Red benzothiazole monoazo dye for polyester fiber, mixed dye containing the same, and method of dyeing polyester fiber using the same

A process for preparing a monoazo dye for polyester fiber represented by formula (I) ##STR14## and having a crystal modification characterized by an X-ray diffraction spectrum (CuK.alpha.) showing a very strong peak at an angle of diffraction (2.theta.) of about 14.2.degree., a strong peak at about 24.5.degree., and four weak peaks at about 16.9.degree., 23.6.degree., 25.3.degree., and 26.8.degree., said monoazo dye which comprises diazotizing a compound represented by formula (II) ##STR15## reacting the resulting diazo compound in an aqueous medium at a temperature of from 0.degree. to 15.degree. C. with a coupling component represented by formula (III) ##STR16## and further subjecting to a crystal transition.

A mixed dye for polyester fiber comprising a monoazo dye represented by formula (I) ##STR17## and having a crystal modification characterized by an X-ray diffraction spectrum (CuK.alpha.) showing a very strong peak at an angle of diffraction (2.theta.) of about 14.2.degree., a strong peak at about 24.5.degree., and four weak peaks at about 16.9.degree., 23.6.degree., 25.3.degree., and 26.8.degree., and a monoazo dye represented by formula (IV) ##STR18## wherein X and Y each represents a hydrogen atom or a chloride atom in a mixing ratio of the monoazo dye of formula (I) to the monoazo dye of formula (IV) is from 10:90 to 90:10 by weight.

A method of dyeing polyester fiber comprising dip dyeing in an aqueous medium having dispersed therein a disperse dye in the presence of a dispersing agent in an amount twice or less the weight of the disperse dye at a dyeing temperature of from 125.degree. to 140.degree. C. and at a liquor ratio of 1:15 or less, wherein said disperse dye is a monoazo dye represented by formula (I) ##STR19## and having a crystal modification characterized by an X-ray diffraction spectrum (CuK.alpha.) showing a very strong peak at an angle of diffraction (2.theta.) of about 14.2.degree., a strong peak at about 24.5.degree., and four weak peaks at about 16.9.degree., 23.6.degree., 23.5.degree., and 26.8.degree..

A method of dyeing polyester fiber comprising dip dyeing in an aqueous medium having dispersed therein a disperse dye in the presence of a dispersing agent in an amount twice or less the weight of the disperse dye at a dyeing temperature of from 125.degree. to 140.degree. C. and at a liquor ratio of 1:15 or less, wherein said disperse dye is a mixed dye comprising a monoazo dye represented by formula (I) ##STR20## and having a crystal modification characterized by an X-ray diffraction spectrum (CuK.alpha.) showing a very strong peak at an angle of diffraction (2.theta.) of about 14.2.degree., a strong peak at about 24.5.degree., and four weak peaks at about 16.9.degree., 23.6.degree., 23.5.degree., and 26.8.degree., and a monoazo dye represented by formula (IV) ##STR21## wherein X and Y each represents a hydrogen atom or a chlorine atom and mixing ratio of the monoazo dye of formula (I) to the monoazo dye of formula (IV) is from 10:90 to 90:10 by weight.