) are preferably phenyl groups having at least one substituent selected from a sulfo group, a carboxy group, and an alkoxy group having 1 to 4 carbon atoms and a sulfo group, and the phenyl group may further have a hydrogen atom, a sulfo group, a carboxy group, an alkoxy group having 1 to 4 carbon atoms and a sulfo group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a halogen group, a nitro group, an amino group, an alkyl-substituted amino group having 1 to 4 carbon atoms, or an alkyl-substituted acylamino group having 1 to 4 carbon atoms.

When the phenyl group has two or more substituents, at least one of the substituents is a sulfo group, a carboxy group, or a lower alkoxy group having a sulfo group, and the other substituents are preferably a sulfo group, a hydrogen atom, a lower alkyl group, a lower alkoxy group, a lower alkoxy group having a sulfo group, a carboxy group, a chloro group, a bromo group, a nitro group, an amino group, a lower alkyl-substituted amino group, or a lower alkyl-substituted acylamino group. The other substituents are more preferably a sulfo group, a hydrogen atom, a methyl group, an ethyl group, a methoxy group, an ethoxy group, a carboxy group, a sulfoethoxy group, a sulfopropoxy group, a sulfobutoxy group, a chloro group, a nitro group, or an amino group, even more preferably a sulfo group, a carboxy group, a hydrogen atom, a methyl group, a methoxy group, a sulfoethoxy group, a sulfopropoxy group, or a sulfobutoxy group, and particularly preferably a sulfo group, a carboxy group, a hydrogen atom, a methyl group, a methoxy group, or a sulfobutoxy group.

The substitution positions of the phenyl group, which may have the above-mentioned substituents, are not particularly limited, but are preferably only the 2-position, only the 4-position, a combination of the 2-position and the 6-position, a combination of the 2-position and the 4-position, or a combination of the 3-position and the 5-position, and particularly preferably only the 2-position, only the 4-position, a combination of the 2-position and the 4-position, or a combination of the 3-position and the 5-position. Note that only the 2-position and only the 4-position mean that only the 2-position or the 4-position has one substituent other than a hydrogen atom.

The phenyl group having the above substituent is preferably represented by the above formula (2).

In the above formula (2), either _Ry9 or _Ry10 is a sulfo group, a carboxy group, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group, and the other is a hydrogen atom, a sulfo group, a carboxy group, an alkoxy group having 1 to 4 carbon atoms and a sulfo group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a halogen atom, a nitro group, an amino group, an alkyl-substituted amino group having 1 to 4 carbon atoms, or an alkyl-substituted acylamino group having 1 to 4 carbon atoms. Also, * in the formula indicates the bonding position with the NH moiety of the terminal amide group in the above formula (1).

Preferably, one of Ry ₉ and Ry ₁₀ is a sulfo group or a carboxy group, and the other is a hydrogen atom, a sulfo group, a carboxy group, a methyl group, or a methoxy group.

The naphthyl group in the naphthyl group that may have the above substituents may be a 1-naphthyl group or a 2-naphthyl group, with a 2-naphthyl group being preferred.

The substituent in the naphthyl group which may have a substituent is not particularly limited, but examples include an aliphatic hydrocarbon group having 1 to 4 carbon atoms which may have a substituent, an alkoxy group having 1 to 4 carbon atoms which may have a substituent, an aryloxy group which may have a substituent, a hydroxy group, a sulfo group, a carboxy group, a substituted or unsubstituted amino group, an amide group, etc., and an alkoxy group having 1 to 4 carbon atoms which may have a substituent and a sulfo group are preferable.

Examples of the "substituted or unsubstituted amino group" include mono-substituted amino groups such as amino group, methylamino group, ethylamino group, n-propylamino group, n-butylamino group, monophenylamino group, and mononaphthylamino group, and di-substituted amino groups such as dimethylamino group, diethylamino group, and diphenylamino group. These substituted amino groups may further have a substituent.

The "substituents" in the aliphatic hydrocarbon group having 1 to 4 carbon atoms which may have a substituent and the alkoxy group having 1 to 4 carbon atoms which may have a substituent are not particularly limited, and examples thereof include a hydroxy group, a sulfo group, a carboxy group, a substituted or unsubstituted amino group, an amide group, etc. The "substituents" in the aryloxy group which may have a substituent, and the "substituents" which the substituted amino group may further have are not particularly limited, and examples thereof include an aliphatic hydrocarbon group having 1 to 4 carbon atoms which may have a substituent.

The naphthyl group which may have the above-mentioned substituent is more preferably a naphthyl group which may have one or more substituents selected from the group consisting of a hydroxy group, a lower alkoxy group having a sulfo group, and a sulfo group.

The naphthyl group which may have the above substituent is more preferably a naphthyl group represented by the above formula (3).

In the above formula (3), _Ry11 is a hydrogen atom, a hydroxy group, an alkoxy group having 1 to 4 carbon atoms and a sulfo group, or a sulfo group, and k is an integer of 1 to 3. In addition, * in the formula indicates the bonding position with the NH moiety of the terminal amide group in the above formula (1). The substitution positions of _Ry11 and the sulfo group can be any positions on the naphthalene ring, so long as they are other than the positions where the bonding position with the NH moiety of the terminal amide group in the above formula (1) is substituted.

In the formula (3), _Ry11 is preferably a hydrogen atom, and k is preferably 2.

In the above formula (3), the position of the sulfo group may be on any benzene nucleus of the naphthalene ring. As the lower alkoxy group having a sulfo group, a straight-chain alkoxy group is preferable, and the substitution position of the sulfo group is preferably the terminal end of the alkoxy group. The lower alkoxy group having a sulfo group is more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group. The positions of the substituents on the naphthyl group are not particularly limited, but when the azo group is substituted at the 2nd position, combinations of the 4th and 8th positions, the 5th and 7th positions, or the 6th and 8th positions are preferable when there are two substituents, and when there are three substituents, combinations of the 3rd, 5th, and 7th positions, or the 3rd, 6th, and 8th positions are preferable.

In the above formula (1), _Ry1 to _Ry8 each independently represent a hydrogen atom or a substituent. The substituent is not particularly limited, but may be the same as that described above in the section on the phenyl group which may have a substituent or the section on the naphthyl group which may have a substituent.

Preferably, Ry ₁ , Ry ₂ , Ry ₇ and Ry ₈ in the above formula (1) are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, more preferably a hydrogen atom, a methyl group, an ethyl group, a methoxy group or an ethoxy group. It is preferred that Ry ₃ to Ry ₆ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group. More preferably, Ry ₃ to Ry ₆ are each independently a hydrogen atom, a methyl group, an ethyl group, a methoxy group, an ethoxy group, a 3-sulfopropoxy group, or a 4-sulfobutoxy group, and even more preferably a hydrogen atom, a methyl group, an ethyl group, a methoxy group, or a 3-sulfopropoxy group. The substitution positions of _Ry3 to _Ry6 are preferably only the 2-position, only the 5-position, a combination of the 2-position and the 6-position, a combination of the 2-position and the 5-position, or a combination of the 3-position and the 5-position, and more preferably only the 2-position, only the 5-position, or a combination of the 2-position and the 5-position. Note that only the 2-position and only the 5-position indicate that only the 2-position or the 5-position has one substituent other than a hydrogen atom.

In the above formula (1), if both s and t are 0, the polarization characteristics will deteriorate, which is not preferable.

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

In the above formula (4), Ay ₁ , Ay ₂ , Ry ₁ to Ry ₈ , s and t each have the same meaning as in formula (1).

In one embodiment, preferably, in the formula (4), _Ay1 and _Ay2 are each independently a phenyl group which may have a substituent selected from the group consisting of an alkoxy group having 1 to 4 carbon atoms and having a sulfo group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a carboxy group, a halogen group, a nitro group, a sulfo group, a substituted or unsubstituted amino group, and an amide group; s and t are each independently 0 or 1, and either s or t is 1; _Ry1 , _Ry2 , _Ry7 , and _Ry8 are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms; and _Ry3 to _Ry6 are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and having a sulfo group. More preferably, _Ay1 and _Ay2 are each independently a phenyl group which may have a substituent selected from the group consisting of a carboxy group, a halogen group, and a sulfo group, s and t are each independently 0 or 1, and either s or t is 1, _Ry1 , _Ry2 , _Ry7 , and _Ry8 are each independently a hydrogen atom, a methyl group, or a methoxy group, and _Ry3 to _Ry6 are each independently a hydrogen atom, a methyl group, a methoxy group, or a 3-sulfopropoxy group. More preferably, _Ay1 and _Ay2 are each independently a 4-sulfophenyl group, a 4-carboxyphenyl group, a 4-chloro-4-carboxyphenyl group, or a 2,4-disulfophenyl group, s and t are each independently 0 or 1, and either s or t is 1, _Ry1 , _Ry2 , _Ry7 , and _Ry8 are each independently a hydrogen atom, a methyl group, or a methoxy group, and _Ry3 to _Ry6 are each independently a hydrogen atom, a methyl group, a methoxy group, or a 3-sulfopropoxy group. Particularly preferably, Ay ₁ and Ay ₂ are each any of a combination of a 4-sulfophenyl group and a 4-carboxyphenyl group, a combination of a 4-carboxyphenyl group and a 4-chloro-3-carboxyphenyl group, a combination of a 4-sulfophenyl group and a 4-chloro-3-carboxyphenyl group, or a combination of a 4-carboxyphenyl group and a 2,4-disulfophenyl group, s and t are each independently 0 or 1, and either s or t is 1, Ry ₁ , Ry ₂ , Ry ₇ , and Ry ₈ are each independently a hydrogen atom, a methyl group, or a methoxy group, and Ry ₃ to Ry ₆ are each independently a hydrogen atom, a methyl group, a methoxy group, or a 3-sulfopropoxy group.

In one embodiment, preferably, in the formula (4), Ay ₁ and Ay ₂ are each independently a naphthyl group which may have a substituent selected from the group consisting of an alkoxy group having 1 to 4 carbon atoms and a sulfo group, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a carboxy group, a halogen group, a nitro group, a sulfo group, a substituted or unsubstituted amino group, or a phenyl group which may have an amido group, either Ay ₁ or Ay ₂ is a naphthyl group which may have a substituent selected from the group consisting of an alkoxy group having 1 to 4 carbon atoms and a sulfo group, s and t are each independently 0 or 1, and either s or t is 1, Ry ₁ , Ry ₂ , Ry ₇ , and Ry ₈ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 _to 4 carbon atoms, and Ry ₁ to Ry ₆ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group. More preferably, Ay 1 and Ay ₂ are each independently a naphthyl group which may have a substituent selected from the group consisting of an alkoxy group having 1 to 4 carbon atoms and a sulfo group, or a phenyl group which may have a substituent selected from the group consisting of a carboxy group, a halogen group, and a sulfo group, either Ay ₁ and/or Ay ₂ is a naphthyl group which may have a substituent selected from the group consisting of an alkoxy group having 1 to 4 carbon atoms and a sulfo group, s and t are each independently 0 or 1, and either s or t is 1, Ry ₁ , Ry ₂ , Ry ₇ , and Ry ₈ are each independently a hydrogen atom, a methyl group, or a methoxy group, and Ry ₃ to Ry ₆ are each independently a hydrogen atom, a methyl group, a methoxy group, or a 3-sulfopropoxy group. More preferably, _Ay1 and _Ay2 are each independently a naphthyl group which may have a substituent selected from the group consisting of a 3-sulfopropoxy group and a sulfo group, s and t are each independently 0 or 1, and either s or t is 1, _Ry1 , _Ry2 , _Ry7 , and _Ry8 are each independently a hydrogen atom, a methyl group, or a methoxy group, and _Ry3 to _Ry6 are each independently a hydrogen atom, a methyl group, a methoxy group, or a 3-sulfopropoxy group. Particularly preferably, _Ay1 and _Ay2 are each 6,8-disulfonaphthalene or 6-sulfo-8-(3-sulfopropoxy)naphthalene, s and t are each independently 0 or 1, and either s or t is 1, _Ry1 , _Ry2 , _Ry7 , and _Ry8 are each independently a hydrogen atom, a methyl group, or a methoxy group, and _Ry3 to _Ry6 are each independently a hydrogen atom, a methyl group, a methoxy group, or a 3-sulfopropoxy group. Most preferably, _Ay1 and _Ay2 are each 6,8-disulfonaphthalene or 6-sulfo-8-(3-sulfopropoxy)naphthalene, s and t are each 1, _Ry1 , _Ry2 , _Ry7 , and _Ry8 are each independently a hydrogen atom, a methyl group, or a methoxy group, and _Ry3 to _Ry6 are each independently a hydrogen atom, a methyl group, a methoxy group, or a 3-sulfopropoxy group.

Specific examples of azo compounds represented by formula (1) are given below. Note that the sulfo group, carboxy group, and hydroxy group in the formula are represented in the form of free acid.

First, specific examples of azo compounds in which _Ay1 and _Ay2 are phenyl groups which may have a substituent are given below.

Next, specific examples of azo compounds in which at least one of _Ay1 and _Ay2 is a naphthyl group which may have a substituent are given below.

The azo compound represented by the above formula (1) may be in the form of a free acid or a salt. Examples of such salts include alkali metal salts such as lithium salts, sodium salts, and potassium salts, ammonium salts, and organic salts such as amine salts, and preferably sodium salts.

The azo compound represented by the above formula (1) or its salt can be produced by diazotization and coupling according to the usual method for producing azo dyes as described in Non-Patent Document 2, and then reacting with a ureidation agent as described in Patent Document 13.

As a specific example of the production method, an aniline having a substituent as shown in the following formula (A) is reacted with an acid chloride as shown in the following formula (B) in the same manner as in Patent Document 18, followed by carrying out a reduction reaction to obtain an aminobenzoylaniline as shown in the following formula (C).

In the above formulas, Ay ₁ , Ry ₁ and Ry ₂ each have the same meaning as in the above formula (1).

Next, an aminobenzoylaniline having a substituent represented by the above formula (C) is diazotized in the same manner as in Non-Patent Document 2, and coupled with an aniline represented by the following formula (D) to obtain a monoazoamino compound represented by the following formula (E).

In the above formulas, Ay ₁ and Ry ₁ to Ry ₄ have the same meanings as in formula (1).

Next, an aniline having a substituent as shown in the following formula (F) is reacted with an acid chloride as shown in the following formula (G) in the same manner as in Patent Document 1, followed by a reduction reaction to obtain an aminobenzoylaniline as shown in the following formula (H).

In the above formulas, Ay ₂ , Ry ₇ and Ry ₈ each have the same meaning as in formula (1).

Next, the aminobenzoylaniline having the substituent represented by the above formula (H) is diazotized in the same manner as in Non-Patent Document 2, and coupled with an aniline represented by the following formula (I) to obtain a monoazoamino compound represented by the following formula (J).

In the above formulas, Ay ₂ and Ry ₅ to Ry ₈ have the same meanings as in formula (1).

To obtain the compound in which s and t are each 1 in the above formula (1), monoazoamino compound (E) and monoazoamino compound (J) are reacted with phenyl chloroformate, which is a ureidating agent.

In order to obtain a compound in which s is 1 and t is 0 in the above formula (1), an aniline having a substituent represented by the following formula (K) is diazotized in the same manner as in Non-Patent Document 2, and coupled with the aniline of the above formula (I) to obtain a monoazoamino compound represented by the following formula (L).

In the above formulas, Ay ₂ , Ry ₅ and Ry ₆ each have the same meaning as in the above formula (1).

Next, the monoazoamino compound (E) and the monoazoamino compound (L) are reacted with phenyl chloroformate, which is a ureidation agent, to obtain the azo compound of the above formula (1).

In order to obtain an azo compound of the above formula (1) in which s is 0 and t is 1, an aniline having a substituent represented by the following formula (M) is diazotized in the same manner as in Non-Patent Document 2, and coupled with an aniline of the above formula (D) to obtain a monoazoamino compound represented by the following formula (N).

In the above formulas, Ay ₁ , Ry ₃ and Ry ₄ each have the same meaning as in the above formula (1).

In the above formula (M), _Ay1 has the same meaning as in the above formula (1). In the above formula (N), _Ay1 , _Ry3 to _Ry4 have the same meaning as in the above formula (1).

Next, the monoazoamino compound (J) and the monoazoamino compound (N) are reacted with phenyl chloroformate, which is a ureidating agent, to obtain the azo compound of the above formula (1).

The diazotization step is carried out either by a forward method in which a nitrite such as sodium nitrite is mixed with an aqueous solution or suspension of a mineral acid such as hydrochloric acid or sulfuric acid of the diazo component, or by a reverse method in which a nitrite is added to a neutral or weakly alkaline aqueous solution of the diazo component and then mixed with a mineral acid. The appropriate temperature for diazotization is -10 to 40°C. The coupling step with anilines is preferably carried out by mixing an aqueous acidic solution of hydrochloric acid, acetic acid, or the like with each of the above diazo solutions under acidic conditions at a temperature of -10 to 40°C and a pH of 2 to 7.

The monoazoamino compound (E), monoazoamino compound (J), monoazo compound (L), and monoazo compound (N) obtained by coupling can be precipitated by acid precipitation or salt precipitation and filtered out, or can be carried to the next step as a solution or suspension. If the diazonium salt is poorly soluble and is in the form of a suspension, it can be filtered and used as a press cake in the next coupling step.

Specific conditions for the ureidation reaction using phenyl chloroformate are, according to the method shown on page 57 of Patent Document 13, preferably a temperature of 10 to 90°C and a pH of 3 to 11, more preferably 20 to 80°C and a pH of 4 to 10, and particularly preferably 20 to 70°C and a pH of 6 to 9. As the ureidation agent, in addition to phenyl chloroformate, phosgene, triphosgene, ethyl chloroformate, butyl chloroformate, isobutyl chloroformate, 4-nitrophenyl chloroformate, 4-fluorophenyl chloroformate, 4-chlorophenyl chloroformate, 4-bromophenyl chloroformate, diphenyl carbonate, bis(2-methoxyphenyl) carbonate, bis(pentafluorophenyl) carbonate, bis(4-nitrophenyl) carbonate, and 1,1'-carbonyldiimidazole can be used, but are not limited to these. The ureidation agent is preferably phenyl chloroformate, 4-nitrophenyl chloroformate, 4-chlorophenyl chloroformate, diphenyl carbonate, or bis(4-nitrophenyl) carbonate, and more preferably phenyl chloroformate or 4-nitrophenyl chloroformate.

