Indigo dyeing process and apparatus and indigo dyed yarns and fabrics made thereby
Processes 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 process for indigo dyeing of textile products comprising the steps of:
(a) introducing an undyed textile product into a dye application chamber having an anaerobic atmosphere;
(b) establishing fluid communication between the anaerobic atmosphere and an oxygen purification system to maintain anaerobic conditions within the dye application chamber;
(c) applying a leuco-indigo dye solution onto the undyed textile product introduced into the dye application chamber according to step (a) within the anaerobic atmosphere thereof to form a leuco-indigo dyed textile product; and thereafter
(d) exposing the leuco-indigo dyed textile product to 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 , wherein the process further comprises prior to step (a), the step of:
(a1) introducing the undyed textile product into an oxygen purge chamber having an inert atmosphere positioned upstream of the dye application chamber; and
(a2) establishing fluid communication between the inert atmosphere of the purge chamber and the purification system to maintain the anaerobic atmosphere within the purge chamber below a predetermined measurable amount of oxygen.
3. The process according to claim 2 , wherein prior to step (d) the process further comprises the step of:
(d1) transitioning the leuco-indigo dyed textile product from the dye application chamber into an anaerobic dwell chamber downstream of the dye application chamber to complete diffusion of the leuco-indigo dye within fibers of the leuco indigo-dyed textile product prior to exposing the leuco indigo-dyed textile product to the oxygen atmosphere.
4. The process according to claim 1 , which further comprises between steps (c) and (d) the step of:
(c1) transferring the leuco-indigo dyed textile product to a drying chamber having an anaerobic atmosphere to dry the leuco-indigo dyed textile product.
5. The process according to claim 3 , wherein step (a1) comprises 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.
6. The process according to claim 5 , wherein each of the roller seal assemblies comprises a pair of support rolls and a pressure roll in contact with the support rolls.
7. The process according to claim 6 , 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.
8. The process according to claim 6 , wherein the support rolls are in sliding contact with a stationary solid low-friction seal member.
9. The process according to claim 3 , 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.
10. The process according to claim 1 , further comprising controlling humidity and pressure of the anaerobic atmosphere within the dye application with a humidity and pressure control unit.
11. The process according to claim 3 , which comprises controlling moisture of the anaerobic atmosphere within the dwell chamber by a moisture generator.
12. The process according to claim 2 , 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.
13. The process according to claim 12 , wherein the inert atmosphere comprises nitrogen gas.
14. The process according to claim 12 , wherein the predetermined amount of measurable oxygen is 30 ppm.
15. The process according to claim 12 , wherein the predetermined amount of measurable oxygen is 15 ppm.
16. The process according to claim 12 , wherein the predetermined amount of measurable oxygen is 10 ppm.
17. The process according to claim 12 , wherein the textile product is a sheet of textile yarn ends arranged side-by-side.
18. The process according to claim 17 , wherein the sheet of yarn ends has a density of less than about 2.0 yarns per millimeter of sheet width.
19. The process according to claim 17 , wherein the sheet of yarns has at least about 40 yarn ends.
20. The process according to claim 17 , wherein the sheet of yarns has 400 yarn ends or more.
21. The process according to claim 20 , wherein the sheet of yarns has between 400 to 480 yarn ends.