MOQ | 100 KGS |
Port | AS PER DISCUSSION |
Packaging | 25KG |
Lead Time | AS PER DISCUSSION |
Form | POWDER |
SULPHUR COLOURS
Sulphur dyes are non-ionic, possess sulphur linkage, are water insoluble and produce shades that are reasonably cheap and wash and light fast. Dyes are applied in reduced and solubilised anionic state possessing affinity for cellulosics. After dyeing, oxidation is carried out to restore parent non-ionic dye structure; sulphur dye-cellulose attachment is established through physical forces with dye aggregation occurring in situ. Stored dyed cellulose is liable to be tendered in humid atmosphere due to presence of loose sulphur. Sodium sulphide, the most effective reducing/solubilising agent pollutes waste water, requiring the adoption of alternative reducing systems such as glucose, hydroxyacetone and reducing sugar.
These are water insoluble dyes and have no affinity for the
cellulosics as such, but solubilised when treated with a weak
alkaline solution of sodium sulphide or any other reducing agent
to form a leuco compound. These leuco compounds are water soluble
and have affinity for the cellulosic materials such as cotton,
viscose, jute and flex etc. These dyes are absorbed by the
cellulosic material in the leuco form from aqueous solution and
when oxidized by suitable oxidizing agents, got converted into
insoluble parent dye, which is fast to normal color fastness
parameters.
Shades lack tinctorial brilliance, limiting production to only deep shades like blue, black, khaki and green while brilliant red, orange and yellow are unsuccessful.
BASIC PROPERTIES:-
1. Economical dyeing with excellent tinctorial value and good build up properties.
2. Good overall colorfastness properties such as wash fastness, light fastness, perspiration fastness etc. Moderate fastness to crocking and poor fastness to chlorines bleaching agents such as bleaching powder and sodium hypochlorite.
3. Limited shade range to produce only dull shades and there is no true red dye in the range.
4. These dyes can be applied by exhaust, semi continuous or continuous dyeing methods on garment, yarn, knits, fabric as well as loose stock etc.
5. Available in powder, granules and liquid forms.
6. Sulphur black 1 is the major black dye used worldwide for dyeing of cellulosics.
7. The conventional dyeing process is not environment friendly due to pollution problems of sodium sulphide as well as sod/pot. Dichromates.
8. When dyed by using non polluting reducing and oxidizing agents the process is environment friendly.
APPLICATION:
Mechanism of the Sulphur Dyeing
The application of the sulfur dyes involves several steps, which
are described as given below,
1. Dissolving the dyestuff:
The dye is taken in an SS vessel (size of the vessel should be
selected as per the quantity and solubility of the dyes) and
pasted well with a good alkali stable wetting agent and small
quantity of soft water. A required quantity of soda ash may be
added to neutralize any acid formed in the dyestuff during
storage. (if the acid is not neutralized, it will react with the
sodium sulphide, resulting into formation of H2S gas, which will
result into incomplete and poor reduction of the dyes). It is
very important that the dye dissolution must be complete
otherwise particles of the undissolved dyes may deposit on the
surface of the substrate resulting into patchy dyeing and poor
rubbing / washing fastness.
2. Reducing the dyes to form a leuco
compound:
Chiefly sodium sulphide is used as a reducing agent for the
sulfur dyeing. The quantity of the reducing agent depends upon
the shade depth and M:L of the bath. For complete reduction the
required quantity of the sodium sulphide is dissolved in a
separate container and solution is allowed to settle for 10-15
min. before decanting the clear solution into the dye dissolving
vessel. Further boiling water is to be added to make up the
required volume , then heated to boil for 10-15 minutes either by
live steam or indirect heating , for complete reduction of the
dyestuff.
3. Dyeing with the reduced dyes:
It is advantageous that the goods are scoured well before dyeing
,to have a satisfactory absorbency for better penetration. The
dye bath is kept ready with small quantity of the alkali stable
and compatible wetting agent , a dye bath stabilizer , sodium
sulphide and caustic soda or soda ash to maintain the alkalinity
of the dye bath. The dye solution is then added through a filter
cloth slowly over 15-25 minutes and then run for another 15
minutes at 40-50 oC , then temperature is raised to 60 oC and
electrolyte is added in at least 3 portions. The quantity of salt
added is depends upon the type of shade , depth and dyestuffs ,
however a maximum quantity does not exceed more than 15 gpl .The
temperature is then raised to above 80 oC or even boil depending
upon the dyes and kept for sufficient time to get the desired
shade.
After getting the correct shade the bath is either dropped by
draining the contents or by collecting it in the storage tanks
for reuse after replenishing with fresh dyestuffs.
4. Washing off the unexhausted
dyestuff:
With an objective of achieving the highest possible color
fastness results such as washing , rubbing , light and
perspiration , the material is washed and rinsed several time
with fresh water to remove maximum possible loose residual dye as
well as sodium sulphide from the material. At the end of the
washing process the water should be clear , with no further
leaching out color . After washing the material is given a hot
wash at 70 0C .
5. Oxidation back to the parent dye:
The oxidation is done to reconvert the leuco compound back to
insoluble parent dye. There are number of methods available for
oxidizing the leuco compound which is used either independent or
in combination, such as
a. Oxidation by exposing the dyed material to atmospheric
oxygen.
b. Oxidation by the dissolved oxygen in the fresh
water.
c. Chemical oxidation , by employing different oxidizing
chemicals, such as
I. acetic acid
II. sodium perborate in cold at neutral pH.
III. Hydrogen peroxide and acetic acid.
IV. Potassium or sodium bicarbonates and acetic acid.
6.
After treatment:
After
oxidation and hot wash , the material is neutralized with soda
ash to adjust the pH and then soaping treatment is done with a
neutral soap and soda ash at boil. Followed by a hot wash at 85
0C
7. Dye fixing treatment:
Optifix F(clariant) is a cationic dyefixing agent , which is
applied in alkaline conditions ( at a pH of 10-11) , and is a
suitable dyefixer for sulphur dyed material to improve the color
fastness.
8. Softening:
A suitable (compatible) softener can be applied to the dyed
material as per the intended end use and dyestuff
applied.
9. Final treatment:
To avoid the tendering of the dyed material final wash is given
to maintain a slight alkaline pH by a weak base or acid
neutralizing agent at the end without further washing. Following
treatments are recommended,
§ Soda ash wash 2-3 gpl
§ Sodium Acetate 2-3 gpl
§ Tetrasodium pyrophosphate 5.0 gpl
§ Lime and tannic acid treatment
10. Use of Standing Bath:
Since a large quantity of the dye always present in the
unexhausted form in the spent liquor , this remaining dye can be
reused , after replenishing with fresh dye. This system is
particularly suitable when producing repeated lots of the same
shade with a single dye , such as black.
The dye liquor at the end of dyeing cycle is collected in the
tanks, to replenish the bath a separately made dye solution is
added and calculated quantities of sodium sulphide , soda ash as
well as salt are added. The final volume is made up to the
required level and reused. Usually a 50 –70% dye is replenished
in case of blacks.
The spent bath use is not recommended in case of mixture shades ,
due to difference in the exhaustion and fixation of individual
dyes.
*Please refer to our technical for further information.