WO1995020643A1

WO1995020643A1 - Method of bleaching jeans fabric

Info

Publication number: WO1995020643A1
Application number: PCT/EP1995/000288
Authority: WO
Inventors: Christoph Erwin Hartmann; Wolfgang Lex; Doris Preidt
Original assignee: Peroxid-Chemie Gmbh
Priority date: 1994-01-28
Filing date: 1995-01-26
Publication date: 1995-08-03
Also published as: AU1536595A; EP0741777B1; AU681490B2; ATE159980T1; CA2181813A1; EP0741777A1; GR3025703T3

Abstract

The invention concerns a single-stage method for bleaching dyed cotton fabric. The method is characterized in that the dyed cotton fabric is treated in an aqueous bath under conditions suitable for lightening the colour of the fabric, the bath containing as the active component a peroxy compound, but no hypochlorites, permanganates or enzymes.

Description

Bleaching of jeans

DESCRIPTION

The present invention relates to a process for lightening or bleaching dyed cotton fabrics in the absence of added hypochlorites, permanganates and enzymes, and to a lightening bath suitable for carrying out this process.

In recent years there has been an increasing demand for dyed cotton fabrics, in particular for cotton jeans dyed with indigo or other dyes, which are lightened or partially decolorized in further processing steps either by mechanically assisted washing processes or / and by chemical processes.

It is known to use denim with hypochlorites, e.g. NaOCl to weaken or lighten the overall color. However, this method has the disadvantage that large amounts of waste water contaminated with AOX are produced, which have to be treated in order to comply with the increasingly strict waste water limit values. In addition, the use of chlorine-containing products and processes for producing consumer products using chlorine-containing chemicals are being criticized more and more by the public due to the physiological questionability of these substances. Manufacturers of dyed cotton fabrics, especially denim fabrics, are therefore trying to develop safer lightening processes in order to save disposal costs or additional production costs due to expensive wastewater treatment processes.

As an alternative to hypochlorite bleaching, the use of dextrose as a reducing agent is known, but it has the disadvantage that the treatment temperature must be at least 80 ° C. and the pH of the whitening bath must be adjusted to 13. Furthermore, the use of ozone Known as an oxidizing agent for the lightening of dyed cotton fabrics, but this process has the disadvantage that the handling of ozone in technical production processes is quite difficult. In addition, the treatment with ozone severely damages the cotton fiber. Furthermore, ketone derivatives are known as reducing agents for lightening cotton fabrics. Although these substances allow normal conditions with regard to the treatment temperature, the pH value of the lightening bath and the duration of the treatment, they have the disadvantage that the values for the biological and chemical oxygen demand of the waste water (BOD ₅ and COD) due to the organic load the wash liquor can be increased. In addition, the use of ketone derivatives as brighteners increases the white-blue contrast in cotton fabrics dyed with indigo, which is undesirable for use.

To avoid the disadvantages of hypochlorite bleaching, treatment of the cotton fabrics with potassium permanganate for the partial oxidation of dyes in the cotton fabric has recently been carried out in order to lighten cotton fabrics. The disadvantage of this method is that the wastewater from the lightening process is contaminated with large amounts of heavy metals. In addition, the use of permanganates significantly increases operating costs. In addition, the fiber turns brown due to Mn0 ₂ .

The use of hydrogen peroxide or peracetic acid in the lightening of dyed cotton fabrics is also known. However, these substances are not used to carry out the lightening step itself, but only to neutralize a cotton fabric which has already been lightened by hypochlorite or potassium permanganate (cf., for example, GB-A-2213 842, US Pat. No. 5,205,835, JP-A- 31027174; US-A-5,238,463; JP-A-3027173). However, as already explained above, these methods have the disadvantage of using hypochlorites or permanganates. Furthermore, the lightening of colored textiles in the presence of an enzyme such as peroxidase or oxidase and H ₂ 0 ₂ as an oxidizing agent is known (W092 / DK / 119). However, due to the use of enzymes, this process is not cost-effective and is therefore not suitable for large-scale processes. The object of the present invention was therefore to at least partially avoid the disadvantages of the prior art and to provide a process for lightening colored cotton fabrics which is comparable in terms of the effect achieved and the costs to the use of hypochlorite, but the advantage of less BOD ₅ and COD values in wastewater on ice.

