HK1133901B - Azo compound and salt thereof, and dye-containing polarizing film comprising the compound or salt - Google Patents

Description

Azo compound and salt thereof, and dye-containing polarizing film comprising the same

Technical Field

[0001]

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

Background

[0002]

In addition to liquid crystals having an optical switching function, polarizing plates having light transmitting and shielding functions are also basic constituent elements of display devices such as Liquid Crystal Displays (LCDs). The application fields of such LCDs have been expanded from early small-sized articles such as electronic computers, watches, and the like to notebook computers, word processors, liquid crystal projectors, liquid crystal televisions, car navigation systems, indoor and outdoor instruments, and the like. In addition, the LCD is used under a wide range of conditions from low temperature to high temperature, low humidity to high humidity, and low light intensity to high light intensity. Therefore, polarizing plates having high polarization performance and excellent durability are required.

[0003]

Currently, polarizing films are prepared as follows: a polarizing film substrate is dyed with iodine or a dichroic dye as a polarizing element or into which iodine or a dichroic dye is introduced, wherein the substrate is a stretched and oriented film of polyvinyl alcohol or a derivative thereof or an oriented film of a polyolefin prepared by dehydrochlorinating a polyvinyl chloride film or dehydrating a polyvinyl alcohol film. Among these polarizing films, an iodine polarizing film using iodine as a polarizing element shows superior initial polarizing performance. On the other hand, the polarizing films are weak in water resistance and thermal properties, and when they are used in a high temperature and high humidity state for a long period of time, problems in durability are generated. In order to improve durability, for example, a method of treating a polarizing film with formalin or an aqueous solution containing boric acid, using a polymer film having low moisture permeability as a protective film, or the like is considered. However, the effect of these methods is not satisfactory. On the other hand, a dye-containing polarizing film containing a dichroic dye as a polarizing element is better than an iodine polarizing film in moisture resistance and heat resistance, but the initial polarizing performance of the dye-containing polarizing element is generally insufficient.

[0004]

In an achromatic polarizing film prepared by adsorbing several dichroic dyes onto a polymer film and orienting the film, if there is light leakage (color leakage) of a specific wavelength in a visible light wavelength range in a state where two polarizing films are stacked on each other and their orientation directions are perpendicular to each other, when these polarizing films are assembled to a liquid crystal display panel, the color tone of the liquid crystal display may be changed in a dark state. Therefore, in order to suppress a color change of the liquid crystal display caused by color leakage of a specific wavelength in a dark state when the polarizing film is assembled to the liquid crystal display, it is necessary to uniformly lower the average light transmittance at a vertical position (vertical average light transmittance) in the visible light wavelength range.

[0005]

In addition, in the case of a color liquid crystal projection display (i.e., a color liquid crystal projector), a polarizing plate is used for a liquid crystal imaging element. In this application, an iodine polarizing plate, which has good polarizing properties and shows a neutral gray color, has been previously used. However, as described above, the iodine polarizing plate has a problem that its light resistance, heat resistance and moist heat resistance are insufficient because iodine is a polarizing agent. To solve such problems, a neutral gray polarizing plate using a dye-containing dichroic colorant as a polarizing agent has been started to be used. In the polarizing plate of neutral gray, colorants of three primary colors are generally used in combination in order to improve light transmittance and polarization performance in the entire visible light wavelength range on average. Therefore, there is a problem in that light transmittance is still insufficient to meet the market demand for brighter color liquid crystal projectors, and in order to achieve brightness, the intensity of the light source must be increased. In order to solve this problem, three polarizing plates corresponding to three primary colors, i.e., a polarizing plate for each of a blue channel, a green channel, and a red channel, have been used.

[0006]

Since the image of such a small area of 0.5 to 3 inches is enlarged to about several tens of inches to one hundred and several tens of inches and light is considerably absorbed by the polarizing plate, a reduction in brightness is inevitable. Therefore, a high-brightness light source is used as the light source. Further, there is a strong demand for further improvement in the luminance of the liquid crystal projector, and as a result, the intensity of the light source used inevitably becomes stronger. Along with this, the amount of light and heat received by the polarizing film is also increasing.

[0007]

However, the conventional polarizing plate has not sufficiently satisfied the market demand in terms of polarization characteristics, absorption wavelength range, color tone, and the like. In addition, among polarizing plates corresponding to three primary colors of a color liquid crystal projector (i.e., polarizing plates for each of blue, green, and red channels), luminance, polarizing performance, durability, and resistance to long-term light radiation under high temperature and high humidity conditions are not good. Improvements are therefore desirable.

[0008]

As the dye having absorption characteristics particularly for the blue channel (400-500nm), the dyes described in c.i. direct yellow 12, c.i. direct yellow 28, c.i. direct yellow 44, c.i. direct orange 39, c.i. direct orange 72, c.i. direct orange 26, and patent documents 1 to 3, and the like are used. However, polarizing films using these dyes have poor polarization characteristics, resulting in a problem that when a white image is displayed, a yellowish image is provided and the color temperature does not rise.

