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Title:
PROCESS FOR DYEING PROTEIN TEXTILE FIBRES OF ANIMAL ORIGIN COMPRISING THE USE OF PURIFIED SYNTHETIC FOOD DYES
Document Type and Number:
WIPO Patent Application WO/2022/123522
Kind Code:
A1
Abstract:
A textile dyeing process is described for dyeing a textile material, product or article consisting of proteic fibers of animal origin, comprising the steps of dipping said textile material, product or article into a dyeing bath comprising at least one detergent substance, a wetting substance, a levelling substance and an acidity regulator; adding to the dyeing bath a dyestuff approved for food use; subjecting the dyed textile material, product or article to washes; and finally subjecting the dyed textile material, product or article to a colour fixing treatment.

Inventors:
BAZZANO NERIO (IT)
Application Number:
PCT/IB2021/061575
Publication Date:
June 16, 2022
Filing Date:
December 10, 2021
Export Citation:
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Assignee:
VEBACHEM S R L S (IT)
International Classes:
D06P1/00; D06P3/14
Domestic Patent References:
WO2020254979A12020-12-24
Foreign References:
CN110306367A2019-10-08
US7393366B22008-07-01
Attorney, Agent or Firm:
PALLADINO, Massimo et al. (IT)
Download PDF:
Claims:
CLAIMS Textile dyeing process for dyeing a textile material, product or article of fibers and fabrics made from protein fibers of animal origin, which includes a dyeing operation of said textile material, product or article with one or more synthetic dyes approved for use in the food industry, in the presence of an acidity regulator selected from citric acid and tartaric acid, wherein said one or more synthetic dyes are selected from those of the following table: Process according to claim 1 , which comprises the following steps, wherein steps 1 ) to 5) take place under stirring:

1 ) dipping the textile material, product or article for a period comprised between 5 and 15 minutes into a water-based dyeing bath having a temperature comprised between 20 and 30 °C, said bath comprising at least: - a detergent substance;

- a wetting substance;

- a levelling substance;

- an acidity regulator selected from citric acid and tartaric acid;

2) adding to the dyeing bath of step 1 one or more synthetic colouring substances approved for use in the food industry, bringing the bath to a temperature comprised between 80 and 120 °C in a time comprised between 50 and 80 minutes, leaving it at this temperature for a time comprised between 30 and 90 minutes, and finally cooling the bath to a temperature comprised between 60 and 80 °C in a time comprised between 10 and 30 minutes;

3) draining the bath and subjecting the textile material, product or article dyed in the previous passages to a first wash in the same machine at a temperature comprised between 35 and 55 °C for a time comprised between 5 and 15 minutes;

4) draining the bath of the first wash and subjecting the textile material, product or article to a second wash in the same machine at a temperature comprised between 20 and 35 °C for a time comprised between 2 and 10 minutes in water, or at 50 °C for a time comprised between 2 and 10 minutes in a solution of sodium acetate in water;

5) draining the bath of the second wash and subjecting the textile material, product or article to a colour fixing treatment in a bath containing a fixing substance with a percentage comprised between 1 % and 6% with respect to the initial weight of the textile material, product or article at a temperature comprised between 20 and 60 °C, for a time comprised between 5 and 30 minutes, and at a pH comprised between 4.5 and 6.5;

6) draining the bath and subjecting the textile material, product or article to drying. Process according to any one of claims 1 or 2, further comprising a preliminary step 0 carried out under stirring, wherein said textile material, product or article to be dyed is dipped into water at a temperature comprised between 20 and 30 °C for a time comprised between 5 and 10 minutes, and wherein all or part of the amount of wetting substance necessary for carrying out step 1 can be added to water. Process according to any one of the preceding claims, wherein:

- said detergent substance is 2,2-dimethyl-1 ,3-propanediol (CAS no. 126-30- 7);

- said wetting substance is selected from polyethylene glycol-10 propyl ether ((C2H4O)nCi 0H22O, CAS no. 160875-66-1 ), petroleum distillate (CAS No. 64742-47-8), undecyl alcohol ethoxylates (CAS No. 127036-24-2) and a mixture of 2-methyl-3(2H)-isothiazolone and 5-chloro-2-methyl-3(2H)- isothiazolone (CAS no. 55965-84-9);

- said levelling substance is selected from 5-sulfosalicylic acid (CAS no. 97- 05-2), polyethoxylated tallow amines (CAS no. 61791 -26-2), quaternary salts of polyethoxylated tallow amines with diethylsulphate (CAS no. 68071 - 95-4) and a mixture of ethoxylated C16-C18 unsaturated alcohols (CAS no. 68920-66-1 ); and

- said acidity regulator is selected from citric acid (CAS no. 77-92-9) and tartaric acid (CAS no. 87-69-4). Process according to claim 4, wherein are used, in percentage by weight with respect to the weight of said textile material, product or article, 1 % of said detergent substance, 1 % of said wetting substance, between 1 % and 2% of said levelling substance and between 5 and 50% of said acidity regulator. Process according to any one of the preceding claims, wherein said one or more synthetic colouring substances approved for use in the food industry are used in an amount comprised between 0.001 % and 6% of the weight of the textile product. Process according to any one of the preceding claims, wherein the fixing substance used in step 5 is selected from an aqueous solution of polyamines, a suspension of silica in water at a concentration of between 2% and 10% by weight, or a mixture thereof. Process according to claim 7, wherein said suspension of silica in water has a concentration of 5% by weight. Process according to any one of claims 7 or 8, wherein the fixing substance further contains diethylene glycol. Process according to any one of the preceding claims, wherein said step 5 is carried out by dipping said textile material, product or article into the bath containing the fixing substance, or with the “foulard” technique when said textile material, product or article is a fabric, or with a spray technique when said textile material, product or article is a finished item of clothing. Process according to any one of the preceding claims, wherein said textile material, product or article is made of wool. Textile material, product or article consisting of textile fibres of protein fibres of animal origin, dyed with the textile process according to any one of claims 1 to 11.

