WO2005038125A1

WO2005038125A1 - Dyeing process for textile matter and obtained dyed matter

Info

Publication number: WO2005038125A1
Application number: PCT/EP2004/011902
Authority: WO
Inventors: Laurence Caramaro; Michel Lorthioir; Joric Marduel
Original assignee: Materials Technics Holding Sa
Priority date: 2003-10-21
Filing date: 2004-10-21
Publication date: 2005-04-28
Also published as: TW200523430A

Abstract

The present invention relates to a new process for the dyeing of textile matter, characterized in that the process uses an alternating electric field to impregnate at least one powdered dye in said textile matter. The process comprises the following steps: (i) introducing a textile matter to be dyed in a device able to produce an alternating electric field (ii) providing at least one powdered dye in said device, (iii) producing an alternating electric field able to apply the powdered dye on the textile matter to be dyed, (iv) and optionally fixing the powdered dye in said matter thereby obtaining a dyed textile matter.

Description

Dyeing process for textile matter and obtained dyed matter Field of the invention The present invention relates to a dry dyeing process for obtaining an impregnation and dyeing of matter. The invention is particularly suitable for dyeing textile matter and more in particular for dyeing polyester or polyester-containing blends. Background of the invention Textile finishing includes operations such as desizing, degreasing, bleaching and dyeing. Textile finishing has a significant economic weight in the textile industry. Textile finishing remains an obligatory step in the textile industry which valorizes and provides its finals characteristics to the textile product. Two types of processes for dyeing textile fibers exist: the exhaust or discontinuous dyeing and the impregnation or continuous dyeing which latter process allows continuous and batch operations alike. All these different exhaust or continuous processes use different types of dyes which may be soluble or not depending on their nature and on the type of support on which they will be used when dyeing. Various categories of soluble dyes are known: Acid dyes - which are used for dyeing wool and polyamide in acidic conditions. They are constituted of one or more sulfonate groups which render them soluble in water. Direct dyes - these dyes have also sulfonate groups but differ from the acid dyes in their affinity to cellulose and protein fibers such as cotton and wool.

Reactive dyes - their molecules contain a chromophore group together with a reactive chemical group permitting the formation of a covalent bond with the fiber. This bond takes place in alkali medium with the hydroxyl groups of the cellulose or the amino groups of wool and polyamide.

Basic dyes or cationic dyes. Theses dyes carry positives ions and are composed of large molecules. These dyes are water-soluble salts. They have direct affinity for wool and silk and can be applied to cotton. However, they are poorly resistant to light and are hardly used anymore. These dyes are mainly used for dyeing acrylic fibers with which good color resistance is obtained, even to sunlight.

Two main types of insoluble dyes are known: Vat dyes - these dyes are named vat dyes because they have to be first solublized in alkaline and reducing conditions before being applied. The dyeing process finishes by an oxidation step bringing the dye in its initial insoluble form in the fiber. Disperse dyes - These dyes although mainly used for dyeing polyesters, are also used for other synthetic fibers such as acetate, polyamide and the like. They are of small size and hydrophobic. Being insoluble, these dyes are applied in water as a suspension or dispersion. These dyes in contact with the fibers will sublime and will be able to migrate in the amorphous zones of the polymer. Other dyes exist which can be used punctually with supports of different natures. The following table shows the different possible associations depending on the chemical nature of the textile support, on the dyeing process used, either exhaustion or impregnation and on the nature of the dye. The table is not exhaustive.

It can be seen from the above table that few alternatives exist for dyeing polyesters and other synthetic fibers.

