6 Dyeing and printine

The molecules of the organic compounds called dyes are

responsible for the
the colour
dyed and printed textile fibre materials. sol.

In white light, the colour of a textile material depends

upon which incident
waves are absorbed and which are reflected from dent
the dye molecules within the nol ligh
system of its fibres (see Table 6.1). olymer

The dye molecule

Why dye molecules are coloured
Dye molecules are coloured because they are
incident light. Light is a form of selectively able to absorb and reflect
energy; it is also the visible
magnetic spectrum as shown in Fig. 8.1. portion of the electre
Organic molecules become coloured, and thus useful dye
at least one of each of the radicals called molecules, if they contan
6.2 and 6.3, and Fig. 6.1).
chromophores and auxochromes (see ]abies
In general, the
the auxochromes
chromophores give the dye molecule its particular colour, "
intensify the hue of the dye molecule's colour, makes the dye mu
Table 6.1 Colours observed when
certain wavelengths from sunlight are absorbed
Predominant wavelength absorbed
Colour observed
ultraviolet
none
violet
blue yellow-green
green-blue yellow
orange
blue-green red
green
yellow-green purple
yellow violet
blue
orange
ed green-blue
infrared blue-green
none

120
 Dyeng and printing

arphores, the radicals or chemical groups without which dye molecules would have no
Table
6.2 Chromophores

u r

N a m e o f c h r o m o p h o r e e
Basic formula of How the chromophore exists
chromophore in the dye molecule

-N N - Azo-benzene radical
Azo g r o u p

-N=N O
H H
Quinonoid group Anthraquinone radical
C=C
O=C C=O
c=c
H H

Tri-aryl methane group

=C

Nitro group -NO

-N
Nitroso group -N = O -NO

Table 6.3 Auxochromes, the radicals or chemical groups which intensify the hues of the chromophores in
dye molecules.

Name of auxochrome Basic formula of auxochrome How the auxochrome exists in

the dye molecule
Acidic auxochromes COOH
Carboxyl group Sodium carboxylate radical,
SOH COONa
Sulphonic group or Sodium sulphonate radical,

S-OH ONA or-S0, Na

Basic auxochromes
Amino group -NH2 H
N
Subsututed
for example,
amino group, H
H H
methyl amino CH
or
or
CH
dimethyl amino CH of
CH

Hydroxyl group
CH cH
OH -OH

121
 Dyeng and printing
Texnle sC7IE .,.lt
difficult for dye molecules to cnter the
dye molecules enter the
may be quite

he fibre.
Once
the dye moleculeis
coloured when
region. the ffibre, a general force ol altraction will draw
lye moloOusto
are
Textile materials not possible for dve
it towards
ncar

thefibres polvmer
systems.
S
Usually, it
enter the molecules newhere

the hbre surt

is not known and onto
how the dye molccule
hbre's polymer enters the
textile fibres, because the inter-polymer spaces in the crystalline aar. coplanar dye
molecule conliguration is
crvstalline regions of the fibres is thought to
are to0 small for the rol
ance of entering the polymer systems of theone
which
regions of
the fibres polymer
systems
relatively large dye syster

the
chan
greatest

havet
sles can be described as having the shape of slips of paper, that having
molecules
hydrogen bonaingThis
where may predominate, the inter. m.
Dye mole
breadth, but relatively little depth or thickness. The linear, is,
In crvstalline regions. polymer
distances would be
no more than about 0.) nn.
is the maximum die coplanar con
molecules means that there are no bulky side groups. This
dye
bond can be effective. OOn the other hand, where van der
across coplanar
which a hydrogen
Waals assists the dye molecules to enter the fhbre's polymer system and enables
the inter-polymer spaces are even smaller; less than aha conng
forces predominate.
those stated, as van der Waals' forces aro L nm, canlanar dye molecule to align itselt within the fibre polvmer. This align
The spaces are usually less than aSsists forces of attraction to ocCCur between dye and fibre. The intensity of these
effective over much shorter distances. e s of attraction will determine the degree of fastness of a particular dye.
Table 6.4 compares the dimensions of dye molecules, for the various dye
classes.
Estimates of the distances between polymers in the amorphous regions of various bres
The information provided by these tables
are given in Table 6.5. two
suggests thati The general theory of dyeing
Table 6.4 Size of dye molecules.
Dyeing is the process of colouring textile materials by immersing them in an aqueous
Class of dye General description
of size of dye
Estimated average dimensions:
Length Breadth Thickness
Relative size solution of dye, called dyetheliquor. Normally the dye liquor consists of dve. water and

moleculees (nm) (nm) (nm)

diagrammatically an auxiliary. To improve effectiveness of dyeing,below,
explained
heat isis usually applied the dve
modified when
to

lquor. The theory of

solvent is substituted for water.
aqueous dyeing, as an organic

Acad and basic Average 1.20 0.80 0.40

of dyeing explains the interaction berween dye, ibre, water and
Azo Small 1.00 0.60 0.40
The general theory
dyeauxiliary. More specifically, it explains:
distinctly linear 2.00 0.70 0.40 **** and
ip to I forces of repulsion which are developed between
2 forces of attraction which are developed between the
the dye molecule water: and
dye molecules and hbres.
3.660

Disperse Very smal 80 0.40 0.40

These forces are responsible for the dye molecules
leaving the aqueous dye liguor and

Mordant
I:I complex 1.20
enteringand attaching themselves to the polymers of the hbres.
and
0.80 0.40
premetallised is
average
2 I complex is The dye molecule
large and bulky
Dye molecules are organic molecules which can be classihed as:
Reactive Average and linear 1.40 0.70 0.40 molecule.
up to
anioniC- in which the colour is caused by the anionic part of the dye
2.70 the cationic part ot the dye molecule
Sulphur Onic- in which the colour is caused by
Distuncuy linear 2.70 0.60
Vat 0.40 sperse -
in which the colour is caused by the whole molecule.
Large to very large The third
is

1.50 0. 0.440 aqueous solution.

annl: wo dye molecule types are applied from an
up to
up applied from an
1.70 1.40 aqueous dispersion.
Table 6.5 Estimated
nter-polymer distances in the
c s in the amorphous regions of the fibre's polymer syste
tem.
The fibree
Fibre
amorphous regions or tnc
Dry fibre (nm) Xle fibres are organic compounds and develop a slight nega:ive
surtace
charge o
and textiie
Cotton and viscose Wet fibre (nm) POLenial who
hen immersed in an aqueous solution. Since the dehereis a tendency
Wool 0.S ibre both becor
.6 2 to 3 and up to 10 for come slightly negatively charged in aqueous solu be built up in
the
Acetate and synthetics dye and the fibre has
Sufficiernt energy de
repel each other.
to
Less tan1 Up to 4 to and textile
nbre

No more than 1 quor to overcome this repulsive force and allow the dve

125
 lexnle sCene.

another, so that
the dye molecules can e n t e r
the
atlracted to one
polymer system of the Why the dye liquor is heated
D,eang and pnnting
fibre
o . Iu is
is a
form of energy. applied
to increase
the
Heat
the dye liquor and thus to increase energy of the
The role of water constituc
the rate of the molecules of all
heat not only results in an
increased dyeingng process. The
dissolving the aye, Warer dcts as the medium throuph . pplicationof

fibre rate of
dyeing but assists the
In addition to
the fibre. which molecules to penetr
polymer system. The dye
molecules are
transferred into e
dye swclls the
hbre polymer
king it easier for the application of heat to
the dye
The polar groups in dye the molecules, and
molecules attract water liquor
enter deeper dye molecules
attracuon between water and dye is on the dye te fibre
surface and amorphous regions. When the to penetrate the
into its
dissolve in water. This the hbres dried, the polymers dye liquor has
molecules resist leaving the water and entering the fibre iesirable, cooled and system will close up
again, that is, return to its
as the dye dimensions, rapping and
however, it is desirable to reduce the rate at which dye leaves the water
ome
instan former entangling the dye
molecules which
van der Waals' forces
circumstances, may develop entered it. In
uniform colouration of the fibre. S the such to assist the
fibre so as to ensure a
retain the dye
molecules within the hbre polymer. polymer system.
general, heat is necessary to encourage the dye to leave the water and ens.. .
fibre, as well as to ensure adequate penetration I the polymer system of the
Heating the dye liquor causes water to dissociate somewhat more than at fibre High temperature dyeing
room temperatures and to become slightly more 1onic. In this state, watcr tend
nueing at temperatures irom
100 to under pressure
130, to about 170 kPa (about
repel the organic dye molecule to a greater extent, ensuring readier uptake of the dve .alcm?) is termed high temperature dyeing. Hydrophobic fibres, such as polyester
molecules by the fibre's polymer sysiem. fbres, are dyed in this way Decause unaer normal atmospheric conditions, their
Water, assisted by heat, also swells hbres that are hydrophilic, making the extremely crystalline polymer system will not allow good dye uptake.
polymer
more accessible to the relatively large dye molecules. When dyeing at dye molecule
system
high temperatures, of the fibre polymer
penetsation
system is increased Signincantuy. At temperatures above 100C and therefore under
The role of electrolytes pressure the heat generates a very large amount of energy in the constituents of the dye
liquor. This swells the fibre, enabling the dye molecules to penetrate the fibre polymer
The addition of an electrolyte to the dye liquor of anionic dye increases the
uptake of system more readily
the dye by the fibre. The electrolytes used in dyeing dissociate
completely in the
dye of repulsion between the dye molecules
aqueous hguor. This increases the forces
and water so the dye is attracted by the hbre.
Dye auxilharies
The of
addition clectrolytes between dye makes the dye liquor more ionic and thus
to the These chemical compounds include carriers or swelling agents, levelling agents, anti-
the clectrolyte and the dye molecules. This foaming agents, dispersing agents, detergents and wetting agents. The way in which
increasesthethe forces of repulsion
fibre these auxiliaries affect the dyeing process and their chemical constitution is fairly com-
attractsFor dye to the and increases the chances of the dye molecules entering the plex and beyond the scope of this book. However, the following provides some ex
bre. the dye to enter the fíbre, theanionic
will have to be neulralised since both
surface charge of the fibre, which is negative,
planation for the way in which carriers and levelling agents are used in the dye liquor
dyes and textile fibres have the same
charge. his is
efected
sodium sulphate. Both these
by the addition of cheap electrolytes such
as sodium chloride or Carriers or swelling agents
electrolytes are extremely soluble and dissociate com
n an aqueuus medium. The presence of these electrolytes makes the dye liqur Carriers are added to the dye liquor to improve the dye exhaustion for highly crysta
more line fibres such as ters. Because of their very crystalline nature, only pale
colours
1onic which, together with the application of heat to the dye liquor, increa pc
energy of the molecules in the dye Can be achieved by aqueous dyeing without carriers. The addition of carrierstoineo
liquor and the forces of repulsion.
The use of electrolytes such as sodium chloride or sodium sulphate maans atosi one
r 551sts the dye to penetrate the extremely crystalline polyester hbre. nere s
of the dissOCiaion products sodium a i y accepted explanation for the way in which carriers improve the ayca bu
is ions (Na. Sodium ions are cado tile carriers help to sweu
uvely charged, and
in the
dye liquor are attracted to the negauvely cnaiB hh nbres. The most widely accepted explanation is that a
hbres. Once u enter the polymer system. As
E
onthe surface of the
fibre, the sodium cations dKE t easier for the dye molecules to
1ace charge of the hbres,
by
forming a layer of Na" about 10 nm thick on u
neutrans he surfac CTS are only used to dye polyester fibres with disperse ayo
of the hbres. The neutralised fibre lecules
hich
nave a
can now attract the
greater affinity for the hbre than the organic dye mo1 eling agents uniform colour
irom the dye liquor to the hbres is accelerated by solution.
aqueous The migrau
the application of heat to nc more
addition of levelling agents to the dye liquor helps proqe of the fibres,
iiquor C b r e s . Levelling agents which tend to slow down ue