27

Description:
PROCESS FOR DYEING PROTEIN TEXTILE FIBRES OF ANIMAL ORIGIN COMPRISING THE USE OF PURIFIED SYNTHETIC FOOD DYES

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FIELD OF THE INVENTION

The present invention relates generally to the field of methods and processes for the treatment of textile products and/or articles, and more particularly to a textile process of dyeing protein fibres of animal origin (yams and textiles derived therefrom) in which purified synthetic dyes, already used in the food industry as well as in the pharmaceutical industry, are used.

BACKGROUND ART

The dyeing of yarns and textile articles in general is a practice with very ancient origins. The number of processes developed in order to dye fabrics is very high, and the details of each process depend on the type of yam, on the dye, and also on the geographical area in the case of processes typical of local traditions.

Textile fibres are essentially of two types, natural and synthetic fibres; natural fibres may in turn be subdivided into vegetable (cotton, linen, hemp,...) and animal fibres (mainly wool and silk). Depending on the type of fibre, and in particular on the chemical composition thereof, the types of dyeing processes that can be applied, the stage of production of the fabric in which dyeing can be carried out, and also the results obtained vary.

For example, synthetic fibres can be dyed "in the mixture", i.e. already in the step in which the material (polyester, polyamide, polyacrylate,...) is still a molten mass, before the production of the fibres; this procedure gives rise to the most resistant colouring, but obviously it is not applicable to natural fibres, which can be dyed for example "in the staple" (that is, at the level of free fibres, before spinning), "in the thread" (on the fibres already spun) or "in the piece" (on the final fabric).

Vegetable fibres are essentially made up of cellulose, which is almost pure in cotton and mixed with components such as lignin and pectin in other fibres. The colouring of cellulose fibres is relatively simple, in particular when the fibres (free or already woven) are subjected to the preparatory process known as "mercerization", which consists in treating the fibres with a caustic solution (sodium carbonate or, more commonly, sodium hydroxide).

The mercerization treatment is not possible instead in the case of animal fibres, in particular of wool, which would undergo the effect known as felting if it was subjected to this treatment, with degradation of its functional and aesthetic qualities. Among animal fibres, wool still continues to be widely used and to present itself as an unsurpassed fibre in terms of characteristics and performance for creating a wide range of textile products and articles. Said fibres, unlike the vegetable ones, are protein, and are in general more difficult to colour than the vegetable ones; in particular, on these fibres it is more difficult to obtain a high colour resistance to washing or exposure to light; the resistance of the colour on the fabrics is known in the sector with the term "fastness".

It is therefore evident that the methods and compounds with which the textile fibres can be coloured are different from fibre to fibre. In fact, depending on the chemical nature of the fibre, the types of chemical bonds to be formed between the surface of the fibre and the dye molecule change, and in a similar way the chemical processes and adjuvants of said processes (fixing agents, mordants,...) may change.

With regards to the dyes used in the textile dyeing sector, they belong to a wide range of compounds that are often harmful and dangerous chemical compounds, and can create serious and not easily solvable problems of environmental pollution in the areas where the textile dyeing plants using them are installed.

It follows that said dyes, as well as the residues and waste of the textile processes that contain them, must normally be treated and disposed of according to appropriate procedures after their use, with consequent significant increases in the cost of the process. Equally felt is the need that the dyes used in the textile sector are also non-toxic and non-irritating, to avoid that dyed textile products and articles, once worn, may create problems of sensitization or irritation of the skin, or secondary effects of accumulation in case of absorption through the skin itself.

To meet these safety and eco-sustainability needs, agreements have been established and global standards have been defined in recent years which set limits on the use of polluting, toxic or carcinogenic substances. Among these standards, the most important ones are GB 18401 -2010 (in force since 2012), which sets minimum fastness limits, the Global Organic Textile Standard 5.0 dated 2017 (GOTS 5.0) and the ZDHC (Zero Discharge of Hazardous Chemicals) programme, which set the maximum values for certain components that can be used in the process (in particular formaldehyde, aromatic amines derived from azo dyes, heavy metals and ethoxylated alkylphenols, referred to in the textile sector as APEO).

These considerations limit the freedom in choosing dyes and processing aids for each specific textile application.

The need for greater environmental sustainability and a for significant reduction in the current significant costs of treatment and disposal of polluting colouring substances is particularly felt in the wool dyeing sector (in the form of yams, fabrics, or finished clothing articles) in consideration of the importance it has in the textile industry.

In consideration of the needs mentioned above, in recent years the world of textile dyeing has turned to the evaluation of the use of colouring substances of natural origin.

