JP6662739B2 - Achromatic polarizing element, achromatic polarizing plate and liquid crystal display using the same - Google Patents

Description

  The present invention relates to an achromatic dye-based polarizing element, and an achromatic polarizing plate and a liquid crystal display using the same.

  A polarizing element is generally manufactured by adsorbing and orienting a dichroic dye, iodine or a dichroic dye, on a polyvinyl alcohol-based resin film. A polarizing plate obtained by bonding a protective film made of triacetyl cellulose or the like to this polarizing element via an adhesive layer is used for a liquid crystal display device or 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 as a dichroic dye, for example, an azo compound having dichroism is a dye-based polarizing plate. Called. Among these, dye-based polarizing plates have high heat resistance, high heat and humidity durability, and high stability, and have the same degree of polarization while being characterized by high color selectivity due to blending of dyes. There is a problem that the transmittance and the contrast are low as compared with the iodine-based polarizing plate. For this reason, a polarizing element which maintains high durability, has various color selectivities, and has higher transmittance and higher polarization characteristics is desired.

  Furthermore, even in the case of a dye-based polarizing plate having various color selectivities, a conventional polarizing element has a positional relationship in which the absorption axis directions of two polarizing elements are parallel to each other (hereinafter, also referred to as “parallel position”). )), There is a problem that the white color exhibits a yellowish white color when the color is displayed in a white color (hereinafter, also referred to as “white display”). In order to improve the problem that white takes on a yellow tint, even with a polarizing element manufactured with a suppressed yellow tint, a polarizing plate up to now has two polarizing elements at positions where absorption axis directions are orthogonal to each other. When black is displayed (hereinafter also referred to as “during black display”) by being arranged in a relationship (hereinafter also referred to as “orthogonal position”), there is a problem that the black color is colored blue. . Therefore, there has been a demand for a polarizing plate that exhibits achromatic white when displaying white and achromatic black when displaying black. In particular, it has been difficult to obtain a polarizing plate having a high-quality white at the time of white display, a so-called paper white polarizing plate.

  In order for a polarizing plate to be achromatic, it is necessary that the transmittance in a parallel position or an orthogonal position be a substantially constant value regardless of the wavelength, but it has been possible to obtain such a polarizing plate. Did not. The reason why the hue differs between white display and black display is that the wavelength dependence of the transmittance is not the same between the parallel position and the orthogonal position, and in particular, the transmittance is not constant over the visible light region. Further, the fact that dichroism is not constant over the visible light region is also one of the factors that makes it difficult to realize an achromatic polarizing plate.

To explain using an iodine-based polarizing plate as an example, an iodine-based polarizing plate using polyvinyl alcohol (hereinafter also referred to as “PVA”) as a base material and using iodine as a dichroic dye generally has a wavelength of 480 nm and 600 nm. It has an absorption centered on It is said that the absorption at 480 nm is caused by a complex of polyiodine I ₃ ⁻ and PVA, and the absorption at 600 nm is caused by a complex of polyiodine I ₅ ⁻ and PVA. Regarding the degree of polarization (dichroism) at each wavelength, the degree of polarization (dichroism) based on the complex of polyiodine I ₅ ⁻ and PVA is better than the degree of polarization (dichroism) based on the complex of polyiodine I ₃ ⁻ and PVA ( Dichroism). In other words, when trying to make the transmissivity at the orthogonal position constant at each wavelength, the transmissivity at the parallel position is higher at 600 nm than at 480 nm, and the white color is colored yellow during white display. Conversely, when trying to keep the transmittance at the parallel position constant, the transmittance at the orthogonal position is lower at 600 nm than at 480 nm, so that black is colored blue when displaying black. If the white color is yellow during white display, it generally gives an impression that the deterioration has progressed, which is not preferable. In addition, when a blue color is displayed during black display, an impression is given that there is no sense of quality because it is not clear black. Further, in the case of an iodine-based polarizing plate, it is difficult to control the hue mainly in the vicinity of 550 nm where the visibility is high because there is no complex based on the wavelength. As described above, since the degree of polarization (dichroism) of each wavelength is not constant, the wavelength dependence of the degree of polarization has occurred. Also, since there are only two dichroic dyes of 480 nm and 600 nm, which are absorptions by a complex of iodine and PVA, the hue could not be adjusted with an iodine-based polarizing plate composed of iodine and PVA.

  A method for improving the hue of an iodine-based polarizing plate is described in Patent Document 1 or Patent Document 2. Patent Literature 1 describes a polarizing plate that calculates a neutral coefficient and has an absolute value of 0 to 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 coloring is adjusted by adding a direct dye, a reactive dye, or an acid dye in addition to iodine. Have been.

  Further, an achromatic dyed polarizing plate has also been developed (for example, Patent Document 3).

Japanese Patent No. 4281261 Japanese Patent No. 3357803 WO2014 / 162635

However, in the polarizing plate of Patent Document 1, as can be seen from the examples, even when the neutral coefficient (Np) is low, the hue of the parallel position obtained from JIS Z 8729 has an a * value of -2 to -1 and , B * value is from 2.5 to 4.0, it can be seen that the color is yellow-green during white display. Further, the hue at the orthogonal position has an a * value of 0 to 1 but a b * value of -1.5 to -4.0, so that the black plate becomes a polarizing plate exhibiting blue. ing.
Further, the polarizing film of Patent Document 2 is obtained by setting the a value and the b value in the UCS color space measured using only one polarizing film to an absolute value of 2 or less, and two polarizing films are stacked. In this case, an achromatic color cannot be simultaneously expressed in both the hue of white display and the hue of black display. Further, 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, indicating a low value. As described above, since the polarizing film of Patent Document 2 has a low transmittance, it does not have a sufficient performance in a field where a high transmittance and a high contrast are required, particularly, in a field such as a liquid crystal display device and an organic electroluminescence. . A polarizing plate having a high transmittance, specifically, a single transmittance of 40% or more, has not been obtained so far. In particular, the higher the transmittance, the more difficult it is to obtain an achromatic polarizing plate. Therefore, a polarizing plate that has a high transmittance and is achromatic in both white when displaying white and black when displaying black is required. Further, since the polarizing film of Patent Document 2 uses iodine as a main dichroic dye, it has a color after a durability test, particularly after a wet heat durability test (for example, an environment of 85 ° C. and a relative humidity of 85%). The change was large and the durability was poor.

  On the other hand, the dye-based polarizing plate is excellent in durability, but the wavelength dependency is different between the parallel position and the orthogonal position as in the iodine-based polarizing plate. Almost no azo compounds exhibiting dichroism exhibiting the same hue at the parallel position and the orthogonal position, and even if present, dichroism (polarization characteristics) is low. Depending on the type of azo compound having dichroism, there is also an azo compound whose wavelength dependence is completely different at the orthogonal position and the parallel position, such as white in yellow when displaying white and yellow in black when displaying black. . In addition, since the sensitivity of human colors also differs depending on the light and darkness of the light, even if the color correction of the dye-based polarizing plate is performed, each of the light and darkness of the light generated by controlling the polarization from the orthogonal position to the parallel position is different. Appropriate color correction is needed. The achromatic polarizing plate cannot be achieved unless the transmittance at each of the parallel position and the orthogonal position has a substantially constant value at each wavelength and has no wavelength dependence. Furthermore, in order to obtain a polarizing element having high transmittance and high contrast, a certain transmittance must be simultaneously satisfied in parallel and orthogonal positions, and in addition, the degree of polarization (dichroic ratio) of each wavelength must be satisfied. It needs to be high and constant. Even when one azo compound is applied to a polarizing element, a constant transmittance is achieved by blending two or more azo compounds, even though the wavelength dependence of the transmittance differs between the orthogonal position and the parallel position. For this purpose, the relationship between two or more dichroic ratios must be precisely controlled in consideration of the transmittance of the parallel position and the transmittance of the orthogonal position for each type.

  On the other hand, even if the transmittance of the parallel position and the transmittance of the orthogonal position and the relationship between the dichroic ratios are precisely controlled and the transmittance can be made constant in each case, high transmittance and high contrast can be obtained. It has not been realized yet. That is, an achromatic polarizing plate having a high degree of polarization or an achromatic polarizing plate having a high transmittance has not been achieved. For this reason, it is very difficult to obtain an achromatic polarizing plate having high transmittance and / or high contrast, and this cannot be achieved by simply applying a dichroic dye having three primary colors. In particular, it is extremely difficult to simultaneously achieve a constant transmittance and high dichroism in the parallel position. White cannot express high-quality white even if it is slightly colored. White in the bright state is particularly important because it has high luminance and high sensitivity. Therefore, a polarizing element that exhibits achromatic white such as high-quality paper during white display and achromatic black during black display, and has a single transmittance of 35% or more and a high degree of polarization is required. Have been. Patent Document 3 also describes an achromatic polarizing plate for white display and black display, but further improvement in performance is desired.

  Accordingly, an object of the present invention is to provide a high-performance achromatic polarized light having a high transmittance and a high degree of polarization, an achromatic color in both white display and black display, and particularly exhibiting high-quality white in white display. An object is to provide an element, an achromatic polarizing plate and a liquid crystal display device using the same.