126 127
 Dyeang and print1ng
or retarders. The use of retarda is essenuual in
agents 1Sually steamed. This is to enable the dye molecules to
also
termed retard1ng and result in an
material is
are
tend to Tush on to nbre fibres and to enter the fibre polymer the
which dves he system.
and ensures better penetrationof the dye and improved colourSteaming
Situations in surface of sweus the fibres
fastness properties of the
textile material. actuve agents, and are chemically related to.

eticLevelling agents
detergents
are surface
and wettung agents. They may be anionic, cationic or non-ionic
Soaps, synth-
anic
textile terial.

ting explains the interaction, on steaming, between the

The ater, thickener and hydrocarbon solvent. More
specifhcally, it explains
ompounds
the printing paste:

Anionic eve. JENts how within

of ulsion are developed between the dye molecules and the
large negatively charged, or
consist or a constituents
The molecules of these compounds anionic, 1 forces printing paste; and
radical. with usually a sodium cation that assiste the
a cationic radical
wnich is of the
organic
kevelling agent's water solubilhty. When anionic agents are added to the dve liquor, forces of traction are develop between the dye molecules and the fibres of the
in the ibre. The anionic levelling ager 2 material to be printed.
their anions will
be attracted to any positive site agent textile
tends to repel the similarly charged anionic dye molecule. As the dye bath is ated,
the anionie dye molecules develop suihcient energy to overcome the repulsive forces The dye molecule
between the retarder and the dye, both of which are anionic. The retarder slows the
results uniformly dyed textile material. This has already been covered under "The general theory of dyeing' on page 125.
dve uptake of the fibre and in a more

Catic Eeling agents The role of the water

The molecules of these compounds consist of a large positively charged, or cationic,
A relatively small amount of water is used; enough
to dissolve the dye into a paste.
organicradical. with an anionic radical which is usually a chloride ion and sometimes a mix, or disperse,
Water is used as it is a convenient and readily available medium
to
bromide 1on the dye molecules in the thickener.
When cationic levelling agents are added o the dye liquor, their cations are attracted
to the anionic dye molecules. This neutralises the electric charge on the dye molecules
and munumises their substantivity for the fibres. The energy provided
from heatingthe The role of the thickener
and the resul-
dve bath will cause the cationic radicals
of the levelling agents to gradually dissociate The purpose of the thickener is to produce a medium for the dye paste
an emulsion of thicken-
the anionic dve molecules. This gradual dissociation of the cationic agents rom 1ant product is called the printing paste. The printing paste is
Irom

hydrocarbon oil, plus a surface

the dhe molecules slowly releases the dye and this ensures a more uniform absorpu
o the dve by the polymer system of the ibre.
er
and hydrocarbon, such as white spirit or verythelight
emulsification of the thickener with
This surface active agent enables
ve agent. of uniform consistency. The
uniform con-
e nydrocarbon to form a printing pasteto as its viscosity (the ease with which the
Scour.g aiter dyeing ncy of the printing paste is referred is very important as it
intluences

Cigaiavs lcaves some dye molecules on the surface of the fibres of the dyea
d textile 4te Wll flow). The viscosity of the printing pasteThe clarity of the printed pattern
da appearance of the printed pattern.
and
thickener used. The physical-chemical prop
materials essential that these dye molecules be removed when
is Com
dyemg very on the particular
much form a nim
pletea. 1 these
removed they may result in two problems
dyes are not after printing, it will
n e thickener must be such that immediately
poor rub-lastness which may result in the dye rubbing off onto adjacent material of e or crack when dry. The thickencr
ncient plasticity and elasticity not to flake to run. The
success Or
priu
to prevent capillary action from causing the dye
excess
poor wash-1astness which may result
dye during laundering.
in other fabrics being
coloured o e and quality of the thickener.
dETIals much on the type
depends very
Ihickeners can be any of the following: from starches

pared
prcpass
The general theory of printing r a l gums, such
and other polysaccharides;
as gum arabic, acacia gums
or gums
cellulose
soluble
water
he
printing the mar for example,
predeter

of textile materials
mined design.
is the application of colour accorais de, natural polymer-based gums, and
lSSuch as carboxymethyl cellulose, methyl euy
The ick
prinung paste which is applied water, th alginate; or viny! alcohol.

consists of dye,
textile material
cner to
and hy applied, t h e textile

drocarbon solvent or oil. After the printing paste occasi

sionally, made-made, synthetic compounds such
20
 does not co Dyeing and printin
thickener, one
must e n s u r e thal it
absorption capacit of thc clectrons ol the
with the fbre
of the dyc molccule. When sunlight chronophores
a gy
When selecting textule maierial is to be
the dve. For
instance, il a cellulosic

Selcction of such printecd, the

paste
iight c turc of
s t r u c t u r e

energy is
or a
brcakdown
ahsorbed,
lelevel, that loosel
t h e c h r o m o p h o r e s aare raiscd to a
the
thickener. a
the
the
kener may cmust
or
cellulosic based in
be mixcd
with a
thickener than held clectrons ol higher Cnergy
energy
not
the dye may be more
substantive t0 the
than to the cause It iis known that
It
aclive.
the raviolet c
ulrav1o1cl is, they
difficulies as
fibre. ne
more
chem:
ctions. Such chemical rcactons will bc
Such
reactions. component of
sunight will in tune
initiatcchcmicalin accleratcd under
Fading sunlight is due partly to ullraviolct radiation
which initiates
most Con

The role of steamn ditjons.

dyc molecule through the looscly held
the
of the chemi
This is done cal
degradøtion
clectrons of the chro
After printung, it is usual to steam the tlexule material. achieve colour- ca ares. Fading of dyed or printed textile matcrials docs noi occur o
readily
artificial light, mainly incandescent
and fluorescent
fastness.
Steaming ensures the adequate penetration of the fibre by aye molecules. This
light, as these light soures do in
quantities of ultraviolet radiatio not
emit significant
possible because steaming:

1 generates sufhcient energy in the dye molecules for them to enter the fibre polvm
Wash-fastness
SVstem and
2swells the fbre so that the dye molecules can enter the fibre polymer svstem the loss of colour during laundering is referred to as a lack of wash-fastnes
h Colour loss will occur during laundering il dyes have been used which are held
bthe fibre; that is, dyes that have not penetrated the ibre
Dry heatng uhich arc held only by weak forces such as hydrogen bonds or van sufficiently dyes
or

der Waals'
fibres tend and do If bleaches arc used at some stage in laundering, then tad1ng may also be the forces
Thermoplastic to be hydrophobic not swell sufficiently
in watcr or result
when subjected
steam1ng. Dry heating, however, Will soften the ibres; that
to
is, it will of chemical degradation of the dye.
cause the polymers in the amorphous regions of the polymer
system to more far
enough apart to allow the entry of ihe dye molccules. T his method of
the printed patterns is particularly suitable when the colourant is a
fixing, or setting pry-cleaning-fastness
pigment. Pigments
have little substantivity for the
polymer system of thc fibre with the result that pigment he loss of colour during dry-cleaning is referred to as a lack of dry-cleaning-fastness.
particles are trapped in the polymer system of the fibre.
olour loss will occur during dry-cleaning if dyes have been used which are held loose-
by the fibre and which are soluble in a dry-cleaning solvent. Loss of colour during
y-clcaning varies according to the particular dye and dry-cleaning solvent used.
Washing off
In general, loss of colour during dry-cleaning is rare.
This has to be done to
remove the thickener and other
which have not entercd the printing paste constutuenis
polymer system of the fibre. There will always be some
molecules left on the surface of the
fibres and these must be removed in the washing
dye stness to perspration
process. o
Spiralion 1s a complex combination of body oils, fats and saline solution. Pers
aon may result in a loss of colour for reasons similar to that given 1or poor
h-fastness and poor
dry-cleaning-fastness.
Fading ls
possible for the constituents
of perspiration to react chemically with the dye and

ChemCal degradation of the dye molecule, but this is somewhat rare

aing is Seen as
a colour loss by the
change in the structure of the dyed printed textile material. It is the res
SOme or It of
with
air pollutants, laundering, dry dye molecule due to absorption O E" action h less to Compounds and bleaches containing chloine
cleaning and/or other agency. "The
actua mechan
ISm which causes
fading is complex and not yet
fully understo0d. c a s the increasing number of swimming pools has meant tna ed
Fastness to sunlight OIcach being used in laundering, chlorine-containing compou
and towes have
T here
an
land eria
in
the oxidation
swimming pools. This means that swimwear
is no
universally accepted explanation effect of chlorinc-containing
in olours niorine for domestic bleaches is compoun
sunight. lt is
suggested that for the fading oi sodium hypochlorite wn
fading may be due to some kinddyed or Pdwn in the s is
usually calcium hypochlorite of uric a
he chemical de
ol
Drca dichloroisOcyal
ffect.
On ol dyes sensitive to both these reagents is due to their oxIdising Ci
1 30
 Texnle s e n e

Dyeing und printiny

to sea water acid. dyes to protein fibres
results in an ionic
Fastness ationol
Theapp. fibre polymer. Thc point of the or salt ink between
sea water is sodum chloride (NaC), also fhbre
The main
constituent of
are wet with sca water, direct, intenso AS olccu d the dye site. In wool ihe dye sites are mer at which the
materials the
salt. When textile
d y ci sa t l a c h e d

hloride to hydrolyse. Theretore, fading from sca water is

er is caus dyeing conditions, the amino
group becomes
many
amino groups
to as fad1ng due to sea wate
also due of the libre.