The dyeing of textile fibres with natural dyes is the object of various patent publications.

Patent application CN 104988711 A describes the use of a pigment extracted from red sorghum for the colouring of aramid fibres (synthetic fibres of the polyamide type); the procedure described requires that the fibre be pretreated in a gaseous plasma for the functionalisation of the surface.

Patent applications CN 109652998 A, CN 104988713 A and CN 109577031 A relate to the colouring of cotton with pigments extracted from natural substances, in particular cochineal red obtained from the carapace of the homonymous insect, or pigments extracted from various plants; the second one of said applications provides for the pretreatment of cotton fibres in plasma.

As mentioned above, the colouring of animal fibres, and in particular of wool, requires processes and reagents different from those used for synthetic or vegetable fibres.

The colouring of said fibres with natural pigments is described in various documents.

Patent application CN 107558261 A reports the colouring of wool with a relatively complex system, which uses as a dye a mixture of pigments extracted from the pomegranate peel, stabilized on the fibre by a shellac modified by fermentation in contact with sewage sludge from urban or industrial waste. The metal ions present in the sludge form complexes inside the modified shellac, and contribute to the fixing of the colour, while the shellac forms a protective and antioxidant layer that improves the fastness thereof. The colouring system of this document is however relatively complex and also does not give guarantees on the control of the components (in particular metal ions) contained therein, and therefore on the fact that the so coloured wool is not irritating to the skin.

Patent application CN 105088831 A describes the colouring of wool with shellac red. In the method of this document formaldehyde for the pretreatment of wool and a metal-based mordant (aluminum sulphate) are used; formaldehyde is a compound whose use is prohibited by the GOTS 5.0 standard, since the mutagenic and potential carcinogenic properties thereof have by now been definitively ascertained.

Patent application CN 108560284 A describes the colouring of a mixed wool- mercerized cotton fabric with a natural pigment extracted from the pomegranate peel, using neodymium chloride or alum as a mordant.

Patent application CN 104894890 A describes the colouring of wool or silk with lutein, extracted from plants or flowers such as spinaches, carrots and marigold.

These natural dyes extracted from plants give rise to non-optimal fastness; the inventors believe that this is due to the interference in the colouring process of the substances contained in the natural extracts, but that not the compound or compounds (pigments) which provide the textile material with the colour. Furthermore, the dyes for wool (or fibres or fabrics containing wool) of the prior art reported above all give colours that vary between yellow, orange and red (depending on the dye, the concentration and other parameters such as the pH in the colouring bath), therefore it is not possible to obtain the entire range of colours required in the textile industry with them. Finally, almost all the colouring processes described use metal-based mordants, which can give rise to sensitization phenomena following prolonged contact with the skin.

None of the above-described processes has therefore proven suitable to meet all the standards recently approved internationally with regard to the eco- compatibility of the processes of the textile industry, i.e. GOTS 5.0, GB 18401 -2010 and ZDHC.

Attempts have also been made to dye textile fibres, including wool, using food dyes, which have no eco-friendliness and toxicity problems.

Turkish patent application TR 2016 03418 A2 describes a process for dyeing textiles, in particular socks made of nylon, mixed nylon and wool, in which food dyes in a solution of glycerine in water in the dyeing step are employed and the colour fixing is carried out using acetic acid. The authors of the Application, however, state on page 4, lines 11 -15 of the text that "In the sock dyeing method of the present invention, currently, the colour black cannot be dyed. For colours that can be obtained by combining several food dyes, satisfactory and reproducible results have not yet been obtained. The intensity of the desired colour cannot be guaranteed. However, we are keeping on working on this"; in other words, the authors themselves acknowledge that the dyeing system they developed is far from effective and reproducible. In addition, no data is provided on the fastness of the dyeing obtained, let alone differentiated data for nylon and wool allowing to assess whether dyeing by the described process is more effective on either material and, if so, on which one.

The article “Effect of low-temperature plasma and chitosan treatment on wool dyeing with Acid Red 27', D. Jocic et al, Journal of Applied Polymer Science, Vol. 97, 2204-2214 (2005) reports the results of a study on the colouring of wool with a dye approved for food use, Acid Red 27. The purpose of the study was to evaluate the dyeability of untreated wool or after different treatments to modify the chemical surface characteristics thereof. The Acid Red 27 dye was chosen as the sample dye not so much to demonstrate the possibility of using food dyes on wool, but because it is one of the dyes most sensitive to changes in pH, temperature and reducing substances (specifically chitosan), and therefore suitable for colouring studies such as the one in this article. The wool treatments analysed in this study consist of surface treatment with low-temperature plasma, surface functionalisation of the wool with chitosan, and a plasma+chitosan combined treatment. The colour fastness results obtained in the study are shown in Table IV on page 2213 of the article; these results are expressed, according to a standardised method in the textile dye industry, in terms of colour release values from the fabric under examination, that is wetted with standard solutions, to an adjacent fabric, and on a scale of 1 to 5, where 1 indicates low fastness (i.e. high colour loss) and 5 indicates maximum fastness (minimum colour release). Only in one case (wool treated with chitosan only, dyeing time 45 minutes) an average fastness value of 2-3 is obtained, while in all other cases the values obtained are poor or very bad, between 1 -2 and 2.