Textile dyeing uses large quantity of water which can be as high as 150 I per kg of treated matter. These waters charged with dyes and dyeing auxiliaries are an important source of pollution. In addition, the costs of used water, the costs for the treatment of non-used colored water, and the cost of the energy needed for drying after bath represents an important fraction of the total dyeing process costs. Polyester is generally dyed by padding. This process consists in applying regularly on the hydrophobic and smooth surface of the fibers finely dispersed dyes practically insoluble in water, such that they do not migrate during the drying conditions. The textile to be dyed is generally immersed in a dyeing bath and then squeezed using padders. Different type of treatments such as drying, thermal fixing, rinsing are needed to fix and stabilize the dye. The drying step aims in evaporating all the liquids present in the padding bath and impregnating the fabric, in order to obtain the dyes as a solid coating. The padding and the drying must be performed in one step and in a continuous manner since the film of dye and auxiliary products applied by padding is very sensitive to contact when humid. Thermal fixation or thermosoling is the step during which a part of the solid dye is transferred from the surface of the fiber into the fiber without any water or other liquids. Many drawbacks exist for the above mentioned processes. The results of thermosol dyeing depend mainly on the care with which one carried out the preliminary treatments of the textile. The defaults which could be made during the preliminary treatment can appear on the finished article. The textile must be treated in the same way and in the same intensity in its totality, so that the dye can be deposited or settled therein in a uniform way during padding and drying, and can penetrate regularly inside the fiber during thermosoling. Textile finishing is responsible for the majority of fossil energy consumption in the textile sector because of the wet processes which requires post drying and which accounts for 50% of fuel consumption of all the textile industry. With more than 600 GWh, the drying operation represents a great part of the energy consumption needed for textile finishing in France annually. In order to solve the problems of water or solvents based processes, alternatives dry dyeing processes were developed:

WO 97/13915 and DE-3906724 describe dyeing processes of textile fibers using supercritical C0₂. These processes use the solvation powers of C0₂ in its super critical state. This technology remains however marginal because it requires important and heavy means and represents a technological break compared to the processes used by the dyers.

US Pat. N° 3,941 ,559 describes a dyeing process by electrostatic projection using continuous voltage. The fabric is first dampened before being dyed and then passed between two electrodes which are arranged one on the top of the other. The dye is then deposited on the bottom electrode which is connected to a continuous high-voltage source. The charged dye particles are attracted towards the fabric to which the particles become bound thanks to its dampness. After applying the dye to the fabric, it is steamed or dried and heat fixed. An electrostatic pulverization process using continuous voltage has also been described, in which, initially, the powdered dye is added to auxiliary products and then fluidized in a spray chamber. The dye is then electrically charged using an electrode under high voltage and brought to the fabric to be dyed through a continuous electric field. The fabric to be dyed is in contact with a metal plate which can be heated. The pulverized dye is then fixed by heating the plate to a temperature needed for the sublimation and the fixing of the dye. The dye must have specific properties for fluidization, in term of particle size, and surface nature in order for the process to function. This process is thus complicated and can only be used with certain types of dyes and polyesters. The aim of the present invention is to provide a solution which permits the dyeing of fibrous or filamentous matter such as polyester in order to provide an efficient cost effective process likely to obviate, at least partially the disadvantages of the solutions known in the art. Summary of the invention The above mentioned aim is attained by the present invention as defined in the enclosed set of claims. To this end, the present invention provides a dyeing process of textile matter, characterized in that the process uses an alternating electric field, to impregnate at least one powdered dye in said textile matter. The process according to the invention comprises the use of an alternating electric field to cold impregnate the powdered dye in the textile matter. The present invention relates to a dyeing process comprising the following steps: (i) introducing a textile matter to be dyed in a device able to produce an alternating electric field (ii) providing at least one powdered dye in said device, (iii) producing an alternating electric field able to apply the powdered dye on the textile matter to be dyed, (iv) and optionally fixing the powdered dye in said matter thereby obtaining a dyed textile matter. In an embodiment steps (i), (ii) and (iii) are performed simultaneously. In another embodiment steps (i), (ii) and (iii) are performed in any order.

In a preferred embodiment of the present invention, the alternating electric field is a low frequency alternating electric field in the range of 1 to 1000 Hertz. In an embodiment of the present invention, the process comprises the steps of: (a) depositing at least one powdered dye on and/or underneath the textile to be dyed and (b) positioning said matter in an alternating electric field to impregnate said powdered dye in said matter to be dyed and (c) optionally fixing said powdered dye in said matter to obtain a dyed textile matter.. In an embodiment, in a preliminary homogenizing step, the powdered dye is first submitted to an alternating electric field. In a preferred embodiment of the present invention, the deposition of the powdered dye described in (a) may be performed with a preliminary dispersion or homogenization and blending of said dye in an alternating electric field as described hereunder. The process according to the present invention may comprise a preliminary step wherein said powdered dye is first dispersed by submitting it to an alternating electric field before being deposited on and/or underneath said matter to be dyed. In an embodiment of the present invention said electric field is ranging from 0.1 to 20 kV/mm. In a preferred embodiment of the invention, the dye impregnated in the matter is then fixed by means of a traditional fixing technique, such as thermal fixation, heat treatment, steaming treatment, high temperature steaming treatment, a treatment by microwaves or waves of radio frequency. In a preferred embodiment of the invention the fixing technique is thermal fixation. The process according to the invention permits the impregnation and the dyeing of textile surfaces and architectures with powdered dyes of different natures by the means of a low frequency alternating electric field.