.nCgativcly charged aye anion. positively charged and

This hydro e This can
should be reterred be
sunlight and
acid which degrades the dve mol
llracis represented as
follows
tic reaction praduces hydrochloric
molecules which provide good colour-iastness to sea water are those : wool NH, H Wool NH
resist prolonged exposure to dlute hydrochloric acid, ultraviolet radiatio can wool polymer hydrogen wool polymer with
with amino or acid
posilively charged
group on
amino group
Fading due to other causes
then
Fading can also be caused by inorganie acids, alkalis, fruit juices, etc. Such fad. wool- NH DSO wool -NH, SO,D
usually a chemical degradation of the dye molecules which results from a reaction wool polymer dye 1onic link lormed
these compounds. ith with positively anion between positively
Fading due
molecules. In the
to dry
case
ironing
of
pressing is the result
and steam the
dry ironing,
of degradation of the d. charged amino

group
charged amino group
on wool polymer and
degradauon the dye molecules is due t
of
dye anion
the heat sensitivity of some dye molecules. Fading due to steam
pressing would be dud
to the inability of some dye molecules to withstand the hydrolytic effects of There are a large number ol amino groups in the wool hbre. As a guide, there are
steaming approximatcly twenty umes as many amino groups on wool as on nylon and five times
as many amino groups on wool as on silk. Dark shades can readily be obtained on wool
Classification of dyes because of the highly amorphous nature of the fibre, which results in relatively casy
penctraion of the ibre polymer by the dye molecule, and because of the presence of
Dves may be classified in two ways: numerous amino groups.
The application of acid dyes to nylon also results in ionic bonds or salt links between
according to the chemical consitution of the
dye molecule, or;
according to the method of the dye molecules and the polymer. The point at which the ionic link is formed is the
In
application of the dye.
this text,
they are classified according to the their method of
application. termnal amino group of nylon. The greater crystalline fibre structure of nylon
pared with wool as well as the relatively lower number of amino groups mcans
com
that
dark shades on
nylon cannot be obtained with acid dyes.
Acid dyes The dyeing of
nylon with acid can be dyes represented as follows:

Acid dyes nylon-NH2 H nylon-NH

are so called because they
nbres most
readily coloured with acid dyes
are usually applied under acidic condiuons. nylon polymer with nylon polymer with positively
are man-made, hydrogen
the natural
protein fibres (mohair, silk, synthetic, nylon hbres a terminal amino group or acid ion charged terminal amino group
wool, etc.). then

Dyeing wth acid dyes nylon- NH, DSO nylon-NH; SO,D

The following abbreviations are used when nylon polymer wilh
dyeing with acid dyes is
describe dye onic link formed between
pOsitivey

DSO, Na positively charged anion charged terminal amino groug m

the generalised formula for the acid dye molecule termunal amino groUp and dye anion
DSO ne dye anion
the colour
radical or component of the acid
dye molecule
nylon polymer
In ad wn J
Na
the sodium ion fibres and dved
H wnen protein and polyamide
the hydrogen ion bonds as well as van der Waals' forces willbe Iornnis etween the
nylon the nylon polymer Cn and the fibre polymer system. However, the n n the dve bein
wool the wool polymer
retained bynolecules i
dominant
and the fibre polymer play a more
3 n der
aals torEs

fibre polymer than the hydrogen bonus

132
Teanik snem. yetng and printng
NH
Somc ot the acid dves have a relatively high substantivity to protein fibres
fore. if the tibres are dved non-unitformlv. it is difhicult if not impossible to NaO,S
unitorm dveing once the uneven result has occurTed. To overcome this, a produ a
SO,Na
needs to e added to the dve lhquor. The addition of an electrolyte, such as der
HN O OH
of ibres with acid dyes.
sulphate. wil retard the rate of
dveing protein The retatarding
effect of sdium sulphate can be explained as follows. CH
and
Because the sulphate
radical is negatively charged smaller than the dve a
nion CaHs
N-CH,
can move more rap1dly in the dve liquor.
The dve sites of the fibre polymer are rapidly
ccupied the
h sulphate radical and in etfect
competeforwith the acid dve anion for the OCH-
dve The dve molecule has the greater affinity the
sites dye site but the
phate NaO3S
radicals
retard the rate which the dve molecule occupies the dye sites. This producs
at

a uniform dyeing The applhcation ot heat assists the dyeing process by increasing the
kinetic energy which are
of the dve molecules slowly overcoming
the retarding
the sulphate radicals Thus. the dye anion will gradually replace the
effectof
sulphate radical
that has been attached to the dye site.
NH

Printing with acid dyes

Once the acd dye printing paste has been applied to the textile material, stecaming of
the printed pattern
is necessary T he steam provides the water molecules and
heat
energv enable the dye molecules of the printing paste to transter trom the
to
fibre
surtace into the polymer svstem.
The process of prinung is different to dyeing in that it
requires a lower liquor ratio
and a thickener to ensure that the acid dye will not run when
applied to the texule
material. However. once the acid dye is attached to the ibre (1.c. after
steaming), the
OR O N

bonds hoiding the acid dye molecule in the fibre polymer system are the same as those
developed during dyeing C
C-N=NOO-N- N-C
Molecular HC CH
confauration and charactenstics Na' O,S SO Na

The chemical consututuon, and thus the molecular structure, of acid gure 62Structural formulae of acid dyes with different levelling characteristcs
dyes varies.
o'5Di m
Ad Bueof45.2 63010-an acid dye with good levelling characteristics, a ight-lastness raing
Generally, acid dyes the sodium salts of sulphonic acids. However, many direst
are
dyes also are the sodium salts of sulphonic acids. Dyes are classified as acid if they can
astness
acid dye with average levelling charactenstics, a light-fastress rating
dr
cd Bue 83, 42660 -

an
aca wash.tastnes rating ot 3 to 4
be applied sat1stactorily to protein fibres. or e
charactenstics, a light-tasthess rating
. ofL2910-an
no rating acid dye with poor levelling
Acid dyes may be divided three distinct types, based on their levellin, charac-
into asn- astness 4 to 5
teristucs (see below), An example of each type of acid dye is shown in Fig. 6.2.
Wasn-tastness
Properties of acid dyes ash fastness rating is about 2-3 for acid dyes with good levellingcnrrive
eveil with p o r
with levelling characteristics, and
Light-fastness
hose
tistics.
average
(See the Glossary entry wash-fastness tor an epla
4- tort a of wasb

lastness ratings.
Dyed and printed acid colours have good light-fastness. The light-fastness rating o textiie

acid dyes is about 4 - . (Reter to the Glossary entry light-fastness for an explanatuon o
ay intluence the wash-fastness of acid dyed
or
prn
rssl attaches itself by and hyurogn
ionie
ight-fastness ratings nylon and wo molecule vater.
The electron arrangement in iOre polymers. These bonds may be hydrolvc mer suthcuenthy
of the acid dye molecules is such
the chromophores tha
acid dyes can resist the degrading eltects of the sun's ultraviolet radiation for a ay be re d r e held loosely or which have not penetratce vlon during aunen undering

cou O v e d from the polymer system of wool and

siderable time.
 Textle sctence Dyeing and pnntingR
and:so are
acid dyes are acidic in
nature
resistant to
acids. Azoic d y e s
Secondly,
such as the detergents used for
they will
combine with alkalis
ed dye molecules combine with the
the washing. TheBeingresul 2
because their molecules
or loosely
attached
alkaline so
alled
called contain
group an
(see azo Table 6.2.
etergenm and
exces are
that material. dyes
removed from
the textile Azoic also called naphthol dyes, ice colours or developed colours.
are
Azd oic dyes a ct readily coloured with azoic dyes are the man-made and
The fibre natural
Levelling charactenstics ViSCOSe, cotton, etc.
fibres, e.g.
are divided into three ir
groups according to their levelling characterisucs
levelline e
cellulose
Acid dves
with azoiC dyes
good levelling
characteristics (see Fig. 6.2a). Dyeing
Acid aves with
extile materials with azoic dyes involves the reaction within the fbre po-
The relatuvely poor substantivity of this type ot acid dye is responsible for
levelling characteristics. As the dye molecules ave less attraction for the for their go Colovsenm of the two components which constitute the azoic dye. These two compo-
migrate only slowly into the polymer systems of he wool or nylon fibres. bre they wu y re the naphthol or coupling component, and the base or diazo component.
Howe
obtain sufficient substantivity, and ensure adequate exhaustion, sulphuri e e Dyeing or printing with
azo1c ayes is a two stage process (See Fig. 6.3).
to the dye liquor to obtain a pH of about 3.5-4.5. Their lack of suhstanadd The frst stage of dyeing with azoic dyes is called naphtholation and involves dissolv.
the naphthol in water using sodium hydroxide. The fibre is impregnated with this
denced by their poor wash-fastness. However, their light-fastness is verygond ing To assist penetration,
lent ciationof naphthol. temperature
is
of80-85°C is used material
a for vis.

ose Tavon, but with cotton room temperature adequate. The impregnated
rollers which squeeze any excess solution from the material.
a y e s with average levellng characteristics (see Fig. 6.2b). is passed through
Aceuc acid is used to acidify the dye liquor to a pH of 5 to 6. At this
pH adeque
Thesecond stage in azoic dyeing, called diazotisation, involves the preparation of
diazo component by converting this component to the soluble diazonium salt using
a

exhausion of the dye occurs; that is, optimum absorption of dye molecules
by the ih sodium nitrite and hydrochloric acid. The dye liquor is now ready for the next stageof
1s obtained.
Lowering the pH would probably lead to uneven dyeing. The wat
fastness of these acid dyes is fair, whilst their light-fastness is azoic dyeing. To this dye liquor, ice may be added, as_ diazonium salts are
good to very good. stable only at relatively low temperatures.
Acia ayes wnth poor levellhng character1st1cs Once the fabric has been treated with the naphthol it is passed through the liquor
(see Fig. 6.2c).
These dyes are also known as fast acid containing the diazonium salt to effect the reaction between the naphthol and diazo-
dyes, acid milling dyes or neutral dyeing acd nium salt. This reaction is referred-te-as_coupling. It is at this stage that the azo
dyes. They have the best substantivity of all the acid
dyes, but have relatively po group-N = N-) is formed. Note: dye manufacturers supply the diazo component
levelling characteristics. Unless care is taken during
stantuvity 1for the fibre may result in too
dyeing, their relatively good su as a stable diazonium salt. When this is used, coupling becomes the second stage in

dyeing.
rapid an and uptake consegquenuy u azoic dyeing.
he
It should be noted that the naphthol component is mostly in the fibre polymer sys
excellent substantivity of these dyes may be attributed to the two,
more, sodum sulphonate groups (NaSO) in their dye molecules. The
someno tem. It is necessary that most of the diazonium salt also enters the polymer system to
oI
polani"
greatersubsat cffect the reaction between the naphthol component and the diazonium salt. However
the acid millhng dyes is due to the extra
sulphonate groups and invariably, some reaction occurs on the surface of the fibre with the result that some of
uvitythus requiring a gives ng
pH range of 6 to 7 in order to obtain slower istion a he azoic dye is formed on the surface of the fibre. The removal of this surface dye5
more level dyeing Exnau
Ihe wash-fastness of these dyes is ential since azoic dyes are insoluble and, unless removed, the textile materialw
tair to
good. The better good to very good, whilst uvepoor rub-fastness properties. This removal is effected by a thorough final rinseo
wash-fastness, tne
greaier number of sodiumcompared with the other two iyp
is due to the ayed material. Care must be taken at each stage of dyeing that most dye 1ormauo
OCcurs within the
sulphonate groups. polymer system of the
nlore
Dye uptake
Heatung
about
of the acid
dye liquor is
essential
Belor Pninting with azoic dyes
40 C, practically no transfer of dyeensure
there is ensure satisfactory dye uptaKc
to
sausiacto dve liquo that of dyeing except that tne
hbre polymer
system. molecules irom fabric azoic dye by printing is similar
is impregnated
O
to
prinied aesSign.
However, the t e m p e r a l u r

with the coupling according to the

rises.
Increasing the rate of
dyeing increases sc This is followed with component
insoiuoic a
ry require byt
the
dye molecules temperature of the application of the diazonium salt to produce
to leave the dye dye liquor provides
the dye. OYthe

liquor and enter the fof the fibr

th
polymer >y
 T e x l e science Dyeng and printing
ater. Although most dye
distinct in groups
insoluble dye is formed wil
v e l y i n s o l u b l e

have molecules
be iaken that the
As in dyeing, care must
of poor rub-fastness.
the polymer Dresent,
the azoic dyes are that the dye
molecule
in which the az
m i n i m i s e the possibility group1 is formed within
system of the fibre to
the
hbre during
the dycing/printing process.