Finally, patent application CN 110306367 A describes a process for dyeing cashmere fabrics consisting in the following steps: introducing the fabric into a dyeing bath containing, by weight percentage, a food dye in an amount comprised between 0.1 % and 2% and acetic acid in an amount between 1 .0 and 1 .5% relative to the fabric and bringing the bath to 90-98 °C for 30-120 minutes; lowering the temperature of the bath to 80-85 °C and adding a mordant, consisting of a mixture of potassium alum and sodium citrate in a molar ratio between 1 :0.8 and 1 :1.2, then maintaining the bath at this temperature for 30-60 minutes. As discussed hereinafter, the results in terms of fastness, in this case as well, are not optimal and sufficient for an industrial application of the process.

It can therefore be concluded that, to date, attempts to dye protein textile fibres of animal origin with food dyes have not been successful, or at least have led to unsatisfactory results in view of an industrial application.

The object of the present invention is to make available a dyeing process for dyeing protein fibres of animal origin, and in particular for dyeing wool, using purified synthetic dyestuffs for food use, which gives results applicable in the textile industry. These dyes respond to the pressing regulatory characteristics established by state or supranational authorities, such as FDA in the USA and the European Food Safety Authority in Europe, in the latter case through the "Directive on Colours" 94/36/EC; it follows therefore that they have no problems in overcoming the drawbacks of the dyes of the prior art from the eco-sustainability perspective by reducing the risks of pollution involved in known dyeing treatments (and the installation costs necessary to avoid such risks), providing a non-toxic and hypoallergenic product both in contact with the skin and with saliva, and fulfilling the fastness requirements of the market, a set of results which, to day, could be obtained neither with natural nor with food synthetic dyes.

SUMMARY OF THE INVENTION

The above-mentioned objects are achieved by a process for dyeing a textile material, product or article made of protein fibres of animal origin, comprising an operation for dyeing such textile material, product or article with a synthetic dye approved for use in the food industry, in the presence of an acidity regulator selected from citric acid or tartaric acid.

In greater detail, the invention relates to a process for dyeing a textile material, product or article consisting of protein fibres of animal origin, comprising the following steps:

1 ) dipping the textile material, product or article for a period comprised between 5 and 15 minutes into a water-based dyeing bath having a temperature comprised between 20 and 30 °C, said bath comprising at least:

- a detergent substance;

- a wetting substance;

- a levelling substance;

- an acidity regulator selected from citric acid and tartaric acid;

2) adding to the dyeing bath of step 1 a synthetic dyeing substance approved for use in the food industry, bringing the bath to a temperature comprised between 80 and 120 °C in a time comprised between 50 and 80 minutes, leaving it at this temperature for a time comprised between 30 and 90 minutes, and finally cooling the bath to a temperature comprised between 60 and 80 °C in a time comprised between 10 and 30 minutes;

3) draining the bath and subjecting the textile material, product or article dyed in the previous passages to a first wash in the same machine at a temperature comprised between 35 and 55 °C for a time comprised between 5 and 15 minutes;

4) draining the bath of the first wash and subjecting the textile material, product or article to a second wash in the same machine at a temperature comprised between 20 and 35 °C for a time comprised between 2 and 10 minutes in water, or at 50 °C for a time comprised between 2 and 10 minutes in a solution of sodium acetate in water;

5) draining the bath of the second wash and subjecting the textile material, product or article to a colour fixing treatment in a bath containing a fixing substance with a percentage comprised between 1 % and 6% with respect to the initial weight of the textile material, product or article at a temperature comprised between 20 and 60 °C, for a time comprised between 5 and 30 minutes, and at a pH comprised between 4.5 and 6.5;

6) draining the bath and subjecting the textile material, product or article to drying.

Particular embodiments of the textile dyeing process, conforming to the present invention, are also defined by the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

- Fig. 1 reproduces a time diagram which schematically represents a characteristic textile dyeing process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the textile dyeing process of the invention, the reference to a respective and specific embodiment and/or application does not exclude that a particular configuration, structure or characteristic described in relation to this embodiment and application can be included also in other embodiments and application of the process, in which for concise reasons it has not been described. This implies that particular configurations and/or characteristics of the dyeing process of the invention can be combined in any suitable and coherent way in one or more embodiments and applications.

The process of the invention applies to textile fibres formed from protein fibres of animal origin.

In the rest of the text and claims, the following conventions and definitions are adopted:

- "synthetic food colouring" means a dye made through chemical synthesis, and normally used in the food industry to colour foodstuffs and beverages;

- "textile product" means a textile fibre of animal origin or any article made with said fibre, therefore the free staple fibre, the fibre in yam, a fabric made with yarn, or a finished item of clothing made of said yarn or fabric;

- “wool” means both a virgin wool and a wool treated to remove the strongly hydrophobic surface layer of flat cells on the outside of the fibre (forming the so- called wool fibre exocuticle), for example the treatment with low-temperature plasma;

- “silk” means both native silk and so-called “scoured” silk, i.e. , silk in which the sericin has been removed from the “filaments” (the silk filaments) by treatment with hot water and/or mildly alkaline solutions (e.g., soaps); - all the percentages of the various components used in the process are to be intended by weight relative to the initial weight of the textile product to be dyed;

- finally, the exact chemical and/or commercial name will be given of all the substances used in the process of the invention; in addition, in order to provide information that is as complete and accurate as possible, the CAS (Chemical Abstract Service) registry number is also indicated for the substances used.

