EP0357548B1 - Method for dyeing and printing cellulosic fibrous materials with vat dyes - Google Patents

Abstract

Process for dyeing and printing cellulosic fiber materials with vat dyes in the presence of enediols as reducing agents and alkali, using in addition small amount of organic water-miscible solvents, for example low molecular weight alcohols, when reducing the vat dyes. The vatting of the vat dyes proceeds uniformly and completely within a relatively short time, and the resulting vat dyes are reproducible and notable for high levelness and fastness properties.

Description

The present invention relates to a process for dyeing and printing cellulosic fiber materials with vat dyes in the presence of endiols as reducing agents and alkali.

The dyeing and printing of cellulosic fiber materials with vat dyes is generally carried out in alkaline media with sodium dithionite (hydrosulfite) as a reducing agent and usually in the presence of considerable amounts of complexing agents. Hydrosulfite already has a high reducing power at low temperature, but is sensitive to oxygen in alkaline solution. Oxidation of the hydrosulfite creates sodium sulfate, which can only be incompletely removed from the paint waste water. Wastewater with a high sulfite / sulfate load is corrosive and can e.g. Destroy sewage pipes (concrete pipes). If sulfate deposits occur, anaerobic degradation can also result in hydrogen sulfide. The presence of the complexing agents in the waste water is also problematic.

Attempts have already been made to completely or partially replace hydrosulfite as a coupling (reducing) agent for dyeing with vat dyes.

For example, from FR-A-2164824 a process for dyeing and printing cellulosic fiber materials with vat or sulfur dyes is known, in which, as the reducing agent, reductones, etc. also endiols, which are characterized by strongly negative redox potentials in alkaline medium, and quinoid compounds are used as oxidation stabilizers. Furthermore, BE-A-686620 discloses a similar process which is carried out in the presence of an aldehyde sulfoxylate, in particular formaldehyde sulfoxylate, and a colorless, saturated carbonyl compound as an oxidation stabilizer.

The investigations into the coupling (reduction) of vat dyes, in particular indigo, with endioles, however, showed only unsatisfactory results, in particular since the coupling was only incomplete and the dyeings obtained meet the high requirements, e.g. in terms of color consistency and levelness.

It was therefore an object of the present invention to provide a process for dyeing and printing cellulosic textile materials with vat dyes while avoiding hydrosulfite as the linking agent, which, when combined as completely as possible, leads to dyeings which meet the high requirements.

It has now been found that the object can be achieved according to the invention by additionally using small amounts of organic, water-miscible (hydrophilic) solvents to reduce the vat dyes.

The present invention therefore relates to a process for dyeing and printing cellulosic fiber materials with vat dyes in the presence of endiols as reducing agents and alkali, characterized in that organic, water-miscible solvents from the group of low molecular weight alcohols, ketones, are additionally used to reduce the vat dyes , Ethers, acetals, glycols, glycol ethers, thioglycols, nitriles, pyridines, lactones, lactams, acid amides, ureas, sulfones, sulfoxides or alkanolamines.

In particular, the process according to the invention for dyeing cellulosic fiber materials with vat dyes from aqueous alkaline dye liquors and in the presence of endiols as reducing agents is characterized in that the dye liquors additionally contain 0.1 to 10% by weight of the water-miscible organic solvent.

The invention furthermore relates to the aqueous alkaline dye liquors or printing pastes for carrying out the dyeing process according to the invention, vat dye preparations (stock vats) from which the dye liquors / printing pastes can be produced, and the dyed and printed (textile) cellulosic fiber materials obtained according to the process.

Vat dyes in the sense of the present invention are to be understood in addition to the indigoid dyes, with indigo itself being preferred also to mean anthrachinoid dyes and possibly also non-pre-reduced sulfur dyes. See the sections for details Vat and sulfur dyes (vat / sulfur dyes) in the Color Index (CI), third edition, 1971, published by the Society of Dyers and Colors.

The aqueous alkaline liquors in which the dyeings are carried out are strongly alkaline, i.e. they have pH values in the range from about 11 to 14, preferably 12 to 14 or 13 to 14.

The pH values are generally set using aqueous alkali metal hydroxide, in particular sodium hydroxide, and optionally also potassium hydroxide solutions.

Endiols are used to reduce vat dyes in the process according to the invention. As a rule, these are α-hydroxycarbonyl compounds which are distinguished by a strongly reducing action in an alkaline medium.