The object of the invention is achieved by a one-step process for lightening dyed cotton fabrics, which is characterized in that dyed cotton fabrics are treated under conditions suitable for lightening the colors of the cotton fabrics with an aqueous bath containing a peroxo compound as an active component, but no added hypochlorites Contains permanganates and enzymes.

Surprisingly, it was found that the use of peroxo compounds as a lightening agent for dyed cotton fabrics, in particular for jeans fabrics, has a very good effect. The method according to the invention has the advantage over known methods that wastewater pollution is avoided, since an AOX contamination by hypochlorites does not occur and other environmentally harmful chemicals do not have to be used or only to a small extent. The COD and BOD ₅ values as wastewater pollution values are not increased by the peroxo compound, but contrary effects can even occur, since peroxo compounds also enter oxygen and thus reduce the oxygen demand of the wastewater.

For reasons of wastewater and exhaust air pollution, the method according to the invention is preferably carried out using a lightening bath which contains the smallest possible amounts of Chlorine, especially less than 5000 ppm, particularly preferably less than 1000 ppm and most preferably less than 200 ppm chlorine (in the form of elemental chlorine, chlorite, hypochlorite etc.).

The conditions suitable for lightening or bleaching the colors of the cotton fabrics are to be understood as those conditions of the concentration of the lightening bath, the temperature and the duration of treatment at which the desired lightening of the colors is achieved without damaging the cotton fiber.

Inorganic peroxides selected from the group consisting of H ₂ O ₂ , perphosphates, perborates, percarbonates, persulfates, percarbamide, peracetic acid and mixtures thereof are preferably used as suitable peroxo compounds for the process according to the invention. The peroxo compound is particularly preferably a persulfate, ie a peroxodisulfate, a peroxomonosulfate or mixtures thereof, and most preferably a peroxodisulfate. An alkaline earth metal (eg Ca), alkali metal (eg Li, Na, K, Rb, Cs) or ammonium peroxodisulfate and in particular potassium, sodium or / and ammonium peroxodisulfate are preferred among the peroxodisulfates. Taking into account their properties, organic peroxides such as ketone peroxides, hydroperoxides, diacyl peroxides or peresters can also be used.

The concentration of the peroxo compound can be varied depending on the reaction conditions and the desired degree of lightening of the cotton fabrics. In general, the peroxo compound can be varied in a concentration of about 21 mmol / l (corresponding to about 5 g / l for sodium peroxodisulfate) up to the solubility limit of the compound or up to a concentration above which an attack on the cotton fiber takes place. The concentration of the peroxo compound in the lightening bath is preferably in the range from 21 mmol / 1 to 2.1 mol / 1, particularly more preferably in the range from 42 mmol / 1 to 1.7 trtol / 1 and most preferably from 42 mmol / 1 to 1.3 mol / 1.

The temperature for carrying out the process according to the invention is advantageously in the range from 15 to 90 ° C., preferably from 40 to 80 ° C. and most preferably from 50 to 65 ° C.

The time for carrying out the lightening process according to the invention depends on the desired degree of lightening, the temperature of the lightening bath and the concentration of the lightening reagent. This period of time can easily be determined by a person skilled in the art by routine experiments. When the process according to the invention is carried out on an industrial scale, the reaction time is generally 2 minutes to 20 hours, preferably 5 minutes to 5 hours and particularly preferably 15 minutes to 1 hour.

The pH of the lightening bath can range from 0 to 12, with pH values in the range from 1 to 10 being preferred and in the range from 4 to 7 being particularly preferred. To adjust the pH range, the lightening bath can be a buffer system, e.g. contain a phosphate buffer.

Other optional components of the lightening bath are surfactants, e.g. Surfactants, complexing agents and other agents known in the relevant art.

