GB1575963A - Process and apparatus for the reoxidation of dyeings with suplhur dyes - Google Patents

Description

(54) PROCESS AND APPARATUS FOR THE REOXIDATION OF DYEINGS WITH SULPHUR DYES (71) We, HOECHST AKTIENGES ELLSCHAFT, a body corporate organised ac cording to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Post fach 80 03 20, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the follow ing statement: The present invention relates to dyeing with sulfur dyes.

Sulfur dyes, by which term there are to be understood in this specification not only the normal sulfur dyes (C.I. Sulphur Dyes) but also soluble sulfur dyes (C.I. Leuco Sulphur Dyes, C.I. Solubilized Sulphur Dyes) and vat sulfur dyes (C.I. Vat Dyes), may be con verted into a soluble form by treatment with a reducing agent, generally sodium sulfide, sodium hydrogenosulfide or, to a smaller extent, sodium dithionite, optionally with the addition of sodium disulfide as a redox stabi lizer, and are usually applied onto textile goods -in this soluble form. For the re-conversion into the original dyestuff a subsequent reoxidation treatment is required.

If the dyeing is carried out by a continuous method, it is evident that the reoxidation of the dyeing must also be effected continuously.

In this case, fast-acting oxidizing agents have to be used which ensure the required constancy of the colour shade obtained, but which, on the other hand, do not produce overoxidation and the consequent inferior fastness properties.

According to the simplest process for sulfur dyes the excess reducing agent is washed off by spraying water onto the material, and the reoxidation is effected by the air. However, besides the high water consumption this method has the drawback that the waste water needs to be worked up because of its content of reducing agent. The use of potassium and/or sodium bichromate and acetic acid is not recommended, either, in view of waste water problems, so that this fast-acting and safe oxidizing agent does not meet present requirements.

The method of oxidation in an alkaline medium with hydrogen peroxide and sodium chlorite is unobjectionable with regard to the waste water, but there are drawbacks of the risk of overoxidation and, in the case of sodium chlorite, the slow reaction development.

Similar conditions to those mentioned for the chlorite are also found in the application of the bromite. In these two latter cases heat must be applied in order to initiate the oxidation.

The present invention provides a process for the oxidation of a sulfur dye (as hereinbefore defined) which has been applied to a material in reduced form, which comprises treating the dyed material with sodium hypochlorite at a temperature of less than 30"C at a pH of at least 10, for example in the range of from 10 to 12. Preferably the treatment is carried out at a temperature in the range of from 15O to 25"C and at a pH in the range of from 10 to 11. The process of the invention is appropriate for continuous operation, the treatment time being preferably less than 1 minute, in particular from about 15 to 25 seconds. The sodium hypochlorite is preferably adjusted so that a constant content of active chlorine, preferably from 0.2 to 0.5 g/l, is maintained in the oxidation bath.

According to the present invention it has now been found that the reoxidation of sulfur dyes may be effected in a surprisingly simple manner by using sodium hypochlorite in an alkaline medium. The suitability of sodium hypochlorite as the oxidizing agent for the reoxidation of dyeings with sulfur dyes is surprising because the sulfur dyes are known to be exteremely sensitive to sodium hypochlorite, which can also be seen from the published fastness data according to DIN 54010, 54034 and 54035. However, it has been found, as indicated above, that a fast and safe reoxidation is possible with sodium hypochlorite in the alkaline medium at relatively low temperatures.Depending on the conditions with regard to the apparatus available and the waste water, the reoxidation according to the process of the invention may be effected directly without prior rinsing of the goods, the total amount of reducing agent remaining from the dyeing process thus being oxidized. On the other hand it is possible first to remove the residual reducing agent by rinsing and recycling it into the dyeing process, optionally increasing its concentration.

The sodium hypochlorite solution may be applied onto the dyed goods according to any usual method, for example by padding, sloppadding, spraying or by means of a foam. A particularly preferred embodiment of the invention consists in carrying out the reoxidation process in a modified open width washing machine, which apparatus comprises a container provided with an overflow and pump recirculation system for the oxidation bath.

The recirculation system is preferably provided with a regeneration system which adds sodium hypochlorite to the bath to maintain a constant active-chlorine content. The present invention also provides such apparatus used for carrying out this preferred embodiment of the process.