and characteristics
Molecular configuration of azoic dyes
the formatuon of the azoic dye molecules
Propertie
in Fig. 6.3 show
The equations
AzO1c dyes are essentially and
non-pelar and
within Light-lastness

polvmer system of the hbre. as

as such as re. Dyed and printed azoic colours have very good to excellent light-fastness which may be

b b u t e d to
the very stable electron arrangement in azoic dyes, particularly in their
chromophores. It requires
prolonged exposure to
sunlight for azoic dyes to be
adversely affected. The light-fastness rating of azoic dyes isa
H
- -C,H O-CpH, Wash-fastness

CI a 0 0 d wash-fastness of textile materials that have

or printed with been dyed
i c dyes is due to the 1act tnat azoic ayes are insoluble. This means that they are
O
unaffected during laundering. 1 he wash-fastness raing of azoic dyes is about 4-5.

H,C
4N
-C O) H,C
HN-C

O Bright colours

AzOic dyes are characterised by their very bright red and orange colours. This means
that the particular azoic dye molecules responsible for these bright, pure colours must
he able to absorb all those wavelengths not responsible for the bright orange and red
colours.

Rub-fastness
NO2- At times textile materials dyed with azoic dyes suffer from poor rub-fastness. This
HO
occurs because of the formation of the insoluble azoic dye on the surface of the fibre
which is not removed during the final stage
is
of dyeing/prinung, thorough rinsing of
a

soaping-ff and involves a

the textile material. This
thorough treatment
rinsing stage referred to
of the dycd/printed textile with a detergent.
as

If all stages of azoic dyeing are carefully controlled and followed by a thorough

NO s0aping-off, poor rub-fastness is unlikely to

occur
HO
N Blinding
called blinding, is
dyes may cause a matt or delustred effect. This effect,
C s az01C
morc viscose
common on
rayon than on cotton.

hought that blinding o c u r s when the dye fibreaggregates of dye molecules

forms
-O-C2H,
not uniformly distributed throughout the polymer. The more ikc
H,C-0-
are is probably due to tne ino
rrCnce of this effect on viscose rayon than on cotton
makes it easier for aggregates
o
amorphe
open structure of viscose rayon which
HN-C-
dye to form.

Figure 6.3 The forrnalion of an azoic dyo

8 The bas0 compornent, in this Case CI Azoic. Diazo Cornpound 20, which is converted to ts
forn the azo group
NN
azonium alt to
Basic dyes
b
The diazoniurn salt of tho baso
conronent. Noto the azo (-N-N-) which enables il to wI dye molecule 1oniscs,
naphthol or coupling onponent to
group o These solution the basic
CThe naphthol cornponent
form tho azo dys rnolecule. are
also called cationic dyes, because in chargedradical
The 320nolecle
or coupling cornponent, in this case
lorfned 1rorm Ihe r6acion betwgon the base
CI AzoicCoupling Compouno anent. In n causing its coloured component to become a cation
or positively
Ca the dye nolcule formed will havo a blue colour component and the cOuping
139
 Dyeng and printing
T'exnle stcT
W'hen thcy were tirst synthesISed, the Dasic dyes were uscd on wool and: silk, with basic dye
Print1ncg
thev had poor colour-lastness properties.
T hey were theretore displaced lor bu Vhen basIC d y e s applied to acrylic nbres by printing, steaming required to
are
is
very

fibres by acnd dyes.

these e pcnctration of the polymer system ot the fibres. The steam
hicve adeqrequircd provides
W'hen acrvlie ibres began
to become estabished a new form of basic
ic dye was cnetgy dor tor the dye molecules to enter the
acrylic tibres and attach them
known as the modified dyes.basie These are now
essentu
evolved atively charged dye sites within the polymer system
of acrvlic fibres
eanme to be
he
which selves to the
textile dyeing and prting. They are generally reter the
only basie dves used in
ly as basi dyes. T'hey
tend to be distingUIshable trom the other classes of tevel Molecular c o n f i g u r a t i o n and charactenistics
cvlour.
dyes
by their brilliance ot
fibres most readily coloured
with basie dyes are mainly the synthetis sue unigue in that the coloured component ot the dye is a catnon, not a dye
The actylie
and modacrylhe tibrecs.
Basic e s e with most other dyes. The anion of basic dyes is usually a chloride
The
anion. the thloride ion
to the
helps make
dye water basic soluble. Once in the dve
dye dissociates into the dye cation and the chloride anion (see Fig. 6.4).
Dyemg witli basc dyes liquor,

Basic dyes ae applied to acrylie tibres from a sligltly acndie dye liquor. Basie dyes have CH CH
exhaust well within narrov limits of tem N
good substantivity tor acrylic fibres and
ue. Because of their poor leveling properties, caremust be exercised when applyng HC N
asic dyes to acrylie tibres to avoiud unlevel dyemg. This 1s achieved through the use of
a retarder and caretully regulating the tennperature during dyeing. C-H
The colouring component of basic dyes is the cation. The dye cation is absorbed on
the ribre surface which is negatively charged. The ncgative potential of the fibre is thus
neutralised. Inereasing the temperature of the dye liquor provides the dye with s
ficient enc1gy to enter the tibre polymer system. It is thought that there is an n
termediate stage in which the dye is dissolved in the tibre to form polar bonds. As the H,C N-CH
number of acid groups in the tibre is limited, one can determine quantitatively the
extent to which the basic dyes can combinc with acrylic libres. Flgure 64 h e atructural formula for Cl Dasic Violet 3, 42555 a
basic dye
The dyeing process can be represented as tollows:

Ac acrylic fibre polymer

Poperlies of basic dyes
negatively charged sulphonate group iht fastness
AcSO acryhe hbre polyer contaning negatively chargod ulphonate group which is the
acidc group and also the dye sito Dyed and puinted acrylic textiles using basic dyes have excellent light-lastness. The
D dye catiorn lhght tastness rating of basic dyes is about 6-7. This excellent light-tastness is attr

buted partly the hycdrophobic nature of acrylic tibres, which minimises their absorp-
to
tactors tend to
AcSO AcSO, D
ho of walcr, and their excellent resistance to sunlight. These two
tlhe destruetive ellect of the ultraviolet rays of sunlight on the dye molecule.
acrylic hbre dye dye attacthed to dye hiise
polymer with Calon site on aciylic fibre polyner
dye site
W.aslh- fastness
As Ayle textiles dyed with basic dyes have very guxnd wash-fastness. This may be attr
statecdadded
retarder
eatier,totheprevent
dye
uneven dycing of acrylie fibres with basic dyes
cationk a
the good substantivity of basic dyes for acrylic fibres
to
and the hydro-
is to
iquor. The cationic vetarder competes witlh tlie cat part ot water into the polyiner
dye molecules tor the dye sites on the
acrylic fibre polymers. This prevenis tne a t u r e of acrylie tibres minmising the absorption
molecules trom rushing onto the tibre.
"The presence of the cationic retardeis on C of acrylic tibes. The vash-fastuess rating of basie dyes is about
dye sites means that the basic dye, which has fibve
greater substantivity tor the aciy Bught colouns
compared with the etanler, will only be able to eplace the catinic retarier lowly,
s The Digat
cusuring a more level dyemg yCs are characterised by their brillianee and intense hues.

140 141
 Dyeng and printing
Tenle siEne

ther
with other ddye
dyes do not usually
Occur
classes. No OH
achieved
explanation
from

can
bas1c
be otflered for this. satisfactotorym N=I N=N -NN
NaO,S
Direct dyes SO Na SO,Na
substantive colours because of their evoat
structural formula for G.I. Direct Blue 71, 34140-a direct dye
dves are also called Flgure 6.5 The
T hes
Direct
ceilulosic textile
materials vity
for
coloured with direct dyes the man. may have
have the same tormula. An examination of their molecular formula
The ibres most
that is,
readily
cotton and viscose fibres.
are
man-made and natural and acid dyes
may
the dye into one class or the other.
cellulose fibres: will not categorise

direct dyes
Dyeng with direct dyes Properties of
aqueous iquor to which i
to cellulosic nbres irom an
Direct dves are applied addeda Light-fastness
sodium chloride. The addition of the electrolvte
electrolyte, which is usually colours have a moderate light-fastness, the light-fastness rat
exhaustion of the dye molecules
the cibre e d and printed direct
is essential to obtain adequate by to lack a stable electron
lhquor
eing about 3. This means that the direct dye anions seem
ing
rrangement, paYticularly in the chromophores. A relatively short exposure to direct
polymer sy'stem.
When sodium chloride is added to the dye liquor it dissociates completelv The resultant break.
sodium ions (Na") and chloride ions (C). The cellulosic fibre in the dye liquor hta
into sIInlight is enough to initiate degradation of the dye molecule.
anion is seen as fading of the dyed or printed cellulosic textile
negative surface charge attracting to it the sOdium cation. This neutralises the negati down of the direct dye
material.
referred to as
surface charge of the fibre, also zeta potential enabling the dye
the anion
of the direct dye to enter the fibre more readily. The presence of the chloride ions in
the dye liquor also asSists the dye anion to leave the dye liquor and enter the fibre Wash-fastness
direct dyes is about 2-3. The comparatively poor wash-
polymer system. This is the result of repulsive forces between the dye anion and the The wash-fastness rating of
with direct dyes can be explained as follows.
chloride anion. fastness of cellulosic textile materials dyed
in the direct dye anion which conri-
The relatively large number of auxochromes
the
Thedyeapplication of heat to the dye liquor increases the energy of the components of
liquor, swells the fibre and accelerates the rate at butes to the aqueous solubility of these dyes
contributes to the poor wash-fastness of
which dyeing occurs.
this class of dye.
attached to the cellulose
Direct dyes, or more specifically the direct dye anion, are
Prining with direct dyes polymers by hydrogen bonds and van der Waals' forces
both of which are weak. Under
these weak bonds may be hydrolysed
aqueous conditions such as occur in launderingof these dyes from the polymer system.
The application of direct dyes by printing is
in principle the same as dyeing.
However
a thickener is added
restrict the dye and thus ensure the colour does not the water molecules resulting in the removal
fhxation is achieved
to
run. D by
Lhe loss of dyes is seen as fading of the cellulosic textile material.
through the application of steam heating which assists u
molecule to leave the printing paste and penetrate into the polymer
nores. Ihe
dye leaves the printing paste for reasons similar to those givensystc
in the
Improving wash-fastness to
section on
dyeing with direct dyes; that is, conditions are ca an textiles. However, although easy
electrolyte and the application of steam to created by une pi rect dyes are relatively easy to apply to cellulosic to the saying easy o
ensure that the dye is
fbre
ib
Pply, they are also relatively easy to remove and this gives rise

cnougn energy for the dye to leave the attractcatne casy off.The advantage of direct dyes is theirforease of application, comparauveiy
system of the cellulosic fibre. printing paste and enter po these reasons that direct dyes
are sulu