The process according to the invention can be carried out in conventional devices and with customary amounts of cotton, which are also used, for example, to carry out a hypochlorite bleaching process. The dyed cotton fabrics are preferably treated in a washing drum with the lightening bath according to the invention. In a particularly preferred embodiment of the process according to the invention, the lightening bath additionally contains an activator which is selected from transition metal compounds and / or halide compounds. Examples of typical transition metals are titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, palladium, tin, molybdenum, silver, cerium, rhutenium, tungsten and rhenium. Preferred transition metals are iron, copper, cobalt, zinc, silver, manganese, chromium, nickel or mixtures thereof. The transition metals can be used in the form of metal salts or complex compounds, with metal salts being preferred. The transition metals are particularly preferably used in the form of their sulfate salts. Iron (III) salts, iron (II) salts and copper (II) salts, in particular iron (III) sulfate, iron (II) sulfate and copper (II) sulfate are on most preferred.

The transition metal compound used as the activator is preferably added to the lightening bath according to the invention in an amount of up to 25 mmol / l, based on the metal. It is preferred to use the. Transition metal compound in an amount of 0.05 to 15 mmol / 1, particularly preferably from 0.05 to 8 mmol / 1 based on the metal.

It is particularly preferred to use copper (II) sulfate, iron / II) sulfate or iron (III) sulfate as the activator if ammonium peroxodisulfate is used as the peroxo compound. Likewise particularly preferred is the use of iron dll) sulfate or iron (II) sulfate as an activator if sodium peroxodisulfate is used as the peroxo compound.

Examples of halide compounds which are suitable as activators are chloride, bromide and iodine compounds, in particular the bromide compounds. Ammonium, alkali metal and alkaline earth metal halides are preferred, with alkali metal halides being particularly preferred. Most preferred are sodium and / or potassium bromide. The halide compound used as the activator is preferably added to the brightening bath according to the invention in an amount of up to 500 mmol / l, based on the halide ion. The halide compound is particularly preferably used in an amount of 0.5 mmol / 1 to 200 mmol / 1, most preferably 1 to 20 mmol / 1, based on the halide ion.

Compared to activation with transition metal compounds, activation with halide ions and in particular with bromide ions has the advantage that the concentration of the peroxo compound can be significantly reduced without deteriorating the bleaching effect. If bromide ions and persulfates are simultaneously present in the brightening bath, concentrations in the range from 21 mmol / 1 to 420 mmol / 1 persulfate (corresponding to 5 to 100 g / 1 for sodium peroxodisulfate) and 0.5 to 200 mmol / 1, in particular 1 to 20 mmol / 1 bromide is particularly preferred, with optimal effects being achieved even at very low bromide concentrations. When selecting optimal process conditions, care is preferably taken to ensure that the concentrations of the halide compound and the peroxo compound are inversely proportional within the specified ranges.

Another embodiment of the present invention comprises treating the dyed cotton fabrics at an alkaline pH. The treatment of the cotton fabrics in alkaline has the advantage that attack by H ⁺ ions, which can lead to a reduction in the tensile strength, is completely ruled out. In this embodiment, the treatment is preferably carried out at a pH range from 9 to 13, particularly preferably from 10 to 12. Since peroxo compounds, for example persulfates, only show a moderate brightening effect in alkaline without added hypochlorite, an activator suitable for alkaline pH values is preferably used. Examples of such activators are transition metal complex compounds which are soluble at alkaline pH values, eg complex compounds of iron, copper, cobalt or nickel, particularly preferably complex compounds of iron.

Specific examples of suitable activators are complexes of transition metals with ammonia, polyamines such as EDTA, rhodanide, cyanide or fluoride. Cyano complexes are preferably used, particularly preferably hexacyanoferrate (II) or hexacyanoferrate (III) complexes. The hexacyanoferrate complexes are e.g. in the form of alkali metal salts, e.g. of sodium or potassium salts.

The complexes are preferably present in an amount of up to 25 mmole / l based on the metal, particularly preferably in an amount of 0.05 to 15 mmole / l, most preferably 0.05 to 8 mmole / l based on the metal used.