A preferred embodiment of the apparatus according to the invention will now be described, by way of example only, with reference to the accompanying drawing. As shown in the drawing the apparatus comprises a container (1) in which the oxidation bath (3) is circulated via an overflow (2), a recirculation conduit (4) and a circulation pump (5). After the circulation pump (5), although it could be before the pump, a measuring instrument (6) is connected to the conduit (4) via a connection (7), which instrument determines the content of active chlorine in the circulating bath at that point. A dosing pump (10), which feeds sodium hypochlorite solution (16) via a dosing pipe (11) from a storage tank (12) into the conduit (4) is controlled by the measured active-chlorine value via a control connection (8) and a control device (9).The bath (3) thus regenerated is recirculated into the container (1) by means of a distributing tube (17) which gives an even feed of the bath over the total width of the container and the material web (13). Following the regeneration of the bath, the content of active chlorine is suitably monitored by means of a further measuring connection (15) in coordination with the measuring instrument (6). In the container (1) with the circulating bath (3) the textile material (13) is guided over and around a series of rollers (14) and is squeezed off by a pair of rollers (18) upon leaving the bath, in order to be freed from excess liquid.

The dosing solution (12) is advantageously made up from commercial sodium hypochlorite solution ("chlorine bleaching liquor") which has an active chlorine content of from 140 to 160 g/l. To facilitate the dosing, this concentration is suitably diluted to about 15 g of active chlorine per litre.

At the beginning of a preferred variant of the process of the invention the container (1) is filled with water having a temperature in the range of from 15 to 25"C, which contains 5 g/l of anhydrous sodium carbonate for the adjustment of the pH value. Furthermore, a sodium hypochlorite concentration in the range of from 0.2 to 0.5 g/l of active chlorine is obtained. The dwelling time of the goods in the oxidation bath is preferably from 15 to 25 seconds and may be adjusted for the continuous process by controlling the material rate. With these values, a sufficient oxidation capacity may be ensured.

According to an embodiment of the process of the invention the dyed goods are thoroughly rinsed in the first two compartments of an open width washing machine. In this process the reoxidation is already initiated, and a large part of the reducing agent and the alkali adhering. to the goods is washed off. In a third compartment the oxidation is effected with sodium hypochlorite. By means of the above-described apparatus of the invention the oxidation bath is constantly circulated. By means of this method the oxidation bath is moved constantly, so as to avoid a local concentration of sodium hypochlorite and to maintain a constant concentration of active chlorine in the system. By using a strongly diluted bleaching liquor it becomes possible to constantly feed a fairly large amount of liquor into the oxidation compartment. Thus, an ample overflow is ensured.The regenerated bath is suitably supplied via a distributing tube over the total width of the washing machine compartment.

Upon leaving the oxidation compartment the goods may be squeezed off and vigourously washed by way of spray pipes. They may then be subjected to the common further treatment.

Another preferred embodiment provides the complete direct oxidation of the total reducing agent remaining from the dyeing process. For this purpose, use is suitably made of the first compartment of an open width washing machine for the oxidation. As in this case the total residual amount of reducing agent is introduced into the oxidation bath, an exact and sufficient dosage of the sodium hypochlorite is a pre-requisite in order to ensure an even dyeing which shows a constant color shade. For this embodiment it may be suitable to provide additionally mixing aggregates, for example cross beaters, besides a distributing tube which is arranged in the direction transverse to the direction of the fabric run, for the oxidation bath fed in.

This latter embodiment ensures that no reducing agent and-owing to the exact dosing of the oxidizing agent-no hypochlorite are introduced into the waste water. A test for reducing agent in the waste water is possible, for example, by means of lead acetate paper, and for oxidizing agent (sodium hypochlorite) after acidification of the bath, by means of potassium iodide starch paper. Since in the oxidation process finely divided elementary sulfur is obtained, it may be advantageous to add a dispersing agent to the oxidation bath, for example the sodium salt of 2,2'-dinaph thylmethane-6,6'-disulfonic acid.

According to another appropriate process variant the sodium hypochlorite is padded onto the dyed goods in the form of a dilute solu tion by means of a padder, and the oxidation is effected in an air passage or in a washing trough of an open width washing machine during about 20 seconds. In this process special care has to be taken when dosing the sodium hypochlorite solution, since a relatively high hypochlorite cencentration is used for the padding and an excess amount of oxidizing agent is unfavorable due to the high sensitive ness of the sulfur dyestuffs to the hypo chlorite.

Since the commercial reducing agents as well as the chlorine bleaching liquor show a varying composition, it is suitable in practice to determine the content of the reagents used beforehand and to control the same in the course of the process, if the process cannot be controlled by means of automatic analysis and controlling devices. A pH control is generally not required, as a sufficient amount of alkali is constantly introduced by the dyed goods as well as by the bleaching liquor, and because the constancy of the color shade is subject only to minor variations at pH values of more than 10. The pH is, however, preferably controlled.

The process of the invention is distinguished by a fast and safe reoxidation of the sulfur dyes as well as by a waste water that does not involve any problems. Furthermore, said process permits the reoxidation by using the economical oxidizing agent sodium hypochlorite, without adversely affecting the dyestuffs which are sensitive to chlorine.

