FORM 2
THE PATENT ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A process for obtaining a dope dyed viscose fibre.
APPLICANTS
Aditya Birla Science and Technology Company Pvt Ltd, Plot number 1 and 1-A/1, Taloja, MIDC, Taluka- Panvel, District- Raigad- 410208, Maharashtra, India.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes this invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
[001] The present invention relates to a process for obtaining a dope dyed viscose fibre. More particularly, the present invention relates to a process for obtaining a dope dyed viscose fibre by using surface modified carbon black as a pigment.
BACKGROUND OF THE INVENTION
[002] Cellulosic fibres of the viscose type are manufactured by dissolving sodium xanthate in caustic soda to form a syrup-like spinning solution known as viscose and commonly referred to as a spinning dope. The spinning dope is spun by extruding it through fine holes / spinnerets into a coagulating bath of sulphuric acid and salts which neutralise the alkaline content of the viscose dope and regenerate the original cellulose as continuous filaments.
[003] Pigments can be added to the spinning solution if coloured fibres are desired. Pigments are usually diluted in water and in-line added to the spinning dope before it is spun through the spinnerets. Generally, dispersing agents are added at this step so that the pigments are better dispersed thereby avoiding any agglomeration. The ability of the fibre to attain the desired colour or shade depends on the distribution pattern of the pigment into the fibres. Pigments that are not stable in the alkaline dope conditions may form unstable dispersion, agglomerate, and/or clump together.
[004] Generally, in order to obtain darker shades, carbon black is used as a pigment. Carbon black is inherently hydrophobic in nature and does not disperse uniformly in any aqueous medium. Homogenous dispersion of the pigment is crucial for getting desired properties. Improper dispersion of the pigment leads to agglomeration of the pigment due to which when a mixture of dope along with pigments is regenerated through the spin bath, carbon black tends to agglomerate and further leads to choking in the spinnerets resulting in

increase in fibre faults and breakages. Further, due to frequent choking there arises a need to frequently change the spinnerets which increases operational cost and reduces production of fibre.
[005] Furthermore, due to the low dispersion property of carbon black, there is a non-uniformity in distribution of the pigment throughout the fibres and a lighter shade in fibre is seen. Moreover, due to the unstable dispersion of carbon black, additives such as surfactants are added to provide a stable dispersion in the dope. These additives help in reducing the tension in the dope thereby leading to a uniform dispersion. However, their use results in an increased operational cost.
[006] Therefore, there is a need for a simple yet an effective process for obtaining a dope dyed viscose fibre using a pigment which exhibits good dispersion properties in the dope and does not form agglomerates thereby avoiding choking of the spinnerets. Also, there is a need of a process for obtaining a dope dyed viscose fibre using a pigment that is uniformly distributed resulting in a darker shade of the fibre. Furthermore, there is a need of a process which uses a pigment that is stable in the dope and at the same time shows a uniform dispersion. Lastly, there is a need of a process for dope dyeing which does not require the use of dispersing agents for effective dispersion of the pigment.
SUMMARY OF THE INVENTION
[007] According to an embodiment of the present invention, there is provided a process for obtaining a dope dyed viscose fibre, comprising the steps of a) mixing one or more pigments with water to obtain a mixture; and b) adding the mixture of step a) to the cellulose dope, wherein at least one pigment in step a) is carbon black which has been surface modified through ozonation.

[008] According to another embodiment of the present invention, there is provided a process for obtaining a dope dyed viscose fibre using surface modified carbon black as a pigment to obtain a colour fast and uniformly distributed dark shade of viscose fibre wherein the carbon black is surface modified through ozonation.
BRIEF DESCRIPTION OF THE DRAWINGS
[009] Figure 1 illustrates graphs showing stability of slurry prepared by using ozonated and unozonated carbon black in the cocobrown shade, according to an embodiment of the present invention;
[010] Figure 2 depicts a difference in darkness of shade between the dope dyed viscose fibres of coco brown shade obtained by using unozonated and ozonated Carbon black , according to another embodiment of the present invention;
[011] Figure 3 shows a comparative graph for the particle size distribution by image analysis of slurry prepared by using ozonated and unozonated carbon black in the navy blue shade, according to an embodiment of the present invention;
[012] Figure 4(a) shows a comparative analysis of the particle size distribution by image analysis of 100% unozonated carbon black, according to an embodiment of the present invention; and
[013] Figure 4(b) shows a comparative analysis of the particle size distribution by image analysis 85:15 unozonated carbon black and ozonated carbon black.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[014] The present invention relates to a process for obtaining a dope dyed viscose fibre. The main purpose of the present invention is to use a pigment during dope dyeing which