The textile dyeing process of the invention comprises a first part, indicated hereinafter also as BT part, in which the textile product to be dyed is dipped and treated in a dyeing bath, and a second part, indicated hereinafter also as TF part, in which the textile product is subjected to a finishing treatment. The bath of the process is water based, i.e. the liquid phase into which the textile product is dipped and the compounds performing the functions of the various steps (detergents, wetting agents, dyes,...) are dissolved, is water.

All steps of the process of the invention are carried out under stirring. The products used in the process are generally dissolved in water in a separate tank and sent to the dyeing machine via a circulation pump which keeps the bath under stirring throughout the process.

All steps of the process take place in water, with a weight ratio between water and the textile product to be dyed which can vary between 10:1 and 40:1 ; said quantities of water are sufficient to completely solubilise all the chemical compounds (detergents, wetting agents, dyes,...) used in the process.

In the case of carded wool yams that are particularly rich in spinning oils, or of wool and silk mixed yams, a scouring treatment is preferably carried out before implementing the process of the invention. These treatments are well known in the field. A scouring treatment useful for the purposes of the present invention can be carried out, for example, in a water bath containing 2% of wetting agent and 2% detergent (percentages with respect to the weight of the yam) at 95 °C for 30 minutes, then allowing the product to cool to a temperature of about 60 °C, washing and finally proceeding to the dyeing process according to the invention.

The process of the invention comprises a preliminary step (also referred to hereinafter as step 0), which consists in leaving the textile product to be coloured dipped into water at a temperature comprised between 20 and 30 °C for a time comprised between 5 and 10 minutes. This preliminary step has the purpose of completely impregnating the fibres with water, so that the components of the bath added subsequently can effectively and quickly contact the textile fibres.

The actual process (BT part) begins with step 1 in which, maintaining the temperature comprised between 20 and 30 °C, at least one detergent substance, a wetting substance, an equalizing substance and an acidity regulator are added to the bath. Said substances essentially have the function of preparing the bath for dyeing the textile product; said substances are known to those skilled in the art, as well as their effects on fibres, and comprise at least:

- a detergent substance (which also acts as an emulsifier) having the function of cleaning the textile product so as to prepare it to be dyed in the same dyeing bath; the detergent substance can be for example 2,2-dimethyl-1 ,3- propanediol (CAS no. 126-30-7);

- a wetting substance having the function of deaerating the textile product; the wetting substance can be, for example, polyethylene glycol-10 propyl ether (general formula (C2H40) n CioH220, CAS no. 160875-66-1 ), petroleum distillate (CAS No. 64742-47-8), undecyl alcohol ethoxylates (CAS No. 127036-24-2) or a mixture of 2-methyl-3(2H)-isothiazolone and 5-chloro-2- methyl-3(2H)-isothiazolone (CAS no. 55965-84-9);

- an equalizing substance having the function of equalizing the characteristics of the textile product so as to prepare it to be dyed homogeneously; the equalizing substance can be for example 5-sulfosalicylic acid (CAS no. 97- 05-2), polyethoxylated tallow amines (CAS no. 61791 -26-2), quaternary salts of polyethoxylated tallow amines with diethylsulphate (CAS no. 68071 - 95-4) or a mixture of ethoxylated C16-C18 unsaturated alcohols (CAS no. 68920-66-1 ); and

- an acidity regulator, selected from citric acid (CAS No 77-92-9) and tartaric acid (CAS No 87-69-4), having the function to maintain the pH constant during treatment.

The following table summarizes the substances that are added in step 1 in the dyeing bath and shows the indicative percentages of said substances in the bath with respect to the weight of the textile product to be dyed.

Step 1 of the process lasts between 5 and 15 minutes.

In a variant of the process, the wetting substance can be added in step 0 described above, or in part in step 0 and the remaining part in step 1 .

Subsequently, at the beginning of step 2 of the process, a purified synthetic food colouring is added to the dyeing bath, according to a salient feature of the dyeing process of the invention. The synthetic colouring substances for food use that can be used in the invention are shown in the following table, in which a chemical or commercial name, the CAS number, the code with which this is designated in the European Union (when available) and the colour that the substance gives to the textile product, are indicated for each substance: Each of said colouring substances can be used alone, or it is possible to use a mixture of two or more of these substances to obtain particular shades of colour; both in the case of a single substance and in the case of a mixture of two or more of these colouring substances, the percentage in the dyeing bath of this component can vary between 0.001 % and 6%. Within this range, the actual amount to be used can be determined using methods and techniques known to the experts in the sector, according to the desired result (for example, the intensity of colour or the tone to be obtained).

For example, it is possible, through a usual laboratory textile dyeing machine, to prepare a plurality of recipes, that is a plurality of dyeing baths having different, even slightly, percentages of a synthetic food dye and then test them to verify their real effect on the textile product to be dyed, in order to select the recipe, that is the dyeing bath with the percentage of synthetic food dyeing substance that provides the best result as regards the dyeing of the textile product.