When using transition metal complex compounds as activators, surprisingly strong brightening was achieved even at very low concentrations of peroxo compounds. The concentration of the peroxo compounds when lightening in alkaline is therefore in the range of e.g. 5 mmol / 1 to 2.1 mol / 1, preferably 5 mmol / 1 to 1 mol / 1, particularly preferably 5 mmol / 1 to 250 mmol / 1. The treatment temperature is preferably 70 to 90 ° C, particularly preferably about 80 ° C. The treatment time depends on the concentration of the peroxo and activator compounds used, but good results have been achieved with a treatment time in the range from 10 minutes to 1 hour, in particular from 10 minutes to 30 minutes.

The dyed cotton fabrics used for the process according to the invention are preferably dyed with dyes selected from the group consisting of vat, direct and sulfur dyes. Typical vat dyes are indigo, thioindigo and other indigoide dyes, indanthrene and other antrachinoid dyes, phthalocyanine and naphthalene dyes. Particularly preferred dyes are all substances used for dyeing cotton fabrics, in particular denim fabrics, in particular indigo, thioindigo and other indigo dyes and sulfur dyes.

After the dyed cotton or jeans fabrics have been lightened by the process according to the invention, they are washed in the usual way, e.g. cleaned from the whitening bath by rinsing and / or neutralizing. Since no discoloration, e.g. After treatment, yellowing that occurs in cotton fibers is generally not necessary. Another advantage of the method according to the invention is that the degree of lightening, i.e. the lightening of the overall color tone of the dyed cotton fabrics can be controlled very well by selecting the treatment duration and temperature, the concentration of the peroxo compound and, if appropriate, the activator compound.

Particularly when using sodium peroxodisulfate and optionally iron (III) sulfate as activator, the wastewater does not contain any environmentally harmful chemicals, since sodium peroxodisulfate decomposes into sodium sulfate and oxygen and also iron sulfate is not a problem, since this substance is added as a flocculant in sewage treatment plants, for example . By using peroxo compounds, in particular persulfates, in the brightening bath, additional oxygen is even introduced into the bath and the oxygen demand of the waste water is thus reduced. The use of halide ions, in particular bromide ions in the low concentrations which are required to activate the peroxo compound, does not result in any significant environmental pollution.

Another object of the present invention is the use of a bath which contains 21 mmol / 1 to 2.1 mol / 1 of a peroxo compound as an active component and is free from added hypochlorites, permanganates and enzymes for the brightening of dyed cotton fabrics. The peroxo compound is preferably selected from the group consisting of H ₂ 0 ₂ , perphosphates, perborates, percarbonates, persulfates, percarbamide, peracetic acid and mixtures thereof. A peroxodisulfate is particularly preferred as the peroxo compound, most preferably potassium, sodium or / and ammonium peroxodisulfate.

The bath can also contain an activator selected from transition metal compounds in a concentration of up to 25 mmol / 1 based on the metal or halide compounds in a concentration of up to 500 mmol / 1 based on the halide ion.

The bath particularly preferably contains 21 mmol / 1 to 420 mmol / 1 of a persulfate as active component and 0.5 to 200 mmol / 1 halide ions as activator.

Another object of the present invention is the use of a bath, which has an alkaline pH, as active components 5 mmol / 1 to 2.1 mol / 1 of a peroxo compound and a transition metal which is soluble at alkaline pH values -Complex compound contains and is free of added hypochlorites, permanganates and enzymes, for the lightening of colored cotton fabrics.

The invention is further illustrated by the following example.

