EP1527228B1 - Method for dyeing with sulphur and sulphur vat dyes - Google Patents

Abstract

The present invention relates to a process for dyeing fiber materials with sulfur dyes by regenerating the dyebath redox potential, which comprises, during the dyeing process, the dyeing liquor being circulated between the dyeing apparatus and an attached electrolytic cell and the sulfur dye which has been unwantedly oxidized in the dyebath being cathodically reduced in the electrolytic cell.

Description

The present invention relates to a process for dyeing fiber materials with sulfur and sulfur vat dyes

The group of sulfur or sulfur vat dyestuffs (hereinafter called sulfur dyestuffs) comprises dyestuffs of the same production principle and the same dyeing proof. The sulfur dyes are formed by reacting suitable organic substances with sulfur, alkali metal sulfides or alkali metal polysulfides. The resulting products contain repeating organic structural elements linked by disulfide groups. The chemical constitution is not known for sure in most cases. For the purpose of dyeing, the sulfur dyes are reduced using different reduction techniques, with part of the disulfide bridges being cleaved reductively (see Equation 1). The resulting products have lower molar masses, are soluble in aqueous alkaline solution, and can be used for the purpose of dyeing, as they also have an affinity for fibers, e.g. Cellulosic fibers.

1. (1) R-S-S-R + 2e^- ↔ R-S^- + R-S^-
2. (2) R-S^- + R-S^- + 1/2O₂ + H₂O ↔ R-S-S-R + 2OH^-

In the presence of atmospheric oxygen, a more or less complete reoxidation of the dye takes place according to Equation 2.

1. (1) RSSR + 2e ^- ↔ RS ^- + RS ^-
2. (2) RS ^- + RS ^- + 1 / 2O ₂ + H ₂ O ↔ RSSR + 2OH ^-

Since during the dyeing process the dye bath containing the reduced dye must be protected against undesired oxidation of the dye by air, either reducing chemicals are added to the dyebath or there is a further cathodic dye reduction during dye production or preparation of the dyeing liquor (see WO 99/11716 ). When working after WO 99/11716 can be dispensed with in the production of reduced dyes and their use in continuous dyeing processes on the further use of reducing agents, if the applied dye concentration is sufficiently high, eg 50 g / l solid sulfur dye, so that introduced with the reduced dye in the dye liquor Reduction equivalents can compensate for the disturbing influence of air oxidation. Such a procedure is particularly suitable for the production of relatively concentrated products or dye liquors, which are also exposed to the oxidative action of atmospheric oxygen for a short time during continuous dyeing. With a content of the dyeing chassis of 25 l at a standard product speed of 60 m / min, a running weight of 200 g / m and a liquor pick-up of 80%, the chassis volume is replaced within less than 3 minutes.

• Pro kg zu färbendes Fasermaterial befinden sich bei einem Flottenverhältnis von 1:10 bei einer Farbtiefe von 5 % (berechnet als fester Schwefelfarbstoff) insgesamt 50 g Farbstoff in 10 I Färbebad, so dass eine Anwendungskonzentration von 5 g/I als Anfangskonzentration errechnet wird. Legt man für den Färbeprozess einen Badauszug von 70 % zugrunde, so hat am Ende des Färbevorgangs die Konzentration an Farbstoff auf 1,5 g/I Farbstoff abgenommen. Bei den Färbeverfahren, die aus dem Stand der Technik bekannt sind, kann in der Ausziehfärberei eine Badstabilisierung gegenüber oxidativen Einflüssen daher nur durch den Zusatz entsprechender Mengen an Reduktionschemikalien wie Glucose oder Hydroxyaceton erfolgen.

