Method of dye clearing textiles

Abstract

A process to remove excess dye from dyed polyester fabric comprising adding a solution of a weak organic acid to the fabric in a dyeing vessel, raising the temperature in the vessel to at least 80 C., allowing the acid to react with the fabric for at least 6 minutes and removing all liquid.

Claims

1. A process to remove excess dye from dyed polyester fabric comprising (a) adding a reduction clearing agent which is a weak organic acid or salt thereof to the fabric in a dyeing vessel, (b) raising the temperature in the vessel, (c) allowing the acid or salt thereof to remain in contact with the fabric for a period of time, (c1) raising the pH to between pH 9 and pH 12, and (d) removing all liquid.

2. The process according to claim 1 which comprises the additional step of removing dyeing liquor from the dyeing vessel prior to (a).

3. The process according to claim 1, where in step (c) the weak organic acid or salt thereof remains in contact with the fabric for at least 6 minutes.

4. The process according to claim 1, where in step (b) the temperature in the vessel is raised to a value in the range of from 60 to 100 C.

5. The process according to claim 1, in which the weak organic acid is selected from those having at least 4 carbon atoms and a pK.sub.a or pK.sub.a1 value of at least 1.

6. The process according to claim 5 wherein the weak organic acid is ascorbic acid or salt thereof.

7. The process according to claim 6 wherein the weak organic acid is ascorbic acid.

8. The process according to claim 1 wherein the salt of the weak organic acid is selected from an alkali metal salt.

9. The process according to claim 1 comprising the additional step of rinsing the fabric with water at ambient temperature after the removal of all liquid.

10. The process according to claim 1 wherein an alkaline hydroxide is used to raise the pH.

11. The process according to claim 1 wherein the weak organic acid or salt thereof is added at a rate of from 80 g to 120 g per litre.

12. The process according to claim 2 wherein the weak organic acid or salt thereof is added at a rate of from 2 g to 50 g per litre.

13. The process according to claim 2, where in step (c) the weak organic acid or salt thereof remains in contact with the fabric for at least 6 minutes.

14. The process according to claim 8 wherein the salt of the weak organic acid is selected from a sodium or potassium salt.

15. The process according to claim 2 comprising the additional step of rinsing the fabric with water at ambient temperature after the removal of all liquid.

16. The process according to claim 10 wherein the alkaline hydroxide is selected from sodium hydroxide, potassium hydroxide or ammonium hydroxide.

17. The process according to claim 2 wherein the weak organic acid or salt thereof is added at a rate of from 80 g to 120 g per litre.

18. The process according to claim 12 wherein the weak organic acid or salt thereof is added at a rate of from 2 g to 10 g per litre.

19. The process according to claim 12 wherein the weak organic acid or salt thereof is added at a rate of 5 g per litre.

20. The process according to claim 1, where in step (c) the weak organic acid or salt thereof remains in contact with the fabric for up to 60 minutes.

21. The process according to claim 2, where in step (c) the weak organic acid or salt thereof remains in contact with the fabric for up to 60 minutes.

22. The process according to claim 3, where in step (c) the weak organic acid or salt thereof remains in contact with the fabric for up to 60 minutes.

23. The process according to claim 13, where in step (c) the weak organic acid or salt thereof remains in contact with the fabric for up to 60 minutes.

Description

DESCRIPTION OF EMBODIMENTS

(1) The weak organic acid is a Brnsted acid that contains at least 4 carbon atoms, and which has a pK.sub.a or pK.sub.a1 value of at least 1, and preferably a pK.sub.a or pK.sub.a1 value of less than 5. A preferred pK.sub.a or pK.sub.a1 range is from 3 to 4.5. The pK.sub.a1 value refers to the first dissociated proton for multiprotonic acids. Examples of such acids include ascorbic acid, citric acid, caprylic acid, adipic acid, succinic acid, maleic acid and butyric acid. Preferred examples are ascorbic acid and citric acid. Salts of the weak organic acid can also be used. Examples of salts include those having monovalent cations, such as alkali metal salts. Preferred salts are sodium or potassium salts. Ascorbic acid or a salt thereof is most preferred. One or more weak organic acids and/or salts thereof can be used.

(2) In the discussion that follows, unless specified otherwise, reference to weak organic acid or examples thereof also includes a reference to their salts.

(3) The temperature in the vessel is preferably raised to a value in the range of from 60 C. to 100 C., most preferably from 75 C. to 80 C. or at least 80 C.

(4) The weak organic acid is preferably maintained in contact with the fabric for at least 6 minutes to allow it to react with the dyed fabric. Preferably, the contact time is up to 60 minutes.

(5) Preferably the dyeing liquor is removed from the dyeing vessel prior to adding the weak organic acid. Alternatively, if an already dyed polyester fabric is exhibiting low dye fastness it is possible to reprocess the dyed fabric using the process of the invention in order to remedy the problem. In this situation the dry dyed fabric may be loaded into a dye bath or suitable vessel to which may be added water and an appropriate amount of the weak organic acid.

(6) The organic acid is added at a rate of 80 g to 120 g per litre, if for example the dyeing liquor is not removed before the organic acid is added. Alternatively, if the dyeing liquor is removed before adding the organic acid 2 g to 50 g per litre, preferably 2 g to 10 g, most preferably 5 g per litre of the acid are used.

(7) Following the removal of all liquid the polyester fabric is preferably rinsed with water at ambient temperature, after which it is spun and dried.

(8) In one embodiment a weak organic acid, or a salt thereof that is still acidic, is utilised as the reduction clearing agent. In contrast to the previously used reduction clearing process utilising sodium dithionite this has the advantage that it is not necessary to change the pH between the dyeing stage, which is typically carried out at a low pH, and the reduction clearing stage.