EXAMPLE

A 4 x 4 cm sample of indigo-dyed blue jeans fabric was placed in 100 ml of a lightening bath. Then the pH was determined. During the lightening process, stirring was carried out continuously to ensure good penetration of the tissue with the lightening solution. The textile piece was then rinsed with distilled water to stop the lightening process. Assessing the whitening degrees were done in a dry state (hot air dried at 50 ° C in a drying cabinet) with an unlightened textile sample as a reference. The degree of brightening effect (decrease in blue color to white) was evaluated in 5 stages as follows:

0 no decrease in blue color

1 slight brightening

2 good brightening (desired effect)

3 stronger brightening

4 heavily bleached

5 very bleached

The whitening effect of ammonium peroxodisulfate (APS), potassium peroxodisulfate (KPS) and sodium peroxodisulfate (NPS) was investigated.

1) Preliminary tests: comparison of different persulfates

No. bleaching conc. Additive conc. Temp. Time assessment tissue averaging

1 APS 100 g / 1 RT 20 h 1 ok

2 KPS 45 g / 1 RT 20 h 0.5 ok

3 NPS 100 g / 1 RT 20 h 1 ok

APS (Vers. 1) and NPS (Vers. 3) in particular show a useful bleaching effect. KPS (Vers. 2) has a lower solubility, but its bleaching effect is comparable to APS and NPS relative to the amount used.

2) Influence of concentration.

No. bleaching conc. Additive conc. Temp. Time assessment tissue averaging

4 NPS 100 g / 1 RT 21 h 2 ok

5 NPS 200 g / 1 RT 21 h 4 ok

6 NPS 300 g / 1 RT 21 h 4.5 ok Experiments 4 to 6 show that the bleaching effect can be controlled via the concentration.

3) Influence of temperature

No. bleaching conc. Additive conc. Temp. Time assessment tissue averaging

7 NPS 100 g / 1 60 ° C 40 min 1 ok 8 NPS 100 g / 1 80 ° C 20 min 2 ok

Experiments 7 and 8 show that the desired degree of brightening can be set by choosing a higher temperature within a considerably shorter treatment time.

4) Effect of NPS with different activators

It was found that transition metal compounds, especially iron (III) in the form of iron (III) sulfate, iron (II) sulfate or copper (II) sulfate, intensify the attack of persulfate on the indigo dye. It is noteworthy that there is no significant damage to the tissue.

No. Bleaching conc. Addition conc. Temp. Time assessment tissue medium (g / D (mmol / 1) (° C) (min))

9 NPS 250 Fe ₂ (S0 ₄ ) ₃ 2.06 60 20 3 ok

10 NPS 250 CuS0 ₄ 6.26 60 20 2 ok

11 NPS 250 CoS0 ₄ 3.65 60 20 1 lighter attack

12 NPS 250 NiS0 ₄ 3.89 60 20 2 ok

13 NPS 250 MnS0 ₄ 5.95 60 20 1 light coloring

14 NPS 250 KCr (S0 ₄ ) ₂ 2.05 60 20 3 ok

15 NPS 100 FeS0 ₄ 2.3 60 20 2 ok

16 NPS 100 FeS0 ₄ 4.5 60 20 3 ok

Experiments 9 to 16 show that different activators are suitable for this application. Iron (III) (experiment 9), chromium (experiment 14) and iron (II) (experiments 15 and 16) had the greatest effect.

5) Comparison of different activator doses no. Bleach conc. Add conc. Temp. Time assessment tissue mean (mmol / 1) division

17 NPS 250 g / 1 Fe ₂ (S0 ₄ ) ₃ 1.25 60 ° C 20 min 2 ok

18 NPS 250 g / 1 Fe ₂ (S0 ₄ ) ₃ 2.5 60 ° C 20 min 3 ok

19 NPS 300 g / 1 Fe ₂ (S0 ₄ ) ₃ 2.5 60 ° C 20 min 3.5 ok

Experiments 17 to 19 show that the concentration of the activator must not be set too high, since otherwise an effect that is too strong can result. In addition, the persulfate concentration and the iron activator concentration must be matched to one another. The optimal values are 200 - 300 g / 1 NPS and 0.75 - 1.8 mmol / 1 iron (III) sulfate.