Wird auf den Einsatz dieser Zusätze verzichtet, so erfolgt während des Färbeprozesses unkontrollierte Rückoxidation des Schwefelfarbstoffs. Mangelnde Reproduzierbarkeit der Farbtiefe, Unegalitäten und schlechte Reibechtheiten werden als Folge beobachtet.
Bei Kettfärbeanlagen sind relative hohe Einsatzkonzentrationen an Farbstoff üblich (50 g/I fester Farbstoff) und relativ hohe Flottenvolumina in der Färbeanlage vorhanden, so dass eine höhere Badstabilität gegenüber Luftoxidation zu bestehen scheint. Bei diesen Färbetechniken wird aber eine sehr lange Verwendungszeit der Bäder gefordert, da üblicherweise mit nasser Ware ins Färbebad eingegangen wird und daher nur geringe Mengen an Färbeflotte aus den Färbebädern ausgetragen werden. Bei einem Badvolumen von 4000 I und einer Produktionsmenge von 15000 kg Kettgarn pro Tag ergeben sich bei einem Abquetscheffekt von 70 % beim Vornetzen und von 95 % beim Färben 15000x0.25 = 3750 I Flottenverbrauch pro Tag, so dass für die Färbeflotte eine durchschnittliche Verweilzeit in der Anlage von 1 Tag errechnet wird. Wird hier auf den Einsatz von Reduktionsmitteln verzichtet, so wären sogenannte Endenabläufe, das heisst Farbtonschankungen innerhalb einer Färbepartie von z.B. 20000 m Länge unvermeidbar.
In der Literatur wurden auch Möglichkeiten zum Einsatz indirekter kathodischer Reduktionsverfahren vorgeschlagen. Siehe beispielsweise Textilveredlung 32 (1997) 204-209 , Journal of Applied Electrochemistry 28 (1998) 1243-1250 , Recent Res. Devel. in Electrochem. 1 (1998) 245-264 und WO 90/15182 . Bei diesen Verfahren übernimmt ein regenerierbares Redoxsystem die Aufgabe des löslichen Reduktionsmittels, so dass die geforderte Badstabilität gewährleistet ist. Beispiele für solche Systeme sind anthrachinoide Körper, Eisenkomplexe mit Aminen oder Hydroxycarbonsäuren. Auch bei diesen Verfahren kann aber auf den Einsatz von Chemikalien nicht verzichtet werden.For the use of sulfur dyes in the exhaust dyeing, for example on dyeing machines, jet dyeing systems, etc., to which, mutatis mutandis, the continuous Kärtgarnfärbeanlagen are counted for denim production, the prior art provides no corresponding method of operation.
The long dyeing time results in long residence times of the dye in the dyebath, which during this time is exposed to continuous oxidative action of the atmospheric oxygen. In addition, the dye concentrations used in the exhaustion dyeing are already relatively low already at the start of dyeing and continue to decrease due to the bath removal during the dyeing process. The instability of the dyebath against unwanted air oxidation therefore increases more and more with increasing dyeing time.
For clarification, in the case of a dark color in the exhaust method, the following calculation of a typical example is used:

• Per kg of fiber material to be dyed are at a liquor ratio of 1:10 at a color depth of 5% (calculated as solid sulfur dye) a total of 50 g of dye in 10 I dyebath, so that an application concentration of 5 g / I is calculated as the initial concentration. If the dyeing process is based on a bath extract of 70%, the dye concentration at the end of the dyeing process has dropped to 1.5 g / l dye. In the dyeing processes which are known from the prior art, bath stabilization against oxidative influences can therefore be carried out in exhaustion dyeing only by the addition of appropriate amounts of reduction chemicals such as glucose or hydroxyacetone.

If the use of these additives is dispensed with, uncontrolled reoxidation of the sulfur dye takes place during the dyeing process. Lack of reproducibility of color depth, unevenness and poor rubbing fastness are observed as a result.
In Kettfärbeanlagen relatively high use levels of dye are common (50 g / l solid dye) and relatively high liquor volumes in the dyeing plant available, so that a higher bath stability seems to exist against air oxidation. In these dyeing techniques, however, a very long period of use of the baths is required, as is usually dealt with wet goods into the dyebath and therefore only small amounts of dye liquor are discharged from the dyebaths. With a bath volume of 4000 l and a production quantity of 15000 kg of warp yarn per day, with a squeezing effect of 70% in prewetting and 95% in dyeing 15000x0.25 = 3750 l liquor consumption per day, so that for the dyeing liquor an average residence time in the system is calculated from 1 day. If the use of reducing agents is dispensed with here, so-called end processes, ie color shade variations within a dyeing range of, for example, 20,000 m in length, would be unavoidable.
The literature has also suggested possibilities for the use of indirect cathodic reduction methods. See for example Textilveredlung 32 (1997) 204-209 . Journal of Applied Electrochemistry 28 (1998) 1243-1250 . Recent Res. Devel. in Electrochem. 1 (1998) 245-264 and WO 90/15182 , In these methods, a regenerable redox system takes over the task of soluble reducing agent, so that the required bath stability guaranteed is. Examples of such systems are anthraquinoid bodies, iron complexes with amines or hydroxycarboxylic acids. Even with these methods but can not be dispensed with the use of chemicals.

