TECHNICAL FIELD

The invention relates to a process for bleaching of dyed textiles.

BACKGROUND ART

Some textiles are bleached after dyeing. As an example, blue jeans made from indigo-dyed denim can be treated with pumice and/or cellulase, followed by bleaching to obtain a desired, worn appearance.

The art relating to bleaching of dyed textiles comprises bleaching of the colored denim textiles with sodium hypochlorite. This process, however, is unwanted from an environmental point of view.

This art also comprises a bleaching with H ₂ 0 ₂ ; however, in cases where a strong bleaching is desired, high concentrations of H ₂ 0 ₂ have to be used, i.e. concentrations in the order of 5-30%, which makes this bleaching method very expensive; and also, the areas around the zippers are bleached too heavily. Furthermore, the pH value has to be very high in order to achieve the desired effect, this being a disadvantage from both an environmental and an economic point of view.

Thus, the known art is associated with heavy drawbacks, and the purpose of the invention is the provision of an economical process for bleaching of dyed textiles, which is acceptable from an environmental point of view.

STATEMENT OF THE INVENTION

It has, surprisingly, been found that the purpose of the invention can be fulfilled by bleaching with enzymes utilizing hydrogen peroxide or molecular oxygen for the oxidation of organic or inorganic substances, including coloured substances, together with a source of H ₂ 0 ₂ or 0 ₂ . Such enzymes are usually termed peroxidases and oxidases, respectively.

In case peroxidase is used in the process according to the invention it has been found that a strong bleaching effect can advantageously be achieved with a concentration of H ₂ 0 ₂ considerably below 100 mM, and at a pH value around neutrality, this being an advantage. 5 Accordingly, the present invention provides a process for bleaching of dyed textiles comprising treatment with a bleach liquor containing (1) H ₂ 0 ₂ or a precursor for H ₂ 0 ₂ and an enzyme exhibiting peroxidase activity or (2) 0 ₂ or a precursor for 0 ₂ and an enzyme exhibiting a suitable oxidase activity.

Surprisingly it has been found that the waste water from the process according to the invention is almost colorless and thus advantageous from an environmental point of view.

It is well recognized in the art (cf. for instance B.C. Saunders et al.,

"eroxidase. London, 1964, p. 10 ff.) that peroxidases act on various amino and phenolic compounds resulting in the production of a colour. In view of this, it must be considered surprising that peroxidases (and certain oxidases) may also exert an effect on coloured substances on textiles.

DETAILED DESCRIPTION OF THE INVENTION

Textile

The process of the invention is applicable to all types of textile materials, particulaly cellulosic fibers such as cotton, e.g. denim.

Textile dve

The textiles may be dyed with any textile color. A comprehensive cata¬ logue of commonly used textile dyes, both synthetic (such as azo dyes) and natural or nature-identical (by which is meant a substance which is produced synthetically, but which in structure and properties is identical to the natural compound), e.g. indigo. A comprehensive catalogue of such dyes is found in the Color Index.3rd ed. Vol. 1-8. Surprisingly, the process of the invention is able to bleach even practically insoluble dyestuffs like indigo.

Enzyme

Examples of suitable oxidases and peroxidases are those which use molecular oxygen or hydrogen peroxide to oxidize aromatic compounds, in particular phenolic, e.g. polyphenolic, For the sake of convenience, such oxidases and per- oxidases are collectively termed bleaching enzymes in the following.

Examples of suitable bleaching enzymes are catechol oxidase (EC 1.10.3.1), laccase (EC 1.10.3.2), peroxidase (EC 1.11.1.7), chloride peroxidase (EC 1.11.1.10) and phenol oxidase (EC 1.14.18.1).

Bleaching enzymes which may be employed for the present purpose may be derived from plants (e.g. horseradish peroxidase) or microorganisms such as fungi or bacteria. Examples of suitable peroxidases are those derived from a strain of Coprinus, e.g. C. cinerius or C. macrorhizus, or from a strain of Bacillus, e.g. β. pumilυs, particularly peroxidase according to PCT/DK 90/00260. Such enzymes may be produced, by methods known in the art, by cultivating the strain on a suitable nutrient medium or by transferring the genetic information to a suitable host organism and cultivating this.

A suitable amount of the enzyme is generally 0.01 - 100 mg of enzyme protein per litre of bleach liquor, particularly 0.1 - 10 mg/l.

Particularly preferred bleaching enzymes are those which are active at pH values of 4 - 10, especially 5-9.