Another characterising component of the process of the invention is the acidity regulator, which, as mentioned, is selected from citric acid and tartaric acid; the inventors have observed that the use of one of these acidity regulators, or a mixture thereof, makes it possible to achieve colour fastness results not achieved by known processes employing food dyes. The acidity regulator can be used in amounts varying within a wide range, from 5 to 50%. The inventors observed that, within this range, larger amounts of the acidity regulator should be used when darker tones are to be obtained, whereas for lighter tones relatively small quantities within this range are sufficient.

As the desired percentage of the synthetic food dye and the acidity regulator is introduced into the dyeing bath, the temperature of the latter is gradually increased, in a time comprised between 50 and 80 minutes, preferably 70 minutes, from the initial temperature, for example 30 °C, at a temperature comprised between 80 and 120 °C, preferably of about 100 °C. After reaching the desired temperature, the bath is left at this temperature for a time comprised between 30 and 90 minutes, preferably 60 minutes, and finally it is cooled to a temperature comprised between 60 and 80 °C, preferably at 70 °C; cooling generally requires a time comprised between 10 and 30 minutes, typically about 15 minutes.

After having been treated and dyed in the dyeing bath, the textile product is subjected to a finishing treatment, indicated as a whole as TF, comprising various steps and interventions. This part can be started immediately after the conclusion of the BT part or later on.

In particular, after having reached 70 °C of the dyeing bath with cooling, the bath is drained to perform a first wash of the dyed textile product in water, corresponding to step 3 of the process of the invention. Said first wash is preferably carried out in the same machine in which the dyeing took place, at a temperature comprised between 35 and 55 °C, preferably 40 °C, for a time comprised between 5 and 15 minutes, preferably for 10 minutes, after which the bath of the first wash is drained from the machine.

Then, the textile product is subjected, preferably in the same machine of the first wash, to a second wash, corresponding to step 4 of the process of the invention; said wash can take place in water at a temperature comprised between 20 and 35 °C, preferably at 30 °C, for a time comprised between 2 and 10 minutes, preferably for 5 minutes; alternatively, the second wash can be carried out at a temperature of 50 °C for a time comprised between 2 and 10 minutes, preferably for 5 minutes, in an aqueous solution containing 5% by weight (with respect to the textile product) of sodium acetate. After the conclusion of this step, the bath of the second wash is drained from the machine.

In step 5 of the process of the invention, the dyed textile product undergoes a colour fixing treatment. This treatment consists in dipping the textile product (inside the same machine of the washing baths or in another machine) into a bath containing a fixing substance in a percentage comprised between 1 % and 6% by weight with respect to the initial textile product, at a temperature comprised between 20 and 60 °C, preferably at 40 °C, for a time comprised between 5 and 30 minutes, preferably 20 minutes, at a pH comprised between 4.5 and 6.5, preferably 5.5. This treatment has the function of increasing the wet fastness, the resistance of the textile product to "pilling" (i.e. the formation of fluff and balls of fibre in the yarn), and also giving water repellency to the final textile product. Alternatively, the fixing substance can be applied by "foulard" (impregnation followed by squeezing and drying) if the textile product is a fabric; or by spraying distribution, particularly suitable when the textile product to be treated is an already finished item of clothing.

Aqueous solutions of polyamines can be used as fixing substances, which replaced formaldehyde in the 1990s due to the hazardous nature of this compound. These solutions generally contain mixtures of different polyamines, e.g. mixtures of copolymers of different allylamines (e.g. diallylamine, N-methyl-diallylamine or similar) with condensates between epialohydrins (mainly epichlorohydrin) and a polyalkylene-polyamine. Polyamine solutions (or concentrates for their preparation) useful for colour fixing in textile dyeing processes are widely available on the market; examples of such commercial products are E-CT 20 and E-CF 30 by the company Eksoy® Sarigam (Adana), Turkey; FIX REA EXTRA CONC. by the company Aleph Sri in Lurate Caccivio (Como) Italy; Fixanol by the company Sarex in Mumbai, India; ZETESAL F by the company ZETA ESSE Tl Sri in Tricerro (Vercelli) Italy; and the products VEBAFIX FFA and VEBAFIX WPS sold by the Applicant.

Alternatively, a suspension of silica in water can be used as a fixative. Silica gel can be produced by suspending in water the product known as "nanometric silica", "colloidal silica" or "fumed silica", which consists of nanometric particles of pure silica (generally obtained by combustion of SiCL) aggregated by electrostatic forces to form micrometer-sized particles; this form of silica is widely available commercially and is sold, for example, by Evonik Resource Efficiency GmbH in Essen (Germany) under the name AEROSIL®, or by Cabot Corporation in Boston, Massachusetts (USA) under the name Cab-O-Sil®. The concentration of the silica suspension in water may be comprised between 2 and 10% by weight, preferably about 5% by weight.

The inventors noted that the use of silica not only improves colour fixing but also achieves certain ancillary effects that are very important in the textile sector, as it increases the stain resistance of the fabric and makes it anti-bacterial and more resistant to wear and tear (reduction in the pilling phenomenon).

Both the aqueous solutions of polyamines described above and the silica suspension can be optionally added with diethylene glycol (CAS 111 -46-6). A mixture of a polyamine-type product and a silica suspension can also be used as a fixing substance, with the possible addition of diethylene glycol in this case as well.

At the end of the fixing treatment, in step 6 of the process the bath is drained, and the textile product is sent for drying in view of any subsequent treatments.

