DISPERSE DYE<>

Disperse dyes were   formulated and  introduced  to  permit  dyeing  of   hydrophobic  thermoplastic fibers   including  acetate,  triacetate, nylon,   polyester, acrylic, and other synthetics. The  disperse  dyes are small  polar  molecules,   usually  containing   anthraquinone  or  azo  groups, which  do not have  charged  cationic or anionic groups  within  the structure. The disperse  dyes  are sparingly  soluble in water and must be dispersed  with aid  of a surfactant  in the dyebath.   As  the small  amount of  dissolved disperse  dye diffuses  into the  fiber, additional  dye  dispersed  in solution  is dissolved, until  the disperse  dye  is nearly  completely  exhausted  onto  the fiber.  A  special class of  reactive disperse  dyes  has been  introduced that can  react  with  fibers  1ike  acetate  and  nylon  after  diffusion   into the fiber.   The  light-  and washfastness of  these  dyes is  generally  good, but difficulty  has  been encountered  with  fume fading with  certain of  the disperse  dyes.   Many disperse  dyes  have  appreciable vapor pressures  at elevated  temperatures  and can  be "dyed" onto thermoplastic  fibers  by subl imation, which  involves  diffusion of  the dye vapors  into the fiber.