A polarizer contains, in a base thereof, at least one of an azo compound represented by Formula (1) or a salt thereof (as compound A), and at least one of an azo compound represented by Formula (2-I), (2-II), (3), (4-I), (4-II), (5-I) or (5-II), or a salt thereof (as compound B).

A polarizer contains, in a base thereof, at least one of an azo compound represented by Formula (1) or a salt thereof (as compound A), and at least one of an azo compound represented by Formula (2-I), (2-II), (3), (4-I), (4-II), (5-I) or (5-II), or a salt thereof (as compound B).

The present invention relates to an azo compound that is useful as a dichroic pigment used in a polarizing plate having excellent polarizing performance and durability and having little color leakage in a visible light region, and used in a neutral gray polarizing plate for vehicle mounting that uses the aforementioned polarizing plate. More specifically, the invention relates to an azo compound that is represented by formula (1) [In the formula, R.sub.1-R.sub.4 each independently represent a hydrogen atom, a C1-5 alkyl group, a C1-5 alkoxy group, a sulfo group, or a C1-5 alkoxy group having a sulfo group, X represents an amino group having a substituent, a benzoylamino group having a substituent, a phenylamino group having a substituent, a phenylazo group having a substituent, or a naphthotriazole group having a substituent, m represents 3 or 4, n represents 1 or 2, and p represents 1, 2, or 3.], or to a salt of said compound.

The present invention relates to an azo compound that is useful as a dichroic pigment used in a polarizing plate having excellent polarizing performance and durability and having little color leakage in a visible light region, and used in a neutral gray polarizing plate for vehicle mounting that uses the aforementioned polarizing plate. More specifically, the invention relates to an azo compound that is represented by formula (1) [In the formula, R.sub.1-R.sub.4 each independently represent a hydrogen atom, a C1-5 alkyl group, a C1-5 alkoxy group, a sulfo group, or a C1-5 alkoxy group having a sulfo group, X represents an amino group having a substituent, a benzoylamino group having a substituent, a phenylamino group having a substituent, a phenylazo group having a substituent, or a naphthotriazole group having a substituent, m represents 3 or 4, n represents 1 or 2, and p represents 1, 2, or 3.], or to a salt of said compound.

This achromatic polarizing plate has a high transmissivity, while expressing an achromatic white color when the absorption axes of the polarizing elements are positioned in parallel, and expressing an achromatic black color when the absorption axes of the polarizing elements are positioned orthogonally to one another. This polarizing element contains at least two specific azo compounds, and the absolute value of the difference between the average transmissivity of 420 nm to 480 nm light and the average transmissivity of 520 nm to 590 nm light is equal to or less than 2.5, and the absolute value of the difference between the average transmissivity of 520 nm to 590 nm light and the average transmissivity of 590 nm to 640 nm light is equal to or less than 2.0.

This achromatic polarizing plate has a high transmissivity, while expressing an achromatic white color when the absorption axes of the polarizing elements are positioned in parallel, and expressing an achromatic black color when the absorption axes of the polarizing elements are positioned orthogonally to one another. This polarizing element contains at least two specific azo compounds, and the absolute value of the difference between the average transmissivity of 420 nm to 480 nm light and the average transmissivity of 520 nm to 590 nm light is equal to or less than 2.5, and the absolute value of the difference between the average transmissivity of 520 nm to 590 nm light and the average transmissivity of 590 nm to 640 nm light is equal to or less than 2.0.

An ink composition includes, as dyes, a dye (Bk-1) represented by the formula (Bk-1); and a dye (Bw-1) represented by the formula (Bw-1), in which a content ratio A (dye (Bk-1):dye (Bw-1)) of the dye (Bk-1) and the dye (Bw-1) is 100:18 to 100:40.