6) Comparison of NPS solution at different pH values

No. Bleaching conc. Addition conc. Temp. Time pH assessment weighting

20 NPS 200 g / 1 - - 60 ° C 40min 2.7 1 ok

21 NPS 200 g / 1 NaOH - 60 ° C 40min 7.0 2 ok

22 NPS 300 g / 1 - - 60 ° C 20min 1.6 1 ok

23 NPS 300 g / 1 NaOH - 60 ° C 20min 7.0 2 ok

24 NPS 250 g / 1 NaH ₂ P0 ₄ 0.5g / l 60 ° C 20min 7.0 0.5 ok

25 NPS 250 g / 1 Na ₂ HP0 ₄ 0.5g / l 60 ° C 20min 5.0 2 ok

In Vers. 21, the pH was set to 7 compared to Vers. 20 (preferred pH range 5 - 12), which shows that the desired degree of brightening 2 is also achieved at this pH. Experiments 22 and 23 show that at 300 g / 1 NPS the bleaching time could be reduced to 20 min even at pH 7. Experiment 25 shows that at a pH of 5, which was set with a buffer mixture, the degree of lightening 2 can be achieved while observing the standard conditions.

7) Compare APS solution with different activators

No. Bleaching Concentration Addition Temp. Time Assessment tissue medium (g / 1) (mmol / 1) (° C) (min)

26 APS 100 60 40 ok

27 APS 100 CuS0 ₄ 6.26 60 40 2.5 ok

28 APS 100 Fe ₂ (S0 ₄ ) ₃ 2.06 60 40 2 ok

29 APS 100 CoS0 ₄ 3.65 60 40 1.5 ok

30 APS 100 ZnS0 ₄ 1.00 60 40 1 ok

Experiments 26 to 30 show various activators with ammonium peroxodisulfate as a bleaching agent. Copper and iron are particularly suitable.

8) Experiments with different halides as activator no. Bleach conc. Add conc. Temp. Time assessment tissue medium (g / 1) (mmol / 1) ° C min. lung

31 NPS 25 NaBr 19 60 • 20 3 ok

32 NPS 25 NaCl 168 60 20 3 ok

33 NPS 25 NaJ 64 60 20 4 yellowish

Experiment 31 shows that bromide achieves a degree of bleaching of 3 with 19 mmol / l.

With chloride, 168 mmol / 1 are necessary to achieve the same effect.

In principle, iodide is also suitable, but it turns yellow.

9) Experiments with different dosages of bromide and NPS No. Bleaching concentration. Addition of concentration. Time. Assessment tissue medium (g / D (mmol / 1) ° C min

34 NPS 25 NaBr 48 60 20 3 ok

35 NPS 25 NaBr 2 60 20 3 ok

36 NPS 12.5 NaBr 9.7 60 20 3 ok

37 NPS 12.5 NaBr 2.6 60 20 2.5 ok

38 NPS 12.5 NaBr 1.2 60 20 2 ok

39 NPS 12.5 NaBr 1 60 20 1.5 ok <J

40 NPS 50 NaBr 4 60 20 4 ok

41 NPS 100 NaBr 8 60 20 4.5 ok

42 NPS 150 NaBr 56 60 20 5 ok

Experiments 34 and 35 show that the optimal effect can be achieved with small amounts of bromide and another

Increasing the bromide concentration no longer causes an improvement.

Experiments 36 to 39 show that the degree of bleaching can also be controlled in this area by reducing the bromide concentration.

Experiments 40 to 42 show that with an increase in the NPS

Content in the bleaching liquor the effect to the full

Discoloration can be increased.

In experiments 35, 40 and 41 a molar ratio of

1:50 (NaBr: NPS) set.

