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Textile Dyeing

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									Introduction to Textile Dyeing


                               By
                         Dr. Abu Yousuf
      Department of Chemical Engineering & Polymer Science
           Shahjalal University of Science & Technology
                     Sylhet-3114, Bangladesh




                                                             1
    Basic Textile Terms and Definitions
Dyestuff is organic or inorganic substances
which can absorb light and reflect some lights
to show color. Actually, the dyestuff is water
soluble substances.
Pigment is a substance that can absorb light
and reflect some lights to show color but it is
water insoluble substances. Normally it is
used for printing (with the presence of binder)
or mass-coloration of the synthetic fibers.


                                                  2
             Choice of dye
 You can not assume that to dye any piece of
 fabric to a given colour, all you need to do is use
 a dye of that particular colour.
 No dye will dye all textile fabrics satisfactorily.
 This means, simply, that you must choose a dye
 that will suit the material (or a material that will
 suit the dye).

 Cost consideration
 Shade and fastness requirements
 Kind of material to be dye                            4
          Classification of Dyestuffs
Dyestuffs can be classified by many methods
as follows:
1. by their ionic (e.g. cationic, anionic and
non-ionic)
2. by their fiber dyeabilities (e.g. on
cellulosic, protein, polyester, polyamide etc.)
3. by their names (e.g. acid, direct, disperse,
reactive, basic etc.)
4. by their chemical structures (e.g. azo,
anthraquinone, stilbene etc.)
5. by their origins (e.g. natural, synthetic)
6. by their colors (e.g. red, green, black etc.) 5
Dyeing Processes can be applied in many
stages such as
1. Mass-coloration of the molten fibers
This method is for dyeing the molten
fibers or plastic chips or textile polymers
with pigment dyes. After that, the molten
or polymers will extrude from a spinneret
to form fibers.
Normally, the synthetic fibers are added
with white pigment in order to give a
hiding power (non-see through fabrics).
Advantage: give excellent fastness
Disadvantage: very difficult to clean         6
2. Fiber Dyeing is the method of dyeing
fibers before blending with other colors to
give fancy yarns or fabrics.
Note: This is used for special purposes only.
3. Yarn Dyeing is the method of dyeing yarns
in forms of hanks or packages dyeing. This
will give Scottish’s style fabrics, carpet with
many colors and styles.
Note: This is used in hand loom weaving in
the Northern and North-eastern parts of
Thailand.

                                              7
4. Fabric Dyeing is the method after
weaving, knitting, or non-woven to make
fabrics. This is very popular method of
dyeing as the dyed fabrics will be processed
further to garment industries very easily.
Dyeing forms of the fabric dyeing can be
used in 2 ways:
a. Open width form using the fabrics to
spread without any creases and dye them.
b. Rope form using the fabrics with the
form like a rope (many creases and look
like “a rope”)
                                               8
 Some people classify into:
 1. Exhaustion Process
 This method is using lot of water as shown
 in “Liquor Ratio (ratio between water and
 goods)” This should immerge the goods
 into dye solution for a long time in order to
 let the dye penetrate into the goods. This
 will lead to produce more waste water than
 the continuous process.
Advantage: inexpensive, no need to train the
worker to look after and run them properly.
Disadvantage: lots of water needed, very
slow process (60-120 min/batch.)               9
2. Continuous Process
This method is designed by putting different
machinery into a sequence so that it can
produce the dyed fabric in one pass.
Advantage: very fast process (10-100
m/min), small amount of water in the
process.
Disadvantage: very expensive, need to train
the worker to look after and run them
properly.


                                               10
6. Garment Dyeing
This method is the last process of the
dyeing of goods. However, the penetration
of the dye solution may not be completely
passed to the fibers such as between the
seams, buttons, zippers etc. Normally, it is
used for lingerie, socks, sweater dyeing etc.




