DESCRIPTION

STATE OF THE ART

The present invention is related to a process for pad-batch dyeing textile articles comprising a treating step with ionized gas or plasma.

More specifically, the present invention is related to a dyeing process comprising a step for padding animal fibre blends and textile articles derived therefrom, preceded by a treating step with ionized gas or plasma.

With the term "pad-batch dyeing process" according to the present invention, a process comprising a padding step is intended, i.e. a continuous impregnation and in-line calendering, followed by a step for fixing the colour on batches of textile articles of any suitable size.

With the term "textile article" according to the present invention, a semi-finished textile fibre product at a variable processing degree is intended: from a ribbon of combed fibres (commonly called tops), to a yarn with variable torsion degree, to an orthogonal fabric, a knitted fabric or a non-woven fabric.

With the term "animal fibre blends" according to the present invention, a textile fibre blends having minimum constituent values equal to at least 20% animal fibres such as wool, cashmere, angora, silk and the like is intended.

Prior Art

Conventional exhaustion dyeing processes for the dyeing of animal fibre blends are known; these comprise the steps of pre-washing the textile material, subsequent immersion of the same in the liquor to be used in dyeing (usually metered in quantities that can be varied from 15 to 30 kg _wate r/kg _f i _b re ) , dosing the dyeing products, heating of the aqueous mass from the initial temperature to the dyeing temperature (usually close to the boiling point, depending on the pressure set to the system) , maintaining the dyeing temperature for a time that is usually variable between 45 and 180 min, indirect cooling of the dye solution down to about 60°C, cooling by diluting the dye bath, final washing and unloading the dyed textile material from the dyeing machinery.

An example of conventional exhaustion dyeing process is described in EP 0 592 979 Al, which illustrates a process for modifying animal fibres or products made with such fibres by means of a plasma treatment at atmospheric pressure, possibly of continuous type for fabrics of moderate thickness, in order to improve their dyeability and to reduce their shrinkage; nevertheless, as in conventional exhaustion dyeing processes and as is clear from Examples 5 and 6 reported in said document, the immersion time and the dye solution volumes according to this process are such as to make it less economically advantageous than the process pursuant to the present invention.

A technological evolution of the conventional exhaustion dyeing process described above is the pad-batch dyeing process, sometimes referred to as "processo di tintura a stoccaggio" in Italian, which, with respect to the preceding process, has the advantages of requiring much lower quantities of primary energy and water, as well as obtaining higher levels of dyeing evenness, fastness and reproducibility, and eventually allowing the attainment of higher productivity values.

The pad-batch dyeing process, as briefly disclosed above, is a semi-continuous dyeing process applicable to any textile article which can be brought through a dye bath of the article itself, and it is usually applied to fabrics; the main steps of the pad-batch dyeing process are:

a) a continuous impregnation step, in which the fabric is immersed in a dye bath, and subsequent squeezing between two or more cylinders which eliminate the exceeding liquid and allow a more effective penetration of the liquid into the fibre interstices; the combination of these operations constitutes the step commonly called padding;

b) a step, defined ageing, in which the impregnated fabric is maintained in controlled conditions in order to allow diffusion and fixation of the dyestuff on the fibre.

In the conventional pad-batch dyeing process, the water need, i.e. the amount of solution with which the fabric is impregnated, is a function of the fabric type one wishes to treat, and is on average in the range between 0.5 ÷ 1.5 kg of liquid per 1 kg of fabric.

The above-described pad-batch process, when it is employed for dyeing fabrics made of animal fibres and/or other fibres that are basically hydrophobic, has a series of drawbacks, such as obtaining a colouration with poor fastness, limited to the external surface of fibres, the formation of stains due to fabric zones characterized by different dye concentration or to agglomerates of chemical products being formed on the fabric surface and other colouration problems due to the reduced physical affinity between the dye solution and the fibre that constitutes the fabric.