The present invention is based on the surprising finding that sulfur dyes can take over the task of a mediator even in Ausziehfärbungen and sufficient bath stability can be achieved if a continuous regeneration of the reduction state can be achieved. This is achieved according to the present invention in that during the dyeing process a sufficient circulation of the dyeing bath is made possible by a suitably coupled electrolysis cell.

The present invention thus relates to a process for dyeing fiber materials with sulfur dyes with regeneration of Färbebadredoxpotentials, which is characterized in that the dyeing liquor between dyeing plant and a coupled electrolytic cell circulates during the dyeing process and the dye bath undesirable oxidized sulfur dye is reduced cathodically in the electrolysis cell.

The process according to the invention can be carried out, for example, as an exhaust process, but also according to the continuous process. Accordingly, dyeing apparatuses, such as, for example, yarn dyeing apparatus, winch skid, tree dyeing apparatus, jet or overflow dyeing plant, are used as dyeing plants in the exhaust process. For the continuous process, however, the usual for this process dyeing systems are used.

The circulation of the dyebath between dyeing plant and electrolysis cell has to be carried out according to the dye concentration and the oxidative load. At high oxidative load and low dye concentration, the circulation has to achieve larger volume flows than at high dye concentration and low oxygen load.

The cathodically reduced dye passes from the electrolysis cell to the dyeing plant, the partially oxidized dyebath flows from the dyeing plant to the electrolysis cell. The required liquor exchange in l / min between electrolysis cell and dyeing plant depends on several conditions. These include, for example, dye concentration, the desired degree of reduction in the dyeing plant, maximum degree of reduction which can be achieved by cathodic reduction in a sulfur dye, color reduction required of the sulfur dye, cell-technically applicable current density and also the oxygen input into the dyeing plant (oxidative load).
At the high concentrations of sulfur dye, as are customary in Kettgarnfärbeprozessen, a batch regeneration of the sulfur dye and thus an intermittent bath circulation can be performed.
With knowledge of the present invention and the essential conditions mentioned, the required mass transfer between cell and dyeing apparatus can also be easily calculated by one of ordinary skill in the art.
For example, assuming a current of 10A per kg of material to be incorporated to compensate for the oxygen input and starting at 0.01 mol / l of dye available in the dye bath circulation, a dyebath circulation of 5 l / min is required to reach the 5 l / min the cell reached sales did not rise above 10% of the existing dye concentration. At a circulation capacity of 10 l / min kg, the dye solution only changes by 5% in the reduction state.
Depending on the framework conditions, the liquor exchange, based on one kg of dyed material, is between 0.5 l / min kg and 100 l / min kg, preferably between 1 and 50 l / min kg and very particularly preferably between 5 and 301 / min kg.

The dye concentration in the dyebath in the process according to the invention is preferably from 0.5 to 100 g / l of pure dye, particularly preferably from 5 to 50 g / l of pure dyestuff.

The inventive method is advantageously carried out at temperatures of 20 to 135 ° C, with 60 to 95 ° C are particularly preferred.

In a preferred embodiment of the method according to the invention, the dyeing process is influenced by controlling the redox potential. This is done by adjusting the cell current, whereby the redox potential in the dyebath can be changed or regulated within certain potential limits. The adjustable potential range is determined by the sulfur dye used, its concentration, as well as by the pH and dyeing temperature.

The cell flow is defined in particular by the oxygen input and moves in conventional dyeing systems between 0.5 and 50 A / kg, preferably between 1 and 10 A / kg. By applying suitable measures, such as a protective gas atmosphere of, for example, nitrogen, the values can be lowered.
The pH of the dyebath is, for example, between 9 and 14, preferably between 11 and 13.
The redox potential in the dyebath is defined by the dye and the desired dyeing failure and is between-300mV and -900mV, preferably between -400mV and -700mV.

To the dyeing plant, an electrolytic cell is coupled with a liquor circulation. As electrolysis cells, it is possible to use customary electrolysis cells available from cell manufacturers or commercially available. Normal or multi-cathode cells can be used. However, in order to avoid anodic reoxidation of the sulfur dye, the electrolysis cell is preferably designed as a divided cell, again using a membrane electrolysis cell being particularly preferred. Most preferably, a cation exchange membrane serves as a separator.