0 ₂ , H ₂ 0 ₂ or precursor

Molecular oxygen will usually be present in sufficient quantity.

Suitable precursors for H ₂ 0 ₂ are for instance a perborate or a percarbonate or an enzymatic system capable of generating H ₂ 0 ₂ .

The concentration of H ₂ 0 ₂ or H ₂ 0 ₂ precursor is preferably 0.1 mM - 100 mM H ₂ 0 ₂ , particularly 0.5 mM - 10 mM H ₂ 0 ₂ . A concentration above 100 mM H ₂ 0 ₂ does not improve the bleaching effect significantly, and a concentration below 0.1 mM H ₂ 0 ₂ tends to be too low in relation to the bleaching effect.

Bleaching liquor

The bleaching liquor preferably has a pH of 4 - 10, particularly 5 - 9. It has surprisingly been found that the addition of another oxidizable substrate (for the bleaching enzyme used in the process of the invention) at the 5 beginning or during the washing and/or rinsing process may enhance the backstaining inhibitory effect of the bleaching enzyme employed. This is thought to be ascribable to the formation of short-lived radicals or other oxidised states of this substrate which participate in the bleaching or other modification of the coloured substance. Examples of such oxidizable substrates are metal ions, e.g. Mn ⁺⁺ , halide ions, e.g. chloride or bromide ions, or organic compounds such as phenols, e.g. p- hydroxycinnamic acid, 2,4-dichIorophenol, p-hydroxybenzene sulphonate, vanillin or p-t /droxybenzoic acid. Other examples of phenolic compounds which may be used for the present purpose are those given in M. Kato and S. Shimizu, Plant Cell Phvsiol.26(7). 1985, pp. 1291-1301 (cf. Table 1 in particular) or B.C. Saunders etal., OD^. cit, p. 141 ff. The amount of oxidizable substrate to be added is suitably between about 1 μM and 10 mM.

Bleaching process

The process according to the invention primarily is a bleaching process, but it has been found that back staining, i.e. coloring of the textile either with small dyestuff particles or with small, dyed textile fibres, is heavily reduced or completely avoided under the conditions prevailing during the process according to the invention.

The bleaching process can be carried out as a separate step, or simultaneously with other steps, e.g. a washing or rinsing step. In the case of denim textiles (especially indigo-dyed denim), the bleaching process according to the invention can be carried out simultaneously with a treatment with cellulase (and optionally pumice) to create a desired worn look by forming local variations in colour density, as described in American dye stuff reporter, Sept. 90, D. Kochavi, T. Videbaek and D. Cedroni, Optimizing processing conditions in enzymatic stone washing.

A preferred embodiment of the process according to the invention is characterized by the fact that the enzyme is a catechol oxidase (EC 1.10.3.1), a laccase (EC 1.10.3.2), a peroxidase (EC 1.11.1.7) or a chloride peroxidase (EC

1.11.1.10), preferably peroxidase derived from a strain of Coprinus, B. pumilus or Phanerochaete. These enzymes are cheap and can be easily provided commercially.

A preferred embodiment of the process according to the invention is characterized by the fact that the amount of enzyme is 0.01 - 100 mg of enzyme protein per litre of bleach liquor, preferably 0.1 - 10 mg/l. With an amount of enzyme below 0.01 mg of enzyme protein per litre of bleach liquor the effect is negligible, and with an amount of enzyme above 100 mg of enzyme protein the process tends to be uneconomical.

A preferred embodiment of the process according to the invention is characterized by the fact that the bleach liquor contains H ₂ 0 ₂ or a precursor for H ₂ O _a in an amount corresponding to 0.1 mM - 100 mM H ₂ 0 ₂ , preferably 0.5 mM - 10 mM H ₂ 0 ₂ . If the concentration of H ₂ 0 ₂ is less than 0.1 mM, the effect is negligible, and if the concentration of H ₂ 0 ₂ or a precursor for H ₂ 0 ₂ is above 100 mM, the H ₂ 0 ₂ tends to inactivate the enzyme.

A preferred embodiment of the process according to the invention is characterized by the fact that the textile is dyed by means of a synthetic dye, preferably an azo dye, or a natural or nature identical dye, preferably indigo. These dyestuffs are ordinarily difficult to bleach, but by means of the process according to the invention they are easily bleachable.

A preferred embodiment of the process according to the invention is characterized by the fact that the pH is 4.0-10.0, preferably 5.0-9.0. In these pH intervals the enzymes exhibit a good activity, and thus, the effect according to the invention is satisfactory.