In industrial practice, a pad-batch dyeing process with continuous impregnation and in-line calendering (padding) aimed at dyeing wool fabrics with reactive dyes and based on pre-treatment of such fabrics with urea and sodium metabisulphite is known; such process provides the addition of the following auxiliary products to the dye solution: 1) urea - used as swelling agent of wool fibres (typical dosage = 300 g/L) ; 2) sodium metabisulphite - used for increasing the number of active sites on wool and, at the same time, decreasing the resistance to diffusion of dyes inside the fibre (typical dosage = 20 g/L); 3) thickeners - products constituted by gums and mucilage, employed for preventing flowing and migration of the dye bath during the process (typical dosage = 10 g/L) . This dyeing method has the disadvantage of requiring the use of considerable amounts of auxiliary products, with obvious environmental and economical problems; additionally, said method has the disadvantage of determining a certain degradation of the treated wool fabric, the degradation action being generated by sodium metabisulphite, which causes the lysis of the cystine bond in wool fibres.

The article "Continuous dyeing of wool fabric containing polyamide fibre and modified by plasma glow discharge" by A.V. Ulesova et al . [Fibre Chemistry, vol. 40, No. 2, 2008] describes a semicontinuous dyeing process (pad-steam) of a plasma-treated wool fabric mixed with polyamide. The plasma treatment occurs by using a KPR-180 plasma device for 18 seconds. In the article "Low-temperature plasma surface modification of textiles made from natural fibre and advanced technologies" by S.F. Sadova et al . [High Energy Chemistry vol. 40, No. 3, 2008] it is specified that the KPR-180 equipment for plasma generation operates at a pressure in the range of 80-120 Pa, hence at a pressure much lower than atmospheric pressure. The use of plasma generators operating at a pressure lower than atmospheric pressure has however several disadvantages, such as high costs due to the energy necessary for operating the apparatus, the impossibility of carrying out continuous treatments, and the presence of vacuum pumps, with related maintenance problems.

WO 00/10703 Al describes a process for improving the dyeability of a material by means of treatment with glow discharge plasma at substantially atmospheric pressure, said material being a polymer and said treatment being of discontinuous type.

EP 0 407 918 Al describes a process for producing sewing threads by means of low-temperature plasma or a Corona treatment before spinning, twisting and/or weaving of the fibres .

Both the processes described in the prior art represented by the above-mentioned documents propose conventional dyeing steps (exhaustion dyeing of conventional type) run with high bath ratios, i.e. with a high ratio between the quantity of water and the corresponding treated textile material.

It would therefore be desirable to provide a process in which the time of contact between the textile article and the dye solution - necessary for obtaining a uniform impregnation - is reduced, with a consequent increase of impregnation speed and reduction of the dye solution volume. In such a manner, the process becomes much more advantageous under an economic standpoint .

It would also be desirable to provide a dyeing process by means of padding that, if applied to fabrics and other textile articles constituted by blends of animal fibres with other fibres, allows obtaining a material without different dye zones or colour stains, reduces the operating time, water need, dye and chemicals consumption, and does not have the disadvantages of the systems operating under vacuum.

Description of the Invention

The object of this invention is therefore to provide a pad- batch dyeing process applicable to the above-mentioned type of materials and semi-finished products, capable of reducing the processing time, in particular the time of contact between the textile article and the dye solution necessary to obtain a uniform impregnation, supplying a dyed textile article with superior quality characteristics and characterized by a high reproducibility, as well as reducing the quantity of dyes, chemicals and water normally employed in dyeing processes, and finally preventing the formation of colour stains or aggregates of chemical compounds on the textile article itself. This and other objects and advantages of the invention are achieved by means of a process for dyeing a textile article comprising the following sequence of steps:

a step for treating the textile article with ionized gas or plasma,

a step for continuous impregnation of the textile article by means of immersion in a dye bath comprising one or more dyes, and subsequent in-line calendering,

a step for ageing the textile article, subsequent to the step for impregnation by means of immersion, in conditions of controlled humidity and temperature,

characterized in that said textile article comprises animal fibres with basically hydrophobic characteristics, in that said step for treating the textile article with ionized gas or plasma is carried out at atmospheric pressure and in a continuous manner, and in that the immersion time in the impregnation step is within the range 0.5 s < t < 300 s, so as to generate a uniform impregnation characterized by concentration differences of the dye which impregnates the textile fibres lower than 0.1% with respect to the average concentration obtained on the textile article being processed .