Patent document 1: JP-A-2001-108828

Patent document 2: JP-A-2001-240762

Patent document 3: JP-A-2003-215338

Patent document 4: JP-A-60-168743

Patent document 5: JP-A-2003-35819

Patent document 6: JP-A-2001-33627

Patent document 7: japanese patent No. 2622748

Patent document 8: JP-A-60-156759

Non-patent document 1: "Senryo Kagaku (Dye Chemistry)" by Yutaka Hosoda (published by Gihodo Co., Ltd., Japan) p.626

Disclosure of Invention

[0009]

An object of the present invention is to provide a high-performance polarizing plate having excellent polarizing properties and moisture-, heat-and light-resistance. Further, another object of the present invention is to provide a high-performance polarizing plate that does not cause color leakage in a vertical position in a wavelength range of visible light and has excellent polarizing properties and moisture-, heat-and light-resistance, and is a non-color polarizing plate prepared by absorbing two or more dichroic dyes in a polymer film and then orienting the film.

It is another object of the present invention to provide a high-performance color polarizing plate which corresponds to the three primary colors of a color liquid crystal projector and is excellent in brightness, polarizing performance, durability and light resistance.

[0010]

In order to achieve these objects, the inventors have conducted intensive studies and, as a result, have found that polarizing films and polarizing plates containing the novel azo compound and/or a salt thereof exhibit excellent polarizing properties and moisture-, heat-and light-resistance. This finding led to the present invention. That is, the present invention includes the following embodiments:

[0011]

(1) an azo compound represented by the following general formula (1):

[0012]

[0013]

wherein R1 and R2 each independently represent a hydrogen atom, a lower alkyl group and a lower alkoxy group; n is 1 or 2.

(2) The azo compound according to (1) wherein R1 and R2 are each independently one of a hydrogen atom, a methyl group and a methoxy group, and salts thereof.

(3) The azo compound according to (1) wherein R1 and R2 are hydrogen atoms, and salts thereof.

(4) Dye-containing polarizing film comprising at least one azo compound according to any one of (1) to (3) and/or a salt thereof in a polarizing film substrate.

(5) Dye-containing polarizing film comprising at least one azo compound according to any one of (1) to (3) and/or a salt thereof, and at least one other organic dye in a polarizing film substrate.

(6) A dye-containing polarizing film comprising two or more azo compounds according to any one of (1) to (3) and/or salts thereof, and at least one other organic dye in a polarizing film substrate.

(7) The dye-containing polarizing film according to any one of (4) to (6), wherein the polarizing film substrate is a film containing a polyvinyl alcohol resin.

(8) A dye-containing polarizing plate comprising a transparent protective layer adhered to at least one surface of the dye-containing polarizing film according to any one of (4) to (7).

(9) A color polarizing plate for a liquid crystal projector, wherein the dye-containing polarizing film or the dye-containing polarizing plate according to any one of (4) to (8) is used.

[0014]

The azo compound of the present invention and salts thereof can be used as a dye for a polarizing film. Polarizing films containing these compounds have high polarizing performance comparable to those of polarizing films using iodine and also have excellent durability. Therefore, the former polarizing film is suitable for use in various liquid crystal displays and liquid crystal projectors, in-aircraft applications requiring high polarizing performance and durability, and in industrial instrument displays used in various environments.

Best mode for carrying out the invention

[0015]

The present invention relates to azo compounds represented by the general formula (1) in the form of a free acid and a salt thereof. In the general formula (1), R1 and R2 are each independently a hydrogen atom, a lower alkyl group and a lower alkoxy group; preferably, R1 and R2 are hydrogen atom and lower alkyl; it is particularly preferred that R1 is a hydrogen atom or a methyl group and R2 is a hydrogen atom; n represents 1 or 2. In the present invention, lower alkyl and lower alkoxy means alkyl and alkoxy each having 1 to 4 carbon atoms. Next, specific examples of the azo compound used in the present invention represented by the general formula (1) are shown below (general formulae (2) to (6)). In the following general formula, sulfonic acid groups, carboxyl groups and hydroxyl groups are shown as free acids.

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

The azo compound represented by the general formula (1) in the form of a free acid can be easily prepared according to a general preparation method of an azo dye, for example, by conducting known diazotization and coupling reactions as described in non-patent document 1. As a specific production method, 4-aminobenzoic acid is diazotized and coupled with aniline represented by the following general formula (a) to obtain a monoazo amino compound (the following general formula (B)).

[0022]

Wherein R1 and R2 represent the same meanings as in the general formula (1).

[0023]

[0024]

Then, the monoazo amino compound is reacted with 4, 4 '-dinitrostilbene-2, 2' -sulfonic acid under basic conditions, followed by reduction with glucose to obtain an azo compound represented by the general formula (1).