Typical compounds that form endiols (endiolates) in an alkaline medium are, in particular, low molecular weight (C₂-C₆) α-hydroxyketones and α-hydroxyaldehydes, such as e.g. Monohydroxyacetone, dihydroxyacetone, glycol aldehyde, dihydroxybutanone, 2,3-dihydroxyacrylaldehyde (triose reductone), ascorbic acid, cyclopentenediol-one (reductic acid).

Mono- and dihydroxyacetone are particularly preferred.

The reducing agents are generally used in amounts of about 20 to 100% by weight, preferably 20 to 80% by weight, based on the dye.

The organic solvents which are suitable for the process according to the invention should be miscible with water, ie with at least in the stated amounts from 0.1 to 10, in particular from 0.1 to 5% by weight in which they are used in the dye baths Water form a homogeneous phase.

However, since it is also possible to start from so-called stock vats, which form the dye baths after appropriate continuous or discontinuous dilution, the solvents mentioned should preferably still be miscible with water in a much larger amount, ie somewhat to 50% by weight (range 0, 1 to 50% by weight).

• ― C₁-C₄-Alkohole, wie z.B. Methanol, Ethanol, n-Propanol, iso-Propanol oder n-Butanol, wobei Methanol und iso-Propanol besonders bevorzugt sind;
• ― Ketone, wie z.B. Aceton, Methylethylketon, Diethylketon, 4-Hydroxy-4-methylpentanon-2 (Diacetonalkohol) und Cyclohexanon;
• ― Ether, wie z.B. Diisopropylether, Dioxan und Tetrahydrofuran;
• ― Acetale, wie z.B. Glykolformal und Glyzerinformal;
• ― Glykole und Glykolether, wie z.B. Ethylenglykol, Propylenglykol, Ethylenglykolmonomethyl-, -ethyl- oder -butylether, Diethylenglykolmonomethyl- oder -ethylether und Ethylenglykoldimethylether;
• ― Thioglykole, wie z.B. Thiodiglykol;
• ― Nitrile, wie z.B. Acetonitril;
• ― Pyridine, wie z.B. Pyridin und die Picoline (α, β, γ);
• ― Lactone, wie z.B. γ-Butyrolacton;
• ― Lactame, wie z.B. Pyrrolidon, N-Methylpyrrolidon und 1,5-Dimethylpyrrolidon;
• ― C₂-C₄ Alkanolamine, z.B. primäre, sekundäre oder tertiäre Alkanolamine, vorzugsweise Ethanolamin, Diethanolamin, Triethanolamin, n-Propanolamin oder iso-propanolamin;
• ― Säureamide niedriger Carbonsäuren oder anorganischer Säuren, wie z.B. Formamid, N,N-Dimethylformamid, Acetamid, N,N-Dimethylacetamid, Tris-(dimethylamido)-phosphat und Bis-(dimethylamido)-methanphosphat;
• ― Harnstoffe, wie z.B. N,N,N′,N′-Tetramethylharnstoff;
• ― Sulfone oder Sulfoxide, wie z.B. Sulfolan (Tetramethylensulfon), 3-Methylsulfolan und Dimethylsulfoxid.

Both protic and aprotic organic solvents can be used, which should not have a reducing effect. In particular, these are low molecular weight solvents, such as, for example,

• - C₁-C₄ alcohols, such as methanol, ethanol, n-propanol, iso-propanol or n-butanol, with methanol and iso-propanol being particularly preferred;
• - Ketones such as acetone, methyl ethyl ketone, diethyl ketone, 4-hydroxy-4-methylpentanone-2 (diacetone alcohol) and cyclohexanone;
• - ethers, such as diisopropyl ether, dioxane and tetrahydrofuran;
• Acetals, such as glycol formal and glycerol formal;
• Glycols and glycol ethers, such as, for example, ethylene glycol, propylene glycol, ethylene glycol monomethyl, ethyl or butyl ether, diethylene glycol monomethyl or ethyl ether and ethylene glycol dimethyl ether;
• Thioglycols, such as thiodiglycol;
• Nitriles, such as acetonitrile;
• - pyridines, such as pyridine and the picolines (α, β, γ);
• Lactones, such as γ-butyrolactone;
• Lactams, such as pyrrolidone, N-methylpyrrolidone and 1,5-dimethylpyrrolidone;
• - C₂-C₄ alkanolamines, for example primary, secondary or tertiary alkanolamines, preferably ethanolamine, diethanolamine, triethanolamine, n-propanolamine or iso-propanolamine;
• - Acid amides of lower carboxylic acids or inorganic acids such as formamide, N, N-dimethylformamide, acetamide, N, N-dimethylacetamide, tris (dimethylamido) phosphate and bis (dimethylamido) methane phosphate;
• - Urea, such as N, N, N ', N'-tetramethyl urea;
• - Sulphones or sulphoxides, such as sulfolane (tetramethylene sulphone), 3-methyl sulfolane and dimethyl sulphoxide.