The dyeing process according to the invention is applicable to any type of textile article but is preferably applied to textile articles constituted by wool, other animal fibres, blends of the same and blends of animal fibres with other fibres, all or partly characterized by basically hydrophobic behaviour .

Summary Description of the Figures

The invention will now be described with reference to the following figures, provided as a non-limiting example, in which :

- Figure 1 is a block diagram which illustrates the process steps according to the present invention; and Figure 2 is a schematic representation of the process according to the present invention.

Detailed Description of the Preferred Embodiment of the Invention

Figure 1 shows a simplified block diagram of the dyeing process steps comprising the steps for pre-treating by means of ionized gas or plasma, impregnation of the textile article by means of immersion in a dye bath comprising one or more dyes, and subsequent in-line calendering (padding) , according to the present invention, as will be described below.

The step for treating the textile article by means of ionized gas or plasma is carried out to increase the affinity of the textile article towards the aqueous phase used for dyeing, up to imparting suitable hydrophilic characteristics. It has been found that the increase of hydrophilic nature obtained by means of the treatment with ionized gas or plasma at atmospheric pressure and in a continuous manner improves the impregnability of the textile article, allowing the attainment of the objectives of improvement of the previously indicated process.

If it is desired to proceed to the padding of textile articles made of animal fibres without ionized gas or plasma treatment at room temperature and in a continuous manner, the time of contact between the textile article and the dye solution necessary for obtaining a uniform impregnation, such as in the dyeing of a fabric constituted by 100% wool, would be in the order of 30 minutes. Consequently, the impregnation speed, and the dye solution volume, would render the process disadvantageous under an economic standpoint. In order to be able to proceed in an effective manner with the dyeing by continuous impregnation and in-line calendering (padding) of textile articles made of blends of animal fibres, it is necessary to substantially modify the affinity of the textile article towards the dye solution, increasing its hydrophilic nature. It was discovered that the hydrophilic level imparted to the textile article must be such as to allow its complete impregnation in a short fraction of the total immersion time, e.g. about 10% of such total time, during which said textile article, when moved inside the trough, is in contact with the dye solution. The time necessary for a complete impregnation of the textile article is well represented by the drop absorption test (BS 4554:1970 Method of test for wettability of textile fabric) and, therefore, the time for complete impregnation of the textile article results equal to about 10% of the drop absorption time measured according to the above method. Based on that set forth above, during the execution of the process according to the present invention, there is the need to operate with trough characterized by a drawing-in length such to ensure, at industrially acceptable drive speeds, times of immersion / passage of the fabric in the dye solution that are sufficiently long to allow the complete impregnation of the textile article being processed. In the specific case of fabrics, the increase of hydrophilic nature is quantifiable through the measurement of the drop absorption time (BS 4554:1970 Method of test for wettability of textile fabric) . Observing the values reported in Table 1, it is possible to appreciate the variation of hydrophilic nature imparted to a 100% wool fabric following plasma treatment at atmospheric pressure and in a continuous manner.

Table 1

The treatment of the textile article with plasma or ionized gas in atmospheric pressure conditions and in a continuous manner is obtained by preferably employing a cold atmospheric plasma technology, such as DBD (Dielectric Barrier Discharge) , APGD (Atmospheric Plasma Glow Discharge) , Corona, or technologies based on plasma generation techniques of hybrid type.

The main operating conditions employed during the treatment of the textile article with the plasma are the following:

electrical energy employed by the generator: 12.5 ÷ 15000 kJ/kg (value referred to the quantity of processed material ) ;

- drive speed of the textile article: 0.1 ÷ 80 m/min;

- process gas: argon, helium, neon, hydrogen, nitrogen, oxygen, mixtures of the aforesaid gases and ambient air;

process gas flow rate: 0 ÷ 20000 NL/kg (value referred to the quantity of processed material);

When an atmospheric plasma technology, such as the Corona type, a flow rate for a specific process gas is not always definable, since the gaseous means subjected to ionization is usually constituted by the ambient air present between the electrodes, driven and refreshed by the movement of the treated textile article.

With reference to Figure 2, the fabric 5 unwound from a beam 10, after having been subjected to the plasma treatment in an equipment 12 according to the above-described procedure, is then impregnated with a dye solution by means of immersion in a trough 14.

