Method for dyeing cotton with indigo

1. A method for dyeing a cellulosic material, wherein the method comprises:

a) preparing a dyebath including particles of indigo pigment and a first additive causing the particles of indigo pigment to become electrically charged in a first polarity;

b) preparing the cellulosic material for dyeing by applying a second additive to the cellulosic material to form a substrate on the cellulosic material having an ionic charge with a polarity opposite the first polarity;

c) immersing the cellulosic material prepared in step b) in the dyebath prepared in step a) to cause the particles of indigo pigment to be ionically attracted to the substrate and retained thereon;

d) chemically reducing the particles of indigo retained on the substrate to form a soluble leuco form entering the cellulosic material; and

e) oxidizing the soluble leuco form to form indigo pigment within the cellulosic material.

2. The method of claim 1 , wherein the first polarity is negative and the second additive is cationic.

3. The method of claim 2 , wherein the first additive is an anionic acrylic copolymer.

4. The method of claim 2 , wherein the second additive crosslinks with the cellulosic material.

5. The method of claim 2 , wherein the second additive is a cationic polymer selected from a group consisting of polyamide and polyamine.

6. The method of claim 2 , wherein a batch of the cellulosic material is prepared for dyeing in step b) by immersion within a preparation bath composed essentially of:

water;

a phosphated alcohol; and

a cationic polymer selected from a group consisting of polyamide and polyamine.

7. The method of claim 6 , wherein the cationic polymer has a weight of 7% of the weight of the batch of cellulosic material.

8. The method of claim 6 , wherein the batch of the cellulosic material is treated in the preparation bath at a temperature of 43° C. for 15 minutes.

9. The method of claim 2 , wherein a dyebath is prepared in step a) to dye a batch of the cellulosic material, and wherein the dyebath is composed essentially of:

water;

indigo powder; and

an anionic acrylic copolymer.

10. The method of claim 9 , wherein the indigo powder and the anionic acrylic copolymer each have a weight of 2–3% of the weight of the batch of the cellulosic material.

11. The method of claim 10 , wherein

the dyebath is prepared in hot water for dyeing the batch of the cellulosic material, and

a phosphated alcohol and calcium chloride are added to the dyebath.

12. The method of claim 2 , wherein a dyebath is prepared in step a) to dye a batch of cellulosic material, and wherein the dyebath is composed essentially of:

water;

indigo powder;

an anionic acrylic copolymer; and

a phthalocyanine organic pigment.

13. The method of claim 12 , wherein

the indigo powder and the phthalocyanine organic pigment each have a weight of 1.5% of the weight of the weight of the batch of the cellulosic material, and

the anionic acrylic copolymer has a weight equal to 3% of the weight of the batch of cellulosic material.

14. The method of claim 1 , wherein, in step d), the particles of indigo retained on the substrate are reduced by immersion in a reduction bath comprising sodium hydroxide and sodium hydrosulfite.

15. The method of claim 14 , wherein the reduction bath is composed essentially of:

water;

sodium hydroxide;

sodium hydrosulfite;

a phosphated alcohol; and

Epsom salt.

16. The method of claim 14 , wherein

sodium hydroxide is added to the reduction bath in a concentration forming a pH of 11–11.5; and

sodium hydrosulfite is added to the reduction bath in a concentration of 6–10 grams per liter of water.

17. The method of claim 1 , wherein

steps b), c), and d) are performed while tumbling the cellulosic material in a rotary dyeing machine,

a bath preparing the cellulosic material for dyeing in step b) is drained from the rotary dyeing machine before the dyebath prepared in step a) is added to the rotary dyeing machine, and

the dyebath is drained from the rotary dyeing machine before a reduction bath for chemically reducing the particles of indigo is added to the rotary dyeing machine.

18. The method of claim 17 wherein step e) is performed by air flowing through the cellulosic material while tumbling the cellulosic material in the rotary dyeing machine.

19. The method of claim 17 , wherein step e) is followed by tumbling the cellulosic material within the rotary dyeing machine in a finish bath including an acrylic binder and a polyamide.

20. The method of claim 1 , wherein

step c) is performed while the cellulosic material is moved entirely through a dyebath within a jig bath vessel at least one time,

the jig bath vessel is shorter than the cellulosic material in a direction in which the cellulosic material is moved,

step d) is performed while the cellulosic material is moved entirely through a reduction bath within the jig bath vessel at least one time, and

the dyebath is drained from the jig dyeing vessel before the reduction bath is added within the jig bath vessel.

21. The method of claim 20 , wherein

the dyebath includes an indigo pigment and an anionic acrylic copolymer, and

the reduction bath includes sodium hydrosulfite and sodium hydroxide.

22. The method of claim 20 , wherein

step a) is performed while the cellulosic material is moved entirely through a preparation bath within a pad vessel separate from the jig bath vessel,

the pad vessel includes a pair of rollers squeezing material from the preparation bath into the cellulosic material, and

the pad vessel is shorter than the cellulosic material in a direction in which the cellulosic material is moved.

23. The method of claim 22 , wherein the preparation bath includes a cationic polymer selected from a group including polyamide and polyamine.

24. The method of claim 20 , wherein step e) is performed while the cellulosic material is moved entirely through an oxidation bath including sodium bromate within the jig bath vessel three times.

25. The method of claim 20 , wherein

step e) is followed by moving the cellulosic material entirely through a finish bath within the jig bath vessel at least one time;

the finish bath includes an acrylic binder and a polyamide.

26. The method of claim 1 , wherein steps b), c), and d) are performed simultaneously as the cellulosic material is moved simultaneously through a first vessel holding a preparation bath in which step b) is performed, a second vessel holding a dyebath in which step c) is performed, and a third vessel holding a reduction bath in which step d) is performed.

27. The method of claim 26 , wherein

the preparation bath includes a cationic polymer selected from a group comprising polyamide and polyamine;

the dyebath includes powdered indigo pigment and an anionic acrylic copolymer, and

the reduction bath includes sodium hydrosulfite and sodium hydroxide.

28. The method of claim 26 , wherein the cellulosic material is dried as moves between the first and second vessels and as it moves between the second and third vessels.

29. The method of claim 26 , wherein the cellulosic material is moved from the third vessel through a steamer.

30. The method of claim 29 , wherein the cellulosic material is steamed for one minute within the steamer.

31. The method of claim 26 , wherein step e) is performed within an oxidation chamber through which the cellulosic material is moved as ozone is supplied to the oxidation chamber.

32. The method of claim 26 , wherein the cellulosic material is additionally moved through a finish bath including an acrylic binder and polyamide within a finish vessel.

33. The method of claim 1 ) additionally including, following step f), immersing the cellulosic material in a finish bath including an acrylic binder and polyamide.