After the ureidation reaction is completed, the resulting azo compound of formula (1) is precipitated by salting out and filtered out. If purification is required, the salting out can be repeated or an organic solvent can be used to precipitate the compound from water. 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 aromatic amines represented by Ay ₁ -NH ₂ and Ay ₂ -NH ₂ , which are starting materials for synthesizing the azo compound represented by formula (1), are naphthylamines or anilines.

Anilines include 4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid, 2-aminobenzenesulfonic acid, 4-aminobenzoic acid, 2-amino-5-methylbenzenesulfonic acid, 2-amino-5-ethylbenzenesulfonic acid, 2-amino-5-propylbenzenesulfonic acid, 2-amino-5-butylbenzenesulfonic acid, 4-amino-3-methylbenzenesulfonic acid, 4-amino-3-ethylbenzenesulfonic acid, 4-amino-3-propylbenzenesulfonic acid, 4-amino-3-butylbenzenesulfonic acid, 2-amino-5-methoxybenzenesulfonic acid, benzenesulfonic acid, 2-amino-5-ethoxybenzenesulfonic acid, 2-amino-5-propoxybenzenesulfonic acid, 2-amino-5-butoxybenzenesulfonic acid, 4-amino-3-methoxybenzenesulfonic acid, 4-amino-3-ethoxybenzenesulfonic acid, 4-amino-3-propoxybenzenesulfonic acid, 4-amino-3-butoxybenzenesulfonic acid, 2-amino-4-sulfobenzoic acid, 2-amino-5-sulfobenzoic acid, 4-amino-3-sulfobenzoic acid, 5-amino-2-chlorobenzoic acid, 5-aminoisophthalic acid, 2-amino-5- Chlorobenzenesulfonic acid, 2-amino-5-bromobenzenesulfonic acid, 2-amino-5-nitrobenzenesulfonic acid, 2,5-diaminobenzenesulfonic acid, 2-amino-5-dimethylaminobenzenesulfonic acid, 2-amino-5-diethylaminobenzenesulfonic acid, 5-acetamido-2-aminobenzenesulfonic acid, 4-aminobenzene-1,3-disulfonic acid, 2-aminobenzene-1,4-disulfonic acid, 4-amino-2-methylbenzenesulfonic acid, 2-(4-aminophenoxy)ethane-1-sulfonic acid, 3-(4-aminophenoxy)ethanesulfonic acid, l) Propane-1-sulfonic acid, 4-(4-aminophenoxy)butane-1-sulfonic acid, 2-(3-aminophenoxy)ethane-1-sulfonic acid, 3-(3-aminophenoxy)propane-1-sulfonic acid, 4-(3-aminophenoxy)butane-1-sulfonic acid, 2-amino-5-(2-sulfoethoxy)benzenesulfonic acid, 2-amino-5-(3-sulfopropoxy)benzenesulfonic acid, 2-amino-5-(4-sulfobutoxy)benzenesulfonic acid, 2-amino-5-(2-sulfoethoxy)benzoic acid, 2-amino-5-(3-sulfopropoxy) 4-amino-3-(2-sulfoethoxy)benzenesulfonic acid, 4-amino-3-(3-sulfopropoxy)benzenesulfonic acid, 4-amino-3-(4-sulfobutoxy)benzenesulfonic acid, 4-amino-3-(2-sulfoethoxy)benzoic acid, 4-amino-3-(3-sulfopropoxy)benzoic acid, 4-amino-3-(4-sulfobutoxy)benzoic acid, 2-(4-amino-3-methylphenoxy)ethane-1-sulfonic acid, 3-(4-amino-3-methylphenoxy)prop 4-(4-amino-3-methylphenoxy)butane-1-sulfonic acid, 2-(4-amino-3-ethylphenoxy)ethane-1-sulfonic acid, 3-(4-amino-3-ethylphenoxy)propane-1-sulfonic acid, 4-(4-amino-3-ethylphenoxy)butane-1-sulfonic acid, 2-(4-amino-3-propylphenoxy)ethane-1-sulfonic acid, 3-(4-amino-3-propylphenoxy)propane-1-sulfonic acid, 4-(4-amino-3-propylphenoxy)butane-1-sulfonic acid, 2-(4-amino-3-propylphenoxy)ethane-1-sulfonic acid, 3-(4-amino-3-propylphenoxy)propane-1-sulfonic acid, 4-(4-amino-3-propylphenoxy)butane-1-sulfonic acid, -butylphenoxy)ethane-1-sulfonic acid, 3-(4-amino-3-butylphenoxy)propane-1-sulfonic acid, 4-(4-amino-3-butylphenoxy)butane-1-sulfonic acid, 2-(4-amino-3-methoxyphenoxy)ethane-1-sulfonic acid, 3-(4-amino-3-methoxyphenoxy)propane-1-sulfonic acid, 4-(4-amino-3-methoxyphenoxy)butane-1-sulfonic acid, 2-(4-amino-3-ethoxyphenoxy)ethane-1-sulfonic acid, 3-(4-amino-3-ethoxyphenoxy)propane-1-sulfonic acid sulfonic acid, 4-(4-amino-3-ethoxyphenoxy)butane-1-sulfonic acid, 2-(4-amino-3-propoxyphenoxy)ethane-1-sulfonic acid, 3-(4-amino-3-propoxyphenoxy)propane-1-sulfonic acid, 4-(4-amino-3-propoxyphenoxy)butane-1-sulfonic acid, 2-(4-amino-3-butoxyphenoxy)ethane-1-sulfonic acid, 3-(4-amino-3-butoxyphenoxy)propane-1-sulfonic acid, 4-(4-amino-3-butoxyphenoxy)butane-1-sulfonic acid, and the like. The amino group of these aromatic amines may be protected. An example of a protecting group is the ω-methanesulfonic group.

As the naphthylamines, it is preferable to use naphthylamines having one or more selected from the group consisting of a hydrogen atom, a hydroxyl group, a lower alkoxy group having a sulfo group, and a sulfo group. Examples of naphthylamines include 4-aminonaphthalenesulfonic acid, 7-aminonaphthalene-3-sulfonic acid, 1-aminonaphthalene-6-sulfonic acid, 1-aminonaphthalene-7-sulfonic acid, 7-aminonaphthalene-1,3-disulfonic acid, 6-aminonaphthalene-1,3-disulfonic acid, 7-aminonaphthalene-1,5-disulfonic acid, and 7-aminonaphthalene-1,3,6-trisulfonic acid. Preferred are 7-aminonaphthalene-3-sulfonic acid, 6-aminonaphthalene-1,3-disulfonic acid, 7-aminonaphthalene-1,4-disulfonic acid, 7-aminonaphthalene-1,5-disulfonic acid, 2-amino-8-hydroxy-naphthalene-6-sulfonic acid, 3-amino-8-hydroxynaphthalene-6-sulfonic acid, 1-aminonaphthalene-3,6,8-trisulfonic acid, 2-amino-5-hydroxynaphthalene-1,7-disulfonic acid, 1-aminonaphthalene-3,8-disulfonic acid, etc.

Examples of naphthylamines having a sulfo group and a lower alkoxy group having a sulfo group include 7-amino-3-(3-sulfopropoxy)naphthalene-1-sulfonic acid, 7-amino-3-(4-sulfobutoxy)naphthalene-1-sulfonic acid, 7-amino-4-(3-sulfopropoxy)naphthalene-2-sulfonic acid, 7-amino-4-(4-sulfobutoxy)naphthalene-2-sulfonic acid, 6-amino -4-(3-sulfopropoxy)naphthalene-2-sulfonic acid, 6-amino-4-(4-sulfobutoxy)naphthalene-2-sulfonic acid, 2-amino-5-(3-sulfopropoxy)naphthalene-1,7-disulfonic acid, 6-amino-4-(3-sulfopropoxy)naphthalene-2,7-disulfonic acid, 7-amino-3-(3-sulfopropoxy)naphthalene-1,5-disulfonic acid, etc.

The aromatic amines (D) and (I) which are primary couplers include aniline, 2-methylaniline, 2-ethylaniline, 2-propylaniline, 2-butylaniline, 3-methylaniline, 3-ethylaniline, 3-propylaniline, 3-butylaniline, 2,5-dimethylaniline, 2,5-diethylaniline, 2-methoxyaniline, 2-ethoxyaniline, 2-propoxyaniline, 2-butoxyaniline, 3-methoxyaniline, 3-ethoxyaniline, 3-propoxyaniline, 3-butoxyaniline, 2-methoxy-5-methylaniline, 2,5-dimethoxyaniline, 3, 5-Dimethylaniline, 2,6-Dimethylaniline, 3,5-Dimethoxyaniline, 3-(2-amino-4-methylphenoxy)propane-1-sulfonic acid, 3-(2-aminophenoxy)propane-1-sulfonic acid, 4-(2-amino-4-methylphenoxy)butane-1-sulfonic acid, 4-(2-aminophenoxy)butane-1-sulfonic acid, 2-(2-amino-4-methylphenoxy)ethane-1-sulfonic acid, 2-(2-aminophenoxy)ethane-1-sulfonic acid, 3-(3-amino-4-methylphenoxy)propane-1-sulfonic acid, 3-(3-aminophenoxy)propane- 1-sulfonic acid, 4-(3-amino-4-methylphenoxy)butane-1-sulfonic acid, 4-(3-aminophenoxy)butane-1-sulfonic acid, 2-(3-amino-4-methylphenoxy)ethane-1-sulfonic acid, 2-(3-aminophenoxy)ethane-1-sulfonic acid, 3-(2-amino-4-methoxyphenoxy)propane-1-sulfonic acid, 4-(2-amino-4-methoxyphenoxy)butane-1-sulfonic acid, 2-(2-amino-4-methoxyphenoxy)ethane-1-sulfonic acid, 3-(3-amino-4-methoxyphenoxy)propane-1-sulfonic acid, 4-(3-amino Examples of the aromatic amines include 2-(3-amino-4-methoxyphenoxy)butane-1-sulfonic acid, 2-(3-amino-4-methoxyphenoxy)ethane-1-sulfonic acid, 3-(2-amino-4-ethoxyphenoxy)propane-1-sulfonic acid, 4-(2-amino-4-ethoxyphenoxy)butane-1-sulfonic acid, 2-(2-amino-4-ethoxyphenoxy)ethane-1-sulfonic acid, 3-(3-amino-4-ethoxyphenoxy)propane-1-sulfonic acid, 4-(3-amino-4-ethoxyphenoxy)butane-1-sulfonic acid, and 2-(3-amino-4-ethoxyphenoxy)ethane-1-sulfonic acid. The amino group of these aromatic amines may be protected. Examples of the protecting group include the ω-methanesulfone group.

Examples of acid chlorides (B) and (G) include 4-nitrobenzoyl chloride, 3-methyl-4-nitrobenzoyl chloride, 2-methyl-4-nitrobenzoyl chloride, 3-ethyl-4-nitrobenzoyl chloride, 2-ethyl-4-nitrobenzoyl chloride, 3-propyl-4-nitrobenzoyl chloride, 2-propyl-4-nitrobenzoyl chloride, 3-butyl-4-nitrobenzoyl chloride, 2-butyl-4-nitrobenzoyl chloride, 3-methoxy-4-nitrobenzoyl chloride, 3-ethoxy-4-nitrobenzoyl chloride, 3-propoxy-4-nitrobenzoyl chloride, 3-butoxy-4-nitrobenzoyl chloride, 2-methoxy-4-nitrobenzoyl chloride, 2-ethoxy-4-nitrobenzoyl chloride, 2-propoxy-4-nitrobenzoyl chloride, and 2-butoxy-4-nitrobenzoyl chloride.

<Polarizing element>
The polarizing element of the present invention comprises an azo compound represented by formula (1) or a salt thereof and a substrate.

In one embodiment, the polarizing element of the present invention may be either a neutral gray polarizing element or a color polarizing element, and is preferably a neutral gray polarizing element. Here, "neutral gray" means that when two polarizing elements are stacked so that their orientation directions are perpendicular to each other (hereinafter also referred to as "orthogonal"), there is little light leakage (color leakage) of a specific wavelength in the visible light wavelength range.

The polarizing element of the present invention contains one or more azo compounds represented by formula (1) or salts thereof as dichroic dyes, and may further contain one or more other organic dyes as necessary. The other organic dyes are not particularly limited, but are preferably dyes that have absorption characteristics in a wavelength range different from the absorption wavelength range of the azo compound represented by formula (1) or salts thereof and have high dichroism. Examples of other organic dyes include C.I. Direct Red 2, C.I. Direct Red 31, C.I. Direct Red 79, C.I. Direct Red 81, C.I. Direct Red 247, C.I. Direct Violet 9, C.I. Direct Blue 202, C.I. Representative examples include dyes described in C.I. Direct Green 80, C.I. Direct Green 59, and Patent Documents 20, 16, 13, 21 to 23, but it is preferable to use dyes developed for polarizing plates such as those described in Patent Documents 20, 16, 13, 21 to 23 depending on the purpose. These organic dyes are used as free acids, alkali metal salts (e.g., Na salt, K salt, Li salt), ammonium salts, or salts of amines.

When other organic dyes are used in combination, the type of organic dye to be blended varies depending on whether the target polarizing element is a neutral gray polarizing element, a color polarizing element for liquid crystal projectors, or other color polarizing elements. The blending ratio is not particularly limited, but generally, it is preferable to use a total of 0.01 to 100 parts by mass of at least one other organic dye per 1 part by mass of the azo compound of formula (1) or its salt, and more preferably a range of 0.1 to 10 parts by mass.

When the desired polarizing element is a neutral gray polarizing element, the type and mixing ratio of other organic dyes used in combination are adjusted so that there is less color leakage when the absorption axis of the polarizing element is perpendicular in the visible light wavelength range of the resulting polarizing element, thereby obtaining a polarizing element that is generally considered to be neutral gray.

When the desired polarizing element is a color polarizing element, the types and blending ratios of other organic dyes used in combination are adjusted so that the resulting polarizing element has a high single-plate average light transmittance in a specific wavelength band and a low average light transmittance in the orthogonal direction, for example, a single-plate average light transmittance of 39% or more in a specific wavelength band and an average light transmittance in the orthogonal direction of 0.4% or less.

The polarizing element of the present invention can be produced by incorporating a dichroic dye containing an azo compound represented by formula (1) or a salt thereof and, if necessary, other dyes into a substrate (e.g., a polymer film) by a known method and orienting the dye, mixing the dye with a liquid crystal, or orienting the dye by a coating method.

In one embodiment, the polarizing element according to the present invention contains, in addition to the azo compound represented by formula (1) above or a salt thereof, an azo compound represented by formula (5) above or a salt thereof and/or an azo compound represented by formula (6) above or a salt thereof.

In one embodiment, the polarizing element of the present invention contains both an azo compound or a salt thereof represented by the above formula (5) and/or the above formula (6) in addition to the azo compound or a salt thereof represented by the above formula (1), thereby realizing a polarizing plate having a higher transmittance and a higher degree of polarization than conventional achromatic polarizing plates, while realizing a high-quality paper-like white color, commonly known as paper white, when displaying white, and achromatic black color, particularly a clear black color with a luxurious feel, when displaying black, and having a higher contrast than conventional dye-based polarizing plates.

The azo compound represented by the above formula (5) is described below.

In the above formula (5), Ar ₁ represents a phenyl group having a substituent or a naphthyl group having a substituent; Rr ₁ to Rr ₄ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group; Dr ₁ represents an azo group or an amido group; j represents 0 or 1; and Xr ₁ represents an amino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent, a benzoyl group which may have a substituent, or a benzoylamino group which may have a substituent.

The above-mentioned phenyl group having a substituent or the naphthyl group having a substituent will be described. When Ar ₁ is a phenyl group having a substituent, it is preferable that the substituent has at least one sulfo group or carboxy group. When the phenyl group has two or more substituents, at least one of the substituents is a sulfo group or a carboxy group, and the other substituent is preferably a sulfo group, a carboxy group, a lower alkyl group, a lower alkoxy group, a lower alkoxy group having a sulfo group, a nitro group, a benzoyl group, an amino group, an acetylamino group, or a lower alkylamino group-substituted amino group, and the other substituent is more preferably a sulfo group, a methyl group, an ethyl group, a methoxy group, an ethoxy group, a carboxy group, a nitro group, a benzoyl group, or an amino group, and particularly preferably a sulfo group, a methyl group, a methoxy group, an ethoxy group, a benzoyl group, or a carboxy group. As the lower alkoxy group having a sulfo group, a straight-chain alkoxy group is preferable, and the substitution position of the sulfo group is preferably the alkoxy group terminal, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably a 3-sulfopropoxy group. The number of sulfo groups in the phenyl group is preferably 1 or 2, and the substitution positions are not particularly limited. However, when the substitution position of the azo group or amido group is the 1st position, only the 4th position, a combination of the 2nd and 4th positions, and a combination of the 3rd and 5th positions are preferred.

When the above Ar ₁ is a naphthyl group having a substituent, it is preferable that the naphthyl group has at least one of a sulfo group, a hydroxy group, and an alkoxy group having 1 to 4 carbon atoms and a sulfo group as a substituent. When the naphthyl group has two or more substituents, at least one of the substituents is a sulfo group, and the other substituent is preferably a lower alkoxy group having a sulfo group, a hydroxy group, a carboxy group, or a sulfo group. As the lower alkoxy group having a sulfo group, a straight-chain alkoxy group is preferable, and the substitution position of the sulfo group is preferably the terminal of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably a 3-sulfopropoxy group. When the number of sulfo groups is 2, the positions of the sulfo groups on the naphthyl group, assuming that the substitution position of the azo group or amide group is the 2nd position, are preferably a combination of the 4th position and the 8th position, and a combination of the 6th position and the 8th position, and more preferably a combination of the 6th position and the 8th position. When the naphthyl group has 3 sulfo groups, the substitution positions of the sulfo groups are preferably a combination of the 3rd position, the 6th position, and the 8th position, and particularly preferably a combination of the 6th position and the 8th position.

The above Rr ₁ to Rr ₄ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group. Rr ₁ to Rr ₄ each independently represent preferably a hydrogen atom, a lower alkyl group, or a lower alkoxy group, more preferably a hydrogen atom, a methyl group, or a methoxy group. As the lower alkoxy group having a sulfo group, a straight-chain alkoxy group is preferred, and the substitution position of the sulfo group is preferably the alkoxy group terminal, more preferably a 3-sulfopropoxy group or a 4-sulfobutoxy group, and particularly preferably a 3-sulfopropoxy group.

