1. Introduction Of Dyes
Presented By
Mr. N. P.badgujar

2.  Introduction
Dye: A coloured organic comp. or mixture that may be used for
imparting colour to a substrate such as cloth, paper, plastic or
leather.
 Requisites of a True Dye:
 Suitable colour
 Attractive colour.
 Able to attach itself.
 Must be water soluble
 Substrates being dyes must be affinity to dye.
 After fixation of dye, it must be fast to washing, cleaning etc.
 Shade & fastness of a given dye may vary depending on the
substrate.

4. GENERAL INTRODUCTION TO THE CHEMISTRY OF DYES
 Dyes possess colour because
1) Absorb light in the visible spectrum (400–700 nm)
2) Have at least one chromophore (colour-bearing group),
3) Have a conjugated system, i.e. a structure with alternating double
and single bonds.
4) Exhibit resonance of electrons, which is a stabilizing force in
organic compounds.

5. • Most dyes also contain groups known as auxochromes (colour
helpers), examples of which are carboxylic acid, sulfonic acid,
amino, and hydroxyl groups.
• While these are not responsible for colour, their presence can
shift the colour of a colourant and they are most often used to
influence dye solubility.

9. Dyes versus Pigments
Solubility : organic colourants fall into two classes, viz. dyes
and pigments
The key distinction is that dyes are soluble in water and/or
an organic solvent.
Pigments are insoluble in both types of liquid media.
Dyes are used to colour substrates to which they have
affinity.
• Pigments can be used to colour any polymeric substrate but
by a mechanism quite different from that of dyes.

10. Classification Systems for Dyes
1. Chemical Classification:
• The most appropriate system for the classification of dyes is
by chemical structure,
• Advantages:
 it readily identifies dyes as belonging to a group that has
characteristic properties.
EX. Azo dyes (strong, good all-round properties, cost-effective)
and anthraquinone, dyes (weak, expensive).
• Azo yellow, an anthraquinone red, and a phthalocyanine
blue.

11.  Usage Classification:
• Classification by usage or application is the principal system
adopted by the Colour Index. Because the most important
textile fibers are cotton and polyester.
• The most important dye types are those used for dyeing
these two fibers, including polyester. cotton blends.
• Other textile fibers include nylon, polyacrylonitrile, and
cellulose acetate.

12.  Classification of Dyes by Use or Application Method
1. Reactive Dyes:
 It possible to achieve extremely high washfastness
properties by relatively simple dyeing methods .
 Chemical structures are much simpler, their absorption
spectra show narrower absorption bands, and the dyeing
are brighter.
• EX. Azo (including metallized azo), triphendioxazine,
phthalocyanine, formazan, and anthraquinone .
• High-purity reactive dyes are used in the ink-jet printing of
textiles, especially cotton.

13. 2. Disperse Dyes:
Water-insoluble non-ionic dyes for application to
hydrophobic fibers from aqueous dispersion.
Used predominantly on polyester and to a lesser extent on
nylon, cellulose, cellulose acetate, and acrylic fibers.
Used in Thermal transfer printing and dye diffusion thermal
transfer processes for electronic photography.

14. Direct Dyes.
Water-soluble anionic dyes, when dyed from aqueous solution in
the presence of electrolytes, are substantive to, i.e., have high
affinity for, cellulosic fibers.
 Uses: dyeing of cotton and regenerated cellulose, paper, leather,
and, to a lesser extent, nylon.
 Polyazo compounds, along with some stilbenes, phthalocyanines,
and oxazines.
 After treatments, frequently applied to the dyed material to
improve wash fastness properties.
 Include chelation with salts of metals (usually copper or
chromium), and treatment with formaldehyde or a cationic dye-complexing
resin.

15. 4. Vat Dyes :
• Water-insoluble dyes are applied mainly to cellulosic fibers as
soluble leuco salts after reduction in an alkaline bath, usually
with sodium hydrogen sulfite.
• The leuco forms are reoxidized to the insoluble keto forms
and after treated, usually by soaping, to redevelop the crystal
structure.
• The principal chemical classes of vat dyes are anthraquinone
and indigoid.

16. 5.Sulfur Dyes:
• These dyes are applied to cotton from an alkaline reducing
bath with sodium sulfide as the reducing agent.
Numerically this is a relatively small group of dyes.
• The low cost and good wash fastness properties of the
dyeing make this class important from an economic
standpoint.

17. 6. Cationic (Basic) Dyes:
• Water-soluble cationic dyes are applied to paper, polyacrylonitrile
modified nylons, and modified polyesters.
• Using for silk, wool, and tannin-mordanted cotton when
brightness of shade was more important than fastness to light and
washing.
• Basic dyes are water-soluble and yield colored cations in
solution.
• Principal chemical classes are diazahemicyanine, triarylmethane,
cyanine, hemicyanine, thiazine, oxazine, and acridine.
• Some basic dyes show biological activity and are used in medicine
as antiseptics.

18. 7. Acid Dyes:
• Water-soluble anionic dyes are applied to nylon, wool,
silk, and modified acrylics.
• Used to some extent for paper, leather, ink-jet printing,
food, and cosmetics.

19. 8. Solvent Dyes:
• Water-insoluble but solvent-soluble dyes are devoid of polar
solubilizing groups such as sulfonic acid, carboxylic acid, or
quaternary ammonium.
• Used for coloring plastics, gasoline, oils, and waxes.
• The dyes are predominantly azo and anthraquinone, but
phthalocyanine and triarylmethane dyes are also used.