Polarizing film, and polarizing plate and display device using the same.

Abstract

To provide a high-performance achromatic polarizing film which offers a high transmittance and high contract and is achromatic when displaying white and when displaying black, and to provide an achromatic polarizing plate using the same, and a display device.SOLUTION: A polarizing film is provided, comprising substances represented by the following formulas (1) and (2).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polarizing film, and to a polarizing plate and display device using the same.

[0002] Polarizing films (also called polarizing elements or polarizing films) are generally manufactured by adsorbing and oriented a dichroic dye, such as iodine or a dichroic dye, onto a polyvinyl alcohol-based resin film. Polarizing plates obtained by laminating this polarizing film with a transparent protective film made of triacetylcellulose or the like via an adhesive layer are used in liquid crystal display devices and the like.

[0003] Polarizing plates that use iodine as a dichroic dye are called iodine-based polarizing plates, while polarizing plates that use dyes such as azo compounds that exhibit dichroism are called dye-based polarizing plates. Of these, dye-based polarizing plates have high heat resistance, high humidity and heat resistance, and high stability, as well as high color selectivity depending on the dye composition. However, they have the problem of lower transmittance and contrast compared to iodine-based polarizing plates with the same degree of polarization. Therefore, there is a need for dye-based polarizing plates that maintain high durability, have diverse color selectivity, and possess higher transmittance and high polarization characteristics.

[0004] Furthermore, even with dye-based polarizers, which offer diverse color selectivity, conventional polarizing films and polarizers have a problem where white appears yellowish when two polarizing films or polarizers are stacked so that their absorption axis directions are parallel to each other (hereinafter also referred to as "parallel position") to display white (hereinafter also referred to as "white display" or "bright display"). To improve this problem of white appearing yellowish, even polarizers manufactured to suppress yellowing still have a problem where black appears blue when two polarizing films or polarizers are stacked so that their absorption axis directions are orthogonal to each other (hereinafter also referred to as "orthogonal position") to display black (hereinafter also referred to as "black display" or "dark display"). Therefore, there has been a demand for polarizing films and polarizers that display achromatic white when white is displayed and achromatic black when black is displayed. In particular, obtaining a polarizer that exhibits a high-quality white when white is displayed, commonly known as "paper white," has been extremely difficult.

[0005] The reason why the hue differs between white and black displays is that the wavelength dependence of transmittance is not the same for parallel and orthogonal positions, and in particular, the transmittance is not constant across the visible light region. Furthermore, the fact that dichroism is not constant across the visible light region is one of the factors that makes it difficult to realize achromatic polarizers.

[0006] To explain using iodine-based polarizers as an example, iodine-based polarizers, which use polyvinyl alcohol (hereinafter also referred to as "PVA") as a base material and iodine as a dichroic dye, generally have absorption bands centered around 480 nm and 600 nm. The absorption at 480 nm is due to polyiodine I 3- The complex with PVA shows that the absorption at 600 nm is due to polyiodine I 5- It is said to be caused by a complex with PVA. The degree of polarization (dichroism) at each wavelength is due to polyiodine I 5- The dichroism based on the complex with PVA is more pronounced than that of polyiodine I 3-This dichroism is higher than that based on the complex with PVA. In other words, when the transmittance at the orthogonal position is kept constant at each wavelength, the transmittance at the parallel position is higher at 600 nm than at 480 nm, resulting in a phenomenon where white appears yellowish when displayed. Conversely, when the transmittance at the parallel position is kept constant, the transmittance at the orthogonal position is lower at 600 nm than at 480 nm, resulting in a black that appears bluish when displayed. When white appears yellow when displayed, it generally gives the impression of deterioration, which is undesirable. Also, when black appears bluish, it does not appear as a clear black, which detracts from the impression of quality. Furthermore, with iodine-based polarizers, there are no complexes based on the wavelength around 550 nm, where luminous sensitivity is high, making hue control difficult. Thus, because the degree of polarization (dichroism) at each wavelength was not constant, wavelength dependence of the degree of polarization occurred. Furthermore, since there were only two dichroic dyes, 480 nm and 600 nm, which were absorbed by the complex of iodine and PVA, hue adjustment was not possible with iodine-based polarizers made of iodine and PVA.

[0007] Methods for improving the hue of iodine-based polarizers are described in Patent Documents 1 and 2. Patent Document 1 describes a polarizer in which the neutral coefficient is calculated and has an absolute value between 0 and 3. Patent Document 2 describes a polarizing film in which the transmittance from 410 nm to 750 nm is 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.

[0008] On the other hand, achromatic polarizing plates have been proposed using dye-based polarizing plates that utilize pigments. (Patent Documents 3 to 7) [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2002-169024 [Patent Document 2] Japanese Patent Application Publication No. 10-133016 [Patent Document 3] WO2014 / 162635 [Patent Document 4] WO2014 / 162633 [Patent Document 5] WO2019 / 117131 [Patent Document 6] Japanese Patent No. 6853010 [Patent Document 7] Japanese Patent No. 6662739 [Patent Document 8] International Publication No. 2021015188 [Non-Patent Document]

[0010] [Non-Patent Document 1] "Applications of Functional Dyes" (CMC Publishing Co., Ltd., First Edition, supervised by Masahiro Irie)

[0011] However, as can be seen from the examples, the polarizing plate of Patent Document 1 has a low neutrality coefficient (Np), and the hue in the parallel direction obtained from JIS Z8729 has an a* value of -1.67 and a b* value of 3.51, indicating that it exhibits a yellow-green color during white display. Also, the hue in the orthogonal direction has an a* value of 0.69 but a b* value of -3.40, resulting in a polarizing plate where black display exhibits a blue color. Further, the polarizing film of Patent Document 2 is obtained by setting the absolute values of the a* value and b* value in the UCS color space measured using only one polarizing film to 2 or less, and it cannot simultaneously express achromatic colors in both the white display and black display hues when two polarizing films are stacked. Additionally, the average value of the single transmittance of the polarizing film of Patent Document 2 was 31.95% in Example 1 and 31.41% in Example 2, showing low values. Thus, due to the low transmittance of the polarizing film of Patent Document 2, it did 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. Moreover, since the polarizing film of Patent Document 2 uses iodine as the main dichroic dye, after the durability test, especially after the damp heat durability test (for example, in an environment of 85°C and 85% relative humidity), there was a large color change and the durability was poor.

[0012] On the other hand, while dye-based polarizers have excellent durability, their wavelength dependence differs between the parallel and orthogonal positions, similar to iodine-based polarizers. There are virtually no azo compounds that exhibit dichroism, showing the same hue in both the parallel and orthogonal positions, and even if they exist, their polarization degree and dichroism (polarization characteristics) are low. Depending on the type of azo compound with dichroism, there are also azo compounds whose wavelength dependence differs completely between the parallel and orthogonal positions, such as white appearing yellow when displayed as white, and black appearing blue when displayed as black. Furthermore, since human color sensitivity differs depending on the brightness of the light, even if color correction is performed on dye-based polarizers, color correction appropriate to the brightness of the light generated by controlling the light from the parallel to orthogonal positions is necessary. Achromatic polarizers can only be achieved if the transmittance is nearly constant at each wavelength in both the parallel and orthogonal positions, and there is no wavelength dependence. In addition, in order to obtain a polarizing film with high transmittance and high contrast, it is necessary to simultaneously satisfy a certain transmittance in both the parallel and orthogonal positions, as well as having high and constant dichroism and polarization degree at each wavelength. Even when applying a single azo compound to a polarizing film, the wavelength dependence of transmittance differs between the orthogonal and parallel positions. Therefore, in order to achieve a constant transmittance by blending two or more azo compounds, it is necessary to consider the transmittance of each compound in the parallel and orthogonal positions and precisely control the balance of polarization degree and dichroism of the two or more compounds.