The step for impregnating the textile article with substances suitable for the dyeing thereof occurs by immersing the textile article, arranged in a flat full width and possibly unwound from a feed beam, in a liquid bath contained in a suitably shaped container. The composition of the dye bath varies as a function of the type of textile article and the final characteristics that one intends to obtain, as is known in the field. Nevertheless, the improved hydrophilic nature of the textile article imparted by the treatment with ionized gas or plasma allows operating with high drive speeds, with lower quantities of dye auxiliaries and lower volumes of dye solution .

The immersion of the textile article in the dye bath serves to impregnate the fibres with the dye solution, possibly allowing, in addition to the formation of a liquid film attached to the fibres, also absorption of the dye solution in between the fibres.

It was surprisingly found that the plasma treatment in atmospheric pressure conditions increases the impregnation kinetics through an increased wettability degree of the substrate. The physicochemical process of impregnation is thus intensified. Indeed, the increase of affinity between the textile article and the dye liquor facilitates the processes of capillarity inside the structure of the textile article, allowing the liquid phase to be distributed in a uniform manner on the surface of the fibres during impregnation .

More specifically, due to the fact that the immersion time of the textile article in the dye liquor is within the range 0.5 s < t < 300 s, preferably within the range 5 s < t < 200 s, more preferably within the range 9 s < t < 15 s, one obtains a concentration difference of the dye which impregnates the textile fibres lower than 0.1% with respect to the average concentration obtained on the article being processed, i.e. one obtains a substantially uniform impregnation.

Following the immersion of the textile article, this is subjected to a squeezing operation carried out through the use of a mangle. Such operation is conducted with the objective of making uniform and redistributing the liquid mass adherent to the substrate, for augmenting the liquid portion absorbable by the fibres. Indeed, the mechanical squeezing action carried out by the mangle rollers causes the discharging of the exceeding liquid amount from the textile article. In addition, due to the mechanical compression action and to the so-called "sponge effect", the distribution uniformity of the liquid present in between the fibres of the manufactured article is considerably increased. At the end of this operation, the dye solution "pick-up", i.e. the amount of liquid adherent to the fibres of the textile article, is found to be on average comprised between 50% and 150% by weight, such values depending on the type of treated textile article .

Depending on the type of textile article to be dyed, the operating conditions of the first treatment step with plasma or ionized gas, and the composition of the dye bath, the impregnation step, also comprising the squeezing, can be repeated a second time to further increase the uniformity of the liquid quantity adherent to the textile article fibres.

The types of chemicals usable in the formulation of the dye bath, to be employed in a typical application of the process pursuant to the present invention, correspond with those normally used in exhaustion dyeing. As an example, a typical formulation of said solution can be composed by the following products :

dyes (approximate concentration in the range: 5 ÷ 50 g/kg _fibre )

acetic acid / sulphuric acid (in a quantity such that the solution has a pH = 2 ÷ 6)

ammonium sulphate (approximate concentration in the range: 0 ÷ 15 g/kg _fibre )

wetting agent (approximate concentration equal to: 0.1 ÷ 1% vol) .

The preferred operating conditions for the impregnation step are the following:

bath temperature between 25 and 102 °C, preferably between 50 and 100 °C, more preferably between 90 and 98 °C; drive speed from 0.1 to 80 m/min, preferably from 15 to 70 m/min, more preferably from 20 to 50 m/min;

- squeezing pressure from 0.5 to 5 bar, preferably from 2 to 4 bar, more preferably between 2.5 and 3 bar;

- immersion time from 0.5 to 300 seconds, preferably from 5 to 200 seconds, more preferably from 9 to 15 seconds.

The ageing step is the process step by means of which the dyeing process is completed, in terms of physicochemical interaction between the components of the dye solution and the fibres constituting the textile article. This operation consists of maintaining the textile article - that had been previously treated with plasma and impregnated - in controlled humidity and temperature conditions.

During the ageing, which, depending on the case, can last from a minimum of 15 min to a maximum of 20 hours, the physical process of dye diffusion in the fibre occur first, followed by the development of the chemical reaction processes between the dyes and the substrate molecules. If a wool textile article is treated, for the purpose of facilitating the dye diffusion in the fibre - required for successful dyeing - the ageing is preferably conducted at a temperature higher than the glass transition temperature.

