Azo dyes containing thienothiophene radicals as radicals of the diazo component

A thienothiophene dye of the formula I ##STR41## where Z is C.sub.1 -C.sub.8 -alkoxycarbonyl or C.sub.1 -C.sub.8 alkoxycarbonyl whose alkyl chain is interrupted by one or more oxygen atoms, or is C.sub.1-4 alkyl, C.sub.1-4 alkoxy or halogen substituted phenoxycarbonyl or unsubstituted phenoxycarbonyl, carbamoyl, C.sub.1 -C.sub.8 -mono-alkylcarbamoyl or -dialkyl-carbamoyl, pyrrolidinocarbonyl, piperidinocarbonyl, morpholinocarbonyl, piperazinocarbonyl, (N-C.sub.1 -C.sub.4 -alkyl)piperazinocarbonyl, carboxyl, cyano, C.sub.1 -C.sub.10 -alkanoyl, C.sub.1-4 alkyl, C.sub.1-4 alkoxy or halogen substituted phenylcarbonyl or unsubstituted phenylcarbonyl, C.sub.1 -C.sub.4 -alkylsulfonyl, C.sub.1-4 alkyl, C.sub.1-4 alkoxy or halogen substituted phenylsulfonyl or unsubstituted phenylsulfonyl or nitro, X is hydrogen, fluorine, chlorine, bromine, Z or a group of the formula --CH.dbd.CT.sup.1 T.sup.2, --CH.dbd.N--OH, --CH.dbd.N--NH--C.sub.6 H.sub.5 or ##STR42## where T.sup.1 and T.sup.2 are identical or different and each is, independently of the other, cyano, C.sub.1 -C.sub.8 -alkoxy carbonyl or C.sub.1 -C.sub.8 -alkoxycarbonyl whose alkyl chain is interrupted by one or more oxygen atoms, or is C.sub.3 -C.sub.6 -alkenyloxycarbonyl, carbamoyl or C.sub.1 -C.sub.4 -monoalkylaminocarbonyl or -dialkylaminocarbonyl and W is hyrogen, methyl or ethyl, Y is hydrogen, chlorine or bromine and K is the radical of a coupling component.