The above j represents 0 or 1. When j is 0, color control is facilitated, and the absolute values of the a* and b* values obtained when measuring the transmittance of natural light according to JIS Z 8781-4:2013 are easily adjusted to 2.0 or less (-2.0≦a*-p≦2.0, -2.0≦b*-p≦2.0) as absolute values when two polarizing elements are arranged so that the absorption axis directions of each are parallel to each other, so this is a preferred embodiment for adjusting color. When j is 1, a high degree of polarization is exhibited, so this is one of the preferred embodiments for improving performance. When j is 1, Dr ₁ represents an azo group or an amide group, and when Dr ₁ is an amide group, it is particularly preferred because it exhibits high polarization performance.

The Xr ₁ represents an amino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent, a benzoyl group which may have a substituent, or a benzoylamino group which may have a substituent. The amino group which may have a substituent is preferably an amino group having one or two substituents selected from the group consisting of a hydrogen atom, a lower alkyl group, a lower alkoxy group, a sulfo group, an amino group, and a lower alkylamino group, and more preferably an amino group having one or two substituents selected from the group consisting of a hydrogen atom, a methyl group, an ethyl group, a methoxy group, an ethoxy group, an amino group, and a lower alkylamino group. The phenylamino group which may have a substituent is preferably a phenylamino group having one or two substituents selected from the group consisting of a hydrogen atom, a lower alkyl group, a lower alkoxy group, a sulfo group, an amino group, and a lower alkylamino group, and more preferably a phenylamino group having one or two substituents selected from the group consisting of a hydrogen atom, a methyl group, a methoxy group, a sulfo group, and an amino group. The benzoyl group which may have a substituent is preferably a benzoyl group having one selected from the group consisting of a hydrogen atom, a hydroxy group, a sulfo group, an amino group, and a carboxyethylamino group. The benzoylamino group which may have a substituent is preferably a benzoylamino group having one selected from the group consisting of a hydrogen atom, a hydroxy group, an amino group, and a carboxyethylamino group. The phenylazo group which may have a substituent is preferably a phenylazo group having one to three selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an amino group, and a carboxyethylamino group. Xr ₁ is preferably an amino group which may have a substituent, a benzoylamino group which may have a substituent, and a phenylamino group which may have a substituent, and more preferably an amino group which may have a substituent, and a phenylamino group which may have a substituent. The position of the substituent is not particularly limited, but when _Xr1 is a group having a phenyl group, it is particularly preferable that one of the substituents is substituted at the p-position with respect to the bonding position indirectly bonding to the naphthalene skeleton shown in formula (5). As a specific example, in the case of a phenylamino group, it is preferable that the substituent is at the p-position with respect to the amino group.

Methods for obtaining the azo compound represented by the above formula (5) include, but are not limited to, the methods described in Patent Documents 4 to 6.

Further specific examples of the azo compound represented by the above formula (5) are shown below in the form of a free acid.

Next, we will explain the compound of formula (6) above.

In the above formula (6), Ag ₁ represents a phenyl group having a substituent or a naphthyl group having a substituent. When Ag ₁ is a phenyl group having a substituent, it is preferable that it has at least one sulfo group or carboxy group as a substituent. When the phenyl group has two or more substituents, it is preferable that at least one of the substituents is a sulfo group or a carboxy group, and the other substituent is a sulfo group, a carboxy group, a lower alkyl group, a lower alkoxy group, a lower alkoxy group having a sulfo group, a nitro group, an amino group, an acetylamino group, or an amino group substituted with a lower alkylamino group. The other substituent is more preferably a sulfo group, a methyl group, an ethyl group, a methoxy group, an ethoxy group, a carboxy group, a nitro group, or an amino group, and particularly preferably a sulfo group, a methyl group, a methoxy group, an ethoxy group, or a carboxy group. As the lower alkoxy group having a sulfo group, a straight-chain alkoxy group is preferable, and the substitution position of the sulfo group is preferably the alkoxy group terminal, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably a 3-sulfopropoxy group. The number of the substituents on the phenyl group is preferably 1 or 2, and the substitution position is not particularly limited, but when the position of the azo group is the 1st position, only the 4th position, a combination of the 2nd and 4th positions, and a combination of the 3rd and 5th positions are preferred. When Ag ₁ is a naphthyl group having a substituent, it is preferred that the group has at least one sulfo group as a substituent. When the naphthyl group has two or more substituents, at least one of the substituents is a sulfo group, a hydroxy group, or an alkoxy group having 1 to 4 carbon atoms and having a sulfo group, and the other substituents are preferably a sulfo group, a hydroxy group, a carboxy group, or a lower alkoxy group having a sulfo group. It is particularly preferred that the naphthyl group has two or more sulfo groups as a substituent. As the lower alkoxy group having a sulfo group, a straight-chain alkoxy group is preferred, and the substitution position of the sulfo group is preferably the terminal of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably a 3-sulfopropoxy group. When the naphthyl group has two sulfo groups, the substitution positions of the sulfo groups, assuming that the azo group is at position 2, are preferably a combination of 4-position and 8-position, and a combination of 6-position and 8-position, and more preferably a combination of 6-position and 8. When the naphthyl group has three sulfo groups, the substitution positions of the sulfo groups, assuming that the azo group is at position 2, are preferably a combination of 3-position, 6-position and 8-position.

In the above formula (6), Bg and Cg are each independently represented by the above formula (7) or the above formula (8), but either Bg or Cg is represented by the above formula (7).

In the above formula (7), Rg ₁ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group, preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, more preferably a hydrogen atom, a methyl group, or a methoxy group. Particularly preferred Rg ₁ is a hydrogen atom or a methoxy group. As the alkoxy group having 1 to 4 carbon atoms and a sulfo group, a linear alkoxy group is preferred, and the substitution position of the sulfo group is preferably the terminal of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably a 3-sulfopropoxy group. In the formula (7), the substitution position of Rg ₁ is preferably the 2nd or 3rd position, more preferably the 3rd position, with the azo group substituted on the Ag ₁ side being the 1st position. p ₁ represents an integer of 0 to 2. When a sulfo group is present ( _p1 is 1 or 2), the substitution position of the sulfo group is preferably the 6-position or 7-position, and more preferably the 6-position.

In the above formula (8), Rg ₂ and Rg ₃ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group, preferably a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group, more preferably a hydrogen atom, a methyl group, a methoxy group, a 3-sulfopropoxy group, or a 4-sulfopropoxy group. The substitution position of Rg ₂ or Rg ₃ can be a combination of only the 2nd position, only the 5th position, the 2nd and 5th positions, the 3rd and 5th positions, the 2nd and 6th positions, or the 3rd and 6th positions, with the azo group substituted on the Ag ₁ side in the above formula (6) being the 1st position, but preferably only the 2nd position, only the 5th position, or the 2nd and 5th positions. Note that only the 2nd position and only the 5th position indicate that only the 2nd or 5th position has one substituent other than a hydrogen atom.

Xg ₁ in the above formula (6) represents an amino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent, a benzoyl group which may have a substituent, or a benzoylamino group which may have a substituent. Xg ₁ is preferably an amino group which may have a substituent or a phenylamino group which may have a substituent, more preferably a phenylamino group which may have a substituent. The amino group which may have a substituent is preferably an amino group having one or two selected from the group consisting of a hydrogen atom, a methyl group, a methoxy group, a sulfo group, an amino group, and a lower alkylamino group, and more preferably an amino group having one or two hydrogen atoms, a methyl group, or a sulfo group. The phenylamino group which may have a substituent is preferably a phenylamino group having one or two substituents selected from the group consisting of a hydrogen atom, a lower alkyl group, a lower alkoxy group, a sulfo group, an amino group, and a lower alkylamino group, and more preferably a phenylamino group having one or two substituents selected from the group consisting of a hydrogen atom, a methyl group, a methoxy group, a sulfo group, and an amino group. The phenylazo group is preferably a phenylazo group having one to three substituents selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an amino group, a hydroxy group, and a carboxyethylamino group. The benzoyl group which may have a substituent is preferably a benzoyl group having one substituent selected from the group consisting of a hydrogen atom, a hydroxy group, an amino group, and a carboxyethylamino group. The benzoylamino group which may have a substituent is preferably a benzoylamino group having one substituent selected from the group consisting of a hydrogen atom, a hydroxy group, an amino group, and a carboxyethylamino group. The position of the substituent is not particularly limited, but when Xg ₁ is a group having a phenyl group, it is particularly preferable that one of the substituents is in the p-position with respect to the bonding position indirectly bonding to the naphthalene skeleton shown in formula (6), and as a specific example, in the case of a phenylamino group, it is preferable that the substituent is in the p-position with respect to the amino group.

The azo compound represented by the above formula (6) or a salt thereof is preferably an azo compound represented by the above formula (9) or a salt thereof, since it has improved performance.

In the above formula (9), _Ag2 has the same meaning as _Ag1 in formula (6). _Rg4 and _Rg5 each independently have the same meaning as _Rg1 in formula (7). _Xg2 has the same meaning as _Xg1 in formula (6). _p2 and _p3 each independently have the same meaning as _p1 in formula (7). In particular, it is preferable that _p2 and _p3 are each independently 1 or 2 in order to improve the polarization characteristics.

In the polarizing element, the content of the azo compound represented by formula (6) or its salt is preferably 0.01 to 5000 parts by mass, more preferably 0.1 to 3000 parts by mass, more preferably 10 to 1000 parts by mass, and even more preferably 40 to 400 parts by mass, relative to 100 parts by mass of the azo compound represented by formula (5).

The azo compound represented by the above formula (6) or its salt can be synthesized by, for example, the methods described in Patent Documents 7 to 12, but is not limited to these.

Specific examples of the azo compound represented by the above formula (6) include, for example, C.I. Direct Blue 34, C.I. Direct Blue 69, C.I. Direct Blue 70, C.I. Direct Blue 71, C.I. Direct Blue 72, C.I. Direct Blue 75, C.I. Direct Blue 78, C.I. Direct Blue 81, C.I. Direct Blue 82, C.I. Direct Blue 83, C.I. Direct Blue 186, C.I. Examples of azo compounds include C.I. Direct Blue 258, Benzo Fast Chrome Blue FG (C.I. 34225), Benzo Fast Blue BN (C.I. 34120), and C.I. Direct Green 51.

Specific examples of the azo compound represented by the above formula (6) are shown below in the form of a free acid.

In the polarizing element, the content of the azo compound represented by formula (1) or its salt is preferably 0.01 to 300 parts by mass, more preferably 0.1 to 200 parts by mass, and even more preferably 30 to 200 parts by mass, per 100 parts by mass of the azo compound represented by formula (5).

The azo compound represented by the above formula (1) particularly affects the transmittance of 400 to 500 nm. In a polarizing element, the transmittance and polarization degree (dichroism) on the short wavelength side of 400 to 500 nm affect the blue bleeding during black display and the yellowing of white during white display. The azo compound represented by formula (1) can improve the polarization characteristics (dichroism) of 400 to 500 nm while suppressing the decrease in the transmittance on the short wavelength side in the parallel position of the polarizing element, and can further reduce the yellowishness during white display and the blue bleeding during black display. By further containing the azo compound represented by formula (1), the polarizing element is preferable because it shows more achromaticity by itself when the single transmittance after luminosity correction is in the range of 35 to 45%, expresses a higher quality paper-like white color during white display, and further improves the polarization degree.

The azo compounds represented by the above formulas (1), (5), and (6) may each be in a free form or in a salt form. The salt may be, for example, an alkali metal salt such as a lithium salt, a sodium salt, or a potassium salt, or an organic salt such as an ammonium salt or an alkylamine salt. The salt is preferably a sodium salt.

The polarizing element contains an azo compound represented by formula (1) and formula (5) and/or formula (6), and thus has a high transmittance and a high degree of polarization in the transmittance and degree of polarization after luminosity correction. Furthermore, the polarizing element can have performance such as a* value and b* value, which are chromaticity in the preferred range described later, single transmittance after luminosity correction, and average transmittance in a specific wavelength band. For example, the transmittance of each wavelength can be made constant in the transmittance of the film alone. Furthermore, the transmittance can be made constant in the parallel position, that is, an achromatic color can be provided in the parallel position. Furthermore, the transmittance can be made constant at the same time in the perpendicular position, that is, an achromatic hue can be provided. For this reason, by containing an azo compound represented by formula (1) and formula (5) and/or formula (6), the polarizing element of the present application can provide not only a polarizing element with high transmittance and high contrast, i.e., a high degree of polarization, but also a polarizing element with an achromatic hue.

It is preferable that the blending ratio of the azo compounds in the polarizing element is further adjusted so that the transmittance and chromaticity are within the preferred ranges described below at the content of each azo compound described above. The performance of the polarizing element varies depending not only on the blending ratio of each azo compound in the polarizing element, but also on various factors such as the swelling degree and stretching ratio of the substrate to which the azo compound is adsorbed, the dyeing time, dyeing temperature, pH during dyeing, and the effect of salt. For this reason, the blending ratio of each azo compound can be determined according to the swelling degree of the substrate, the dyeing temperature, time, pH, type of salt, salt concentration, and even the stretching ratio.

(Base material)
The substrate is preferably a film obtained by forming a hydrophilic polymer capable of adsorbing a dichroic dye, particularly an azo compound. The hydrophilic polymer is not particularly limited, but may be, for example, a polyvinyl alcohol resin, an amylose resin, a starch resin, a cellulose resin, or a polyacrylate resin. From the viewpoint of dyeability, processability, crosslinkability, etc. of the dichroic dye, the hydrophilic polymer is most preferably a polyvinyl alcohol resin or a derivative thereof. A polarizing element can be produced by adsorbing an azo compound or a salt thereof to the substrate and applying an orientation treatment such as stretching.

(Transmittance after visibility correction)
The transmittance after luminosity correction is a transmittance corrected to the luminosity of the human eye, as determined according to JIS Z 8722:2009. The transmittance of each wavelength used for correction can be measured by measuring the spectral transmittance of a measurement sample (for example, a polarizing element or a polarizing plate) for each wavelength of 400 to 700 nm using a C light source (2-degree visual field) every 5 nm or 10 nm, and correcting the transmittance to luminosity according to JIS Z 8722:2009. The transmittance after luminosity correction includes a single transmittance after luminosity correction when a polarizing element or a polarizing plate is measured alone, a parallel transmittance after luminosity correction when the transmittance when two polarizing elements or polarizing plates are used and the absorption axes of each are parallel is corrected to luminosity, and a perpendicular transmittance after luminosity correction when the transmittance when two polarizing elements or polarizing plates are used and the absorption axes of each are perpendicular is corrected to luminosity.

(I) Difference in Average Transmittance Between Two Wavelength Bands In the above polarizing element, it is preferable that the difference in average transmittance between specific wavelength bands is equal to or less than a predetermined value. The average transmittance is the average value of the transmittance of each wavelength in a specific wavelength band.

The wavelength bands 420nm to 480nm, 520nm to 590nm, and 600nm to 640nm are the main wavelength bands based on the color matching functions used in calculations to indicate colors in JIS Z 8781-4:2013. Specifically, in the XYZ color matching functions of JIS Z 8701, which is the basis of JIS Z 8781-4:2013, when the maximum values of x(λ) with a maximum value of 600nm, y(λ) with a maximum value of 550nm, and z(λ) with a maximum value of 455nm are taken as 100, the wavelength bands 420nm to 480nm, 520nm to 590nm, and 600nm to 640nm respectively show wavelengths that are 20 or more.

The transmittance of the polarizing element measured at each wavelength in a state where two polarizing elements are stacked so that the absorption axis directions are parallel (during light display or white display) is also referred to as the "parallel transmittance" of each wavelength. The average transmittance of each wavelength from ○ nm to △ nm is also referred to as "AT _○-△ ". With respect to the parallel transmittance of each wavelength of the polarizing element of the present invention, the absolute value of the difference between AT _420-480 and AT _520-590 is preferably 2.5% or less, more preferably 1.8% or less, even more preferably 1.5% or less, and particularly preferably 1.0% or less. Furthermore, with respect to the parallel transmittance of each wavelength, the absolute value of the difference between AT _520-590 and AT _600-640 is preferably 3.0% or less, more preferably 2.0% or less, even more preferably 1.5% or less, and particularly preferably 1.0% or less. Such a polarizing element can display high-quality paper-like white in the parallel position.

Furthermore, the transmittance measured at each wavelength in a state where two polarizing elements are stacked so that the absorption axis directions are perpendicular (during black display or during dark display) is also referred to as the "orthogonal transmittance" of each wavelength. Regarding the orthogonal transmittance at each wavelength of the polarizing element of the present invention, it is preferable that the absolute value of the difference between AT _420-480 and AT _520-590 is 1.0% or less, and the absolute value of the difference between AT _520-590 and AT _600-640 is 1.0% or less. Such a polarizing element can display achromatic black in the orthogonal phase. Furthermore, regarding the orthogonal transmittance, it is preferable that the absolute value of the difference between AT _420-480 and AT _520-590 is 0.6% or less, more preferably 0.3% or less, and even more preferably 0.1% or less. Regarding the crossed transmittance, the difference between AT _520-590 and AT _600-640 is preferably 1.0% or less in absolute value, more preferably 0.6% or less, further preferably 0.3% or less, and particularly preferably 0.1%.

Furthermore, the average transmittances for each wavelength of the single transmittance, parallel transmittance, and orthogonal transmittance in each of the wavelength bands 380 nm to 420 nm, 480 nm to 520 nm, and 640 nm to 780 nm are preferably adjusted to some extent, although the effect on the hue of the polarizing element is not large, when the average transmittances in the wavelength bands 420 nm to 480 nm, 520 nm to 590 nm, and 600 nm to 640 nm are adjusted as described above. With regard to the single transmittance at each wavelength, it is preferable that the difference between AT _380-420 and AT _420-480 is 15% or less as an absolute value, the difference between AT _480-520 and AT _420-480 is 15% or less as an absolute value, the difference between AT _480-520 and AT _520-590 is 15% or less as an absolute value, and the difference between AT _640-780 and AT _600-640 is 20% or less as an absolute value.