A preferred embodiment of the process according to the invention is characterized by the fact that the bleach liquor contains an additional oxidisable substrate, preferably a metal ion, a halide ion or an organic compound, preferably a phenol, more preferably p-hydroxycinnamic acid, 2,4-dichlorophenol, p- hydroxybenzene sulphonate, vanillin or p-hydroxybenzoic acid. By means of these bleach boosters the bleaching activity is considerably increased.

A preferred embodiment of the process according to the invention is characterized by the fact that the amount of the additional oxidisable substrate is between about 1 μM and about 10 mM. With an amount of the additional oxidasable substrate below 1 μm the booster activity tends to be negligible, and with an amount 5 of the additional oxidisable substrate above 10 mM the process tends to be uneconomical.

A preferred embodiment of the process according to the invention is characterized by the fact that the textile is denim, preferably indigo-dyed denim. With this textile, which is commercially significant the effect has been domonstrated satisfactorily.

A preferred embodiment of the process according to the invention for simultaneous bleaching and formation of localized colour variation is characterized by the fact that the bleaching liquor further contains a cellulase and/or pumice. In this manner the desired worn look is generated satisfactorily. It has previously been reported that peroxidases may decolourize certain pigments (cf. for instance W. Schreiber, Biochem. Biophvs. Res. Commun. 63 (2), 1975, pp. 509-514, describing the degradation of 3-hydroxyflavone by horseradish peroxidase; A. Ben Aziz, Phvtochemistrv 10, 1971, pp. 1445-1452, describing the bleaching of carotene by means of a peroxidase; and B.P. Wasserman, J. Food Sci. 49, 1984, pp. 536-538, describing the decolourization of betaiain by horseradish peroxidase). Ben Aziz et al. and Wasserman et al. present the bleaching action of peroxidases on carotene and betaiain, respectively, as a problem when using these pigments as food colourants, which problem must be counteracted by including an antioxidant in the foodstuff in question. Thus, they do not consider the peroxidase- mediated bleaching of these pigments to have any practical utility in itself.

Although these publications describe test methods whereby the respective pigments are incubated with the enzyme in solution, the pigments in question are all pure compounds of natural origin and are also readily bleached by the bleaching agents usually incorporated in modern detergents (cf. for instance Second World Conference on Detergents. A.R. Baldwin (ed.), American Oil Chemist's Society, 1978, pp. 177-180).

Contrary to this, the commonly used textile dyes are generally resistant to oxidation by atmospheric oxygen and also, to a greater or lesser extent, to the bleaching agents currently used in detergents.

WO-A-8909813, GB-A-2101167, WO-A-8707639, DE-A-1918729 and DE- C-747889 describe bleaching of undyed textiles or stained textiles. This bleaching activity is or is equivalent to the traditional perborate bleaching activity. In contradistinction hereto the invention comprises a process for bleaching of dyed textiles. Bleaching of undyed textiles is an area quite distinct from bleaching of dyed textiles.

EXAMPLES 1 - 7

Prewashed, desized denim fabric was cut into swatches with a dimension of 5x5 cm, then folded and sewn together. By means of a laboratory washing machine (Launderometer, Atlas LP1) with 20 cups, 5.0 g of the sewn denim fabric and five metal balls were added to each cup. Two white cotton/polyester (50/50%) swatches (7x7 cm) were added in order to measure the redeposition of the indigo color on the fabric (backstaining). 150 ml of buffer or buffer containing enzymes, as later indicated, was added to each cup. The cups were then tumbled at 55°C for 60 minutes. Each sample was run in duplicate.

After the tumbling, the liquid was poured off and filtered through a weighed Whatmann G glass fibre filter. The filter was left in the tunnel for two hours to drain off liquid. It was then dried for 1 hour at 90°C and then weighed. The amount of lint trapped on the filter from the washing liquid was then measured as the weight gain of the filter.

Blanks, with no enzyme, were included. After deducting the blank lint formation, the cellulase activity under washing conditions was expressed as lint formation, Δ LF.

The color of the filtrate was in some cases measured by the absorption at 680 nm of a well shaken sample by means of a spectrophotometer (Milton Roy Spectronic 3000 Array, 1 cm quartz cell).