[0025]

In the above reaction, the diazotization step may be carried out according to a general method of mixing a nitrite such as sodium nitrite into a solution or suspension of the diazo component in an aqueous solution of a mineral acid such as an aqueous hydrochloric acid solution or an aqueous sulfuric acid solution, or may be carried out according to a reverse method in which a nitrite is previously added to a neutral or weakly alkaline aqueous solution of the diazo component and then the solution is mixed with a mineral acid. The diazotisation temperature is suitably in the range-10 to +40 ℃.

Furthermore, the coupling step with aniline was carried out as follows: an acidic aqueous solution of aniline in aqueous hydrochloric acid, aqueous acetic acid, or the like is mixed with the corresponding diazo solution described above and reacted at a temperature of-10 to +40 ℃ and an acidic pH of 2 to 7.

[0026]

In the reaction of the monoazo amino compound with 4, 4 '-dinitrostilbene-2, 2' -sulfonic acid, the condensation step under basic conditions is carried out under strongly basic conditions by using sodium hydroxide, lithium hydroxide, or the like. The concentration of the base is suitably 2-10% and the temperature is suitably 70-100 ℃. The value of n in the general formula (1) can be adjusted by changing the charging ratio of the monoazo-amino compound and 4, 4 '-dinitrostilbene-2, 2' -sulfonic acid. In the glucose reduction step, 0.5 to 1.2 equivalents of glucose are generally used under alkaline conditions.

[0027]

Further, in the present invention, the azo compound represented by the general formula (1) can be used as a free acid, as well as a salt. Salts include alkali metal salts such as lithium, sodium, potassium, and the like; an ammonium salt; and organic salts such as amine salts. Sodium salts are generally used.

[0028]

In the synthesis of the azo compound represented by the general formula (1), the substituents of the main coupling component (aniline which may have a substituent (R1, R2)) include methyl, ethyl, methoxy, and ethoxy groups. Any one or two of these substituents may be attached. The linking position thereof, with respect to the amino group, is 2-position, 3-position, 2-position and 5-position, 3-position and 5-position, or 2-position and 6-position. Of these, connection to 3 bits, and 2 bits and 5 bits is preferable. Examples of the aniline include, for example, aniline, 2-methylaniline, 3-methylaniline, 2-ethylaniline, 3-ethylaniline, 2, 5-dimethylaniline, 2, 5-diethylaniline, 2-methoxyaniline, 3-methoxyaniline, 2-methoxy-5-methylaniline, 2, 5-dimethoxyaniline, 3, 5-dimethylaniline, 2, 6-dimethylaniline and 3, 5-dimethoxyaniline. The amino groups of these anilines may be protected. As the protecting group, an ω -methane sulfonic acid group may be mentioned.

[0029]

In the polarizing film or the polarizing plate of the present invention, the azo compound represented by the general formula (1) or a salt thereof may be used alone or in combination of two or more. Further, one or more other organic dyes may be used together as needed. The organic dyes to be used together are not particularly limited, but they are preferably dyes having absorption characteristics in a wavelength range different from that of the azo compound or salt thereof according to the present invention and being highly dichroic. Examples include c.i. direct red 2, c.i. direct red 31, c.i. direct red 79, c.i. direct red 81, c.i. direct red 247, c.i. direct green 80, c.i. direct green 59, and dyes described in patent documents nos. 5 to 8. These dyes can be used as free acids, alkali metal salts (e.g., Na salts, K salts, Li salts), ammonium salts, and amine salts.

[0030]

When other organic dyes are used together as needed, the kind of the dye to be incorporated varies depending on whether the intended polarizing film is a neutral polarizing film, a color polarizing film for a liquid crystal projector, or other color polarizing films. The proportion of the one or more organic dyes described above to be combined together is not particularly limited, but is usually preferably 0.1 to 10 parts by weight based on the weight of the azo compound of the formula (1) or a salt thereof.

[0031]

Polarizing films (having various hues and achromatic colors) used for the polarizing plate of the present invention or the polarizing plate for a liquid crystal projector may be prepared as follows: the azo compound represented by the general formula (1) or a salt thereof, together with other organic dyes as needed, is incorporated into a polymer film, which is a material of the polarizing film, by a known method. The resulting polarizing film is provided with a protective film to produce a polarizing plate, and then, as necessary, a protective layer or an AR (anti-reflection) layer, a support, and the like are disposed thereon for use in liquid crystal projectors, electronic computers, watches, notebook computers, word processors, liquid crystal televisions, car navigation systems, indoor and outdoor instruments, displays, and the like.

[0032]

As the substrate (polymer film) for the polarizing film of the present invention, a polyvinyl alcohol substrate is preferable. As the polyvinyl alcohol base material, there can be cited, for example, polyvinyl alcohol or a derivative thereof, and a polyvinyl alcohol film formed by coating a polyvinyl alcohol film with an olefin such as ethylene and propylene; unsaturated carboxylic acids such as crotonic acid, acrylic acid, methacrylic acid, and maleic acid, and the like. Among them, a film containing polyvinyl alcohol or a derivative thereof is preferably used from the viewpoint of dye adsorption property and orientation property. The thickness of the substrate is generally about 30 to 100. mu.m, preferably about 60 to 90 μm.