shows good dispersion property resulting in a darker shade and is uniformly distributed in the fibre.
[015] According to the process of the present invention, coloured fibres are produced from spinning processes using desired pigments. In an embodiment, a surface modified pigment is used in combination with other different coloured pigments to produce fibre with dark coloured shades. Preferably, a surface modified carbon black is used as a pigment to give dark coloured shades. The dark coloured fibres are obtained by using surface modified carbon black that exhibits excellent colour uniformity and/or colour retention.
[016] In a preferred embodiment, the carbon black is modified by ozone treatment. Preferably, carbon black is treated with ozone in dry state which modifies the surface of the carbon black. The surface modification of carbon black is achieved by gaseous treatment of carbon black wherein the gas consists of a mixture of air and ozone at ambient temperature. Preferably, the surface modification makes the carbon black hydrophilic resulting in excellent dispersion properties. During the ozone treatment, oxidation of the carbon black surface takes places and introduces hydrophilic functional groups on carbon black surface further imparting surface acidity to it. Additionally, due to increase in functional groups on the surface of carbon black, increase in volatile content is also observed. This hydrophilic property of the surface modified carbon black permits it to be more dispersible in an aqueous medium. In other words, the surface modification is such that it results in a homogenous distribution of the surface modified carbon black throughout the aqueous medium. In an embodiment, the ozone treated carbon black shows excellent dispersion properties in the viscose dope and does not agglomerate thereby saving the spinnerets from choking. In another embodiment, while using surface modified carbon

black in manufacturing coloured viscose fibres, the surface modification of carbon black is such that it is stable in the spinning solution.
[017] In an embodiment, the surface modified carbon black is homogeneously dispersed such that there is no need to use any dispersing agent and/or surfactant.
[018] In a further embodiment of the present invention, the uniform distribution of surface modified carbon black results in darker shade of fibre. This may also result in use of lower carbon black loading to achieve the desired shade.
[019] In an embodiment of the present invention, the percentage of volatile content in the surface modified carbon black is in the range of about 1 to 6%.
[020] In another embodiment of the present invention, acid content of the surface modified carbon black is in the range of about 0.4 to 2.5 mMole/gram of carbon black.
[021] In a further embodiment of the present invention, the percentage of surface modified carbon black in the pigment and water mixture is not more than 50%. Further the percentage of surface modified carbon black in the pigment and water mixture is in the range of about 0.1 to 40%.
[022] In an embodiment of the present invention, the percentage of surface modified carbon black in the dope is not more than 0.5% and not less than 0.01%.
[023] In another embodiment of the present invention, the percentage of ozone in air used for ozone treatment is in the range of about 0.5 to 5%.
[024] In a further embodiment of the present invention, the surface modified carbon black has a surface area in the range of about 70 to 500 m2/g and average particle size in the range of about 25 to 30 nm.

EXPERIMENTAL DATA
[025] The following experimental examples are illustrative of the invention but not limitative of the scope thereof:
[026] In the following examples, unozonated carbon black (conventional) based pigment formulation was replaced by ozonated carbon black along with other colour pigments for coloured fibres and a mixture of ozonated and unozonated carbon black for obtaining a black fibre.
[027] Pre-determined quantity of surface modified carbon black was added to water. Uniform dispersion in water was obtained by dispersing surface modified carbon black pigment with the aid of ultrasonication. via a horn type ultrasonication probe. [028] Moreover, the fibres were spun using dope containing unozonated carbon black and/or ozonated carbon black . The depth of colour for the spun fibres was measured in terms L*, a* and b* values on a colour spectrophotometer. L* can take values from 0 to 100. Minimum L* value of 0 represents black, while maximum value 100 represents a perfect reflecting diffuser reflector (white). a* measures a colour’s position between red/magenta and green (a* values: -ve green, +ve magenta, indicate), while b* measures its position between blue and yellow (b* values: -ve blue, +ve yellow). In general, lower L values represent darker shades.
Example 1: Depth of Shade
[029] Dope dyed viscose fibres of coco brown shade were obtained by addition of three individual pigment formulations comprising red, yellow and black (carbon black based) in a predetermined ratio as a slurry in water to the dope. Both ozonated and unozonated carbon black formulations were used. The stability of the slurry was measured by UV Visible Spectroscopy.

