Friday 29 December 2017
Delustring
Introduction
ð Rayon
fibres are having a bright metallic luster.
ð The
high metallic luster of this fibre is not acceptable by the consumer.
ð Consumer
needs a little luster approximately to that of natural silk.
ð In
order to make the highly lustred rayons appear like natural silk, it is
necessary to reduce the luster and that is known as DELUSTRING.
Mechanism
To delustre the bright metallic
lustrous fibre, it is necessary:-
(1) To
scatter the light from the external surface.
(2) To
reflect the scattering light in a diffused manner which penetrate into the
interior of the fibre.
Methods
1) Internal
delustring
2) External
delustring
Internal Delustring
ð In
this method the delustring of rayon is done by adding the delustring agent in
the spinning bath during the manufacture of filament itself.
ð Various
substances which have high refractive index (more than 1.5) are added in the
spinning solutions of the filaments and then the filaments are extruded.
ð The
filaments are finished before the filament formation itself.
|
Chemical
|
Refractive
index
|
Delustring
effectiveness
|
|
TiO2
|
2.5
|
0.5
%
|
|
Zinc sulphate
|
2.37
|
1 %
|
|
Barium
|
1.637
|
4 %
|
Advantages
of TiO2
ð It
has a high refractive index of 2.5
ð It
has very small particle size of 0.75 micron and will not block the spinneret.
External
Delustring
ð The
mechanism is precipitating some insoluble substances on the fibre using various
delustring agent.
ð An
after treatment to rayon fabrics is carried out which is known as external
delustring method.
ð Here,
the refractive index and particle sizes are not important.
ð External
delustring can be done by two methods.
·
One bath method
·
Two bath method
ð These
methods involve external white pigment coating uniformly on the surface of the
fabric.
One
Bath Method
ð In
this method, matting agents are made in advance and applied in presence of
certain additives which brings attachment to the fibre.
ð China
clay, aluminium oxide, zinc oxide, titanium oxide and barium sulphate are
widely used.
ð Among
with the above compounds 5 % softener, 15 % of resin may be added.
ð The
fabric becomes unnecessarily harsh and stiff by the use of TiO2.
Two
Bath Method
ð In
this method, the fabric is first impregnated with Barium hydroxide.
ð Chemicals
like stearamide can be added in the bath if higher exhaustion is required.
ð The
impregnated fabric is then impregnated again in a bath containing H2SO4.
ð The
H2SO4 reacts with Ba(OH)2 to form BaSO4
which is insoluble.
Ba(OH)2 + H2SO4 à
BaSO4 + 2H2O
Process
Pad – Dry – Cure
ð However,
the two bath method is the most effective since the surface deposition will be
less. The fabric does not become too harsh and stiff.
Polyester Printing
Printing of Polyester by Direct Style
Principle
Polyester fabric can be printed with disperse
dye as per the dyeing procedure.
ð Printing of Polyester
is differs from dyeing as below:-
·
Various disperse dyes can be used in combination with each other.
·
No
blocking effect occurs.
·
Colour
build up is better.
·
Fastness
to water, sea water, perspiration and chlorine is essential.
Ingredients
(1)
Dyes:-
·
Disperse
dyes are the most suitable for printing of polyester fibre materials.
·
Selected
dyes with good steaming and thermofixation fastness are suitable.
(2)
Thickeners:-
·
Thickeners
having high solid content are best suitable for this printing.
·
Natural
gums, starch ethers and modified locust bean gums (gum indalca) are the best
commonly used thickeners.
·
Alginate
thickener is less suitable since it imparts the brightness of the print with
disperse dyes especially in the thermofixation.
·
Prints
with Carboxy methyl cellulose are normally level and sharp and have good yield.
·
Starch
ethers have not satisfactory wash off properties.
·
British
gum produces dull prints.
·
Emulsion
thickeners increase levelness and penetration of the dye in the fibre.
(3)
Dispersing
agent:-
·
Disperse
dyes are insoluble in water, and should be kept in dispersion form.
·
Therefore,
paste should contain dispersing agent, like Setamol WS
(4)
Wetting
agent or Solvent:-
·
For
pasting of disperse dye, due to its insolubility in water, the dye should be
wetted by wetting agent, eg. TRO and dyes are solubilising in dispersion form
using solvent like ethylene glycol.
(5)
Acid:-
·
Since
most of the disperse dyes are sensitive to alkali, medium of paste is kept
acidic using organic acid. A small amount of citric acid or tartaric acid is
added to bring down the pH about 6.0
(6)
Oxidising
agent:-
·
Sodium
chlorate is used to protect the brightness of the dye against any possible
reduction of the dye under the prolonged steaming conditions.
