NATURAL DYE

Natural  dyes  and  pigments  are derived   from  mineral,  animal, or  plant  sources  and  generally  are complex mixtures  of materials. A number of  natural   dye s can  be classified   as  acid  or  vat  dyes  and  can  be readily mordanted. In general, the  natural dyes  give  more  muted  tones than synthetic dyes  and  are useful   only on natural  or  regenerated   fibers.

PIGMENTS

Pigments as a class  are colored  materials  that  are  insoluble    in their  medium  of  application. As a  result,  they cannot penetrate or become readily   fixed to a  fiber  and  must  be  "locked"  onto  the  fiber  surface by use of a  polymeric adhesive binder that  encapsulates  and  holds   the pigment  onto the  fibers. Pigments  include inorganic salts,  insoluble azo  or  vat  dyes, toners, lakes, metallic  complexes,  and  organ metallic  complexes. Some binders are  preformed  water-insoluble  polymers   applied  from  solvents or  as emulsions,   whereas  others are  water-soluble or emulsifiable polymers which can  be chemically crosslinked  and  insolubilized  after  application  by  drying and  heating. The  pigment binder systems   tend  to  stiffen textiles,  and  have moderate   to  poor  fastness,  since  they  are  surface  treatments.

DYE AND DYE CLASSIFICATION

Dyes as  colored  unsaturated organic molecules must  have affinity for fibers  to  be  effectively applied. The   dye s on  fibers  are  physically bound to the  fiber by one or more  physical  forces  including hydrogen   bonding, vander  Waals, or  ionic forces   and   in certain cases chemically bound  by covalent  bonds. Dyes  may  be  classified  in a number of  ways,   including color,  intended use,  trade  name, chemical constitution, and  basis   of  application. Of  these classification  methods, chemical constitution  and  basis of  application  have been  mo st  widely used. Chemical constitution  indicates the  major  chromophoreS  present  in the dye but  does not indicate more  than  such structural aspects of  the  dye. A classification scheme for dyes   has  been  developed and  evolved  for  use by dyers which  is  based on the method  of application and to a lesser degree  on  the  chemical constitution  of  the  dye  class. The classification  scheme  and  major dye classes are outline below.

Dyes Containing Anionic Functional Groups	Dyes  Requiring    Chemical Reaction   before   Application
Acid  dyes	Vat  dyes
Direct   dyes	Azoic   dyes
Direct   dyes	Sulfur  dyes
Mordant   dyes
Reactive    dyes

                                                  

Dyes Containing Cationic Groups	Special  Colorant  Classes
Basic  dyes	Disperse    dyes
	Solvent   dyes
	Pigments
	Natural    dyes

      Dyes  classified  by this scheme  are assigned  standard  designations according   to  dye  class,   color, and  overall constitution   by  the  Society of

Dyers and  Colorists in the Color Index   (e.g"  Acid  Blue 141, Vat Green 17,

Disperse   Red  17).