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Home » Dyestuff » Naphthol Dyes

Naphthol Dyes

Naphthol Dyes
Naphthol dyes offered by us are insoluble Azo dyestuffs that are produced on fiber through application of Naphthol to fiber and then combining it with diazotized base at low temperatures. This helps in producing insoluble dye molecule within fiber.

Classified as fast dyes, Naphthol dyes are slightly cheaper than Vat dyeing with the method of application complex and range of colors limited. Naphthols are:
  • Phenols
  • Soluble in alkaline solution
  • Substantive to cotton (particularly in presence of salt)

Anilides of BON acid are soluble in dilute NaOH solution, forming corresponding naphtholate ion. These small molecules are of low to moderate substantivity for cotton and diffuse rapidly into fibres.

Naphtholate ions are always coplanar and have elongated molecular structures. With a behavior as colorless, low molecular weight direct dyes, its substantivity increases with an increase in molecular size of naphtholate ion. The addition of salt also promotes better exhaustion of bath with more being needed for Naphtols of lower substantivity.

Bases:
These are available as free amine base or amine salts like hydrochloride with many of amines used being simple substituted aniline derivatives with no ionic substituent.

General Dyeing Procedure:
Application of naphthols consists of following steps:
  • Dissolution of naphthol component
  • Exhaustion of naphthol solution onto substrate/absorption of naphtholate ion by cotton
  • Removal of excess naphthol from material by squeezing/ or brine washing
  • Diazotization of base component
  • Development/treatment with diazonium ion solution to bring about coupling
  • Neutralization, Soaping at boil to remove superficial pigment (followed by rinsing & drying)

Application:
Napthols can be applied through several methods such as:
  • Tub-dip
  • Open beck
  • Jigger
  • Padding
  • Circulating liquor

Properties:
  • Naphthols are available in micro pulverized form
  • These dyes are water insoluble and contain simple water soluble diluents
  • Nature of solutions of Naphthols during application is highly alkaline having approx. pH of 12-14

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