The textile article subjected to ageing can be wound on a beam and suitably protected from undesired drying by suitable protection membranes, usually polymers, or by saturating (in terms of relative humidity) the ageing environment, or by using both means.

If one operates according to the above-described procedure, to prevent dye liquor percolation between the winding layers of the textile article, which would negatively affect the dyeing quality, the beam is maintained in a slow though constant rotation, with a number of turns preferably in the range 5 ÷ 8 rpm. By operating in such a manner, one prevents the percolation without generating centrifugation of the dye solution impregnating the fibres. The main operating conditions employed in the ageing step are the following:

temperature between 50 and 102 °C, preferably between 70 e 100 °C, more preferably between 90 and 98 °C;

- rotation speed from 1 to 20 rpm, preferably from 5 to 10 rpm, more preferably from 5 to 8 rpm;

ageing time from 0.25 to 20 hours, preferably from 1 to 15 hours, more preferably between 2 and 10 hours.

Several embodiments of the dyeing process according to the invention are illustrated below as non-limiting examples. Such examples refer to dyeing of wool-based fabrics.

For the purpose of ensuring a successful outcome of the process, it is necessary to suitably pre-treat the textile material by means of washing and drying of the same. In addition, as in all dyeing processes of conventional type, at the end of the ageing step it is opportune to subject the textile article, in this case a fabric, to a further washing, possibly executed open-width and aimed at removing the likely unfixed dyes and dye auxiliaries used.

EXAMPLES

The fabric that is the object of the dyeing process described in the following Examples 1, 2 and 4 is a fabric constituted by 100% by weight wool fibres and is characterized by a unitary weight of about 150 g/m ² . The fabric that is the object of the dyeing process described in the following Example 3 is a fabric constituted by 80% by weight wool fibres and 20% by weight nylon fibres, and this fabric is characterized by a unitary weight of about 150 g/m ² .

The plasma treatment, applied to the fabrics that are the object of the experiments described in the following Examples 1, 2 and 3, is executed in a continuous manner by using a cold atmospheric plasma equipment. Example 4 refers to an experiment in which the fabric is not subjected to any plasma treatment, and is therefore considered as a comparison example .

The process comprises the following operating steps:

- washing and drying

- plasma treatment

- impregnation

- ageing

- washing and drying.

EXAMPLE 1

Before being subjected to the dyeing process according to the present invention, the fabric is suitably washed and dried for the purpose of preparing the surface of the fibres to receive the dye solution. An open-width washing method is used; the washing liquor employed is an aqueous solution with 0.1% by volume of dispersing agent, maintained at the temperature of 60°C. At the end of the washing, the fabric is rinsed in water at room temperature, squeezed in a mangle and open-width dried until the water content is slightly lower than the moisture regain of the wool at room temperature.

With reference to the process diagram shown in Figure 2, indicated as a non-limiting example, the fabric 5 unwound from the beam 10 is pre-treated according to the above- indicated procedure. Then, the fabric is subjected to plasma treatment by using the equipment 12 with hybrid technology of cold atmospheric nitrogen plasma type, Post Discharge Plasma Jet .

The operating conditions employed in carrying out the plasma pre-treatment were the following ones:

electrical energy supplied to the generator = 1000 kJ/kg,

nitrogen flow rate = 1660 NL/kg,

drive speed of the fabric = 4 m/min,

drop absorption time (after plasma treatment) = 20 s. The plasma-treated fabric, characterized by a water drop absorption time close to 20 seconds, is then impregnated with the dye solution by means of immersion in the trough 14 and is subjected to a subsequent squeezing in the mangle 16.

The composition of the dye solution used was the following: monosulphonic premetallized dyes (~ 40 g/kg _fibre )

acetic acid (in a concentration such that pH = 3.5) wetting agent (0.1% by volume) .

The conditions of fabric immersion in the dye solution and relative squeezing were the following ones:

dye solution maintained at a temperature of 90°C, drive speed of the fabric = 4 m/min

immersion time of the fabric = 9 s

- pressure applied to the fabric during the squeezing step = 2.5 bar .

The impregnated fabric is wound on the beam 18 and subjected to ageing at the following conditions:

rotation speed of the beam = 8 rpm

duration of the ageing period = 10 h

- ageing temperature = 90 °C.

