Important thickener used in printing
Important thickener used in printing and their properties
various gums and starches,
Alginates, modified celluloses, emulsions, and synthetic thickeners are used as
thickeners in printing; their names and preparation are given below.
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| Important thickener used in printing |
Starch:
Both wheat starch and
maize starch is used by M thickeners. When starch is most widely used. A 10% the paste is prepared by taking 100g of starch,
Made into a smooth slurry
with cold water followed by the addition of 4ml castor oil and 900 ml water, it is
boiled with continuous stirring till a thick paste is obtained.
The paste is then cooled
under continuous stirring. If It is not stirring while cooling, it may form a
jelly which is of no use in printing.
Gum Tragacanth
(Gum Dragon):
A 6% paste of this gum is usually
propend by taking 60 g of gum (in the form of dry honey scales or leaves) in
940 ml of cold water and allowing.
It to stand for 2 to 3
days with occasional stirring. its a homogeneous paste is not obtained, then
the mixture is boiled with stirring until the gum is dissolved giving a
homogeneous pesto.
This is cooled while
stirring and then strained. The paste is not affected by alkali.
Starch-tragacanth
Paste:
This paste is prepared by mixing
100 g of wheat starch with 300 ml of water and 600 g of gum tragacanth paste
(6%) under stirring and boiling for half an hour with constant stirring.
It is then cooled and
strained. No other gum works well with starch except gum tragacanth because
starch paste is spoiled by other natural gums.
Gum Arabic
(Gum Senegal):
A 50% paste of the gum is
prepared by soaking the gum in water for several hours and at rained; the paste
is slightly acetic and is neutralized before use.
It is the most common thickener
used in block and screen printing
Locust Bean Gum:
A 3% paste of this gum is
prepared by sprinkling the gum over cold water when it swells; it is then boiled
till it forms a smooth homogenous pate. Only sufficient
paste require for use is prepared at a lime as
it has poured keeping qualities.
It is coagulated by alkali
and this property la utilized in lash age' process in the printing of vat dyes.
Guar Guin:
This gum is cheaper than
gum tragacanth and is obtained from the seed of gaur plants. A %2 V solution
gives is a trick paste, It is prepared by sprinkling the dry powder over water
under constant stirring and is allowed to thicken at least for Iwo hours.
It is non-ionic in nature
which is responsible for its constant viscosity over a pH range of 1 to 10.5
and Its compatibly with dyes and chemicals.
Its derivatives are used
in printing synthetic fabrics. Meypro gum is a modified guar gum; 5% of the paste of Mapro gum CRX is prepared by boiling the gum in the water of 20 minutes.
It is resistant to acids and alkalis.
Indalca Gums:
These are modified guar gum thickeners
suitable tor screens printing. Both hand and machine printing.
They are manufactured by India
gum industries ltd. there are three series of this gum viz. indica U series
indica AG series an indica Pa series. The percentage of paste to be prepared varies
from 5 to 9. The paste is prepared by adding the powder to cold water under
high speed stirring for 1/2 hour and leaving it: over right.
The pastes are usually alkaline
and are made acidic by acetic, formic, tartaric, or citric acid.
Nafka Crystal Gum:
This gum is similar to gum
Arabic but it has 3 to 4 times the thickening power of natural gums. A 20% past
is prepared by dissolving the gum in cold water and allowing t 10 stands
overnight. It is widely used for printing polyester, nylon and acetate rayon
and in roller and screen printing of all fibers, the pate is very stable.
British Gum or
Dextin:
This is obtained from
starch by converting by hydrolysis into soluble dextrin, A 5% paste is prepared
by boiling the product with water under constant stirring for about 1/2 hour
Light British Gum i.e. yellow dextrin contains little starch which is not
converted whereas dark British gum has the whole of starch converted it to
dextrin,
Sodium Alginate:
This is obtained from sea
weed and had assumed great importance because of its use in the printing of reactive
dye with which it does not react
It gives a viscous solution
in water with low adhesive power. Acid makes the paste thinner. It is,
th9rafore, used where neutral or alkaline thickening is required. A 6%paste of
alginate is prepared by sprinkling the powder over the cold or warm water under the
high-speed stirrer.
It is also used in combination with emulsions of kerosene as thickeners. It is the market under various trade names such as Lanitux, ProtakP. Manutax and Algogel, Protakyp is special alginate resistant to alkali and is therefore suitable for use in the printing of rapid fast and raping a dye
