azoic colours
DESCRIPTION
TRANSCRIPT
DYEING WITH AZOIC COLOURS
INTRODUCTIONIt is called azoic colour and not a dye as there is no dye present. The dye is formed on the substrate itself i.e. on fibre, yarn or fabric.
To have a azoic colour we require 2 components – Naphthol (coupling component) and Base or salt (Diazo component)
INTRODUCTION
• There are 34 naphthols and 50 bases/ salts• The combinations can produce about 2000
shades but only a few of them are used as either they are very expensive and there are
cheaper substitutes for them, or they have poor reproducibility and brightness
How is colour formed?OH
NH
NO
2
2
Β naphtholP-nitroaniline
2
2
NO
NH
NO 2
N NCl-
OH
OH
N=N NO2
Diazotised p-nitro anilineOn coupling, colour is formed
NAPHTHOLSOH OH
COOH
β naphthol BON acid (β oxy napthoic acid)
β naphthol has no affinity so then the cloth has to be dried and then coupled. This was a limiting factor as drying is a costly process and during dyeing the naphthol even migrates
NAPHTHOLS….contd
Naphthol ASHas affinity for cotton and so drying is not
required. It is a naphthol developed from BON acid
OH
CONH
NAPHTHOLS….contd
Anilides of BON acid (RED naphthols)
By changing amine different naphthols can be obtained.
CONH
OH
H N2
+COOH
OH
NH
CH3
NH
NO2
NH
Naphthol ASD Naphthol ASBS Naphthol AS-SW
NAPHTHOLS….contd
Anilides of Anthracene and Carbazole hydroxy carboxylic acids
OH
CONH
CH3
NH
OH
CONH
OCH
CH
3
3
Green naphthol
Brown naphthol
NAPHTHOLS….contd
Acyl acetic acid anilides
Only naphthol where coupling takes place as aliphatic CarbonProduces Yellow colourLow substantivity
CH - C - CH - C - NH - NH - C - CH - C - CH3 22 3
CH CH3 3
DIAZOTIZABLE BASES
Aniline derivatives
Examples
Red OrangeGC Bordeaux GP
A base will give only 1 colour but can have tonal changes
NH2
R
2NH
NO2
2NH
Cl
2NH
NO
OCH
2
3
DIAZOTIZABLE BASES...contd
Amino Azo derivatives
N=N NH2
R R1 2
This class will have 2 azo groups in their structure (Bisazo)
Garnet GBC base
Garnet, Bordeaux and Corinth shades are produced using this class
N=N
CH CH
NH
3 3
3
DIAZOTIZABLE BASES...contd
Substituted p-Benzoyl Amino Anilines
CO-NH NH2
R
R
1
2
NH2CO-NH
OCH
OCH
3
3
3OCH
CO-NH NH2
CH3O
Fast Blue RR
Fast Violet B
Bases are banned now as potential carcinogens
Diamines
DIAZOTIZABLE BASES...contd
NH NHH N2 2
Cl
Cl
NHH N 22
Black B
Brown 2R
Cheap ways of producing brown shades is by using this base with carbazole based or Naphthol AS base
DIAZOTIZABLE BASES...contd
Colour Coupling component Diazo component
Yellow Amides of acetoacetic acid (Ex - Naphthol ASG)
Aniline derivativeRed Anilides of Bon acid (Red
naphthol)
Bordeaux
6-methoxy derivative of Bon acid OR
Red acid Aminoazo benzene derivative
Violet Red naphthol p-Benzoyl amino anilinesGreen Green naphthol Violet/Blue BB base
Brown Anthracene derivative (Brown naphthol)
Various fast bases or salts
BlackRed naphthol Black bases
OR Black naphthol Red base or salt
APPLICATION OF AZO DYES
1. Treatment with naphthol2. Diazotization of base3. Coupling of naphthol4. After treatment
Naphthols are not soluble in water. Dissolution -
Can be done by 2 methods - 1. Hot dissolution method
2. Cold dissolution method
Treatment with Naphthols
OH
CONH
NaOH
CONH
O-Na+
Hot dissolution Method
• Naphthol is pasted with a wetting agent such as TRO (sulphonated
castor oil) and a fine paste prepared.
• Soft water is added and dispresion is heated to near boil. If hard
water is used it may result in precipitation of the naphthol or alkali
• If soft water is not available, a sequestering agent is added
• Then calculated amount NaOH is added with stirring
• Naphthol dissolves slowly to give olive green to light brown colour
• Solution is then cooled and diluted to required amount
NaOH required
Naphthol AS 1.5 L NaOH (27.8%) /kg
Naphthol ASBR 2.5 L NaOH (27.8%) /kg
Naphthol AS-G 3.0 L NaOH (27.8%) /kg
Quantity of NaOH used is more than stoichiometric
quantity required
Cold dissolution method
• Paste is prepared with TRO & NaOH & then alcohol (ethyl
alcohol) (1.5-2 times quantity of naphthol) added
• Then cold water is added to get required concentration of
naphthol
• Generally used in printing where small quantity of liquor is
required to be used
• Naphthol can react with carbon dioxide and get precipitated. To protect it formaldehyde is added as a stabiliser.