With the objective of preventing a possible drying of the fabric wound in the beam 18, the air present inside the ager is maintained saturated in terms of relative humidity.

At the end of the ageing process, the fabric is subjected to a washing and drying process. Such operation is carried out to facilitate the removal of the dyeing products in excess, improving the fastness of the colouration and allowing the neutralization of the fabric acidity.

The fabric dyed according to the modes pursuant to the present example was subjected to a quality control, carried out by evaluating the fabric fastness and the chromatic characteristics obtained. The evaluation of the fastness was carried out according to the current standards in the textile field, by conducting the tests listed in the following table

Fastness Reference standard Acidic perspiration Basic perspiration

Discharge on wool UNI EN ISO 105 - E04 5 5

Discharge on acrylic UNI EN ISO 105 - E04 5 4 material

Discharge on UNI EN ISO 105 - E04 4 4 polyester

Discharge on nylon UNI EN ISO 105 - E04 3/4 3

Discharge on cotton UNI EN ISO 105 - E04 4 4

Discharge on acetate UNI EN ISO 105 - E04 5 5

Dry Moist

With rubbing UNI EN ISO 105 - X12 5 3

With artificial light UNI EN ISO 105 - B02 5 Regarding the chromatic characteristics of the manufactured article, the tone and the colouration evenness were measured by means of a suitable visual analysis, receiving a positive evaluation, according to the opinion of the persons skilled in the art .

After having concluded the above-mentioned operations, the fabric can be subjected to conventional finishing processes, if provided for.

The quality of dyeing resulted optimal, without stain formation and/or coloration unevenness, exhibiting a more than suitable colourfastness .

EXAMPLE 2

The fabric, pre-treated according to the washing procedures described in Example 1, is subjected to an atmospheric continuous plasma treatment. This step is carried out by using an equipment with Corona type hybrid technology surrounded by atmospheric air, which provides for a front/back treatment of the fabric. Such technology does not imply the use of a specific process gas, since the gaseous means subjected to ionization is constituted by ambient air existing between the electrodes, carried in and refreshed by the movement of the treated fabric.

The employed operating conditions were the following ones: electrical energy supplied to the generator = 25 kJ/kg, drive speed of the fabric = 8 m/min,

- drop absorption time (after plasma treatment) = 15 s.

The fabric thus treated is impregnated with the dye solution by immersing in a trough and subsequently squeezing it in a mangle at the following operating conditions:

dye solution maintained at a temperature of 90°C,

- drive speed of the fabric = 8 m/min

immersion time of the fabric = 4.5 s

pressure applied to the rollers = 2.5 bar.

The composition of the dye solution used is the following: monosulphonic premetallized dyes (~ 40 g/kg _f i _br e)

- acetic acid (at a concentration such that pH = 3.5)

wetting agent (0.1% by volume) .

The impregnated fabric is wound on the beam and subjected to ageing at the following conditions:

rotation speed of the beam = 8 rpm

- duration of the ageing period = 10 h

ageing temperature = 90 °C.

With the objective of preventing a possible drying of the wound fabric, the air present inside the ager is maintained saturated in terms of relative humidity.

At the end of the ageing process, the fabric is subjected to a washing and drying process. Such operation is carried out to facilitate the removal of the exceeding dyeing products, improving the colourfastness and allowing the neutralization of the fabric acidity. The fabric dyed according to the modes pursuant to the present example was subjected to a quality control, carried out by evaluating its fastness and the chromatic characteristics obtained.

The fastness evaluation was carried out according to the current standards in the textile field, by conducting the tests listed in the following table:

FASTNESS Reference standard Acidic perspiration Basic perspiration

Discharge on wool UNI EN ISO 105 - E04 5 5

Discharge on acrylic

UNI EN ISO 105 - E04 5 5 material

Discharge on

UNI EN ISO 105 - E04 4 4 polyester

Discharge on nylon UNI EN ISO 105 - E04 4 3

Discharge on cotton UNI EN ISO 105 - E04 4 3/4

Discharge on acetate UNI EN ISO 105 - E04 5 3/4

Dry Moist

With rubbing UNI EN ISO 105 - X12 5 4

With artificial light UNI EN ISO 105 - B02 5

Regarding the chromatic characteristics of the manufactured article, the tone and the colouration evenness were measured by means of a suitable visual analysis, receiving a positive evaluation, according to the opinion of the persons skilled in the art .