（式中、Ａｒ_１は置換基を有するフェニル基またはナフチル基を示し、Ｒｒ_１およびＲｒ_２は各々独立に、水素原子、低級アルキル基、低級アルコキシ基、またはスルホ基を有する低級アルコキシ基を示し、Ｘｒ_１は置換基を有してもよいアミノ基、置換基を有してもよいフェニルアミノ基、置換基を有してもよいフェニルアゾ基、置換基を有してもよいベンゾイル基、または置換基を有してもよいベンゾイルアミノ基を示す。）

（式中、Ａｂ_１は置換基を有するフェニル基またはナフチル基を示し、Ｒｂ_１からＲｂ_６は各々独立に、水素原子、低級アルキル基、低級アルコキシ基、またはスルホ基を有する低級アルコキシ基を示し、Ｘｂ_１は置換基を有してもよいアミノ基、置換基を有してもよいフェニルアミノ基、置換基を有してもよいフェニルアゾ基、置換基を有してもよいナフトトリアゾール基、置換基を有してもよいベンゾイル基、または置換基を有してもよいベンゾイルアミノ基を示す。）

（式中、Ａｇ_１およびＡｇ_２は各々独立に、スルホ基、低級アルキル基、低級アルコキシ基、スルホ基を有する低級アルコキシ基、カルボキシ基、ニトロ基、アミノ基、および置換アミノ基からなる群から選択される置換基を少なくとも１つ有するナフチル基またはフェニル基を示し、Ｒｇ_１およびＲｇ_２は各々独立に、水素原子、低級アルキル基、低級アルコキシ基、またはスルホ基を有する低級アルコキシ基を示す。）
［２］ 前記偏光素子２枚を吸収軸方向が互いに平行になるように重ねて配置した状態で求められる透過率について、４２０ｎｍから４８０ｎｍの平均透過率と５２０ｎｍから５９０ｎｍの平均透過率との差の絶対値が２．５％以下であり、かつ、５２０ｎｍから５９０ｎｍの平均透過率と６００ｎｍから６４０ｎｍの平均透過率との差の絶対値が２．０％以下である［１］に記載の偏光素子。
［３］ ＪＩＳ Ｚ ８７８１−４：２０１３に従って自然光の透過率測定時に求められるａ＊値およびｂ＊値の絶対値が、
前記偏光素子単体で、ともに１以下であり、
前記偏光素子２枚をその吸収軸方向が互いに平行になるように重ねて配置した状態で、ともに２以下である［１］または［２］に記載の偏光素子。
［４］ 前記偏光素子の単体透過率が３５％から６０％であり、
前記偏光素子２枚をその吸収軸方向が互いに平行になるように重ねて配置した状態で求められる５２０ｎｍから５９０ｎｍの平均透過率が２５％から５５％である［１］〜［３］のいずれかに記載の偏光素子。
［５］ 前記式（２）で表されるアゾ化合物が、式（４）で表されるアゾ化合物である［１］〜［４］のいずれかに記載の偏光素子。

（式中、Ａｂ_１、Ｒｂ_１からＲｂ_４、およびＸｂ_１は、式（２）におけるものと同じものを示す。）
［６］ 前記式（２）で表されるアゾ化合物が、式（５）で表されるアゾ化合物である［１］〜［５］のいずれか偏光素子。

（式中、Ａｂ_１、Ｒｂ_２、Ｒｂ_４、およびＸｂ_１は、式（２）におけるものと同じものを示す。）
［７］ 式（６）で表されるアゾ化合物またはその塩をさらに含有する［１］〜［６］のいずれかに記載の偏光素子。

（式中、Ｒｙ_１およびＲｙ_２は各々独立に、スルホ基、カルボキシ基、ヒドロキシ基、低級アルキル基、または低級アルコキシル基を示し、ｎは１〜３の整数を示す。）
［８］ 前記偏光素子２枚をその吸収軸方向が互いに直交するように重ねて配置した状態で求められる透過率について、４２０ｎｍから４８０ｎｍの平均透過率と５２０ｎｍから５９０ｎｍの平均透過率との差の絶対値が０．６以下であり、かつ、５２０ｎｍから５９０ｎｍの平均透過率と６００ｎｍから６４０ｎｍの平均透過率との差の絶対値が０．６以下である［１］〜［７］のいずれかに記載の偏光素子。
［９］ 前記偏光素子２枚をその吸収軸方向が互いに直交するように重ねて配置した状態で、ＪＩＳ Ｚ ８７８１−４：２０１３に従って自然光の透過率測定時に求められるａ＊値およびｂ＊値の絶対値が２以下である［１］〜［８］のいずれかに記載の偏光素子。
［１０］ 前記偏光素子が、ポリビニルアルコール系樹脂フィルムを基材として含む［１］〜［９］のいずれかに記載の偏光素子。
［１１］ ［１］〜［１０］のいずれかに記載の偏光素子と、前記偏光素子の片面または両面に設けられた透明保護層とを備える偏光板。
［１２］ ［１］〜［１０］のいずれかに記載の偏光素子または［１１］に記載の偏光板を備える液晶表示装置。 The present inventor has conducted intensive studies to solve the above problems, and as a result, by mixing a specific azo compound, dichroism has no wavelength dependence, and is achromatic at each of the parallel position and the orthogonal position, and It has been found that a polarizing element having a higher degree of polarization can be manufactured. The present inventor has found for the first time that it is possible to achieve wavelength independence in the visible light region even with a high transmittance, and is higher than that capable of realizing high-quality paper-like white, commonly known as paper white. A polarizing element with a degree of polarization has been developed. That is, the present invention relates to the following [1] to [12].
[1] An azo compound represented by the formula (1) or a salt thereof, an azo compound represented by the formula (2) or a salt thereof, and an azo compound represented by the formula (3) or a salt thereof are contained. Polarizing element.

(Wherein, Ar ₁ represents a phenyl group or a naphthyl group having a substituent, and Rr ₁ and Rr ₂ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group. , Xr ₁ is an amino group optionally having a substituent, a phenylamino group optionally having a substituent, a phenylazo group optionally having a substituent, a benzoyl group optionally having a substituent, or A benzoylamino group which may have a substituent is shown.)

(In the formula, Ab ₁ represents a phenyl group or a naphthyl group having a substituent, and Rb ₁ to Rb ₆ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group. , Xb ₁ represents an amino group optionally having a substituent, a phenylamino group optionally having a substituent, a phenylazo group optionally having a substituent, a naphthotriazole group optionally having a substituent, A benzoyl group which may have a substituent or a benzoylamino group which may have a substituent.)

(Wherein, Ag ₁ and Ag ₂ are each independently a group consisting of a sulfo group, a lower alkyl group, a lower alkoxy group, a lower alkoxy group having a sulfo group, a carboxy group, a nitro group, an amino group, and a substituted amino group. It represents a naphthyl group or a phenyl group having at least one selected substituent, and Rg ₁ and Rg ₂ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group. )
[2] Regarding the transmittance determined in a state where the two polarizing elements are stacked so that the absorption axis directions are parallel to each other, the difference between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is obtained. The polarizing element according to [1], wherein the absolute value is 2.5% 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 2.0% or less. .
[3] The absolute values of the a * value and b * value obtained at the time of measuring the transmittance of natural light in accordance with JIS Z 8781-4: 2013 are as follows:
The polarizing element alone, both 1 or less,
The polarizing element according to [1] or [2], wherein the two polarizing elements are two or less in a state where the two polarizing elements are arranged so as to be parallel to each other in an absorption axis direction.
[4] The single transmittance of the polarizing element is from 35% to 60%,
Any one of [1] to [3], wherein the average transmittance from 520 nm to 590 nm obtained in a state where the two polarizing elements are stacked so that their absorption axis directions are parallel to each other is 25% to 55%. 4. The polarizing element according to item 1.
[5] The polarizing element according to any one of [1] to [4], wherein the azo compound represented by the formula (2) is an azo compound represented by the formula (4).

(In the formula, Ab ₁ , Rb ₁ to Rb ₄ , and Xb ₁ are the same as those in Formula (2).)
[6] The polarizing element according to any one of [1] to [5], wherein the azo compound represented by the formula (2) is an azo compound represented by the formula (5).

(In the formula, Ab ₁ , Rb ₂ , Rb ₄ , and Xb ₁ are the same as those in Formula (2).)
[7] The polarizing element according to any one of [1] to [6], further comprising an azo compound represented by the formula (6) or a salt thereof.

(In the formula, Ry ₁ and Ry ₂ each independently represent a sulfo group, a carboxy group, a hydroxy group, a lower alkyl group, or a lower alkoxyl group, and n represents an integer of 1 to _3. )
[8] Regarding the transmittance determined in a state where the two polarizing elements are stacked so that their absorption axis directions are orthogonal to each other, the difference between the average transmittance from 420 nm to 480 nm and the average transmittance from 520 nm to 590 nm is obtained. Any of [1] to [7], wherein the absolute value is 0.6 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 0.6 or less. 4. The polarizing element according to item 1.
[9] In the state where the two polarizing elements are arranged so that the absorption axis directions thereof are orthogonal to each other, the a * value and the b * value obtained at the time of measuring the transmittance of natural light in accordance with JIS Z 8781-4: 2013. The polarizing element according to any one of [1] to [8], whose absolute value is 2 or less.
[10] The polarizing element according to any one of [1] to [9], wherein the polarizing element includes a polyvinyl alcohol-based resin film as a base material.
[11] A polarizing plate comprising: the polarizing element according to any one of [1] to [10]; and a transparent protective layer provided on one or both surfaces of the polarizing element.
[12] A liquid crystal display device comprising the polarizing element according to any one of [1] to [10] or the polarizing plate according to [11].

  The present invention has a high transmittance and a high degree of polarization, and is an achromatic color in both white display and black display, and especially a high-performance achromatic polarizing element that exhibits high-quality white in white display, and And a liquid crystal display device using the same.

<Polarizing element>
The polarizing element according to the present invention includes an azo compound or a salt thereof represented by the formula (1), an azo compound or a salt thereof represented by the formula (2), and an azo compound or a salt thereof represented by the formula (3). And salt. The polarizing element according to the present invention may optionally further contain an azo compound represented by the formula (6). Preferably, the polarizing element includes these azo compounds or salts thereof, and a substrate on which the azo compounds or salts thereof are adsorbed.

  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, and examples thereof include a polyvinyl alcohol-based resin, an amylose-based resin, a starch-based resin, a cellulose-based resin, and a polyacrylate-based resin. The hydrophilic polymer is most preferably a polyvinyl alcohol-based resin or a derivative thereof from the viewpoints of dyeability, processability, crosslinkability, and the like of the dichroic dye. A polarizing element can be manufactured by adding an azo compound or a salt thereof to a film formed from a hydrophilic polymer and subjecting the film to an orientation treatment such as stretching.

The azo compound represented by the formula (1) will be described.

In the formula (1), Ar ₁ represents a phenyl group having a substituent or a naphthyl group having a substituent.
When Ar ₁ is a phenyl group, it preferably has at least one sulfo group or carboxy group as a substituent. 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 substituents are a sulfo group, a carboxy group, a lower alkyl group, a lower alkoxy group, a sulfo group, A lower alkoxy group having a group, a nitro group, a benzoyl group, an amino group, an acetylamino group and a lower alkylamino group-substituted amino group are preferable, and a sulfo group, a methyl group, an ethyl group, a methoxy group, an ethoxy group, and a carboxy group are more preferable. Group, nitro group, benzoyl group and amino group, particularly preferably sulfo group, methyl group, methoxy group, ethoxy group, benzoyl group and carboxy group. As the lower alkoxy group having a sulfo group, a straight-chain alkoxy group is preferable, the substitution position of the sulfo group is preferably at the terminal of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably. 3-sulfopropoxy group. The number of sulfo groups in the phenyl group is preferably 1 or 2, and the substitution position is not particularly limited, but only the 4-position is preferably a combination of the 2-, 4-, and 3-positions.
When Ar ₁ is a naphthyl group having a substituent, the substituent preferably has at least one sulfo group, and when it has two or more substituents, at least one of the substituents is a sulfo group; As the other substituent, a sulfo group, a hydroxy group, a carboxy group, and a lower alkoxy group having a sulfo group are preferable. As the lower alkoxy group having a sulfo group, a straight-chain alkoxy group is preferable, the substitution position of the sulfo group is preferably at the terminal of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably. 3-sulfopropoxy group. When the number of substituents of the sulfo group is 2, the position of the sulfo group of the naphthyl group is preferably a combination of 4,8 and 6,8 positions, and more preferably a combination of 6,8 positions. When the number of sulfo groups contained in the naphthyl group is 3, the combination of the 1,3,6-position is particularly preferable as the substitution position of the sulfo group.