[0033]

In incorporating the azo compound of the formula (1) or a salt thereof into such a polymer film, a method of dyeing the polymer film is generally employed. For example, dyeing is performed as follows. First, the azo compound and/or a salt thereof according to the present invention and other organic dyes as required are dissolved in water to prepare a dye bath. The concentration of the dye in the dye bath is not particularly limited and is generally selected to be about 0.001 to 10 wt%. In addition, a dyeing assistant may be used as needed, for example, sodium sulfate is suitably used at a concentration of about 0.1 to 10 wt%. The dyeing is performed by immersing the polymer film in the prepared dye bath for 1 to 10 minutes. The dyeing temperature is preferably about 40-80 ℃.

[0034]

The orientation of the water-soluble dye is carried out by stretching the polymer film dyed as described above. As the stretching method, any known method such as a wet method, a dry method, or the like may be employed. In some cases, stretching of the polymer film may be performed prior to dyeing. In this case, the orientation of the water-soluble dye is performed at the time of dyeing. The polymer film containing therein the water-soluble dye and oriented with the water-soluble dye is subjected to a post-treatment such as boric acid treatment by a known method, as necessary. Such post-treatment is performed in order to improve the transmittance and the degree of polarization of the polarizing film. The conditions of the boric acid treatment vary depending on the kind of the polymer film used and the kind of the dye used. In general, the concentration of boric acid in its aqueous solution is from 0.1 to 15% by weight, preferably from 1 to 10% by weight, and the treatment is carried out by immersion at a temperature of from 30 to 80 ℃, preferably from 40 to 75 ℃, for from 0.5 to 10 minutes. In addition, the polymer film may be subjected to the fixing treatment simultaneously with the aqueous solution containing the cationic polymer, as required.

[0035]

A transparent protective film excellent in optical transparency and mechanical strength can be adhered to one or both surfaces of the dye-containing polarizing film of the present invention thus obtained to produce a dye-containing polarizing plate. As a material for forming the protective film, for example, a cellulose acetate film, an acrylic film, a fluorinated film such as a tetrafluoroethylene/hexafluoropropylene copolymer, and a film composed of a polyester resin, a polyolefin resin, or a polyamide resin can be used. Preferably, triacetyl cellulose (TAC) film or cycloolefin film may be used. The thickness of the protective film is usually 40 to 200 μm.

Adhesives that may be used to adhere the polarizing film and the protective film together include polyvinyl alcohol (PVA) adhesives, urethane emulsion adhesives, acrylic adhesives, polyester-isocyanate adhesives, and the like. Among them, a polyvinyl alcohol binder is suitable.

[0036]

In addition, a transparent protective layer may be provided on the surface of the dye-containing polarizing plate of the present invention. As the protective layer, for example, an acrylic or silicone hard coat layer and a urethane protective layer can be cited. In addition, in order to further improve the single-plate light transmittance, it is preferable to provide an AR layer on this protective layer. The AR layer may be formed, for example, by vapor deposition or sputtering of a substance such as silicon dioxide or titanium dioxide. The AR layer may also be formed by coating a thin layer of a fluorinated substance. In addition, the dye-containing polarizing plate of the present invention can also be used as an elliptical polarizing plate in which a phase difference plate is adhered.

[0037]

The dye-containing polarizing plate of the present invention thus constituted has an achromatic color, does not cause color leakage in a vertical position in the wavelength range of visible light, and exhibits excellent polarizing performance. Furthermore, it has the following characteristics: it shows no discoloration, no degradation of polarization properties, and little light leakage in the vertical position in the visible range even under conditions of high temperature and high humidity.

[0038]

In the present invention, the color polarizing plate of the liquid crystal projector includes the azo compound represented by the general formula (1) or a salt thereof as a dichroic molecule and, in addition, the above-mentioned other organic dye as necessary. In addition, the polarizing film of the color polarizing plate for a liquid crystal projector is prepared by the same method as for the above dye-containing polarizing film. A protective film is further attached to the polarizing film to prepare a dye-containing polarizing plate, which is provided with a protective layer, an AR layer, a support, and the like as necessary, and is used as a color polarizing plate for a liquid crystal projector.

[0039]

As the color polarizing plate of the liquid crystal projector, it is preferable that the single-plate average light transmittance is 39% or more and the average light transmittance at the vertical position is 0.4% or less in the wavelength range necessary for the polarizing plate (A. when an ultra-high pressure mercury lamp is used: 420-500nm for the blue channel, 500-580nm for the green channel, and 600-680nm for the red channel; B. peak wavelength when a three primary color LED lamp is used: 430-450nm for the blue channel, 520-535nm for the green channel, and 620-635nm for the red channel). More preferably, in the wavelength range necessary for the polarizing plate, the single-plate average light transmittance is 41% or more and the average light transmittance in the vertical position is 0.3% or less, more preferably 0.2% or less. More preferably, in a wavelength range necessary for the polarizing plate, the single-plate average light transmittance is 42% or more and the average light transmittance in the vertical position is 0.1% or less. As described above, the color polarizing plate of the liquid crystal projector of the present invention has brightness and excellent polarizing performance.

