On the basis of origin, there are 2 types of mordant dyes:
1. Natural
mordant dyes
2. Synthetic
mordant dyes
Now they are described below:
1 ) Natural Mordant Dyes:
Very few natural dyes are color fast with fibres. So
mordants are used to fix a dye with the fibre. These dyes as derived from
natural source e.g. plants, are natural mordant dyes.
Among the naturally occurring dyes alizarin(1,2-dihydroxy
anthraquinine) is extracted from the roots of madder. Alizarin produces red,
pink, brown and yellowish brown color when treated with compounds of Al, Sn, Fe
and Cu respectively.
Dyeing with natural mordant dyes is a time consuming
process. So they are used in lesser extent. In all these dyes chromium or other
metals combine chemically with certain groups present in dye and further
bounded by other force.
2 ) Synthetic Mordant Dyes:
As all synthetic mordant dyes are obtain from acid dyes,
they are called acid chrome dyes. That is to say,
Acid color + Cr -----àAcid
chrome
These dyes can co-ordinate easily with chromium. They can be
dyed as acid dyes and mordanted by after treatment with K2Cr2O7
or Na2Cr2O7
.
These acid chrome dyes are extensively used for wool and
polyamide fibres dyeing. They have good wet fastness and most of them possess
satisfactory light fastness.
The commonest method of application is to dye in an acid dye
bath and when exhaustion is complete, add appropriate amount of dichromate to
the liquor. Then boil it for 30 minutes
Example of some synthetic mordant dyes are as below:
Dye
|
C.I> Number
|
Chrome Fast Orange R
|
Mordant Orange 10
|
Solochrome Red B
|
Mordant Red 9
|
Eriochrome Black T
|
Mordant Black 11
|