Polarizing film of a hydrophilic polymer film containing a novel azo compound

The present invention is concerned with a novel azo compound represented by formula (1), (2) or (3), a water-soluble dye comprising this azo compound, and a polarizing film containing this azo compound. The obtained polarizing film has high hydrothermoresistance and a high polarization degree and is excellent in optical characteristics: ##STR1## wherein each of R.sub.1, R.sub.3 and R.sub.12 is independently a hydrogen atom, halogen atom, hydroxyl group, alkyl group having 1 or 2 carbon atoms, or alkoxy group having 1 or 2 carbon atoms; each of R.sub.2, R.sub.4, R.sub.8 and R.sub.9 is independently a hydrogen atom, hydroxyl group, alkyl group having 1 or 2 carbon atoms, alkoxy group having 1 or 2 carbon atoms, or acetylamino group; R.sub.5 is a hydroxyl group or amino group at the o-position or p-position to the azo group; each of R.sub.6 and R.sub.10 is a hydrogen atom, carboxyl group, or alkoxy group having 1 or 2 carbon atoms; each of R.sub.7 and R.sub.11 is a hydrogen atom, hydroxyl group, amino group, methylamino group, .beta.-hydroxyethylamino group, acetylamino group, or phenylamino or benzoylamino group in which the phenyl nucleus may be substituted by a nitro group, amino group, hydroxyl group, alkyl group having 1 or 2 carbon atoms, carboxyl group, sulfonic group or chlorine atom; p is 0 or 1; and q is 0, 1 or 2.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a novel azo compound, its metal complex 
compound, a water-soluble azo dye containing the same, and a polarizing 
film having a high polarization degree in which the above-mentioned dye is 
contained and oriented as a dichromatic dye in a polymer film. 
2. Description of the Prior Art 
As a polarizing element for use in a polarizing film, iodine has heretofore 
been used, and in recent years, the utilization of organic dyes has also 
been investigated. 
However, iodine which has heretofore been used has a high polarization 
performance, but since having large sublimation properties, iodine is 
disadvantageously poor in heat resistance, when added as the polarizing 
element to a polarizing film. 
In order to overcome this drawback, there have been suggested some 
polarizing films containing organic dyes as the polarizing elements and 
having improved heat resistance in Japanese Patent Publication Nos. 
61988/1990 [CA 102(4): 26357w], 50944/1992 [CA 104(10): 70283j], 
61893/1992 [CA 104(10): 69953w), U.S. Pat. No. 4,514,559, Japanese Patent 
Application Laid-open Nos. 269136/1990 (U.S. Pat. No. 5,007,942), 
222459/1990 (U.S. Pat. No. 5,272,259), 226162/1992 (U.S. Pat. No. 
5,122,557); 68902/1991 (CA 115(24): 266442g) and 89203/1991 [CA 116(22): 
224369d). 
However, such polarizing films are not always satisfactory from the 
standpoint of polarizing performance. 
Thus, it is desired to develop a dye for a dye-based polarizing film which 
can exert the polarizing performance comparable to that of an iodine-based 
polarizing film. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an azo compound suitable 
for a polarizing film containing a polymer film as a base material, and a 
high-performance polarizing film having excellent polarizing properties 
and heat resistance obtained by orienting and adding the compound. 
The present inventors have conducted research with the intention of 
obtaining a polarizing film containing an azo compound as a polarizing 
element that has excellent polarizing performance and high 
hydrothermo-resistance, and as a result, the present invention has now 
been attained. That is, one aspect of the present invention is directed to 
an azo compound represented by formula (1), (2) or (3): 
##STR2## 
wherein each of R.sub.1 and R.sub.3 is independently a hydrogen atom, 
halogen atom, hydroxyl group, alkyl group having 1 or 2 carbon atoms, or 
alkoxy group having 1 or 2 carbon atoms; each of R.sub.2 and R.sub.4 is 
independently a hydrogen atom, hydroxyl group, alkyl group having 1 or 2 
carbon atoms, alkoxy group having 1 or 2 carbon atoms, or acetylamino 
group; R.sub.5 is a hydroxyl group or amino group at the o-position or 
p-position to the azo group; R.sub.6 is a hydrogen atom, carboxyl group, 
or alkoxy group having 1 or 2 carbon atoms; R.sub.7 is a hydrogen atom, 
hydroxyl group, amino group, methylamino group, .beta.-hydroxyethylamino 
group, acetylamino group, or phenylamino or benzoylamino group in which 
the phenyl nucleus may be substituted by a nitro group, amino group, 
hydroxyl group, alkyl group having 1 or 2 carbon atoms, carboxyl group, 
sulfonic group or chlorine atom; p is 0 or 1; and q is 0, 1 or 2, 
##STR3## 
wherein each of R.sub.8 and R.sub.9 is independently a hydrogen atom, 
hydroxyl group, alkyl group having 1 or 2 carbon atoms, alkoxy group 
having 1 or 2 carbon atoms, or acetylamino group; R.sub.10 is a hydrogen 
atom, carboxyl group, or alkoxy group having 1 or 2 carbon atoms; R.sub.11 
is a hydrogen atom, hydroxyl group, amino group, methylamino group, 
.beta.-hydroxyethylamino group, acetylamino group, or phenylamino or 
benzoylamino group in which the phenyl nucleus may be substituted by a 
nitro group, amino group, hydroxyl group, alkyl group having 1 or 2 carbon 
atoms, carboxyl group, sulfonic group or chlorine atom; R.sub.12 is a 
hydrogen atom, hydroxyl group, alkyl group having 1 or 2 carbon atoms, or 
alkoxy group having 1 or 2 carbon atoms; p is 0 or 1; q is 0, 1 or 2; and 
M is copper, nickel, zinc or iron, 
##STR4## 
wherein each of R.sub.8 and R.sub.9 is independently a hydrogen atom, 
hydroxyl group, alkyl group having 1 or 2 carbon atoms, alkoxy group 
having 1 or 2 carbon atoms, or acetylamino group; R.sub.10 is a hydrogen 
atom, carboxyl group, or alkoxy group having 1 or 2 carbon atoms; R.sub.11 
is a hydrogen atom, hydroxyl group, amino group, methylamino group, 
.beta.-hydroxyethylamino group, acetylamino group, or phenylamino or 
benzoylamino group in which the phenyl nucleus may be substituted by a 
nitro group, amino group, hydroxyl group, alkyl group having 1 or 2 carbon 
atoms, carboxyl group, sulfonic group or chlorine atom; p is 0 or 1; q is 
0, 1 or 2; and M is copper, nickel, zinc or iron. 