(9) If, however, the dyed polyester fabric is to be subsequently treated, for example to render it water-repellent, then, following the reduction clearing treatment using a weak organic acid, the pH is raised to between pH 9 and pH 12. This is achieved by the addition of an alkaline hydroxide such as sodium hydroxide potassium hydroxide or ammonium hydroxide at a rate of from 1.4 g to 1.7 g per litre.

(10) According to a second aspect of the invention there is provided the use of a weak organic acid to remove excess dye from a dyed polyester fabric wherein a solution of the weak organic acid is added to the fabric in a dyeing vessel, the temperature in the vessel is raised to at least 80 C. and the acid is allowed to react with the fabric for at least 6 minutes. All liquid is subsequently removed.

(11) One advantage of the process of the present invention is that it avoids the need to use sulphur containing compounds, such as sodium dithionite, that act as sulphonating agents which can act on residual surfactants remaining in the fabric making the surfactants more persistent. This persistence causes problems in later textile finishing processes such as the application of water-repellent treatments to the polyester fabric.

(12) Other advantages of using a weak organic acid in the reduction clearing process are that the process is safer to operate, less polluting of the environment as well as being cheaper to operate.

(13) The present invention will be further described by way of reference to the following examples.

Example 1

(14) In a suitable dyeing vessel, a dye bath was prepared to the following composition by subsequently adding, whilst under continual mixing, the components below: Water (40 C., deionised)5 litres Carrier (DOWANOL EPh, Dow Chemicals)50 g (10 g/litre) Dispersing Agent (Basojet PEL-200, BASF Chemicals)50 g (10 g/litre) Dyestuff (Permasil Red F3BS 150%, Standard Colors)150 g (30 g/litre)

(15) After the addition of the dyestuff, the temperature of the bath was slowly raised at a rate of approximately 1 C./minute to 95 C. At this point the pH of the dye bath was adjusted to between 4.0 and 5.0 with the addition of acetic acid (80% Technical grade)25 g (5 g/litre).

(16) A 500 g sample of un-dyed polyester microfibre fabric with a weight of 215 g/m.sup.2 was added to the dye bath. With continual mixing, the dye bath was heated to the boil and maintained at a steady temperature for a period of 90 minutes. During this time, the pH of the dye bath was maintained by the addition of further doses of acetic acid at the rate of 5 g every 15 minutes, if necessary.

(17) After 90 minutes, the dye bath was allowed to cool to a temperature of 60 C. before the liquid contents of the dyeing vessel were drained. The fabric was then washed in the dyeing vessel with three separate washes of Tergitol 15-S-7 (10 g in 5 litres of deionised water at 60 C. for two minutes).

(18) The dyeing vessel was then refilled with water (5 litres of deionised water at 60 C.) and sodium hydroxide was added (20 g, 4 g/litre). The temperature of the dyeing vessel contents was then raised to 80 C. and the following was added in the prescribed order: Dispersing Agent (Basojet PEL-200, BASF Chemicals)20 g (4 g/litre) Trisodium citrate dehydrate (Jungbunzlaur)50 g (10 g/litre)

(19) The temperature of the dyeing vessel contents were maintained at 80 C. for a further 25 minutes. The dyeing vessel was then drained of the liquid contents. The fabric was then rinsed using five separate charges of water (5 litres of deionised water at 20 C. for two minutes). In the final rinse, the pH of the dye was lowered to between 6.0 and 7.0 with the addition of acetic acid (80% Technical grade). The dyeing vessel was then drained of the liquid contents and the dyed fabric was recovered and air dried.

(20) The colour fastness of the final fabric was assessed using the American Association of Textile Chemists and Colorists (AATCC) test method 8-2013 (Colorfastness to Crocking: AATCC Crockometer Method) on both wet and dry samples. The results were evaluated against the AATCC Chromatic Transference Scale. Both samples were recorded as having a grade of 4.5 which indicates an acceptably low level of dye transfer from the test fabric.

Example 2

(21) A 50 kg batch of dyed black polyester microfibre fabric (fabric weight of 150 g/m.sup.2) which was showing unacceptably low dye fastness was reprocessed to remedy the problem.

(22) The fabric was loaded into a Fong's Minitec3-1T high temperature dyeing machine. The service tank of the machine was charged with the following components in the prescribed order: water (20 C., deionised)150 litres sodium hydroxide400 g ascorbic acid750 g

(23) Once the contents of the service tank had fully dissolved, the contents of the tank were charged into the dyeing loop. After charging, the machine jet pumping system was activated to enable the circulation of the fabric rope. The temperature of the machine content is raised using the inbuilt heater to 90 C. Circulation of the fabric was continued for a period of 60 minutes. After this time the machine jet pumping system was deactivated and the machine was emptied of liquid. The machine was then recharged via the addition of 200 litres of water (20 C., deionised) from the service tank after which the fabric was circulated with the jet pumping system for 10 minutes. The pH of the machine contents was then adjusted to 7.0 by the addition of acetic acid (80% Technical grade) via the service tank (typically 24 g/litre). The liquid contents of the machine were then drained and the fabric was removed via the service door.

(24) After air-drying for 48 hours, the colour fastness of the final fabric was assessed using the American Association of Textile Chemists and Colorists (AATCC) test method 8-2013 (Colorfastness to Crocking: AATCC Crockometer Method) on both wet and dry samples. The results were evaluated against the AATCC Chromatic Transference Scale. Both samples were recorded as having a grade of 5 which indicates no detectable dye transfer from the sample.