Azo dyes for thermal transfer printing

In a process for thermal transfer printing, the improvement comprising transferring an azo dye of formula I ##STR5## in which the substituents have the following meanings:

• R.sup.1 is hydrogen, amino, hydroxyl or C.sub.1 -C.sub.3 -alkyl,
• R.sup.2 is hydrogen, acetyl, carbamoyl or cyano,
• R.sup.3 is .omega.-phenoxy-, .omega.-tolyloxy-, .omega.-benzyloxy- or .omega.-cyclohexyloxy-C.sub.1 -C.sub.12 -alkyl whose carbon chain may be interrupted by one or two of the following nonadjacent members:
• --O--, --CO--, --O--CO-- or --CO--O--
• and which may carry one or two of the following substituents:
• halogen, hydroxyl, C.sub.1 -C.sub.2 -alkyl, phenyl or cyclohexyl,
• R.sup.4 and R.sup.5 are each hydrogen, halogen, cyano, nitro, trihalomethyl or a radical of the formula --CO--H, --CO--R.sup.6, --O--CO--R.sup.6, --CO--OR.sup.6, --SO--OR.sup.6, --O--SO--OR.sup.6, --CO--NR.sup.7 R.sup.8, --O--CO--NR.sup.7 R.sup.8, --SO.sub.2 --NR.sup.7 R.sup.8 or --O--SO.sub.2 --NR.sup.7 R.sup.8 where
• R.sup.6 is C.sub.1 -C.sub.12 -alkyl or .omega.-phenoxy-, .omega.-tolyloxy-, .omega.-benzyloxy- or .omega.-cyclohexyloxy-C.sub.1 -C.sub.12 -alkyl, in each of which the carbon chain may be interrupted by one or two oxygen atoms in ether function,
• R.sup.7 is C.sub.1 -C.sub.12 -alkyl, and
• R.sup.8 is hydrogen or has one of the meanings of R.sup.7 ;
• by diffusion from a transfer source to a substrate utilizing a heat source.