Furthermore, the present invention is directed to a water-soluble dye 
comprising the above-mentioned compound, a polarizing film in which the 
above-mentioned compound is oriented and contained in a polymer film, and 
a method for preparing a polarizing film which comprises stretching, at a 
stretch ratio of from 2 times to 9 times, a polymer film dyed with the 
above-mentioned water-soluble dye. 
The water-soluble dye comprising the novel azo compound of the present 
invention and the polarizing film using this dye can provide industrially 
valuable and remarkable effects such as high hydrothermoresistance and 
high polarization degree, and optical characteristics comparable to those 
of a conventional polarizing film using iodine.

DETAI LED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The azo compound represented by formula (1) of the present invention can be 
prepared by a known diazotization and coupling technique in accordance 
with a usual preparation method of the azo compound. 
That is, the azo compound represented by formula (1) can be obtained in the 
form of a free acid in accordance with a known process, for example, by 
first tetrazotizing a diaminostilbene of formula (4): 
##STR5## 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are as defined in formula 
(1), in a known manner, for example, with sodium nitrite at 
0.degree.-30.degree. C. in a mineral acid, and then coupling with a 
naphthalene represented by formula (5): 
##STR6## 
wherein R.sub.5, R.sub.6, R.sub.7, p and q are as defined in formula (1), 
at a temperature of 0.degree. to 30.degree. C. at pH 5-10. Needless to 
say, the azo compound of the present invention can also be prepared by a 
preparation route other than this procedure. 
A preferable example of the compound represented by formula (1) is a 
compound wherein R.sub.5 is a hydroxyl group or amino group at the 
o-position to the azo group, and R.sub.7 is a hydrogen atom, hydroxyl 
group, amino group, methylamino group, .beta.-hydroxyethylamino group, 
acetylamino group, phenylamino group or benzoylamino group. 
The azo compound represented by formula (2) of the present invention can be 
prepared by a known diazotization and coupling technique in accordance 
with a usual preparation method of an azo dye. 
That is, an aminostilbene represented by formula (6): 
##STR7## 
wherein R.sub.8, R.sub.9 and R.sub.12 are as defined in formula (2), is 
tetrazotized in a known manner, for example, with sodium nitrite at 
0.degree.-30.degree. C. in a mineral acid, and then coupled with a 
naphthalene represented by formula (7): 
##STR8## 
wherein R.sub.10, R.sub.11, p and q are as defined in formula (2), at a 
temperature of 0.degree. to 30.degree. C. at pH 5-10 to obtain an azo 
compound represented by formula (8): 
##STR9## 
wherein R.sub.8, R.sub.9, R.sub.10, R.sub.11, R.sub.12, p and q are as 
defined in formula (2), 
in the form of a free acid. Needless to say, the azo compound of the 
present invention can also be prepared by a preparation route other than 
this procedure. 
The thus obtained azo compound represented by formula (8) can be easily 
complexed with a transition metal by the following process to form a 
transition metal-containing azo compound represented by formula (2) of the 
present invention. 
For example, the azo compound represented by formula (8) is dissolved or 
dispersed in water and/or a hydrophilic solvent, for example, a mixed 
solvent of water and ethylene glycol or ethyl cellosolve, and the solution 
is then mixed with an aqueous solution of copper sulfate, copper chloride, 
tetraminecopper, copper acetate, nickel sulfate, nickel chloride, nickel 
acetate, zinc sulfate, zinc chloride, iron sulfate or iron chloride at a 
temperature of 50.degree. to 100.degree. C., preferably 90.degree. C. or 
more under alkaline conditions, preferably in the presence of ammonia, 
monoethanolamine or diethanolamine, thereby obtaining the desired 
transition metal-containing azo compound represented by formula (2). 
A preferable example of the compound represented by formula (2) is a 
compound wherein R.sub.11 is a hydrogen atom, hydroxyl group, amino group, 
methylamino group, .beta.-hydroxyethylamino group, acetylamino group, 
phenylamino group or benzoylamino group. 
Moreover, the azo compound represented by formula (3) of the present 
invention can be prepared by a known diazotization and coupling technique 
in accordance with a usual preparation method of an azo dye. 
That is, a diaminostilbene represented by formula (9): 
##STR10## 
wherein R.sub.8 and R.sub.9 are as defined in formula (3), is tetrazotized 
in a known manner, for example, with sodium nitrite at 
0.degree.-30.degree. C. in a mineral acid, and then coupled with a 
naphthalene represented by formula (10): 
##STR11## 
wherein R.sub.10, R.sub.11, p and q are as defined in formula (3), at a 
temperature of 0.degree. to 30.degree. C. at pH 5-10 to obtain an azo 
compound represented by formula (11): 
##STR12## 
wherein R.sub.8, R.sub.9, R.sub.10, R.sub.11, p and q are as defined in 
formula (3), 
in the form of a free acid. Needless to say, the azo compound of the 
present invention can also be prepared by a preparation route other than 
this procedure. 
The thus obtained azo compound represented by formula (11) can be easily 
complexed with a transition metal by the following process to form a 
transition metal-containing azo compound represented by formula (3) of the 
present invention. 