(II) Single transmittance after luminosity correction The polarizing element preferably has a single transmittance after luminosity correction of 35% to 66%. The single transmittance after luminosity correction is the transmittance corrected to luminosity according to JIS Z 8722:2009 for one measurement sample (for example, a polarizing element or a polarizing plate). A higher transmittance is required for the performance of the polarizing plate, but if the single transmittance after luminosity correction is 35% to 60%, it can express brightness without discomfort even when used in a display device. Since the higher the transmittance, the lower the degree of polarization tends to be, from the viewpoint of balance with the degree of polarization, the single transmittance after luminosity correction is more preferably 37% to 50%, more preferably 38% to 50%, and extremely preferably 38% to 45%. If the single transmittance after luminosity correction exceeds 65%, the degree of polarization may decrease, but if a bright transmittance of the polarizing element or a specific polarization performance or contrast is required, the single transmittance after luminosity correction may exceed 65%.

(III) Average transmittance in a specific wavelength band The polarizing element preferably has an AT _520-590 measured in a parallel position of 25% to 50%. When such a polarizing element is provided in a display device, it can be a bright, clear display device with high luminance. The transmittance of each wavelength in the wavelength band of 520 nm to 590 nm is one of the main wavelength bands based on the color matching function used in calculations to indicate colors in JIS Z 8781-4:2013. In particular, each wavelength band of 520 nm to 590 nm is the wavelength band with the highest visibility based on the color matching function, and the transmittance in this range is close to the transmittance that can be confirmed by the naked eye. For this reason, it is very important to adjust the transmittance of each wavelength in the wavelength band of 520 nm to 590 nm. The AT _520-590 measured in a parallel position is more preferably 28% to 45%, and even more preferably 30% to 40%. Furthermore, the degree of polarization of the polarizing element in this case may be 80% to 100%, but is preferably 90% to 100%, more preferably 97% to 100%, even more preferably 99% or more, and particularly preferably 99.5% or more. A high degree of polarization is preferable, but in the relationship between the degree of polarization and the transmittance, the transmittance and degree of polarization can be adjusted to an appropriate value depending on whether importance is placed on brightness or on the degree of polarization (or contrast).

(Chromaticity a* and b* values)
The chromaticity a* and b* values are values obtained when measuring the transmittance of natural light according to JIS Z 8781-4:2013. The method of displaying object colors defined in JIS Z 8781-4:2013 corresponds to the method of displaying object colors defined by the International Commission on Illumination (abbreviated as CIE). The chromaticity a* and b* values are measured by irradiating a measurement sample (for example, a polarizing element or a polarizing plate) with natural light. In the following, the chromaticity a* and b* values obtained for one measurement sample are indicated as a*-s and b*-s, the chromaticity a* and b* values obtained for a state in which two measurement samples are arranged so that their absorption axis directions are parallel to each other (when displaying white) are indicated as a*-p and b*-p, and the chromaticity a* and b* values obtained for a state in which two measurement samples are arranged so that their absorption axis directions are perpendicular to each other (when displaying black) are indicated as a*-c and b*-c.

In the above polarizing element, the absolute values of a*-s and b*-s are preferably 1.0 or less, and the absolute values of a*-p and b*-p are preferably 2.0 or less. Such a polarizing element is a neutral color by itself, and can display high-quality white when displaying white. The absolute values of a*-p and b*-p of the polarizing element are more preferably 1.5 or less, and even more preferably 1.0 or less. Furthermore, the absolute values of a*-c and b*-c of the polarizing element are preferably 2.0 or less, and even more preferably 1.0 or less. Such a polarizing element can display achromatic black when displaying black. Even if there is a difference of only 0.5 in the absolute values of the chromaticity a* value and b* value, humans can perceive the difference in color, and some people may feel the difference in color to be large. For this reason, it is very important to control these values in the polarizing element. In particular, when the absolute values of a*-p, b*-p, a*-c, and b*-c are each 1.0 or less, a good polarizing plate can be obtained in which other colors are hardly visible in the white color when white is displayed and in the black color when black is displayed. Achromaticity in the parallel position, that is, a high-quality paper-like white color, can be realized, and achromatic, clear, luxurious black color can be realized in the orthogonal position. However, the influence of the hue that gives the black color of the display device is not limited to this, and in the first place, in a state where there is no light (dark), even if the hue is present, it appears black. Therefore, when the degree of polarization is high, that is, when the orthogonal transmittance of each wavelength is low, the polarizing element can give black even if the absolute values of a*-c and b*-c are not each 2.0 or less. As a result of our investigations, we found that when the cross-phase transmittance is 1% or less or the polarization degree is about 97% or more in the wavelength bands of 420 nm to 480 nm, 520 nm to 590 nm, and 600 nm to 640 nm, it is preferable because black can be visually imparted regardless of the absolute values of a*-c and b*-c. When the cross-phase transmittance is 0.6% or less or the polarization degree is 98% or more in the wavelength bands of 420 nm to 480 nm, 520 nm to 590 nm, and 600 nm to 640 nm, it is more preferable because black can be visually imparted, and when the cross-phase transmittance is 0.3% or less or the polarization degree is 99% or more, it is particularly preferable.

In view of the above, a preferred method for imparting a black hue when two polarizing elements are stacked so that their absorption axis directions are perpendicular to each other is to satisfy any one of the following 1) to 3):
1) With respect to the transmittance at each wavelength (hereinafter also referred to as "orthogonal transmittance") measured in a state in which two polarizing elements are overlapped so that the absorption axis directions are orthogonal (during black display or dark display), the absolute value of the difference between AT _420-480 and AT _520-590 is 1.0% or less, and the absolute value of the difference between AT _520-590 and AT _600-640 is 1.0% or less. 2) The absolute values of a*-c and b*-c are each 2.0 or less. 3) The orthogonal transmittance in each of the wavelength bands 420 nm to 480 nm, 520 nm to 590 nm, and 600 nm to 640 nm is 1% or less, or the degree of polarization is approximately 97% or more.

The polarizing element of the present invention has high contrast and high transmittance, while also having achromaticity and a high degree of polarization by itself. Furthermore, the polarizing element of the present invention can express a high-quality paper-like white color (paper white) when displaying white, and can express an achromatic black color, particularly a clear black color with a luxurious feel, when displaying black. Until now, no polarizing element has existed that combines such high transmittance and achromaticity. The polarizing element of the present invention is also highly durable, particularly resistant to high temperatures and high humidity.

The polarizing element according to the present invention has the advantage that it generates little heat even when exposed to sunlight or other light because it absorbs less light with wavelengths of 700 nm or more than commonly used iodine-based polarizing plates and Patent Document 3. For example, when a liquid crystal display is used outdoors, sunlight is irradiated onto the liquid crystal display, and as a result, the polarizing element is also irradiated. Sunlight also contains light with wavelengths of 700 nm or more, including near-infrared light that has a heat-generating effect. For example, a polarizing element using an azo compound as described in Example 3 of JP-B-02-061988 absorbs near-infrared light with a wavelength of about 700 nm, and generates some heat, but the polarizing element of the present invention absorbs very little near-infrared light, so it generates little heat even when exposed to sunlight outdoors. The polarizing element of the present invention is excellent in that it generates little heat and therefore deteriorates little.

(Method of manufacturing a polarizing element)
A specific method for producing a polarizing element will be described below, taking as an example a case where an azo compound is adsorbed onto a substrate made of a polyvinyl alcohol resin. Note that the method for producing a polarizing element according to the present invention is not limited to the following method.

(Preparing the original film)
The raw film can be produced by forming a film of a polyvinyl alcohol resin. The polyvinyl alcohol resin is not particularly limited, and may be a commercially available one or may be one synthesized by a known method. The polyvinyl alcohol resin can be obtained, for example, by saponifying a polyvinyl acetate resin. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The saponification degree of the polyvinyl alcohol resin is usually preferably about 85 to 100 mol%, and more preferably 95 mol% or more. The polyvinyl alcohol resin may be further modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can also be used. The degree of polymerization of the polyvinyl alcohol resin means the viscosity average degree of polymerization, which can be determined by a method well known in the art. Generally, the degree of polymerization is preferably about 1,000 to 10,000, and more preferably about 1,500 to 6,000.

The method for forming the polyvinyl alcohol resin into a film is not particularly limited, and the film can be formed by a known method. In this case, the polyvinyl alcohol resin film may contain glycerin, ethylene glycol, propylene glycol, low molecular weight polyethylene glycol, etc. as a plasticizer. The amount of the plasticizer is preferably 5 to 20 mass % of the total amount of the film, and more preferably 8 to 15 mass %. The thickness of the raw film is not particularly limited, but is, for example, about 5 μm to 150 μm, and preferably about 10 μm to 100 μm.

(Swelling process)
The raw film obtained as described above is subjected to a swelling treatment. The swelling treatment is preferably performed by immersing the raw film in a solution at 20 to 50°C for 30 seconds to 10 minutes. The solution is preferably water. The stretching ratio is preferably adjusted to 1.00 to 1.50 times, and more preferably 1.10 to 1.35 times. When the time required to manufacture a polarizing element is to be shortened, the raw film also swells during the dyeing treatment described below, so the swelling treatment can be omitted.

(Dyeing process)
In the dyeing process, the resin film obtained by swelling the raw film is adsorbed with and impregnated with an azo compound. If the swelling process is omitted, the swelling process of the raw film can be performed simultaneously in the dyeing process. The process of adsorbing and impregnating the azo compound is a process for coloring the resin film, so it is called the dyeing process.

As the azo compound used in the dyeing process, an azo compound represented by formula (1) or a salt thereof is used, and further, optionally, an azo compound represented by formula (5) and/or formula (6) or a salt thereof, and/or an azo compound which is a dichroic dye as exemplified in Non-Patent Document 1, etc. may be used to adjust the color to an extent that does not impair the performance of the polarizing element of the present application. These azo compounds are used in the form of free acid, or a salt of the compound may be used. Such salts are, for example, alkali metal salts such as lithium salts, sodium salts, and potassium salts, or organic salts such as ammonium salts and alkylamine salts, and preferably sodium salts.

The dyeing process is not particularly limited as long as it is a method for adsorbing and impregnating the dye into the resin film, but for example, it is preferably performed by immersing the resin film in the dyeing solution, or it can also be performed by applying the dyeing solution to the resin film. The content of each azo compound in the dyeing solution can be adjusted, for example, within the range of 0.001 to 10 mass %. The solution temperature in this process is preferably 5 to 60°C, more preferably 20 to 50°C, and particularly preferably 35 to 50°C. The time for immersion in the solution can be adjusted appropriately, but is preferably adjusted to 30 seconds to 20 minutes, and more preferably 1 to 10 minutes.

In addition to the azo compound, the dyeing solution may further contain a dyeing assistant as necessary. Examples of dyeing assistants include sodium carbonate, sodium bicarbonate, sodium chloride, sodium sulfate, anhydrous sodium sulfate, and sodium tripolyphosphate. The content of the dyeing assistant can be adjusted to any concentration depending on the time and temperature depending on the dyeing properties of the dye, but the content of each is preferably 0.01 to 5 mass %, and more preferably 0.1 to 2 mass %, in the dyeing solution.

(Cleaning process 1)
After the dyeing step, a cleaning step (hereinafter also referred to as "cleaning step 1") can be performed before the next step. The dyeing step 1 is a step of cleaning the dyeing solution attached to the surface of the resin film in the dyeing step. By performing the cleaning step 1, it is possible to suppress the transfer of the dye into the liquid to be treated next. In the cleaning step 1, water is generally used as the cleaning liquid. The cleaning method is preferably immersed in the cleaning liquid, but cleaning can also be performed by applying the cleaning liquid to the resin film. The cleaning time is not particularly limited, but is preferably 1 to 300 seconds, more preferably 1 to 60 seconds. The temperature of the cleaning liquid in the cleaning step 1 must be a temperature at which the material constituting the resin film (for example, a hydrophilic polymer, here a polyvinyl alcohol-based resin) does not dissolve. The cleaning process is generally performed at 5 to 40°C. However, since there is no problem with performance even if the cleaning step 1 is not performed, the cleaning step can be omitted.

(Step of Adding a Crosslinking Agent and/or a Water Resistant)
After the dyeing step or washing step 1, a step of incorporating a crosslinking agent and/or a water-resistant agent can be carried out. The method of incorporating a crosslinking agent and/or a water-resistant agent in the resin film is preferably immersion in the treatment solution, but the treatment solution may also be applied or coated on the resin film. The treatment solution contains at least one crosslinking agent and/or water-resistant agent and a solvent. The temperature of the treatment solution in this step is preferably 5 to 70°C, more preferably 5 to 50°C. The treatment time in this step is preferably 30 seconds to 6 minutes, more preferably 1 to 5 minutes.

Examples of the crosslinking agent include boron compounds such as boric acid, borax, or ammonium borate, polyaldehydes such as glyoxal or glutaraldehyde, polyisocyanate compounds such as biuret, isocyanurate, or block, and titanium compounds such as titanium oxysulfate. Other examples include ethylene glycol glycidyl ether and polyamide epichlorohydrin. Examples of the water-resistant agent include succinic peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride, or magnesium chloride, with boric acid being preferred. The solvent for the crosslinking agent and/or water-resistant agent is preferably water, but is not limited to this. The concentration of the crosslinking agent and/or water-resistant agent can be appropriately determined by a person skilled in the art depending on the type of agent, but taking boric acid as an example, the concentration in the treatment solution is preferably 0.1 to 6.0 mass%, more preferably 1.0 to 4.0 mass%. However, if it is not essential to include a crosslinking agent and/or water-resistant agent and it is desired to shorten the time, or if crosslinking or water-resistant treatment is not required, this treatment step may be omitted.

(Stretching process)
After the dyeing step, washing step 1, or the step of incorporating a crosslinking agent and/or a water-resistant agent, the stretching step is performed. The stretching step is performed by uniaxially stretching the resin film. The stretching method may be either a wet stretching method or a dry stretching method. The stretching ratio is preferably 3 times or more, more preferably 4 to 8 times, and particularly preferably 5 to 7 times.

In the case of the wet stretching method, it is preferable to stretch the resin film in water, a water-soluble organic solvent, or a mixed solution thereof. It is preferable to perform the stretching process while immersing in a solution containing at least one crosslinking agent and/or water-resistant agent. The crosslinking agent and water-resistant agent may be the same as those described above for the process of adding the crosslinking agent and/or water-resistant agent. The concentration of the crosslinking agent and/or water-resistant agent in the solution in the stretching process is, for example, preferably 0.5 to 15 mass%, more preferably 2.0 to 8.0 mass%. The stretching temperature is preferably 40 to 60°C, more preferably 45 to 58°C. The stretching time is usually 30 seconds to 20 minutes, but more preferably 2 to 5 minutes. The wet stretching process can be performed in one stage, but can also be performed in multiple stages of two or more stages.

In the case of the dry stretching method, if the stretching heating medium is air, it is preferable to stretch the resin film when the temperature of the air medium is between room temperature and 180°C. In addition, it is preferable to set the humidity in the atmosphere at 20 to 95% RH. Examples of heating methods include inter-roll zone stretching, roll heating stretching, rolling stretching, and infrared heating stretching, but the stretching method is not limited. The stretching process can be performed in one stage, but can also be performed in multiple stages of two or more stages.

(Washing process 2)
After the stretching step, the crosslinking agent and/or water-resistant agent may precipitate on the surface of the resin film, or foreign matter may adhere to the surface of the resin film. Therefore, a washing step (hereinafter also referred to as "washing step 2") for washing the surface of the resin film may be performed. The washing time is preferably 1 second to 5 minutes. The washing method is preferably to immerse the resin film in a washing solution, but washing can also be performed by applying or coating the solution on the resin film. The washing solution is preferably water. The washing treatment can be performed in one stage, or in multiple stages of two or more stages. The solution temperature in the washing step is not particularly limited, but is usually 5 to 50°C, preferably 10 to 40°C.

Examples of the processing liquid or its solvent used in the processing steps up to this point include, in addition to water, alcohols such as dimethyl sulfoxide, N-methylpyrrolidone, methanol, ethanol, propanol, isopropyl alcohol, glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, or trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine, but are not limited to these. The processing liquid or its solvent is most preferably water. Furthermore, these processing liquids or their solvents can be used alone or as a mixture of two or more.

(Drying process)
After the stretching step or the washing step 2, a drying step of the resin film is carried out. The drying treatment can be carried out by natural drying, but in order to increase the drying efficiency, it can be carried out by compressing with a roll, removing moisture from the surface with an air knife or a water absorbing roll, and/or by air drying. The drying treatment temperature is preferably 20 to 100°C, and more preferably 60 to 100°C. The drying treatment time is, for example, 30 seconds to 20 minutes, and preferably 5 to 10 minutes.

In the method for producing a polarizing element, the swelling degree of the substrate in the swelling step, the compounding ratio of each azo compound in the dyeing step, the temperature, pH, type and concentration of salt such as sodium chloride, mirabilite, sodium tripolyphosphate, and dyeing time, and the stretching ratio in the stretching step are preferably adjusted so that the polarizing element satisfies at least one of the following conditions (i) to (v), and more preferably so that the polarizing element further satisfies conditions (vi) and (vii):
(i) With regard to the parallel transmittance, the absolute difference between AT _420-480 and AT _520-590 is 2.5% or less, and the absolute difference between AT _520-590 and AT _600-640 is 3.0% or less.
(ii) With respect to the crossed transmittance, the absolute difference between AT _420-480 and AT _520-590 is 1.0% or less, and the absolute difference between AT _520-590 and AT _600-640 is 1.0% or less.
(iii) The single transmittance after visibility correction is 35% to 45%.
(iv) The absolute values of the a* and b* values are each 1.0 or less for the polarizing element alone, and 2.0 or less in the parallel position.
(v) The absolute values of the a* and b* values measured in the orthogonal direction are each 2 or less.
(vi) The parallel transmittance is 28 to 45% for AT _520-590 .
(vii) In the single transmittance or crossed transmittance at each wavelength, the absolute value of the difference between AT _380-420 and AT _420-480 is 15% or less, the absolute value of the difference between AT _480-520 and AT _420-480 is 15% or less, the absolute value of the difference between AT _480-520 and AT _520-590 is 15% or less, and/or the absolute value of the difference between AT _640-780 and AT _600-640 is 20% or less.

By the above method, a polarizing element containing at least a combination of azo compounds represented by formula (5) and/or formula (6) and formula (1) can be manufactured. Such a polarizing element has a higher transmittance and a higher degree of polarization than conventional polarizing elements, and can express a high-quality paper-like white color when two polarizing elements are stacked so that the absorption axis directions are parallel, and has a hue that is neutral (neutral gray) by itself. Furthermore, when two polarizing elements are stacked so that the absorption axis directions are perpendicular to each other, the polarizing element exhibits a high-class achromatic black. In addition, the polarizing element has high durability against high temperatures and high humidity.