[0013] On the other hand, even if the relationship between the transmittance in the parallel position and the transmittance in the orthogonal position and the dichroism ratio can be precisely controlled and the transmittance in each position can be kept constant, achieving high transmittance and high contrast has not yet been achieved. In other words, the higher the transmittance or the higher the degree of polarization, the more difficult it is to make it achromatic, and a high-transmittance achromatic polarizer has not been achieved. Obtaining a high-transmittance and / or high-contrast achromatic polarizer is extremely difficult and cannot be achieved simply by applying dichroic dyes of the three primary colors. In particular, achieving constant transmittance and high dichroism at each wavelength in the parallel position simultaneously is extremely difficult. Even a slight tint of color makes it impossible to represent high-quality white. Furthermore, white when displayed is especially important because it has high brightness and high sensitivity. Therefore, there is a need for a polarizing film that shows a high-quality, paper-like achromatic white when displaying white, shows an achromatic black when displaying black, and has a single-unit transmittance of 35% or more and a high degree of polarization after luminous sensitivity correction. Patent Document 3 also describes a polarizing plate that is achromatic when displaying white and black, but further improvements in performance are needed.

[0014] Patent document 4, which proposes a high-performance achromatic polarizing plate, describes the development of an achromatic polarizing plate with a polarization degree of 99% or more when the single-color transmittance is 40%. However, there is no description of the two-color ratio or contrast, and the performance as a polarizing plate remains unclear.

[0015] Patent Document 5 similarly describes the results for achromatic polarizers with a polarization degree of 99% or more at a single-element transmittance of around 40%. However, it is evident that there is considerable variation in contrast at comparable single-element transmittances, making it extremely difficult to stably produce achromatic polarizers with high transmittance. Furthermore, some of the samples presented in the examples have an absolute value of hue in black representation exceeding (a*-c, b*-c)2.0, and therefore cannot be considered achromatic polarizers.

[0016] Furthermore, while Patent Document 6 (Tables 1A and 1B) proposes achromatic polarizing plates with a single-unit transmittance of 40% or less and a polarization degree of 99% or more, their transmittance is at most around 38.5%, making them unsuitable for existing liquid crystal display devices and optical films for organic electronics.

[0017] Patent Document 7 (Table 1), which proposes achromatic polarizers with controlled single-element transmittance, describes the development of achromatic polarizers with single-element transmittances of 40% to 60% or less, achieving a wide range of achromaticity within the visible light spectrum. However, the contrast of polarizers with single-element transmittances of 40% or more is low, and it cannot be denied that the polarization performance of the proposed achromatic polarizers is poor.

[0018] As demonstrated in Patent Document 8, azo compounds have been developed that exhibit a constant degree of polarization in the 530-550 nm range. These are considered beneficial for the production of achromatic polarizing films and polarizing plates, and the development of new azo compounds is therefore desired.

[0019] Thus, conventional technologies can achieve achromaticity by keeping the transmittance in the visible region constant, but high performance (high polarization, high contrast, high dichromatic ratio) has yet to be achieved, and its realization is needed. [Overview of the Initiative] [Problems that the invention aims to solve]

[0020] Therefore, the object of the present invention is to provide a high-performance achromatic polarizing film that has high transmittance and high contrast, is achromatic in both white and black display, and exhibits a high-quality white in white display and a high-quality black in black display, as well as an achromatic polarizing plate and display device using the same. [Means for solving the problem]

[0021] As a result of intensive studies to solve the above problems, the present inventors have found that a high-performance polarizing film that exhibits achromatic color during white display and black display and has high contrast can be produced by blending specific azo compounds.

[0022] That is, the present invention relates to [1] to

[10] . [1] A polarizing film containing an azo compound represented by formula (1) or a salt thereof and an azo compound represented by formula (2) or a salt thereof. [Chemical formula] (In formula (1), R 1 ~R 6 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a halogen atom, a carboxy group, a sulfo group, an alkoxy group having 1 to 4 carbon atoms having a sulfo group, a hydroxy group, an amino group, an acetylamino group, or a benzoylamino group that may have a substituent.) [Chemical formula] (In formula (2), Ay 21 and Ay 22 each independently represent a naphthyl group that may have a substituent or a phenyl group that may have a substituent, Ry 21 , Ry 22 , Ry 27 , Ry 28 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 Ry 23 ~Ry 26 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 having a sulfo group, and s and t each independently represent 0 or 1.) [2] The polarizing film according to the above [1], which contains one or more organic dyes other than the azo compounds represented by formula (1) and formula (2) or salts thereof. [3] The polarizing film according to the above [1] or [2], wherein the polarizing film contains a hydrophilic polymer film as a base material. [4] A polarizing film as described in any one of the preceding paragraphs [1] to [3], wherein the absolute values ​​of the a* and b* values ​​obtained when measuring the transmittance of natural light in accordance with JIS Z 8781-4:2013 are both 5.0 or less for the polarizing film alone. [5] A polarizing film according to any one of the preceding items [1] to [3], wherein, when two of the polarizing films are stacked so that their absorption axis directions are parallel to each other, the absolute values ​​of the a* and b* values ​​obtained when measuring the transmittance of natural light in accordance with JIS Z 8781-4:2013 are 2.0 or less. [6] A polarizing film according to any one of the preceding items [1] to [3], wherein, when two of the polarizing films are stacked so that their absorption axis directions are perpendicular to each other, the absolute values ​​of the a* and b* values ​​obtained when measuring the transmittance of natural light in accordance with JIS Z 8781-4:2013 are 2.0 or less. [7] A polarizing film according to any one of the preceding paragraphs [1] to [3], wherein, when two of the polarizing films are stacked and arranged so that their absorption axis directions are parallel to each other, the absolute value of the difference between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is 2.0 or less, and the absolute value of the difference between the average transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 640 nm is 2.0 or less. [8] A polarizing film according to any one of the preceding paragraphs [1] to [3], wherein, with respect to the transmittance obtained when two of the polarizing films are stacked so that their absorption axis directions are perpendicular to each other, the absolute value of the difference between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is 0.5 or less, and the absolute value of the difference between the average transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 640 nm is 0.5 or less. [9] A polarizing plate comprising a transparent protective layer provided on one or both sides of a polarizing film as described in any one of the preceding paragraphs [1] to [3].

[10] A liquid crystal display device comprising a polarizing film as described in any one of the preceding paragraphs [1] to [3], or a polarizing plate as described in [9]. [Effects of the Invention]

[0023] The present invention provides a high-performance polarizing film that exhibits achromaticity in white and black displays and has high contrast, as well as a polarizing plate and a display device. [Modes for carrying out the invention]

[0024] In this specification and in the claims, unless explicitly referring to a free form, "azo compound or salt thereof" may be simply referred to as "azo compound." Also, in this specification and in the claims, "substituents" may include hydrogen atoms, and therefore, for convenience, hydrogen atoms may be described as "substituents." "May have substituents" means that it also includes cases without substituents. For example, "phenyl group that may have substituents" includes both an unsubstituted, simple phenyl group and a phenyl group with substituents. Furthermore, unless otherwise specified, "lower" in this application, such as lower alkyl groups and lower alkoxy groups, indicates that the number of carbon atoms is 1 to 4, preferably 1 to 3.

[0025] The polarizing film of the present invention contains an azo compound represented by the following formula (1) or a salt thereof, and an azo compound represented by the following formula (2) or a salt thereof. [ka] (In formula (1), R 1 ~R 6 Each of these independently represents a hydrogen atom, a C1-C4 alkyl group, a C1-C4 alkoxy group, a halogen atom, a carboxyl group, a sulfo group, a C1-C4 alkoxy group having a sulfo group, a hydroxyl group, an amino group, an acetylamino group, or a benzoylamino group which may have substituents.

[0026] [ka] (In equation (2), Ay 21 and Ay 22 Each is independently a optionally substituted naphthyl group or an optionally substituted phenyl group, and Ry 21 , Ry 22 , Ry 27 , Ry 28 However, each is independently a hydrogen atom, a C1-4 alkyl group, and a C1-4 alkoxy group, and Ry 23 ~Ry 26 However, each of these independently represents a hydrogen atom, a C1-4 alkyl group, a C1-4 alkoxy group, or a C1-4 alkoxy group having a sulfo group, and s and t independently represent 0 or 1.

