Water-soluble azo dyes and polarizing films using the dyes

A polarizing film comprising a polymer film of at least one material selected from the group consisting of polyvinyl alcohol, polyvinyl formal, polyvinyl acetal and polyvinyl butyral;

• modified polyvinyl alcohol, polyvinyl formal, polyvinyl acetal and polyvinyl butyral;
• and cellulose resins, dyed with a water-soluble dye comprising an azo dye represented by the following formula (1) or a copper complex salt dye obtained by complexing the azo dye with copper and represented by the following formula (7):
• ##STR110## wherein A means a benzene or naphthalene ring having a sulfone group or a sodium, potassium or lithium salt thereof, Y and Z individually denote a group of the following formula (a):
• ##STR111## and Z.sup.2 denotes a group of the following formula (b):
• ##STR112## wherein R.sup.2 is a hydrogen atom, a methyl group, a methoxyl group or an ethoxyl group and R.sup.3 is a methyl, methoxyl or ethoxyl group, R.sup.1 represents an amino, C.sub.1-4 alkylamino, C.sub.2-4 alkylcarboxyamino, benzoylamino or phenylamino group bonded to the 6 or 7 position of the naphthalene ring and X denotes a hydrogen, sodium, potassium or lithium atom, with the proviso that Y and Z are different except when both R.sup.2 's are hydrogen atoms and both R.sup.3 's are methoxyl groups, then Y and Z may be the same, and the formula (a) is not complexed with copper when R.sup.3 in Z is a methyl group.