This process is a dry process and is different from the existing processes in that it neither employs water, nor solvent. It allows moreover obtaining a homogeneous blend of fibers and powders. It makes it possible to impregnate in only one step large thicknesses of matter with a good reproducibility. In addition, it may be applied to a large variety of textiles and powders being thus suitable to very different fields of applications. The process according to the invention permits to carry out the impregnation of the fibers without thermal contribution or heat, and without using solvent or water. The advantages of the process of the present invention compared to traditional processes are: absence of solvents and thus of pollution, absence of water (heated) and thus low energy consumption. The present invention permits to obtain a homogeneous impregnation and to reduce the quantities of auxiliary products used. The process according to the invention can be performed in a continuous or in a discontinuous manner alike. In a preferred embodiment of the invention, not only the dyeing is performed continuously but also the fixation of the dyes on the matter to be dyed. The process according to the invention is particularly suitable for the printing of patterns, drawings, letters, continuously or discontinuously, using one or more colors, by depositing the powdered dye with a stencil system or the like. The process of the invention is adapted to the dyeing of materials such as natural, synthetic or artificial fibers of organic nature, which can be chemically modified or not. These fibers can be selected from the group comprising fibers or thread of polyester, polyamide, aramide, acetate and polyacetate fibers, the chlorofibers, acrylic fibers, polypropylene, polyurethanes, polyamide-imides, PVC fibers, polyvinyl fibers, polyacrylonitrile fibers, cotton, wool, flax, silk and any blend thereof. The present invention is particularly adapted for the dyeing of polyester fibers or blends comprising polyester and other natural or synthetic fibers. The preferred dyes according to an embodiment of the present invention are the disperse dyes, but other types of dyes can also be used. In the case of the dyeing of pure polyester or blend of polyester and other fibers, the process according to the present invention can be used to replace the padding of the disperse dyes usually necessary to the dyeing of the polyester part. A polyester/cotton blend can also be dyed according to the process of the invention, by using vat dyes able to dye at the same time polyester and cotton. These vat dyes can be applied in a similar way than the disperse dyes, in a continuous manner for example, using the process of the invention. After impregnation of the dyes by the process of the invention, the impregnated textile is then subjected, classically, to padding with an alkaline reducing agent and to steam fixing to finalize the dyeing of the cotton. When the process uses disperse/reactive dyes, it is possible to dye in two times: the disperse dyes are then applied by the process of the invention and are thermally fixed before passing through the padders of reactive dyes which will in their turn be fixed in a traditional way on the cotton. The process according to the invention thus makes it possible to impregnate reactive and disperse dyes together, to thermally fix the disperse dyes, and then to process the matter through a padder comprising the products needed for the dyeing of reactive dyes and to fix them in a traditional way.

The process of the invention is also applicable to the dyeing of other blends comprising polyester and other fibers such as wool, polyamide and acetate. The process according to the invention, also allows the use of a mixture of disperse/vat dyes. In this case the dyeing can be carried out by impregnating all together the vat and disperse dyes. A drying would follow then a thermal fixation. The matter can then be padded with an alkaline reducing agent, steamed, re-oxidized and then soaped to fix the vat dye. The process according to the present invention can be also carried out with solubilized dyes such as naphthol and sulfur dyes, in so far as these dyes originally insoluble can be impregnated directly within the fiber before being solubilized. Thereafter they are made insoluble again. The same applies to reactive dyes, which must be fixed to the fiber following a chemical reaction. The use of these dyes in the process of the present invention allows the dyeing of textile matters such as cotton, wool and polyamide. In an embodiment of the invention, the at least one powdered dye used is selected from the group comprising disperse dyes, plastosolubles, reactive dyes, vat dyes, solubilized dyes such as naphtol and sulfur dyes or a mixture thereof. Preferably, the at least one dye used is a disperse powdered dye. The process according to the invention allows the use of powdered dye without additive, and in particular without solubilizing agent. The process of the invention thus permits to make savings on the quantity of water used and on some dyeing auxiliary products used, as well as on the energy needed for heating. Thanks to the process of the invention, several dyes can be impregnated simultaneously in the matter to be dyed. The process according to the invention allows also the consecutive application of powdered dyes. The process can thus be used to first impregnate a first type of dye on the matter to be dyed, then in a second step to impregnate the matter treated beforehand, with another type of powdered dye. The process according to the invention permits minimizing the quantity of dyes used, especially when these dyes are expensive. Savings in the costs of raw materials can thus be made by using the process of the invention.

