Tuesday, May 2, 2017

Properties / Characteristics of Acid Dyes

Most of the acid dyes are the salts of sulphuric acid, but there are a few containing carboxylic groups, which are water soluble. Acid dyes can be easily applied on wool, silk and polyamide fibers. This dyes are highly water soluble, and its light fastness is better than basic dyes.

Acid dyes are anionic in nature. The acid dyestuffs are so called because, this dyes are applied in a both containing mineral or organic acid and the anions are the active colored component.

 
Fig: Acid dyes
Classification of acid dyes on the basis of application:
There are three groups of acid dye are following:
  1. Leveling acid dyes
  2. Milling acid dyes
  3. Super milling acid dyes
Characteristics or properties of acid dyes:
Properties
Leveling acid dyes
Milling acid dyes
Super milling acid dyes
Introduction
Corresponds to molecularly split acid dyes, light fastness is generally good, exhaustion is satisfactory also referred to as “strong acid dyes”.
Correspond to partially aggregated used where good washing fastness is the main consideration, also referred to as “week acid dyes”.
Applied from neutral solutions, don’t form true solution in water but form colloidal dispersed solution, on boiling they split, also referred to as “neutral acid dyes”.
Additive to bath
Sulphuric acid
Acetic acid
Ammonium acetate
pH
2-4
4-6
6-7
Leveling property
Good
Moderate
Very poor
Wet fastness
Poor
Good
Very good
Molecular weight
Low
High
High
Solubility in water
High
Low
Low
State of division in water
Molecularly split
Colloidal
Colloidal
Affinity to protein
Low
High
Very high
Action on cellulosic fiber
No staining
Staining
Staining