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Title:
PROCESS FOR DYEING SYNTHETIC TEXTILE FIBERS, IN PARTICULAR POLYAMIDE, COMPRISING THE USE OF PURIFIED SYNTHETIC FOOD DYES
Document Type and Number:
WIPO Patent Application WO/2022/130326
Kind Code:
A1
Abstract:
A textile dyeing process is described for dyeing a textile material, product or article made of synthetic fibers, in particular polyamide, comprising the steps of soaking said textile material, product or article in a first bath comprising at least a detergent substance, a wetting agent, a leveling substance and an acidity regulator; adding to the first bath a dye substance approved for food use, forming a dyeing bath; subjecting the dyed textile material, product or article to washes; and finally subjecting the dyed textile material, product or article to a color fixation treatment.

Inventors:
BAZZANO NERIO (IT)
BASSO GIOVANNI (IT)
Application Number:
PCT/IB2021/061936
Publication Date:
June 23, 2022
Filing Date:
December 17, 2021
Export Citation:
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Assignee:
VEBACHEM S R L S (IT)
TINTORIA DI POLLONE S P A (IT)
International Classes:
D06P1/00; D06P3/24
Foreign References:
TR201603418A22017-10-23
US5922088A1999-07-13
CN109972418A2019-07-05
CN106012589A2016-10-12
Other References:
ARVANITOYANNIS I ET AL: "INTERACTION OF DYES USED FOR FOODS WITH FOOD PACKAGING POLYAMIDES", JOURNAL OF APPLIED POLYMER SCIENCE, JOHN WILEY & SONS, INC, US, vol. 49, no. 10, 10 September 1993 (1993-09-10), pages 1733 - 1749, XP000461003, ISSN: 0021-8995, DOI: 10.1002/APP.1993.070491005
Attorney, Agent or Firm:
PALLADINO, Massimo et al. (IT)
Download PDF:
Claims:
CLAIMS Textile dyeing process for dyeing a textile material, product or article made of synthetic fibers, comprising the following steps, wherein steps 1 ) to 5) occur under stirring:

1 ) forming a first bath, having a temperature between 20 and 30 °C, comprising water, a detergent agent, a wetting agent, a leveling agent and an acidity regulator selected from citric acid, tartaric acid, diethyleneglycol diformate and triethanolamine, and soaking said textile material, product or article in the first bath for a time between 5 and 15 minutes;

2) adding to the first bath at least one synthetic dye compound approved for use in the food industry, thus forming a dyeing bath in a machine in the presence of an acidity regulator selected from citric acid, tartaric acid, diethyleneglycol diformate and triethanolamine, bringing this bath to a temperature between 80 and 120 °C in a time between 50 to 80 minutes, leaving it at this temperature for a time between 30 and 90 minutes and finally cooling the bath to a temperature between 60 and 80 °C in a time between 10 and 30 minutes;

3) draining the dyeing bath and subjecting the textile material, product or article dyed in the previous step to a first wash in the same machine at a temperature between 35 and 55 °C for a time 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 between 20 and 35 °C for a time between 2 and 10 minutes in water, or at 50°C for a time 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 color fixation treatment at a temperature between 20 and 60 °C for a time between 5 and 30 minutes and at a pH between 4.5 and 6.5 in a bath containing a fixing agent present in a percentage between 1 and 6% with respect to the initial weight of the textile material, product or article;

6) draining the fixation bath and subjecting the textile material, product or article to drying. Process according to claim 1 , wherein said synthetic fibers are polyamide fibers. Process according to any one of the preceding claims, further comprising a preliminary step 0 carried out under stirring, wherein said textile material, product or article to be dyed is soaked in water at a temperature between 20 and 30 °C for a time between 5 and 10 minutes, and wherein all or part of the quantity of wetting agent necessary for carrying out step 1 can be added to the water. Process according to any one of the preceding claims, wherein in said first bath:

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

- said wetting agent 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 leveling agent is selected from 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 C16-C18 ethoxylated unsaturated alcohols (CAS no. 68920-66-1 ); and