(7)
Acid Liberating agent:-
·
The
print paste should remain acidic during steaming, so Ammonium sulphate is used
as an acid liberating agent. Carrier is also used to improve colour yield.
Procedure
·
The
printing paste is prepared as follows:-
50 parts Disperse dye
10 – 20 parts Dispersing agent (setamol WS)
10 – 20 parts TRO
10 – 20 parts Citric
acid or (1 – 2 parts Tartaric acid)
160 parts Water
10 parts Ethylene Glycol
710 parts Thickener
5 parts Ammonium sulphate
5 parts Sodium
Chlorate
1000 parts
·
After
printing, fabric is dried and fixation is done by three different methods.
(1)
Steaming:- Printed fabric is steamed for 30
minutes at 128ºC (30 psi pressure). This system produces full colour yield and
bright prints. This is a batch wise process and needs more labour.
(2)
High temperature steaming (curing):- Printed
fabric is cured at 180ºC for 1 – 2 minutes. This is a continuous process and
gives full colour yield and bright prints.
(3)
Thermofixation:- Printed fabric is thermofixed
at 210ºC for 30 seconds. This is a continuous process of fixation, and carried
out on stenter or a backing machine. In this method, the dyes are selected on
the bases of their sublimation fastness properties.
·
After
fixation, fabric is rinsed with cold water and hot water, reduction cleared (at 40 – 50ºC for 15minutes) in following bath:-
20 parts Sodium hydrosulphite
30 parts Sodium hydroxide
10 parts Polyvinyl pyrrolidone (stripping
assistant)
1000 parts
·
Finally,
the cloth is rinsed, soaped at the boil, washed and dried.
Acrylic Printing
Printing of Acrylic by Direct Style
Principle
Acrylic fabric can be printed with cationic
dye as per the dyeing procedure.
ð Printing of Acrylic
is differs from dyeing as below:-
·
Dyes
of various (Cationic/Basic) classes can be used in combination with each other.
·
No
blocking effect occurs.
·
Colour
build up is better.
Ingredients
(1)
Dyes:-
·
Cationic,
disperse and vat dyes are suitable for printing acrylic fibres.
·
Cationic
dyes are the most important and most widely used class of dyes for printing of
acrylic fabric.
·
Prints
produced with cationic dyes have excellent wet and rubbing fastness.
·
Disperse
dyes give dull shades when printed on acrylic fabric.
·
Sharp
outline with black colour is produced using disperse dyes only.
(2)
Thickeners:-
·
Thickeners
having high solid content are best suitable for this printing.
·
Modified
gaur gum, tragacanth, British gum etc. are suitable thickeners for printing of
acrylic
·
Since
the fabric is hydrophobic in nature thickener selection is important factor.
·
Modified
guar gum is alkaline in nature and hence has to be neutralised with acid.
·
British
gum – gum tragcanth mixtures perform well.
(3)
Swelling
agent:-
·
To
increase the diffusion of dyes in the fibre and colour value, fibre swelling
agents are added in the paste.
·
Excessive
use of swelling agents may result in increased bleeding of dyes.
·
Eg.
Resorcinol, Phenol
(4)
Wetting
agent or Solvent:-
·
Thiodiethylene
glycol is a solvent for the cationic dyes, some of which may be sparingly
soluble in water, especially at low temperature.
·
Addition
of swelling and oxidising agent decreases the solubility of the dye, hence
addition of solvent is desirable.
(5)
Acid:-
·
Paste
contains acetic acid as well as tartaric acid to improve the solubility of the
dyes and to adjust the pH of paste.
·
Since
acetic acid is lost by evaporation during drying of the prints, non-volatile
acid (tartaric acid) supplies the necessary acidity during steaming.
(6)
Oxidising
agent:-
·
Sodium
chlorate is used to protect the brightness of the dye against any possible
reduction of the dye under the prolonged steaming conditions.
Procedure
·
The
printing paste is prepared as follows:-
50 parts Cationic (Basic) dye
20 parts Acetic acid (50 %)
20 – 30 parts Thidiethylene
glycol
20 – 30 parts Tartaric
acid
165 parts Water
5 parts Sodium
chlorate
680 parts Thickener
20 parts Resorcinol/Phenol
1000 parts
·
After
printing, fabric is dried and steamed in star ager at 103ºC for 40 minutes.
·
A
temperature of 105ºC is the maximum allowable steaming temperature.
·
If
it exceeds 105ºC undesirable effects like alteration of hand, bleeding,
increased fabric shrinkage etc. result.
·
The
steamed fabric is after treated with a bath containing 1 to 2 gpl anionic
detergent at 60ºC for 30 minutes.
·
Finally,
the cloth is rinsed, washed and dried.
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