Alkaline solutions, preferably alkaline solutions of alkali metal salts, in particular of sodium hydroxide, potassium hydroxide, sodium carbonate, common salt or Glauber's salt, are preferably used as the conducting electrolyte. Particularly preferably, the liquor added to the dyebath, advantageously sodium hydroxide solution, potassium hydroxide solution or soda, is used. The salts added during the dyeing, preferably common salt or Glauber's salt, can also improve the conductivity as electrolytes.

In a further preferred embodiment of the method according to the invention, this is carried out under an inert atmosphere. For this purpose, the dyebath in the dyeing apparatus with nitrogen or a noble gas, more preferably argon, superimposed.
Since the oxidative base load is reduced by reducing the partial pressure of the atmospheric oxygen, thus the required electrolysis cells can be dimensioned with smaller cell currents and thus more economical.

The process according to the invention can be used without restriction for all sulfur dyes. It is possible to use both oxidized dyes, filter cakes from the synthesis, as well as cathodically or chemically prereduced dyes and dye preparations. Particular preference is given to sulfur dyes produced by cathodic reduction, as described, for example, in US Pat DE-A 1 906 083 or WO 99/11716 are used.

According to the method of the invention, it is possible to dye all fiber materials which are basically dyeable with sulfur dyes. These are in particular fiber materials made of cellulose and polyamide, and of cellulose / polyester and cellulose / polyamide mixtures. Fiber materials preferably mean textile fiber materials.

When dyeing with sulfur dyes, atmospheric oxygen introduced into the dyebath is reduced by the existing reduced sulfur dye. In the method according to the invention, the redox behavior of Sulfur dyes, which is characterized by several reduction stages (see, for example Journal of Applied Electrochemistry 28 (1998) 1243-1250 and Recent Res. Devel. in Electrochem. 1 (1998) 245-264 ), advantageously exploited by working with sufficient cell circulation and cathodic re-reduction of the oxidized sulfur dye, so that stable bath conditions can be realized.
The sulfur dye takes over in the inventive method, the task of the indispensable in exhaust extraction reductant or cathodically regenerable mediators. The use of chemicals that cause costs in procurement and sanitation can therefore be dispensed with and a favorable overall ecological balance is obtained. Unexpectedly enough for the implementation of the method according to the invention, the low concentrations of sulfur dye, as used in exhaust processes. The process according to the invention is very particularly advantageous for dyeing on a standing bath, where only the sulfur dye discharged with the product has to be added to the dyebath.

The following application examples 1-5 show typical possibilities for the method according to the invention. To clearly demonstrate its effect, the pattern dyeings were started with oxidized sulfur dye, which is not immediately suitable for dyeing and can only be applied to the material after cathodic reduction.

Use Example 1 Dyeing in the Extraction Process with Sulfur Black 1

As the electrolytic cell, a cell divided by a cation exchange membrane is used.
Cathode: stainless steel cathodes, total area (surface area) cathode 0.43 m ² area, total volume 2 l.
Anode: Stainless steel plate with 0.01 m ² surface. Volume 0.3 l.
The anolyte used is 0.1 M NaOH.
Cell current: 0.9 A, cell voltage between 2.7 V and 4.1 V

The dyebath (2 l total volume) is pumped through the cathode compartment at 150 ml / min so that a continuous regeneration of the dyebath takes place by exchange with the catholyte.

Dyebath / catholyte composition:

10 g / l paste Cassulfon ^® Carbon CMR DyStar Textile dyes GmbH & Co. Germany KG
0.6 g / l wetting agent
3 g / l NaOH The dyebath contains a bleached cotton knitted fabric (sample 1) with a mass of 6.9 g. The liquor circulation and heating takes place by means of a magnetic stirrer.
The Katholyttemperatur is brought to 70 ° C. During an electrolysis time of 197 min, the redox potential drops from - 259 mV (vs. Ag / AgCl, 3 M KCl reference) to - 499 mV. The dyed pattern 1 is removed, rinsed with water and oxidized according to the usual methods with peroxide / acetic acid.
In the dyebath another pattern (pattern 2, mass 6.9 g) is introduced and dyed for 30 minutes while continuing the electrolysis process. The redox potential drops to - 545 mV. The pattern 2 is removed after 30 minutes and completed as already described.
The pH of the dyebath is about 12.2
The color depth can be described by color location measurement.