- said acidity regulator is selected from citric acid (CAS no. 77-92-9), tartaric acid (CAS no. 87-69-4), diethyleneglycol diformate (CAS no. 120570-77-6) and triethanolamine (CAS no. 102-71 -6). Process according to claim 4, wherein 1 % of said detergent agent, 1 % of said wetting agent, between 1 % and 2% of said leveling agent and between 1 and 20% of said acidity regulator are used, in percentage by weight with respect to the weight of said textile material, product or article. Process according to any one of the preceding claims, wherein said at least one synthetic dye compound approved for use in the food industry is selected from the compounds of the following table: Process according to any one of the preceding claims, wherein said at least one synthetic dye compound approved for use in the food industry is used in an amount between 0.001 % and 6% of the weight of the textile material, product or article. Process according to any one of the preceding claims, wherein the fixing agent used in step 5 is selected from an aqueous solution of polyamines, a suspension of silica in water at a concentration between 2% and 10% by weight, and a mixture thereof. Process according to claim 8, wherein said suspension of silica in water has a concentration of 5% by weight. Process according to any one of claims 8 or 9, wherein the fixing agent further contains diethylene glycol. Process according to any one of the preceding claims, wherein said step 5 is carried out by soaking said textile material, product or article in the bath containing the fixing agent, 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. Textile material, product or article consisting of synthetic fibers, dyed with the textile process according to any one of claims 1 to 11.

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Description:
PROCESS FOR DYEING SYNTHETIC TEXTILE FIBERS, IN PARTICULAR POLYAMIDE, COMPRISING THE USE OF PURIFIED SYNTHETIC FOOD DYES ******************

FIELD OF THE INVENTION

The present invention generally relates to the field of methods and processes for the treatment of textile products and/or articles, and more particularly to a textile dyeing process of synthetic textile fibers (as well as yams and fabrics derived from these fibers), in particular polyamide, 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 yams and textile articles in general is a practice with very ancient origins. The number of processes developed for the purpose of dyeing 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 fibers are essentially of two types, natural and synthetic fibers; natural fibers can in turn be subdivided into fibers of vegetable origin (cotton, linen, hemp, ...) and animal fibers (mainly wool and silk). Depending on the type of fiber, and in particular the chemical composition of the same, the types of dyeing processes which can be applied, the level of production of the fabric in which dyeing can be carried out, and also the results obtained can vary.

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

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

With regards to the dyes used in the textile dyeing field, 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 which 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 field are also non-toxic and non-irritating, to avoid that dyed textile products and articles, once worn, can create problems of sensitization or irritation of the skin, or secondary effects of accumulation in case of absorption through the skin itself.

To meet said 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 are GB 18401 -2010 (in force since 2012), which sets minimum limits for the resistance of the color to washing or exposure to light (the resistance of color on textiles is known in the industry as "fastness"), the Global Organic Textile Standard 5.0 of 2017 (GOTS 5.0) and the ZDHC (Zero Discharge of Hazardous Chemicals) program, which set maximum values for certain agents which 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 field as APEO).

These considerations limit the freedom of choice of dyes and processing adjuvants for each specific textile application.

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

These natural dyes extracted from plants give rise to non-optimal fastness; the inventors believe that this is due to the interference of the substances contained in the natural extracts in the coloring process, but that neither the compound nor compounds (pigments) provide the textile material with the color. Furthermore, almost all the coloring processes described use metal-based mordants, which can give rise to sensitization phenomena following prolonged contact with the skin.

The dyeing of textile fibers with natural dyes is the object of various patent publications. Patent US 5,922,088 describes a process for dyeing synthetic fabrics, in which food dyes can be used, but a mixture of polymethacrylic acid (or a copolymer thereof with an olefinic comonomer) and sulfamic acid is used as the color fixative. The patent application which led to this document dates back to 1997, and sulfamic acid is no longer considered acceptable under current toxicity and environmental regulations.

Patent application CN 109972418 A describes the use of dyes used in the food industry to dye non-woven fabrics based on cellulose fibers, of which the preferred ones are viscose and cotton; for their dyeing, these fibers are modified with cationic dyes.