Fig. 1 represents a time diagram which schematically shows the time/temperature profile of a typical dyeing process according to the invention, which is reported by way of example. As shown in the figure, the process consists of a first BT part (in which the textile product is coloured) and a second TF part (finishing treatments, in which the colour is fixed). Each of the steps of the process (including the preliminary step 0) is indicated with the corresponding number in the lower part of the diagram (near the time axis).

In the process of the example in Fig. 1 , the preliminary step 0 (impregnation of the textile product with water) and step 1 (addition of detergent, wetting agent, equalizing agent and acidity regulator) are both carried out at 30 °C, each with a duration of 5 minutes. The actual dyeing step, 2, which begins by adding the chosen dye to the bath, comprises a first part of increasing the temperature from 30 °C to 100 °C in 70 minutes, holding the bath containing the textile product at 100 °C for 60 minutes, cooling from 100 °C to 70 °C in 15 minutes and subsequent cooling to temperatures around room temperature.

There is no fixed temporal relationship between the end of the BT part and the beginning of the TF part of the process: this condition is represented by the broken axis of the times between these two parts of the process.

The TF part of the process starts at the minute zero of this part, with step 3 (first wash) which is carried out at 40 °C for a 10-minute period, followed by a step 4 (second wash) carried out at 30 °C for 5 minutes, and subsequently by the colour fixing step 5, which is carried out at 40 °C for 20 minutes. Step 6 (drain of the finished textile product from the last bath and subsequent operations) does not have a precise temperature and duration.

As said, the one represented in Fig. 1 is only one possible example of the process of the invention; as will be evident to the person skilled in the art, each of the steps represented in the figure and described in detail below could be carried out at a temperature or for a duration of time different from those indicated in the figure, provided that these temperatures and durations fall within the ranges previously reported; in particular, remaining within said intervals, the duration of each of the steps of the process will generally be the shorter the higher the temperature at which it is carried out, and vice versa.

The process of the invention can also admit other variations, modifications and improvements with respect to what has been described and illustrated so far.

For example, without prejudice to the use, for preparing the BT dyeing bath, of a purified synthetic dye already used in the food sector, which use corresponds to the salient feature of the invention, the other conventional substances, included in the BT dyeing bath and used in the TF finishing treatment of the textile product, may vary with respect to those previously described and illustrated with reference to the dyeing process, in particular as a function of the specific characteristics that the textile product, once dyed, must satisfy.

The invention will be further described by the following examples.

EXAMPLE 1

Six samples of wool fabric have been dyed according to processes of the invention and according to processes not of the invention. The samples obtained in preparations 1A, 1 B, 2A and 2B have been produced with processes that do not satisfy the conditions of the invention, and are therefore comparative samples; the samples 11N and 2IN are instead samples obtained according to the process of the invention.

To allow the comparison of the results, the thermal profile (temperature/time) adopted in the preparation process is the same for all six samples and corresponds to the thermal profile described above with reference to Fig. 1. The components adopted in the various steps of the process for the six samples are shown in Table 1. The components employed in each of the tests are identified by the E-number (and an indication of the corresponding colour) in the case of dyes, and by the CAS number for the other compounds apart from silica, which is referred to simply as SiO2. Sodium sulphate and formic acid are used in the comparison tests as they are typical components of dyeing baths of the prior art. For each of the components used, the table shows the amount used (in% by weight on the weight of the sample of wool fabric to be coloured).

Table 1

The mixtures of yellow, red and blue dyes in tests 1A, 1 B and 11N give a "moss tone" colour after dyeing; the mixtures of yellow, red and black dyes in tests 2A, 2B and 2IN give a "dark green tone" colour after dyeing.

EXAMPLE 2

The six samples obtained in Example 1 have been subjected to a colour release test according to the UNI EN ISO 105-E04 standard test, which is the most severe and selective test to pass the GB 18401 standard; according to this standard, the test simulates the release of colour by a fabric in the presence of alkaline perspiration (alkaline perspiration is simulated with a basic solution specifically sold to carry out this test). The test is carried out by impregnating each sample with the diluted soda solution and then placing the sample in contact with a "witness", that is, a strip of fabric made with six different materials (acetate, cotton, polyamide, polyester, acrylic and wool), and by evaluating the intensity of the colour acquired by the various parts of the witness through release from the sample under examination; the more intense the colouring of the witness, the greater the release from the examined tissue and therefore the worse the result is considered.

The values are reported on a grey scale with values varying between 1 and 5, in which the lower the value, the poorer the fastness. GB 18401 accepts 3-4 as a minimum dye-fading value.

The results of the tests carried out on the six samples 1 A, 1 B, 11N, 2A, 2B and 2IN are shown in Table 2.

Table 2

From the results of the tests reported in Table 2 it can be deduced that the purified synthetic dyes for food use applied in the textile field to dye the protein fibres, if used with the known process (samples 1 B and 2B) would only have the advantage of being eco-sustainable compared to the same not purified dyes (samples 1 A and 2A); on the other hand, if applied with the process of the invention (samples 11N and 2IN) in addition to eco-sustainability, the purified synthetic dyes for food use also allow excellent wet colour fastness to be obtained.