Wide range of available colours. It is

used on cellulosic textile materials. to
Molecular the development of means improv
Figure 6.5
configuration and characteristics mportance of direct dyes has resulted in
sn-tastness. These after-treatments, as they
are called, all
aim to
n
ease the
illustrates the characteristic system the of nore
The ncar configuration
linear of direct dye molecue it is located within the polymer the
of
auxochromes in the dye molecule are resp configura solubility The laroe aye molecule once
increases the forces of
attraction between dye moecue
direct dyes. esponsible for the good aqueous
Many direct dyes are sodium and the Dol lecule
din
The increased molecular size makes it
direct In this respect more
dyes are similar salts of sulphonic Fe polymer.
to acid dyes. In fact, aciu
some dves which are applied
dyes OVed (washed out) from the polymer system.
142 143
 Dyang and printing
.sic fibres, cspecially the acetate fibres and polyester, and less often
-fastness
wash-fas of diro
Some ot thc
icthods
usod tor
improving
Ilulosics are as n d

a n d n y l o n .
acrvlic

tollows

Dyeing w i t h th disperse dyes

to the base of azoic dve:
Dhaaotisati similar
with surtace active agent to form
d r e t dves
have a
structure

case withwith
Th:
azoic dyes.
azoic dyes.
This increases hese are added
added to
t water
o w ate a
an
aqueous disper
Certain as 1s the
case
the dyes
hility of the disperse dyes enables them to leave the dye liquor as they
with naphthoIs
cellulosic Ah.
ibre and improves SIZe
Dispersc
dves to
be treatod system of the cellulosic
system
on. The insolubility

within the polymer organic fbre than to the relatively inorganic aqueous dye
the dve
molevule D1azotisation does, howe.ever, ca
s u b s t a n t i v e
to
of
wash-fastness
trom poor to good. has to
a c t o r has considered wh
be considered n altera.
when this are
more

The aDplication of
heat to
the aye lhquor increases the energy of the dye mole
dves
hue of the direct dye and
this method liquor.
accelerates the dyeing
of the textile fibre.
the of direct dyes.
cules and
tuon in wash-fastness
the anuhe dve liquor swells the fibre to some extent and assists the dye to penetrate
Is used to impnove

e r ater tieatment Heaalvmer system resulting in the dye being

ef
located in themolecules
amorphous regions of
system, the held by dye are
copper sulphate chemical reaction wIthin c rpoyimer
a Once
dyes are treated
with bre. Waals' force
with the dye molecule. The metol
When certain v a n der
bonds and
forms a metal complex hydrogen
which opper and results in slight i are extremely crystalline and hydrophobic, and it is difficult to
in size than the original dye
molecule a
Polvester fibres the boil. In order obtain medium
slightly larger medium or dark shades even by dyeing at to
in wash-tastness.
shades, polyester
nbres are dyed using carriers or by using high temperature
t dark
Tattonic agents dyeing techniques.
be after-treated with
A cellulosic textile that has been dyed with direct dye may sperie
Dyeing with carriers
cationie agents. In aqueous
solution the direct dye molecules situated in the fhre.
and their colour Component becomes an anion, i.e. nature of polyester fibres presented problems in obtaining
polvmer system ionise sightly, The extremely crystalline of the dye
As soon as the catuonic agent 1s added to the aqueous solution it shades by conventional dyeing methods, even with the temperature
negatively charged. dark the
wll also ionise, and the main, important component of the cationic agent becomes a at the boil. Then it was found that certain organic compounds assisted
liquor dark shades to be produced.
cauon, i.e. positüively charged. The cation of the cationic agent is attracted to the anion
dyes to enter the polyester fibre polymer enabling
disperse for the way in which carriers assist in
of the direct dye, the result being a complex molecule which is also much bigger than There is no universally accepted explanation
common explanaüon is that
fibres using disperse dyes. The most
the original direct dye molecule. It will now be more to wash out this bigger,
difficult dyeing polyester
in so doing allow the disperse dye mole-
complex molecule and the direct dyed textile will therefore have a somewhat better carriers swell the polyester fibre polymer and
wash-fastness. On the other hand, cationic after-treatment of textile material which has cules to enter the polyester fibre more readily.
been coloured with direct dyes results in a reduced light-fastness for which no explana-
uon can as yet be given. High temperature dyeing
above the boil (in the range 100
Fomaldehyde after-treatment
This dyeing technique is carried out at temperatures
also
170 kPa. This method of dyeing is
150C) and under pressures ranging from 0
to
the highly crystalline synthetic fibres
or
Certain direct dyes will react with formaldehyde (HCHO) when heated to about 70- used for
80 under slightly acid conditions. Dye molecules appear to be joined together oy called pressure dyeing; it is generally The swell even
for fibre blends contain ng these fibres. technique causes the fibres to
deeper into the hbre's
very large dye molecule complexes which are much more
wash out ofgiving
nethyieneto cross-inks, and penetrate
more than at 100°C, so that dye molecules
enter
diffcult the fibre.
High temperature dyeing is particularly useful for dyeing polyester
Nole: yner system. add exura cost and, in most cases, nave
although after-treatments improve the wash-fastness of to sonC ex OTCS.Tt eliminates the need for carriers which
direct dyes scouring and rinsing
tent, the improvement achieved still leaves much to be desired. unpleasant odour which has to be removed by thorough
ner
of the material.

Disperse dyes Printing with disperse dyes

fixation in the nere
printing methods. Dye
These dyes derive their name from their
insoluble aqueous properties and the
to
Polv yes can be applied by normal steaming the material. In both cases the ne
ply them írom an ne sachieved by wet or dry adequate penetrauon
he hbres most
aqueous dispersion. applied in n e energy of the dye molecules,
ensuring their
readily coloured by disperse dyes are the man-made ester of the fibre
the fibre polymer system.
144 145
 Dyeing and printing
by open gas fires or when
xide is producca nitrogen and oxygen are
from
trom 1709
170° 1o ed hot ele
elements of clectric hcaters. caused
Transter Punting

atble to
subime
at temperatures
tcmperatures

250°C. he by the
r e d hot Nitrous oxide is also
dves are varics accordino
to the react cars, present in
Disperse sublimation
occurs tParlicularPCCihe
ar disperse to
from

hy nitrous oxidc can be minimised by treat1ng the textule

f u m e s

at
which the process of
temperature
ot disperse
ayes nas enabicd
disperse dyes
accorddnster
printing to be exhaust
cause
material
dve. This property involves printing
m terial are then predetermin
Fading

wIth chemical
based o n
an azoic hiophene-benzene complex.
The improved resust
developed.
This process paper and the textile as-fading Occurs because the nitrous ox1de will react with this compiex in
a

suitable paper.The printed temperature. Under

ed emperature. Under thes
these conditionePassed ancc to gas-
disperse dye molecule.
design on rollers at the requirea
refercncc to the

ng processdisis
heated m a t e r i a l . The transfer
transicr to he textile
between

r s e dve
molecules
least 6565 per cent ther
per cent
on
materials
textile
with at least
thermoplastic fibres and S u b l i m a t i o n

used mainly are used. have the ability to undergo sublimation, that is, they can be
invarnably disperse
dyes dyes vapor1sed
Disperse
thout a
ificant change in their colour, ight-1astness or wash-fastness. The abl1ty
significant

and characteristics is the result of a stable clectron

Molecular configuration isperse dyes
to subliine
arrangement. prOpertyproperty This

have the smallest molecules of all the com

f used to advantage
so be
in
a
transier printing. The ability of disperse dves to indelergo sub
disadvantage. Excessive hot pressing or ironing of disperse dyed
As a rule disperse dyes
and 6.5 provide an
indication ot therelauve size of disperse dve r i m t e d textiles may result in colour lOss, by the heat applied causing the disperse
Fig. 6.66.4is an
Tables example of the anthraquinone type of disperse dyes. A fea disper
lack ot polar groupS, evidenced by the insolubility of d e
or plectules to vaporise or sublime and thus leave the fibres. Fading is apparent after
dve molecules is their disperse the application
of the heat.
dyes. NH2