  In the present specification, “lower” of a lower alkyl group, a lower alkoxy group, and a lower alkylamino group indicates that the number of carbon atoms is 1 to 4, preferably 1 to 3. In the specification of the present application, a “substituent” includes a hydrogen atom for convenience.

Rr ₁ and Rr ₂ 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 and Rr ₂ are each independently preferably a hydrogen atom, a lower alkyl group, or a lower alkoxy group, and 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 preferable, the substitution position of the sulfo group is preferably at the terminal of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably. 3-sulfopropoxy group.

Xr ₁ is an amino group optionally having a substituent, a phenylamino group optionally having a substituent, a phenylazo group optionally having a substituent, a benzoyl group optionally having a substituent, or A benzoylamino group which may have a substituent is shown. The amino group which may have a substituent is preferably 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 has 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. It is an amino group. The phenylamino group which may have a substituent is preferably one or two substituents 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 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 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 carboxyethyl amino group. It is a phenylazo group having 1 to 3 selected. Xr ₁ is preferably a benzoylamino group which may have a substituent and a phenylamino group which may have a substituent, and more preferably a phenylamino group. The position of the substituent is not particularly limited, but is preferably p-position when there is one substituent.

  Examples of the method for obtaining the azo compound represented by the formula (1) include the methods described in JP-A-2003-215338, JP-A-9-302250, and Patent No. 3881175. However, the present invention is not limited to this.

  Specific examples of the azo compound represented by the formula (1) include, for example, C.I. I. Direct Red 81, C.I. I. Direct Red 117, C.I. I. Direct Violet 9 and C.I. I. Direct Red 127, and azo compounds described in JP-A-2003-215338, JP-A-9-302250, and Japanese Patent No. 3881175. Further specific examples of the azo compound represented by the formula (1) are shown below in the form of a free acid.

［化合物例２］

［化合物例３］

［化合物例４］

［化合物例５］

［化合物例６］

［化合物例７］

［化合物例８］

［化合物例９］

［化合物例１０］

［化合物例１１］

［化合物例１２］

［化合物例１３］

［化合物例１４］

[Compound Example 1]

[Compound Example 2]

[Compound Example 3]

[Compound Example 4]

[Compound Example 5]

[Compound Example 6]

[Compound Example 7]

[Compound Example 8]

[Compound Example 9]

[Compound Example 10]

[Compound Example 11]

[Compound Example 12]

[Compound Example 13]

[Compound Example 14]

Next, the azo compound represented by the formula (2) will be described.

In the formula (2), Ab ₁ represents a phenyl group or a naphthyl group having a substituent. When Ab ₁ is a phenyl group, it preferably has at least one sulfo group or carboxy group as a substituent. When the phenyl group has two or more substituents, at least one of the substituents is preferably a sulfo group or a carboxy group, and the other substituent is preferably a sulfo group, a carboxy group, or 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, more preferably a sulfo group, a methyl group, an ethyl group, or a methoxy group. Group, ethoxy group, carboxyl group, nitro group and amino group, particularly preferably sulfo group, methyl group, methoxy group, benzoyl group and carboxy group. The lower alkoxy group having a sulfo group is preferably a straight-chain alkoxy group, the substitution position of the sulfo group is preferably at the end of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably 3 -A sulfopropoxy group. The number of substituents of the phenyl group is preferably 1 or 2, and the substitution position is not particularly limited. However, only the 4-position is preferably a combination of the 2- and 4-positions, and a combination of the 3- and 5-positions is preferred.
When Ab ₁ is a naphthyl group having a substituent, the substituent preferably has at least one sulfo group. When the naphthyl group has two or more substituents, at least one of the substituents is a sulfo group, and the other substituents include a sulfo group, a hydroxy group, a carboxy group, and a lower alkoxy group having a sulfo group. preferable. The lower alkoxy group having a sulfo group is preferably a straight-chain alkoxy group, the substitution position of the sulfo group is preferably at the end of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably 3 -A sulfopropoxy group. When the number of substituents of the sulfo group is 2, the substitution position of the sulfo group in the naphthyl group is preferably a combination of 4,8 or 6,8, and more preferably a combination of 6,8. When the number of substituents of the sulfo group is 3, the substitution position of the sulfo group in the naphthyl group is preferably a combination of 1, 3, and 6 positions.

Rb ₁ to Rb ₆ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group. Rb ₁ to Rb ₆ are each independently preferably a hydrogen atom, a methyl group, or a methoxy group. The lower alkoxy group having a sulfo group is preferably a straight-chain alkoxy group, the substitution position of the sulfo group is preferably at the end of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably 3 -A sulfopropoxy group.

Xb ₁ is 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 naphthotriazole group which may have a substituent, It represents a benzoyl group which may have a substituent or a benzoylamino group which may have a substituent. Xb ₁ is preferably a benzoylamino group optionally having a substituent or a phenylamino group optionally having a substituent, and more preferably a phenylamino group. The amino group which may have a substituent is preferably any one or two selected from the group consisting of a hydrogen atom, a lower alkyl group, a lower alkoxyl group, a sulfo group, an amino group, and a lower alkylamino group. An amino group having two substituents, preferably one or two substituents 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. Amino group. The phenylamino group which may have a substituent is preferably one or two selected from the group consisting of a hydrogen atom, a lower alkyl group, a lower alkoxyl group, a sulfo group, an amino group, and a lower alkylamino group. A phenylamino group having a substituent, 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 which may have a substituent is preferably a 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. And a phenylazo group having 1 to 3 substituents selected from The naphthotriazole group which may have a substituent is preferably a naphthotriazole group having one or two substituents selected from the group consisting of a hydrogen atom, a sulfo group, an amino group, and a carboxyl 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, a sulfo group and an amino 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 substitution position is not particularly limited, but is preferably p-position when there is one substituent.

  The azo compound represented by the formula (2) is preferably an azo compound represented by the formula (4) because the polarization performance of the polarizing element can be improved.

式（４）中、Ａｂ_１、Ｒｂ_１からＲｂ_４、およびＸｂ_１は、式（２）について上述されたものと同じものを示す。

In Formula (4), Ab ₁ , Rb ₁ to Rb ₄ , and Xb ₁ represent the same as described above for Formula (2).

  The azo compound represented by the formula (2) is more preferably an azo compound represented by the formula (5), since the polarization performance of the polarizing element can be further improved.

式（５）中、Ａｂ_１、Ｒｂ_２、Ｒｂ_４、およびＸｂ_１は、式（２）について上述されたものと同じものを示す。

In formula (5), Ab ₁ , Rb ₂ , Rb ₄ , and Xb ₁ represent the same as described above for formula (2).

  Examples of the method for obtaining the azo compound represented by the formula (2) include the methods described in WO2012 / 108169 and WO2012 / 108173, but are not limited thereto.

  Specific examples of the azo compound represented by the formula (2) include the azo compounds described in WO2012 / 108169, WO2012 / 108173, and the like. Further specific examples of the azo compound represented by the formula (2) are shown below in the form of a free acid.

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［化合物例３１］

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［化合物例３３］

［化合物例３４］

［化合物例３５］

［化合物例３６］

［化合物例３７］

［化合物例３８］

［化合物例３９］

［化合物例４０］

［化合物例４１］

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［化合物例４３］

［化合物例４４］

[Compound Example 15]

[Compound Example 16]

[Compound Example 17]

[Compound Example 18]

[Compound Example 19]

[Compound Example 20]

[Compound Example 21]

[Compound Example 22]

[Compound Example 23]

[Compound Example 24]

[Compound Example 25]

[Compound Example 26]

[Compound Example 27]

[Compound Example 28]

[Compound Example 29]

[Compound Example 30]

[Compound Example 31]

[Compound Example 32]

[Compound Example 33]

[Compound Example 34]

[Compound Example 35]

[Compound Example 36]

[Compound Example 37]

[Compound Example 38]

[Compound Example 39]

[Compound Example 40]

[Compound Example 41]

[Compound Example 42]

[Compound Example 43]

[Compound Example 44]

  Next, the azo compound represented by the formula (3) will be described.

In the formula (3), Ag ₁ and Ag ₂ each independently comprise a sulfo group, a lower alkyl group, a lower alkoxy group, a lower alkoxy group having a sulfo group, a carboxy group, a nitro group, an amino group, and a substituted amino group. A naphthyl group or a phenyl group having at least one substituent selected from the group;

When Ag ₁ and / or Ag ₂ is a phenyl group, it preferably has at least one sulfo group or carboxy group as a substituent thereof. 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 a sulfo group, a carboxy group, a lower alkyl group, a lower alkoxy group, a sulfo group. A lower alkoxy group having a group, a nitro group, an amino group, an acetylamino group, or a lower alkylamino group is preferably a substituted amino group, and the other substituents are more preferably a sulfo group, a methyl group, an ethyl group, A methoxy group, an ethoxy group, a carboxyl 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. The lower alkoxy group having a sulfo group is preferably a straight-chain alkoxy group, the substitution position of the sulfo group is preferably at the end of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably 3 -A sulfopropoxy group. The number of substituents of the phenyl group is preferably 1 or 2, and the substitution position is not particularly limited. However, only the 4-position is preferably a combination of 2-position and 4-position, and a combination of 3-position and 5-position.
When Ag ₁ and / or Ag ₂ is a naphthyl group having a substituent, the substituent preferably has at least one sulfo group. When the naphthyl group has two or more substituents, at least one of the substituents is a sulfo group, and the other substituent is a sulfo group, a hydroxy group, a carboxy group, or a lower alkoxy group having a sulfo group. preferable. The naphthyl group particularly preferably has two or more sulfo groups as substituents. As the lower alkoxy group having a sulfo group, a straight-chain alkoxy group is preferable, the substitution position of the sulfo group is preferably at the terminal of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably. 3-sulfopropoxy group. When the number of sulfo groups in the naphthyl group is 2, the sulfo group substitution position is preferably a combination of the 4,8 position and a combination of the 6,8 position, and more preferably a combination of the 6,8 position. When the number of the sulfo groups contained in the naphthyl group is 3, the substitution position of the sulfo group is preferably a combination of 1, 3, and 6 positions.

