FIELD OF INVENTION
This invention relates to a process for continuous dyeing of rayon and rayon blends with indigo.
BACKGROUND OF INVENTION
It is known that rayons are man-made cellulose fibres and comprise viscose, acetate and cuprammonium rayons. Though indigo is known as a dye, the commercial use of indigo for industrial application has been restricted essentially to cotton fibres.
U.S. Patent no. 5,984,980 recognizes that the method of dyeing of cellulose containing textile materials with vat dyes requires that it is first necessary to change the vat dye into a water-soluble leuco form by reduction and then oxidize the leuco form into a dye pigment. Such a step was required to suhably fix the dye on the textile material. In the leuco form, there is a high affinity of the dye, but resulting in a high bath exhaustion. However, leuco-indigo has a low absorption by the fiber, and whereby it was necessary to subject the fiber to a plurality of repeated steps of dyeing with intermittent oxidation between each step of dipping in the dye liquor. In order to avoid such repeated steps, the
aforesaid patent suggested an aqueous dye liquor containing reducing agents, alkali and a dissolved metal salt. The reduced indigo absorbed by the fiber is then oxidized and whereby the process of dyeing consisted of only a single operation.
U.S. patent no. 5,935,273 granted to the same inventors additionally recognized the problem of insufficient crocking fastness arising from low bath exhaustion. Thus, such a patent discloses an aqueous dye liquor containing deoxidizers. alkali and a dissolved alkali metal salt. The reduced indigo applied to the fiber is subjected to the normal step of oxidation.
U.S. Patent no. 6,090,166 discloses a method of dyeing denim fabric with indigo which resists wear and fading. Briefly, and without describing each step of the process of the aforesaid patent, indoxyl solution is used in the dye liquor, and which is subjected to oxidation during passage from one vat to another. The oxidation progressively increases from the initial vat to the end vat.
OBJECTS OF THE INVENTION
An object of this invention is to propose a continuous process for dyeing of
rayon and rayon blends.
Another object of this invention is to propose a continuous process for dyeing of
rayon and rayon blends which is efficient.
Still another object of this invention is to propose a continuous process for
dyeing of rayon and rayon blends employing commercially available machines.
Yet another object of this invention is to propose a continuous process for
dyeing of rayon and rayon blends in the form of yarns, woven and knitted
fabrics.
DESCRIPTION OF INVENTION :-
In accordance with this invention there is provided a process for continuous dyeing of viscose yarn or blends thereof in rop, form which comprises the steps of :-
a) ball warping of yarn into rope formation,
b) subjecting the rope to a plurality of steps of dyeing in an indigo dye liquor followed by oxidation after each step of dyeing;
c) subjecting the dyed rope to the step of beam formation by the step of rebeaming;
d) sizing
e) weaving, fabric setting and finishing.
Further, in accordance there is provided a process for the continuous dyeing of rayon and rayon blends by slasher dyeing which comprises in direct warping of rayon yarn, subjecting the warped yarn to the step of the indigo dyeing cum sizing, weaving and the known steps of finishing.
Still further according to this invention there is provided a process for the continuous dyeing of rayon and rayon blends by slasher dyeing which comprises in dyeing of hank in batch form, oxidation and to the steps of washing and drying.
In accordance with this invention, the speed of the machine for log formation and beam formation is preferably 100-120 mpm. The creel tension is 25-30 gms at the step of log formation. The rope tension at the step of rebeaming is 5-10 psi. The flow sheet for rope dyeing of rayon is shown hereinbelow.
PROCESS FLOW CONTINUOUS YARN DYEING IN ROPE FORM
(Figure Removed)
Reference is now made to the parameters employed for rope dyeing, and as
shown hereinbelow: cRITICAL PROCESS PARAMETERS WITH DYEING RECIPE FOR ROPE DYEING OF RAYON YARN :
critical process parameters for Indigo Dyeing of RAYON yarn on Rope Dyeing is shown in Fig 2.
(Figure Removed)The numerical values referred to hereinabove are by way of example and without intending to imply any limitation on the scope of the invention.
The recipe employed in the dye both is as follows
(Figure Removed)
Reference is now made to slasher dyeing process of rayon yarn. The flow sheet and the recipe of the dye both is as follows:
(Figure Removed)
Reference is now made to dyeing of rayon in hank form. The flowchart and recipe of the dye both is as follows:-
HANK INDIGO DYEING OF RAYON MATERIAL :
Rayon Material is dyed with Indigo Hank form in batch wise process
(Figure Removed)