For example, the azo compound represented by formula (11) is dissolved or 
dispersed in water and/or a hydrophilic solvent, for example, a mixed 
solvent of water and ethylene glycol or ethyl cellosolve, and the solution 
is then mixed with an aqueous solution of copper (II) sulfate, copper (II) 
chloride, tetramminecopper (II), copper (II) acetate, nickel (II) sulfate, 
nickel (II) chloride, nickel (II) acetate, zinc (II) sulfate, zinc (II) 
chloride, iron (II) sulfate or iron (II) chloride at a temperature of 
50.degree. to 100.degree. C., preferably 90.degree. C. or more under 
alkaline conditions, preferably in the presence of ammonia, 
monoethanolamine or diethanolamine, thereby obtaining the desired 
transition metal-containing azo compound represented by formula (3). 
A preferable example of the compound represented by formula (3) is a 
compound wherein R.sub.11 is a hydrogen atom, hydroxyl group, amino group, 
methylamino group, .beta.-hydroxyethylamino group, acetylamino group, 
phenylamino group or benzoylamino group. 
The azo compounds represented by formulae (1), (2) and (3) of the present 
invention are usually utilized in the form of sodium salts, but they can 
also be utilized in the form of free acids or other salts such as 
potassium salts, lithium salts, ammonium salts, alkylamine salts and 
ethanolamine salts. 
In the present invention, the diaminostilbenes represented by formulae (4), 
(6) and (9) can be prepared by usual methods. For example, typical known 
preparation methods of these diaminostilbenes are described in Kogyo 
Kagaku Zasshi (J. Chem. Soc. Jpn. Ind. Chem. Sect.), Vol. 73, No. 1, pp. 
187-194 (1970) or Indian Journal of Chemistry, Vol. 25B, pp. 485-488, May 
1986. 
That is, in the case of a typical example, a compound represented by 
formula (12) and a compound of formula (13) are reacted with each other at 
a temperature of 100.degree. to 200.degree. C. in the presence of a base 
such as piperidine in an aprotic polar solvent such as 
N,N-dimethylformamide, or alternatively, they are reacted at a temperature 
of 10.degree. to 100.degree. C. in the presence of a catalyst such as 
benzyltriethylammonium chloride (BTEA) in an aqueous alkaline solution to 
obtain a compound represented by formula (14): 
##STR13## 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are as defined in formula 
(1). 
Furthermore, nitro groups of the compound represented by formula (14) can 
be reduced in a known manner to obtain any of the desired diaminostilbenes 
represented by formulae (4), (6) and (9). 
Typical examples of the naphthalenes represented by formulae (5), (7) and 
(10) include 1-hydroxy-6-aminonaphthalene-3-sulfonic acid (hereinafter 
abbreviated to "J acid"), N-phenyl J acid, N-methyl J acid, N-acetyl J 
acid, N-methyl-N-acetyl J acid, N-benzoyl J acid, N-(3- or 
4-carboxyphenyl) J acid, N-(3-or 4-sulfophenyl) J acid, 
N-(4-amino-3-sulfophenyl) J acid, N-(4-hydroxy-3-carboxyphenyl) J acid, 
N-(4-aminobenzoyl) J acid, N-(4-amino-3-sulfobenzoyl) J acid, 
N-(4-hydroxy-3-carboxybenzoyl) J acid, N-(4-nitrophenyl) J acid, 
N-(4-nitrobenzoyl) J acid, N-(4-amino-3-methylbenzoyl) J acid, N-(3- or 
4-carboxybenzoyl) J acid, N-(3-or 4-sulfobenzoyl) J acid, 
N-(.beta.-hydroxyethyl) J acid, 1-hydroxy-7-aminonaphthalene-3-sulfonic 
acid (hereinafter abbreviated to ".gamma. acid"), N-phenyl .gamma. acid, 
N-methyl .gamma. acid, N-acetyl .gamma. acid, N-methyl-N-acetyl .gamma. 
acid, N-benzoyl .gamma. acid, N-(3- or 4-carboxyphenyl) .gamma. acid, 
N-(3- or 4-sulfophenyl) .gamma. acid, N-(4-amino-3-sulfophenyl) .gamma. 
acid, N-(4-hydroxy-3-carboxyphenyl) .gamma. acid, N-(4-aminobenzoyl) 
.gamma. acid, N-(4-amino-3sulfobenzoyl) .gamma. acid, 
N-(4-hydroxy-3-carboxybenzoyl) .gamma. acid, N-(4-nitrophenyl) .gamma. 
acid, N-(4-nitrobenzoyl) .gamma. acid, N-(4-amino-3-methylbenzoyl) .gamma. 
acid, N-(3- or 4-carboxybenzoyl) .gamma. acid, N-(3- or 4-sulfobenzoyl) 
.gamma. acid, N-(.beta.-hydroxyethyl) .gamma. acid, 
1-hydroxy-8-aminonaphthalene-3,6-disulfonic acid (hereinafter abbreviated 
to "H acid"), N-acetyl H acid, N-benzoyl H acid, N-(p-toluenesulfonyl) H 
acid, N-(benzenesulfonyl) H acid, N-(p-chlorobenzoyl) H acid, 
1-hydroxy-8-aminonaphthalene-3,5-disulfonic acid (hereinafter abbreviated 
to "K acid"), N-acetyl K acid, 1-hydroxy-8-aminonaphthalene-5,7-disulfonic 
acid, 1-hydroxy-7-aminonaphthalene-3,6-disulfonic acid, N-(p-methylphenyl) 
J acid, 1-naphthol-3,6-disulfonic acid and 
1-amino-2-ethoxynaphthalene-6-sulfonic acid. A part of these naphthalenes 
are commercially available. 
A preferable example of the polymer film for use in the polarizing film of 
the present invention is a hydrophilic polymer film, and typical examples 
of its material include polyvinyl alcohol, polyvinyl formal, polyvinyl 
acetal, polyvinyl butyral, copolymers thereof with ethylene, propylene, 
acrylic acid or N-acryloyhnaleimide, and cellulosic resins. These high 
polymers are particularly useful, because they are excellent in solubility 
in water or a hydrophilic organic solvent, compatibility with the compound 
of the present invention and film-forming properties, and they also permit 
the compound of the present invention to be easily oriented at the time of 
stretching/orientation after the film formation. 