Mordant dyes
OCH
The term mordant is derived from the Latin mordeo, which means to bite or to take
NH2 is attached to the textile fibre by a mordant, which can be an
hold of. The mordant dye
Disperse Red 11. 62015- a disperse dye substance. The most commonly used mordant is inorganic chro-
Figure 6.6 The structural formula tor C. organic or inorganic
such as aluminium, copPper, iron and in, and orga-
mium. Other inorganic mordants,
are rarely used. Since chromium is used so exten-
Properties of disperse dyes nic mordants, such as tannic acid,
sively, dyes are sometimes called chrome dyes.
mordant
Light-fastness Fibres readily dyed with mordant dyes are the natural protein fibres, particu-
most
Textile materials which have been coloured with disperse dyes have a fair to good and nylon.
larly wool; and sometimes the synthetic fibres modacrylic
The
light-fastness. nature
light-fastness
of
rating is about 4-5. This may be attributed in part to
the non-polar the dye molecule which will not readily attract water molecules
and other polar agents that may have a degrading effect. Further, the aromatic or ben
zenestructure of disperse dyes gives them a relatively stable structure. Only with Dyeing with mordant dyes
prolonged exposure to the ultraviolet component of sunlight will any significant loss or
textile
colour occur in a disperse coloured textile material. Three methods are used to apply mordant dyes to
materials
Wash-fastness Chrome mordant method
Textile materials coloured with
disperse dyes have a moderate to good was tness.
s method of dye application has two stages. In the first stage, mordanung, ne
The wash-fastness raung is about 3-4. mordanted e x u e
material. In the second stage the
dye molecules
This is due partly to the
insolubility or dp a n t 1s applied to the textile
and partly to the
hydrophobic nature of the fibres to which disperse uy material is put in the dye liquor.
are usually applied. Th is applied to the textile from an aqueous medium containing tne nor
n raant and an acid such as acetic acid. Mordantng
Gas-fading O r potassium dichromate,
n the presence of nitrous oxide, textile materials dyed with certain blue ana et
anvolves boiling the textile material in the The
aqueous solution contan
mordanted textile is
then transferred t transterred to

disperse dyes with an

anthraquinone the aau ree quarters of an hour.
mordant dye and acid
and the temperdtu
structure will fade.
slowly o n containing the
to edboil.
th This stage of dyeing can take up to about 7
146
 Tennik sm Dryen 4nd prntng
achieve adcquate exhaustion the
.
and
order to
obhrain a
attaches itseit
ievel dveing
to the mordant which
already
dye. Dunng th
dve moieculc
stAge the forms ompicxes
svTem
which are called
and
Iakes O
polvmer
polvmcr sVstem
by the mordansthough
forming a link with
rdant which to
ckd an the fihre
Which
is formed within the fibre has formed
alank wth
the hbre polvmer 1he compiex
due topolymer
provides dveings
with good wet-fastness. s
relatrvels large and
torces which bind the larger molecules
is
the
n
On2
W aals d the presence
cnr of an der
system of the ibre which
honds within the polymer
hvdrogen
thc dve molecules in aqueous trcatmentis such as launderine
removal of
OH
Metachrome method
Thas is a one stagc process in which he aye and the mordant are applie
sumultancousl This method can only be used with dyes which do not form fhbre Chromium

the dve
mordant cothpicx immediately on coming together, that i5, the mordant and the
cation
on the hbre

do not form the complex until they

have cnterca the polymer system dve
naon

In tact. the dve complex can be 1ormed in the dye liquor and care must be
of the fte
taken th re 6 7 The formation of a mordant dye moecule within the ibre The dye shown s C I Acd ocie 2 2 o s
thas does not occur This will give rise to po0or rub-fastness.) To minimise the b e noted that, while mordant dye molecules can be synthesised as such, they can aiso ce uat uo a

taon of the complex in the dye liquor, the mordant is forma

dye added and the textile mate axes wthin
the hbre from certain acid and direct dye molecules
treated with the dve lhquor and the temperature is raised to about 50 C. At this etia.
oint ae dye h a s slignt negative polarity

he mordant is added and the temperature of the dye liquor raised to the boil slowiv n
Tre dyechnarged
molecubecause
les comb1ines
of the
with the chromium cation Thisis now caliled a laxo or dye compies whuch

positvety
Note This laxe can also
chromium cation
be regarded as a1
It may theretore combirne with another
1 metal complex dye molecule
dye moiecuie

about 45 minutes and dyeing conunucd at the boil 1or about 60 minutes.
The method dye complex Is now
of attachment of the dye to the hbre is the same as for the
cThis mucn
larger lake or negatively charged and can,theretore, combane
wi he *male

chrome mordant method positrvery charged lake (b) to torm an even greater lake Thus iakes of mordant dyes are bit o to orode ar
'astness of those coloured textile tabrics dyed with them. Note This lake can aiso be
gooc nas as
rarde
e : chr ome methoa 2 metal complex dye molecule

hus method involves a two-stage process which is the reverse of the chrome mordant
The after-chrome method involves the The other three bonds have molecules of water attached to them. It is thought that the
application
method

of the dye followed by

three molecules of water are there as an intermediate step only and will be
graduailv
mordanting This method involves the use of certain mordant dyes, which are actual dye moiecules
a d

dves which be
mordanted. The dyes are applied to the textile material Irom an
can replaced by another mordant dye anion. Thus, two mordant torm
aqueous solutuon which contains the dye and sodium sulphate. The textile materal complex with the chromium cation to form a lake or a dye chromum compicz he
s of these relatively large complexes results in the very good wash tastnes of
ealed

wThere
in this iquor by slowly raising the temperature of the dye liquor to the bou tormation
this class of dye.
it is kept 1or about an
hour. At
this point, the mordant is added and the
ure temper
dye
maintained at the boul for another 45 minutes to one hour. During
this perio
the dye
compicxes to
are formed within the fibre polymer
system; the mode of attachnca rOperties of mordant dyes
the fibre is the same as for the
chrome mordant method.
Printng with mordant
Ligrastness
The presence of the hrouu
dyes ic astness ratung of mordant dyes is about 5.
dye
molecule contributes to the very good
Exle
MOr dant dyes rarely, if
ever,
are
used for prinung top ugntta the chromophures
textiie materals with other classes as it is more convenc als The presence of the chromium adds to the stabulity ot
of dyes. g in added resistance to the ultraviolet component ot
sunugn
Molecular confhguratuon and Vn faStness
Figure 6.7 15 an
exampie of a
mordant dye
charactenistics ordant dstnessrating of mordant dyes is about 4-
The verygou
wa/t
iastness

complex. The and shows the formation materials dyed with mordant dyes is due to the large
dve c a a d h t s v to

whach is chromnum catuon Fig. 67 has a vale

in o as has si six
bonds ,
me
uies. der

dant represented by the six

lines directed
valency of 6 (that isatom. The mor
being arge med within the polymer
Thee
system of the fibre donts
d van

dye is shown to be toward the chron and also heid by

een
hvdroge"
attached to the the Six
bonds

aas torces. difficult to remove, are

chromiun cation by uthree of
TOmium cation
Texnie saen Dyeng and printing
colours
Dull and limited range of
colours in the mordant dye class and these are alsa
There is a limited range of rela HO
It is that it is the presence of the metal chromium which is
thought luvely
dull
responsible HO OH
for the dullness of colour and the limited colour range.

Disadvantages of using mordant dyes

This class of dye is now used to a lesser extent, for the following reasons: NaOjS
Colour matching is diffñcult as the process of mordanung means that the Coles SO
olour NN C-C
builds up gradually.
ON
2 Lengthy periods of application are both detrimental to protein and polyamide fhr
and rather costly.
ibres
3 Dichromate salts such as sodium and potasSium become pollutants once thev
are
discharged into the sewerage. H,C-0,s
These disadvantages have contributed to the replacement of mordant dyes with
N= N-
the premetallised dyes.
O

Premetallised dyes
Premetallised dyes are so called brcause the metal, usually chromium, is already in- o
corporated in the dye molecule during its manufacture. These dyes are also referred to -NN-
The
as
metal complex dyes. into the dye molecule has
incorporation of the metal
meant that the dye can be more readily
applied to the fibre, thus eliminating part of the O,S-CH
lengthy dyeing process. Figure 6.8 Structural formulae for metal complex dyes.
ypes of
There are two premetallised dyes: 1:1
premetallised dyes, which have one
dye molecule for every metal atom (sec Fig. 6.8a); and 2:1 premetallised dyes,
a a11 metal complex dye molecule-C.I. Acid Orange 74, 18745
b a2 1metal complex dye molecule-C.I. Acid Violet 78, 12205

which have two dye molecules for every metal atom (see Fig. 6.8b).
The fibres most readily coloured with premetallised dyes are man-made synthetic ising groups in the dye molecule. The coloured component of the dye is anuonae and

nylon and natural protein fibres. attracted like acid dyes to the positively charged amine groups of protein a2d
polyamide fibres.
Dyeing with premetallised dyes wool--NH Dye
wool-NH Dye
I premetallised dyes wool polymer anionic dye 1Onic links formed
between positivery
with positively radical of
The 1:1 premetallised dyes have to be
achieve adequate exhaustion, therefore
applied in very acid conditions in order o charged amino a 2:1 premetallised charged amino group
anc
on wool polymer
they have largely been replaced by tne group dye molecule
anionic dye radical
premetallised dyes. premetailised
The very acid conditions needed to of a 21
apply these dyes can detrimentally affect u dye molecule

propertue of the textile materials on

which they are used. The 2:1 premetallisea a
are more easy to apply and
require only slightly acid or neutral dye liquor. Thereio that
u van
the 1:1 premetallised dyes are used
only in .ddition to the ionic link, the large dye molecule means vause

exceptional circumstances. y aSignificant role in holding the dye in the fibre polymer svSte dve molecule
forces holding the
21 premetallised dyes
tne dye molecule and the strong but have ver
Within the ore, 2 are slow dyeing
l premetallised dyes
The 2:1 premetallised dyes are :
applied from a slightly acid neutral aye hi
or
1or.
fastnese
These dyes are soluble in an aqueous
liquor because of the presence of anion
151
 Dyeing and prnting
Texile scence
witn reactive dyes
Pnnting with premetallised dyes Dyeing
the
as other Classes of pplication ot reacuve dyes involves the formation of a covalent bond between
dyes, premetallised dyes arc rarely uscd for printing
KC mordant
dye can be applied morc conveniently to textile matcrials.
ur molecule and the polymer of the particular fibre. The process of apply1ng recacuve
ues is considered below lor cellulosic, protein and nylon fibres.
Molecular configuration and characteristicCs and natural cellulosic hbres
Man-made The
in a manner similar to that for applying direct dyes.
the two types of premctal. dye liquor is prepared
he 1ormulac in Figs 6.8a and 6.8b show the structure of as these can be re
The
in to which an clectrolyte is added to assist exhaustion of
lhscd dyes. Little will be said about the 1:1 premetallised dyes reactive dye is dissolved water the aye is ex
unlike the 1:1 premetallised textile material 1s then introduced to the dye liquor and
garded as being obsolcte. The 2:1 premctallised dyes, the dye. The
atom at the centre. This sym- the fibres.
dyes, have a symmetrical structure with the chromium hausted onto
be added to the dye
metrical structure contributes to the stability of the dye molecule as well as to its between dye and hbre to take place, alkali must
For the reaction this reaction with alkali can be carried out at room
resistance to degradation. The aqucous solubility of the 2:1 premetallised dye mole liquor. With
some reactive dyes
of the dye liquor
cules is due to non-1onic groups, such as the S02-CH3 or methyl sulphone group with most reacuve dyes, the temperature
temperature. However,
-

betweeen the dye

shown in Fig. 6.86. in some cases to
the boil, to eifect the reaction
must be increased, hbre. Reactive dyes have speciñc temperatures
of the
molecule and the polymer system are optimum. In any
case the formation of the
reaction between dye and fibre
Properties of premetallised dyes at which
the addition of an alkali.
covalent link requires and the hydroxyl groups of
Light-fastness formed between the dye molecule
The covalent link is covalent bond
6.9, 6.10 and 6.11 show the formation of the
The ight-fastness rating of premetallised dyes about 5. The reasons for this very the cellulosic fibre. Figures
good light-fastness are the same as those given for mordant dyes on page 000. molecule and fibre polymer.
between the dye

