Azo colorants
As azo colorants is referred colorant containing at least one azo group contain. Historically, they are the oldest synthetic organic colorants. There are both
- azo pigments insoluble in the application medium , as well as
- azo dyes soluble in the application medium .
Azo dyes represent the largest group in terms of numbers , both in the pigments and in the dyes group. The oldest dye is aniline yellow (CI Solvent Yellow 1), the oldest pigment parrot (CI Pigment Red 1).
Manufacturing
Production takes place in two steps: diazotization and coupling . Depending on the properties of the resulting substance, it is assigned to the group of azo dyes or that of azo pigments. Since this separation is related to the application medium, a particular substance can be both pigment and dye. Azo pigments can be produced from azo dyes by laking , i.e. by forming salts from dissolved dye and metal ions.
Properties and use
As diverse as the representatives of the azo colorants are, their properties and areas of application are just as varied.
Almost all color shades can be represented with azo colorants, but this is not useful in all cases. For example, it is no longer common to use azo pigments for green and blue pigments. These have been replaced by copper phthalocyanine pigments , which are both more cost-effective and have higher durability.
Azo dyes can be used for coloring textiles, fats and oils, food coloring (selected substances), leather coloring and acid-base or redox indicators . If you add the azo pigments, the range of applications is expanded to include cheap printing inks , plastics and emulsion paints and high-quality paints . Representatives of the benzimidazolone pigments (a subgroup of the azo pigments), e.g. B. CI Pigment Yellow 154 or CI Pigment Orange 36 , can even achieve the level of fastness required for facade paints and automotive coatings. Nevertheless, in the last few decades azo pigments have been replaced by even more stable polycyclic pigments such as quinacridones , especially in the case of very high-quality products .
In general, azo dyes that contain a releasable carcinogenic arylamine component are currently under suspicion of having a carcinogenic potential.
Individual evidence
- ↑ K. Herbst, W. Hunger; Industrial organic pigments ; 2nd Edition; Wiley-VCH; Weinheim; 1997