[0027] In the above equation (1), R 1 ~R 6 Each of these independently represents a hydrogen atom, a C1-C4 alkyl group, a C1-C4 alkoxy group, a halogen atom, a carboxyl group, a sulfo group, a C1-C4 alkoxy group having a sulfo group, a hydroxyl group, an amino group, an acetylamino group, or a benzoylamino group which may have a substituent, preferably a hydrogen atom, a sulfo group, or a carboxyl group. 1 ~R 2 It is even more preferable that one or both of them are sulfo groups or carboxyl groups.

[0028] In the above equation (2), Ay 21 and Ay 22 Each is independently a optionally substituted naphthyl group or an optionally substituted phenyl group, and Ry 21 , Ry 22 , Ry 27 , Ry 28 However, each is independently a hydrogen atom, a C1-4 alkyl group, and a C1-4 alkoxy group, and Ry 23 ~Ry 26 However, each is independently a hydrogen atom, a C1-4 alkyl group, a C1-4 alkoxy group, or a C1-4 alkoxy group having a sulfo group, and s and t are independently 0 or 1. Preferably, either s or t is 1.

[0029] In equation (2) above, Ay 21and Ay 22 Each of these is independently a optionally substituted naphthyl group or an optionally substituted phenyl group, preferably an optionally substituted naphthyl group.

[0030] In equation (2) above, Ay 21 and Ay 22 Each of these is independently a optionally substituted naphthyl group or an optionally substituted phenyl group, and the optionally substituted groups are not limited, but are preferably a sulfo group, a carboxyl group, a hydroxyl group, or a C1-C4 alkoxy group having a sulfo group, and more preferably a sulfo group.

[0031] In equation (2) above, Ry 21 , Ry 22 , Ry 27 , Ry 28 Each of these is independently a hydrogen atom, a C1-4 alkyl group, or a C1-4 alkoxy group, preferably a hydrogen atom and a C1-4 alkyl group.

[0032] In equation (2) above, Ry 23 ~Ry 26 However, each is independently a hydrogen atom, a C1-4 alkyl group, a C1-4 alkoxy group, or a C1-4 alkoxy group having a sulfo group, preferably a hydrogen atom, a methyl group, a methoxy group, or a sulfopropoxy group.

[0033] The base material for the polarizing film is preferably a film obtained by forming a polymer film that can adsorb and contain dichroic materials such as azo compounds or iodine.

[0034] More preferably, the polymers are hydrophilic polymers, and while they are not particularly limited, most preferably they are polyvinyl alcohol-based resins, amylol-based resins, starch-based resins, cellulose-based resins, polyacrylic acid-based resins, and derivatives or modified versions thereof.

[0035] The azo compounds represented by formulas (1) and (2) above, or their salts, can be easily produced by known diazotization and coupling in accordance with the conventional methods for producing azo dyes, as described in Non-Patent Document 1. More specifically, formula (1) can be produced by referring to Japanese Patent Application No. 6892432, and formula (2) can be produced by referring to International Publication No. 2019124161.

[0036] Specific examples of azo compounds or salts thereof represented by formula (1) are given below. Note that azo compounds are expressed in the form of free acids.

[0037] [ka]

[0038] [ka]

[0039] Specific examples of azo compounds or salts thereof represented by formula (2) are given below. Note that azo compounds are expressed in the form of free acids.

[0040] [ka]

[0041] [ka]

[0042] [ka]

[0043] [ka]

[0044] [ka]

[0045]

change

[0046]

change

[0047]

change

[0048]

change

[0049]

change

[0050]

change

[0051]

change

[0052]

change

[0053]

change

[0054]

change

[0055] [ka]

[0056] The polarizing film of the present invention can be made into a colorless polarizing film or polarizing plate by containing and adsorbing azo compounds shown in formulas (1) and (2).

[0057] Furthermore, it is preferable to include one or more organic dyes in addition to the azo compounds shown in formulas (1) and (2) in order to further improve the polarization performance.

[0058] Organic dyes that can be used include, for example, organic compounds as shown in Non-Patent Document 1, with those exhibiting high dichroism being particularly preferred. Examples include CI Direct Yellow 12, CI Direct Yellow 28, CI Direct Yellow 44, CI Direct Orange 26, CI Direct Orange 39, CI Direct Orange 107, CI Direct Red 2, CI Direct Red 31, CI Direct Red 79, CI Direct Red 81, CI Direct Red 247, CI Direct Green 80, CI Direct Green 59, and organic dyes described in Patent Documents 1 to 7. These organic dyes can be used as free acids, alkali metal salts (e.g., Na salts, K salts, Li salts), ammonium salts, or salts of amines. However, the dichroic dyes are not limited to these, and known dichroic dyes can be used. The optical properties are improved when the azo compound is a free acid, a salt thereof, or a copper complex salt dye thereof.

[0059] In the present invention, the content of the azo compound represented by formula (2) is preferably 0.01 to 5000 parts by mass, and more preferably 0.1 to 3000 parts by mass, based on 100 parts by mass of the azo compound of formula (1).

[0060] In the present invention, the content of organic dyes other than those of formulas (1) and (2) is preferably 0.01 to 5000 parts by mass, and more preferably 0.1 to 3000 parts by mass, based on 100 parts by mass of the azo compound of formula (1).

[0061] The polarizing film of the present invention contains a combination of one or more azo compounds represented by formula (1), an azo compound represented by formula (2), and other organic dyes, thereby achieving high transmittance and high polarization while also realizing a higher quality paper white when displaying white and a clearer, more luxurious black when displaying black.

[0062] The azo compound represented by formula (1) and the azo compound represented by formula (2) may be in free form or in 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.

[0063] The polarizing film of the present invention contains an azo compound represented by formula (1) or (2), and optionally further contains other organic dyes. The polarizing film of the present invention can have the following properties: desired chromaticity a* and b* values, single-element transmittance, and average transmittance in a specific wavelength band.

[0064] A polarizing film is made by adsorbing azo compounds and iodine, which are dichroic materials, onto a polymer film, preferably a hydrophilic polymer film, and then stretching it uniaxially. This causes the dichroic materials to orient in the same direction as the stretching direction, resulting in the development of polarizing properties. The stretching method may be a dry heat stretching method in which heat is applied during stretching, or more preferably a wet stretching method in which uniaxial stretching is performed in an aqueous solution.

[0065] The blending ratio of the above azo compounds in the polarizing film is preferably further adjusted so that the transmittance and chromaticity are within the preferred range described later, based on the content of each azo compound as described above. The performance of the polarizing film is affected not only by the blending ratio of each azo compound in the polarizing film, but also by various factors such as the degree of swelling of the base film on which the azo compound is adsorbed, the stretching ratio, the dyeing time, the dyeing temperature, the pH during dyeing, and the effect of salt, for example, when wet stretching is used. For this reason, the blending ratio of each azo compound can be determined according to the degree of swelling of the base film, the temperature during dyeing, the dyeing time, the pH of the dyeing bath, the type of salt, the salt concentration, and even the stretching ratio and stretching temperature.

[0066] The transmittance is the transmittance after luminous sensitivity correction, determined according to JIS Z 8722:2009. The transmittance can be measured by taking spectral transmittance at 5 nm or 10 nm intervals for each wavelength of 380 to 780 nm or 400 to 700 nm in the sample (e.g., polarizing film or polarizing plate), and correcting this for luminous sensitivity, for example, using a C light source with a 2-degree field of view.

[0067] In the above-mentioned transmittance after luminous efficiency correction, the transmittance measured with one polarizing film or polarizing plate is called the single-piece transmittance (Ys), the transmittance obtained from measurements with the absorption axes of two polarizing films or polarizing plates set parallel to each other is called the parallel-position transmittance (Yp), and the transmittance obtained from measurements with the absorption axes of two polarizing films or polarizing plates set perpendicular to each other is called the orthogonal-position transmittance (Yc).

