Metal-complex dyes that are otherwise known as pre-metallized dyes shows great affinity towards protein fibres. Generally it has been seen that metal complex dyes are Chromium or Cobalt complexes. Among the popular metal-complex dyes, a variety known as 1:2 metal-complex dyes finds application for dyeing polyamide fibres. For dyeing wool, metal complex dyes are the most favoured. The following table shows a comparison between 1:1 metal-complex and 1:2 metal complex dye.

Metal-complex dyes generally cannot be said as belonging to a particular application dye class. In fact, Metal-complex dyes belong to numerous application classes of dyes. For example, they are found among direct, acid, and reactive dyes. When applied in the dyeing processes, metal-complex dyes are used in pH conditions that is regulated by user class and the type of fibre type (wool, polyamide, etc). The pH levels for wool typically ranges from:

• Strongly acidic (ranging from 1.8 - 4 for 1:1 metal-complex dyes)
• Moderately acidic neutral (ranging from 4 - 7 for 1:2 metal-complex dyes)

Chemically speaking, Metal copmplex Dyes can be broadly classified into two classes. 1:1 metal-complexes, where, one dye molecule gets co-ordinated with a single metal atom. In 1:2 metal complexes, one metal atom is co-ordinated with double dye molecules. The dye molecules are typically a monoazo structure which can contain additional groups like hydroxyl, carboxyl or amino groups. They can form strong co-ordination complexes with transition metal ions, like Nickel, Chromium, Cobalt and Copper. One point to note here is that phthalocyanine dyes are not classified as metal-complex dyes.


Typical molecular structures of 1.1 metal-complex dyes


Typical molecular structures of 1.2 metal-complex dyes

• Excellent, light-fastness.
• Medium washing fastness.
• Shows very good level dyeing and penetration characteristics.
• Can cover up for the irregularities in the substrates.

Metal Complex Dyes is using for a variety of applications like wood stains, leather finishing, stationery printing inks, inks, coloring for metals, plastic etc.