[030] Fibres were then spun and the shade depth was measured. The fibre prepared using ozonated carbon black showed higher depth compared to that prepared using unozonated carbon black.
[031] Figure 1 depicts a graph of absorbance (y-axis) vs wavelength (x-axis) and describes a comparative analysis of the slurry stability between unozonated and ozonated carbon black in the cocobrown shade. It was observed that there was no decrease in absorbance of the pigment with time in the ozonated carbon black slurry. The UV-Vis Spectroscopy analysis showed that ozonated carbon black in cocobrown slurry remained stable at the end of 48 hrs while the unozonated carbon black slurry showed a decrease in stability.
[032] The two Cocobrown shade fibres are shown in Figure 2 while the L*, a* and b* values are summarized in Table 1.
Table 1 – L*, a* and b* values of dope dyed viscose fibers of coco brown shade.

Coco brown shade
Image Carbon Black type in coco brown shade L* a* b* % Strength
Unozonated 22.31 25.03 21.23 100.00

Ozonated 13.09 23.81 16.82 213.00

Example 2: Navy Blue Shade
[033] Dope dyed viscose fibres of navy blue shade were obtained by addition of three individual pigment formulations comprising red, blue and black (carbon black based) in a

predetermined ratio as a slurry in water. Both unozonated carbon black and ozonated carbon black were used. As evident from Table 2, ozonated carbon black in dope resulted in darker shade of fibres due to improved dispersion of ozonated carbon black in dope.
Table 2 – L*, a* and b* values of dope dyed viscose fibers of navy blue shade.

Navy Blue Shade
Carbon Black type in navy blue shade L* a* b* % Strength
Unozonated 18.39 1.85 -7.42 100.00
Ozonated 17.72 1.90 -6.93 106.65
[034] Moreover, Figure 3 compared the high resolution optical images of dope containing aqueous dispersions of unozonated and ozonated carbon black. These images were analysed by shadowgraphy to determine particle size distribution as shown in Table 3
Table 3: Particle size distribution of Ozonated and unozonated carbon black based navy blue slurry

Particle size Slurry containing Unozonated carbon black Slurry containing ozonated carbon black
<2 micron 43.3 46.4
>2 micron 56.7 53.6
Example 3:
[035] A part of unozonated carbon black used in black dope dyed fibres was replaced with ozonated carbon black. Dope dyed fibres of black shade were prepared by using both unozonated carbon black and a blend of unozonated and ozonated black (85:15). Fibres obtained from the above blended formulation were darker in shade than those with only unozonated carbon black formulation.

[036] Figure 4(a) shows the particle size distribution obtained by image analysis for 100% unozonated carbon black.
[037] Figure 4(b) shows the particle size distribution obtained by image analysis for a blend of unozonated carbon black and ozonated carbon black in the ratio 85:15.
[038] As evident from Table 4, presence of ozonated carbon black in the blend resulted in darker shade of fibres due to improved dispersion of ozonated carbon black in dope.
Table 4 – L*, a* and b* values of dope dyed viscose fibers of Black shade

Black Shade
Carbon Black type in black shade L* a* b* % Strength
Unozonated (100%) 16.76 0.23 0.52 100.00
Unozonated /Ozone treated (85:15) Blend 15.91 0.26 0.44 108.41
[039] The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obvious modifications and variations are possible in light of the above teachings.

We Claim:
1. A process for obtaining a dope dyed viscose fibre, comprising the steps of:
(a) mixing one or more pigments with water to obtain a mixture; and
(b) adding the mixture of step (a) to cellulose dope,
wherein at least one pigment in step (a) is carbon black which has been surface modified through ozonation.
2. The process as claimed in claim 1, wherein the percentage of surface modified carbon black in the mixture is not more than 50%.
3. The process as claimed in claim 1, wherein the percentage of surface modified carbon black in the mixture is in the range of 0.1% to 40%.
4. The process as claimed in claim 1, wherein the percentage of surface modified carbon black in the dope is in the range of 0.01% to 0.5%.
5. The process as claimed in claim 1, wherein the surface modified carbon black has a surface area in the range of 70 to 500 m2/g and average particle size in the range of 25 to 30 nm.
6. The process as claimed in claim 1, wherein the pigments consist of colour pigments such as green, blue, red, black and/or yellow.
7. A dope dyed viscose fibre using surface modified carbon black as a pigment to obtain a colour fast and uniformly distributed dark shade of viscose fibre wherein the carbon black is surface modified through ozonation.