[0040]

The color polarizing plate for a liquid crystal projector of the present invention is preferably a polarizing plate having an AR layer, which is produced by providing the above AR layer on a polarizing plate composed of a polarizing film and a protective film. In addition, a polarizing plate having an AR layer and a support, which is produced by attaching the polarizing plate having an AR layer to a support such as a transparent glass plate, is more preferable.

[0041]

Further, the single-plate average light transmittance is an average value of light transmittance in a specific wavelength range when natural light enters a piece of polarizing plate which is not provided with either an AR layer or a support such as a transparent glass plate (hereinafter simply referred to as "polarizing plate" in the same sense). The average light transmittance at the vertical position is an average value of light transmittances in a specific wavelength range when natural light enters two sheets of polarizing plates, which are stacked in the orientation directions perpendicular to each other.

[0042]

The color polarizing plate used in the liquid crystal projector of the present invention is generally used as a polarizing plate having a support. The support preferably has a flat portion because the polarizing plate is adhered thereto. Further, the support is preferably a molded article of glass because the polarizing plate is used for optical purposes. As the molded article of glass, for example, a glass plate, a lens, a prism (e.g., a triangular prism or a cubic prism) can be cited. The lens to which the polarizing plate is attached may be used as a condensing lens having the polarizing plate in a liquid crystal projector. In addition, a prism to which a polarizing plate is attached may be used as a polarizing color separator with a polarizing plate or a dichroic prism with a polarizing plate in a liquid crystal projector. In addition, a polarizing plate may be attached to the liquid crystal cell. As the glass material, inorganic glass such as soda glass, borosilicate glass, and sapphire glass; organic glass such as acrylic glass and polycarbonate glass, etc. Inorganic glasses are preferred. The thickness and dimensions of the glass plate can be selected as desired. In addition, in order to further improve the single-plate light transmittance of the polarizing plate having glass, it is preferable to provide an AR layer on one or both surfaces of the glass surface or the surface of the polarizing plate.

[0043]

To prepare a polarizing plate having a support for a liquid crystal projector, for example, a transparent adhesive (pressure-sensitive adhesive) is coated on a flat part of the support, and then the polarizing plate of the present invention is attached to this coated surface. In addition, a transparent adhesive (pressure-sensitive adhesive) may be coated on the polarizing plate, and then a support may be attached to this coated surface. As the adhesive (pressure-sensitive adhesive) used herein, for example, an acrylic ester adhesive is preferable. Further, when this polarizing plate is used as an elliptically polarizing plate, generally, the side of the phase difference plate is adhered to the support, but the side of the polarizing plate may be adhered to the glass molded article.

[0044]

In a color liquid crystal projector using the polarizing plate of the present invention, the polarizing plate of the present invention is disposed on one or both of the light incident side and the light exit side of the liquid crystal cell. The polarizing plate may or may not be in contact with the liquid crystal cell, but for the sake of durability, it is preferable that the plate is not in contact with the liquid crystal cell. When the polarizing plate is in contact with the liquid crystal cell on the light exit side, the polarizing plate of the present invention having the liquid crystal cell as a carrier can be used. When the polarizing plate is not in contact with the liquid crystal cell, it is preferable that the polarizing plate of the present invention using a support other than the liquid crystal cell can be used. In addition, the polarizing plate of the present invention is preferably arranged on both the light incident side and the light exit side of the liquid crystal cell in view of durability. In addition, it is preferable that the polarizing plate surface of the polarizing plate of the present invention is disposed on the liquid crystal cell side with its support surface on the light source side. In addition, the light incident surface of the liquid crystal cell is referred to as the light source surface, and the opposite surface is referred to as the light exit surface.

[0045]

In the color liquid crystal projector using the polarizing plate of the present invention, it is preferable to dispose an ultraviolet cut filter between the light source and the polarizing plate having the support on the light incident side. In addition, the liquid crystal cell used is preferably, for example, an active matrix type liquid crystal cell formed by encapsulating liquid crystal between a transparent substrate on which an electrode and a TFT (thin film transistor) are formed and another transparent substrate on which a counter electrode is formed. Light emitted from a light source such as an ultra-high pressure mercury lamp (UHP lamp), a metal halide lamp, a white LED, etc. passes through an ultraviolet light cut filter and is separated into three primary colors, after which they pass through respective color polarizing plates having carriers for blue, green, and red channels. The light is then integrated, magnified by a projection lens, and projected onto a screen. Alternatively, using LEDs corresponding to blue, green, and red, light emitted from the LED having each color passes through a respective color polarizing plate having a support for each of blue, green, and red channels, then is integrated, enlarged by a projection lens, and projected onto a screen.