The article "Interaction of dyes used for foods with food packaging polyamides", I. Arvanitoyannis et al., Journal of Applied Polymer Science 49, 10 (1993), pp. 1733-1749, presents a theoretical study on the color transfer from foods containing food dyes to polyamide packaging materials, and thus the staining problems of the latter, which make the final products unappreciated by the end customers. The study explores the staining of polyamides with two blue food dyes under different conditions of temperature, acidity and dye concentration; one of the acids used in the study to adjust the pH is citric acid. Since the aim of this study is not to determine conditions for the effective dyeing of polyamide materials with high fastness, no actual dyeing process is described; for example, no thermal cycles characteristic of dyeing processes are reported, nor is the use of fixatives. Furthermore, the experimental tests described are carried out with insignificant concentrations of blue dye (in the order of ppm) with respect to those required for a dyeing process, and of course no information is given on the fastness of the dyeing obtained.

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

Attempts have also been made to dye textile fibers using food dyes, which do not have problems of environmental friendliness and toxicity.

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

Therefore, none of the processes described above were able to meet all of the recently approved international standards for eco-friendly processes in the textile industry, i.e., GOTS 5.0, GB 18401 -2010 and ZDHC, and at the same time result in a dye with sufficient fastness for industrial application.

An object of the present invention is to provide a dyeing process for dyeing synthetic fibers and in particular for dyeing polyamide, through the use of purified food-grade synthetic dyes, which gives results applicable in the textile industry. These dyes respond to the stringent regulatory features established by national or supranational authorities, such as the FDA in the USA and the European Food Safety Authority in Europe, in the latter case through the "Directive on Colours" 94/36/EC; therefore, it follows that the same have no problems in exceeding the limits of the dyes of the prior art from the point of view of eco-sustainability, reducing the risks of pollution presented by 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 meeting the market fastness demands, a set of results which to date have not been successfully obtained with either natural dyes or synthetic food dyes.

SUMMARY OF THE INVENTION

The aforesaid objects are achieved by a process for dyeing a textile material, product or article made of synthetic fibers, in particular polyamide, comprising an operation for dyeing said 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, tartaric acid, diethyleneglycol diformate and triethanolamine.

More in detail, the invention relates to a process for dyeing a textile material, product or article made of synthetic fibers, in particular polyamide, comprising the following steps, in which steps 1 ) to 5) are carried out under stirring:

1 ) forming a first bath, having a temperature between 20 and 30 °C, comprising water, a detergent agent, a wetting agent, a leveling agent and an acidity regulator selected from citric acid, tartaric acid, diethyleneglycol diformate and triethanolamine, and soaking said textile material, product or article in the first bath for a time between 5 and 15 minutes;

2) adding to the first bath at least one synthetic dye compound approved for use in the food industry, thus forming a dyeing bath in a machine in the presence of an acidity regulator selected from citric acid, tartaric acid, diethyleneglycol diformate and triethanolamine, bringing this bath to a temperature between 80 and 120 °C in a time between 50 to 80 minutes, leaving it at this temperature for a time between 30 and 90 minutes and finally cooling the bath to a temperature between 60 and 80 °C in a time between 10 and 30 minutes;

3) draining the dyeing bath and subjecting the textile material, product or article dyed in the previous steps to a first wash in the same machine at a temperature between 35 and 55°C for a time 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 between 20 and 35 °C for a time between 2 and 10 minutes in water, or at 50°C for a time 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 color fixation treatment at a temperature between 20 and 60 °C for a time between 5 and 30 minutes and at a pH between 4.5 and 6.5 in a bath containing a fixing agent present in a percentage between 1 and 6% with respect to the initial weight of the textile material, product or article;

6) draining the fixation 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 feature described in relation to said 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 features 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 fibers formed by synthetic fibers, in particular polyamide fibers.

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

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

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

- "soak" means both the possibility that the textile product is added to an already formed bath, and also the possibility that water and the components necessary for the specific bath are added to the textile product already in a container (or also the intermediate possibility that the textile product is added to water only, and the further components necessary for the specific bath are then added to the water);

- all the percentages of the various components used in the process are meant by weight relative to the initial weight of the textile product to be dyed unless otherwise stated;

- 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 which is as complete and accurate as possible, the register number (Chemical Abstract Service) is also indicated for the substances used.