As methods for preparing the polarizing film of the present invention by 
the use of the above-mentioned high polymer and the compound of the 
present invention, there are (1) a method which comprises forming a film 
from the high polymer, stretching the film, and then dyeing the stretched 
film with the compound of the present invention; (2) a method which 
comprises forming a film from the high polymer, dyeing the film with the 
compound of the present invention, and then stretching the dyed film; and 
(3) a method which comprises adding the compound of the present invention 
to a solution of the high polymer, forming a dyed film and then stretching 
the dyed film. 
The above-mentioned method (3) for preparing the dyed film can be usually 
carried out by the following procedure. That is, the high polymer is 
dissolved in water and/or a hydrophilic organic solvent such as an 
alcohol, glycerin or dimethylformamide, adding the compound of the present 
invention to the solution to perform dope-dyeing, and then forming the 
dyed film from the dyed solution by flow casting, solution coating, 
extrusion or the like. 
The concentration of the high polymer which is dissolved in the solvent 
depends upon the kind of high polymer itself, but it is in the range of 5 
to 30 wt %, preferably 10 to 20 wt %. Furthermore, the concentration of 
the compound of the present invention which is dissolved in the solvent 
depends upon the kind of high polymer, the kind of compound, the thickness 
of the formed film, the required performance of the obtained polarizing 
film and the like, but it is in the range of about 0.1 to 5 wt %, 
preferably about 0.8 to 2.5 wt % based on the weight of the high polymer. 
The above-mentioned methods (1) and (2) can be carried out by the following 
procedure. That is, if necessary, an inorganic salt such as sodium 
chloride or Glauber's salt and a dyeing assistant such as a surface active 
agent are added to a dye bath containing 0.1 to 5 wt %, preferably 0.8 to 
2.5 wt % of the compound of the present invention based on the weight of 
the film, and the high polymer film is then immersed in the dye bath at 
20.degree.-80.degree. C., preferably 30.degree.-50.degree. C. for a period 
of 1-60 minutes, preferably 3-20 minutes to dye the film, followed by 
drying. 
As techniques of the stretching in the above-mentioned (1), (2) and (3), 
there are draw stretching in a wet manner, draw stretching in a dry manner 
and compressive stretching between rolls in a dry manner, and any of these 
techniques can be employed. A stretch ratio is in the range of from 2 
times to 9 times, but when polyvinyl alcohol or its derivative is used, 
the stretch ratio is preferably in the range of from 2.5 times to 6 times. 
After the stretching/orientation treatment, a boric acid treatment is 
carried out for the purpose of improving the water resistance and the 
polarizing properties of the stretched film. The boric acid treatment 
permits the improvement of the light transmission and the polarization 
degree of the polarizing film. Conditions for the boric acid treatment 
depend upon the kind of hydrophilic high polymer to be used and the kind 
of the azo compound, but in general, the concentration of boric acid is in 
the range of 1 to 15 wt %, preferably 3 to 10 wt % and a treatment 
temperature is in the range of 30.degree. to 80.degree. C., preferably 
40.degree. to 80.degree. C. If the concentration of boric acid is less 
than 1 wt % and/or the treatment temperature is less than 30.degree. C., 
the effect of this treatment is low, and if the concentration of boric 
acid is more than 15 wt % and/or the treatment temperature is more than 
80.degree. C., the obtained polarizing film is liable to be brittle. 
The azo compounds represented by formulae (1), (2) and (3) can be used 
singly or in combination thereof, and these compounds may be blended with 
another dye to prepare the polarizing film having an optional hue and the 
high polarization degree. 
As the other dye usable in this case, any dye can be used, so long as it is 
a dye having a high dichroism and having an absorption in a wavelength 
region different from that of the compound which are obtained in the 
present invention. Particularly preferable examples of the dye include, in 
terms of C. I. Generic Names, C. I. Direct Yellow 12, C. I. Direct Yellow 
44, C. I. Direct Yellow 28, C. I. Direct Yellow 142, C. I. Direct Red 2, 
C. I. Direct 10 Red 79, C. I. Direct Red 81, C. I. Direct Red 247, C. I. 
Direct Violet 9, C. I. Direct Violet 51, C. I. Direct Orange 26, C. I. 
Direct Orange 39, C. I. Direct Orange 107, C. I. Direct Blue 1, C. I. 
Direct Blue 71, C. I. Direct Blue 78, C. I. Direct Blue 168, C. I. Direct 
Brown 106, C. I. Direct Brown 223, C. I. Direct Green 85, C. I. Direct 
Black 17 and C. I. Direct Black 19. 
When the compound represented by formula (1), (2) or (3) is used as the 
blend component for gray or black which is particularly often used, the 
polarizing film having an excellent polarizing performance and preferable 
absorption characteristics can be obtained. In addition, the polarizing 
film is also excellent in hydrothermo-resistance. 
The thus prepared polarizing film can be used, after being subjected to 
some of various treatments. For example, in addition to its direct usage 
as the film or sheet, a protective layer of a polymer such as a 
triacetate, acrylate or urethane may be formed on the polarizing film by 
lamination prior to use, or a transparent conductive film such as an 
indium-tin oxide may be formed on the surface of the polarizing film by 
vapor deposition, sputtering or coating in compliance with the intended 
purpose. 
Next, the present invention will be described in detail with reference to 
examples, but these examples are merely exemplary and the scope of the 
present invention should not be limited to them. In the examples, part and 
parts mean part by weight and parts by weight, respectively. 
In the present invention, the polarization degree is a value measured in 
the following manner. That is, two polarizing films were put on a light 
path of a spectrophotometer, with the two polarizing films being 
superposed upon each other so that the stretching directions of these 
films might be parallel, and a light transmission (Tp) at a maximum 
absorption wavelength in a visible region was measured. On the other hand, 
the two polarizing films were superposed upon each other so that the 
stretching directions of these films might cross at right angles, and 
another light transmission (Tc) was measured at the same wavelength. On 
the basis of the thus measured values (Tp) and (Tc), the polarization 
degree (V) was calculated by the use of the following formula: 
##EQU1## 
EXAMPLE 1 
10 parts (0.035 mol) of 4,4'-diaminostilbene 2HCl were suspended in 200 
parts of water, and 14.6 parts of concentrated hydrochloric acid were then 
added thereto. Afterward, the solution was cooled to 5.degree.-10.degree. 