After having concluded the above-mentioned operations, the fabric can be subjected to conventional finishing processes, if provided for.

The quality of the dyeing resulted optimal, without formations of stains and/or coloration unevenness, exhibiting a more than suitable colourfastness .

EXAMPLE 3 Before being subjected to the dyeing process according to the present invention, the fabric - made with 80% by weight wool fibres and 20% by weight nylon fibres, is suitably prepared according to the procedure described in Example 1. At the end of the washing, the fabric is rinsed in water at room temperature, squeezed in a mangle and open-width dried until obtaining a water content that is slightly lower than the moisture regain of wool at those conditions.

With reference to the process diagram shown in Figure 2, indicated as a non-limiting example, the fabric 5 unwound from the beam 10 is pre-treated according to the above- indicated procedure. Then, the fabric is subjected to plasma treatment by using the equipment 12 with atmospheric cold nitrogen plasma technology, APGD (Atmospheric Plasma Glow Discharge) .

The operating conditions employed in carrying out the plasma pre-treatment are the following ones:

electrical energy supplied to the generator = 30 kJ/kg, gas flow rate = 5 NL/kg,

- gas composition = 40% vol. He and 60% vol. Ar,

drive speed of the fabric = 8 m/min,

drop absorption speed (after plasma treatment) = 10 s.

The plasma-treated fabric, characterized by a water drop absorption time close to 10 seconds, is then impregnated with the dye solution by means of immersion in the trough 14 and is subjected to a subsequent squeezing in the mangle 16.

The composition of the dye solution used is the following: monosulphonic premetallized dyes (~ 100 g/kg _fibre )

acetic acid (at a concentration such that pH = 4.5)

- wetting agent (0.1% by volume)

The conditions of immersion in the dye solution and squeezing of the fabric are the following ones:

dye solution maintained at a temperature of 90°C, drive speed of the fabric = 8 m/min

immersion/impregnation time of the fabric = 4.5 s

pressure applied to the fabric during the squeezing step = 2.5 bar

The impregnated fabric is wound on the beam 18 and subjected to ageing at the following conditions:

rotation speed of the beam = 8 rpm

duration of the ageing period = 5 h

ageing temperature = 95 °C.

With the objective of preventing a possible drying of the fabric wound on the beam 18, the air existing inside the ager is maintained saturated in terms of relative humidity.

At the end of the ageing process, the fabric is subjected to a washing and drying process. Such operation is carried out to facilitate the removal of the exceeding dyeing products, improving the colourfastness and allowing the neutralization of the fabric acidity.

The fabric dyed according to the modes pursuant to the present example was subjected to a quality control, carried out by evaluating its fastness and the chromatic characteristics obtained.

The evaluation of the fastness was carried out according to the current standards in the textile field, by conducting the tests listed in the following table:

FASTNESS Reference standard Acidic perspiration Basic perspiration

Discharge on wool UNI EN ISO 105 - E04 5 5

Discharge on acrylic UNI EN ISO 105 - E04 5 5 material

Discharge on UNI EN ISO 105 - E04 4/5 4/5 polyester

Discharge on nylon UNI EN ISO 105 - E04 ¾ 3/4

Discharge on cotton UNI EN ISO 105 - E04 5 5

Discharge on acetate UNI EN ISO 105 - E04 5 5 Dry Moist

With rubbing UNI EN ISO 105 - X12 5 4/5

With artificial light UNI EN ISO 105 - B02 5

Regarding the chromatic characteristics of the manufactured article, the tone and the colouration evenness were measured by means of a suitable visual analysis, receiving a positive evaluation, according to the opinion of the persons skilled in the art .

After having concluded the above-mentioned operations, the fabric can be subjected to conventional finishing processes, if provided for.

The quality of the dyeing resulted optimal, without formation of stains and/or coloration unevenness, exhibiting a more than suitable colourfastness .