Wash-fastness Nylon ibres the

fibres. Heat is applied to assist
slightly acid for nylon
made
The wash-fastness rating of premetallised dyes is about 40-5.
This very good wash-
fastness is attributed to the ionic link between the dye and fibre. In addition there are
The dye liquor is
exhaustion of the dye, with the chemical reaction being effected by
the addiuon of
amino
molecule and the terminal
van der Waals' forces which occur because of the formed between the dye
relatively large dye molecule and alkali. The covalent link is
make it difficult for the dye molecule to be removed during
laundering. fibre polymer (see Fig. 6.9).
group of the polyamide
Dull and l1mited range of colours
Protein fbres Formation of
acid conditions.
There is limited range of rather dull colours in the
a
premetallised dye class. As with Reactivedyes are applied protein fibres under slightly
to
fibre polymer occurs as the tempera-
mordant dyes, this is thought to be because of the
presence of the metal chromium. the covalent link between the dye molecule and reacuve
depends on the spec1hc
ture is increased. Once again the optümum temperature
Advantages of premetallised dyes over mordant dyes
The 2:1 premetallised dyes NH2
are water soluble, have very good wash-fastness and col-
our matching is much casier than with the mordant
dyes. Premetallised dyes do not
have the disadvantages listed for mordant dyes on page 000.
-SONa

Reactive dyes u
vinyl sulphone
Reactive dyes are so called because their molecules react sodium sulphale
chemically with the fibre radical
polymers of some fibres to form a covalent bond between the
dye molecule and fibre
polymer. CH2-CH2OSO,Na
CI Heacive
The fibres most readily coloured with reactive derivalive reactive dye- Remazol Brilhant Blue.

cellulose fibres, synthetic nylon, and natural

dyes are the man-made and natural
Flgure 6.9 Structural lormula
for a vinyl sulphone
protein fibres. Blue 19, 61200

153
152
 Textle science
rease cxhaustion as
dyes used. The application of heat to the dye liquor servese. Reaction with further Dyeing and print1ng
well as to effect covalent bond formation between dye and ath to about 8-8.5 with
bath to aoo
the pH of the dyc
dye fibres can be effected by raising
ammonia. bonds with one of the SONa
covalent
h e reactive dyes used for protein
fibres can form HO-cellulose poymer
side chain amino ETOups, the -SH
H

fibre: the terminal and

nany grups in the protein
group of cystein and the hydroxyl group
most of the covalent bonds
o c c u r with the
amino acid
of the tyrosine
residue. However.

amino groups Since these are more

wool and
numer.
r e a c u v e ayes 1s shown
in
-N-NO CH
NH-

N
C HO-cellulose polymer
ous than the other groups.
The reaction between
Fig. 6.10. SOgNa 2HCI given off
Procion Yellow
Printing with reactive dyes cellulose polymer
textile materials such as cellulosics and wool
Reactive dyes c a n be used for printing ensure dye molecule penctration of the Do. SoNa
steamed to
The printed materials are wet
the formation of the covalent bond.
lymer system of the fibre and

Molecular configuration and

characteristics -N-NO O-cellulose polymer
have characteristic in common; namely, their ability to CH
The many rcactive dyes one

form a covalent bond with the fibre to which they are applied. (See Figs 6.10 and SOgNa
6.11.) The Procion Yellow molecule
in Figs 6.10 and 6.11 show a dye molecule
The formulae of the reactive dyes given has now attached itself
with a hbre polymer to form a covalent to the cellulose
which incorporates a group capable of reacting polymer
is somewhat similar to those of acid,
bond. The colour component of the reactive dye Flaure 6.11 How a
reactive dyes have been derived from dyes in Procion-type reactive
Is Procion Yellow (C.l. Reactive Yellow dye molecule attaches itsell to cellulose polymers. The dye shown here
direct and disperse dyes. In fact some 3, 13245),a
dichlorotriazinyl reactive dye.
these other classes.

Properties of reactive dyes

OH celulose polymer
Light-fastness
or In general, textile materials
O O-CH2-CH2 OSONa +H2N wool polymer the light-fastness coloured
with reactive
dyes have very good light-fastness,
or rating being about 6.
provide very good resistance1These
HN-nylon polymer ment and dyes have a very stable electron
to the arrange
ponent of sunlight. There are, however, some degrading effect of the ultuaviolet com-
fastness. reactive dyes with only fair
light-
-cellulose polymer Wash-fastness
or
uextile materials coloured with reactive dyes have
ness rating is about 4-5J This is very good wash-fastness; the
o wash
o-CH2-CH2N- s between the dye molecule and theattributed
Wool polymer +NaHSO3 to the very stable covalent
fibre polymer. Under the usual bond that
or
dry-nOng Cconditions one laundering ana
effect finds in the home, there are few chemicals that have an
the covalent bond. (See page 156 under
-N nylon polymer 'Effect of chlorine)

Fgure 6.10 The vinylofsuiphone

dtaches itsen, by
sodium sulphate radical of a Remazol-type reactive dye moleculG
and how Washing-off
covalent
way bonding,
to nbre polymers and sco s which are coloured with reactive dyes have to be thoroughly rinsed
*cave dyes can react with the hydroxyl groups of the water nolcu
154
 Pyeng and printing
Texnle science

molecules with poor

substantivity for the
fibre. In fact it is these Anlecular conhguration and characternst
produce dye process, involving scourine Little is knowr
wn about the structure of
removed by a washing-off
cules which have to be
ot dye are not removed, poor
rub-fastness may resul
d
cally reacting compounds süch sulphur dyes. Sulphur dyes produd
chemic. as duced are by
rinsing. If these molecules
sulphur. Sulphur dyes
p-aminophenol and dinitronaphthalene
thought to contain
are with
thiazine and a
ring, to contain
Effect of acids links within their molecules. (See Figs 6.12 and 6.13). sulphur
The formation of
the covalent bond between dye and
fibre occurs under alkaline
condi. The following equations show how sulphur dyes are reduced to their
reverse this process.erspiration
and atmosphe Cm and are then oxidised, While the hbre, back to the insoluble form.
in
soluble leuco
The presence of acids may
tions.
a r e both slightly acid may
affect textile materials coloured with r
pollution which Dye-S-S-Dye 2H
tuve dyes and result in some fading. Dye -SH HS-Dye
water insoluble
reducing the di-sulphide bond of
Effect of chlorine sulphur dye agent Sulphur dye molecule
introduced it was found that some of them were adverse
molecule represented has been split, the
When reactive dyes were first here by
which contained chlorine. This is significant when you consider
resultant-SH radicals
Iy affected by bleaches hydrogen make the reduced
homes in Australia has a swimming pool which is kept clean
sulphur
that one out of every ten dye molecule water soluble,
by the addition of chlorine. Swimwear, therefore,
has
to be coloured with dyes resis. this is the leuco form

tant to chlorine bleach.

This can be achieved if the right reactive dyes are chosen.
then
otherwise the swimwear will fade.
Dye-SH + HS-Dye Dye-S-S-Dye + H,O

the water soluble Oxidising the insoluble water

or leuco form ofthe agent sulphur dye formed
Sulphur dyes sulphur dye molecule
within the fibre
represented
rere by
molecule has
reformed
from th
H and O
called because they contain sulphur atoms in their molecules. .

These dyes are so oxygen

the natural and man-made
The fibres most readily coloured with sulphur dyes are

cellulos1c fibres. N

Dyeing with sulphur dyes

6.12 The thiazine ring thought to characterise sulphur dye molecules
of the sulphur dye is effected Figure
Sulphur dyes are insoluble in water. An aqueous solution
with sodium hydrosul.
by reacting some sulphur dyes with sodium sulphide and others
or sodium hydrosulphite is to reduce the sulphur
phite.to The role of scdium sulphide the add- HaN-
dye produce the water soluble or leuco form of the dye. In some instances
tion of sodium carbonate may be necessary to achieve the desired alkalinity. In this
reduced or leuco form, sulphur dyes are substantive to cellulosic fibres. To achieve
sodium chloride to tne
adequate exhaustion, it is necessary to add an electrolyte such as

dye liquor.
To obtain adequate penetration and a satisfactory rate of dyeing, the dye liquo0r the complele
structural formula is incomplete because
heated. This increases the energy of the constituents of the dye liquor, increasing 1 Portion of a sulphur dye molecule. This
composition and structure of sulphur dye molecules is not known.
rate of dyeing, and ensures adequate penetration of the fibre
polymer system its
Once the dye is within the fibre polymer, the reduced sulphur dye 1s conve en
original insoluble form. This is achieved by an oxidation treatment with a mild reagc
such as sodium perborate.
Properties of sulphur dyes
Light-fastness This fair light-tastness y
Printing with sulphur dyes -Iastness rating of sulphur dyes is about 4. a ight-1astness o
im metallic salts to give
proved somewhat by an after-treatment with
Sulphur dyes are not used for printing textile materials.
157
 Textle scence Dyeing und printing
fair light-fastnesS
1s due to a lack ot stability of the
stability of the
dye molecule with vat dyes
about 5. The of sunlight which degrade: the in the Dyeing
presence of
the ulraviolet component
sulphur dye
molecule.1 in hght-fastness with
he improvement h a achromophore
metallic
T h e a p p l i c a t i o n
vat dyes to celluloSiC materials occurs in
five stages.
the
increased stability of the chromophores through
sal.
attributed to the f the Aqueous dispersion

metal atom vat dye 1s dispersed in water.

rLe insoluble
Wash-fastness
The wash-fastness rating of sulphur dyes is about 3-4. This fair wash-faer.
stness Vatting
T h i ss t e p i n v o l v e s slves the chemical reduction of the vat
dye to produce
partly to the aqueous insoluhil.due the soluble,
partly to the relatively large dye molecule and
re-
in the dye molecule
Ot the leuco form of tthe dye. This is achieved
by sodium hydrosulphite, sodium
lack ot any signincant polar groups ced or
dve molecule. The hydroxide and wate and The sodium hydrosulphite chemically reduces the vat
water.
the dve is retained
within the hbre because or t s S1Ze, 1ts aqueous
insolubilit dye in the
ty and nditions created by the presence of sodium hydroxide. Note: The
der Waals' forces of
attraction. alkaline
the original colour of the dye vatting
t e m p o r a r i l y alters
van
stage also

Colour range of sulphur dyes molecules by the fibre

Absorption of dye
Sulphur dyes have a colour range which is mainly limited to black, brown, blueand TLe vatted dye molecules are substantive to the cellulosic material when this is intro-
olive. Sulphur dyed textile materials are also dull. No satistactory explanation can be To achieve
Aucdinto the dye
liquor. adequate exhaustion, electrolyte is
an added to
offered for this.
the dye liquor ofthe
and temperature mayto be increased depending on the specißc dye.
vat
The application and dye molecule
the the fibre occurs
range trom 20°
attemperatures specific
60°C. The addition of the electro-
to
to a