The process according to the invention also permits regulating in less than ten minutes the dyeing intensity, during continuous dyeing, according to the product obtained, by the adjustment of the quantity of powdered dye deposited on and/or underneath the matter to be dyed.

The process of the invention is also effective to print patterns such as lines or other decorative elements. It allows the use of stencil systems and the printing of multicolored patterns by the use of several successive scattering devices. Using the process of the invention for dyeing, allows to avoid the use of padders and to reduce considerably the tension during the processing of the matter. The process of the invention allows the dyeing of knitted items contrarily to the padding/thermosol process, with which it is not possible to dye knitted items because of the tension which deforms these items. Other features and advantages of the present invention will become apparent on reading the description which follows and the examples illustrating it. Brief description of the figures Figure 1 represents a schematic view illustrating the operation of the dyeing process of the invention according to an embodiment of the invention. Figure 2, 3, 4 and 5 represent schematic views illustrating different embodiments of the process according to the invention, wherein a preliminary step in the process comprises submitting the powdered dye to an alternating electric field. Detailed description of the invention The process according to the invention permits the impregnation and the dyeing of textile surfaces and architectures with powdered dyes of different natures by means of a low frequency alternating electric field. . The terms "matter", "textile", "textile matter" or "fabric" are presently used interchangeably, and relate to all porous, fibrous or filamentous materials which can be subjected to a dyeing process according to the invention. The articles "a" and "an" are used herein to refer to one or to more than one, i. e. to at least one, the grammatical object of the article. By way of example, "a dye" means one dye or more than one dye.

The terms "machine" or "treatment unit" are presently used interchangeably and refer to the device for implementing embodiments of the present invention.

The dry dyeing process of the invention can replace the traditional wet processes and has the following advantages: absence of solvent and thus of pollution, considerable reduction of the quantity of auxiliary products used, absence of heated water and thus lower energy consumption compared to the traditional processes. The process according to the present invention allows moreover obtaining homogeneous impregnation of the treated matter.

The process according to the invention comprises the following steps: a) depositing a powdered dye on the surface of the matter to be dyed, b) applying a low frequency and high voltage alternating field allowing a homogeneous impregnation throughout all the thickness of the matter, and c) a thermal fixation step allowing the dye to sublimate and migrate in the structure of the fiber. This step can be carried out using various manners depending on the studied support and on the dyeing quality required. Non-limiting examples of thermal fixation include for example: dry heat thermal fixation, wet heat thermal fixation, a calendering of the type used during print transfer making it possible to confine the impregnated support and to diminish the losses of dyes during sublimation and to force the dye to dissolve in the structure of the polymer by applying pressure during calendering. In an embodiment of the invention, the matter to be dyed can have undergone beforehand a dyeing operation by means for example of the process according to the invention or by means of another traditional process. In an embodiment of the invention, a preliminary step of the process comprises scattering the powder to be impregnated on the top of the textile matter. The powdered dye can be deposited on the matter to be dyed or on the belt conveying the matter to be dyed or on both. This powder can be homogenized and dispersed beforehand by submitting it to an alternating electric field of 0.1 to 20 kV/mm. This process allows applying directly, in situ, in the powdered dye the energy needed to mix, disperse and/or homogenize the dye, apparently by displacement and mutual repulsion of the dye particles or grains thereof. The low frequency alternating electric field can be produced in the space separating two electrodes connected to the poles of an AC generator. These electrodes are generally isolated electrically from each other by a dielectric. The generator, the electrodes and the dielectric which can be used for implementing the scattering and/or homogenization of the powdered dye are the same as those described hereunder for the dyeing and impregnating process according to the invention.