Rg ₁ and Rg ₂ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group. Preferably, Rg ₁ and Rg ₂ are each independently a hydrogen atom, a lower alkyl group, or a lower alkoxy group, and more preferably a hydrogen atom, a methyl group, or a methoxy group. Particularly preferably, at least one of Rg ₁ and Rg ₂ is a methoxy group. The lower alkoxy group having a sulfo group is preferably a straight-chain alkoxy group, the substitution position of the sulfo group is preferably at the end of the alkoxy group, more preferably a 3-sulfopropoxy group and a 4-sulfobutoxy group, and particularly preferably 3 -A sulfopropoxy group.

  The azo compound represented by the formula (3) or a salt thereof can be synthesized by a method described in, for example, WO2012 / 165223.

  Specific examples of the azo compound represented by the formula (3) are shown below in the form of a free acid.

［化合物例４６］

［化合物例４７］

［化合物例４８］

［化合物例４６］

[Compound Example 45]

[Compound Example 46]

[Compound Example 47]

[Compound Example 48]

[Compound Example 46]

  Since the polarizing element contains a combination of the azo compounds represented by the formulas (1) to (3), it has a higher transmittance and a higher degree of polarization than a conventional achromatic polarizing plate, but has a white display. Sometimes, high-quality paper-like white, commonly known as paper white, can be realized, and when displaying black, achromatic black, particularly high-quality clear black can be realized.

In order to further improve the performance, the polarizing element may further contain an azo compound represented by the formula (6) in addition to the azo compound represented by the formulas (1) to (3). preferable.

In the formula, Ry ₁ and Ry ₂ are each independently a sulfo group, a carboxy group, a hydroxy group, a lower alkyl group, or a lower alkoxyl group, preferably a sulfo group or a carboxy group. n shows the integer of 1-3. At least one of Ry ₁ and Ry ₂ is preferably a sulfo group or a carboxy group.

  The azo compound represented by the formula (6) affects the transmittance at 400 to 500 nm. In the polarizing element, in particular, the transmittance and the degree of polarization (dichroism) on the short wavelength side of 400 to 500 nm affect blue coloring during black display and yellowing of white during white display. The azo compound represented by the formula (6) does not decrease the transmittance on the short wavelength side of the parallel position of the polarizing element, improves the polarization characteristics (dichroism) of 400 to 500 nm, and improves the white display. It is possible to further reduce blue coloration during yellowing and black display. By further containing the azo compound represented by the formula (6), the polarizing element exhibits a more neutral hue when the single transmittance is in the range of 35% to 60%, and provides higher quality paper when displaying white. And the degree of polarization can be further improved.

  The azo compound represented by the formula (6) or a salt thereof can be synthesized by a method described in, for example, WO2007 / 138980, or a commercially available product can be obtained.

  Specific examples of the azo compound represented by the formula (6) include, for example, C.I. I. Direct Yellow 4, C.I. I. Direct Yellow 12, C.I. I. Direct Yellow 72, and C.I. I. Direct Orange 39, azo compounds having a stilbene structure described in WO2007 / 138980, and the like, but are not limited thereto.

［化合物例５１］

（ｎは１または２の整数を示す。）
［化合物例５２］

［化合物例５３］

Further specific examples of the azo compound represented by the formula (6) are shown below. In addition, the compound example is represented in the form of a free acid.
[Compound Example 50]

[Compound Example 51]

(N represents an integer of 1 or 2.)
[Compound Example 52]

[Compound Example 53]

  The azo compounds represented by the formulas (1) to (6) may be in a free form or a salt form. The salt can be, for example, an alkali metal salt such as a lithium salt, a sodium salt, and 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 according to the present invention contains an azo compound represented by the formulas (1) to (3), and optionally further contains an azo compound represented by the formula (6). According to the polarizing element of the present invention, performances such as chromaticity a * value and b * value, single transmittance, and average transmittance in a specific wavelength band can be set in preferable ranges described later.

  It is preferable that the compounding ratio of the azo compound in the polarizing element is adjusted so that the transmittance and the chromaticity fall in the preferable ranges described later. The performance of the polarizing element is not limited to the compounding ratio of each azo compound in the polarizing element, but also the swelling degree and stretching ratio of the substrate on which the azo compound is adsorbed, the dyeing time, the dyeing temperature, the pH at the time of dyeing, the influence of salt, etc. It depends on various factors. For this reason, the compounding ratio of each azo compound can be determined according to the degree of swelling of the substrate, the temperature and time during dyeing, the pH, the type of salt, the concentration of salt, and the stretching ratio. Such adjustment of the compounding ratio can be performed by a person skilled in the art without trial and error based on the description below.

(Transmissivity)
(I) Difference in average transmittance between two wavelength bands In the polarizing element of the present invention, the difference in average transmittance between specific wavelength bands is preferably equal to or less than a predetermined value. The average transmittance is an average value of the transmittance in a specific wavelength band. The transmittance is the transmittance after visibility correction, which is obtained according to JIS Z 8722: 2009. The transmittance is measured by measuring the spectral transmittance of a measurement sample (for example, a polarizing element or a polarizing plate) every 5 nm or 10 nm for each wavelength of 400 to 700 nm, and measuring the spectral transmittance twice using a visual field (C light source). It can be obtained by correcting the visibility.

  Wavelength bands of 420 nm to 480 nm, 520 nm to 590 nm, and 600 nm to 640 nm are main wavelength bands based on a color matching function used in calculation when indicating a color in JIS Z 8781-4: 2013. Specifically, in the XYZ color matching function of JIS Z 8701 based on JIS Z 8781-4: 2013, x (λ) having a maximum value of 600 nm, y (λ) having a maximum value of 550 nm, and 455 nm Assuming that the maximum value of z (λ) as the maximum value is 100, the wavelengths indicating values of 20 or more are the wavelength bands of 420 nm to 480 nm, 520 nm to 590 nm, and 600 nm to 640 nm. In the polarizing element of the present invention, it is preferable that the transmittance in each of these wavelength bands is adjusted to a value within a predetermined range.

  The polarizing element of the present invention has a transmittance (hereinafter, also referred to as a “parallel transmittance”) obtained by measuring two polarizing elements in a state of being superposed and arranged so that the absorption axis directions are parallel to each other (during white display). ), 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 2.5% or less, more preferably 1.8% or less. Is 1.5% or less, particularly preferably 1.0% or less. Further, regarding the parallel position 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 2.0% or less, more preferably 1.5% or less. , More preferably 1.0% or less. Such a polarizing element can display white like a parallel high-quality paper.

  Furthermore, the transmittance (hereinafter, also referred to as “orthogonal position transmittance”) obtained by measuring two polarizing elements in a state where they are arranged so that the absorption axis directions are orthogonal to each other (during black display) is obtained. 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 0.6% or less, and the average transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 640 nm. Is preferably 0.6% or less. Such a polarizing element can display achromatic black at an orthogonal position. Further, regarding the orthogonal position transmittance, 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 more preferably 0.3% or less, further preferably 0.2% or less. Especially preferably, it is 0.1% or less. Regarding the 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 more preferably 0.3% or less, further preferably 0.2% or less, and particularly preferably. Is 0.1% or less.

  Further, the average transmittance of each of the single transmittance, the parallel transmittance, and the orthogonal transmittance in each of the wavelength bands of 380 nm to 420 nm, 480 nm to 520 nm, and 640 nm to 780 nm is, respectively, the above-described wavelength band of 420 nm to 480 nm, 520 nm to 590 nm, When the average transmittance from 600 nm to 640 nm is adjusted as described above, the average transmittance is hardly affected by the dye, but is preferably adjusted to some extent. The difference between the average transmittance from 380 nm to 420 nm and the average transmittance from 420 nm to 480 nm is preferably 15% or less, and the difference between the average transmittance from 480 nm to 520 nm and the average transmittance from 420 nm to 480 nm. Is 15% or less, the difference between the average transmittance from 480 nm to 520 nm, the average transmittance from 520 nm to 590 nm is 15% or less, and the difference between the average transmittance from 640 nm to 780 nm and the average transmittance from 600 nm to 640 nm is 20%. The following is preferred.

(II) Single Transmittance The polarizing element according to the present invention preferably has a single transmittance of 35% to 60%. The single transmittance is the transmittance of one measurement sample (for example, a polarizing element or a polarizing plate) corrected to luminosity according to JIS Z 8722: 2009. As the performance of the polarizing plate, a higher transmittance is required, but if the single transmittance is 35% to 60%, the brightness can be expressed without discomfort even when used for a display device. If the single transmittance exceeds 60%, the degree of polarization may be significantly reduced, which is not preferable. Since the degree of polarization tends to decrease as the transmittance increases, the single transmittance is more preferably from 36% to 55%, and still more preferably from 37% to 55%, from the viewpoint of the balance with the degree of polarization. is there.

(III) Average Transmittance in Specific Wavelength Band The polarizing element preferably has an average transmittance in the wavelength band of 520 nm to 590 nm measured in parallel at 25% to 55%. When such a polarizing element is provided in a display device, it can be a bright and clear display device with high luminance. The transmittance 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 the calculation when indicating a color in JIS Z 8781-4: 2013. In particular, each wavelength band from 520 nm to 590 nm is a wavelength band having the highest visibility based on the color matching function, and the transmittance in this range is close to the transmittance that can be visually confirmed. Therefore, it is very important to adjust the transmittance in the wavelength range of 520 nm to 590 nm. The average transmittance in the wavelength band of 520 nm to 590 nm measured in parallel is more preferably 27% to 45%, and even more preferably 28% to 40%. Further, the degree of polarization of the polarizing element at this time is preferably 50% to 100%, more preferably 60% to 100%, and further preferably 70% to 100%. The higher the degree of polarization, the better. However, in the relationship between the degree of polarization and the transmittance, the transmittance and the degree of polarization are adjusted to an appropriate value depending on whether importance is placed on brightness or degree of polarization (or contrast). can do.