Mixtures of the solvents mentioned can also be used.

The process according to the invention, which is carried out using a combination of endiols as reducing agents and organic, water-miscible solvents, is practically suitable for all dyeing and printing processes with vat dyes, in particular indigo.

These processes can be carried out in the temperature range from room temperature (15 to 20 ° C.) to about 120 ° C., in particular 15 to 80 ° C. The good stability of the reducing agents in comparison with the relatively unstable hydrosulfite allows when working from a dye bath, e.g. on the jigger, on the reel runner, on the cheese winder and on the foulard, the use of significantly smaller amounts of reducing agents than previously used. For the same reason, dyeing can be carried out on the above-mentioned apparatus at higher temperatures than before, which results in very level dyeings.

The method according to the invention is also suitable for continuous dyeing, e.g. Suitable as a pad-steam process or as a cold storage process. In the pad-steam process, the vat dye (as a pigment) is applied to the textile material, which is then usually dried; then an aqueous liquor with the reducing agent / solvent combination is applied and at higher temperatures, e.g. in a steam atmosphere at 100 ° C, developed (reduced) and then, as usual, e.g. Rinsing, oxidizing and soaping finished.

The pad-steam process using hydroxyacetone as the reducing agent results in a saving of more than 50% by weight of reducing agent compared to the dithionite previously used for this process.

The same advantages can also be achieved if the cold storage process is used. According to this process, a fabric padded with vat or sulfur dye is impregnated with a reducing agent liquor of the specified composition, the fabric is wound up and stored for a few hours at room temperature, the dye being reduced and fixed. It is then finished in the usual way.

If appropriate, the process according to the invention can also be carried out as a single-bath padding process by applying an aqueous liquor, which contains the vat dye, alkali, the reducing agent and the organic solvent, to the textile material and developing the dyeing by steaming or cold storage and then finishing as usual.

Finally, the method according to the invention can also be carried out as a printing method, e.g. as a two-phase printing process by printing on the vat dyes with a printing paste containing conventional thickeners and reducing agents, intermediate drying, padding on a padding liquor containing solvents and alkali, and developing in a damper suitable for two-phase printing, again being finished as usual by rinsing, oxidizing and soaping.

In the direct printing process, the printing paste contains the dye, thickener, alkali, reducing agent and solvent.

The aqueous dyeing liquors / printing pastes for carrying out the dyeing process according to the invention from a bath (single bath) are a further subject of the present invention. They are characterized in that they contain the vat dye, an alkali metal hydroxide, an endiol as a reducing agent and 0.1 to 10% by weight, based on the dyeing liquor / printing paste, a water-miscible organic solvent and other conventional auxiliaries.

The amounts of dye, alkali and reducing agent in these dyeing liquors can vary within wide limits.

As a rule, the amount of dye, which is dependent on the desired depth of color, is 0.1 to 7% by weight, based on the substrate to be colored.

The amount of alkali should be sufficient to set a pH in the range from 11 to 14, preferably 12 to 14 or 13 to 14.

The amount of reducing agent is about 0.01 to 10 wt .-%, based on the weight of the dye liquor.

To prepare the aqueous dyeing liquors / printing pastes as used according to the invention, (concentrated) vat dye preparations - and these are a further subject of the present invention - can be used, in addition to the vat dye, the reducing agents and solvents mentioned, and optionally also conventional auxiliaries such as dispersing and adjusting agents, and water.

The amount of reducing agent is about 1 to 2, preferably 1.4 to 1.6, so-called linking equivalents per equivalent of dye, the linking equivalent being the amount of reducing agent which can ensure adequate (complete) linking.

The amount of solvent is chosen so that the specified amount of 0.1 to 10% by weight is present after the dyeing liquors have been prepared.

The amount of water depends on whether it is solid, dough-like or liquid vat dye preparations.

To keep them stable, they are acidic or neutral. Immediately before they are used to prepare the dye liquors mentioned, they are then made alkaline (pH 11 to 14) by adding suitable alkalis and, if appropriate, diluted with water.

The vat dyes can be linked during the actual dyeing / printing process, but also separately (pre-linked dye preparations which can be used to produce dyeing liquors or printing pastes).