• Temporary bonding only as it is on coupling site. • It should not be added when the fabric dyed is to be
subsequently discharge printed or when naphtholation of substrate is to be carried out at high temperature as at high temperature naphthol forms crosslinks with formaldehyde.
OH
CONH
R
HCHO
R
CONH
OH
CH OH2
Substantivity of naphtholate ion
• For exhaust/ batch method high substantive naphthol should
be used
• For continuous method, low substantive naphthol should be
used
• Direct dyes are negatively charged and salt is added for its
exhaustion. Naphtols are also negatively charged and hence in
exhaustion method salt is added
• Within very short of time most of the naphthol and
subsequently only a small amount of naphthol is absorbed
Substantivity of naphtholate ion
Naphthols AS-D, AS, AS-OL have low substantivityNaphthols AS-BR, AS-LC, AS-L3G have high substantivity
Diazotization of base
O N NH 2 2 + HCl
2O N N Cl
+
H H H
NaNO2 + HCl HNO2 + NaCl
HHH
+N ClO N
2HNO2
2O N N - N =OCl
H H
+ -
-+
H
O N2 N=N-OHCl2
O N N_ _ Cl+ -
• Diazotization reaction is carried out at 5-10oC which is obtained
by adding ice. Hence these colours are also called as ice colours
• To diazotise 1 mole of amine, 2 moles of hydrochloric acid and 1
mole os sodium nitrite is required
• In practise amount of hydrochloric acid added is more than 2
moles
Diazotization of base
Diazotization of base1. Base is pasted with TRO. HCl added and solution is heated so
that base dissolves2. Water and ice added to bring down the temperature to 5-10oC3. In separate vessel, NaNO2 is dissolved and added to base
solution gradually with stirring4. Presence of nitrous acid is checked with starch iodide paper5. Presence of HCl checked with congo red paper 6. Excess HCl is neutralized by adding sodium acetate which
reacts with HCl forming acetic acid and sodium acetate mixture which acts as buffer of pH 4-5
Cloth is worked in naphthol for half an hour, squeezed and then passed through base solution to produce colour
Coupling energy of diazo component
Group Coupling energy pH range I High 4-5 II Medium 5.5-6.5 III Low 6-7 IV Very low 7-8.2
Residual alkali from naphthol application can pass onto the base solution. To avoid this alkali-binding agents are so as to maintain pH.
Alkali binding agents are – 1.Acetic acid2.Aluminium suphate (in the form of alum)3.Zinc sulphate
After naphtolation and coupling, the fabric is washed with water and then soaping treatment is given. Soaping improves the wash fastness as well as the light fastness.
Alternative options
Since the whole naphtolation, diazotization and coupling is a lengthy process, the following different systems were developed –1.Fast Colour salts – Stabilised diazotised bases
Fast Red Salt RC
All are formed by dyeing diazotised base under vacuum and then treating with required chemical which results in stabilised salt. Most common chemical is zinc chloride
2
+- -
2ZnCl
3OCH
Cl
N_ _ N
Alternative options
OCH
N_ _ NO N
3
2
+
SO
HSO
3
3
-
+
2
3
O N N_ _ N
OCH
BF4
Fast Red Salt B
Fast Red RL
Alternative options
2. Rapid Fast Colours – Mixture of naphthol and stabilised base
Syn-Diazotate Anti-DiazotateStabilized base is prepared by treating base with NaOH at high temperature . Anti diazotate is stabilized form of base. This is used extensively by small scale printers. On printing, fabric is left in sunlight. The CO2 neutralizes the alkali & then base reacts with naphthol to give colour.
N
NO- -ON
N
Alternative options3. Rapidogen Colours – Naphthol + stabilized base.
Base is stabilized by reacting it with an amino compound called diazo compound. Colour is developed by acid steaming.
4. Rapidozols – Not used much
Cl
CH
N_ _ N
R
H-N
COOH
SO H
3
3CH
Cl
+3
3SO H
COOH
N N N
R
Derivative of sulphoanthranilic acid
Diazoamino compound
Advantages of azoic colours
• Does not have any solubilising group so have good wash fastness. The colour is mechanically entrapped and so cannot be removed easily
• Bright shades produces• Cheap to apply• In deep shades, light fastness is also good• Choice of application of colours is taken
advantage off in printing – batik, tie and dye etc.
Disadvantages of azoic colours
• Colour range/ gamut is limited – only orange, red, yellow, blue, brown & blacks produced
• Poor rubbing fastness