10) Try alkaline pH

No. reagent conc. Conc. Addition conc. Conc. Temp. Time PH bleaching rα / n tmmol / 11 [mmol / 1] rα / π [C ° l [min] crrad

43 NPS 3 12.6 - - 80 30 11 1.5

44 KPS 3.4 12.6 - - - 80 30 11 1.5

45 NPS 3 12.6 Kaiium hexacyanoferrate II 2.37 1 80 30 11 4.5

46 KPS 3.4 12.6 Kaiium hexacyanoferrate II 1.18 0.5 80 20 12 4

47 NPS 3 12.6 Potassium hexacyanoferrate II 2.37 1 80 30 7.5 1 1

48 NPS 3 12.6 Kaiiumhexacyanoferrät II 2.37 1 80 30 11 4.5 J

49 NPS 3 12.6 Kaiium hexacyanoferrate II 2.37 1 60 30 11 2

50 NPS 3 12.6 potassium hexacyanoferrate II 2.37 1 80 20 11 4 |

51 NPS 3 12.6 Kaiium hexacyanoferrate III 3.04 1 80 20 11 4

52 NPS 3 12.6 Potassium hexacyanoferrate II 1.18 0.5 80 30 11 4

53 NPS 3 12.6 Potassium hexacyanoferrate II 1.18 0.5 80 30 12 4

54 NPS 3 12.6 Kaiium hexacyanoferrate II 0.59 0.25 80 30 11 2.5

Experiments 43 and 44 show that only little bleaching takes place in the alkaline state without the addition of an activator. Experiments 45 and 46 show that the addition of an activator in the alkaline range significantly increases the bleaching effect of persulfate. Experiment 47 shows that no effect of the activator can be seen in the neutral range (pH 7.5).

Experiments 48 and 49 show that the bleaching effect at a bath temperature of 80 ° C is significantly higher than at a bath temperature of 60 ° C.

Experiments 50 and 51 show that the activation with potassium hexacyanoferrate (III) works just as well as the activation with potassium hexacyanoferrate (II).

Experiment 52 shows that the activator concentration can still be reduced to approximately 1 mmol / l without a reduction in the brightening effect being found. Experiment 53 shows that a strong bleaching effect is achieved even at a pH of 12. Experiment 55 shows that a further reduction in the _^ .Aktivators in the bleaching solution, the effect of the whitening can be controlled.

Claims

PATENT CLAIMS

1. One-step process for lightening dyed cotton fabrics, characterized in that dyed cotton fabrics are treated under conditions suitable for lightening the colors of the cotton fabrics with an aqueous bath which contains a peroxo compound as an active component, but does not contain any added hypochlorites, permanganates and enzymes .

2. The method according to claim 1, characterized in that the peroxo compound is selected from the group consisting of H ₂ 0 ₂ , perphosphates, perborates, percarbonates, persulfates, percarbamide, peracetic acid and mixtures thereof.

3. The method according to claim 1 or 2, characterized in that the peroxo compound is selected from peroxodisulfates, peroxomonosulfates and mixtures thereof.

4. The method according to claim 3, characterized in that the peroxo compound is selected from an alkaline earth metal, alkali metal or ammonium peroxodisulfate or mixtures thereof.

5. The method according to claim 4, characterized in that one uses potassium, sodium or / and ammonium peroxodisulfate.

6. The method according to any one of claims 1 to 5, characterized in that the peroxo compound is used in a concentration of 21 mmol / 1 to 2.1 mol / 1, preferably 42 mmol / 1 to 1.7 mol / 1.

7. The method according to any one of claims 1 to 6, characterized in that the treatment of the cotton fabrics is carried out at a temperature of 15 to 90 ° C, preferably 40 to 80 ° C.

8. The method according to any one of claims 1 to 7, characterized in that the brightening is carried out for a period of from 2 minutes to 20 hours, preferably from 5 minutes to 5 hours.

9. The method according to any one of claims 1 to 8, characterized in that the brightening is carried out at a pH of the bath which is from 1 to 10, preferably from 4 to 7.

10. The method according to any one of claims 1 to 9, characterized in that a bath is used which additionally contains an activator selected from transition metal compounds and / or halide compounds.

11. The method according to .Anspruch 10, characterized in that compounds of iron, copper, cobalt, zinc, silver, manganese, chromium, nickel or mixtures thereof are used as the activator.

12. The method according to claim 11, characterized in that the activator used is Fe (III) salts, Fe (II) salts or Cu (II) salts.

