Indigo dyeing process and apparatus and indigo dyed yarns and fabrics made thereby
Processes and apparatus are disclosed which substantially eliminate the formation of oxidized indigo dye before and during dye application onto a natural fiber yarn or fabric while allowing the leuco-indigo dye molecule to diffuse fully into the natural fibers of the yarn where it can fix to the fibers prior to oxidation (i.e., exposure of the leuco-dyed yarns to oxygen). Indigo dyed textile products (e.g., dyed cotton yarns that may be twill woven to form a denim fabric) exhibit exceptionally high colorfastness as determined by the AATCC Crock Test.
1. A continuous process for indigo dyeing of textile products comprising the steps of:
(a) introducing an undyed textile product into an oxygen purge chamber having an inert atmosphere, the purge chamber comprising a purification system in fluid communication with the inert atmosphere therein;
(b) transferring the undyed textile product from the purge chamber to a dye application chamber having an anaerobic atmosphere;
(c) applying a leuco-indigo dye solution onto the undyed textile product within the anaerobic dye application chamber to form a leuco-indigo dyed textile product;
(d) transitioning the leuco-indigo dyed textile product from the dye application chamber into an anaerobic dwell chamber to complete diffusion of the leuco-indigo dye within fibers of the textile product; and
(e) discharging the leuco-indigo dyed textile product into an oxygen-containing atmosphere to oxidize the leuco-indigo dye applied to the textile product and thereby form an indigo-dyed textile product.
2. The process according to claim 1 , which further comprises between steps (d) and (e) a step of:
(f) transferring the leuco-indigo dyed textile product to a drying chamber having an anaerobic atmosphere to dry the leuco-indigo dyed textile product.
3. The process according to claim 1 , which further comprises the step of advancing the undyed textile product through roller seal assemblies positioned at least at an inlet of the purge chamber and an outlet of the dwell chamber.
4. The process according to claim 3 , wherein each of the roller seal assemblies comprises a pair of support rolls and a pressure roll in contact with the support rolls.
5. The process according to claim 4 , wherein at least an outer surface region of the support rolls is formed of a relatively hard material, and at least the outer surface of the pressure roll is formed of a relatively soft material.
6. The process according to claim 4 , wherein the support rolls are in sliding contact with a stationary solid low-friction seal member.
7. The process according to claim 1 , wherein the dye application chamber is operated at a pressure condition which is greater than ambient atmospheric pressure, and wherein the pressure condition of the dye application chamber is greater than pressure conditions of the purge chamber and the dwell chamber.
8. The process according to claim 1 , wherein the dye application chamber comprises a humidity and pressure control unit to control the anaerobic atmosphere within the dye application chamber.
9. The process according to claim 2 , wherein the dwell chamber includes a moisture generator to control relative humidity of the anaerobic atmosphere within the dwell chamber.
10. The process according to claim 1 , wherein the inert atmosphere within the purge chamber comprises nitrogen gas, and wherein step (a) comprises the steps of:
(a1) purifying the nitrogen gas within the purge chamber by withdrawing nitrogen gas from the purge chamber,
(a2) flowing the withdrawn nitrogen gas through the purification system to form purified nitrogen gas, and thereafter
(a3) introducing the purified nitrogen gas into the purge chamber.
11. The process according to claim 10 , wherein the purification system comprises a regenerable catalytic purifier to remove oxygen from the nitrogen gas withdrawn from the purge chamber.
12. The process according to claim 1 , wherein step (a) comprises:
(a1) determining measurable oxygen in the inert atmosphere of the purge chamber; and
(a2) activating the purification system to remove oxygen from the inert atmosphere in response to a determination according to step (a1) that the measurable oxygen is more than a predetermined amount.
13. The process according to claim 12 , wherein step (a2) comprises:
(i) withdrawing the inert atmosphere containing an amount of measurable oxygen from the purge chamber;
(ii) removing the measurable oxygen from the inert atmosphere by the purification system until the amount of the measurable oxygen is below the predetermined amount to thereby obtain purified inert atmosphere, and
(iii) returning the purified inert atmosphere to the purge chamber.
14. The process according to claim 13 , wherein the inert atmosphere comprises nitrogen gas.
15. The process according to claim 13 , wherein the predetermined amount of measurable oxygen is 30 ppm.
16. The process according to claim 13 , wherein the predetermined amount of measurable oxygen is 15 ppm.
17. The process according to claim 13 , wherein the predetermined amount of measurable oxygen is 10 ppm.
18. The process according to claim 13 , wherein the textile product is a sheet of textile yarn ends arranged side-by-side.
19. The process according to claim 18 , wherein the sheet of yarn ends has a density of less than about 2.0 yarns per millimeter of sheet width.
20. The process according to claim 18 , wherein the sheet of yarns has at least about 40 yarn ends.
21. The process according to claim 20 , wherein the sheet of yarns has 400 yarn ends or more.
22. The process according to claim 21 , wherein the sheet of yarns has between 400 to 480 yarn ends.