According to the method according to the invention, the (pre) linking of the dyes and the actual dyeing and printing of textile materials can also be continuously connected to one another by directly using the (stable) preparations with the linked dyes for dyeing and printing

The stability of the vat dye preparations or the dyebaths / printing pastes and thus their application properties can, if appropriate, also be improved further by adding water, alcohols, reducing agents, surfactants, alkali metal hydroxides and other components from the suspensions containing the sparingly soluble vat dyes optionally contain other conventional additives, uses ultrasound. Dye preparations or dyebaths or printing pastes can be obtained by such an ultrasonication, which have a much more homogeneous and fine-grained distribution of vat dyes, which at the same time enables an improved reduction (higher concentration of the conjugated dye) and thus also a higher dye yield on the substrate.

The amount of reducing agents and the other components used can thus generally be reduced.

The procedure is generally such that the dye suspension is first stirred and then the dye agglomerates are ground using ultrasound. The process of dissolving and combining the vat dyes can thus be shortened considerably; as indicated, this also opens up the possibility of continuously carrying out the dyeing process with the vat dyes.

The ultrasonic waves that are used according to the method are generated in a conventional ultrasonic generator. Their frequency is in the range of 16 kHz and above, e.g. in the range from 18 to 35 kHz, preferably 20 to 25 kHz. The ultrasonic energy to be used depends on the type of dye but also on the other reaction conditions, such as temperature, solvent, grain size of the dye, etc. Typically, 50 to 100 watts (5 to 10 mkg / s) of energy is sufficient for dye preparations as used in the examples below.

The process according to the invention for dyeing and printing with vat dyes can be used for cellulosic fiber materials in a wide variety of textile processing states. For example, Fibers, threads, yarns, woven or knitted fabrics made of preferably native and / or regenerated cellulose, but also mixed fabrics or blended fabrics, which additionally contain a fiber from other natural or synthetic fibers, e.g. Usual polyamide or polyester fibers, contain, colored or printed. If the non-cellulosic fiber content is also to be colored, the appropriate dyes (e.g. acid or dispersion dyes) can be used.

The process according to the invention achieves surprising advantages in the field of dyeing and printing cellulosic textile fiber materials with vat dyes, in particular indigo.

Among others, the uniform and complete reduction of vat dyes (no over-reduction); the high stability of the reduced (combined) dye liquor - no precipitation of the combined dye up to relatively high concentrations - which is particularly important when using so-called vats, which should have a sufficiently long service life (several hours). This makes dyeing in deep shades easier and gives you level dyeings.

Next is the improvement of the textile mechanical properties of the dyed textile fiber material due to the low salt content in the Wash baths (reduced salt deposits on the fiber materials), the simple dosing of the (liquid) reducing and organic solvents and the good reproducibility of the dyeings.

The dyestuffs (indigo) can optionally be recovered from the dyeing wastewater in a relatively simple manner and without being disturbed by excessive salt content, e.g. through ultrafiltration. In a subsequent biological purification stage, organic components can be removed from the wastewater and this wastewater purified in this way can finally be returned to the dyeing process.

The possibility of purifying and reusing the waste water in this way results in particular from the fact that the presence of sulfites / sulfates in the waste water can be avoided.

A significant reduction in the wastewater load is thus achieved.

Finally, the solvents can at least partially be recovered and reused or otherwise used.

The present invention is explained in more detail in the examples below, without restricting it to the examples. Parts and percentages are by weight. The temperature is given in degrees Celsius.

example 1

Pre-cleaned cotton fabric is placed in a jigger containing a dye liquor of the following composition:

The temperature of the fleet is 50 ° C. The liquor ratio is 1: 6.

After a dyeing time of 30 minutes, the fabric is oxidized and soaped as usual.

A level, deep blue dyeing with good fastness properties is obtained.

The residual dye is recovered from the almost exhausted fleet by means of ultrafiltration and the residual waste water can be sent directly to biological disposal and reused if necessary.

Example 2

Raw yarn is dyed continuously at a speed of 40 m / minute in a corresponding dyeing machine using a stock vat method. The stock vat is continuously introduced into the dye bath at a 1:20 dilution. The trunk is linked outside the dye bath at 50 ° C. The trunk has the following composition:

The temperature of the dye liquor is 40 ° C. The liquor absorption is 60% by weight.

It is then oxidized and finished as usual.

You get a deep blue colored yarn with good general fastness properties.