[0068] The polarizing film or polarizing plate of the present invention preferably has a Ys of 35% to 65%. In terms of performance, the higher the transmittance of the polarizing plate, the brighter the display can be, but if the individual transmittance is between 35% and 65%, it can be used in a display device to express brightness without any unnatural feeling.

[0069] As the degree of polarization tends to decrease with increasing transmittance, from the standpoint of balancing transmittance and degree of polarization, a single-element transmittance of 37% to 50% is more preferable, and even more preferable is 38% to 45%. If the single-element transmittance Ys exceeds 65%, the degree of polarization may decrease, but in cases where high transmittance of 65% or more is required, or when specific polarization performance or contrast is desired, the single-element transmittance may exceed 65%.

[0070] The polarizing film or polarizing plate of the present invention preferably has a difference in average transmittance between specific wavelength bands that is less than or equal to a predetermined value. Average transmittance is the average value of transmittance in a specific wavelength band.

[0071] 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 when indicating color in JIS Z 8781-4:2013. Specifically, in the XYZ color matching function of JIS Z 8701, which is the basis for 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 set to 100, the wavelength bands that show values ​​of 20 or more are 420nm to 480nm, 520nm to 590nm, and 600nm to 640nm.

[0072] The polarizing film of the present invention preferably has a parallel transmittance Yp such that the absolute value of the difference between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is 2.0% or less, more preferably 1.8% or less, even more preferably 1.5% or less, and particularly preferably 1.0% or less. Furthermore, the absolute value of the difference between the parallel transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 640 nm is preferably 2.0% or less, more preferably 1.5% or less, and even more preferably 1.0% or less. Such a polarizing film or polarizing plate can display a high-quality white color in the parallel position (also referred to as white display or bright display).

[0073] Furthermore, for the Yc obtained by measuring with two polarizing films stacked so that their absorption axis directions are orthogonal (when displaying black or when displaying dark), the absolute value of the difference between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is preferably 10% or less, and the absolute value of the difference between the average transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 640 nm is preferably 2.0% or less, and more preferably 1.0% or less. Such polarizing films can display achromatic black in orthogonal positions. Furthermore, for the Yc of the polarizing film of the present invention, the absolute value of the difference between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is preferably 2.0% or less, and more preferably 1.0% or less. With respect to orthogonal transmittance, the absolute value of the difference between the average transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 640 nm is preferably 0.5% or less, more preferably 0.2% or less, and even more preferably 0.1% or less.

[0074] The average transmittances of the single element, parallel element, and orthogonal element in the wavelength bands 380nm to 420nm, 480nm to 520nm, and 640nm to 780nm are less affected by the dye if the average transmittances in the wavelength bands 420nm to 480nm, 520nm to 590nm, and 600nm to 640nm are adjusted as described above, but it is preferable that they be adjusted to some extent. Preferably, the difference between the average transmittance in the wavelength band 380nm to 420nm and the average transmittance in the wavelength band 420nm to 480nm is 15% or less; preferably, the difference between the average transmittance in the wavelength band 480nm to 5520nm to 590nm is 15% or less; and preferably, the difference between the average transmittance in the wavelength band 640nm to 780nm and the average transmittance in the wavelength band 600nm to 630nm is 20% or less.

[0075] The polarizing film preferably has an average transmittance of 28% to 50% in the wavelength band from 520nm to 590nm, measured in parallel. When such a polarizing film is installed in a display device, it can result in a bright, high-luminosity, and clear display device. The transmittance in the wavelength band from 520nm to 590nm is one of the main wavelength bands based on the color matching functions used in calculations when indicating color in JIS Z 8781-4:2013. In particular, each wavelength band from 520nm to 590nm is the wavelength band with the highest visual sensitivity based on color matching functions, 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 in the wavelength band from 520nm to 590nm. The average transmittance in the wavelength band from 520nm to 590nm, measured in parallel, is more preferably 29% to 45%, and even more preferably 30% to 40%. Furthermore, the polarization degree of the polarizing film at this time is preferably 80% to 100%, more preferably 95% to 100%, and even more preferably 99% to 100%. A higher polarization degree is preferable, but the transmittance and polarization degree can be adjusted to suit the relationship between polarization degree and transmittance, depending on whether brightness or polarization degree (or contrast or dichroism) is prioritized.

[0076] Chromaticity a* and b* values ​​are obtained when measuring the transmittance of natural light in accordance with JIS Z 8781-4:2013. The method of representing object color specified in JIS Z 8781-4:2013 corresponds to the method of representing object color specified by the International Commission on Illumination (CIE). Chromaticity a* and b* values ​​are measured by irradiating the sample (e.g., a polarizing film or polarizing plate) with natural light. In the following, the chromaticity a* and b* values ​​obtained for one sample are denoted as chromaticity a*-s and b*-s, the chromaticity a* and b* values ​​obtained for two samples arranged in a parallel position (indicated in white) with their absorption axis directions parallel to each other are denoted as a*-p and b*-p, and the chromaticity a* and b* values ​​obtained for two samples arranged in an orthogonal position (indicated in black) with their absorption axes perpendicular to each other are denoted as chromaticity a*-c and b*-c.

[0077] In the polarizing film and polarizing plate according to the present invention, the absolute values ​​of a*-s and b*-s are preferably 5.0 or less, more preferably 1.0 or less. The absolute values ​​of a*-p and b*-p are preferably 2.0 or less. Such a polarizing film is neutral in itself and can display a high-quality white when displaying white. The absolute values ​​of a*-p and b*-p are more preferably 1.5 or less, even more preferably 1.0 or less. Furthermore, in the polarizing film and polarizing plate, the absolute values ​​of a*-c and b*-c are preferably 20 or less, more preferably 10 or less, even more preferably 3.0 or less, and particularly preferably 1.0 or less. Such a polarizing film and polarizing plate can display achromatic black when displaying black. Even a difference of 0.5 in the absolute values ​​of the chromaticity a* and b* values ​​can be perceived by humans as a difference in color, and some people may perceive a large difference in color. For this reason, controlling these values ​​in a polarizing film is extremely important. 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 almost no other colors are visible in the white when white is displayed and in the black when black is displayed. It is possible to achieve achromaticity in the parallel position, that is, a high-quality paper-like white, and a clear, high-quality achromatic black in the orthogonal position.

[0078] The polarizing film or polarizing plate of the present invention possesses high contrast and high transmittance while also exhibiting achromaticity and high polarization degree on its own. Furthermore, the polarizing film of the present invention can express a high-quality paper-like white (paper white) when displaying white, and due to its high contrast, it can express achromatic black, especially a clear, high-quality black, when displaying black. Until now, no polarizing film or polarizing plate has existed that combines such high transmittance and achromaticity. The polarizing film or polarizing plate of the present invention is also highly durable, and is particularly resistant to high temperatures and high humidity.

[0079] The compounds (1) and (2) used in this invention are azo compounds, and as is well known, their polarization performance is superior to that of iodine-based polarizers even when exposed to environmental conditions (e.g., dry heat, wet heat, heat cycles, xenon light, carbon arc light, etc.), comparable to polarizing films and polarizers made using azo compounds.

[0080] The following describes a specific method for producing a polarizing film or polarizing plate by adsorbing an azo compound onto a film substrate made of polyvinyl alcohol-based resin. However, the method for producing a polarizing film according to the present invention is not limited to the following.

[0081] <Preparation of the raw film roll> The raw film can be produced by forming a film of polyvinyl alcohol-based resin. The polyvinyl alcohol-based resin is not particularly limited, and commercially available films may be used, or those synthesized by known methods may be used. The polyvinyl alcohol-based resin can be obtained, for example, by saponifying a polyvinyl acetate-based resin. Examples of polyvinyl acetate-based resins 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 degree of saponification of the polyvinyl alcohol-based resin is usually preferably around 85 to 100 mol%, and more preferably 95 mol% or more. The polyvinyl alcohol-based resin may be further modified; for example, polyvinyl formal and polyvinyl acetal modified with aldehydes can also be used. Furthermore, the degree of polymerization of the polyvinyl alcohol-based resin refers to the viscosity-average degree of polymerization, which can be determined by methods well known in the art, and is usually preferably around 1,000 to 10,000, and more preferably around 1,500 to 6,000.