C. on ice, and 5.2 parts (0.075 mol) of sodium nitrite were then added and 
tetrazotization was carried out for 1 hour. Next, excess sodium nitrite 
was removed with sulfamic acid. The resulting aqueous tetrazonium salt 
solution was added dropwise at 5.degree.-10.degree. C. to a solution 
obtained by dissolving 26.6 parts (0.078 mol) of monosodium 
1-amino-8-naphthol-2,4-disulfonate in 550 parts of a 3.3% aqueous caustic 
soda solution to perform coupling. After stirring for 2 hours, a large 
excess of sodium chloride was added to conduct salting-out. After stirring 
overnight, the resulting precipitate was collected by filtration, washed 
with a 3% aqueous sodium chloride solution, and then dried to obtain 28 
parts of an azo compound represented by the following formula (15). Its 
yield was 91.8%. 
##STR14## 
Composition formula: C.sub.34 H.sub.26 N.sub.6 O.sub.14 S.sub.4 
______________________________________ 
Values of elemental analysis: 
C H N S 
______________________________________ 
Found (%) 46.89 3.01 9.65 14.73 
Calcd. (%) 46.72 3.00 9.57 14.80 
______________________________________ 
A 0.3 g/l dye bath of the compound of formula (15) was prepared and then 
maintained at 42.degree. C. Afterward, a polyvinyl alcohol film having a 
thickness of 75 .mu.m was immersed in the dye bath, and then dyed for 2 
minutes. The wet dyed film was stretched 5 times at 43.degree. C. in a 3% 
aqueous boric acid solution, washed with water in this state, and then 
dried to form a blue polarizing film. A polarization degree V of this 
polarizing film at an absorption maximum .lambda..sub.max was measured, 
and as a result, single plate transmission was 43%, .lambda..sub.max was 
650 nm, and V was 99.4%. 
This polarizing film was allowed to stand for 500 hours under conditions of 
80.degree. C. and a relative humidity of 85%, but a change of hue and the 
deterioration of the polarization degree were not substantially observed. 
EXAMPLE 2 
The same procedure as in Example 1 was carried out except that monosodium 
1-amino-8-naphthol-2,4-disulfonate was replaced with 26.6 parts (0.08 mol) 
of monosodium 1-hydroxy-8-aminonaphthalene-3,6-disulfonate, to obtain 29 
parts of an azo compound represented by the following formula (16). Its 
yield was 95.1%. 
##STR15## 
Composition formula: C.sub.34 H.sub.26 N.sub.6 O.sub.14 S.sub.4 
______________________________________ 
Values of elemental analysis: 
C H N S 
______________________________________ 
Found (%) 46.89 3.01 9.65 14.73 
Calcd. (%) 46.81 2.96 9.80 14.61 
______________________________________ 
A polyvinyl alcohol film was treated with an aqueous solution of the 
compound of formula (16) in the same manner as in Example 1 to prepare a 
polarizing film. This polarizing film was blue. A polarization degree V of 
the polarizing film at an absorption maximum .lambda..sub.max was 
measured, and as a result, single plate transmission was 43%, 
.lambda..sub.max was 630 nm, and V was 99.0%. 
This polarizing film was allowed to stand for 500 hours under conditions of 
80.degree. C. and a relative humidity of 85%, but a change of hue and the 
deterioration of the polarization degree were not substantially observed. 
EXAMPLE 3 
8 parts (0.033 mol) of 3-methoxy-4,4'-diaminostilbene were suspended in 160 
parts of water, and 20.6 parts of concentrated hydrochloric acid were then 
added thereto. Afterward, the solution was cooled to 5.degree.-10.degree. 
C. on ice, and 5.0 parts (0.072 mol) of sodium nitrite were then added and 
tetrazotization was carried out for 1 hour. Next, excess sodium nitrite 
was removed with sulfamic acid. The resulting aqueous tetrazonium salt 
solution was added dropwise at 5.degree.-10.degree. C. to a solution 
obtained by dissolving 25 parts (0.073 mol) of monosodium 
1-amino-8-naphthol-2,4-disulfonate in 550 parts of a 9% aqueous sodium 
carbonate solution to perform coupling. After stirring for 2 hours, a 
large excess of sodium chloride was added to conduct salting-out. After 
stirring overnight, the resulting precipitate was collected by filtration, 
washed with a 3% aqueous sodium chloride solution, and then dried to 
obtain 28 parts of an azo compound represented by the following formula 
(17). Its yield was 94.3%. 
##STR16## 
Composition formula: C.sub.35 H.sub.28 N.sub.6 O.sub.15 S.sub.4 
______________________________________ 
Values of elemental analysis: 
C H N S 
______________________________________ 
Found (%) 46.66 3.13 9.33 14.23 
Calcd. (%) 46.48 3.20 9.45 14.16 
______________________________________ 
A polyvinyl alcohol film was treated with an aqueous solution of the 
compound of formula (17) in the same manner as in Example 1 to prepare a 
polarizing film. This polarizing film was blue. A polarization degree V of 
the polarizing film at an absorption maximum .lambda..sub.max was 
measured, and as a result, single plate transmission was 42%, 
.lambda..sub.max was 660 nm, and V was 99.0%. 
This polarizing film was allowed to stand for 500 hours under conditions of 
80.degree. C. and a relative humidity of 85%, but a change of hue and the 
deterioration of the polarization degree were not substantially observed. 
EXAMPLE 4 
The same procedure as in Example 3 was carried out except that monosodium 
1-amino-8-naphthol-2,4-disulfonate was replaced with 25 parts (0.073 mol) 
of monosodium 1-hydroxy-8-aminonaphthalene-3,6-disulfonate, to obtain 29 
parts of an azo compound represented by the following formula (18). Its 
yield was 97.6%. 