[0046]

The polarizing plate for a color liquid crystal projector thus constructed has the following features: it is excellent in polarization properties and, in addition, discoloration and deterioration of polarization properties do not occur even in a high-temperature and high-humidity state.

Examples

[0047]

Hereinafter, the present invention will be described in more detail by examples. However, these examples are for illustrative purposes only and should not be construed as limiting the invention in any way. Unless otherwise specified, "%" and "parts" in the examples are by weight.

[0048]

[ example 1]

13.7 parts of 4-aminobenzoic acid are added to 500 parts of water and dissolved with sodium hydroxide. After cooling, 32 parts of 35% aqueous hydrochloric acid and subsequently 6.9 parts of sodium nitrite are added at a temperature of 10 ℃ or less, and the reaction mixture is stirred at 5 to 10 ℃ for 1 hour. To this was added 20.9 parts of sodium aniline- ω -methanesulfonate, and while stirring the reaction mixture at 20-30 ℃, sodium carbonate was added to adjust the pH to 3.5. By further stirring, the coupling reaction was completed and the monoazo compound was obtained by filtration. The obtained monoazo compound was stirred at 90 ℃ in the presence of sodium hydroxide to obtain 17 parts of a monoazo compound represented by the following general formula (7).

[0049]

[0050]

After 12 parts of the monoazo compound represented by the general formula (7) and 21 parts of 4, 4 '-dinitrostilbene-2, 2' -sulfonic acid were dissolved in 300 parts of water, 12 parts of sodium hydroxide was added and the reaction mixture was allowed to undergo a condensation reaction at 90 ℃. Then, the reaction mixture was reduced with 9 parts of glucose, salted out with sodium chloride, and filtered to obtain 16 parts of an azo compound represented by the general formula (2). This compound is orange in color and its solution in 20% aqueous pyridine shows maximum absorption at a wavelength of 444 nm.

[0051]

[ example 2]

After 12 parts of the monoazo compound represented by the general formula (7) and 10 parts of 4, 4 '-dinitrostilbene-2, 2' -sulfonic acid were dissolved in 300 parts of water, 24 parts of sodium hydroxide was added and the reaction mixture was allowed to undergo condensation reaction at 90 ℃. Then, the reaction mixture was reduced with 18 parts of glucose, salted out with sodium chloride, and filtered to obtain 20 parts of an azo compound represented by the general formula (3). This compound was orange in color and its solution in 20% aqueous pyridine showed maximum absorption at a wavelength of 428 nm.

[0052]

[ example 3]

To 500 parts of water, 13.7 parts of 4-aminobenzoic acid was added and dissolved with sodium hydroxide. After cooling, 32 parts of 35% aqueous hydrochloric acid and subsequently 6.9 parts of sodium nitrite are added at a temperature of 10 ℃ or less, and the reaction mixture is stirred at 5 to 10 ℃ for 1 hour. To this was added 13.7 parts of 2-methoxy-5-methylaniline, and while stirring the reaction mixture at 20 to 30 ℃, sodium carbonate was added to adjust the pH to 3.5. By further stirring, the coupling reaction was completed and the reaction mixture was filtered to obtain a monoazo compound. The obtained monoazo compound was stirred at 90 ℃ in the presence of sodium hydroxide to obtain 26 parts of a monoazo compound represented by the following general formula (8).

[0053]

[0054]

14 parts of a monoazo compound represented by the general formula (8) and 21 parts of 4, 4 '-dinitrostilbene-2, 2' -sulfonic acid were dissolved in 300 parts of water, and condensation was performed at 90 ℃ after 12 parts of sodium hydroxide was added. Then, the reaction mixture was reduced with 9 parts of glucose, salted out with sodium chloride, and filtered to obtain 16 parts of an azo compound represented by the general formula (6). This compound was red in color and its solution in 20% aqueous pyridine showed maximum absorption at a wavelength of 444 nm.

[0055]

[ example 4]

A polyvinyl alcohol film having a thickness of 75 μm was dipped in an aqueous solution, which was maintained at 45 ℃ and contained the compound (2) obtained in example 1 at a concentration of 0.01% and sodium sulfate at a concentration of 0.1%, for 4 minutes. This film was stretched five times in a 3% boric acid aqueous solution at 50 ℃ and washed with water in the stretched state, and dried to obtain a polarizing film.

Table 1 shows (a) the maximum absorption wavelength, (b) the single-plate light transmittance, (c) the polarization coefficient, and (d) the contrast ratio, and (b) to (d) are measured at the maximum absorption wavelength of the obtained polarizing film.

[0056]

The transmittance of polarized light (transmittance of fully polarized light (parallel: Ky, perpendicular: Kz)) radiated in directions parallel and perpendicular to the orientation of the polarizing film obtained above was measured by a spectrophotometer (U-4100, manufactured by Hitachi, ltd.).