[0082] The method for forming the polyvinyl alcohol-based resin film is not particularly limited and can be done by known methods. In this case, the polyvinyl alcohol-based resin film may contain plasticizers such as glycerin, ethylene glycol, propylene glycol, and low molecular weight polyethylene glycol. The amount of plasticizer is preferably 5 to 20% by mass, and more preferably 8 to 15% by mass, in the total amount of film. The film thickness of the raw material film is not particularly limited, but for example, it is about 5 μm to 150 μm, preferably about 10 μm to 100 μm.

[0083] <Swelling Process> A swelling process is performed on the obtained raw film, which involves immersing it in an aqueous solution. In the swelling process, the raw film is immersed in a solution at 0 to 60°C for 30 seconds to 10 minutes. Water is preferred as the solution, and although the water temperature is not particularly limited, 20°C to 50°C is preferred. The stretching ratio is preferably adjusted to 1.00 to 1.50 times, and more preferably to 1.10 to 1.35 times. If the time for manufacturing the polarizing film is to be shortened, the swelling process can be omitted because the raw film also swells during the dyeing process described later. The swelling process can be performed in one stage, but it can also be performed by multi-stage stretching of two or more stages.

[0084] <Dyeing process> The process of adsorbing and impregnating an azo compound into a resin film obtained by swelling the raw film is called the dyeing process. If the swelling process is omitted, the swelling of the raw film can be performed simultaneously in the dyeing process. The process of adsorbing and impregnating with an azo compound is called the dyeing process because it is a process of coloring the resin film.

[0085] As the azo compound, azo compounds represented by formula (1) or (2) or salts thereof, and other dichroic dyes can be used. In addition, azo compounds that are dichroic dyes, as exemplified in "Applications of Functional Dyes" (CMC Publishing Co., Ltd., 1st edition, supervised by Masahiro Irie, pp. 98-100), may be used to adjust the color to an extent that does not impair the performance of the polarizing film of this application. Those with high dichroism are particularly preferred. Examples include CI Direct Yellow 12, CI Direct Yellow 28, CI Direct Yellow 44, CI Direct Orange 26, CI Direct Orange 39, CI Direct Orange 107, CI Direct Red 2, CI Direct Red 31, CI Direct Red 79, CI Direct Red 81, CI Direct Red 247, CI Direct Green 80, CI Direct Green 59, and organic dyes described in Patent Documents 1 to 7. These organic dyes can be used as free acids, alkali metal salts (e.g., Na salts, K salts, Li salts), ammonium salts, or amine salts. However, the dichroic dyes are not limited to these and known dichroic dyes can be used.

[0086] The dyeing process is not particularly limited as long as it involves adsorbing and impregnating the base film with a dye, but it is preferably carried out by immersing the base film in a dyeing solution, for example, and can also be carried out by applying the dyeing solution to a resin film. Each azo compound in the dyeing solution can be adjusted in a range of, for example, 0.001 to 10% by mass.

[0087] The temperature of the staining solution in this process is preferably 5 to 60°C, more preferably 20 to 50°C, and even more preferably 35 to 50°C. The immersion time in the solution can be adjusted appropriately, but it is preferably adjusted to 30 seconds to 20 minutes, and more preferably 1 to 15 minutes. The stretching ratio is preferably adjusted to 1.00 to 3.00 times, and more preferably to 1.10 to 1.55 times. The stretching process may be a single-stage stretching or a multi-stage stretching of two or more stages may be applied.

[0088] The staining solution may contain, in addition to the azo compound, staining aids as needed. Examples of staining aids include sodium carbonate, sodium bicarbonate, sodium chloride, sodium sulfate, anhydrous sodium sulfate, and sodium tripolyphosphate. The content of the staining aids can be adjusted to any concentration depending on the time and temperature required for the dyeing properties of the dye, but the content of each is preferably 0.01 to 5% by mass, and more preferably 0.1 to 2% by mass, in the staining solution.

[0089] <Washing process 1> After the dyeing process, a washing process (hereinafter also referred to as "washing process 1") can be performed before proceeding to the next process. Washing process 1 is a process of washing the dyeing solution that adheres to the surface of the raw film during the dyeing process. By performing washing process 1, it is possible to suppress the migration of dye into the liquid to be processed next. In washing process 1, water is generally used as the washing solution. The washing method is preferably immersion in the washing solution, but it is also possible to wash by applying the washing solution to the resin film. The washing time is not particularly limited, but is preferably 1 to 300 seconds, more preferably 1 to 60 seconds. The temperature of the washing solution in washing process 1 must be such that the material constituting the resin film (for example, a hydrophilic polymer, in this case, a polyvinyl alcohol-based resin) does not dissolve. Generally, the washing treatment is performed at 5 to 40°C. However, since there is no problem with performance even if washing process 1 is omitted, the washing process can be omitted. The stretching ratio is preferably adjusted to 1.00 to 3.00 times, and is 1.10 to 1.55 times. Furthermore, the stretching process may be a single-stage stretching process, or a multi-stage stretching process of two or more stages may be applied.

[0090] <Step of adding a crosslinking agent and / or a water-resistant agent> After the dyeing or washing step 1, a step of incorporating a crosslinking agent and / or a water-resistant agent can be performed. The method of incorporating the crosslinking agent and / or water-resistant agent into the raw film is preferably by immersion in a treatment solution, but the treatment solution may also be applied or coated onto 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. The stretching ratio is preferably adjusted to 1.00 to 3.00 times, and is 1.10 to 1.55 times. The stretching step may be a single-stage stretching or a multi-stage stretching of two or more stages may be applied.

[0091] Examples of crosslinking agents include boric acid, boron compounds such as borax or ammonium borate, polyhydric aldehydes such as glyoxal or glutaraldehyde, polyhydric isocyanate compounds such as biuret type, isocyanurate type or block type, and titanium compounds such as titanium oxysulfate. Other options include ethylene glycol glycidyl ether and polyamide epichlorohydrin. Examples of water-resistant agents include succinic acid peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride, or magnesium chloride, but boric acid is preferred. Water is preferred as the solvent for the crosslinking agent and / or water-resistant agent, but is not particularly limited. The concentration of the crosslinking agent and / or water-resistant agent can be appropriately determined by a person skilled in the art depending on its type, but taking boric acid as an example, a concentration of 0.1 to 6.0% by mass in the treatment solution is preferred, and 1.0 to 4.0% by mass is more preferred. However, if the inclusion of the crosslinking agent and / or water-resistant agent is not essential, and if time is to be shortened, this treatment step may be omitted if the crosslinking treatment or water-resistant treatment is unnecessary.

[0092] <Stretching process> After the dyeing process, washing process 1, or the process of incorporating a crosslinking agent and / or a water-resistant agent, a stretching process is performed. The stretching process is carried out by stretching the raw film in a uniaxial direction. Either a wet stretching method or a dry stretching method may be used. The stretching ratio is preferably 3 times or more, more preferably 4 to 8 times, and particularly preferably 5 to 7 times.

[0093] In the case of the dry stretching method, if the stretching heating medium is air, it is preferable to stretch the resin film at a temperature of room temperature to 180°C. Furthermore, it is preferable to maintain a humidity of 20-95% RH. Examples of heating methods include the inter-roll zone stretching method, roll heating stretching method, rolling stretching method, and infrared heating stretching method, but the stretching method is not limited to these. The stretching process can be performed in a single stage, or it can be carried out using a multi-stage stretching method of two or more stages.