##STR17## 
Composition formula: C.sub.35 H.sub.28 N.sub.6 O.sub.15 S.sub.4 
______________________________________ 
Values of elemental analysis: 
C H N S 
______________________________________ 
Found (%) 46.66 3.13 9.33 14.23 
Calcd. (%) 46.52 3.29 9.37 14.38 
______________________________________ 
A polyvinyl alcohol film was treated with an aqueous solution of the 
compound of formula (18) in the same manner as in Example 1 to prepare a 
polarizing film. This polarizing film was blue. A polarization degree V of 
the polarizing film at an absorption maximum .lambda..sub.max was 
measured, and as a result, single plate transmission was 43%, 
.lambda..sub.max was 645 nm, and V was 99.0%. 
This polarizing film was allowed to stand for 500 hours under conditions of 
80.degree. C. and a relative humidity of 85%, but a change of hue and the 
deterioration of the polarization degree were not substantially observed. 
EXAMPLE 5 
9 parts (0.033 mol) of 3,3'-dimethoxy-4,4'-diaminostilbene were suspended 
in 160 parts of water, and 20.6 parts of concentrated hydrochloric acid 
were then added thereto. Afterward, the solution was cooled to 
5.degree.-10.degree. C. on ice, and 5.0 parts (0.072 mol) of sodium 
nitrite were then added and tetrazotization was carried out for 1 hour. 
Next, excess sodium nitrite was removed with sulfamic acid. The resulting 
aqueous tetrazonium salt solution was added dropwise at 
5.degree.-10.degree. C. to a solution obtained by dissolving 25 parts 
(0.073 mol) of monosodium 1-amino-8-naphthol-2,4-disulfonate in 550 parts 
of a 9% aqueous sodium carbonate solution to perform coupling. After 
stirring for 2 hours, a large excess of sodium chloride was added to 
conduct salting-out. After stirring overnight, the resulting precipitate 
was collected by filtration, washed with a 3% aqueous sodium chloride 
solution, and then dried to obtain 29 parts of an azo compound represented 
by formula (19). Its yield was 94.5%. 
##STR18## 
Composition formula: C.sub.36 H.sub.30 N.sub.6 O.sub.16 S.sub.4 
______________________________________ 
Values of elemental analysis: 
C H N S 
______________________________________ 
Found (%) 46.45 3.25 9.03 13.78 
Calcd. (%) 46.52 3.41 8.95 14.01 
______________________________________ 
A polyvinyl alcohol film was treated with an aqueous solution of the 
compound of formula (19) in the same manner as in Example 1 to prepare a 
polarizing film. This polarizing film was blue. A polarization degree V of 
the polarizing film at an absorption maximum .lambda..sub.max was 
measured, and as a result, single plate transmission was 42%, 
.lambda..sub.max was 675 nm, and V was 99.0%. 
This polarizing film was allowed to stand for 500 hours under conditions of 
80.degree. C. and a relative humidity of 85%, but a change of hue and the 
deterioration of the polarization degree were not substantially observed. 
EXAMPLE 6 
The same procedure as in Example 5 was carried out except that monosodium 
1-amino-8-naphthol-2,4-disulfonate was replaced with 25 parts (0.073 mol) 
of monosodium 1-hydroxy-8-aminonaphthalene-3,6-disulfonate, to obtain 30 
parts of an azo compound represented by the following formula (20). Its 
yield was 97.7%. 
##STR19## 
Composition formula: C.sub.36 H.sub.30 N.sub.6 O.sub.16 S.sub.4 
______________________________________ 
Values of elemental analysis: 
C H N S 
______________________________________ 
Found (%) 46.45 3.25 9.03 13.78 
Calcd. (%) 46.59 3.16 9.18 13.85 
______________________________________ 
A polyvinyl alcohol film was treated with an aqueous solution of the 
compound of formula (20) in the same manner as in Example 1 to prepare a 
polarizing film. This polarizing film was blue. A polarization degree V of 
the polarizing film at an absorption maximum .lambda..sub.max was 
measured, and as a result, single plate transmission was 43%, 
.lambda..sub.max was 660 nm, and V was 99.0%. 
This polarizing film was allowed to stand for 500 hours under conditions of 
80.degree. C. and a relative humidity of 85%, but a change of hue and the 
deterioration of the polarization degree were not substantially observed. 
EXAMPLES 7 TO 26 
Following the same procedure as in Examples 1 to 6, compounds of formula 
(1) shown in Table 1 were prepared. In this table, hue, .lambda..sub.max, 
single plate transmission and polarization degree were all measured for 
dyed PVA films. With regard to hydrothermoresistance, each polarizing film 
was allowed to stand for 500 hours under conditions of 80.degree. C. and a 
relative humidity of 85%, and afterward, the change of hue and the 
deterioration of the polarization degree were observed. The polarizing 
film in which neither change of hue nor the deterioration of the 
polarization degree was observed was evaluated to be .largecircle.. 
3 TABLE 1 
- Example Structural Formula .lambda..sub.max (nm) A*.sup.1 B*.sup.2 
Hue C*.sup.3 
7 
##STR20## 
610 41 98 Blue .smallcircle. 
8 
##STR21## 
650 42 98 Blue .smallcircle. 
9 
##STR22## 
595 42 99 Violetblue .smallcircle. 
10 
##STR23## 
545 41 99 Red .smallcircle. 
11 
##STR24## 
615 41 98 Blue .smallcircle. 
12 
##STR25## 
620 42 97 Blue .smallcircle. 
13 
##STR26## 
645 42 98 Blue .smallcircle. 
14 
##STR27## 
625 42 99 Blue .smallcircle. 
15 
##STR28## 
635 42 99 Blue .smallcircle. 
16 
##STR29## 
650 42 99 Blue .smallcircle. 
17 
##STR30## 
620 42 99 Blue .smallcircle. 
18 
##STR31## 
610 42 99 Blue .smallcircle. 