-II-
DESCRJPTION WITH RESPECT TO ACCOMPANYING DRAWING
Further objects and advantages of this invention will be more apparent from the ensuing description and wherein:
Fig. 1 shows a schematic drawing of the rope dyeing machine employed in the present
invention.
Fig. 2 shows a schematic drawing of a slasher dyeing machine; and
Fig.3 shows a schematic drawing of a loop dyeing machine.
Referring to fig. 1 the rope passes through a creel section 1 and then onto a scouring box 2 and a prewash 3. The conditioned rope then passes through indigo dye boxes 4 to 9 and then washed in post wash boxes 10 to 12. The washed and dyed rope passes through a drying 13 and a coiling section 14. Sections 1 to 14 comprise the indigo rope dye range.
The slasher dyeing machine of fig.2 is similar to that of fig. 1 with respect to the creel, scouring, prewash and dye sections, and accordingly the same reference numerals 1 to 9 appear in fig.2 as in fig.l However, the post wash sections consist of only two sections 10 and 11 followed by the accumulator 15 and predrying section 16. The yarn from the predrying section 16, then passes through the size box 17, drying 18 and warping head stock 19.
Reference is now made to fig.3, which illustrates the creel section 1 similar to that of figs. 1 and 2. The loop dyeing machine further comprises a pre-wetting section 21 followed by a dye box 22, post wash sections 23 and 24 and accumulator 25. The yarn is then passed through a pre-drying section 26, size box 27, drying 28 and finally warping head stock 29.

WE CLAIM:
1. A process for continuous dyeing of viscose yarn or blends thereof in
rope form which comprises the steps of -
a) ball warping of yarn into rope formation,
b) subjecting the rope to a plurality of steps of dyeing in an indigo dye liquor followed by oxidation after each step of dyeing;
c) subjecting the dyed rope to the step of beam formation by the step of rebeaming;
d) sizing
e) weaving, fabric setting and finishing.

2. A process for the continuous dyeing of rayon and rayon blends by slasher dyeing which comprises in direct warping of rayon yarn, subjecting the warped yarn to the step of indigo dyeing cum sizing, weaving and the known steps of finishing.
3. A process for the continuous which comprises in dyeing of rayon and rayon blends by slasher dyeing which comprises in dyeing of hank in batch form; oxidation and to the steps of washing and drying.
4. A process as claimed in claims 1 to 3 wherein the speed of the machine for log formation is 100-120 mpm and a creel tension 25-30 gms.
5. A process as claimed in claims 1 to 3 wherein the speed of the machine for rebeaming is 100-120 mpm and a rope tension 5-10 psi.
6. A process as claimed in claims 1 to 3 wherein the speed of the machine in the dye section is 16 to 28 mpm.
7. A process as claimed in claims 1 to 3 wherein the dye bath comprises:
Dyeing Recipe Range
Caustic Soda 1.5-3.0 gpl
Sodium Hydrosulphite 1.8-3.0 gpl
Indigo 0.5-5.0gpl
An Ionic Wetting agent 0.05-0.5gpl
(Primasol NF-Salt of phosphoric acid easter)
An ionic Dispersing Agent 0.05-0.5gpl
(Setamol WS- Condensation product of an aromatic sulphonic acid)
Dye-bath Temp. 25°C-35°C
pH 11.2-12.5
8. A process for continuous dyeing of viscose yarn or blends thereof in
rope form substantially as herein described.