Dyeing With Direct Dyes
Dyeing With Direct Dyes
• Cheap Dyes
• Very easily dyed onto cellulosic fabrics
• Defination: Anionic dyes which have affinity for cellulosic fibre and are generally dyed from water in the presence of salt.
• Name is ‘Direct Dye’ as dye can be directly applied on fibres/fabrics without any treatment.
IMPORTANT FACTORS
1. DYES
2. PROCESS
3. AFTERTREATMENTS
4. DYE-FIBRE INTERACTIONS
GROUPS THAT SHOW SUBSTANTIVITY
1 OR MORE GROUP CAN BE PRESENT
N = N Azo
Diphenyl
Stilbene
CH=CH
J -acid
NH2 NaO3S
OH
Gamma-acid NaO3S
OHNH2
ThiazoleS
HC
HCN
CH
STRUCTURE OF DYES
1. CONGO RED
This dye is no longer used as (a) at pH 3 or below it gives blue colour
(b) It is made from benzidene amine which is carcinogenic
Congo Red
N=N N=N
NH2
SO3Na
NH2
SO3Na
STRUCTURE OF DYES..contd
2. CHLORANTINE FAST GREEN BLL
Blue dye and yellow dye are connected via triazine ring to get a green dye
Chlorantine Fast Green BLL
OO
SO3Na
H2N NH
NO3S
NH
N N
N
NH
NH N =N OH
COONa
STRUCTURE OF DYES..contd
3. C.I. Direct Yellow 12
This dye can be applied on cotton, wool and silk.
C.I. Direct Yellow 12
H5C2O N=N CH=CH N=N OC2H5
SO3Na
SO3Na
STRUCTURE OF DYES..contd4. COPPER PHTHALOCYANINE
This is a general molecule which can be used as direct dye, acid dye or a reactive dye can be made based on them.
Copper Phthalocyanine
N
NaO3S
N
N
N
N
N
N
SO3Na
N-
-
Cu2+
CHROMOPHORES IN DIRECT DYES
1. Azo (90%)
2. Stilbene
3. Dioxane
4. Quinoline
5. Thiazole
6. AnthraquinoneAll direct dyes have a solubilising group Ex- SO3Na in Congo
Red and so they form anionic molecule in water
DYEING PROCESS
The requirements are –
1. DYE
2. AUXILLARY
3. pH
4. TEMPERATURE
5. MLR
METHODS FOR DYEING
1. BATCH PROCESS
2. SEMI-CONTINUOUS PROCESS
3. CONTINUOUS PROCESS
Only batch process is used for direct dyes as the dyes have a high affinity for fibre.
Dye 1 has high affinity for fibre.Dye 2 has high affinity for waterPartition coefficient = K= [D]f [D]sHigher the K, more is the dye taken up by the fibre, which is preferable for Batch Process.
• For continuous or semi-continuous process, dye should have very low affinity, because if the dye has high affinity it will be preferentially taken up which is called Tailing effect. • At high temperature, dye has low affinity as dyeing is exothermic process. So for direct dyes high temperature should be used.
AUXILLARY
• Salt is used as an auxillary in direct dyeing.
• Commercial dye 40-60%Dye + 40-60%
Deluent
• Here the deluent is salt / electrolyte. So some dyeing occurs even if extra salt is not added.
EFFECT OF ELECTROLYTE
• Zeta Potential• Dye is negatively charged DSO3Na <=> DSO3
- + Na+
• So there is repulsion between dye and fibre. • To overcome charge on surface or to suppress the
dissociation reaction of dye, salt is used.• Ex- NaCl, Na2SO4.10H2O (Glauber’s salt)
pH
• Normally neutral pH is used.
• In viscose rayon, if pH becomes alkaline, dye gets reduced and so lower shade is obtained.
• Optimum pH is 6-7’
TEMPERATURE
• For all direct dyes there is an optimum temperature
Example- C.I.Direct yellow 12 …….20oC
C.I.Direct Red 81………..60oC
C.I.Direct Yellow 28……100oC
• Many shades are obtained by mixing 2-3 dyes.
Dyeing of direct dye is carried out at 90-100oC for 1-2hrs
MATERIAL TO LIQUOR RATIO
• MLR is a function of the machine being used.
• Higher the MLR, lower is the dye uptake.