To obtain a given degree of mixing, dispersing and/or homogenizing effect of the powdery matter requires applying the alternating electric field during a sufficient duration. The duration depends in particular on the nature and the inhomogeneity degree of the powdered dye and on other parameters of the process, such as the intensity and the frequency of the alternating field, the shape of the signals and the electrodes configurations. The sufficient duration will be easily determined by the man skilled in the art and routine experiments. In general it is less 0.1 s, often less then 0.5 s, in particular less than 2s. While not wishing to be bound by any particular theory, it is believed that a plausible mechanism to explain the mixing, dispersion and/or homogenization effect of the alternating electric field on the powdered dye seems to be as follows: the alternating electric field may successively charge the powdered dye and accelerate it towards the electrodes connected to the two poles of the high-voltage generator. The powdered dye then fully occupies the space available between the electrodes. As each grain of powdered dye receives electric charges of the same sign, a mutual repulsion of the particles will be observed which could explain the specific homogenization, dispersion or mixing capacity. The powdered dye will be thus perfectly dispersed and mixed and the eventual agglomerates will be separated. The separation of agglomerates is believed to also take part in the homogenization of the powdered dye. The powdered dye can be formed of only one dye of a given chemical nature and particle size, or of several dyes of different chemical nature and/or particle size. The matter thus covered with the powder can then be placed in the treatment unit and be subjected to a high voltage and low frequency alternating electric field in order for the powder to penetrate in the matter. In certain cases, and in particular when the matter is very thick or not very porous, it is possible to carry out all together a scattering on the top and underneath the matter to be dyed by scattering part of the powder on the lower belt which introduces the matter into the treatment unit. Scattering is generally carried out on the whole surface of the matter to impregnate. In certain cases, it is possible to use a localized scattering or to use a stencil to impregnate only certain zones of the matter. Once the powder deposited on the matter to be dyed, an alternating electric field is used. This alternating electric field can be produced in the space separating two series of electrodes connected to the poles of an AC generator. A high-tension generator can be used to generate the alternating electric field. This low frequency generator can comprise one or more high voltage transformers able to raise the voltage delivered by a primary variable- oltage regulator which can be constituted of an auto-transformer. One of the poles of the AC generator is the phase and the other pole is the neutral which is in general connected to the ground for safety reasons, in particular when the AC generator is a high- voltage generator. The frequency of the high-voltage generator can be variable in order to optimize the impregnation performances depending on the nature and the particle size of the powder to be impregnated. The frequency may vary in a range of 1 Hertz to 1000 Hertz depending on the situation, this range being in the low frequencies domain. The shape of the electric signal applied to the electrodes also influences the impregnation of the powder. Square, sinusoidal or triangles signals can be employed as well as more complex signals forms. In a preferred embodiment of the invention, the matter to be dyed is positioned perpendicularly to the alternating electric field. In particular the matter to be dyed circulates perpendicularly to the alternating electric field. In a preferred embodiment of the invention, the process is characterized in that the alternating electric field used has a voltage of at least 0.1 kV/mm for a duration of at least 2 s, preferably between 5 kV/mm and 100 kV/mm for a duration between 5s and 100s, more preferably between 10 kV/mm and 50 kV/mm for a duration between 15 s and 50 s. The feeding speed of the continuous processing machine depends: on the treatment duration which is needed for a particular application, and on the application length of the electric field, and therefore on the length of the machine. Depending on the situation, the feeding speed can be adapted to the needs of the production, particularly by adapting the length of the machine, from for example less than 1m/min to 100 m/min, and more if necessary. In an embodiment of the invention, the process is preferably implemented by using a treatment unit generally comprising two series of electrodes connected on the one hand to the phase of a high voltage supply and on the other hand to the neutral of the same high- voltage generator. The neutral could itself be connected to the ground in particular when the high-voltage generator consists of a high voltage transformer.

According to an embodiment, the electrodes comprise strongly conducting elements in order to guarantee an equivalent voltage over all their length and to minimize heat loss by warming. Metals such as for example copper, nickel, aluminum, silver or gold are particularly suitable therefor.

A system of insulators, also called dielectrics, covers at least one of the electrodes in order to constitute an electric insulation limiting the current between the electrodes to avoid the appearance of an electric arc constituting a short-circuit when using an electric field higher than the air dielectric strength.