The following Examples illustrate the invention; the percentages are by weight, and the oxidation is carried out at a pH of at least 10: EXAMPLE 1: A dyeing on a cotton fabric using 45 g/kg of the dyestuff Solubilized Sulphur Brown 12 (C.I. No. 53 724) and 23 g/kg of sodium hydrogenosulfide solution (21%) as well as 5 g/kg of sodium carbonate (anhydrous) is rinsed after steaming in the first two compartments of an open width washing machine serving for the oxidation and the after-treatment and is oxidized in the third compartment with sodium hypochlorite. According to the Figure, this process is described as follows: The third trough (1) is charged with 5 g/l of sodium carbonate (anhydrous) and 2 ml/l of commercial chlorine bleaching liquor having a content of active chlorine of 150 g/l.The temperature of the oxidation bath (3) is 1S"C.

The goods (13) are guided in the third trough (1) by means of the deflection pulleys (14) in such a way that a dwelling time of 20 seconds results, while considering the material rate in this calculation.

At the outgoing side of the oxidation compartment (1) there is an overflow trough (2) where the overflowing liquor (3) is collected and from where it is led via a pipe system (4) having an inner diameter of 100 mm to a circulation pump (5). The pump (5) presses the liquor (3) back to the distributing device which is arranged at the inlet of the trough (1). Said device has been designed as to provide a fast and even distribution of the liquor (3) fed in over the entire width of the trough.

Into the pipe system (4) there have been inserted the probes (7) of a measuring device (6) for continuous measuring which determines directly the content of active chlorine.

The measured values thus obtained control a dosing pump (10) via control pipes (8) and an electric controlling device (9) in a way that the previously established content of active chlorine of 0.3 g/l is maintained by the dosing pump (10) feeding doses of dilute sodium hypochlorite solution from the storage tank (12) via the dosing pipe (11) into the pipe system (4).

By way of a further measuring pipe (15) it is possible to stop the dosing, after the desired concentration has been reached, through another measuring of the active chlorine content behind the junction of (11) into (4).

The chlorine bleaching liquor added in doses is diluted with water in the ratio of 1:10.

Upon leaving the third trough (1) of the open width washing machine, the goods (13) are squeezed off, are washed with cold water by way of spray pipes and are after-treated.

An evenly oxidized brown dyeing is obtained without any impairment of the color shade or the color depth.

EXAMPLE 2: A dyeing on cotton twill using 30.6 g/kg of the dyestuff Solubilized Sulphur Green 9 (C.I. No. 53 006), 10.8 g/kg of the dyestuff Solubilized Sulphur Brown 21 (C.I. No. 53 066) and 82 g/kg of sodium sulfide (61%) is rinsed after steaming in the first two troughs of an open width washing machine serving for the oxidation and the after-treat ment and is oxidized in the third trough with 3 ml/l of chlorine bleaching liquor having a content of active chlorine of 160 g/l, in accordance with Example 1.

The content of the active chlorine in the oxidation bath is 0.48 g/l, and this value is constantly maintained over the entire opera tion by means of the device according to Example 1.

An evenly oxidized olive dyeing is obtained.

EXAMPLE 3: A dye using 85 g/kg of Sulphur Black 1 (C.I. No.

53 185), 210 g/kg of sodium sulfide (61%) and 5 g/kg of sodium disulfide solution (15%) on cotton fabric is oxidized after steaming with 3 ml/l of chlorine bleaching liquor (160 g/l of active chlorine) in accordance with the conditions given in Example 1, while con tinuously replacing the sodium hypochlorite consumed.

A black dyeing is obtained which has been oxidized in an unobjectionable manner.

EXAMPLE 4: A dye using 140 g/kg of Leuco Sulphur Black 1 (C.I.

No. 53 185) on cotton fabric is reoxidized according to Example 3.

A black dyeing is obtained which corresponds to that of Example 3. (The dyestuff already contains the required reducing agents in its commercial form).

EXAMPLE 5: A continuous dyeing on cotton twill used for vocational clothing which has been obtained with 25 g/kg of Vat Blue 43 (C.I. No. 53 630) 31 g/kg of sodium hydroxide solution (32.5%) and 31 g/kg of sodium dithionite is rinsed after steaming in two compartments of an open width washing machine. The third compartment has been provided with a device as described in Example 1. It is charged with 2 ml/l of chlorine bleaching liquor (150 g/l of active chlorine) and 5 g/l of sodium carbonate (anhydrous). The bath temperature is 20 C. During the passage of the goods, fresh dilute chlorine bleaching liquor is continuously added in doses, with the amount corresponding to the amount consumed, so that a constant content of 0.3 g/l of active chlorine is maintained in the oxidation bath. The dwelling time of the goods in the oxidation bath is 20 seconds.

Subsequently the goods are rinsed by spray ing and are after-treated in common manner.