The textile dyeing process of the invention comprises a first step, indicated hereinafter as step BT, in which the textile product to be dyed is prepared for dyeing and then soaked and treated in a dyeing bath, and a second step, indicated hereinafter also as step TF, in which the textile product is subjected to a finishing treatment.

All the baths of the process are water based, i.e. , the liquid phase into which the textile product is soaked and the compounds which perform the functions of the various steps (detergents, wetting agents, dyes, ...) are dissolved, is water.

All the steps of the process of the invention occur under stirring, apart from possibly drying. 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 the steps of the process occur with a weight ratio between water and the textile product to be dyed which can vary between 10:1 and 40:1 ; these quantities of water are sufficient to completely solubilize all the chemical compounds (detergents, wetting agents, dyes, ...) used in the process.

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 dyed soaked in water at a temperature between 20 and 30 °C for a time between 5 and 10 minutes. This preliminary step has the purpose of completely impregnating the fibers with water, so that the components of the bath added subsequently can effectively and quickly contact the textile fibers.

The actual process begins with step 1 in which, maintaining the temperature between 20 and 30 °C, a first bath is formed by adding to the water of step 0 at least one detergent agent, a wetting agent, a leveling agent and an acidity regulator selected from citric acid, tartaric acid, diethyleneglycol diformate and triethanolamine. These components, which are known to those skilled in the art as well as their effects on fibers, essentially have the function of preparing the bath for dyeing the textile product and comprise at least:

- a detergent agent (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 agent can be for example 2,2-dimethyl-1 ,3-propanediol (CAS no. 126-30-7);

- a wetting agent having the function of deaerating the textile product; the wetting agent can be, for example, polyethylene glycol-10 propyl ether (general formula (C2H40)nCioH220, 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);

- a leveling agent having the function of leveling the features of the textile product so as to prepare it to be dyed homogeneously; the leveling agent can be for example 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 C16-C18 ethoxylated unsaturated alcohols (CAS no. 68920-66-1 ); and

- an acidity regulator, selected from citric acid (CAS no. 77-92-9), tartaric acid

(CAS no. 87-69-4), diethyleneglycol diformate (CAS no. 120570-77-6) and triethanolamine (CAS no. 102-71 -6), having the function of regulating the pH during the treatment.

The following table summarizes the components which are added in the dyeing bath in step 1 , and gives the approximate percentages of these components 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 variation of the process, the wetting agent can be added in step 0 described above, or partly in step 0 and the remainder in step 1 .

Subsequently, at the beginning of step 2 of the process, a purified synthetic food dye is added to the dyeing bath, according to a salient feature of the dyeing process of the invention. The synthetic food-grade dye compounds which 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 and the color which the compound gives to the textile product, are indicated for each compound:

Each of said dye compounds can be used alone, or it is possible to use a mixture of two or more of these compounds to obtain particular shades of color; both in the case of a single compound and in the case of a mixture of two or more of these dye compounds, the percentage in the dyeing bath of this component can vary between 0.001 % and 6%. Within this range, the actual quantity to be used can be determined using methods and techniques known to those skilled in the art, as a function of the desired result (for example, the intensity of color or the tone to be obtained).

For example, it is possible, through a usual laboratory textile dyeing machine, to prepare a plurality of recipes, i.e., a plurality of dyeing baths having different percentages, even slightly, of said 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, i.e. , the dyeing bath with the percentage of synthetic food dye compound which provides the best result as regards dyeing the textile product.

Another characterizing component of the process of the invention is the acidity regulator, which, as mentioned above, is selected from citric acid, tartaric acid, diethyleneglycol diformate and triethanolamine; the inventors have observed that the use of one of these acidity regulators, or a mixture thereof, makes it possible to achieve color fastness results not achieved by the known processes which use food dyes. The acidity regulator can be used in quantities which vary within wide margins, from 1 to 20%. The inventors have observed that, within this range, larger quantities of the acidity regulator should be used when darker tones have to be obtained, whereas for lighter tones relatively small quantities within this range are sufficient.