                                                11
Name of Dyestuffs   Fibers that can be dyed
Acid                Silk, wool, polyamide,
                    leather
Basic               Acrylic
Direct              Cellulosic, viscose
Disperse            Acetate, triacetate,
                    polyamide, polyester,
                    acrylic
Reactive            Cellulosic, viscose,
                    protein
Vat                 Cellulosic
Sulphur             Cellulosic
                                              12
Factors that give some choices of the
dyestuffs
1. Cheap
2. Non-toxic
3. Compatible to other dyes and chemicals
4. High color strength
5. Better brightness
6. Better fastness
7. Good levelness on the materials


                                        13
         Dyes for Cellulosic Fibers

            Direct Dyes (Anionic)
They can be dyed directly on cellulosic
fibers. Without the presence of salt, when
the fibers are immerged in water, it will show
anionic charge which repels the dyes.
Adding salt into the dye bath, it will reduce
anionic on the fibers so the dyes can get
closer and adsorb into the fibers.
Advantage: cheap, easily dyed on fibers
Disadvantage: poor wet fastness and some
dyes have poor light fastness.                14
Textile Auxiliaries
1. Salt - reduce negative charges on the
fibers
2. Water - dyeing media
3. Fixing Agent - enhance wet fastness but
usually reduce light fastness

Dyeing Conditions (Exhaustion)
dyeing 100oC x 30-90 min
fixing 60oC x 20 min
(Continuous)
pad --> dry --> steam --> wash --> soap -->
                                              15
dry
          Reactive Dyes (Anionic)
They can be dyed on cellulosic fibers. The
mechanism is nearly the same as described in
Direct dyes.
Advantage: high wet fastness due to covalent
bonding (Chemical Bonding) between fibers
and dyes, easily dyed on fibers
Disadvantage: Expensive




                                           16
             Dyeing Conditions
1. Continuous Process
1.1 Pad-dry-bake
This is very easy method for cotton or cotton
blends fibers.
1.2 Pad-dry-Pad (Chemical)-Steam
This will give brighter and more intense
color than method 1.1.
1.3 Pad-batch
This will put the goods into the dye solution
and squeeze with 2 rubber rollers to get rid of
excess water and then batch at room
temperature for 1-2 days.                      17
2. Exhaustion Process
This method will be used in small factory.
Dyeing conditions will be 40-80oC for 30-90
min depending to the types and structures of
the dyes.




                                           18
              Textile Auxilaries
1. Salt - reduce negative charges on the
fibers
2. Water - dyeing media
3. Soda Ash - excite the dye to link with the
fibers with covalent bonding. Therefore, it
enhances wet fastness
4. Fixing Agent - enhance wet fastness for
heavy shade but usually reduce light fastness.



                                             19
       Vat Dye (Anionic when soluble)
The dye is named from the container (Vat)
that used for rotting the dye with alkali
solution. This crucial process will reduce the
dye from insoluble to soluble dye (suitable
for exhaustion in the cellulosic fibers). Now
the manufacturer can synthesize man-made
vat dye.




                                                 20
                Dyeing Process
1. Dissolve dye into water (insoluble dye)
2. Vatting process by reducing the insoluble
dye in alkali condition. (soluble dye)
3. Absorb into fibers (soluble dye)
4. After dyeing, oxidize the dye with
oxidizing agent (insoluble dye)
5. Wash and soap the goods




                                               21
             Dyeing Conditions
1. Continuous Process
1.1 Pad-dry-Pad (Chemical)
The solution of the dye is prepared without
adding reducing agent to ensure leveling
dyeing. After that, the goods are passed to
chemical bath to reduce the dye into soluble
dye and fix within the goods. Oxidizing
agent is added to the goods and converted to
insoluble dyes.


                                               22
1.2 Pad-oxidize-pad-oxidize (many times)
This will put the goods into the dye solution
and squeeze with 2 rubber rollers to get rid of
excess water, oxidize with the air and then
immerse into the dye solution again and
again to allow the dye penetrate into the
goods.




                                              23
               Textile Auxilaries
1. Salt - reduce the negative charges on the
fibers
2. Sodium hydroxide - adjust pH to the
dyeing bath and make the suitable conditions
for reducing agent.
3. Sodium hydrosulfite - reducing agent for
the vat dyes.
4. Water - dyeing media
5. Oxidizing agents - (Hydrogen peroxide or
Acetic acid or Air) oxidize the soluble to
insoluble dye
                                               24
    Sulfur Dye (Anionic when soluble)
The dyeing process has the same process as
described in the vat dye except that using
Sodium sulfide instead of Sodium
hydrosulfide.