Bronzing Daricular dye occurs in a vat

Sulphur dyed textiles may show a metallic or bronze sheen which is referred to as iquor so as to increase the substantivity
Iyte alters the equilibrium of the dye this he
During stage of dye application the textile material
bronzing. This elfect is undesirable as it detracts from the aesthetic appeal of the dye molecules for the fibre.
in the dye liquor to prevent premature oxidation of the leuco
dyed textile material, as well as giving rise to poor rub-fastness. This
effect is usually must be kept immersed
present in heavy or dark shades and can be caused by excessively heavy dyeing, expo- compound.
sure of textile materials to the atmosphere during dyeing causing premature oxidation
of the following dyeing, or an insuficient Re-oxidation of dye molecules within the fibre
dye, failure to remove dye liquor
excess leuco form of the vat dye has to be
amount of in dye
sodium sulphide the an after-treatment
liquor to keep the dye in its soluble form. The Once within the polymer system of the fibre the
form of the dye. Oxida-
bronzing effect can be removed the excess
by in an aqueous solution of dilute
Oxidised and converted to its original colour and the insoluble
tüon of the leuco compound can be achieved by atmospheric oxygen although this is
sodium sulphide which will remove
surface of the textile material.
dye molecules that are present on the
mild oxidising reagent such as sodium perborate is used
Somewhat slow. In practice, a

to convert the soluble leuco compound into the original insoluble

vat dye.
Cost of sulphur dyes
The relaively low cost of sulphur dyes has meant their continued
Soaping-off vat dyes
use particularly 10 be deposited on the surface of
dark colours such as navy and black. During the previous stage some insoluble vat dye may poor rub-fastness as well as a
removed to prevent
C extile material. This has to be removal of this surface deposit. doap
POSS1ble change of shade due to the subsequent a liquor containing
some suitable
Which is the boiling of the dyed material in
1, was derived from the
act
Vat dyes ent, removes this surface dye. The term soaping-off
surlace
Delore the development of detergents, soap was used
to remove the uye
The name vat was derived from frst
a
the large wooden vessel from which vat re
applied. Vat dyes provide textile materials with the best colour-fastness
dyes the ue
dyes
in common use.
or
a Printing with vat dyes of
a paste
The fibres the preparation
most readily coloured with vat dyes the natural and
-made materials with dyes is achieved through and dye
nxaton

cellulosic fibres. are ma with stab::ale The fabric is printed with the design
reduced d vat dye.

159 159
 Texnie scEncE

Dhyang and pmniing

to achieve adequate penetratuon of the fibre
fibre
poly by O
as in the mer
obtained by steaming
is
material is then oxidised and soaped-off as the dve
molecule. The text1le case ot
dycins
Molecular conñguraton
and characteristics
(see Figs 6.14 and
Vat dves based on indigo and anthraquinone
are 6.15). The e HC
propertues of texule matenals coloured
with vat dyes is at
exce CH
lent fastness
of the vat dye molecule and in part to its aqueons
pan
ibuted in NaO so
to the very large
size

general, vat dyes based

on anthraquinone have
better fastness
properties than va insolubilit OSONa
derived from indigo.
been developed (see Fig. 6.16)
Solubilised forms of vat dyes have te
leuco ester part of the dye molecule
that is responsible tor the aqueous solhshil the
dyes.
ubility ol vaa HC-0
O-CH
Solubilising vat dyes
Awater
Flqure 6. 16 insoluble anthroquinone type of vat dye - C i Vat Green 1, 59825. By reacting this dye to accept
it
Decomes water soiuble.
cdium sulphonate groups.
SoSolubilised Val Green 1, S98z0 Ihis is tne leuco sulphunc ester of C.I Vat Green 1, 59825
tis a

R N
water
solude vat dye

Properties of vat dyes

Light fastness

The light-fastness rating of vat dyes is about 7. The excellent light-fastness of textiles
aloured with vat dyes is attributed to the stable electron arrangement in the chro
molecule. The presence of the numerous benzene rings
CSISomer trans-isomer mophores of the vat dye
contributes to the stability of the vat dye molecule.
Figure 6.14 Indigo, CI Vat Blue 1, 7300 - a n indigo ype vat
dye ihe
diagram shows the structural tormulae ot
synthetic indigo dye It always exists as these wo
iSomers. but dyeing only the co-planar trans-isomer is take
on
up by the fibre s polymer system Indigo has a tair
light-tastness. moderate wash-fastness, and poor fastness to Wash-fastness
ble aching
The wash-fastness rating of vat dyes is about 4-5. The excellent wash-fastness of tex-
tile materials coloured with vat dyes is attributed to the large vat dye molecule as well
as

its aqueous insolubility. The large vat dye

molecule is trapped within the polymer
and is absorbed within
O system of the fibre because of its size and aqueous insolubility
the fibre polymer system by van der Waals' forces.

Cost of vat dyes

other dye classes and are

at dyes have always been very expensive compared with

N invariably used when good fastness properties are required.
O
Solubilised vat dyes has
has been developed. This
th sulphur dyes, a solubilised form of the vat dye
dae vat dyes easier to handle and results in more level dyeings
(se Fig. 0. l0).

Fluorescent brighteners (OBAs),

Figure 6.15 CI Vat Green 8. 71050- an anthraquinone type of vat dye which illustrates the enormous iaze val brightening agents
dye molecules can have and gives the excelent wash- cent which are also known as optical
brighteners, let mponen
of sunlight is
fastness of vat dyed and printed texies are
colourless dyes. Fluorescence occurs when the ultrav
160
 H

w.
Textile science
blue light.
ed as additional bluc light. When applicd
retlected
additonal

as to reflect m o r e blue
blue light which
to textile - 0 -
O-CH
absorbed
and
subsequently
material
textile is H Na O,S
H
sO,Na
OBAs cause
the
BAs
OBAS are
for white textilSCrVed
used for:
are usually uscd H a C - O
CH
materials,

whiter, brighter
textile material.
hese
compounds a arer e not
bleaches an 1aterials
as a w h i t e r and brighter. is p r e s e n t
as sunlight,
these appear radiation,
Such
making

O
ultraviolet

only
when
effective

Digileners may be applied

N
N
-N
fluorescent O Na' O,S SOTNa
Fibres to which textile fibres. Domec
are
available for m o s t
ndry deter orighteners
Fluorescent
brighteners
fluorescent
brighteners
but these are usually only suitable
are usually
able for 6.18
FluoresCent
brighterner-C.I. Fl
Fluorescent Brightener 34, 406055
contain ure
blue fluorescent the Blankapnor type GIL Fluorescent Brightener 30, 40600
gents usually
textile
materials. Apure D re
scent brightener of
cellulosic fibre bAvio
of iluorescent brighteners
Fluorescence Properties
brighteners contain conjugated
double bonds; that Whiteners a n d b r i g h t e n e r s
Molecules of fluorescent covalent bonds. The el mole
Single and double inthe textile material has a slight vellow
cules which contain
alternating
the invisible ultraviolet radiati. the trained
observer,
even icacnea or white
conjugated systems
are capable of absorbing
the solar spectum comp To
This small amount
oI
yellow Can give
the
impresion of slight soiling and may
this in the visible region of the
nent of sunlight
and reflecting
s00-400 nm range
Thus,
(the invisible ultra- detract from their aesthetic appeal. l he presence of a slight amount of blue gives
OBAs absorb electromagnetic
radiation in
the is whiter. Before the advent of OBAs, improved
reflect this in the 400-S00
nm range (visible blue light). ression that the textile material which is a blue pigment.
violet radiation) and was obtained
laundry blue,
using a
whiteness meant that this slight addition of blue can be
The development OBAs has
reflected by the OBAs in the presence of ultraviolet radia-
Application of fuorescent brighteners ohtained through the light
'white' textile materials 'whiter and 'brighter'. Coloured textile mate
similar to dyes and they can be classified in tion. This makes
OBAs have chemical structures which are brighter.
the same way as dyes; that is, according to their application. Details of their applica- rials tend to appear
suitable for
tion can be obtained from the manufacturers of the compounds. For effective brighten- OBAs are in most domestic detergents but these are usually only
present
cellulosic textile materials.
ing, each type of textüle fibre requires its own specific type of OBA.

Light-fastness When ap-

Molecular configuration and characteristics There is a large variation in the light-fastness rating of these compounds.
to cellulosic and protein fibres their light-fastness ranges
from 1 to 2, and in some
Over four-ffths of the commonly available fluorescent brighteners are derived from plied out that this poor light-fastness
is not too
stilbene (see Fig. 6.17). instances may reach 3. It should be pointed
of the OBA's effect due to sunlight
Molecules of fluorescent
brighteners contain conjugated bonds such as-C C-C= =
mportant in the case of cellulosics, since any loss
C-C C or -N = C-C = C-C = C-C-N = C-C-C- occurring in aromatic will be replaced in subsequent laundering with domestic detergents. rating of 4 with selectea
heterocyclic or linear structures. It is the presence of these conjugated double bonds orescent brighteners on nylon can reach a light-fastness case of acrylic fibres
a
lhght
visible as high as 7 for polyesters, and in the
that enables ultraviolet light from
blue light. Figure 6. 18 shows
sunlight to be absorbed and re-emitted as
f fastness rating
of about 4-5.
examples of fluorescent brighteners.
is due to ther continuous
e poor overall light-fastness of fluorescent brighteners
p o n and emission of light which results in their chemical degradaton.

Wash-fastness
wash-fastness
ne wash-fastness rating of fluorescent brighteners is about 3. The fair
OTuorescent substantivity for textile mate
is due partly to their lack of astness may
Figure
1als and thei teners The tair wase
exposure to sunlight.
6.17 Stilbene, the organic radical upon which fiuorescent Eradual degradation by
brightening agents are Das
162 163
Texnie smen OBAs iinn d
of OBAs
of .
of the presence domestic
cellulosics
because
fibres they are applied deter
used on other
d inin the
the
noticeable in
he are
the ev
not brighteners
When
fluorescent
arechosen which will last the
h will expected
gents situation
and brightcners
manufactunng

the textilc article.

to polyamides and wool

brighteners
fluorescent
period
Applying to sunlight over a ce

yellow when exposed

nylon tibres
obtain a white which
and has
Both wool OBAs to cason
treated with selected
can be not applied to wool. Not onl
do
Nvlon fibres OBAS are
and washing. vellow
f a s t n e s s to
both sunlight accelerate the of
able on wool
but they may
fastness properties
they have poor
to sunlight.
wool on exposure

textiles
Solvent dyeing of has become
in a non-polluting form
of water and its disposal
years, the use alternative methods of applying
In recent
development of
nore cxpensive.
This has led to the

colour to textile
materials. of organic solvents
solvents. The use
is through the use of organic
Onc such method largely due to the cost of
of dyeing is still
comparatively expensive,
the purposes used for this method
for re-used. The equipment
the organic solvent which is
recovering

when compared with

of dyeing is cxpensive. con-
and uneconomic
untried
Solvent dyeing is still relatively in the
preclude its possible
use
this does not
ventional techniques. However,
dyeing
future

164