The dye pigment detached during the washing process is recovered using an ultrafiltration system and the permeate is disposed of anaerobically.

Example 3

• (a) Cotton yarn wound on packages is dyed on a commercial yarn dyeing machine at a liquor ratio of 1:12 in a bath of the following composition:
  
  The temperature of the liquor is increased from 20 ° C. to 60 ° C. within 15 minutes and dyeing is carried out at this temperature for 30 minutes. Then it is rinsed, oxidized and finished as usual.
  The coloring is characterized by a good winding flow and high levelness.
• (b) Example (3a) is repeated; However, before the dye bath is filled into the yarn dyeing apparatus, it is treated with ultrasound (22 kHz, 70 watts, 55 ° C.), which accelerates the dye's coupling and increases the degree of coupling. This results in an improved dye yield on the fiber and dyeings with greater depth of color.
• (c) Example (3a) is mixed with 10 parts of the dye of formula C.I. Vat Blue 6 (C.I. No. 69825) repeated. The dyeing also has good levelness and fastness.

Example 4

• (a) Cotton fabric is dyed on a commercial jet system at a liquor ratio of 1:10 at 60 ° C. The dyebath is prepared in a similar way to a trunk vat process.
  The trunk has the following composition:
  
  The viling takes place at 60 ° C; after about 30 minutes of reaction, the stock vat is diluted with water in a ratio of 1: 5, so that the proportion of methanol in the dyebath is only about 4% by weight. The liquor thus diluted is fed to the dyeing machine and circulated for 40 minutes. There is practically no foaming. It is then oxidized and finished as usual.
  The blue color obtained is characterized by a high level of levelness.
• (b) Example (4a) is mixed with 40 parts of dye C.I. Vat Orange 29 repeats. A level dyeing with good general fastness properties is also obtained.

Example 5

A cotton fabric is printed with a printing paste containing a non-pre-reduced sulfur dye and monohydroxyacetone and dried. This is followed by padding on an aqueous solution containing alkali and solvent of the following composition:

Steam is then fixed using saturated steam for 30 seconds, followed by the oxidation and rinsing process. The completion is carried out as usual.

A black-dyed cotton fabric with good levelness is obtained.

The process is characterized by its good reproducibility in terms of color strength and levelness. Another advantage is the high durability of the paste despite the presence of the reducing agent.

Example 6

Pre-cleaned cotton fabric is dyed in a jigger containing the following dye liquors:

The liquor ratio is 1:20, the pH 13.1. After a dyeing time of 45 minutes, the fabric is oxidized and soaped as usual.

With the dyes specified in Table 1, level and real dyeings are obtained in the shades mentioned.

Instead of methanol, you can also use ethanol, n-propanol, iso-propanol, n-butanol, acetone, methyl ethyl ketone, cyclohexanone, diisopropyl ether, dioxane, tetrahydrofuran, glycerol formal, glycol formal, ethylene glycol, propylene glycol, ethylene glycol dimethyl ether, ethylene glycol monomethyl ether, with analog results - or -butyl ether, diethylene glycol monomethyl or ethyl ether, thiodiglycol, acetonitrile, pyridine, γ-butyrolactone, pyrrolidone, N-methylpyrrolidone, 1,5-dimethylpyrrolidone, formamide, N, N-dimethylformamide, acetamide, N, N-dimethylacetamide, tris - (Dimethylamido) phosphate, bis (dimethylamido) methane phosphate, N, N, N ', N'-tetramethylurea, tetramethylene sulfone, β-methylsulfolane, dimethyl sulfoxide, ethanolamine, diethanolamine, triethanolamine, n-propanolamine or isopropanolamine.

Instead of 100 parts of aqueous sodium hydroxide solution (40%), it is also possible to work with dye liquors which contain 50 parts of the aqueous sodium hydroxide solution mentioned.

Example 7

Cotton fabric is placed on a commercial jet system at a fleet. ratio of 1:10 at 55 to 60 ° C. The dyebath is prepared in a similar way to a vat process:

The trunk has the following composition:

The viling takes place at 55 ° C; the pH is 12.9. After about 20 minutes of reaction, the stock vat is diluted 1: 5 with water.

The dye liquor obtained in this way is pumped into the dyeing machine and circulated there at 55 to 60 ° C. for 45 minutes. It is then oxidized and finished as usual.

Using the dyes specified in Table 2, level and true dyeings are obtained in the specified shades.

If you use a stock vat with 10 parts of monohydroxy acetone, you can further accelerate the vatting (reduction) of the dyes.