                                             25
          Dyes for Synthetic Fiber

 Disperse Dye (polyester, nylon, and acetate)
                  (non-ionic)
The dye is named from less water soluble
and normally appeared in dispersion in water.
The dye shows no charge due to the groups
presented in the dye molecules.
              Dyeing Conditions
    Insoluble    Less water   Water insoluble
      dye in      soluble      in polyester
      water                       fibers
                                                26
1. Exhaustion Process
1.1 At boil with carrier
This process is suitable for acetate fiber and
pale shade polyester fiber dyeing. Carrier is
an auxiliary for swollen fiber in order to
allow more dyes absorbing in. Now the use
of carrier is reduced because it may be a
carcinogen.
1.2 At 130̊C without carrier
With the high temperature, the dyes will be
dissolved into smaller molecules and the void
in fiber structure will be opened. This will
give heavy shade.                              27
2. Continuous Process
Pad --> Pre-dry (100oC x 30 sec) -->
Thermofixation (180oC x 30 sec) -->
reduction clearing (RC) --> wash --> dry
        Printing with Disperse Dyes
With the sublimation property, the dyes can
be printed on paper, place the fabric with a
printed paper and then using an iron with
high temperature pressed on the paper. The
dyes will transfer from paper to polyester
fiber. This is called “Transfer Printing”.     28
               Textile Auxilaries
1. Dispersing Agent - make the dye solution
stable and disperse in the dye bath.
2. Acid - adjust pH to the suitable condition
for the dye bath.
3. Carrier - swell the fiber and dissolve the
dye to make the dye getting into fiber.
4. Leveling agent - make more leveling
dyeing (some will have adverse effect on
slower dyeing)
5. Water - dyeing media
                                                29
         Reduction Clearing (R.C.)
After dyeing process, the dyed goods should
be removed excess dyes on the fiber surface.
R.C. will give higher washing and rubbing
fastness of the dyed goods.
Using alkali solution, sodium hydrosulfide
and dispersing agent, the R.C. will be done at
60oC x 20 min.
Note: Do not use more than the
recommended temperature because sodium
hydrosulfide can be decomposed.
                                             30
              Acid Dye (Anionic)
The dye is called acid because it needs acidic
dyeing condition. It can be dyed on protein
fibers (silk, wool, other animal fibers) and on
polyamide fibers.
Acidic condition will give the fibers showing
positive charge. As the negative charge will
attach directly to positive charge, and
penetrate into the fibers.
               Dyeing conditions
100oC x 30-60 min

                                                  31
              Textile Auxiliaries
1. Leveling agent - for levelness dyeing
2. Retarding agent - for inhibiting the dye not
attach to fibers too fast
3. Acid - adjust the dyeing condition and
make the fibers to show positive charges
4. Water - dyeing media




                                                  32
            Basic Dye (Cationic)
The dye shows positive charge. Normally,
the dye can be applied on wool, silk and
polyacrylonitrile (acrylic).
             Dyeing Conditions
100oC x 30-60 min




                                           33
              Textile Auxiliaries
1. Leveling agent - for levelness dyeing
2. Retarding agent - for inhibiting the dye not
attach to fibers too fast
3. Acid - adjust the dyeing condition and
make the fibers to show negative charges
4. Water - dyeing media




                                                  34
     Dyes        Dyeing Condition (pH)
Acid (Wool)             2-4, 4-6, 6-8 (depends
                        on types of dyes)
Acid (Nylon)            4.5-5.5, 6-7 (depends
                        on types of dyes)
Basic                   3.5-4
Direct                  7.0
Disperse (Polyester) 5-6
Disperse (Acetate)      6.5-7.0
Disperse (Triacetate) 4.5-6.5
Reactive                7.0 (Exhaustion)
                        11.0 (Fixing)
                                                 35
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