The polarization coefficient, the single-plate transmittance of natural light, the transmittance at a vertical position when two polarizing plates are vertically superimposed on each other in orientation, and the contrast ratio were calculated from Ky and Kz values obtained by the above measurement according to the following formulas (1) to (4).

(polarization coefficient) ═ k (Ky-Kz)/(Ky + Kz) (1)

(single-plate transmittance) ((Ky + Kz)/2 (2))

(light transmittance in vertical position) ═ Ky × Kz/100 (3)

(contrast ratio) ═ Ky/Kz (4)

[00571

[ example 5]

A polarizing film was produced in the same manner as in example 4, using a dye containing the compound (3) obtained in example 2 at a concentration of 0.03% and an aqueous solution containing sodium sulfate at a concentration of 0.01%, which were maintained at 45 ℃. Table 1 shows (a) the maximum absorption wavelength, (b) the single-plate transmittance, (c) the polarization coefficient, and (d) the contrast ratio, which are measured at the maximum absorption wavelength.

[0058]

[ comparative example 1]

A polarizing film was produced in the same manner as in example 4, except that a 0.01% aqueous solution of c.i. direct orange 39 (a dye containing a compound represented by the following structural formula (9) as a main component) was used in place of the compound (2) obtained in example 1. The (a) maximum absorption wavelength, (b) single plate transmittance, (c) polarization coefficient and (d) contrast ratio are shown in table 1, where (b) - (d) were measured at the maximum absorption wavelength, which shows that the polarization coefficient and contrast ratio are much worse than in examples 4 and 5 at the same transmittance.

[0059]

[0060]

TABLE 1

	Compound (I)	Maximum absorption wavelength	Transmittance of single plate	Polarization coefficient	Contrast ratio
						Example 4	(2)	462nm	43.79％	99.55％	443
Example 5	(3)	445nm	43.82％	99.43％	350
						Comparative example 1	(9)	447nm	43.79％	99.24％	262

[0061]

[ example 6]

A polyvinyl alcohol film having a thickness of 75 μm was immersed in an aqueous solution maintained at 45 ℃ and containing the compound (2) obtained in example 1 at a concentration of 0.01%, c.i. direct red 81 at a concentration of 0.01%, a dye represented by the following structural formula (10) (described in example 1 of patent document 7) at a concentration of 0.03%, a dye represented by the following structural formula (11) (disclosed in example 23 of patent document 8) at a concentration of 0.03%, and sodium sulfate at a concentration of 0.1% for 4 minutes. This film was stretched five times in a 3% boric acid aqueous solution at 50 ℃ and washed with water in the stretched state, and dried to obtain an achromatic (gray in parallel position, black in vertical position) polarizing film. The single-plate average light transmittance, polarization coefficient and contrast ratio of the polarizing plate obtained in the entire visible light range are shown in table 2 and have a high polarization coefficient.

In addition, TAC films (film thickness 80 μm, trade name TD-80U, manufactured by Fujifilm Corporation) were adhered on both surfaces of the polarizing film using a PVA adhesive to obtain the polarizing plate of the present invention. On one side of this polarizer plate, an acrylic pressure sensitive adhesive is applied to provide an adhesive backed polarizer plate. This polarizing plate was cut into a size of 30mm × 40mm and adhered to a glass plate of the same size. When this polarizing plate was stored under high temperature conditions of 105 ℃ for 1200 hours and under high temperature and high humidity conditions of 85 ℃x85% RH for 1200 hours, the change in polarization coefficient was less than 0.1%, showing long-term durability of the polarizing plate even under the high temperature and high humidity conditions.

[0062]

[0063]

[0064]

[ comparative example 2]

An achromatic polarizing film was prepared in the same manner as in example 6, except that a 0.01% aqueous solution of c.i. direct orange 39 was used instead of the compound (2) obtained in example 1. The average transmittance of the single plate, the polarization coefficient and the contrast ratio over the entire visible light range are shown in table 2. Not only was the average transmittance of the single sheet low, but the polarization characteristics and contrast ratio were far inferior to those of the polarizing film of example 6.

[0065]

TABLE 2

	Transmittance of single plate	Polarization coefficient	Contrast ratio
				Example 6	43.99％	99.61％	511
Comparative example 2	43.82％	99.28％	277

[0066]

[ example 7]