[0094] 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 the film in a solution containing at least one crosslinking agent and / or water-resistant agent. The same crosslinking agent and / or water-resistant agent as described above for the step of incorporating the crosslinking agent and / or water-resistant agent can be used. The concentration of the crosslinking agent and / or water-resistant agent in the solution during the stretching process is preferably, for example, 0.5 to 15% by mass, and more preferably 2.0 to 8.0% by mass. The stretching temperature is preferably 40 to 70°C, and more preferably 45 to 60°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 it can also be performed in two or more stages.

[0095] <Washing process 2> After the stretching process, crosslinking agents and / or water-resistant agents may precipitate on the surface of the resin film, or foreign matter may adhere to it. Therefore, a cleaning process (hereinafter also referred to as "cleaning process 2") can be performed to clean the surface of the resin film, and the cleaning time is preferably 1 second to 5 minutes. The cleaning method is preferably immersing the resin film in a cleaning solution, but the solution can also be applied to or coated onto the resin film for cleaning, with water being particularly preferred as the cleaning solution. Furthermore, the cleaning process can be performed in one stage or in two or more stages. The solution temperature in the cleaning process is not particularly limited, but is usually 5 to 50°C, preferably 10 to 40°C.

[0096] The processing liquid or solvent used in the processing steps up to this point may include, but is not limited 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. The processing liquid or solvent is most preferably water. These processing liquids or solvents may be used individually or as a mixture of two or more.

[0097] After the stretching or washing process 2, a drying process is performed on the resin film. The drying process can be carried out by natural drying, but to improve drying efficiency, it can be carried out by compression with a roll, removal of surface moisture with an air knife or water-absorbing roll, etc., and / or by forced air drying. The drying temperature is preferably 20 to 100°C, and more preferably 60 to 100°C. The drying time is, for example, 30 seconds to 20 minutes, but preferably 5 to 10 minutes.

[0098] In the method for producing a polarizing film, it is preferable to adjust the degree of swelling of the raw film in the swelling step, the mixing ratio of each azo compound in the dyeing step, the temperature and pH of the dyeing solution, the type and concentration of salts such as sodium chloride, sodium sulfate, and sodium tripolyphosphate, and the dyeing time, as well as the stretching ratio and stretching speed in the stretching step, so that the polarizing film satisfies at least one of the following conditions (i) to (iv), and it is even more preferable to adjust them so that they further satisfy conditions (v) and (vi). (i) With respect to parallel transmittance, the absolute value of the difference between the average transmittance from 420nm to 480nm and the average transmittance from 520nm to 590nm is 2.0 or less, and the absolute value of the difference between the average transmittance from 520nm to 590nm and the average transmittance from 600nm to 640nm is 2.0 or less. (ii) With respect to orthogonal transmittance, the absolute value of the difference between the average transmittance from 420nm to 480nm and the average transmittance from 520nm to 590nm is 10 or less, and the absolute value of the difference between the average transmittance from 520nm to 590nm and the average transmittance from 600nm to 640nm is 2.0 or less. (iii) The single-unit transmittance will increase from 35% to 65%. (iv) The absolute values ​​of the a* and b* values ​​are both 2.0 or less for the polarizing film alone, both 2.0 or less in the parallel position, and also 2.0 or less in the orthogonal position. (v) Regarding parallel transmittance, the average transmittance from 520 nm to 590 nm is 25-45%. (vi) The difference between the average transmittance from 380nm to 420nm and the average transmittance from 420nm to 480nm is 15% or less, the difference between the average transmittance from 480nm to 520nm and the average transmittance from 420nm to 480nm is 15% or less, the difference between the average transmittance from 480nm to 520nm and the average transmittance from 520nm to 590nm is 15% or less, and / or the difference between the average transmittance from 640nm to 780nm and the average transmittance from 600nm to 640nm is 20% or less.

[0099] By the above method, a polarizing film containing at least an azo compound represented by formula (1) or (2) and a combination of other azo compounds can be manufactured. The polarizing film of the present invention has a higher transmittance and a higher degree of polarization than conventional polarizing films, and when two polarizing films are stacked and arranged so that their absorption axes are parallel, it can produce a high-quality paper-like white color, and a polarizing film and polarizing plate that have a neutral color (neutral gray) on their own and have high contrast. In addition, the polarizing plate has high durability against high temperature and high humidity.

[0100] The polarizing plate according to the present invention is equipped with a transparent protective layer on one or both sides for the purpose of improving the water resistance and handling of the polarizing film.

[0101] 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 film, and is preferably made of a plastic that has excellent transparency, mechanical strength, thermal stability, moisture shielding properties, etc. Equivalent functions can also be provided by forming an equivalent layer. Examples of plastics that constitute the protective film include films obtained from thermoplastic resins such as polyester resins, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, and acrylic resins, as well as thermosetting resins such as acrylic, urethane, acrylic urethane, epoxy, and silicone, or UV-curable resins. Among these, polyolefin resins include amorphous polyolefin resins that have polymerization units of cyclic polyolefins such as norbornene monomers or polycyclic norbornene monomers. Generally, it is preferable to select a protective film that does not impair the performance of the polarizing film after lamination, and triacetylcellulose (TAC) and norbornene, which are made of cellulose acetate resin, are particularly preferred as such protective films. Furthermore, the protective film may be treated with a hard coat, or with a treatment for preventing or diffusing sticking, or an anti-reflective treatment such as anti-glare or anti-reflection, as long as it does not impair the effects of the present invention.

[0102] The polarizing plate of the present invention preferably further comprises an adhesive layer between the transparent protective layer and the polarizing film for bonding the transparent protective layer to the polarizing film. The adhesive constituting the adhesive layer is not particularly limited, but a polyvinyl alcohol-based adhesive is preferred. Examples of polyvinyl alcohol-based adhesives include, but are not limited to, Gosenol NH-26 (manufactured by Nippon Synthetic Co., Ltd.). A crosslinking agent and / or a water-resistant agent can be added to the adhesive. As the polyvinyl alcohol-based adhesive, a maleic anhydride-isobutylene copolymer is preferred, and an adhesive mixed with a crosslinking agent can be used if 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 polyvalent epoxy compounds include Denacol EX-521 (manufactured by Nagase Chemtec Co., Ltd.) and Tetrat-C (manufactured by Mitsui Gas Chemical Co., Ltd.). In addition, known adhesives other than polyvinyl alcohol-based resins, such as urethane-based, acrylic-based, and epoxy-based adhesives, can also be used. In particular, it is preferable to use acetoacetyl-modified polyvinyl alcohol, and it is even preferable to use a polyvalent aldehyde as a crosslinking agent. Furthermore, to improve the adhesive strength or water resistance of the adhesive, additives such as zinc compounds, chlorides, and iodides can be included individually or simultaneously at a concentration of about 0.1 to 10% by 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 film with the adhesive, a polarizing plate can be obtained by drying or heat-treating at an appropriate temperature.

[0103] The polarizing plate of the present invention may, in some cases, be bonded to a display device such as a liquid crystal display device (including transmissive, semi-transmissive, reflective, direct-viewing, etc.) or an organic electroluminescent device (OLED or OEL, organic EL), and various functional layers for improving viewing angle and / or contrast, as well as layers or films for improving brightness, may be provided on the surface of the protective layer or film that will later become an unexposed surface. The various functional layers are, for example, layers or films that control phase difference. It is preferable that the polarizing plate be bonded to these films or display devices with an adhesive.

[0104] The polarizing plate of the present invention may have various known functional layers, such as an anti-reflective layer, an anti-glare layer, and a hard coat layer, on the exposed surface of the protective layer or film. A coating method is preferred for producing these functional layers, and the functional film is bonded via an adhesive or tack. It is also possible.

[0105] The polarizing plate of the present invention is a highly durable polarizing plate that can achieve achromaticity while having high transmittance and high polarization degree, and in particular can express a high-quality paper-like white when displaying white, and can express high contrast.