Machine MLR
Jigger 1:4
Winch 1:20
CLASSIFICATION OF DIRECT DYES
• Class A : Self levelling (20%)
• Class B : Salt controllable (40%)
• Class C : Salt & Temperature
Class A- Self leveling direct dyes
Dyes in this group have good leveling characteristics and are capable of dyeing uniformly even when the electrolyte is added at the beginning of the dyeing operation. They may require relatively large amounts of slat to exhaust well.
Class B - Salt Controllable Dyes
These dyes have relatively poor leveling or migration characteristics. They can be batch dyed uniformly by controlled addition of electrolyte, usually after the dye bath has reached the dyeing temperature.
Class C - Salt and Temperature Controllable Dyes
These dyes show relatively poor leveling or migration and their substantivity increases very rapidly with increasing temperature. Their rate of dyeing is controlled by controlling the rate of rise of the dyebath temperature as well as controlling the salt addition. Some of these dyes require very little salt to show good exhaustion in light shades.
TESTS TO FIND CLASS OF DYE
1. Levelling or migration test
(i) 2.5g hank of cotton, 1%shade, 20%NaCl, M:L::1:30, boil, 30mins
(ii) Dyed hank + Undyed hank(2.5g), 10%NaCl, M:L::1:30, boil, 30mins
The 2 hanks are compared,
If almost equal shade Class A
If large difference Class B or Class C
2. Salt test
• 3 dye baths are dyed with 1% shade
Quantity of salt varied- 0.6%, 0.8%, 1%
MLR:1:30, 100oC, 30mins
Hanks squeezed and removed.
• Salt conc increased to 20% in all baths and 2nd set of hanks inserted.
If Set 1 lighter or equal to Set 2 Class B
If Set 1 darker than Set 2 Class C
AFTER TREATMENTS
• Direct dyes have W.F. of 2-3
L.F. of 3-4 generally
Hence, after treatment is required.
• Dye molecule size is low low wash fastness.
• If molecule size is increased, the fastness will improve.
AFTER TREATMENTS…contd.
1. Diazotisation and DevelopmentAmino group of dye can be diazotised and coupled.
NaNO2 + HCl HNO2 + NaCl
Additional azo group change in shade
D-NH2 + HNO2 + HCl --> D-N _
NCl + 2H2O-+
D-N ___ NCl + OH
OH
+ HClN=ND
Developer ( beta napthol)
AFTER TREATMENTS…contd.
• Developers used are-
Β-Napthol, m-phenylene diamine phenol, resorcinol.
• Dyes that are used in such way are called D&D dyed (Dyed & Developed dyes)
AFTER TREATMENTS…contd.
• If Dyes does not have –NH2 group, coupling is done with diazonium salt.
NH2
p-Nitro aniline
C.I. Azoic Diazo Component 37
NO2
O2N N N-Cl
Diazotised p-nitro aniline
+___ -
AFTER TREATMENTS…contd.
2. Treatment with Metal Salts
• CuSO4 or K2Cr2O7 or mixture of both.
• Improves the L.F. & to a extent W.F.also.
• Trade names of dyes- Cuprofix, Cuprophenyl, Cuprantine
AFTER TREATMENTS…contd.Dyes that have the following structure can be
treated with Cu.
OH groups at o,o’ position to azo ring or derivatives of
Treatment is 0.25-2% CuSO4 + 1% CH3COOH, 20-30min at 60oC
Treatment with metal salts
N=N N=N
OH OH O OCu_ _
OH COOH
N=N
OH
COOH
AFTER TREATMENTS…contd.
3. Formaldehyde Treatment
Given to those dyes which have amino group situated at p-position to azo group.
2-3% HCHO(30%)+ 1% CH3COOH(30%), 30min, 30oC
Formaldehyde treatmentNH2
H N
D
+ HCHO +
NH
D
NH
D
NH
H N
D
NH
NHCH2
2
22
2
2
2
AFTER TREATMENTS…contd.
4. Cationic Fixing AgentDifferent kinds-a) Quarternary ammonium compoundsb) Amino triazine condensatesc) Pyridinium derived basesAll have a quarternary NitrogenNowadays, Condensation product of dicyandiamide,
formaldehyde and ammonium chloride are most commonly used.
AFTER TREATMENTS…contd.
Bond is weak, so can withstand only few washes.
Sometimes reduces L.F.
+N O S Dye-
3