EXAMPLE 3

The test in Example 1 was repeated on a mixed yam of SWwool (Super Wash non-shrinkable wool) and silk, containing by weight 70% SW wool and 30% silk. In the test were used: - a mixture of food dyes consisting of 0.1 % Blue E133, 0.3% Red E124 and 1.8% Black E151 ("dark green tone");

- wetting agent (CAS 55965-84-9), 1 %;

- detergent (CAS 126-30-7), 1 %;

- levelling agent (CAS 61791 -26-2), 1 %;

- pH regulator citric acid 50%;

- fixing agent, a mixture comprising 5% SiO2 and 4% VEBAFIX WPS polyamine.

As in Example 1 , the percentage amounts given above are percentages by weight with respect to the weight of the dyed wool fabric sample.

The colour fastness results according to standard EN ISO 105-E04 are shown in Table 3.

EXAMPLE 4

The test in Example 1 was repeated on a mixed yam of cashmere wool and silk, containing by weight 70% cashmere wool and 30% of silk. In the test were used:

- a mixture of food dyes consisting of 0.3% Yellow E102, 0.3% Red E124 and 0.3% Blue E133 ("moss tone");

- wetting agent (CAS 55965-84-9), 1 %;

- detergent (CAS 126-30-7), 1 %;

- levelling agent (CAS 61791 -26-2), 1 %;

- pH regulator citric acid 20%;

- fixing agent, polyamide VEBAFIX WPS, 4%.

The colour fastness results according to standard EN ISO 105-E04 are shown in Table 3.

Table 3

EXAMPLE 5

In this example the results obtained with the processes of the present invention and of patent application CN 110306367 A are compared.

Four colouring tests with food dyes were carried out, tests 3 and 4 having followed the process of document CN 110306367 A and tests 3IN and 4IN according to the process of the present invention.

Each of the four tests was carried out by dyeing a 10 g piece of cashmere fabric, using a bath volume of 200 ml.

The amounts of the components of the four baths, in weight percentages relative to the weight of the fabric, and the temperatures and times of the main steps, are reported in Table 4.

Table 4

(*Albegal® is a registered trademark of Huntsman Corporation)

Since CN 110306367 A indicates the use of a penetrating agent without specifying its composition, the wetting agent of the examples of the present invention (mixture of 2-methyl-3(2H)-isothiazolone and 5-chloro-2-methyl-3(2H)- isothiazolone, CAS No. 55965-84-9) was used in tests 3 and 4.

As reported in the table, test pairs 3 and 3IN and 4 and 4IN are performed at the same temperatures and colouring treatment times. On the other hand, the fixing conditions are different, as required by the document of the prior art and the present invention.

In particular, fixing according to CN 110306367 A was performed in tests 3 and 4 with two mixtures containing, in weight percentages with respect to the tissue, 0.9% sodium citrate and 1.6% potassium alum in test 3, and 0.7% sodium citrate and 1 .3% potassium alum in test 4.

Fixing according to the present invention was instead carried out with SiO2/polyamine VEBAFIX WPS mixture, respectively in amounts of SiO2 0.8% - polyamine VEBAFIX WPS 0.7% (1.5% in total) in test 3IN, and SiO 2 1.95% - polyamine VEBAFIX WPS 1 .55% (3.5% in total) in test 4IN.

EXAMPLE 6

The four samples obtained in Example 5 were submitted to colour release tests according to the standard tests UNI EN ISO 105-C06, concerning the colour release after washing at 40 °C, and UNI EN ISO 105-E04, concerning the colour release from a fabric in the presence of alkaline sweat. The tests were carried out as described above in Example 2. The results obtained in the tests are shown in Tables 5 and 6, respectively for washing at 40 °C and for release to alkaline sweat.

Table 5

Table 6

Comments The new textile dyeing process of the invention, which uses purified synthetic dyes approved for the food industry and citric and tartaric acid as acidity regulators, also widely used in the food industry, allows to fully achieve the set goals and in particular makes available both a new innovative textile dyeing process capable of eliminating all the negative effects connected to the use, in conventional textile dyeing, of synthetic and natural dyes, and also a new and innovative use of purified dyes of synthetic origin which are usually and currently used in the food industry.

This process offers a series of relevant and unique advantages, some of which have already been illustrated above, among which the following can be mentioned:

- the dyes used in the textile dyeing process, being synthetic but purified, do not feature any toxicity or harmfulness to the operators and workers who run the textile dyeing processes and plants in which said dyes are used;

- in particular, the purified synthetic dyes used are metal-free, do not contain allergenic substances, are not mutagenic, and the respective powders do not contain any type of free amines or other substances harmful to the health of the operators who must handle said dyes;

- the process allows a significant reduction in costs for treating and disposing of the residues and waste produced by the textile dyeing, since the used dyes are free of polluting substances;

- there are better and healthier working conditions in textile dyeing plants;

- the dyeing costs of textile products and/or articles are competitive with those of the conventional textile dyeing processes, that is, those using conventional dyes;

- the textile products dyed through the process of the invention meet the GB18401 , GOTS 6.0 standards and the requirements of the ZDHC programme;

- as all the components used are highly biodegradable, the process of the invention is fully included in circular economy processes;

- with the process of the invention, very high colour fastnesses are obtained in all cases, with values of at least 4 and often 5 (maximum value on the fastness assessment scale) in almost all cases, whereas with known processes, for example that according to document CN 110306367 A, the fastness values obtained are much lower.