[0106] The polarizing film or polarizing plate of the present invention, optionally equipped with a protective or functional layer and a transparent support such as glass, quartz, or sapphire, is applicable to liquid crystal projectors, calculators, watches, laptop computers, word processors, liquid crystal televisions, polarizing lenses, polarizing glasses, car navigation systems, and indoor and outdoor measuring instruments and displays. In particular, the polarizing film or polarizing plate of the present invention is suitably used in liquid crystal display devices, such as reflective liquid crystal display devices, semi-transparent liquid crystal display devices, and organic electroluminescence. A liquid crystal display device using the polarizing film or polarizing plate of the present invention can express high-quality paper-like white and high contrast. Furthermore, the display device has high durability and reliability, and is a display device that maintains high contrast and high color reproducibility over the long term.

[0107] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0108] [Example 1] (Fabrication of polarizing films) A polyvinyl alcohol film (PVA film: manufactured by Kuraray Co., Ltd.: product name: VF-PE) with a saponification degree of 99% or higher was immersed in 35°C warm water for 1 minute to swell and achieve a stretch ratio of 1.20 times. The swollen film was then immersed for 600 seconds in a 48°C dyeing solution containing 1500 parts by mass of water, 1.5 parts by mass of sodium tripolyphosphate, 1.5 parts by mass of anhydrous sodium sulfate, 0.5 parts by mass of compound example 1-12 as compound (1), 0.3 parts by mass of compound example 2-84 as compound example (2), and 0.5 parts by mass of a dichroic dye shown in compound example (1-10) described in Patent Document International Publication No. 2019117131, while incorporating an azo compound into the film, and achieving a stretch ratio of 1.30 times. The dyed film was washed, and then the resulting film was immersed for 1 minute in a 40°C aqueous solution containing 20 g / L of boric acid (manufactured by Societa Chimica Larderellos.pa) to achieve a stretch ratio of 1.2. After immersion, the film was rinsed with water and then stretched to 6.0 times while being stretched for 5 minutes in a 58°C aqueous solution containing 30.0 g / L of boric acid. While maintaining the tension of the resulting film, it was immersed in 25°C water for 15 seconds to perform a washing treatment. The washed film was dried at 70°C for 3 minutes to obtain a polarizing film. This polarizing film was used as the measurement sample for Example 1.

[0109] [Examples 2-8] In Examples 2 to 8, polarizing films were prepared using the same procedure as in Example 1, except that the immersion time in the dyeing process was adjusted to control the transmittance within the range of 300 to 660 seconds.

[0110] [Comparative Example 1] A polarizing film was prepared using the same composition as in Example 1, except that Compound Example 1-12, used as the compound of formula (1) in Example 1, was replaced with the azo compound shown in formula (1-A-14) described in Example 6 of International Patent Publication No. 2017146212, and the immersion time in the dyeing process was changed to 720 seconds, except that the procedure was the same as in Example 1.

[0111] [Comparative Examples 2-6] In Comparative Examples 2 to 6, polarizing plates were prepared using the same procedure as in Example 1, except that the immersion time in the dyeing process was adjusted to control the transmittance within the range of 330 seconds to 660 seconds.

[0112] [evaluation] The polarizing films obtained in Examples 1-8 and Comparative Examples 1-6 were evaluated as follows.

[0113] <Parallel polarized transmittance (Ky) and orthogonal polarized transmittance (Kz)> The maximum absorption wavelength, parallel polarization transmittance (Ky), and orthogonal polarization transmittance (Kz) of the polarizing film were measured using a spectrophotometer (Hitachi UH-4150). Here, Ky is the transmittance when the absorption axis of the absolute polarizer and the absorption axis of the polarizing film are aligned parallel to each other, and Kz is the transmittance when the absorption axis of the absolute polarizer and the absorption axis of the polarizing film are aligned orthogonally. The parallel polarization transmittances Ky and Kz for each wavelength were measured at wavelength intervals of 1 to 10 nm from 380 nm to 780 nm.

[0114] <Single-element transmittance (Ts), parallel transmittance (Tp), orthogonal transmittance (Tc)> Single-layer transmittance (Ts) refers to the spectral transmittance of a single polarizing film, parallel transmittance (Tp) refers to the spectral transmittance when two polarizing films are placed with their absorption axes parallel to each other, and orthogonal transmittance (Tc) refers to the spectral transmittance when two polarizing films are placed with their absorption axes orthogonal to each other. The values ​​were calculated from Ky and Kz at the maximum absorption wavelength obtained by measurement using the following formulas (I) to (III). Ts(%)=(Ky+Kz) / 2 Calculation formula (I) Tp(%)=(Ky2 +Kz 2 ) / 200 Formula (II) Tc(%)=(Ky×Kz) / 100 Calculation formula (III)

[0115] <Single-point transmittance (Ys), parallel-point transmittance (Yp), orthogonal-point transmittance (Yc)> The single-sample transmittance (Ys(%)), parallel-sample transmittance (Yp(%)), and orthogonal-sample transmittance (Yc(%)) after luminous efficiency correction were determined for each measurement sample. Ys, Yp, and Yc are transmittances corrected for luminous efficiency according to JIS Z 8722:2009 for each wavelength Ts, Tp, and Tc obtained in the wavelength range of 380 to 780 with wavelength intervals of 1 to 10 nm. Specifically, the single-sample transmittance Ts, the parallel-sample transmittance Tp, and the orthogonal-sample transmittance Tc for each wavelength obtained from calculation formulas (I) to (III) were substituted into the following formulas (IV to VI) to calculate each value. In the following formulas (IV to VI), Pλ represents the spectral distribution of the standard light (C light source), and yλ represents the 2-degree field-of-view color matching function. TIFF0007876377000023.tif40156

[0116] <Contrast (CR)> The contrast (CR) was determined by calculating the ratio (Yp / Yc) of the parallel-position transmittance Yp and the orthogonal-position transmittance Yc after luminous efficiency correction.

[0117] <Polarization degree ρy after visual sensitivity correction> The degree of polarization ρy of each measurement sample after luminous efficiency correction was determined by substituting the luminous efficiency-corrected parallel transmittance Yp and the luminous efficiency-corrected orthogonal transmittance Yc into the following equation (VII). TIFF0007876377000024.tif11156

[0118] <Dichromatic ratio (Rd) after luminous efficiency correction> The dichromatic ratio Rd of each measured sample after visual sensitivity correction was obtained by substituting the visual sensitivity-corrected Ys and Yc into the following equations (VIII) and (IX) to convert them to Ky and Kz, and then substituting the calculated Ky and Kz values ​​into the following equation (X) to find the dichromatic ratio Rd. TIFF0007876377000025.tif21155

[0119] For each sample, the chromaticity a* and b* values ​​were measured in accordance with JIS Z 8781-4:2013, during the measurement of the single-element transmittance Ts and the parallel-element transmittance Tp. The above spectrophotometer was used for the measurements, and both transmitted and reflected colors were measured with the light incident from the outside. A C light source was used as the light source. 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 ​​during the measurement of the single-element transmittance Ts, the parallel-element transmittance Tp, and the orthogonal-element transmittance Tc, respectively.

[0120] Table 1 shows the Ys, Yp, Yc, CR, ρy, and Rd values ​​for each sample obtained from Examples 1-8 and Comparative Examples 1-6.

[0121] [Table 1]

[0122] As shown in Table 1, the polarizing films produced in Examples 1 to 8 exhibited superior optical properties (ρy, Rd) compared to the polarizing films produced in Comparative Examples 1 to 6. Comparing Example 1 and Comparative Example 1, which have equivalent Ys values, the polarizing film of Example 1 shows an increase of approximately 1 in the dichromatic ratio and an improvement of approximately 800 in contrast compared to the polarizing film of Comparative Example 1. Similarly, comparing Example 5 and Comparative Example 5, both the dichromatic ratio and contrast are increased. Even when comparing polarizing films with similar Ys values ​​in the examples and comparative examples, it is clear that the optical properties of the polarizing films of the present invention (Examples 1 to 8) are superior.

[0123] Table 2 shows the chromaticity a* and b* results for each of the samples obtained in Examples 1-8 and Comparative Examples 1-6.