<Polarizing Plate>
The polarizing plate of the present invention has excellent polarizing performance as well as moisture resistance, heat resistance and light resistance since it includes the above-mentioned polarizing element of the present invention.

The polarizing plate according to the present invention comprises a polarizing element and a transparent protective layer provided on one or both sides of the polarizing element. The transparent protective layer is provided for the purpose of improving the water resistance and ease of handling of the polarizing element.

The transparent protective layer is a protective film formed using a transparent material. The protective film is a film having a layer shape that can maintain the shape of the polarizing element, and is preferably a plastic having excellent transparency, mechanical strength, thermal stability, moisture shielding properties, etc. It is also possible to provide an equivalent function by forming a layer equivalent to this. Examples of plastics that constitute the protective film include films obtained from thermoplastic resins such as polyester-based resins, acetate-based resins, polyethersulfone-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, polyolefin-based resins, acrylic-based resins, and fluorine-based resins such as tetrafluoroethylene/hexafluoropropylene-based copolymers, acrylic-based, urethane-based, acrylic urethane-based, epoxy-based, and silicone-based thermosetting resins or ultraviolet-curing resins, and among these, polyolefin-based resins include amorphous polyolefin-based resins having polymerization units of cyclic polyolefins such as norbornene-based monomers or polycyclic norbornene-based monomers. In general, it is preferable to select a protective film that does not impair the performance of the polarizing element after lamination, and triacetyl cellulose (TAC) and norbornene, which are made of cellulose acetate resins, are particularly preferable as such protective films. In addition, the protective film may be subjected to a hard coat treatment, an anti-reflection treatment, or a treatment for the purpose of preventing sticking, diffusing, anti-glare, etc., as long as the effect of the present invention is not impaired. The thickness of the transparent protective layer is usually preferably 10 to 200 μm.

It is preferable that the polarizing plate further includes an adhesive layer for bonding the polarizing element and the transparent protective layer. Examples of adhesives constituting the adhesive layer include polyvinyl alcohol adhesives, urethane emulsion adhesives, acrylic adhesives, and polyester-isocyanate adhesives, with polyvinyl alcohol adhesives being preferred.

Examples of polyvinyl alcohol adhesives include, but are not limited to, Gohsenol NH-26 (manufactured by Nippon Gosei Co., Ltd.) and Exeval RS-2117 (manufactured by Kuraray Co., Ltd.). A crosslinking agent and/or a water-resistant agent can be added to the adhesive. As the polyvinyl alcohol adhesive, it is preferable to use a maleic anhydride-isobutylene copolymer, and an adhesive mixed with a crosslinking agent can be used as necessary. Examples of maleic anhydride-isobutylene copolymers include Isoban #18 (manufactured by Kuraray Co., Ltd.), Isoban #04 (manufactured by Kuraray Co., Ltd.), ammonia-modified Isoban #104 (manufactured by Kuraray Co., Ltd.), ammonia-modified Isoban #110 (manufactured by Kuraray Co., Ltd.), imidized Isoban #304 (manufactured by Kuraray Co., Ltd.), and imidized Isoban #310 (manufactured by Kuraray Co., Ltd.). In this case, a water-soluble polyvalent epoxy compound can be used as the crosslinking agent. Examples of water-soluble polyfunctional epoxy compounds include Denacol EX-521 (manufactured by Nagase Chemtec Corporation) and Tetrat-C (manufactured by Mitsui Gas Chemicals Co., Ltd.). In addition, known adhesives such as urethane-based, acrylic-based, and epoxy-based adhesives can also be used as adhesives other than polyvinyl alcohol-based resins. In particular, it is preferable to use acetoacetyl-modified polyvinyl alcohol, and further it is preferable to use a polyhydric aldehyde as its crosslinking agent. In addition, in order to improve the adhesive strength or water resistance of the adhesive, additives such as zinc compounds, chlorides, and iodides can be contained alone or simultaneously at a concentration of about 0.1 to 10 mass %. The additives to the adhesive are not particularly limited and can be appropriately selected by those skilled in the art. After bonding the transparent protective layer and the polarizing element with an adhesive, a polarizing plate can be obtained by drying or heat treatment at an appropriate temperature.

The polarizing element or polarizing plate may have various known functional layers, such as an AR layer (anti-reflection layer), an anti-glare layer, and a hard coat layer, on the exposed surface of the transparent protective layer or film. A coating method is preferred for producing these layers with various functions, but a film with the function can also be attached via an adhesive or pressure-sensitive adhesive.

Examples of the hard coat layer include an acrylic or polysiloxane hard coat layer and a urethane protective layer. The AR layer is expected to further improve the transmittance. The AR layer can be formed by vapor deposition or sputtering of a material such as silicon dioxide or titanium oxide, or by applying a thin layer of a fluorine-based material.

In some cases, when the polarizing element or polarizing plate is attached to a display device such as a liquid crystal or organic electroluminescence (commonly known as OLED or OEL), various functional layers for improving the viewing angle and/or contrast, and layers or films having brightness improving properties can be provided on the surface of the transparent protective layer or film that will later become the unexposed surface. The various functional layers are, for example, layers or films that control the phase difference (hereinafter, also referred to as "phase difference plates"). By attaching a phase difference plate, the polarizing plate of the present invention can also be used as an elliptical polarizing plate. The polarizing plate is preferably attached to these films or display devices with an adhesive.

In a liquid crystal display device, the polarizing plate of the present invention is disposed on either the entrance side or the exit side or both of the liquid crystal cell. The polarizing plate may or may not be in contact with the liquid crystal cell, but from the viewpoint of durability, it is preferable that it is not in contact. When the polarizing plate is in contact with the liquid crystal cell on the exit side of the liquid crystal cell, the liquid crystal cell can be used as the support of the polarizing plate. When the polarizing plate is not in contact with the liquid crystal cell, it is preferable to use a polarizing plate provided with a support other than the liquid crystal cell. From the viewpoint of durability, it is preferable that polarizing plates are disposed on both the entrance side and the exit side of the liquid crystal cell, and further, it is preferable to dispose the polarizing plate surface of the polarizing plate on the liquid crystal cell side and the support surface on the light source side. The entrance side of the liquid crystal cell refers to the light source side, and the opposite side is called the exit side.

The liquid crystal cell provided in the liquid crystal display device is preferably, for example, an active matrix type, and is formed by sealing liquid crystal between a transparent substrate on which electrodes and TFTs are formed and a transparent substrate on which an opposing electrode is formed. Light emitted from a light source such as a cold cathode fluorescent lamp or a white LED passes through a polarizing plate, then passes through the liquid crystal cell, a color filter, and another polarizing plate, and is projected onto the display screen.

The polarizing plate may be either a neutral gray polarizing plate or a color polarizing plate depending on the application.

The neutral gray polarizing plate has a neutral color, has little color leakage in the orthogonal direction in the polarization region of the visible light range, has excellent polarization performance, and is highly durable and inhibits discoloration and deterioration of polarization performance even under high temperature and high humidity conditions, making it suitable for use in vehicle-mounted display devices or outdoor display devices. Examples of display devices that use the polarizing plate of the present invention include OLEDs and liquid crystal display devices, but it can be particularly suitable for use in liquid crystal display devices.

The above liquid crystal display device is highly reliable and does not easily discolor or lose its polarization performance even in high temperature and high humidity conditions such as inside a car or outdoors because the polarizing plate of the present invention has brightness, excellent polarization performance, polarization properties, and light resistance.

The polarizing element used in the color polarizing plate of the in-vehicle display device or the outdoor display device may be provided with a protective layer or an AR layer and a support, etc., as necessary, in the same manner as the neutral gray polarizing plate. The color polarizing plate with the support can be obtained, for example, by applying a transparent adhesive (adhesive) to the flat surface of the support and then attaching a polarizing plate to this applied surface. Alternatively, a transparent adhesive (adhesive) may be applied to the polarizing plate and then attaching a support to this applied surface. The adhesive (adhesive) is preferably, for example, an acrylic ester-based adhesive. When this polarizing plate is used as an elliptical polarizing plate, the retardation plate side of the polarizing plate with retardation plate is usually attached to the support to form a layer order of polarizing plate/retardation plate/support, but the side without the retardation plate may be attached to the support to form a layer order of retardation plate/polarizing plate/support.

In addition to the polarizing element and the transparent protective layer, the neutral gray polarizing plate for vehicle mounting or outdoor display is preferably provided with an AR layer to further improve the transmittance, and an AR layer and a polarizing plate with a support, in which both an AR layer and a support such as a transparent resin are attached, are more preferable. The AR layer can be provided on one side or both sides of the polarizing plate. The support is preferably provided on one side of the polarizing plate, and may be provided directly on the polarizing plate, or the AR layer may be provided on the support. The AR layer and the polarizing plate with a support are preferably provided with a support provided with an AR layer/polarizing plate/AR layer in this order. The support preferably has a flat portion for attaching the polarizing plate, and is preferably a transparent substrate because it is for optical use. Transparent substrates are broadly divided into inorganic substrates and organic substrates, and include inorganic substrates such as soda glass, borosilicate glass, quartz substrates, sapphire substrates, and spinel substrates, as well as organic substrates such as acrylic, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, and cycloolefin polymers, with organic substrates being preferred. The thickness and size of the transparent substrate can be any desired size.

The above color polarizing plate has excellent polarization performance and is resistant to discoloration and deterioration of polarization performance even under high temperature and high humidity conditions, making it suitable for use in liquid crystal projectors and display devices such as in-vehicle and outdoor displays.

The color polarizing plate for liquid crystal projectors has brightness and excellent polarization performance, and in the necessary wavelength band of the polarizing plate (A. When using an ultra-high pressure mercury lamp: 420-500 nm for blue channel, 500-580 nm for green channel, 600-680 nm for red channel, B. Peak wavelength when using a three-primary color LED lamp: 430-450 nm for blue channel, 520-535 nm for green channel, 620-635 nm for red channel), the single plate average light transmittance of each wavelength is 39% or more, and the average light transmittance of each wavelength in the orthogonal direction is 0.4% or less, more preferably the single plate average light transmittance of each wavelength in the necessary wavelength band of the polarizing plate is 41% or more, and the average light transmittance of each wavelength in the orthogonal direction is 0.3% or less, more preferably 0.2% or less. Even more preferably, the single plate average light transmittance of each wavelength in the necessary wavelength band of the polarizing plate is 42% or more, and the average light transmittance of each wavelength in the orthogonal direction is 0.1% or less.

The single plate average transmittance is the average value of the transmittance in a specific wavelength range when natural light is incident on a single polarizing plate (hereinafter simply referred to as a "polarizing plate") that does not have an AR layer or a support such as a transparent glass plate. The orthogonal average transmittance is the average value of the light transmittance in a specific wavelength range when natural light is incident on two polarizing plates that are stacked so that their orientation directions are perpendicular to each other.

In one aspect, the polarizing plate of the present invention is a highly durable polarizing plate that can achieve achromaticity while having high transmittance and a high degree of polarization, and in particular can express a high-quality paper-like white color when displaying white, and a neutral black color when displaying black.

<Display Device>
The polarizing element or plate of the present invention, which has no wavelength dependency in the single, parallel, or orthogonal positions and has a nearly constant transmittance for each wavelength, can be suitably used to improve the reproducibility of the display color of a display device because its hue does not change even when used in the single, parallel, or orthogonal positions. By utilizing this property, a protective layer or functional layer and a transparent support such as glass, quartz, or sapphire are provided as necessary, and the polarizing element or plate is suitably applied to liquid crystal projectors, calculators, clocks, notebook computers, word processors, liquid crystal televisions, polarizing lenses, polarizing glasses, car navigation systems, and indoor and outdoor measuring instruments and displays.

In one aspect, the polarizing element or polarizing plate of the present invention can be particularly suitably used in liquid crystal display devices, such as reflective liquid crystal display devices, semi-transmissive liquid crystal display devices, and transmissive liquid crystal display devices, and can achieve high color reproducibility even in ambient light without the need for color correction even in the absence of a backlight. Conventional polarizing plates have low short-wavelength transmittance in the parallel position when the contrast is high, and therefore turn yellow in the parallel position in ambient light (natural light). For this reason, it was necessary to correct the color using a backlight or color filter, but on the other hand, problems such as the color turning blue in the perpendicular position occurred when color correction was performed in the parallel position. Even when displaying in such ambient light (without using a backlight), the polarizing element or polarizing plate does not color, so color reproducibility is high, and there is no color change between displaying in ambient light and displaying using a backlight. Taking advantage of these advantages, the polarizing element or polarizing plate can be suitably used in liquid crystal display devices, such as reflective liquid crystal display devices, semi-transmissive liquid crystal display devices, and transmissive liquid crystal display devices. Taking advantage of these characteristics, the polarizing element or polarizing plate can be particularly suitably used in reflective liquid crystal display devices and semi-transmissive liquid crystal display devices. In other words, a liquid crystal display device using the polarizing element or polarizing plate of the present invention can display high-quality paper-like white and neutral black. Furthermore, the liquid crystal display device has high durability and high reliability, and has high contrast and high color reproducibility over the long term. The polarizing element or polarizing plate of the present application is also suitable for use in organic electroluminescence and other devices other than liquid crystal display devices to prevent reflection of ambient light.

The present invention will be described in more detail below with reference to examples, but these are merely illustrative and do not limit the present invention in any way. Percentages and parts in the examples are by weight unless otherwise specified.

<<Example A>>

(Example A1: Synthesis of azo compound of formula (1-A4))
17.3 parts of 4-amino-benzenesulfonic acid was added to 400 parts of water, dissolved with sodium hydroxide, and 18.6 parts of 4-nitrobenzoyl chloride was added and stirred for 6 hours at 40 to 60° C. Then, 10.0 g of iron powder and 13 parts of 35% hydrochloric acid were added and stirred at 80° C. for 5 hours to complete the reaction. After removing the iron powder, the mixture was filtered to obtain 23.4 parts of an aminobenzoylaminobenzene compound represented by the following formula (1-A4-1).

23.4 parts of the obtained aminobenzoylaminobenzene compound (1-A4-1) was added to 400 parts of water, dissolved with sodium hydroxide, 5.5 parts of sodium nitrite was added, and 25.1 parts of 35% hydrochloric acid was added at 10 to 30° C., and the mixture was stirred at 10 to 30° C. for 1 hour to be diazotized.
To this was added 19.7 parts of 3-(2-amino-4-methylphenoxy)propane-1-sulfonic acid, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and then filtered to obtain 30.7 parts of a monoazoamino compound represented by the following formula (1-A4-2).

30.7 parts of the obtained monoazoamino compound (1-A4-2) was added to 400 parts of water, dissolved with sodium hydroxide, and 9.1 parts of phenyl chloroformate was stirred at 50-70°C for 6 hours to form an ureido compound. Salting out with sodium chloride and filtration were performed to obtain 10.0 parts of the ureido compound represented by the above formula (1-A4). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 423 nm.

(Example A2: Synthesis of azo compound of formula (1-A11))
17.3 parts of 4-amino-benzenesulfonic acid was added to 400 parts of water, dissolved with sodium hydroxide, and 20.0 parts of 3-methyl-4-nitrobenzoyl chloride was added and stirred for 6 hours at 40 to 60° C. Then, 10.0 g of iron powder and 13 parts of 35% hydrochloric acid were added and stirred at 80° C. for 5 hours to complete the reaction. After removing the iron powder, the mixture was filtered to obtain 24.5 parts of an aminobenzoylaminobenzene compound represented by the following formula (1-A11-1).

24.5 parts of the obtained aminobenzoylaminobenzene compound (1-A11-1) was added to 400 parts of water, dissolved with sodium hydroxide, 5.5 parts of sodium nitrite was added, and 25.1 parts of 35% hydrochloric acid was added at 10 to 30° C., and the mixture was stirred at 10 to 30° C. for 1 hour to be diazotized.
To this was added 11.0 parts of 2-methoxy-5-methylaniline, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and then filtered to obtain 25.5 parts of a monoazoamino compound represented by the following formula (1-A11-2).

25.5 parts of the obtained monoazoamino compound (1-A11-2) was added to 400 parts of water, dissolved with sodium hydroxide, and 9.1 parts of phenyl chloroformate was stirred at 50-70°C for 6 hours to form an ureido compound. Salting out with sodium chloride and filtration were performed to obtain 10.0 parts of the ureido compound represented by the above formula (1-A11). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 423 nm.

(Example A3: Synthesis of azo compound of formula (1-A26))
The procedure of Example A1 was repeated except that 13.7 parts of 4-aminobenzoic acid was used instead of 17.3 parts of 4-amino-benzenesulfonic acid, to obtain 10.0 parts of the ureido compound represented by the above formula (1-A26). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 425 nm.

(Example A4: Synthesis of azo compound of formula (1-A36))
The procedure of Example A1 was repeated except that 17.2 parts of 5-amino-2-chlorobenzoic acid was used instead of 17.3 parts of 4-amino-benzenesulfonic acid to obtain 9.2 parts of the ureido compound represented by the above formula (1-A36). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 419 nm.

(Example A5: Synthesis of azo compound of formula (1-A71))
23.4 parts of the aminobenzoylaminobenzene compound (1-A4-1) obtained in the same manner as in Example A1 was added to 400 parts of water, dissolved with sodium hydroxide, 5.5 parts of sodium nitrite was added, and 25.1 parts of 35% hydrochloric acid was added at 10 to 30° C., followed by stirring at 10 to 30° C. for 1 hour to perform diazotization.
To the mixture, 11.0 parts of 2-methoxy-5-methylaniline was added, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and then filtered to obtain 24.7 parts of a monoazoamino compound represented by the following formula (1-A71-L2).

17.2 parts of 5-amino-2-chlorobenzoic acid was added to 300 parts of water, dissolved with sodium hydroxide, and 18.6 parts of 4-nitrobenzoyl chloride was added and stirred for 6 hours at 40 to 60° C. Then, 10.0 g of iron powder and 13 parts of 35% hydrochloric acid were added and stirred at 80° C. for 5 hours to complete the reaction. After removing the iron powder, the mixture was filtered to obtain 23.3 parts of an aminobenzoylaminobenzene compound represented by the following formula (1-A71-R1).