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

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

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 occurred, at a temperature between 35 and 55 °C, preferably 40°C, for a time between 5 and 15 minutes, preferably 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 occur in water at a temperature between 20 and 35 °C, preferably 30°C, for a time between 2 and 10 minutes, preferably 5 minutes; alternatively, the second wash can be done at a temperature of 50 °C for a time between 2 and 10 minutes, preferably 5 minutes, in an aqueous solution containing 5% by weight (with respect to the textile product) of sodium acetate.

After the conclusion of step BT, the bath of the second wash is drained from the machine.

In step 5 of the process of the invention, the dyed textile product is subjected to a color fixation treatment. This treatment consists of soaking the textile product (in the same machine of the washing baths or in another machine) in a bath containing a fixing agent in a percentage between 1 % and 6% by weight with respect to the initial textile product, at a temperature between 20 and 60 °C, preferably 40 °C, for a time between 5 and 30 minutes, preferably 20 minutes, at a pH between 4.5 and 6.5, preferably 5.5. This treatment has the function of increasing wet fastness, the resistance of the textile product to abrasion, and also conferring water repellency to the final textile product. Alternatively, the fixing agent can be applied "by foulard" (impregnation followed by squeezing and drying) if the textile product is a fabric; or by spray 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 agents, which replaced formaldehyde in the 1990s due to the hazardous nature of this compound. These solutions generally contain mixtures of different polyamines, for example 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 color fixing in textile dyeing processes are widely commercially available.

Alternatively, a suspension of silica in water (forming a diluted silica gel) can be used as a fixing agent. This suspension can be formed by suspending the product known as "nanometric silica", "colloidal silica" or "fumed silica” in water; this form of silica is widely available commercially and is sold for example by the company Evonik Resource Efficiency GmbH from Essen (Germany) under the name AEROSIL®, or by the company Cabot Corporation from Boston, Massachusetts (USA) under the name Cab-O-Sil®. The suspension can have a silica concentration between 2 and 10% by weight, preferably about 5% by weight (meant as a percentage by weight in the suspension itself, i.e. , with respect to the sum of the weights of water and silica, and not the weight of the dry textile product).

The inventors have observed that the use of silica not only improves the color fixation but also achieves certain ancillary effects which are very important in the textile field, as it increases the stain resistance of the fabric and makes it antibacterial and more resistant to wear and tear

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 agent, also in this case with the possible addition of diethylene glycol.

At the end of the fixation 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 step BT (in which the textile product is dyed) and a second step TF (finishing treatments, in which the color is fixed). Each step 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, leveling 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 selected 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 step BT and the beginning of step TF of the process: this condition is represented by the broken time axis between these two steps of the process. The beginning of step TF of the process (minute zero of this step) coincides with the start of step 3 (first wash) which is carried out at 40 °C for 10 minutes, followed by step 4 (second wash) carried out at 30 °C for 5 minutes, and then by step 5 of color fixation, which is carried out at 40 °C for 20 minutes. Step 6 (draining the finished textile product from the last bath and subsequent operations) does not have a precise temperature and duration.

As aforementioned, in Fig. 1 is represented only one possible example of the process of the invention; as will be evident to those skilled in the art, each step represented in the figure could be carried out at a different temperature or duration of time from those indicated in the figure, as long as these temperatures and durations fall within the ranges previously reported; in particular, remaining within said intervals, the shorter the duration of each step of the process will generally be, 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 in the dyeing bath of a purified synthetic dye already used in the food industry and of a pH regulator among those mentioned above (salient features of the invention), the other compounds, agents and products included in the dyeing bath or those used in the finishing treatment TF of the textile product can vary with respect to those described above, as a function of specific features that the textile product, once dyed, must satisfy.

The invention process offers a series of significant and unique advantages, some of which have already been outlined above, including the following:

- 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 manage 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 dyes used are free of polluting substances;

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

- the textile products dyed with the process of the invention meet the standards

GB18401 , GOTS 5.0 and the requirements of the ZDHC program.