19 
##STR32## 
625 42 99 Blue .smallcircle. 
20 
##STR33## 
620 42 99 Blue .smallcircle. 
21 
##STR34## 
655 42 99 Blue .smallcircle. 
22 
##STR35## 
660 42 99 Blue .smallcircle. 
23 
##STR36## 
615 42 99 Blue .smallcircle. 
24 
##STR37## 
655 42 99 Blue .smallcircle. 
25 
##STR38## 
645 42 99 Blue .smallcircle. 
26 
##STR39## 
595 42 99 Blue .smallcircle. 
*.sup.1 : Single plate transmission 
*.sup.2 : Polarization degree 
*.sup.3 : Hydrothermoresistance 
EXAMPLE 27 
15 parts (0.017 mol) of the compound represented by formula (17) described 
in Example 3 were dissolved in 300 parts of water, and 10 parts (0.164 
mol) of monoethanolamine, 5.3 parts (0.034 mol) of anhydrous copper (II) 
sulfate and 4.2 parts (0.034 mol) of aqueous ammonia were then added 
thereto, followed by heating at 80.degree. C. for 8 hours. Next, a large 
excess of sodium chloride was added to conduct salting-out, and after 
stirring overnight, the resulting precipitate was collected by filtration, 
washed with a 3% aqueous sodium chloride solution, and then dried to 
obtain 15.5 parts of an azo compound represented by the following formula 
(21). Its yield was 96.2%. 
##STR40## 
Composition formula: C.sub.34 H.sub.24 N.sub.6 O.sub.15 S.sub.4 Cu 
______________________________________ 
Values of elemental analysis: 
C H N S 
______________________________________ 
Found (%) 43.06 2.55 8.86 13.52 
Calcd. (%) 42.88 2.60 8.90 13.75 
______________________________________ 
A polyvinyl alcohol film was treated with an aqueous solution of the 
compound of formula (21) in the same manner as in Example 1 to prepare a 
polarizing film. This polarizing film was blue. A polarization degree V of 
the polarizing film at an absorption maximum .lambda..sub.max was 
measured, and as a result, single plate transmission was 42%, 
.lambda..sub.max was 690 nm, and V was 99.5%. 
This polarizing film was allowed to stand for 500 hours under conditions of 
80.degree. C. and a relative humidity of 85%, but a change of hue and the 
deterioration of the polarization degree were not substantially observed. 
EXAMPLE 28 
The same procedure as in Example 27 was carried out except that the 
compound of formula (17) and anhydrous copper sulfate were replaced with 
15 parts (0.017 mol) of the compound represented by formula (18) in 
Example 4 and 5.3 parts (0.038 mol) of nickel (II) sulfate, respectively, 
to obtain 15 parts of an azo compound represented by the following formula 
(22). Its yield was 93.8%. 
##STR41## 
Composition formula: C.sub.34 H.sub.24 N.sub.6 O.sub.15 S.sub.4 Ni 
______________________________________ 
Values of elemental analysis: 
C H N S 
______________________________________ 
Found (%) 43.28 2.56 8.91 13.59 
Calcd. (%) 43.19 2.60 8.85 13.75 
______________________________________ 
A polyvinyl alcohol film was treated with an aqueous solution of the 
compound of formula (22) in the same manner as in Example 1 to prepare a 
polarizing film. This polarizing film was blue. A polarization degree V of 
the polarizing film at an absorption maximum .lambda..sub.max was 
measured, and as a result, single plate transmission was 42%, 
.lambda..sub.max was 685 nm, and V was 99.0%. 
This polarizing film was allowed to stand for 500 hours under conditions of 
80.degree. C. and a relative humidity of 85%, but a change of hue and the 
deterioration of the polarization degree were not substantially observed. 
EXAMPLE 29 
15 parts (0.016 mol) of the compound represented by formula (19) described 
in Example 5 were dissolved in 300 parts of water, and 20 parts (0.328 
mol) of monoethanolamine, 10.3 parts (0.065 mol) of anhydrous copper (II) 
sulfate and 8.4 parts (0.067 mol) of aqueous ammonia were then added 
thereto, followed by heating at 80.degree. C. for 8 hours. Next, a large 
excess of sodium chloride was added to conduct salting-out, and after 
stirring overnight, the resulting precipitate was collected by filtration, 
washed with a 3% aqueous sodium chloride solution, and then dried to 
obtain 16 parts of an azo compound represented by formula (23). Its yield 
was 97.3%. 
##STR42## 
Composition formula: C.sub.34 H.sub.24 N.sub.6 O.sub.16 S.sub.4 Cu.sub.2 
______________________________________ 
Values of elemental analysis: 
C H N S 
______________________________________ 
Found (%) 39.73 2.35 8.18 12.48 
Calcd. (%) 39.92 2.29 8.10 12.39 
______________________________________ 
A polyvinyl alcohol film was treated with an aqueous solution of the 
compound of formula (23) in the same manner as in Example 1 to prepare a 
polarizing film. This polarizing film was blue. A polarization degree V of 
the polarizing film at an absorption maximum .lambda..sub.max was 
measured, and as a result, single plate transmission was 42%, 
.lambda..sub.max was 695 nm, and V was 99.5%. 
This polarizing film was allowed to stand for 500 hours under conditions of 
80.degree. C. and a relative humidity of 85%, but a change of hue and the 
deterioration of the polarization degree were not substantially observed. 
EXAMPLE 30 
The same procedure as in Example 29 was carried out except that the 
compound of formula (19) and anhydrous copper sulfate were replaced with 
15 parts (0.016 mol) of the compound represented by formula (20) in 
Example 6 and 5.5 parts (0.038 mol) of zinc (II) sulfate, respectively, to 
obtain 16 parts of an azo compound represented by the following formula 
(24). Its yield was 97.0%. 