An evenly oxidized blue dyeing of the voca tional twill fabric is obtained.

EXAMPLE 6: A dyeing on a cotton fabric having a weight of 210 g/ of running meter and using 70 g/l of Sulphur Brown (C.I. No. 53 000) and 35 g/l of sodium sulfide conc. (commercial, about 60% of Na2S) which has been padded with a liquor pick-up of 70% is introduced after steaming via a short air passage with a material rate of 30 m/min. into the first compartment of an open width washing machine which has been charged with water of 20"C and 5 g/l of sodium carbonate (anhydrous).

As soon as the dyed goods are introduced into the bath, the addition in doses of commercial chlorine bleaching liquor (about 150 g/l of active chlorine3 is started. This bleaching liquor is diluted with water via a dosing blender in the ratio of 1 : 10, is introduced by means of a distributing pipe over the total width of the washing machine compartment directly into the bath and is distributed there in an even and rapid manner by means of, for example, cross beaters or other stirring devices.

By the addition of water in doses in the ratio of 1 : 10, there is a bath overflow at the exit of the washing compartment of about 10 1/mien. which can still be increased by adding a further amount of water. Said overflow serves to limit the concentration of alkali. The time of passage of the goods through the washing compartment is 20 seconds, subsequently the material is rinsed in the following compartment, and the dyeing which is now reoxidized is then after-treated in common manner. An evenly oxidized dyeing is obtained which does not show any impairment of the color shade or the color depth.

No reducing agent can be detected any more in the everfiowing water.

EXAMPLE 7: A continuous dyeing on cotton fabric using 10 g/kg of Sulphur Brown 52 (C.I. No. 53 320) and 20 g/kg of sodium sulfide conc. (61%), which has been obtained with a liquor pick-up of 70%, is padded over with a liquor pick-up of 110%, after steaming and a short air passage, in a padder having a small trough, with a sodium hypochlorite solution having been prepared from water and a commercial chlorine bleaching liquor with 150 g/l of active chlorine. 1 Liter of this bath of 20"C contains 325 ml/l of bleaching liquor.

Following an air passage of 15 seconds, the goods are washed and are subjected to the common after-treatment. An evenly oxidized brown dyeing is obtained. No reducing agent is contained any more in the rinsing water.

WHAT WE CLAIM IS: 1. A process for the oxidation of a sulfur dye (as hereinbefore defined) which has been applied to a material in reduced form, which comprises treating the dyed material with sodium hypochlorite at a temperature of less than 30"C and at a pH of at least 10.

2. A process as claimed in claim 1, wherein the pH is in the range of from 10 to 12.

3. A process as claimed in claim 2, wherein the pH is in the range of from 10 to 11.

4. A process as claimed in any one of claims 1 to 3, wherein the temperature is in the range of from 15 to 25"C.

5. A process as claimed in any one of claims 1 to 4, wherein the oxidation is carried out using an aqueous sodium hypochlorite liquor having an active chlorine content in the range of from 0.2 to 0.5 grams per litre.

6. A process as claimed in any one of claims 1 to 5, which is carried out in a continuous manner with an oxidation treatment time of less than 1 minute.

7. A process as claimed in claim 6, wherein the material is contacted with the sodium hypochlorite for a period in the range of from 15 to 25 seconds.

8. A process as claimed in any one of claims 1 to 7, wheren the dyed material is rinsed with water prior to the oxidation treatment.

9. A process as claimed in any one of claims 1 to 7, wherein the dyed material is not rinsed prior to the oxidation treatment and any reducing agent adhering to the material is oxi- dized during the oxidation treatment.

10. A process as claimed in any one of claims to to 9, wherein the sodium hypochlorite is applied via an oxidation bath through which the dye material is passed, the oxidation bath being in a container provided with an overflow and pump recirculation system.

11. A process as claimed in claim 10, wherein the recirculation system is provided with a regeneration system which adds sodium hypochlorite to the bath to maintain a constant active-chlorine content.

12. A process as claimed in claim 1, conducted substantially as described herein.

13. A process as claimed in claim 1, conducted substantially as described in any one of the Examples.

14. Apparatus comprising a container which contains an oxidation bath and which is provided with an overflow and pump recirculation system, when used for a process as claimed

Claims (1)

1. in claim 10.

   15. Apparatus as claimed in claim 14, wherein the recirculation system is provided with a regeneration system which adds sodium hypochlorite to the bath to maintain a constant active-chlorine content, when used for a process as claimed in claim 11.

   16. A device as claimed in claim 15, substantially as described herein with reference to, and as illustrated in, the accompanying drawing.

   17. A process for the reoxidation of dyeings with sulfur dyes in an alkaline medium, which comprises carrying out the oxidation with sodium hypochlorite at a temperature of less than 30"C and in a pH range of from 10 tp 12.