The white swatches were washed thoroughly with running tap water and dried. The remission at 420 nm and at 680 nm was then measured on a Datacolor Elrephometer (the higher the remission numbers, the smaller the intensity of the color). The remission of an untreated white swatch was measured and the numbers 5 were subtracted from the values of the treated swatches, this result representing an estimate of the amount of backstaining (ΔR 420 and ΔR 680). Hunter color difference coordinates (ΔE) were calculated (a value of 0 here indicates no change in color in comparison to the untreated swatch and increasing numbers correspond to a visual impression of deeper color). Three cellulases were used in the experiments:

Cellulase A From Trichoderma reesei Cellulase B From Humicola insolens Cellulase C Derived from Humicola insolens as described in International patent application no. PCT/DK91/00123from Novo Nordisk A/S.

The activity of cellulase A and B is measured by EGU/ml (Novo Nordisk analytical method AF 275/1 - available on request from Novo Nordisk A/S, Novo Allέ, DK-2880 Bagsvasrd, Denmark) and the activity of Cellulase C measured by ECU/ml (Novo Nordisk analytical method AF 302/1 - available on request from Novo Nordisk A/S, Novo alle, DK-2880 Bagsvasrd, Denmark). CiP is used as an abbreviation for peroxidase derived from Coprinus cinerius. The activity is measured in PODU/ml (Novo Nordisk analytical method AF 310/1 - available on request from Novo Nordisk A/S, Novo Alle, DK-2880 Bagsvasrd, Denmark).

EXAMPLE 1

This example shows that there is a slight effect of the peroxidase with respect to inhibition of backstaining at cellulase concentrations relevant for industrial application (ΔLF ranging from about 20 to 50). The Hunter coordinate ΔE is reduced from 8 to 6 by addition of 1 mM H ₂ 0 ₂ and peroxidase together with 500 ECU cellulase per cup.

Table 1

EXAMPLES 2 AND 3

In these examples 0.04 g parahydrolxybenzenesulfonate (PHBS) / cup (1.3 mM) is added together with the peroxidase as accelerator. This generates a highly significant reduction of backstaining. As appears from Table 3 ΔE at a ΔLF of 40-50 is reduced from 9 to 3 by addition of peroxidase + accelerator. It should be noted that it is necessary to add the double amount of cellulase when peroxidase + accelerator is being used in order to generate the same amount of lint formation. This is due to deactivation of the cellulase. Table 3 gives an indication of the reproducibility of the tests.

Table 2

Table 3

EXAMPLES 4 AND 5

In both examples a concentration of 0.02 g PHBS/cup is used. The variation in PHBS and H ₂ 0 ₂ concentration generates results similar to the results in Example 3.

Table 4

Table 5

EXAMPLE S

Except for the two cups with no cellulase, no CiP, no PHBS and no H (first horizontal line In Table 6) all cups contained 0.2 g/l of Berol 08 (HEFA-80), a product of Berol Nobel, Sweden, a non-ionic, ethoxylated dispersant known to reduce backstaining.

It appears from Table 6 that the color of the released textile fibres (the lint) is reduced (observed visually) when peroxidase and accelerator is present. Also, the ODg _ao of the fibres containing washing liquid exhibits the highest value when no accelerator is used.

Table 6

10

EXAMPLE 7

0.04 g of PHBS is added to the cups with peroxidase. Table 7 shows the action of different cellulases. In all cases a very significant reduction in backstaining is observed when peroxidase + accelerator is used.

Table 7

EXAMPLE 8

Prewashed, desized denim fabric was cut into circular swatches with a diameter of 3 cm and a weight of 0.5 g. 6 swatches were introduced into a beaker together with 28 ml of buffer or water, and MnS0 ₄ , and H ₂ 0 ₂ and enzyme (Mn peroxidase from Phanerochaete chrysosporium, obtained from Tienzyme, Inc., in an amount of 273 units) in the amounts appearing from the below indicated table. One Mn peroxidase unit is defined as one μmole of oxidized phenol red formed per minute under the following assay conditions.

50 mM Na succinate, pH 4.5 50 mM Na lactate, pH 4.5 0.1 mM MnS0 ₄ • 3 mg/ml gelatin 0.1 mM phenol red 50 μM HA

As appears from the table only test 8A is according to the invention, tests 8B-8F being references.

The swatches were stirred for 1 hour at 40°C. After the test the swatches were removed from the beaker.

The color of the bleaching liquid was measured by the absorption at 680 nm of a well shaken sample by means of a spectrophotometer (Milton Roy Spectronic 3000 Array, 1 cm quartz cell), vide the below indicated table.

It appears from the above table that the bleaching liquid according to the invention is much more acceptable from an environmental point of view than the references.