EXAMPLE 4

The present example is related to a fabric that is not subjected to any plasma treatment, hence characterized by a typically hydrophobic behaviour. The fabric is pre-treated according to the washing procedure described in Example 1 and subsequently subjected to dyeing by following only the padding and ageing steps. The washed fabric, not treated with plasma, characterized by a water drop absorption time of about 1800 seconds, is impregnated with the dye solution by immersing it in a trough and subsequently squeezing it in a mangle at the following operating conditions:

dye solution maintained at a temperature of 90 °C, drive speed of the fabric = 4 m/min

immersion time of the fabric = 9 s

drop absorption time > 3600 s

pressure applied to the rollers = 2.5 bar.

The composition of the dye solution used is the following: monosulphonic premetallized dyes (~ 40 g/kg _fibre ) acetic acid (at a concentration such that pH = 3.5) wetting agent (0.1% vol).

The impregnated fabric is wound on a beam and subjected to ageing at the following conditions:

rotation speed of the beam = 8 rpm

duration of the ageing period = 10 h

ageing temperature = 90 °C.

With the objective of preventing a possible drying in the fabric winding, the air existing inside the ager is maintained saturated in terms of relative humidity.

At the end of the ageing process, the fabric is subjected to a washing and drying process. Such operation is carried out to facilitate the removal of the exceeding dyeing products, improving the colourfastness and allowing the neutralization of the fabric acidity.

The fabric dyed according to the modes pursuant to the present example was subjected to a quality control, carried out by evaluating its fastness and the chromatic characteristics obtained.

The evaluation of the fastness was carried out according to the current standards in the textile field, by conducting the tests listed in the following table.

Fastness Reference standard Acidic perspiration Basic perspiration

Discharge on wool UNI EN ISO 105 - E04 3 2.5

Discharge on acrylic UNI EN ISO 105 - E04 4 3 material

Discharge on UNI EN ISO 105 - E04 3.5 3 polyester

Discharge on nylon UNI EN ISO 105 - E04 3 2.5

Discharge on cotton UNI EN ISO 105 - E04 3 3

Discharge on acetate UNI EN ISO 105 - E04 3.5 3

Dry Moist With rubbing UNI EN ISO 105 - X12 3 2

With artificial light UNI EN ISO 105 - B02 4

Regarding the chromatic characteristics of the manufactured article, the tone and the colouration evenness were measured by means of a suitable visual analysis, receiving a positive evaluation, according to the opinion of the persons skilled in the art .

The tests carried out showed that the textile articles subjected to a dyeing process according to the present invention had fastness and dyeing evenness values higher than those of the products dyed following conventional dyeing processes. This was due to the optimal combination of the plasma pre-treatment , which induces an increase of hydrophilic nature, with the subsequent operations of padding and ageing, which ensure uniform distribution and fixation of the dyes in the manufactured textile article.

As far as the characterization of the process is concerned, the water need, energy requirement and productivity values of dyeing operations by means of padding according to the present invention and according to the exhaustion dyeing method of conventional type are reported in Table 2.

Table 2

The results show the convenience of the dyeing process according to the invention with respect to the conventional process .

From the above-detailed description, the advantages deriving from the process for dyeing a textile article according to the present invention are clear; in particular:

the obtainment of a dyed textile article with high quality characteristics, i.e. which does not have zones with different dye intensity or colour stains or aggregates of chemical compounds on the textile article itself and is characterized by a high colourfastness ;

- the possibility to carry out a dyeing operation, applicable to many different types of textile articles, characterized by a high reproducibility;

the reduction of the process duration, and particularly of the time of contact between the textile article and the dye solution necessary to obtain a uniform impregnation;

the reduction of the amount of energy, water, dyes and chemicals used.

One particularly advantageous aspect of the atmospheric and continuously operating plasma generators, used in the process for dyeing a textile article according to the present invention, is given by their excellent operating performances .

In particular, the following advantages are indicated:

- a reduced energy consumption required for operating the equipment ;

no operation and maintenance problems associated to the use of vacuum pumps;

optimization of production cycles thanks to the treatment continuity.

It is clear that the process for dyeing a textile article according to the present invention, described herein by means of preferred embodiments provided as a non-limiting example, can be modified according to modes known to the man skilled in the art of the technical field, without departing from the protective scope of the present invention.