23.3 parts of the obtained aminobenzoylaminobenzene compound (1-A71-R1) was added to 400 parts of water, dissolved with sodium hydroxide, 5.5 parts of sodium nitrite was added, and 25.1 parts of 35% hydrochloric acid was added at 10 to 30° C., and the mixture was stirred at 10 to 30° C. for 1 hour to be diazotized.
To this was added 19.7 parts of 3-(2-amino-4-methylphenoxy)propane-1-sulfonic acid, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and then filtered to obtain 30.6 parts of a monoazoamino compound represented by the following formula (1-A71-R2).

23.3 parts of the obtained monoazoamino compound (1-A71-L2) and 30.6 parts of the monoazoamino compound (1-A71-R2) were added to 600 parts of water, dissolved with sodium hydroxide, and 8.7 parts of phenyl chloroformate were stirred at 50-70°C for 8 hours to form an ureido compound. Salting out with sodium chloride and filtration were performed to obtain 10.8 parts of the ureido compound represented by the above formula (1-A71). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 424 nm.

(Example A6: Synthesis of azo compound of formula (1-A100))
25.3 parts of 4-aminobenzene-1,3-disulfonic acid was added to 400 parts of water, dissolved with sodium hydroxide, 18.6 parts of 4-nitrobenzoyl chloride was added, and the mixture was stirred for 6 hours at 40 to 60° C. Then, 10.0 g of iron powder and 13 parts of 35% hydrochloric acid were added, and the mixture was stirred for 5 hours at 80° C. to complete the reaction. After removing the iron powder, the mixture was filtered to obtain 29.8 parts of an aminobenzoylaminobenzene compound represented by the following formula (1-A100-L1).

29.8 parts of the obtained aminobenzoylaminobenzene compound (1-A100-L1) was added to 400 parts of water, dissolved with sodium hydroxide, 5.5 parts of sodium nitrite was added, and 25.1 parts of 35% hydrochloric acid was added at 10 to 30° C., and the mixture was stirred at 10 to 30° C. for 1 hour to be diazotized.
To this was added 9.7 parts of 2,5-dimethylaniline, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and then filtered to obtain 28.3 parts of a monoazoamino compound represented by the following formula (1-A100-L2).

11.0 parts of 4-aminobenzoic acid was added to 300 parts of water, cooled, and 25.0 parts of 35% hydrochloric acid was added at 10° C. or lower, followed by addition of 5.5 parts of sodium nitrite, and the mixture was stirred at 5 to 10° C. for 1 hour to effect diazotization.
11.0 parts of 2-methoxy-5-methylaniline was added thereto, and while stirring at 10 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and filtered to obtain 16.0 parts of a monoazoamino compound represented by the following formula (1-A100-R).

28.3 parts of the obtained monoazoamino compound (1-A100-L2) and 16.0 parts of the monoazoamino compound (1-A100-R) were added to 600 parts of water, dissolved with sodium hydroxide, and 8.7 parts of phenyl chloroformate were stirred at 50-70°C for 8 hours to form an ureido compound. Salting out with sodium chloride and filtration were performed to obtain 8.9 parts of the ureido compound represented by the above formula (1-A100). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 424 nm.

(Examples A7 to A12: Preparation of polarizing elements)
A 75 μm thick polyvinyl alcohol was immersed for 4 minutes in a 45° C. aqueous solution (dye bath) containing 0.03% of each of the azo compounds of the above formulas (1-A4), (1-A11), (1-A26), (1-A36), (1-A71), and (1-A100) obtained in Examples A1 to A6 and 0.1% of sodium sulfate. This film was stretched 5 times in a 3% boric acid aqueous solution at 50° C., washed with water while maintaining tension, and dried to obtain a polarizing element. The maximum absorption wavelength and polarization rate of the obtained polarizing element are shown in Table A1. As shown in Table A1, all of the polarizing elements prepared using these compounds had high polarization rates.

The measurement of the maximum absorption wavelength of the polarizing element and the calculation of the polarization ratio were calculated using the parallel transmittance (Ky) at each wavelength at the time of polarized light incidence and the orthogonal transmittance (Kz) at each wavelength at the time of polarized light incidence measured using a spectrophotometer (U-4100 manufactured by Hitachi, Ltd.). Here, the parallel transmittance (Ky) at each wavelength at the time of polarized light incidence is the transmittance measured by setting the absorption axis of the absolute polarizer (polarizing plate with a polarization degree of 99.99%) parallel to the absorption axis of the polarizing element, and the orthogonal transmittance (Kz) at each wavelength at the time of polarized light incidence indicates the transmittance measured by setting the absorption axis of the absolute polarizer perpendicular to the absorption axis of the polarizing element.
The parallel transmittance at each wavelength when polarized light was incident and the orthogonal transmittance at each wavelength when polarized light was incident were measured at 1 nm intervals from 380 to 780 nm. Using the measured values, the polarization rate at each wavelength was calculated from the following formula (I), and the highest polarization rate at each wavelength when polarized light was incident and its maximum absorption wavelength (nm) were obtained.

Polarization rate (%) for each wavelength when polarized light is incident
= [(Ky-Kz)/(Ky+Kz)] × 100 (I)

(Comparative Example AB1: Preparation of Polarizing Element)
A polarizing element was prepared in the same manner as in Example A7, except that CI Direct Orange 39 was used instead of the compound of formula (1-A4).

(Comparative Example AB2: Preparation of Polarizing Element)
A polarizing element was produced in the same manner as in Example A7, except that CI Direct Yellow 44 was used instead of the compound of formula (1-A4).

One index of image quality is contrast, which indicates the difference in luminance between white and black displays. The contrast at the maximum absorption wavelength of the polarizing elements obtained in Examples A7 to A12 and Comparative Examples AB1 and AB2 is shown in Table A2.
Here, contrast refers to the ratio of the parallel transmittance when polarized light is incident at each wavelength to the orthogonal transmittance when polarized light is incident at each wavelength (contrast = parallel transmittance when polarized light is incident at each wavelength at the maximum absorption wavelength (Ky) / orthogonal transmittance when polarized light is incident at each wavelength at the maximum absorption wavelength (Kz)), and the larger this value is, the better the polarization performance of the polarizing plate is. Note that, for evaluation of the polarization performance, samples were prepared so that the parallel transmittance of the polarizing element at the maximum absorption wavelength was the same, and then compared.
As shown in Table A2, the polarizing elements of Examples A7 to A12 all had higher contrast than the polarizing elements of Comparative Examples AB1 and AB2.

(Example A13: Preparation of neutral gray polarizing plate)
A polarizing element was prepared in the same manner as in Example A6, except that a 45°C aqueous solution containing 0.1% of the compound of formula (1-A26) obtained in Example A3, 0.2% of C.I. Direct Red 81, 0.05% of C.I. Direct Blue 274, and 0.1% of sodium sulfate was used as the dye bath. The obtained polarizing element had a single-plate average transmittance of 42% at each wavelength in the range of 380 to 700 nm, and an average transmittance in the orthogonal direction at each wavelength of 0.02%, and had a high degree of polarization.
A triacetyl cellulose film (TAC film: Fuji Film Corporation: product name TD-80U) was laminated on both sides of this polarizing element via an adhesive of a polyvinyl alcohol aqueous solution, and a support provided with an AR layer was attached using a pressure-sensitive adhesive to obtain a polarizing plate (neutral gray polarizing plate) in which TAC/polarizing element/TAC/AR support were laminated in this order.

(Example A14: Preparation of neutral gray polarizing plate)
A polarizing element was prepared in the same manner as in Example A6, except that an aqueous solution at 45° C. containing 0.1% of the compound of formula (1-A36) obtained in Example A4, 0.2% of C.I. Direct Red 81, 0.05% of C.I. Direct Blue 274, and 0.1% of sodium sulfate was used as the dye bath. The obtained polarizing element had a single-plate average transmittance of 42% at each wavelength in the range of 380 to 700 nm, and an average transmittance in the orthogonal direction at each wavelength of 0.02%, and had a high degree of polarization.
A triacetyl cellulose film (TAC film: Fuji Film Corporation: product name TD-80U) was laminated on both sides of this polarizing element via an adhesive of a polyvinyl alcohol aqueous solution, and a support provided with an AR layer was attached using a pressure-sensitive adhesive to obtain a polarizing plate (neutral gray polarizing plate) in which TAC/polarizing element/TAC/AR support were laminated in this order.

(Example A15: Preparation of neutral gray polarizing plate)
A polarizing element was prepared in the same manner as in Example A6, except that a 45°C aqueous solution containing 0.1% of the compound of formula (1-A100) obtained in Example A6, 0.2% of C.I. Direct Red 81, 0.05% of C.I. Direct Blue 274, and 0.1% of sodium sulfate was used as the dye bath. The obtained polarizing element had a single-plate average transmittance of 42% at each wavelength in the range of 380 to 700 nm, and an average transmittance in the orthogonal direction at each wavelength of 0.02%, and had a high degree of polarization.
A triacetyl cellulose film (TAC film: Fuji Film Corporation: product name TD-80U) was laminated on both sides of this polarizing element via an adhesive of a polyvinyl alcohol aqueous solution, and a support provided with an AR layer was attached using a pressure-sensitive adhesive to obtain a polarizing plate (neutral gray polarizing plate) in which TAC/polarizing element/TAC/AR support were laminated in this order.

The neutral gray polarizing plates obtained in Examples A13 to A15 showed no change in the single-plate average transmittance at each wavelength even after 400 hours under conditions of 80°C and 90% RH, demonstrating long-term durability even under high temperature and high humidity conditions. Furthermore, the neutral gray polarizing plates of Examples A13 to A15 showed no change in the single-plate average transmittance at each wavelength even after 200 hours in a xenon light resistance test, demonstrating excellent light resistance to long-term exposure to light. These results demonstrate that all of the neutral gray polarizing plates of Examples A13 to A15 have excellent polarizing performance and are high-performance polarizing plates that are moisture-resistant, heat-resistant, and light-resistant.

<<Example B>>

(Example B1: Synthesis of azo compound of formula (1-B24))
30.3 parts of 7-aminonaphthalene-1,3-disulfonic acid was added to 400 parts of water, dissolved with sodium hydroxide, 20.5 parts of 4-nitrobenzoyl chloride was added, and the mixture was stirred for 6 hours at 40 to 60° C. Then, 15.0 g of iron powder and 13 parts of 35% hydrochloric acid were added, and the mixture was stirred for 5 hours at 80° C. to complete the reaction. After removing the iron powder, the mixture was filtered to obtain 33.9 parts of an aminobenzoylaminonaphthalene compound represented by the following formula (1-B24-1).

33.9 parts of the obtained aminobenzoylaminonaphthalene compound (1-B24-1) was added to 400 parts of water, dissolved with sodium hydroxide, 5.5 parts of sodium nitrite was added, and 25.1 parts of 35% hydrochloric acid was added at 10 to 30° C., and the mixture was stirred at 10 to 30° C. for 1 hour to be diazotized.
To the mixture, 11.0 parts of 2-methoxy-5-methylaniline was added, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and then filtered to obtain 32.1 parts of a monoazoamino compound represented by the following formula (1-B24-2).

32.1 parts of the obtained monoazoamino compound (1-B24-2) was added to 400 parts of water, dissolved with sodium hydroxide, and 9.1 parts of phenyl chloroformate was stirred at 50-70°C for 6 hours to form an ureido compound. Salting out with sodium chloride and filtration were performed to obtain 10.0 parts of the ureido compound represented by the above formula (1-B24). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 424 nm.

(Example B2: Synthesis of azo compound of formula (1-B26))
33.9 parts of aminobenzoylaminonaphthalene compound (1-B24-1) obtained in the same manner as in Example B1 was added to 400 parts of water, dissolved with sodium hydroxide, added with 5.5 parts of sodium nitrite, added with 25.1 parts of 35% hydrochloric acid at 10 to 30° C., and stirred for 1 hour at 10 to 30° C. to diazotize. 9.9 parts of 2-methoxyaniline was added thereto, and while stirring at 20 to 30° C., sodium carbonate was added to adjust the pH to 3, and further stirred to complete the coupling reaction, followed by filtration to obtain 22.3 parts of a monoazoamino compound represented by the following formula (1-B26-2).

22.3 parts of the obtained monoazoamino compound (1-B26-2) was added to 300 parts of water, dissolved with sodium hydroxide, and 6.3 parts of phenyl chloroformate was stirred at 50-70°C for 6 hours to form an ureido compound. Salting out with sodium chloride and filtration yielded 6.7 parts of the ureido compound represented by the above formula (1-B26). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 413 nm.

(Example B3: Synthesis of azo compound of formula (1-B29))
33.9 parts of the aminobenzoylaminonaphthalene compound (1-B24-1) obtained in the same manner as in Example B1 was added to 400 parts of water, dissolved with sodium hydroxide, 5.5 parts of sodium nitrite was added, and 25.1 parts of 35% hydrochloric acid was added at 10 to 30° C., followed by stirring at 10 to 30° C. for 1 hour to perform diazotization.
To the mixture, 19.7 parts of 3-(2-amino-4-methylphenoxy)propane-1-sulfonic acid was added, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and then filtered to obtain 38.2 parts of a monoazoamino compound represented by the following formula (1-B29-2).

38.2 parts of the obtained monoazoamino compound (1-B29-2) was added to 300 parts of water, dissolved with sodium hydroxide, and 8.8 parts of phenyl chloroformate was stirred at 50-70°C for 6 hours to form an ureido compound. Salting out with sodium chloride and filtration yielded 11.5 parts of the ureido compound represented by the above formula (1-B29). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 424 nm.

(Example B4: Synthesis of azo compound of formula (1-B57))
28.4 parts of 7-aminonaphthalene-1,3-disulfonic acid was added to 400 parts of water, 29.3 parts of 35% hydrochloric acid and 6.5 parts of sodium nitrite were added, and the mixture was stirred at 10 to 30° C. for 1 hour for diazotization.
To the mixture, 11.6 parts of 2-methoxyaniline was added, and while stirring at 20 to 30° C., sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and then filtered to obtain 31.3 parts of a monoazoamino compound represented by the following formula (1-B57-R).

31.3 parts of the obtained monoazoamino compound (1-B57-R) and 32.1 parts of the monoazoamino compound represented by the above formula (1-B24-2) were added to 600 parts of water, dissolved with sodium hydroxide, and 8.7 parts of phenyl chloroformate were stirred at 50-70°C for 8 hours to form an ureido compound. Salting out with sodium chloride and filtration yielded 12.7 parts of the ureido compound represented by the above formula (1-B57). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 421 nm.

(Example B5: Synthesis of azo compound of formula (1-B62))
The procedure of Example B4 was repeated except that 37.8 parts of the monoazoamino compound represented by the formula (1-B29-2) was used instead of 32.1 parts of the monoazoamino compound represented by the formula (1-B24-2), to obtain 14.0 parts of the ureido compound represented by the formula (1-B62). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 423 nm.

(Example B6: Synthesis of azo compound of formula (1-B63))
30.3 parts of 7-aminonaphthalene-1,3-disulfonic acid was added to 400 parts of water, dissolved with sodium hydroxide, 21.6 parts of 3-methoxy-4-nitrobenzoyl chloride was added, and the mixture was stirred for 6 hours at 40 to 60° C. Then, 15.0 g of iron powder and 13 parts of 35% hydrochloric acid were added, and the mixture was stirred for 5 hours at 80° C. to complete the reaction. After removing the iron powder, the mixture was filtered to obtain 36.2 parts of an aminobenzoylaminonaphthalene compound represented by the following formula (1-B63-L1).

36.2 parts of the obtained aminobenzoylaminonaphthalene compound (1-B63-L1) was added to 400 parts of water, dissolved with sodium hydroxide, 5.5 parts of sodium nitrite was added, and 25.1 parts of 35% hydrochloric acid was added at 10 to 30° C., and the mixture was stirred at 10 to 30° C. for 1 hour to be diazotized.
To the mixture, 19.7 parts of 3-(2-amino-4-methylphenoxy)propane-1-sulfonic acid was added, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and then filtered to obtain 39.7 parts of a monoazoamino compound represented by the following formula (1-B63-L2).

39.7 parts of the obtained monoazoamino compound (1-B63-L2) and 31.3 parts of the monoazoamino compound represented by the above formula (1-B57-R) were added to 600 parts of water, dissolved with sodium hydroxide, and 8.7 parts of phenyl chloroformate were stirred at 50-70°C for 8 hours to form an ureido compound. Salting out with sodium chloride and filtration yielded 14.2 parts of the ureido compound represented by the above formula (1-B63). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 429 nm.

(Example B7: Synthesis of azo compound of formula (1-B64))
Except for using 20.0 parts of 3-methyl-4-nitrobenzoyl chloride instead of 21.6 parts of 3-methoxy-4-nitrobenzoyl chloride, the procedure of Example B6 was repeated to obtain 13.5 parts of the ureido compound represented by the above formula (1-B64). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 422 nm.

(Example B8: Synthesis of azo compound of formula (1-B94))
16.0 parts of the monoazoamino compound represented by the above formula (1-A100-R) and 32.1 parts of the monoazoamino compound represented by the above formula (1-B24-2) were added to 600 parts of water, dissolved with sodium hydroxide, and 8.7 parts of phenyl chloroformate were stirred at 50 to 70°C for 8 hours to form an ureido compound. Salting out with sodium chloride and filtration gave 9.6 parts of the ureido compound represented by the above formula (1-B94). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 423 nm.

(Example B9: Synthesis of azo compound of formula (1-B98))
13.7 parts of 5-amino-2-chlorobenzoic acid was added to 300 parts of water, cooled, and 25.0 parts of 35% hydrochloric acid was added at 10° C. or lower, followed by addition of 5.5 parts of sodium nitrite, and the mixture was stirred at 5 to 10° C. for 1 hour to effect diazotization.
To this was added 9.7 parts of 2,5-dimethylaniline, and while stirring at 10 to 30°C, sodium carbonate was added to adjust the pH to 3, and the mixture was further stirred to complete the coupling reaction, followed by filtration to obtain 17.0 parts of a monoazoamino compound represented by the following formula (1-B98-R).

17.0 parts of the obtained monoazoamino compound (1-B98-R) and 38.2 parts of the monoazoamino compound represented by the above formula (1-B29-2) were added to 600 parts of water, dissolved with sodium hydroxide, and 8.7 parts of phenyl chloroformate were stirred at 50-70°C for 8 hours to form an ureido compound. Salting out with sodium chloride and filtration yielded 11.0 parts of the ureido compound represented by the above formula (1-B98). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 418 nm.