(Chromaticity a * value and b * value)
The chromaticity a * value and b * value are values determined at the time of measuring the transmittance of natural light in accordance with JIS Z 8781-4: 2013. The object color display method defined in JIS Z 8781-4: 2013 corresponds to the object color display method defined by the International Commission on Illumination (abbreviation: CIE). The measurement of the chromaticity a * value and b * value is performed by irradiating a measurement sample (for example, a polarizing element or a polarizing plate) with natural light. In the following, the chromaticity a * value and b * value required for one measurement sample are set to a * -s and b * -s, and the two measurement samples are arranged so that their absorption axis directions are parallel to each other. The chromaticity a * value and b * value obtained in the state (during white display) are a * -p and b * -p, and two measurement samples are arranged such that their absorption axis directions are orthogonal to each other ( The chromaticity a * value and b * value obtained in black display) are denoted by a * -c and b * -c.

In the polarizing element according to the present invention, each of the absolute values of a * -s and b * -s is preferably 1.0 or less, and each of the absolute values of a * -p and b * -p is 2. It is preferably 0 or less. Such a polarizing element has 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 still more preferably 1.0 or less. Furthermore, in the polarizing element, each of the absolute values of a * -c and b * -c is preferably 2.0 or less, and more preferably 1.0 or less. Such a polarizing element can display achromatic black when displaying black.
Even if there is a difference of 0.5 between the absolute values of the chromaticity a * value and the b * value, a human can perceive a color difference, and a person may feel a large color difference. For this reason, it is very important to control these values in the polarizing element. In particular, when the values of the absolute values of a * -p, b * -p, a * -c, and b * -c are 1.0 or less, respectively, the white display during white display and the black display during A good polarizing plate is obtained in which no other color can be confirmed in black. More specifically, it is possible to realize achromatic color, that is, high-quality paper-like white in the parallel position, and to realize achromatic, high-quality, clear black in the orthogonal position.

  The polarizing element according to the present invention has achromaticity and a high degree of polarization by itself while having high contrast and high transmittance. Further, the polarizing element of the present invention can express high-quality paper-like white (paper white) in white display, and expresses achromatic black, particularly high-grade clear black in black display. be able to. Until now, there has been no polarizing element having such high transmittance and achromaticity. The polarizing element of the present invention is also highly durable, and in particular has durability against high temperature and high humidity.

  In addition, the polarizing element according to the present invention has an advantage in that since it absorbs light having a wavelength of 700 nm or more extremely little, it generates less heat even when irradiated with light such as sunlight. For example, when a liquid crystal display is used outdoors or the like, the liquid crystal display is irradiated with sunlight, and as a result, the polarizing element is also irradiated. Sunlight also has light having a wavelength of 700 nm or more, and includes near-infrared rays that have a heating effect. For example, a polarizing element using an azo compound as described in Example 3 of Japanese Patent Publication No. 02-061988 absorbs near-infrared light having a wavelength of around 700 nm, and thus slightly generates heat. Since the polarizing element absorbs very little near-infrared light, it generates little heat even when exposed to sunlight outdoors. The polarizing element of the present invention is excellent in that heat generation is small and deterioration is small.

  Hereinafter, a specific method for manufacturing a polarizing element will be described, taking as an example a case where an azo compound is adsorbed on a substrate made of a polyvinyl alcohol-based resin. In addition, the manufacturing method of the polarizing element according to the present invention is not limited to the following manufacturing method.

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

  The method for forming the polyvinyl alcohol-based resin is not particularly limited, and the film can be formed by a known method. In this case, the polyvinyl alcohol-based resin film may contain glycerin, ethylene glycol, propylene glycol, low molecular weight polyethylene glycol, or the like as a plasticizer. The amount of the plasticizer is preferably 5 to 20% by mass, more preferably 8 to 15% by mass in the total amount of the film. 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 thus obtained 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 stretch ratio is preferably adjusted to 1.00 to 1.50, and more preferably adjusted to 1.10 to 1.35. When shortening the time for manufacturing the polarizing element, the swelling treatment can be omitted because the raw film swells also during the dyeing treatment described below.

(Dyeing process)
In the dyeing step, an azo compound is adsorbed and impregnated in a resin film obtained by swelling the raw film. When the swelling step is omitted, the swelling treatment of the raw film can be performed simultaneously in the dyeing step. Since the treatment of adsorbing and impregnating the azo compound is a step of coloring the resin film, it is a dyeing step.

  As the azo compound, a mixture of the azo compound represented by the formula (1), the formula (2) and the formula (3) or a salt thereof, and optionally the azo compound represented by the formula (6) or a salt thereof is further added. Can be used. Further, an azo compound which is a dichroic dye exemplified in “Applications of Functional Dyes” (CMC Publishing Co., Ltd., 1st printing edition, supervised by Masahiro Irie, pp. 98-100) can be used as the polarized light of the present invention. The color may be adjusted to the extent that the performance of the element is not impaired. These azo compounds may be used in the form of a free acid, or a salt of the compound may be used. Such salts are, for example, alkali metal salts such as lithium, sodium and potassium salts, or organic salts such as ammonium salts and alkylamine salts, preferably sodium salts.

  The dyeing step is not particularly limited as long as it is a method of adsorbing and impregnating the dye into the resin film. For example, the dyeing step is preferably performed by immersing the resin film in a dyeing solution, and is performed by applying the dyeing solution to the resin film. You can also. Each azo compound in the dyeing solution can be adjusted, for example, within a range of 0.001 to 10% by mass.

  The solution temperature in this step is preferably 5 to 60C, more preferably 20 to 50C, and particularly preferably 35 to 50C. The time for immersion in the solution can be adjusted appropriately, but is preferably adjusted from 30 seconds to 20 minutes, more preferably from 1 to 10 minutes.

  The dyeing solution may further contain a dyeing aid, if necessary, in addition to the azo compound. Examples of the dyeing aid include sodium carbonate, sodium hydrogen carbonate, sodium chloride, sodium sulfate, anhydrous sodium sulfate, and sodium tripolyphosphate. The content of the dyeing aid can be adjusted at any concentration depending on the time and temperature depending on the dyeability of the dye, but the content of each is preferably 0.01 to 5% by mass in the dyeing solution, and 0.1 to 5% by mass. 2% by mass is more preferred.

(Washing process 1)
After the dyeing step, a washing step (hereinafter, also referred to as “washing step 1”) can be performed before entering the next step. The dyeing step 1 is a step of washing the dyeing solution attached to the surface of the resin film in the dyeing step. By performing the washing step 1, it is possible to suppress the dye from migrating into the solution to be processed next. In the cleaning step 1, water is generally used as the cleaning liquid. The washing is preferably performed by dipping in a washing liquid, but the washing can also be performed by applying the washing liquid to a 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 cleaning liquid in the cleaning step 1 needs to be a temperature at which the material (for example, a hydrophilic polymer, here, a polyvinyl alcohol-based resin) constituting the resin film is not dissolved. Generally, the washing treatment is performed at 5 to 40 ° C. However, even if there is no washing step 1, there is no problem in performance, so the washing step can be omitted.

(Step of containing a crosslinking agent and / or a water-proofing agent)
After the dyeing step or the washing step 1, a step of adding a crosslinking agent and / or a water-proofing agent can be performed. The method of adding a crosslinking agent and / or a water resistance agent to the resin film is preferably immersion in a treatment solution, but the treatment solution may be applied or coated on the resin film. The treatment solution contains at least one crosslinking agent and / or water-proofing agent and a solvent. The temperature of the processing solution in this step is preferably 5 to 70C, more preferably 5 to 50C. The processing time in this step is preferably 30 seconds to 6 minutes, more preferably 1 to 5 minutes.

  As the crosslinking agent, for example, boric acid, boron compounds such as borax or ammonium borate, polyvalent aldehydes such as glyoxal or glutaraldehyde, biuret type, polyisocyanate compounds such as isocyanurate type or block type, titanium oxy Titanium compounds such as sulfate can be used, but ethylene glycol glycidyl ether, polyamide epichlorohydrin and the like can also be used. Examples of the water-proofing agent include succinic acid peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride and magnesium chloride, and preferably boric acid. Used. As the solvent for the cross-linking agent and / or the water-proofing agent, water is preferable but not limited. The concentration of the cross-linking agent and / or the water-proofing agent can be appropriately determined by those skilled in the art according to the type of the cross-linking agent. % Is preferable, and 1.0 to 4.0% by mass is more preferable. However, it is not essential to include a cross-linking agent and / or a water-proofing agent, and if it is desired to shorten the time or if the cross-linking treatment or the water-proofing treatment is unnecessary, this treatment step may be omitted. .

(Stretching process)
After performing the dyeing step, the washing step 1, or the step of including a crosslinking agent and / or a waterproofing agent, a 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 dry stretching method, when the stretching heating medium is an air medium, it is preferable to stretch the resin film at a temperature of the air medium from normal temperature to 180 ° C. The humidity is preferably in an atmosphere of 20 to 95% RH. Examples of the heating method include an inter-roll zone stretching method, a roll heating stretching method, a pressure stretching method, and an infrared heating stretching method, but the stretching method is not limited. The stretching step can be performed in one step, but can also be performed in two or more steps.

  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. The stretching treatment is preferably performed while immersing in a solution containing at least one crosslinking agent and / or water-resistant agent. As the cross-linking agent and the water-proofing agent, the same ones as described above for the step of including the cross-linking agent and / or the water-proofing agent can be used. The concentration of the crosslinking agent and / or the waterproofing agent in the solution in the stretching step 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 from 40 to 60C, more preferably from 45 to 58C. The stretching time is usually from 30 seconds to 20 minutes, preferably from 2 to 5 minutes. The wet stretching step can be performed in one step, but can also be performed in two or more steps.

(Washing process 2)
After performing the stretching step, the cross-linking agent and / or the water-proofing agent may precipitate on the resin film surface or foreign substances may adhere to the resin film surface. Therefore, the cleaning step of cleaning the resin film surface (hereinafter, also referred to as “cleaning step 2”) ) Can be performed. The washing time is preferably from 1 second to 5 minutes. In the washing method, it is preferable that the resin film is immersed in the washing liquid, but it is also possible to wash the resin film by applying or applying the solution to the resin film. As the cleaning liquid, water is preferable. The cleaning process can be performed in one stage, or a multi-stage process of two or more stages can be performed. 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 treatment liquid or the solvent used in the treatment steps up to this point include, in addition to water, for example, dimethyl sulfoxide, N-methylpyrrolidone, methanol, ethanol, propanol, isopropyl alcohol, glycerin, ethylene glycol, propylene glycol, diethylene glycol, and triethylene glycol. Examples include alcohols such as glycol, tetraethylene glycol or trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine, but are not limited thereto. The treatment liquid or its solvent is most preferably water. These treatment 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 performed. The drying treatment can be carried out by natural drying, but in order to further enhance the drying efficiency, it can be carried out by compressing with a roll or removing water on the surface with an air knife, a water absorbing roll or the like, and / or by blowing and drying. You can do it too. The drying temperature is preferably from 20 to 100 ° C., more preferably from 60 to 100 ° C. The drying time is, for example, 30 seconds to 20 minutes, and preferably 5 to 10 minutes.