A polyvinyl alcohol film having a thickness of 75 μm was immersed in an aqueous solution containing the compound (2) obtained in example 1 at a concentration of 0.05%, c.i. direct yellow 28 at a concentration of 0.01%, a dye represented by the following structural formula (12) (described as compound No.1 in patent document 3) at a concentration of 0.01%, and sodium sulfate at a concentration of 0.1% held at 45 ℃ for 4 minutes. This film was stretched five times in a 3% boric acid aqueous solution at 50 ℃ and washed with water in the stretched state, and dried to obtain a polarizing film. The maximum absorption wavelength (λ max) of the obtained polarizing film was 450nm, and in the range of 430-500nm, the single-plate average light transmittance, the average light transmittance at the vertical position, and the contrast ratio were as shown in table 3 and had a high polarization coefficient. In addition, a TAC film (film thickness 80 μm, trade name TD-80U, manufactured by Fujifilm Corporation) having one side formed with a UV (ultraviolet light) curable hard film layer in a thickness of about 10 μm was adhered to one side of the polarizing film using a PVA adhesive and the other side, to obtain the polarizing plate of the present invention. An acrylic ester pressure sensitive adhesive is applied to one side of the polarizing plate to provide a polarizing plate having a pressure sensitive adhesive layer. In addition, an AR (anti-reflection) multi-coating treatment is performed on the outer surface of the hard coat layer by vacuum deposition. This polarizing plate was cut into a size of 30mm × 40mm and adhered to a transparent glass plate having an AR layer on one side of the same size to obtain the color polarizing plate with an AR support for a liquid crystal projector (for blue channel) of the present invention. The color polarizing plate for a liquid crystal projector of the present embodiment has a high polarization coefficient, and in addition, exhibits long-lasting durability even under high temperature and high humidity conditions. Furthermore, the resistance to long-term light irradiation is excellent.

[0067]

[0068]

[ example 8]

A polarizing plate was produced in the same manner as in example 7, except that a dye containing the compound (3) obtained in example 2 at a concentration of 0.05%, c.i. direct yellow 28 at a concentration of 0.01%, a dye represented by the general structural formula (12) (described as compound No.1 in patent document 3), and an aqueous solution containing sodium sulfate at a concentration of 0.1%, which were maintained at 45 ℃, were used. The average transmittance of the single plate, the average transmittance at the vertical position, and the contrast ratio of the polarizing plate having a high polarization coefficient in the range of 430-500nm are shown in table 3.

[0069]

[ comparative example 3]

A polarizing plate was produced in the same manner as in example 7, except that c.i. direct orange 39 was contained at a concentration of 0.05%, a dye represented by the above general structural formula (12) (described as compound No.1 in patent document 3) was contained at a concentration of 0.02%, and an aqueous solution containing sodium sulfate at a concentration of 0.1%, which was maintained at 45 ℃. The polarizing plate exhibited the average transmittance of the single plate, the average transmittance at the vertical position, and the contrast ratio as listed in table 3 in the range of 430-500 nm. When the average light transmittance in the vertical position was adjusted to the same level as in examples 7 and 8, the single-plate average light transmittance was reduced by about 1% and the contrast ratio was still insufficient. In addition, when the average light transmittance of the single plate was adjusted to the same level as in examples 7 and 8, the performance of the contrast ratio was far inferior, being 1/3 or less.

[0070]

TABLE 3

	Average light transmittance of single plate	Average light transmittance in vertical position	Contrast ratio
				Example 7	41.71％	0.01％	3854
Example 8	41.68％	0.01％	3577
				Comparative example 3 (when the average light transmittance in the vertical position is adjusted)	40.89％	0.01％	3041
Comparative example 3 (when the average light transmittance of a single plate is adjusted)	41.67％	0.04％	1037

Industrial applicability

[0071]

The azo compound of the present invention and salts thereof can be used as a dye for a polarizing film. Therefore, the compound and the salt are used for various liquid crystal displays and liquid crystal projectors. More particularly, they are suitable for in-aircraft applications and display applications for industrial instruments.

Claims (9)

1. An azo compound represented by the following general formula (1):

wherein R1 and R2 each independently represent a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms, and a lower alkoxy group having 1 to 4 carbon atoms; n is 1 or 2.

2. The azo compound and a salt thereof according to claim 1, wherein R1 and R2 are each independently one of a hydrogen atom, a methyl group, and a methoxy group.

3. The azo compound according to claim 1, wherein R1 and R2 are hydrogen atoms, and salts thereof.

4. Dye-containing polarizing film comprising at least one azo compound according to any of claims 1 to 3 and/or salts thereof in the substrate of the polarizing film.

5. Dye-containing polarizing film comprising at least one azo compound according to any of claims 1 to 3 and/or salts thereof and at least one further organic dye in the substrate of the polarizing film.

6. Dye-containing polarizing film comprising two or more azo compounds according to any of claims 1 to 3 and/or salts thereof and at least one further organic dye in the substrate of the polarizing film.

7. The dye-containing polarizing film according to any one of claims 4 to 6, wherein the polarizing film substrate is a film containing a polyvinyl alcohol resin.

8. A dye-containing polarizing plate comprising a transparent protective layer adhered to at least one surface of the dye-containing polarizing film according to any one of claims 4 to 7.

9. The color polarizing plate for a liquid crystal projector, wherein the dye-containing polarizing film or the dye-containing polarizing plate according to any one of claims 4 to 8 is used.