13. The method according to claim 12, characterized in that the activator used is Fe (III) sulfate, Fe (II) sulfate or Cu (II) sulfate.

14. The method according to any one of claims 10 to 13, characterized in that the activator is used in an amount of up to 25 mmol / 1 based on the metal.

15. The method according to claim 14, characterized in that one uses the .Aktivator in an amount of 0.05 to 15 mmol / 1, preferably from 0.05 to 8 mmol / 1 based on the metal.

16. The method according to any one of claims 10 to 15, characterized in that ammonium peroxodisulfate is used as the peroxo compound and Cu (II) sulfate, Fe- (II) sulfate or Fe- (III) sulfate as the activator compound.

17. The method according to any one of claims 10 to 15, characterized in that sodium peroxodisulfate is used as the peroxo compound and Fe (III) sulfate or Fe (II) sulfate is used as the activator.

18. The method according to claim 10, characterized in that halide compounds are used as the activator.

19. The method according to claim 18, characterized in that bromide compounds are used as the activator.

20. The method according to claim 19, characterized in that one uses as .Activator sodium and / or potassium bromide.

21. The method according to any one of claims 18 to 20, characterized in that one uses the .Aktivator in an amount of up to 500 mmol / 1 based on the halide ion.

22. The method according to .Anspruch 21, characterized in that the activator is used in an amount of 0.5 mmol / 1 to 200 mmol / 1, preferably from 1 to 20 mmol / 1 based on the halide ion.

23. The method according to any one of claims 18 to 22, characterized in that a peroxodisulfate, preferably sodium peroxodisulfate, and an alkali metal or alkaline earth metal bromide, preferably sodium or / and potassium bromide, are used as the peroxo compound.

24. The method according to any one of claims 1 to 8 or 10 to 11, characterized in that the treatment is carried out at an alkaline pH and uses a transition metal complex compound which is soluble at alkaline pH as the activator.

25. The method according to claim 24, characterized in that one carries out the treatment at a pH of 10 - 12.

26. The method according to claim 24 or 25, characterized in that one uses complex compounds of iron.

27. The method according to any one of claims 24 to 26, characterized in that one uses cyano complexes.

28. The method according to any one of claims 24 to 27, characterized in that one uses hexacyanoferrate (II) - or hexacyanoferrate (III) complexes.

29. The method according to any one of claims 24 to 28, characterized in that the activator is used in an amount of up to 25 mmol / l based on the metal.

30. The method according to claim 29, characterized in that the activator is used in an amount of 0.05 to 15 mmol / l, preferably 0.05 to 8 mmol / l, based on the metal.

31. The method according to any one of claims 1 to 30, characterized in that cotton fabrics are used which are dyed with dyes selected from the group consisting of vat, direct and sulfur dyes.

32. The method according to claim 31, characterized in that cotton fabrics are used which are dyed with indigo, thio indigo or indigo dyes.

33. Use of a bath which contains 21 mmol / l to 2.1 mol / 1 of a peroxo compound as an active component and is free from added hypochlorites, permanganates and enzymes for lightening colored cotton fabrics.

34. Use according to claim 33, characterized. that the peroxo compound is selected from the group consisting of H ₂ 0 ₂ , perphosphates, perborates, percarbonates, persulfates, percarbamide, peracetic acid and mixtures thereof.

35. Use according to claim 33 or 34, characterized in that the bath further contains an activator selected from transition metal compounds in a concentration of up to 25 mmol / l based on the metal.

36. Use according to claim 33 or 34, characterized in that the bath further contains an activator selected from halide compounds in a concentration of up to 500 mmol / l based on the halide ion.

37. Use according to claim 36, characterized in that the bath contains 21 mmol / l to 420 mmol / l of a persulfate as an active component and 0.5 to 200 mmol / l halide ions as an activator.

38. Use of a bath which has an alkaline pH, contains as active components 5 mmol / l to 2.1 mol / 1 of a peroxo compound and a transition metal complex compound which is soluble at alkaline pH values and is free from added hypochlorites, permanganates and Enzymes are used to lighten dyed cotton fabrics.