In the method for producing a polarizing element, the degree of swelling of the substrate 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 of salt, the salt concentration, and the dyeing time, and the stretching in the stretching step The magnification is preferably adjusted so that the polarizing element satisfies at least one of the following conditions (i) to (v), and is further adjusted so as to further satisfy the conditions (vi) and (vii). Is more preferable.
(I) Regarding the parallel position transmittance, 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 becomes 2.5 or less, and the average transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 640 nm. The absolute value of the difference from the average transmittance is 2.0 or less.
(Ii) Regarding the orthogonal position transmittance, 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 0.6 or less, and the average transmittance from 520 nm to 590 nm and the average from 600 nm to 640 nm. The absolute value of the difference from the transmittance is 0.6 or less.
(Iii) Single transmittance becomes 35% to 60%.
(Iv) Each of the absolute values of the a * value and the b * value is 1 or less for the polarizing element alone and 2 or less for the parallel position.
(V) Each of the absolute values of the a * value and the b * value measured at the orthogonal position is 2 or less.
(Vi) Regarding the parallel transmittance, the average transmittance from 520 nm to 590 nm is 25 to 55%.
(Vii) The difference between the average transmittance from 380 nm to 420 nm and the average transmittance from 420 nm to 480 nm is 15% or less, and the difference between the average transmittance from 480 nm to 520 nm and the average transmittance from 420 nm to 480 nm is 15% or less, 480 nm And the difference between the average transmittance from 520 nm to 590 nm and the average transmittance from 520 nm to 590 nm is 15% or less, and / or the difference between the average transmittance from 640 nm to 780 nm and the average transmittance from 600 nm to 640 nm is 20% or less.

  By the above method, a polarizing element containing at least a combination of the azo compounds represented by the formulas (1) to (3) can be manufactured. Such a polarizing element has a higher transmittance and a higher degree of polarization than before, but expresses a high-quality paper-like white color when two polarizing elements are arranged so that the absorption axis directions are parallel to each other. It is a hue that has a neutral color (neutral gray) on its own. Furthermore, when two polarizing elements are arranged so that the absorption axis directions are orthogonal to each other, the polarizing element exhibits a classy achromatic black. Further, the polarizing element has high durability.

<Polarizing plate>
The polarizing plate according to the present invention includes 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 handleability of the polarizing element.

  The transparent protective layer is a protective film formed using a transparent substance. The protective film is a film having a layer shape capable of maintaining the shape of the polarizing element, and is preferably a plastic or the like having excellent transparency, mechanical strength, heat stability, moisture shielding properties, and the like. An equivalent function may be provided by forming an equivalent layer. Examples of the plastic constituting the protective film include polyester resins, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, thermoplastic resins such as polyolefin resins and acrylic resins, Acrylic, urethane, acrylic urethane, epoxy and silicone-based thermosetting resins or films obtained from UV-curable resins, etc., among which polyolefin-based resins include amorphous polyolefin-based resins And a resin having a polymerized unit of a cyclic polyolefin such as a norbornene-based monomer or a polycyclic norbornene-based monomer. Generally, it is preferable to select a protective film that does not hinder the performance of the polarizing element after laminating the protective film. As such a protective film, triacetyl cellulose (TAC) made of a cellulose acetate resin and norbornene are particularly preferable. . The protective film may be subjected to a hard coat treatment, an anti-reflection treatment, a treatment for preventing sticking, diffusion, anti-glare, or the like, as long as the effects of the present invention are not impaired.

  The polarizing plate preferably further includes an adhesive layer for bonding the transparent protective layer to the polarizing element between the transparent protective layer and the polarizing element. Although the adhesive constituting the adhesive layer is not particularly limited, a polyvinyl alcohol-based adhesive is preferable. Examples of the polyvinyl alcohol-based adhesive include, but are not limited to, Gohsenol NH-26 (manufactured by Nippon Gohsei) and Exeval RS-2117 (manufactured by Kuraray). A crosslinking agent and / or a waterproofing agent can be added to the adhesive. As the polyvinyl alcohol-based adhesive, it is preferable to use a maleic anhydride-isobutylene copolymer, and if necessary, an adhesive mixed with a crosslinking agent can be used. Examples of the maleic anhydride-isobutylene copolymer include, for example, Isoban # 18 (Kuraray), Isoban # 04 (Kuraray), ammonia-modified Isoban # 104 (Kuraray), and ammonia-modified Isoban # 110 (Kuraray) ), Imidized isoban # 304 (manufactured by Kuraray), imidized isoban # 310 (manufactured by Kuraray) and the like. In this case, a water-soluble polyvalent epoxy compound can be used as a crosslinking agent. Examples of the water-soluble polyepoxy compound include Denacol EX-521 (manufactured by Nagase Chemtech) and Tetrat-C (manufactured by Mitsui Gas Chemical). In addition, as the adhesive other than the polyvinyl alcohol-based resin, a known adhesive such as a urethane-based, acrylic, or epoxy-based adhesive can be used. In particular, it is preferable to use polyvinyl alcohol modified with an acetoacetyl group, and it is more preferable to use a polyhydric aldehyde as a crosslinking agent. In addition, for the purpose of improving the adhesive strength of the adhesive or improving the water resistance, additives such as zinc compounds, chlorides and iodides may be contained alone or simultaneously at a concentration of about 0.1 to 10% by mass. Can also. 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, the polarizing plate can be obtained by performing drying or heat treatment at an appropriate temperature.

  In some cases, when a polarizing plate is attached to a display device such as a liquid crystal or an organic electroluminescence (commonly called OLED or OEL), the polarizing plate is used to improve the viewing angle and / or the contrast on the surface of a protective layer or a film which will be a non-exposed surface later. Functional layers, layers or films having a luminance improving property can be provided. The various functional layers are, for example, layers or films that control retardation. It is preferable that the polarizing plate is attached to these films or display devices with an adhesive.

  The polarizing plate may be provided with various known functional layers such as an anti-reflection layer, an anti-glare layer, and a hard coat layer on the exposed surface of the protective layer or the film. A coating method is preferable for producing the layers having various functions, but a film having the functions can also be laminated via an adhesive or a pressure-sensitive adhesive.

  The polarizing plate according to the present invention can realize achromaticity while having a high transmittance and a high degree of polarization, and can express high-quality paper-like white when displaying white, and black. It is a highly durable polarizing plate capable of expressing neutral black during display.

  The polarizing element or the polarizing plate of the present invention is provided with a protective layer or a functional layer and a transparent support such as glass, crystal, and sapphire as necessary, and a liquid crystal projector, a calculator, a clock, a notebook computer, a word processor, a liquid crystal television, It is applied to polarized lenses, polarized glasses, car navigation, indoor and outdoor measuring instruments and displays. In particular, the polarizing element or the polarizing plate of the present invention is suitably used for a liquid crystal display device, for example, a reflective liquid crystal display device, a transflective liquid crystal display device, and organic electroluminescence. The liquid crystal display device using the polarizing element or the polarizing plate of the invention can express white and neutral black like high-quality paper. Further, the liquid crystal display device has high durability, high reliability, high contrast for a long time, and high color reproducibility.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[Example 1]
A polyvinyl alcohol film (VF-PS manufactured by Kuraray Co., Ltd.) having a saponification degree of 99% or more and an average degree of polymerization of 2400 was immersed in warm water at 45 ° C. for 2 minutes, and a swelling treatment was applied to set the stretching ratio to 1.30 times. The swelled film was 2,000 parts by mass of water, 2.0 parts by mass of sodium tripolyphosphate, 2.0 parts by mass of anhydrous sodium sulfate, 0.039 parts by mass of Compound Example 1, and 0.130 parts by mass of Compound Example 22. Then, the film was immersed in a solution containing 0.400 parts by mass of Compound Example 46 and 0.14 parts by mass of Compound Example 50 (CI Direct Orange 39) at 45 ° C. for 20 minutes and 00 seconds. Stained. The obtained film was immersed in a 40 ° C. aqueous solution containing 20 g / l of boric acid (manufactured by Societa Chimica Laderello sp.) For 1 minute. The obtained film was stretched for 5.0 minutes in an aqueous solution containing 30.0 g / l of boric acid at 50 ° C. while being stretched 5.0 times. The stretched film was treated with water at 25 ° C. for 20 seconds while maintaining the tension. Thereafter, the obtained film was dried at 70 ° C. for 9 minutes to obtain a polarizing element. An alkali-treated triacetyl cellulose film (Fuji Photo Film Co., Ltd., ZRD-60) was laminated on the polarizing element using a polyvinyl alcohol adhesive to obtain a polarizing plate. The obtained polarizing plate maintained the optical performance of the polarizing element, in particular, the single transmittance, the hue, the degree of polarization, and the like. This polarizing plate was used as a measurement sample of Example 1.

[Examples 2 to 9]
In the dyeing process, the dyeing time was changed to 18 minutes, 10 minutes, 8 minutes, 5 minutes 30 seconds, 3 minutes 30 seconds, 2 minutes 30 seconds, 1 minute 30 seconds, and 40 seconds in Examples 2 to 9, respectively. Except for this point, a polarizing element was obtained in the same manner as in Example 1 to produce a polarizing plate.