##STR43## 
Composition formula: C.sub.34 H.sub.24 N.sub.6 O.sub.16 S.sub.4 Zn.sub.2 
______________________________________ 
Values of elemental analysis: 
C H N S 
______________________________________ 
Found (%) 39.59 2.34 8.15 12.43 
Calcd. (%) 39.71 2.28 8.30 12.41 
______________________________________ 
A polyvinyl alcohol film was treated with an aqueous solution of the 
compound of formula (24) in the same manner as in Example 1 to prepare a 
polarizing film. This polarizing film was blue. A polarization degree V of 
the polarizing film at an absorption maximum .lambda..sub.max was 
measured, and as a result, single plate transmission was 42%, 
.lambda..sub.max was 695 nm, and V was 99.0%. 
This polarizing film was allowed to stand for 500 hours under conditions of 
80.degree. C. and a relative humidity of 85%, but a change of hue and the 
deterioration of the polarization degree were not substantially observed. 
EXAMPLES 31 TO 56 
Following the same procedure as in Examples 27 to 30, compounds of formulae 
(2) and (3) shown in Table 2 were prepared. In this table, hue, 
.lambda..sub.max, single-plate transmission and polarization degree were 
all measured for dyed PVA films. With regard to hydrothermoresistance, 
each polarizing film was allowed to stand for 500 hours under conditions 
of 80.degree. C. and a relative humidity of 85%, and afterward, the change 
of the hue and the deterioration of the polarization degree were observed. 
The polarizing film in which neither change of the hue nor the 
deterioration of the polarization degree was observed was evaluated to be 
.largecircle.. 
3 TABLE 2 
- Example Structural Formula .lambda..sub.max (nm) A*.sup.1 B*.sup.2 
Hue C*.sup.3 
31 
##STR44## 
630 42 99 Blue .smallcircle. 
32 
##STR45## 
675 42 98 Blue .smallcircle. 
33 
##STR46## 
685 42 99 Blue .smallcircle. 
34 
##STR47## 
625 42 99 Blue .smallcircle. 
35 
##STR48## 
670 42 98 Blue .smallcircle. 
36 
##STR49## 
615 42 98 Blue .smallcircle. 
37 
##STR50## 
635 41 98 Blue .smallcircle. 
38 
##STR51## 
670 42 99 Blue .smallcircle. 
39 
##STR52## 
685 42 99 Blueishgreen .smallcircle. 
40 
##STR53## 
685 42 99 Blueishgreen .smallcircle. 
41 
##STR54## 
625 42 99 Blue .smallcircle. 
42 
##STR55## 
615 42 98 Blue .smallcircle. 
43 
##STR56## 
695 42 99 Blueishgreen .smallcircle. 
44 
##STR57## 
650 42 99 Blue .smallcircle. 
45 
##STR58## 
670 42 98 Blue .smallcircle. 
46 
##STR59## 
630 42 99 Blue .smallcircle. 
47 
##STR60## 
680 42 98 Blue .smallcircle. 
48 
##STR61## 
625 42 98 Blue .smallcircle. 
49 
##STR62## 
650 41 98 Blue .smallcircle. 
50 
##STR63## 
675 42 98 Blue .smallcircle. 
51 
##STR64## 
700 42 98 Blueishgreen .smallcircle. 
52 
##STR65## 
695 42 98 Blueishgreen .smallcircle. 
53 
##STR66## 
695 42 99 Blueishgreen .smallcircle. 
54 
##STR67## 
695 42 99 Blueishgreen .smallcircle. 
55 
##STR68## 
645 42 99 Blue .smallcircle. 
56 
##STR69## 
630 42 99 Blue .smallcircle. 
*.sup.1 : Single plate transmission 
*.sup.2 : Polarization degree 
*.sup.3 : Hydrothermoresistance 
COMATIVE EXAMPLE 1 
The same procedure as in Example 1 was carried out except that the compound 
synthesized in Example 1 was replaced with a dye represented by C. I. 
Direct Blue 202 (the following structural formula A), to obtain a 
polarizing film. 
At a maximum absorption wavelength of 695 nm and a single plate 
transmission of 43%, a polarization degree of the polarizing film was 96%, 
which meant that the dye was worse than the compounds of the present 
invention. 
##STR70## 
COMATIVE EXAMPLE 2 
The same procedure as in Example 2 was carried out except that the compound 
synthesized in Example 2 was replaced with a dye represented by the 
following formula B disclosed in Example 2 of Japanese Patent Application 
Laid-open No. 222459/1990, to obtain a polarizing film. 
At a maximum absorption wavelength of 645 nm and a single plate 
transmission of 46%, a polarization degree of the polarizing film was 88%, 
which meant that the dye was worse than the compounds of the present 
invention. 
##STR71## 
COMATIVE EXAMPLE 3 
The same procedure as in Example 1 was carried out by the use of 0.08 wt % 
of a compound of the following structural formula (C) disclosed in Example 
10 of Japanese Patent Application Laid-open No. 68902/1991, 0.045 wt % of 
C. I. Direct Red 2, 0.006 wt % of C. I. Direct Yellow 12 and 0.04 wt % of 
C. I. Direct Violet 9 to prepare a neutral polarizing film. The 
polarization degree of the polarizing film at a single plate transmission 
of 41% was 97%. 
##STR72## 
On the other hand, the same procedure as described above was carried out 
except that the compound of formula (C) was replaced with 0.08 wt % of the 
compound represented by formula (15), to prepare a neutral polarizing 
film. The polarization degree of the polarizing film at a single plate 
transmission of 41% was 99%, which meant that the polarizing film of the 
present invention was superior. 
Furthermore, the same procedure as described above was carried out except 
that the compound of the formula (C) was replaced with 0.09 wt % of the 
compound represented by formula (21), to prepare a neutral polarizing 
film. The polarization degree of the polarizing film at a single polate 
transmission of 41% was 99%, which meant that the polarizing film of the 
present invention was superior. 
In addition, the same procedure as described above was carried out except 
that the compound of the formula (C) was replaced with 0.08 wt % of the 
compound represented by formula (23), to prepare a neutral polarizing 
film. The polarization degree of the polarizing film at a single plate 
transmission of 41% was 99%, which meant that the polarizing film of the 
present invention was superior.