Results:

As the L values show, Pattern 2 is darker, although the dyeing time was shorter. This is due to the further development of the redox potential in the dyebath. Thus, despite the low dye concentration, successful dye reduction under exhaust dyeing conditions can be confirmed. L value (brightness) a-value (red-green) b-value (yellow-blue) Pattern 1 26,06 -1.02 -3.42 Pattern 2 22,07 -1.34 -2.66

Application Example 2 Dyeing in the Extraction Process with Sulfur Black 1

As the electrolytic cell, a cell divided by a cation exchange membrane is used.
Cathode: stainless steel cathodes, total area (surface area) cathode 0.43 m ² area, total volume 2 I.
Anode: Stainless steel plate with 0.01 m ² surface. Volume 0.3 I.
The anolyte used is 0.1 M NaOH.
Cell current: 0.9 A, cell voltage between 3.0 V and 4.7 V

The dyebath (2 l total volume) is pumped through the cathode compartment at 150 ml / min so that a continuous regeneration of the dyebath takes place by exchange with the catholyte.

Dyebath / catholyte composition:

10.5 g / l paste Cassulfon ^® Carbon CMR from DyStar textile colors GmbH & Co. KG Germany
0.6 g / l wetting agent
3 g / l NaOH
In the dyebath is a bleached cotton knit (pattern 3) with a mass of 6.8 g. The liquor circulation and heating takes place by means of a magnetic stirrer.
The catholyte temperature is brought to 62-64 ° C. During an electrolysis time of 175 min, the redox potential drops from - 309 mV (vs. Ag / AgCl, 3 M KCl reference) to - 440 mV. The colored pattern 3 becomes removed, rinsed with water and oxidized according to the usual methods with peroxide / acetic acid.
In the dyebath another pattern (pattern 4, mass 7.0 g) is introduced and stained for 80 min while continuing the electrolysis process. The redox potential during this time is at - 437 - -431 mV. The pattern 4 is removed after 80 minutes and finished as already described.
The pH of the dyebath is about 12.1-12.2.
The color depth can be described by color location measurement.

Results:

As the L values show, pattern 4 is darker, although the dyeing time was shorter. This is due to the further development of the redox potential in the dyebath. Thus, despite the low dye concentration, the successful dye reduction under the exhaust dyeing conditions can be confirmed. L value (brightness) a-value (red-green) b-value (yellow-blue) Pattern 3 38,00 -1.05 -3.71 Pattern 4 31.58 0.97 -3.64

Application Example 3 Dyeing on a Laboratory Denim Dyeing Plant Electrolysis cell:

As the electrolytic cell, a cell divided by a cation exchange membrane is used.
Cathode: stainless steel cathodes, total area (surface area) cathode 1 m ² , total volume of catholyte 10 l.
Anode: Ti electrode with mixed oxide coating, expanded metal with 0.04 m ² geometric area. Volume 1.5l.
The anolyte used is 1 M NaOH.
Cell current: 10 A, cell voltage between 3.0 V and 4.7 V

A looptex laboratory dyeing plant for denim dyeings is coupled to the cell as a dyeing plant. After an electrolysis time of 17.5 hours at 10 A (75 Ah) to reach the dyeing potential, a portion of the catholyte (4 I) is pumped from the cell to the dyeing plant and at a temperature of 50 ° C (-491 mV) Sample 5 or dyed at 80 ° C (-567 mV) Sample 6 (yarn strand with a length of 150 m, cotton yarn raw).
Dyeing program: Prewetting (3 g / l wetting agent), squeezing, immersion in sulfur chick, squeezing, air oxidation, followed by rinsing in cold water.
After dyeings 5 and 6, the dyebath is returned to the cell and again reduced by cathodic reduction.
After a reduction time of 3.7 hours at 10 A (3.7 Ah), part of the cell contents is again conveyed to the dyeing plant and samples 7 (57 ° C., 538 mV) and 8 (83 ° C., -536 ° C.) are obtained mV) according to the already described program.
Total volume of dyebath: 12 l

Dyebath / catholyte composition:

80.25 g / l filter cake Sulfur Black 1 (50% water content)
2.0 g / l wetting agent
4 ml / l 50% sodium hydroxide solution
By regenerating the bath contents, a maintenance of the reduction state can thus be ensured.
The pH of the dyebath is about 12.5 - 12.7.
The color depth can be described by color location measurement.