[Example 10]
The liquid containing the azo compound in the dyeing step used in Example 1 was 2,000 parts by mass of water, 2.0 parts by mass of sodium tripolyphosphate, 2.0 parts by mass of anhydrous sodium sulfate, and 0.040 mass of Compound Example 1 In the same manner as in Example 1 except that the liquid was changed to a liquid containing 0.115 parts by mass of Compound Example 15, 0.115 parts by mass of Compound Example 46, 0.400 parts by mass of Compound Example 46, and 0.135 parts by mass of Compound Example 50. I got

[Example 11]
The liquid containing the azo compound in the dyeing step used in Example 1 was 2,000 parts by mass of water, 2.0 parts by mass of sodium tripolyphosphate, 2.0 parts by mass of anhydrous sodium sulfate, and 0.045 parts by mass of Compound Example 1 In the same manner as in Example 1 except that the liquid was changed to a liquid containing 0.090 parts by mass of Compound Example 43, 0.030 parts by mass of Compound Example 46, and 0.130 parts by mass of Compound Example 50. I got

[Example 12]
The liquid containing the azo compound in the dyeing step used in Example 1 was 2,000 parts by mass of water, 2.0 parts by mass of sodium tripolyphosphate, 2.0 parts by mass of anhydrous sodium sulfate, and 0.037 parts by mass of Compound Example 1. In the same manner as in Example 1 except that a liquid containing 0.120 parts by mass of Compound Example 20, 0.100 parts by mass of Compound Example 46, and 0.445 parts by mass of Compound Example 50 was used. I got

Example 13
The liquid containing the azo compound in the dyeing step used in Example 1 was 2,000 parts by mass of water, 2.0 parts by mass of sodium tripolyphosphate, 2.0 parts by mass of anhydrous sodium sulfate, and 0.033 parts by mass of Compound Example 1 In the same manner as in Example 1 except that a liquid containing 0.115 parts by mass of Compound Example 44, 0.100 parts by mass of Compound Example 46, and 0.440 parts by mass of Compound Example 50 was used. I got

[Example 14]
The liquid containing the azo compound in the dyeing step used in Example 1 was 2,000 parts by mass of water, 2.0 parts by mass of sodium tripolyphosphate, 2.0 parts by mass of anhydrous sodium sulfate, and 0.024 parts by mass of Compound Example 1 In the same manner as in Example 1 except that the liquid was changed to a liquid containing 0.095 parts by mass of Compound Example 29, 0.400 parts by mass of Compound Example 46, and 0.125 parts by mass of Compound Example 50. I got

[Example 15]
The liquid containing the azo compound in the dyeing step used in Example 1 was 2,000 parts by mass of water, 2.0 parts by mass of sodium tripolyphosphate, 2.0 parts by mass of anhydrous sodium sulfate, and 0.036 parts by mass of Compound Example 1. Parts, Compound Example 35 was changed to 0.120 parts by mass, Compound Example 46 was changed to 0.420 parts by mass, and Compound Example 50 was changed to a liquid containing 0.140 parts by mass. I got

[Example 16]
The liquid containing the azo compound in the dyeing step used in Example 1 was 2,000 parts by mass of water, 2.0 parts by mass of sodium tripolyphosphate, 2.0 parts by mass of anhydrous sodium sulfate, and 0.036 parts by mass of Compound Example 1. Parts, Compound Example 41 was changed to 0.115 parts by mass, Compound Example 46 was changed to 0.420 parts by mass, and Compound Example 50 was changed to 0.140 parts by mass. I got

[Example 17]
In the solution containing the azo compound in the dyeing step used in Example 1, 0.036 parts by mass of Compound Example 1 was changed to 0.089 parts by mass of Compound Example 12 (CI Direct Red 81). A polarizing plate was obtained in the same manner as in Example 1 except for the above.

[Example 18]
In the liquid containing the azo compound in the dyeing step used in Example 1, 0.036 parts by mass of Compound Example 1 was changed to 0.077 parts by mass of Compound Example 11 (CI Direct Red 117). A polarizing element and a polarizing plate of the invention were obtained in the same manner as in Example 1 except for the above.

[Example 19]
In the solution containing the azo compound in the dyeing step used in Example 1, the procedure was the same as in Example 1 except that 0.036 parts by mass of Compound Example 1 was changed to 0.055 parts by mass of Compound Example 14. And a polarizing plate.

[Example 20]
In the solution containing the azo compound in the dyeing step used in Example 1, the same procedure as in Example 1 was performed, except that 0.400 parts by mass of Compound Example 46 was changed to 0.410 parts by mass of Compound Example 48. And a polarizing plate.

[Example 21]
In the solution containing the azo compound in the dyeing step used in Example 1, the same procedure as in Example 1 was performed, except that 0.140 parts by mass of Compound Example 50 was changed to 0.095 parts by mass of Compound Example 51. A polarizing plate was obtained.

[Example 22]
In the solution containing the azo compound in the dyeing step used in Example 1, 0.140 parts by mass of Compound Example 50 was replaced with 0.135 parts by mass of C.I. I. A polarizing plate was obtained in the same manner as in Example 1, except that Direct Yellow 28 was used.

[Example 23]
In the solution containing the azo compound in the dyeing step used in Example 1, 0.140 parts by mass of Compound Example 50 was replaced with 0.110 parts by mass of C.I. I. A polarizing plate was obtained in the same manner as in Example 1 except that Direct Orange 72 was used.

[Comparative Examples 1 to 6]
According to the method of Example 1 of Patent Document 3, a polarizing element was obtained. At this time, the immersion time in the aqueous solution containing the azo compound was changed to 13 minutes, 11 minutes and 30 seconds, 10 minutes, 8 minutes, 6 minutes, and 4 minutes in Comparative Examples 1 to 6, respectively. Using the polarizing element thus obtained, a polarizing plate was obtained in the same manner as in Example 1.

[Comparative Example 7]
A high transmittance dye-based polarizing plate SHC-115 having a neutral gray color and manufactured by Polatechno was obtained and used as a measurement sample.

[Comparative Example 8]
A neutral gray, high contrast, SHC-128 known as a dye-based polarizing plate manufactured by PORA TECHNO CORPORATION was obtained and used as a measurement sample.

[Comparative Examples 9 to 14]
A polarizing plate was prepared in the same manner as in Example 1 except that an iodine-based polarizing plate containing no azo compound was prepared by arbitrarily changing the iodine-containing time according to the formulation of Comparative Example 1 of JP-A-2008-065222. Obtained and used as a measurement sample.

[Comparative Example 15]
An iodine-based polarizing plate SKW-18245P manufactured by PORA TECHNO, which shows a paper white color in the parallel position, was obtained and used as a measurement sample.

[Comparative Example 16]
According to the method of Example 1 of JP-A-11-218611, which is a dye-based polarizing plate, a polarizing plate was obtained and used as a measurement sample.

[Comparative Example 17]
According to the method of Example 3 of Japanese Patent No. 4162334, which is a dye-based polarizing plate, a polarizing plate was obtained and used as a measurement sample.

[Comparative Example 18]
According to the method of Example 1 of Japanese Patent No. 4360100 which is a dye-based polarizing plate, a polarizing plate was obtained and used as a measurement sample.

[Comparative Example 19]
0.039 parts by mass of Compound Example 1 was combined with 0.087 parts by mass of C.I. I. A polarizing plate was obtained and used as a measurement sample in the same manner as in Example 1 except that the transmittance at the orthogonal position was adjusted to be substantially constant and the color was black, instead of using Direct Red 80.

[Comparative Example 20]
0.039 parts by mass of Compound Example 1 was combined with 0.080 parts by mass of C.I. I. A polarizing plate was obtained and used as a measurement sample in the same manner as in Example 1 except that the transmittance at the orthogonal position was adjusted to be substantially constant and the color was black instead of using Direct Red 84.

[Comparative Example 21]
0.039 parts by mass of Compound Example 1 was combined with 0.052 parts by mass of C.I. I. A polarizing plate was obtained and used as a measurement sample in the same manner as in Example 1 except that the transmittance at the orthogonal position was designed to be substantially constant and the color was black, instead of Direct Red 7.

[Comparative Example 22]
0.039 parts by mass of Compound Example 1 was combined with 0.061 parts by mass of azo compound C.I. I. A polarizing plate was obtained and used as a measurement sample in the same manner as in Example 1, except that the transmittance at the orthogonal position was designed to be substantially constant and the color was black, instead of Direct Red 45.

[Comparative Example 23]
0.130 parts by mass of Compound Example 22 was combined with 0.075 parts by mass of C.I. I. A polarizing plate was obtained and used as a measurement sample in the same manner as in Example 1, except that the transmittance in the orthogonal position was designed to be substantially constant and the color was black, instead of Direct Blue 6.

[Comparative Example 24]
0.130 parts by mass of Compound Example 22 was combined with 0.085 parts by mass of C.I. I. A polarizing plate was obtained and used as a measurement sample in the same manner as in Example 1 except that the transmittance in the orthogonal position was designed to be substantially constant and the color was black, instead of Direct Blue 15.

[Comparative Example 25]
0.130 parts by mass of Compound Example 22 was combined with 0.105 parts by mass of C.I. I. A polarizing plate was obtained and used as a measurement sample in the same manner as in Example 1, except that the transmittance in the orthogonal position was designed to be substantially constant and the color was black, instead of Direct Blue 71.

[Comparative Example 26]
0.400 parts by mass of Compound Example 46 was combined with 0.43 parts by mass of C.I. I. Instead of Direct Blue 199, a polarizing plate was obtained and used as a measurement sample in the same manner as in Example 1 except that the transmittance at the orthogonal position was designed to be substantially constant and the color was black.

[Comparative Example 27]
Instead of using 0.400 parts by mass of Compound Example 46, a direct dye of the same color, which is the same coppering dye C.I. I. A polarizing plate was obtained in the same manner as in Example 1 except that 0.41 parts by mass of Direct Blue 218 was used so that the transmittance in the orthogonal position was almost constant and the color in the orthogonal position was black. And a measurement sample.

[Evaluation]
The evaluation of the measurement samples obtained in Examples 1 to 23 and Comparative Examples 1 to 27 was performed as follows.
(A) Single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc
The individual transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc of each measurement sample were measured using a spectrophotometer (“U-4100” manufactured by Hitachi, Ltd.). Here, the single transmittance Ts is the transmittance at each wavelength when one measurement sample is measured. The parallel transmittance Tp is a spectral transmittance of each wavelength measured by superimposing two measurement samples so that their absorption axis directions are parallel. The orthogonal position transmittance Tc is a spectral transmittance measured by superposing two polarizing plates such that their absorption axes are orthogonal to each other. The measurements were made over a wavelength of 400-700 nm.
The average value at 420 to 480 nm, the average value at 520 to 590 nm, and the average value at 600 to 640 nm of each of the parallel position transmittance Tp and the orthogonal position transmittance Tc are determined and are shown in Table 1.

(B) Single transmittance Ys, parallel transmittance Yp, and orthogonal transmittance Yc
The single transmittance Ys, the parallel transmittance Yp, and the orthogonal transmittance Yc of each measurement sample were determined. The single transmittance Ys, the parallel transmittance Yp, and the orthogonal transmittance Yc are the single transmittance Ts and the parallel transmittance determined at predetermined wavelength intervals dλ (here, 5 nm) in the wavelength region of 400 to 700 nm. For each of Tp and orthogonal transmittance Tc, the transmittance is corrected to luminosity according to JIS Z 8722: 2009. Specifically, the simplex transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc were calculated by substituting into the following equations (I) to (III). In the following formulas (I) to (III), Pλ represents a spectral distribution of standard light (C light source), and yλ represents a two-degree color matching function. Table 1 shows the results.