If necessary, the veneer can also be sonicated by the trunk (55 ° C, frequency: 20 kHz, 50 to 100 watts), e.g. for dyes C.I. Vat Red 10 or C.I. Vat Green 3, speed up.

Claims (14)

1. A process for dyeing and printing cellulosic fibre materials with vat dyes in the presence of enediols as reducing agents and alkali, which comprises using in addition organic water-miscible solvents, selected from lower molecular weight alcohols, ketones, ethers, acetals, glycols, glycol ethers, thioglycols, nitriles, pyridines, lactones, lactams, amides, ureas, sulfones, sulfoxides or alkanolamines, to reduce the vat dyes.

2. A process according to claim 1 for dyeing cellulosic fibre materials with vat dyes from aqueous alkaline dyeing liquors in the presence of enediols as reducing agents, wherein the dyeing liquors additionally contain 0.1 to 10% by weight of the water-miscible organic solvent.

3. A process according to claim 1, wherein the organic solvent is a C₁-C₄alcohol, acetone, methyl ethyl ketone, cyclohexanone, diisopropyl ether, dioxane, tetrahydrofuran, glycerol formal, glycol formal, ethylene glycol, propylene glycol, ethylene glycol dimethyl ether, ethylene glycol monomethyl, monoethyl or monobutyl ether, diethylene glycol monomethyl or monoethyl ether, thiodiglycol, acetonitrile, pyridine, γ-butyrolactone, pyrrolidone, N-methylpyrrolidone, 1,5-dimethylpyrrolidone, formamide, N,N-dimethylformamide, acetamide, N,N-dimethylacetamide, tris(dimethylamido) phosphate, bis(dimethylamido)methane phosphate, N,N,N′,N′-tetramethylurea, tetramethylene sulfone, β-methyl sulfolane or dimethyl sulfoxide.

4. A process according to claim 3, wherein the organic solvents are ethanol, n-propanol, n-butanol and in particular methanol or isopropanol.

5. A process according to claim 1, wherein the organic solvent is ethanolamine, diethanolamine, triethanolamine, n-propanolamine or, isopropanolamine.

6. A process according to claim 2 for dyeing cellulosic fibre materials with vat dyes from aqueous alkaline dyeing liquors at a pH of 11 to 14 and temperatures of 15 to 120°C and in the presence of mono- or dihydroxyacetone as reducing agent, wherein the dyeing liquors additionally contain 0.1 to 10% by weight of methanol, ethanol or isopropanol.

7. A process according to claim 2 for dyeing cellulosic fibre materials with indigo from aqueous alkaline dyeing liquors in the presence of monohydroxyacetone as reducing agent, wherein the dyeing liquors additionally contain 0.1 to 10% by weight of methanol, ethanol, or isopropanol.

8. A process according to any one of claims 1 to 7, wherein the reduction of the vat dyes is optionally carried out separately from the actual dyeing/printing process.

9. A process according to claim 8, wherein the separate reduction of the vat dyes and the dyeing/printing process are carried out in a continuous manner.

10. A process according to either of claims 8 and 9, wherein ultrasound is used for reducing the vat dyes, for the dyeing/printing process or for both steps.

11. An aqueous dyeing liquor or print paste for carrying out a process according to any one of claims 1 to 10, which contains a vat dye, an alkali metal hydroxide, an enediol as reducing agent and additionally 0.1 to 10% by weight, based on the dyeing liquor/print paste, of the water-miscible oragnic solvent, an optionally customaty assistants.

12. An aqueous dyeing liquor or print paste according to claim 11, which contains 0.1 to 7% by weight, based on the substrate to be dyed, of a vat dye, an alkali metal hydroxide in an amount to establish a pH of 11 to 14, 0.01 to 10% by weight, based on the weight of the dyeing liquor/print paste, of an enediol, and 0.1 to 10% by weight, based on the weight of the dyeing liquor/print paste, of the water-miscible organic solvent.

13. A dyeing liquor or print paste according to either of claims 11 and 12, which contains mono- or dihydroxyacetone as the enediol and methanol, ethanol or isopropanol as the organic solvent.

14. A stable vat dye preparation for preparing an aqueous dyeing liquor or print paste according to claim 12, which contains as well as the vat dye an enediol as reducing agent in an amount of 1 to 2 vatting equivalents per equivalent of dye and the water-miscible organic solvent, and optionally customary assistants, and is transformable by pH adjustment to 11-14, optionally after dilution with water, into the aqueous dyeing liquor/print paste.