(Example B10: Synthesis of azo compound of formula (1-B100))
The procedure of Example B9 was repeated except that 19.7 parts of 3-(2-amino-4-methylphenoxy)propane-1-sulfonic acid was used instead of 9.7 parts of 2,5-dimethylaniline, to obtain 14.0 parts of the ureido compound represented by the above formula (1-B100). The maximum absorption wavelength of this compound in a 20% aqueous pyridine solution was 424 nm.

(Example B11: Synthesis of azo compound of formula (1-B102))
33.9 parts of the aminobenzoylaminonaphthalene compound represented by the above formula (1-B24-1) was added to 400 parts of water, dissolved with sodium hydroxide, 5.5 parts of sodium nitrite was added, and 25.1 parts of 35% hydrochloric acid was added at 10 to 30° C., followed by stirring at 10 to 30° C. for 1 hour to perform diazotization.
To this was added 9.6 parts of 2,5-dimethylaniline, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and then filtered to obtain 31.1 parts of a monoazoamino compound represented by the following formula (1-B102-L2).

31.1 parts of the obtained monoazoamino compound (1-B102-L2) and 24.0 parts of a monoazoamino compound represented by the following formula (1-B102-R) were added to 600 parts of water, dissolved with sodium hydroxide, and 8.7 parts of phenyl chloroformate were stirred at 50 to 70°C for 8 hours to form an ureido compound. Salting out with sodium chloride and filtration gave 11.0 parts of the ureido compound represented by the above formula (1-B102). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 415 nm.

(Example B12: Synthesis of azo compound of formula (B-117))
30.3 parts of 7-aminonaphthalene-1,3-disulfonic acid was added to 400 parts of water, dissolved with sodium hydroxide, 20.0 parts of 3-methyl-4-nitrobenzoyl chloride was added, and the mixture was stirred for 6 hours at 40 to 60° C. Subsequently, 15.0 g of iron powder and 13 parts of 35% hydrochloric acid were added and the mixture was stirred for 5 hours at 80° C. to complete the reaction. After removing the iron powder, the mixture was filtered to obtain 34.9 parts of an aminobenzoylaminonaphthalene compound represented by the following formula (B-117-L1).

34.9 parts of the obtained aminobenzoylaminonaphthalene compound (B-117-L1) was added to 400 parts of water, dissolved with sodium hydroxide, 5.5 parts of sodium nitrite was added, and 25.1 parts of 35% hydrochloric acid was added at 10 to 30° C., and the mixture was stirred at 10 to 30° C. for 1 hour to be diazotized.
11.0 parts of 2-methoxy-5-methylaniline was added thereto, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and filtered to obtain 32.1 parts of a monoazoamino compound represented by the following formula (B-117-L2).

11.0 parts of 3-aminobenzoic acid was added to 300 parts of water, cooled, and 25.0 parts of 35% hydrochloric acid was added at 10° C. or lower, followed by addition of 5.5 parts of sodium nitrite, and the mixture was stirred at 5 to 10° C. for 1 hour to effect diazotization.
11.0 parts of 2-methoxy-5-methylaniline was added thereto, and while stirring at 10 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and filtered to obtain 16.0 parts of a monoazoamino compound represented by the following formula (B-117-R).

32.1 parts of the obtained monoazoamino compound (B-117-L2) and 16.0 parts of the obtained monoazoamino compound (B-117-R) were added to 600 parts of water, dissolved with sodium hydroxide, and 8.7 parts of phenyl chloroformate were stirred at 50 to 70°C for 8 hours to form an ureido compound. Salting out with sodium chloride and filtration were performed to obtain 11.0 parts of the ureido compound represented by the above formula (B-117). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 422 nm.

(Example B13: Synthesis of azo compound of formula (B-122))
28.4 parts of 7-aminonaphthalene-1,3-disulfonic acid was added to 400 parts of water, 29.3 parts of 35% hydrochloric acid and 6.5 parts of sodium nitrite were added, and the mixture was stirred at 10 to 30° C. for 1 hour for diazotization.
11.6 parts of 2-methoxy-5-methylaniline was added thereto, and while stirring at 20 to 30°C, sodium carbonate was added to adjust the pH to 3. The mixture was further stirred to complete the coupling reaction, and filtered to obtain 25.3 parts of a monoazoamino compound represented by the following formula (B-122-R).

25.3 parts of the obtained monoazoamino compound (B-122-R) and 24.7 parts of the monoazoamino compound represented by the above formula (1-A71-L2) were added to 600 parts of water, dissolved with sodium hydroxide, and 8.7 parts of phenyl chloroformate were stirred at 50-70°C for 8 hours to form an ureido compound. Salting out with sodium chloride and filtration yielded 10.0 parts of the ureido compound represented by the above formula (B-122). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 425 nm.

(Example B14: Synthesis of azo compound of formula (1-B37))
The procedure of Example B1 was repeated except that 36.1 parts of 6-amino-4-(3-sulfopropoxy)naphthalene-2-sulfonic acid was used instead of 30.3 parts of 7-aminonaphthalene-1,3-disulfonic acid, to obtain 12.0 parts of the ureido compound represented by the above formula (1-B37). The maximum absorption wavelength of this compound in a 20% pyridine aqueous solution was 425 nm.

(Examples B15 to B28: Preparation of polarizing elements)
Polarizing elements were obtained in the same manner as in Examples A7 to A12, except that the azo compounds of the above formulas (1-B24), (1-B26), (1-B29), (1-B57), (1-B62), (1-B63), (1-B64), (1-B94), (1-B98), (1-B100), (1-B102), (B-117), (B-122), and (1-B37) obtained in Examples B1 to B14 were used instead of the azo compounds of the formula (1) used in Examples A7 to A12. The maximum absorption wavelength and polarization rate of the obtained polarizing element are shown in Table B1. As shown in Table B1, the polarizing elements prepared using these compounds all had high polarization rates.

As in Table A2, Table B2 shows the contrast at the maximum absorption wavelength of the polarizing elements obtained in Examples B15 to B28 and Comparative Examples AB1 and AB2. As shown in Table B2, the polarizing elements of Examples B15 to B28 all had higher contrast than the polarizing elements of Comparative Examples AB1 and AB2.

(Example B29: Preparation of neutral gray polarizing plate)
A polarizing element was prepared in the same manner as in Example B15, except that an aqueous solution at 45° C. containing 0.1% of the compound of formula (1-B24) obtained in Example B1, 0.2% of C.I. Direct Red 81, 0.05% of C.I. Direct Blue 274, and 0.1% of sodium sulfate was used as the dye bath. The single-plate average transmittance of the obtained polarizing element at each wavelength in the range of 380 to 700 nm was 42%, and the average transmittance at the orthogonal angle at each wavelength was 0.02%, indicating that the polarizing element had a high degree of polarization.
A triacetyl cellulose film (TAC film: Fuji Film Corporation: product name TD-80U) was laminated on both sides of this polarizing element via an adhesive of a polyvinyl alcohol aqueous solution, and a support provided with an AR layer was attached using a pressure-sensitive adhesive to obtain a polarizing plate (neutral gray polarizing plate) in which TAC/polarizing element/TAC/AR support were laminated in this order.

(Example B30: Preparation of neutral gray polarizing plate)
A polarizing element was prepared in the same manner as in Example B13, except that an aqueous solution at 45° C. containing 0.1% of the compound of formula (1-B29) obtained in Example B3, 0.2% of C.I. Direct Red 81, 0.05% of C.I. Direct Blue 274, and 0.1% of sodium sulfate was used. The single-plate average transmittance of the obtained polarizing element at each wavelength in the range of 380 to 700 nm was 42%, and the average transmittance at the orthogonal angle at each wavelength was 0.02%, indicating that the polarizing element had a high degree of polarization.
A triacetyl cellulose film (TAC film: Fuji Film Corporation: product name TD-80U) was laminated on both sides of this polarizing element via an adhesive of a polyvinyl alcohol aqueous solution, and a support provided with an AR layer was attached using a pressure-sensitive adhesive to obtain a polarizing plate (neutral gray polarizing plate) in which TAC/polarizing element/TAC/AR support were laminated in this order.

(Example B31: Preparation of neutral gray polarizing plate)
A polarizing element was prepared in the same manner as in Example B13, except that an aqueous solution at 45° C. containing 0.1% of the compound of formula (1-B64) obtained in Example B7, 0.2% of C.I. Direct Red 81, 0.05% of C.I. Direct Blue 274, and 0.1% of sodium sulfate was used. The single-plate average transmittance of the obtained polarizing element at each wavelength in the range of 380 to 700 nm was 42%, and the average transmittance at the orthogonal angle at each wavelength was 0.02%, indicating that the polarizing element had a high degree of polarization.
A triacetyl cellulose film (TAC film: Fuji Film Corporation: product name TD-80U) was laminated on both sides of this polarizing element via an adhesive of a polyvinyl alcohol aqueous solution, and a support provided with an AR layer was attached using a pressure-sensitive adhesive to obtain a polarizing plate (neutral gray polarizing plate) in which TAC/polarizing element/TAC/AR support were laminated in this order.

(Example B32: Preparation of neutral gray polarizing plate)
A polarizing element was prepared in the same manner as in Example B13, except that an aqueous solution at 45° C. containing 0.1% of the compound of formula (1-B100) obtained in Example B10, 0.2% of C.I. Direct Red 81, 0.05% of C.I. Direct Blue 274, and 0.1% of sodium sulfate was used. The single-plate average transmittance of the obtained polarizing element at each wavelength in the range of 380 to 700 nm was 42%, and the average transmittance at the orthogonal angle at each wavelength was 0.02%, indicating that the polarizing element had a high degree of polarization.
A triacetyl cellulose film (TAC film: Fuji Film Corporation: product name TD-80U) was laminated on both sides of this polarizing element via an adhesive of a polyvinyl alcohol aqueous solution, and a support provided with an AR layer was attached using a pressure-sensitive adhesive to obtain a polarizing plate (neutral gray polarizing plate) in which TAC/polarizing element/TAC/AR support were laminated in this order.

(Example B33: Preparation of neutral gray polarizing plate)
A polarizing element was prepared in the same manner as in Example B13, except that an aqueous solution at 45° C. containing 0.1% of the compound of formula (1-B117) obtained in Example B12, 0.2% of C.I. Direct Red 81, 0.05% of C.I. Direct Blue 274, and 0.1% of sodium sulfate was used. The single-plate average transmittance of the obtained polarizing element at each wavelength in the range of 380 to 700 nm was 42%, and the average transmittance at the orthogonal angle at each wavelength was 0.02%, indicating that the polarizing element had a high degree of polarization.
A triacetyl cellulose film (TAC film: Fuji Film Corporation: product name TD-80U) was laminated on both sides of this polarizing element via an adhesive of a polyvinyl alcohol aqueous solution, and a support provided with an AR layer was attached using a pressure-sensitive adhesive to obtain a polarizing plate (neutral gray polarizing plate) in which TAC/polarizing element/TAC/AR support were laminated in this order.

The neutral gray polarizing plates obtained in Examples B29 to B33 showed no change in the single-plate average transmittance at each wavelength even after 400 hours under conditions of 80°C and 90% RH, demonstrating long-term durability even under high temperature and high humidity conditions. Furthermore, the neutral gray polarizing plates of Examples B29 to B33 showed no change in the single-plate average transmittance at each wavelength even after 200 hours in a xenon light resistance test, demonstrating excellent light resistance to long-term exposure to light. These results demonstrate that all of the neutral gray polarizing plates of Examples B29 to B33 have excellent polarizing performance, and are high-performance polarizing plates that are also moisture-resistant, heat-resistant, and light-resistant.

<<Example C>>

[Example C1]
A polyvinyl alcohol film with a saponification degree of 99% or more (VF-PE#6000 manufactured by Kuraray Co., Ltd.) was immersed in 40°C warm water for 3 minutes, and a swelling treatment was applied to the stretching ratio to 1.30 times. The swollen film was immersed for 2 minutes and 30 seconds in a 45°C dyeing solution containing 1500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.3 parts by mass of a compound of formula (5-1) which is a compound of formula (5), 0.8 parts by mass of a compound of formula (6-3) which is a compound of formula (6), and 0.55 parts by mass of a compound of formula (1-B150) which is a compound of formula (1), to incorporate an azo compound into the film. The obtained film was immersed for 1 minute in a 40°C aqueous solution containing 20 g/l of boric acid (manufactured by Societa Chimica Larderello s.p.a.). The immersed film was stretched 5.0 times while being stretched in a 50°C aqueous solution containing 30.0 g/l of boric acid for 5 minutes. The obtained film was washed by immersing it in 25°C water for 20 seconds while maintaining the tension. The washed film was dried at 70°C for 9 minutes to obtain a polarizing element. A 4% solution of polyvinyl alcohol (NH-26, Nippon Vinyl Poval Co., Ltd.) in water was used as an adhesive to laminate an alkali-treated triacetyl cellulose film (ZRD-60, Fuji Film Co., Ltd.) to this polarizing element to obtain a polarizing plate. The obtained polarizing plate maintained the optical performance of the polarizing element, particularly the single transmittance, hue, and polarization degree of each wavelength. This polarizing plate was used as the measurement sample for Example C1.

[Example C2]
The swollen film was treated for 7 minutes in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.08 parts by mass of the compound of formula (5-1), 0.26 parts by mass of the compound of formula (6-10), and 0.28 parts by mass of the compound of formula (1-B150), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C3]
The swollen film was treated for 8 minutes 30 seconds in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.04 parts by mass of the compound of formula (5-4), 0.13 parts by mass of the compound of formula (6-10), and 0.10 parts by mass of the compound of formula (1-B150), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C4]
The swollen film was treated for 10 minutes in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.04 parts by mass of the compound of formula (5-14), 0.14 parts by mass of the compound of formula (6-4), and 0.10 parts by mass of the compound of formula (1-B150), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C5]
The swollen film was treated for 8 minutes 30 seconds in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.04 parts by mass of the compound of formula (5-36), 0.12 parts by mass of the compound of formula (6-10), and 0.10 parts by mass of the compound of formula (1-B150), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C6]
The swollen film was treated for 9 minutes in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.04 parts by mass of the compound of formula (5-41), 0.12 parts by mass of the compound of formula (6-17), and 0.14 parts by mass of the compound of formula (1-B150), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C7]
The swollen film was treated for 7 minutes and 30 seconds in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, and 0.13 parts by mass of the compound of Example 1 in Patent Document 14 (Japanese Patent No. 4,825,235) as a compound having a structure of Formula (5), 0.26 parts by mass of the compound of Formula (6-17), and 0.31 parts by mass of the compound of Formula (1-B150). A polarizing plate was produced in the same manner as in Example C1 except that an azo compound was added.

[Example C8]
The swollen film was treated for 8 minutes and 15 seconds in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.08 parts by mass of the compound of formula (5-1), 0.30 parts by mass of the compound of formula (6-10), and 0.34 parts by mass of the compound of formula (1-B69), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C9]
The swollen film was treated for 8 minutes and 15 seconds in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.27 parts by mass of the compound of formula (5-28), 0.37 parts by mass of the compound of formula (6-10), and 0.29 parts by mass of the compound of formula (1-B69), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C10]
The swollen film was treated for 3 minutes in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.13 parts by mass of the compound of formula (5-28), 0.21 parts by mass of the compound of formula (6-10), and 0.21 parts by mass of the compound of formula (1-B69), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C11]
A polarizing plate was produced in the same manner as in Example C1 except that the swollen film was immersed in the dye solution for 1 minute 15 seconds and contained an azo compound.

[Example C12]
The swollen film was treated for 7 minutes in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.16 parts by mass of the compound of formula (5-22), 0.26 parts by mass of the compound of formula (6-10), and 0.27 parts by mass of the compound of formula (1-B69), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C13]
The swollen film was treated for 8 minutes and 15 seconds in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.61 parts by mass of the compound of formula (5-26), 0.30 parts by mass of the compound of formula (6-10), and 0.3 parts by mass of the compound of formula (1-B69), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C14]
The swollen film was treated for 9 minutes 30 seconds in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.15 parts by mass of the compound of formula (5-7), 0.27 parts by mass of the compound of formula (6-25), and 0.27 parts by mass of the compound of formula (1-B69), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C15]
The swollen film was treated for 4 minutes and 40 seconds in a dyeing solution at 45° C. containing 1500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.04 parts by mass of C.I. Direct Red 117 as an azo compound having a structure of formula (5), 0.24 parts by mass of a compound of formula (6-17), and 0.11 parts by mass of a compound of formula (1-A19), and a polarizing plate was produced in the same manner as in Example C1 except that an azo compound was contained.

[Example C16]
The swollen film was treated for 6 minutes and 10 seconds in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.21 parts by mass of the compound of formula (5-28), 0.29 parts by mass of the compound of formula (6-17), and 0.29 parts by mass of the compound of formula (1-A115), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Example C17]
The swollen film was treated for 7 minutes and 15 seconds in a dyeing solution at 45° C. containing 1,500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 0.20 parts by mass of the compound of formula (5-22), 0.30 parts by mass of the compound of formula (6-17), and 0.30 parts by mass of the compound of formula (1-A74), to produce a polarizing plate in the same manner as in Example C1 except that an azo compound was added.

[Comparative Example C1]
As a typical dye-based polarizing plate, a high transmittance dye-based polarizing plate SHC-115 having a neutral gray color manufactured by Polatechno Co., Ltd. was procured and used as a measurement sample.

[Comparative Example C2]
As a typical dye-based polarizing plate, a neutral gray dye-based polarizing plate SHC-128 having high contrast manufactured by Polatechno Co., Ltd. was procured and used as a measurement sample.

[Comparative Example C3]
A polarizer was prepared as per Example 1 of US Pat. No. 5,399,633 for dye-based polarizers.

[Comparative Example C4]
A polarizer was prepared as per Example 3 of US Pat. No. 5,399,633 for dye-based polarizers.

[Comparative Example C5]
A polarizer was prepared as per Example 1 of US Pat. No. 5,399,633 for dye-based polarizers.

[Comparative Example C6]
A polarizer was prepared according to Example 15 No. 1 of US Pat. No. 5,993,333 relating to a dye-based polarizer.

[Comparative Examples C7 to C12]
According to the manufacturing method of Comparative Example 1 of Patent Document 19, except that the iodine-containing time was 5 minutes 30 seconds in Comparative Example C7, 4 minutes 45 seconds in Comparative Example C8, 4 minutes 15 seconds in Comparative Example C9, 3 minutes 30 seconds in Comparative Example C10, 4 minutes in Comparative Example C11, and 5 minutes 15 seconds in Comparative Example C12, iodine-based polarizing plates, i.e., polarizing plates not containing an azo compound, were prepared and used as measurement samples.