Results:

Dyeing bath potential mV L value (brightness) a-value (red-green) b-value (yellow-blue) Pattern 5 -491 25.54 -1.40 -4.24 Pattern 6 -567 22.18 -0.69 -3.07 Pattern 7 -538 22,35 -0.85 -3.39 Pattern 8 -536 18.54 -0.18 -2.29

Application Example 4 - EC staining of EC reduced sulfur black

A solution of 20 ml / l Cassulfon ^® Carbon CMR from DyStar textile colors GmbH & Co. KG Germany (30-40% solution of Leuco Sulfur Black 1) is free from water in the presence of 20 g / l Na ₂ SO ₄ at pH 12 and room temperature in a plant according to application example 1 electrolyzed. Sodium hydroxide solution (40 g / l NaOH) is again used as the anolyte. The solution of the reduced sulfur dye has a content of reducing agent equivalents of 0.075 mol / l at the beginning of the electrolysis in the iodometric titration. The cathodic reduction is carried out according to the low content of sulfur dye in the catholyte at a current density of 0.26 mA / cm ² . The electrolysis is terminated at an analytically determined content of 0.125 mol / l. The solution now has a content of reducing agent equivalents of 335 Ah based on 1 kg of solid sulfur dye. The solution of the sulfur dye prepared in this way can be used directly for dyeing, for example as described in Application Example 1.

Application Example 5 Dyeing in the Extraction Process with Sulfur Black 1 on a Jet Dyeing Plant Under Protective Gas (Nitrogen Atmosphere)

As the electrolytic cell, a cell divided by a cation exchange membrane is used.
Cathode: Three-dimensional stainless steel cathodes, viewing area cathode 60x55 cm, 0.33 m ² area, total volume of cathode chamber 100 I.
Anode: Titanium electrode with Pt mixed oxide coating with 0.3 m ² area.
The anolyte used is 0.1 M NaOH.
Cell current: 85 A, cell voltage between 5.3 V and 5.7 V

The dyebath (230 l total volume) is pumped through the cathode space so that a continuous regeneration of the dyebath or the reduced dyestuff takes place by exchange with the catholyte.

Dyebath / catholyte composition:

4.5 g / l paste Cassulfon ^® Carbon CMR from DyStar textile colors GmbH & Co. KG Germany (= electrochemically prereduced dye)
1.0 g / l wetting agent
7 g / l NaOH 38 ° Bé
The dyebath contains a pre-washed, bleached cotton knit with a weight of 8 kg. Flottenumwälzung and goods movement done by the existing jet in the pump. An indirect steam heating is used for heating. The dyeing takes place under a protective gas atmosphere (nitrogen) to minimize the admission of air. For this purpose, a volume flow of 10 i / min nitrogen is continuously fed into the apparatus.
The goods speed is 50 m / min. The liquor circulation through the cell is 30 l / min.
The catholyte temperature is brought to about 55 ° C, then the coupling of the cell circulation and further heating to 76 ° C takes place. During an electrolysis time of about 80 minutes, the redox potential is measured in the cell between -630 mV and -720 mV and measured in the jet dyeing plant between -460 mV and -432 mV (vs. Ag / AgCl, 3 M KCl reference).
The pH of the dyebath is about 12.1-12.2.
After rinsing in the overflow, the black goods are finished in a customary manner, for example by oxidation with hydrogen peroxide / acetic acid, rinsing and buffering.

Claims (8)

1. A process for dyeing fiber materials with sulfur dyes by regenerating the dyebath redox potential, which comprises, during the dyeing process, the dyeing liquor being circulated between the dyeing apparatus and an attached electrolytic cell and the sulfur dye which has been unwantedly oxidized in the dyebath being cathodically reduced in the electrolytic cell.
2. A process as claimed in claim 1, wherein the dyebath redox potential is closed loop controlled by the cell current.
3. A process as claimed in claim 1 and/or 2, wherein the electrolytic cell used is a divided electrolytic cell and more advantageously a membrane electrolytic cell.
4. A process as claimed in one or more of claims 1 to 3, wherein the conducting electrolyte used is selected from alkaline solutions and more preferably from alkaline solutions of alkali metal salts, especially of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium chloride or sodium sulfate.
5. A process as claimed in one or more of claims 1 to 4, wherein the dye concentration in the dyebath is in the range from 0.5 to 100 g/l of pure dye and more preferably in the range from 5 to 50 g/l of pure dye.
6. A process as claimed in one or more of claims 1 to 5, conducted at a temperature in the range from 20 to 135°C and more preferably in the range from 60 to 95°C.
7. A process as claimed in one or more of claims 1 to 6, conducted under an inert atmosphere.
8. A process as claimed in one or more of claims 1 to 7, wherein the fiber materials used are fiber materials composed of cellulose or polyamide or cellulosepolyester or cellulose-polyamide blends.