(C) Absolute value of difference between average transmittances of two wavelength bands Table 2 shows parallel transmittance Tp and orthogonal transmittance Tc of the measurement samples obtained in Examples 1 to 23 and Comparative Examples 1 to 27. The absolute value of the difference between the average value at 520 to 590 nm and the average value at 420 to 480 nm and the absolute value of the difference between the average value at 520 to 590 nm and the average value at 600 to 640 nm are shown.

  As shown in Tables 1 and 2, the average value at 520 to 590 nm of the parallel transmittance Tp of the measurement samples obtained in Examples 1 to 23 was 25% or more, and the average value at 420 to 480 nm was not less than 25%. The absolute value of the difference between the average value at 520 and 590 nm and the average value at 520-590 nm, and the absolute value of the difference between the average value at 520-590 nm and the average value at 600-640 nm both showed extremely low values of 1.0%. . Further, the orthogonal transmittances Tc of the measurement samples obtained in Examples 1 to 23 were the absolute value of the difference between the average value at 420 to 480 nm and the average value at 520 to 590 nm, and the average value at 520 to 590 nm. Both the absolute value of the difference from the average value at 600 to 640 nm was 0.6% or less, indicating a very low value. On the other hand, in the measurement samples of Comparative Examples 7 to 27, the absolute value of the difference in the average value of the parallel transmittance Tp between the wavelength bands and the absolute value of the difference in the orthogonal transmittance Tc between the wavelength bands were measured. At least one showed a high value.

(D) degree of polarization ρy
For each measurement sample, the degree of polarization ρy was determined. The degree of polarization ρy was obtained by substituting the parallel transmittance Yp and the orthogonal transmittance Yc into the following equation. Table 3 shows the results.
ρy = {(Yp−Yc) / (Yp + Yc)} ^1/2 × 100

(E) Chromaticity a * value and b * value For each measurement sample, according to JIS Z 8781-4: 2013, at the time of measuring the single transmittance Ts, at the time of measuring the parallel transmittance Tp, and at the time of measuring the orthogonal transmittance Tc, respectively. The chromaticity a * value and b * value in were measured. For the measurement, the above-mentioned spectrophotometer was used, and both the transmitted color and the reflected color were measured from the outside of the room. The C light source was used as a light source. Table 3 shows the results. Here, a * -s and b * -s, a * -p and b * -p, and a * -c and b * -c are a single transmittance Ts, a parallel transmittance Tp and an orthogonal transmittance Tc. Respectively correspond to the chromaticity a * value and the b * value at the time of measurement.

(F) Observation of Color For each measurement sample, two identical measurement samples were superimposed on a white light source in each of the parallel position and the orthogonal position, and the color observed at that time was examined. The observation was performed visually by 10 observers, and Table 3 shows the most observed colors. In Table 3, the color in the parallel position means a color in a state where two identical samples are overlapped so that their absorption axis directions are parallel to each other (when displaying white), and the color in the orthogonal position is the same. It means the color in a state where two samples are stacked so that their absorption axis directions are orthogonal to each other (during black display). Basically, the polarization color is such that the color at the parallel position is “white” and the color at the orthogonal position is “black”, but in the embodiment, for example, white with a yellow tint is “yellow”, Black with a ting is indicated as "purple".

As shown in the results of Table 3, the measurement samples of Examples 1 to 23 had a single transmittance of 35% or more. In the measurement samples of Examples 1 to 23, the absolute values of a * -s, b * -s, a * -c, and b * -c were 1.0 or less, and a * -p and b Each absolute value of * -p was 2.0 or less, indicating a very low value. Even when the measurement samples of Examples 1 to 23 were visually observed, they exhibited parallel-like high-quality paper-like white at the parallel position and high-grade clear black at the orthogonal position. On the other hand, in Comparative Examples 7 to 27, at least one of a * -s, b * -s, a * -p, b * -p, a * -c, and b * -c shows a high value, It was not achromatic at the parallel or orthogonal position when visually observed.
Therefore, the polarizing element of the present invention can express high-quality paper-like white when the absorption axis of the polarizing element is installed in parallel, and has a neutral color ( It can be seen that the color has a neutral hue (neutral gray), a high degree of polarization, and an achromatic color in a parallel position even at a high transmittance. Furthermore, when the absorption axis of a polarizing element is installed orthogonally, it turns out that it is possible to obtain a high-quality polarizing element showing achromatic black.
Furthermore, in the measurement samples obtained in Examples 1 to 23, the transmittance is such that the average transmittance of each wavelength is substantially constant, and even if the transmittance is high, a highly achromatic hue and its white It turned out that it has the degree of polarization which can express black.

(G) Contrast The contrast was confirmed by calculating the ratio (Yp / Yc) between the parallel transmittance and the orthogonal transmittance measured using two identical measurement samples. Comparing Example 1 in which the single transmittance is about 37% with Comparative Example 1, the contrast of Example 1 is 3337, the contrast of Comparative Example 1 is 2219, and the contrast of Example 1 is about 1.5 of Comparative Example 1. It was twice. Further, comparing Example 3 in which the single transmittance is about 39.5% and Comparative Example 3, the contrast of Example 3 is 276, the contrast of Comparative Example 3 is 137, and the contrast of Example 3 is about twice. Had the following contrast. From this, it has been found that the polarizing plate of the present invention has improved performance as compared with Patent Document 3 which is a conventional achromatic polarizing plate.

(H) Durability test The measurement samples of Examples 1 to 23 and Comparative examples 9 to 15 were applied to an environment of 85 ° C and a relative humidity of 85% RH for 240 hours. As a result, in Comparative Examples 9 to 15, the degree of polarization was reduced by 10% or more, b * -c became lower than -10, and the appearance color changed to blue. In particular, two measurement samples were arranged at orthogonal positions. In some cases the black color was very blue. Specifically, in Comparative Example 12, the single substance transmittance changed to 67.1% and the degree of polarization changed to 30.8%, and in Comparative Example 15, the transmittance changed to 83.3% and the degree of polarization changed to 5.4%. It was confirmed that the durability was low. On the other hand, in the measurement samples of Examples 1 to 23, no change in the transmittance and the degree of polarization and no change in the hue were observed.
This indicates that the liquid crystal display device using the polarizing element or the polarizing plate according to the present invention is a liquid crystal display device having high reliability, high contrast for a long time, and high color reproducibility.

Claims (12)

A polarizing element comprising an azo compound represented by the formula (1) or a salt thereof, an azo compound represented by the formula (2) or a salt thereof, and an azo compound represented by the formula (3) or a salt thereof.

(Wherein, Ar ₁ represents a phenyl group or a naphthyl group having a substituent, and Rr ₁ and Rr ₂ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group. , Xr ₁ is an amino group optionally having a substituent, a phenylamino group optionally having a substituent, a phenylazo group optionally having a substituent, a benzoyl group optionally having a substituent, or A benzoylamino group which may have a substituent is shown.)

(In the formula, Ab ₁ represents a phenyl group or a naphthyl group having a substituent, and Rb ₁ to Rb ₆ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group. , Xb ₁ represents an amino group optionally having a substituent, a phenylamino group optionally having a substituent, a phenylazo group optionally having a substituent, a naphthotriazole group optionally having a substituent, A benzoyl group which may have a substituent or a benzoylamino group which may have a substituent.)

(Wherein, Ag ₁ and Ag ₂ are each independently a group consisting of a sulfo group, a lower alkyl group, a lower alkoxy group, a lower alkoxy group having a sulfo group, a carboxy group, a nitro group, an amino group, and a substituted amino group. It represents a naphthyl group or a phenyl group having at least one selected substituent, and Rg ₁ and Rg ₂ each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a lower alkoxy group having a sulfo group. )   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 determined for the transmittance obtained in a state where the two polarizing elements are stacked so that the absorption axis directions are parallel to each other. 2. The polarizing element according to claim 1, wherein 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. The absolute values of the a * value and the b * value obtained at the time of measuring the transmittance of natural light according to JIS Z 8781-4: 2013 are as follows
The polarizing element alone, both 1 or less,
3. The polarizing element according to claim 1, wherein the two polarizing elements are two or less in a state where the two polarizing elements are arranged so that their absorption axis directions are parallel to each other. 4. The single transmittance of the polarizing element is 35% to 60%,
The average transmittance from 520 nm to 590 nm determined in a state in which the two polarizing elements are stacked so that their absorption axis directions are parallel to each other is 25% to 55%. Polarizing element. The polarizing element according to any one of claims 1 to 4, wherein the azo compound represented by the formula (2) is an azo compound represented by the formula (4).

(In the formula, Ab ₁ , Rb ₁ to Rb ₄ , and Xb ₁ are the same as those in Formula (2).) The polarizing element according to any one of claims 1 to 5, wherein the azo compound represented by the formula (2) is an azo compound represented by the formula (5).

(In the formula, Ab ₁ , Rb ₂ , Rb ₄ , and Xb ₁ are the same as those in Formula (2).) The polarizing element according to claim 1, further comprising an azo compound represented by the formula (6) or a salt thereof.

(In the formula, Ry ₁ and Ry ₂ each independently represent a sulfo group, a carboxy group, a hydroxy group, a lower alkyl group, or a lower alkoxyl group, and n represents an integer of 1 to _3. )   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 determined for the transmittance obtained in a state where the two polarizing elements are stacked so that their absorption axis directions are orthogonal to each other. 8. The method according to claim 1, wherein the difference between the average transmittance from 520 nm to 590 nm and the average transmittance from 600 nm to 640 nm is 0.6% or less. Polarizing element.   In a state where the two polarizing elements are arranged so that their absorption axis directions are orthogonal to each other, the absolute values of the a * value and the b * value obtained at the time of measuring the transmittance of natural light according to JIS Z 8781-4: 2013 are as follows. The polarizing element according to claim 1, wherein the number is 2 or less.   The polarizing element according to claim 1, wherein the polarizing element includes a polyvinyl alcohol-based resin film as a base material.   A polarizing plate, comprising: the polarizing element according to claim 1; and a transparent protective layer provided on one or both surfaces of the polarizing element.   A liquid crystal display device comprising the polarizing element according to claim 1 or the polarizing plate according to claim 11.