[Comparative Example C13]
An iodine-based polarizing plate SKW-18245P manufactured by Polatechno Co., Ltd., which exhibits a paper white color in the parallel position, was procured and used as a measurement sample.

[evaluation]
The measurement samples obtained in Examples C1 to C17 and Comparative Examples C1 to C13 were evaluated as follows.
(a) Single transmittance Ts of each wavelength, parallel transmittance Tp of each wavelength, and perpendicular transmittance Tc of each wavelength
The single transmittance Ts, parallel transmittance Tp, and cross transmittance Tc of each wavelength of each measurement sample were measured using a spectrophotometer (Hitachi, Ltd. "U-4100"). Here, the single transmittance Ts of each wavelength is the transmittance of each wavelength when one measurement sample is measured. The parallel transmittance Tp of each wavelength is the spectral transmittance of each wavelength measured by overlapping two measurement samples so that their absorption axis directions are parallel. The cross transmittance Tc of each wavelength is the spectral transmittance measured by overlapping two polarizing plates so that their absorption axes are perpendicular. The measurement was performed over a wavelength range of 400 to 700 nm. The average values of the parallel transmittance Tp and cross transmittance Tc of each wavelength at 420 to 480 nm, the average values of ...

(b) Single transmittance Ys after luminosity correction, parallel transmittance Yp after luminosity correction, and perpendicular transmittance Yc after luminosity correction
The luminosity-corrected single transmittance Ys (%), the luminosity-corrected parallel transmittance Yp (%), and the luminosity-corrected orthogonal transmittance Yc (%) of each measurement sample were obtained. The luminosity-corrected single transmittance Ys (%), the luminosity-corrected parallel transmittance Yp (%), and the luminosity-corrected orthogonal transmittance Yc (%) are transmittances corrected to luminosity according to JIS Z 8722:2009 for the single transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc of each wavelength obtained at a predetermined wavelength interval dλ (here, 5 nm) in the wavelength range of 400 to 700 nm. Specifically, the single transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc of each wavelength were substituted into the following formulas (V to VII) to calculate the values. In the following formulas (V to VII), Pλ represents the spectral distribution of standard light (C light source), and yλ represents the color matching function for a 2-degree visual field. The results are shown in Table C1.

(c) Contrast The contrast was calculated by calculating the ratio (Yp/Yc) of the parallel transmittance after luminosity correction to the cross transmittance after direct luminosity correction, which were measured using two identical measurement samples. The results are shown in Table C1.

(d) Absolute Value of Difference in Average Transmittance for Each Wavelength in Two Wavelength Bands Table C2 shows the absolute value of the difference between the average value of the parallel transmittance Tp and the orthogonal transmittance Tc for each wavelength of each measurement sample in the range of 520 to 590 nm and the average value of the wavelength in the range of 420 to 480 nm, and also shows the absolute value of the difference between the average value of the parallel transmittance Tp and the average value of the orthogonal transmittance Tc for each wavelength of each measurement sample in the range of 520 to 590 nm and the average value of the wavelength in the range of 600 to 640 nm.

As shown in Tables C1 and C2, the parallel transmittance Tp of each wavelength of the measurement samples of Examples C1 to C17 was 30% or more, which was a high transmittance, and the difference between the average value of each wavelength from 420 to 480 nm and the average value of each wavelength from 520 to 590 nm was 2.5% or less as an absolute value, and the difference between the average value of each wavelength from 520 to 590 nm and the average value of each wavelength from 590 to 640 nm was 3.0% or less as an absolute value, both of which were very low values. In addition, the difference between the average value of each wavelength in the range of 420 to 480 nm and the average value of each wavelength in the range of 520 to 590 nm was 1.0% or less as an absolute value, and the difference between the average value of each wavelength in the range of 520 to 590 nm and the average value of each wavelength in the range of 600 to 640 nm was 1.0% or less as an absolute value, both of which were very low values. Therefore, it was shown that the average transmittance of each wavelength was almost constant for the measurement samples obtained in Examples C1 to C17.
On the other hand, comparative examples C1 to C6 showed high values for at least one of the absolute value of the difference in the average values of the parallel transmittance Tp of each wavelength shown in Table C2 between the above-mentioned wavelength bands and the absolute value of the difference in the average values of the orthogonal transmittance Tc of each wavelength between the above-mentioned wavelength bands.

(e) Degree of polarization ρy after visibility correction
The degree of polarization ρy after luminosity correction of each measurement sample was calculated by substituting the parallel transmittance Yp after luminosity correction and the crossed transmittance Yc after luminosity correction into the following formula. The results are shown in Table C3.

ρy={(Yp-Yc)/(Yp+Yc)} ^1/2 ×100 Formula (VIII)

(f) Chromaticity a* and b* values For each measurement sample, the chromaticity a* and b* values were measured according to JIS Z 8781-4:2013 when the single transmittance Ts of each wavelength was measured, when the parallel transmittance Tp of each wavelength was measured, and when the orthogonal transmittance Tc of each wavelength was measured. The above-mentioned spectrophotometer was used for the measurement, and both the transmitted color and the reflected color were measured by being incident from the outside of the room. Illuminant C was used as the light source. The results are shown in Table C3. Here, a*-s and b*-s, a*-p and b*-p, and a*-c and b*-c correspond to the chromaticity a* and b* values when the single transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc were measured, respectively.

(g) Observation of color For each measurement sample, two identical measurement samples were stacked on a white light source in parallel and perpendicular positions, and the colors observed at that time were investigated. Observation was performed visually by 10 observers, and the most frequently observed colors are shown in Table C3. In Table C3, the color in the parallel position means the color when two identical samples are stacked so that their absorption axis directions are parallel to each other (when displaying white), and the color in the perpendicular position means the color when two identical samples are stacked so that their absorption axis directions are perpendicular to each other (when displaying black). Basically, the color in the parallel position is "white" and the color in the perpendicular position is "black", but in the examples, for example, a yellowish white is shown as "yellow" and a blue-purple black is shown as "blue-purple".

As shown in Table C3, the measurement samples of Examples C1 to C17 had a single transmittance after luminosity correction of 35% or more. It was also found that the measurement samples of Examples C1 to C17 were able to fully express white and black. In particular, when the luminosity-corrected single transmittance was 40 to 42%, they had a high degree of polarization of 99% or more. Furthermore, the measurement samples of Examples C1 to C15 and C17 had absolute values of a*-s, b*-s, and a*-p of 1.0 or less, and the absolute value of b*-p was 2.0 or less, which were very low values. The measurement samples of Examples C1 to C17 expressed a high-quality paper-like white color in the parallel position even when observed visually. In addition, the cross-phase transmittance in each of the wavelength bands 420 nm to 480 nm, 520 nm to 590 nm, and 600 nm to 640 nm was 1% or less, or the degree of polarization was about 97% or more, so they expressed black. On the other hand, in comparative examples C1 to C12, at least one of a*-s, b*-s, a*-p, b*-p, a*-c, and b*-c showed high values.

From the above, it has been shown that the polarizing element of the present invention can express a high-quality paper-like white color in the parallel position while maintaining high single-piece transmittance and parallel-position transmittance, and has a hue that has a high-quality neutral color (neutral gray) that is not colored by itself. Furthermore, it can be seen that the polarizing element of the present invention maintains high transmittance, expresses achromaticity in the parallel position, and also has a high degree of polarization. Furthermore, it can be seen that the polarizing element of the present invention makes it possible to obtain a polarizing element that exhibits a high-quality achromatic black even in the perpendicular position.

(h) Durability Test The measurement samples of Examples C1 to C17 and Comparative Examples C7 to C13 were subjected to an environment of 85°C and 85% RH for 240 hours. As a result, the measurement samples of Examples C1 to C17 did not show any change in transmittance or hue. In contrast, the single transmittance after luminosity correction of Comparative Examples C7 to C13 increased by 2% or more, the polarization degree decreased by 10% or more, and b*-c became lower than -10, and the apparent color changed significantly to blue, and especially when two measurement samples were arranged at right angles (when black was displayed), the color was very blue. Therefore, it was found that Examples C1 to C17 have high durability.

The polarizing plate of the present invention has higher contrast and durability than conventional polarizing plates, and can be suitably used in in-vehicle displays, liquid crystal projectors, OLEDs, and other devices that require high durability. The present invention makes it possible to achieve both the durability that was an issue with conventional polarizing plates and the high contrast required for high definition.

In one aspect, the polarizing element of the present invention is a high-performance achromatic polarizing element that has high transmittance and a high degree of polarization, is achromatic in both white and black display, and exhibits high-quality white color particularly in white display, and is an achromatic polarizing plate and liquid crystal display device using the same, which are extremely useful.

Claims (31)

An azo compound represented by formula (1) or a salt thereof:

In the formula, _Ay1 and _Ay2 each independently represent a naphthyl group which may have a substituent, or a phenyl group which may have a substituent, and the phenyl group does not have a hydroxy group as a substituent;
the substituent in the phenyl group which may have a substituent is at least one selected from the group consisting of a sulfo group, a carboxy group, an alkoxy group having 1 to 4 carbon atoms and a sulfo group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a halogen atom, a nitro group, an amino group, an alkyl-substituted amino group having 1 to 4 carbon atoms, and an alkyl-substituted acylamino group having 1 to 4 carbon atoms;
the substituent in the naphthyl group which may have a substituent is selected from the group consisting of a hydroxy group, an alkoxy group having 1 to 4 carbon atoms and having a sulfo group, and a sulfo group,
s and t each independently represent 0 or 1, and either s or t represents 1;
_Ry1 , Ry2 _, Ry7 _{, and} Ry8 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms, and Ry3 _to Ry6 _each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group . 2. The azo compound or a salt thereof according to claim 1, wherein at least one of _Ay1 and _Ay2 is a phenyl group which may have a substituent. The azo compound or a salt thereof according to claim 2 , wherein the phenyl group which may have a substituent has at least one substituent selected from the group consisting of a sulfo group, a carboxy group, and an alkoxy group having 1 to 4 carbon atoms and a sulfo group. The azo compound or salt thereof according to claim 2 or 3 , wherein the phenyl group which may have a substituent is represented by the following formula (2):

In the formula, either _Ry9 or _Ry10 is a sulfo group, a carboxy group, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group, and the other is a hydrogen atom, a sulfo group, a carboxy group, an alkoxy group having 1 to 4 carbon atoms and a sulfo group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a halogen atom, a nitro group, an amino group, an alkyl-substituted amino group having 1 to 4 carbon atoms, or an alkyl-substituted acylamino group having 1 to 4 carbon atoms, and * in the formula indicates the bonding position with the NH moiety of the terminal amide group in formula (1) above. 5. The azo compound or a salt thereof according to claim 4 , wherein one of _Ry9 and _Ry10 is a sulfo group or a carboxy group, and the other is a hydrogen atom, a sulfo group, a carboxy group, a methyl group, or a methoxy group. 6. The azo compound or a salt thereof according to claim 2 , wherein _Ay1 and _Ay2 each independently represent a phenyl group which may have a substituent. 6. The azo compound or a salt thereof according to claim 1 , wherein at least one of _Ay1 and _Ay2 is a naphthyl group which may have a substituent. The azo compound or a salt thereof according to claim 7, wherein the naphthyl group which may have a substituent is a naphthyl group which may have a substituent selected from the group consisting of a hydroxy group, an alkoxy group having 1 to 4 carbon atoms and having a sulfo group, and a sulfo group. The azo compound or a salt thereof according to claim 7 or 8 , wherein the naphthyl group which may have a substituent is represented by the following formula (3):

In the formula, _Ry11 is a hydrogen atom, a hydroxy group, an alkoxy group having 1 to 4 carbon atoms and a sulfo group, or a sulfo group, k is an integer of 1 to 3, and * in the formula indicates the bonding position with the NH moiety of the terminal amide group in the above formula (1), and the substitution positions of _Ry11 and the sulfo group can be any positions on the naphthalene ring other than the bonding position with the NH moiety of the terminal amide group in the above formula (1). The azo compound or a salt thereof according to claim 9 , wherein, in the formula (3), Ry ₁₁ is a hydrogen atom and k is 2. 11. The azo compound or a salt thereof according to claim 1 , wherein Ry ₃ to Ry ₆ are each independently a group selected from the group consisting of a hydrogen atom, a methyl group, an ethyl group, a methoxy group, and a 3-sulfopropoxy group. The azo compound or a salt thereof according to any one of claims 1 to 11 , wherein the formula (1) is represented by the following formula (4):

In the formula, Ay ₁ , Ay ₂ , Ry ₁ to Ry ₈ , s and t each have the same meaning as in the above formula (1). A polarizing element comprising the azo compound or a salt thereof according to any one of claims 1 to 12 . The polarizing element according to claim 13 , further comprising one or more organic dyes having a structure other than that represented by formula (1). 15. The polarizing element according to claim 14 , comprising an azo compound represented by formula (5) or a salt thereof and/or an azo compound represented by formula (6) or a salt thereof.

In the formula, Ar ₁ represents a phenyl group having a substituent or a naphthyl group having a substituent, Rr ₁ to Rr ₄ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group, Dr ₁ represents an azo group or an amido group, j represents 0 or 1, Xr ₁ represents an amino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent, a benzoyl group which may have a substituent, or a benzoylamino group which may have a substituent;

In the formula, _Ag1 represents a phenyl group having a substituent or a naphthyl group having a substituent, Bg and Cg are each independently represented by the following formula (7) or formula (8), either one of which is represented by formula (7), and _Xg1 represents an amino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent, a benzoyl group which may have a substituent, or a benzoylamino group which may have a substituent:

In the formula, _Rg1 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group, _p1 represents an integer of 0 to 2;

In the formula, _Rg2 and _Rg3 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group. 16. The polarizing element according to claim 15 , comprising both an azo compound represented by formula (5) or a salt thereof and an azo compound represented by formula (6) or a salt thereof. 17. The polarizing element according to claim 15 , wherein Cg in the formula (6) is represented by the formula (7). The polarizing element according to claim 17 , wherein the azo compound represented by the formula (6) or a salt thereof is an azo compound represented by the following formula (9) or a salt thereof:

In the formula, Ag ₂ represents a phenyl group having a substituent or a naphthyl group having a substituent; Rg ₄ and Rg ₅ each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms and a sulfo group; Xg ₂ represents an amino group which may have a substituent, a phenylamino group which may have a substituent, a phenylazo group which may have a substituent, a benzoyl group which may have a substituent, or a benzoylamino group which may have a substituent; and p ₂ and p ₃ each independently represent an integer of 0 to 2. The polarizing element according to claim 18 , wherein _p2 and _p3 in the formula (9) are each 1 or 2. 20. The polarizing element according to claim 15 , wherein Xr ₁ in the formula (5) is a phenylamino group which may have a substituent. The polarizing element according to any one of claims 15 to 20 , wherein Xg ₁ in the formula (6) or Xg ₂ in the formula (8) is a phenylamino group which may have a substituent. The polarizing element according to any one of claims 13 to 21, wherein the difference between the average transmittance at each wavelength of 420 nm to 480 nm and the average transmittance at each wavelength of 520 nm to 590 nm, which are obtained by stacking two of the polarizing elements so that the absorption axis directions of the two elements are parallel to each other and measuring the difference is 2.5% or less in absolute value, and the difference between the average transmittance at each wavelength of 520 nm to 590 nm and the average transmittance at each wavelength of 600 nm to 640 nm, is 3.0% or less in absolute value. In accordance with JIS Z 8781-4:2013, the absolute values of the a* value and the b* value obtained when measuring the transmittance of natural light are
Each of the polarizing elements alone is equal to or less than 1.0 (-1.0≦a*-s≦1.0, -1.0≦b*-s≦1.0),
When the two polarizing elements are stacked and arranged so that the absorption axis directions of the two polarizing elements are parallel to each other, both of the polarizing elements have a value of 2.0 or less (-2.0≦a*-p≦2.0, -2.0≦b*-p≦2.0).
A polarizing element according to any one of claims 13 to 22, wherein a*-s indicates the a* value when the polarizing element is a single element, b*-s indicates the b* value when the polarizing element is a single element, a*-p indicates the a* value in the parallel position, and b*-p indicates the b* value in the parallel position. The polarizing element has a single transmittance after visibility correction of 35% to 45%,
The average transmittance of each wavelength from 520 nm to 590 nm obtained when the two polarizing elements are stacked so that the absorption axes of the two polarizing elements are parallel to each other is 28% to 45%.
The polarizing element according to any one of claims 13 to 23 . In the transmittance obtained when the two polarizing elements are stacked and arranged so that the absorption axis directions of the polarizing elements are perpendicular to each other,
The polarizing element according to any one of claims 13 to 24, wherein the difference between the average transmittance at each wavelength of 420 nm to 480 nm and the average transmittance at each wavelength of 520 nm to 590 nm is 1.0% or less as an absolute value, and the difference between the average transmittance at each wavelength of 520 nm to 590 nm and the average transmittance at each wavelength of 600 nm to 640 nm is 1.0% or less as an absolute value. The polarizing element according to any one of claims 13 to 25 , wherein the cross-phase transmittance at each wavelength in the wavelength bands of 420 nm to 480 nm, 520 nm to 590 nm, and 600 nm to 640 nm is 1% or less, or the degree of polarization is 97% or more. The polarizing element according to any one of claims 13 to 26, wherein the absolute values of a* and b* values obtained when measuring the transmittance of natural light according to JIS Z 8781-4:2013 in a state where two of the polarizing elements are stacked and arranged so that the absorption axis directions of the respective polarizing elements are perpendicular to each other, are both 2.0 or less (-2.0≦a*-c≦2.0, -2.0≦b*-c≦2.0), (a*-c indicates the a* value in the orthogonal position, and b*-c indicates the b* value in the orthogonal position). The polarizing element according to any one of claims 13 to 27 , comprising a polyvinyl alcohol-based resin film as a substrate. A polarizing plate comprising the polarizing element according to any one of claims 13 to 28 , and a transparent protective layer provided on one or both sides of the polarizing element. A neutral gray polarizing plate comprising the polarizing element according to any one of claims 13 to 28 or the polarizing plate according to claim 29 . A display device comprising the polarizing element according to any one of claims 13 to 28 or the polarizing plate according to claim 29 or 30 .