[0124] [Table 2]

[0125] Table 2 shows the chromaticity of Examples 1-8 and Comparative Examples 1-6, and it can be seen that a*-s and b*-s are 5.0 or less, a*-p and b*-p are 2.0 or less, and a*-c and b*-c are also 2.0 or less. Therefore, it can be said that all the polarizing films produced are achromatic polarizing films with a high-quality paper white and neutral gray hue. Furthermore, as shown in Table 1, the polarizing films of Examples 1-8 also have excellent optical properties, so it can be said that they are achromatic polarizing films with high optical properties.

[0126] Tables 3 and 4 show the average values ​​of Tp and Tc at 420-480 nm, 520-590 nm, and 600-640 nm for each of the samples obtained in Examples 1-8 and Comparative Examples 1-6.

[0127] [Table 3]

[0128] [Table 4]

[0129] Tables 5 and 6 show the average values ​​of Tp and Tc in the 520-590 nm range and the absolute values ​​of the differences between the average values ​​of Tp and Tc in the 420-480 nm and 600-640 nm ranges for the samples of Examples 1-8 and Comparative Examples 1-6. [Table 5]

[0130] [Table 6]

[0131] Table 5 shows that the Tp values ​​of the measured samples in Examples 1-8 and Comparative Examples 1-6 were such that the absolute difference between the average value at 420-480 nm and the average value at 520-590 nm was 1.5 or less, and the absolute difference between the average value at 520-590 nm and the average value at 600-640 nm was 2.0 or less. This indicates that the Tp values ​​have a flat transmittance in the visible region, although there was almost no difference between the examples and comparative examples. On the other hand, as shown in Table 6, the Tc values ​​of the measured samples in Examples 1-8 and Comparative Examples 1-5 were such that the absolute difference between the average value at 420-480 nm and the average value at 520-590 nm was 0.5 or less, and the absolute difference between the average value at 520-590 nm and the average value at 600-640 nm was 0.5 or less, whereas Comparative Example 6 exceeded 0.5. In Example 2, the absolute difference between the average value at 420-480 nm and the average value at 520-590 nm was 0.056, and the absolute difference between the average value at 520-590 nm and the average value at 600-640 nm was 0. In contrast, in Comparative Example 4, the absolute difference between the average value at 420-480 nm and the average value at 520-590 nm was 0.296, and the absolute difference between the average value at 520-590 nm and the average value at 600-640 nm was 0.01, showing a significant difference in Tc transmittance.

[0132] From the above, it was shown that the polarizing films of Examples 1 to 8 maintain high values ​​for both single-piece transmittance and parallel-position transmittance, while also being able to express a high-quality, paper-like white color in the parallel position and possessing a neutral color (neutral gray) in their single-piece state. Furthermore, it was found that the polarizing films of Examples 1 to 8 maintain high transmittance, exhibit achromaticity in the parallel and orthogonal positions, and also possess high optical properties.

[0133] (Fabrication of polarizing plates) The polarizing films of Examples 1-8 and Comparative Examples 1-6 were laminated on both sides with triacetylcellulose film (TAC film: Fujifilm Corporation: product name TD-80U) via an adhesive of an aqueous polyvinyl alcohol solution, and dye-based polarizing plates (neutral gray polarizing plates) were obtained with layers of TAC / polarizing film / TAC. One side of the obtained neutral gray polarizing plate was attached to glass using an adhesive, and polarizing plate measurement samples were prepared with layers of TAC / polarizing film / TAC / glass in this order.

[0134] The obtained polarizing plate samples showed no change in their average transmittance even after 500 hours under ambient temperature conditions of 105°C, and also after 500 hours under ambient temperature conditions of 80°C and relative humidity of 90%, demonstrating long-term durability even under high temperature and high humidity conditions. Furthermore, the samples from Examples 1 to 8 showed no change in their average transmittance even after 200 hours in a xenon lightfastness test (Suga Test Instruments SX-75) at 60W and ambient temperature of 50°C, demonstrating excellent lightfastness against long-term exposure to light. These results demonstrate that the achromatic polarizing plates of Examples 1 to 8, prepared using the compound of the present invention, possess excellent polarization performance and are high-performance dye-based polarizing plates with good durability (moisture resistance, heat resistance, and light resistance). [Industrial applicability]

[0135] The polarizing film and polarizing plate using the dichroic dye of the present invention can be optionally equipped with a protective or functional layer and a transparent support such as glass, quartz, or sapphire, and can be applied to liquid crystal projectors, calculators, watches, laptop computers, word processors, liquid crystal televisions, polarizing lenses, polarizing glasses, car navigation systems, and indoor and outdoor measuring instruments and displays. In particular, the polarizing film or polarizing plate of the present invention can be suitably used in liquid crystal display devices, such as reflective liquid crystal display devices, semi-transparent liquid crystal display devices, and organic electroluminescence devices other than liquid crystal display devices.

Claims

1. A polarizing film containing an azo compound represented by formula (1) or a salt thereof, and an azo compound represented by formula (2) or a salt thereof. 【Chemistry 1】 (In formula (1), R １ ~R ６ Each of these independently represents a hydrogen atom, a C1-C4 alkyl group, a C1-C4 alkoxy group, a halogen atom, a carboxyl group, a sulfo group, a C1-C4 alkoxy group having a sulfo group, a hydroxyl group, an amino group, an acetylamino group, or a benzoylamino group which may have substituents. The ring structure containing the dotted line at the left end of formula (1) represents a phenyl group or a naphthyl group. R1 and R2 indicate that they may be present in either the phenyl group or the naphthyl group. 【Chemistry 2】 (In Formula (2), Ay ２１ and Ay ２２ are each independently a naphthyl group which may have a substituent or a phenyl group which may have a substituent, Ry ２１ , Ry ２２ , Ry ２７ , Ry ２８ are each independently a hydrogen atom, a C1-4 alkyl group, or a C1-4 alkoxy group, Ry ２３ to Ry ２６ are each independently a hydrogen atom, a C1-4 alkyl group, a C1-4 alkoxy group, or a C1-4 alkoxy group having a sulfo group, and s and t each independently represent 0 or 1.)

2. The polarizing film according to claim 1, comprising one or more organic dyes other than azo compounds represented by formulas (1) and (2) or salts thereof.

3. The polarizing film according to claim 1, wherein the polarizing film includes a hydrophilic polymer film as a base material.

4. The polarizing film according to any one of claims 1 to 3, wherein the absolute values ​​of a* and b* obtained when measuring the transmittance of natural light in accordance with JIS Z 8781-4:2013 are both 5.0 or less for the polarizing film alone.

5. The polarizing film according to any one of claims 1 to 3, wherein when two of the polarizing films are stacked and arranged so that their absorption axis directions are parallel to each other, the absolute values ​​of the a* and b* values ​​obtained when measuring the transmittance of natural light in accordance with JIS Z 8781-4:2013 are 2.0 or less.

6. The polarizing film according to any one of claims 1 to 3, wherein when two of the polarizing films are stacked so that their absorption axis directions are perpendicular to each other, the absolute values ​​of the a* and b* values ​​obtained when measuring the transmittance of natural light in accordance with JIS Z 8781-4:2013 are 2.0 or less.

7. The polarizing film according to any one of claims 1 to 3, wherein, with respect to the transmittance obtained when two of the polarizing films are stacked and arranged so that their absorption axis directions are parallel to each other, the absolute value of the difference between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is 2.0 or less, and the absolute value of the difference between the average transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 640 nm is 2.0 or less.

8. The polarizing film according to any one of claims 1 to 3, wherein, with respect to the transmittance obtained when two of the polarizing films are stacked and arranged so that their absorption axis directions are perpendicular to each other, the absolute value of the difference between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is 0.5 or less, and the absolute value of the difference between the average transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 640 nm is 0.5 or less.

9. A polarizing plate comprising a transparent protective layer provided on one or both sides of a polarizing film according to any one of claims 1 to 3.

10. A liquid crystal display device comprising a polarizing film according to any one of claims 1 to 3.

11. A liquid crystal display device comprising the polarizing plate described in Claim 9.

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