The insulators used in the process have preferably a high dielectric strength and a good behavior on ageing. Materials like quartz, glass, ceramics, alumina show interesting characteristics to constitute these dielectrics. These materials can accumulate a low quantity of space charges when subjected to an electric field. Quartz is particularly appreciated as dielectric insulator because of its high dielectric strength and good behavior on ageing. The thickness of the dielectric depends on the level of electric field applied to the electrodes. Dielectric thicknesses of 1 mm to 20 mm are appropriate with preferably thicknesses ranging between 2 and 5 mm. Depending on the strength of the field applied to the material, it is possible to isolated only one electrode's pole or both. The maximum insulation will be obtained with a dielectric insulator on both electrodes' poles. For materials being able to be impregnated with an electric field lower than the air breakdown voltage, it is possible to use directly air as insulator between the metal electrodes. The electrodes permit to apply an alternating electric field to the matter to be dyed and to the powder. The shape of the electrodes should favor an intense electric field on the material. Plane electrodes permit obtaining a large uniform field on the whole of the treatment and impregnation surface of the matter to be treated. Tubes or other sections can also be used as electrodes. These electrodes permit to carry out treatments over widths superior to 2 meters. These tubular electrodes can present a circular, rectangular section or a form making it possible to apply a uniform or concentrate field. Similarly to the plate electrodes, the tubular electrodes can comprise a dielectric and a metal part allowing to apply voltage on the surface of the electrode. Various configurations can be used to arrange these tubes and to apply an electric field to the product to be impregnated. Depending on the matter to be dyed, on the feeding speed and on the impregnation duration sought, a more or less important spacing between the tubes of same potential can be retained. The tubes can for example be arranged in quincunx, or opposite each other. It is also possible to use mixed shapes of electrodes by combining different forms on the side connected to the phase and on the side connected to the neutral of the high-voltage generator. For all the different types of electrodes suitable for the process, the interelectrode distance can be adjusted according to the nature and the geometry of the powder and of the fibrous or porous network to impregnate. The interelectrode distance can be fixed for the whole of the treatment zone or can vary between the entry and the exit so as to have different electric fields for different zones. For example, a weaker field can be needed at the exit of the matter to homogenize the powder in the material. Generally, the interelectrode distance can vary from 1 mm to 200 mm depending on the nature and the thickness of the matter to be dyed.

A non-limiting example of a treatment unit which can be used for implementing the process of the invention is shown in Figure 1. The treatment unit comprises two electrodes 5 and 6 connected to a high-voltage AC generator 4. The treatment unit further comprises two dielectric plates 7 and 8 covering the electrodes 5 and 6 allowing the uniform repartition of the electric field and avoiding the direct discharges between the electrodes 5 and 6. The powdered dye 2 is first scattered on the surface of the matter to be dyed 1 and then the scattered matter is introduced continuously into the unit treatment. The matter to be dyed can circulate by feeding or for example by means of two conveying belts. The textile sample 1 on which the powder 2 was deposited will circulate between the dielectric plates 7 and 8. The distance between dielectrics is adjusted according to the thickness of the textile and/or the impregnation percentages to be obtained. Under the effect of the high voltage alternating field 3 applied to the electrodes 5 and 6, the air between the dielectric 7 and 8 ionizes by plasma effect thereby charging by induction effect the powder grains 2 and the textile fibers 1. The grains charged and accelerated by the electric field 3 will be able to occupy the space between the dielectric 7 and 8 and to penetrate in the matter as a result of their kinetic energy. The successive shocks on the fibers and the repulsion of the grains of the same sign will allow, according to the porosity of the textile, a homogeneous diffusion of the powder in the matter to be dyed. At the exit of the unit treatment, the powder is impregnated in the matter 9. Once the matter impregnated with the powdered dye, the dye can be fixed by thermal fixation. The thermal fixation can be carried out at a temperature between 70 and 240 °C, and can last from 0.1 to 10 minutes. The most adapted dyes for this process are preferably dyes which sublimate. In a preferred embodiment of the invention, one can use disperse or plastosolubles dyes. Other dyes can be used such as vat dyes and some reactive dyes which are also likely to sublimate and migrate entirely or partially in the thickness of the fiber. The process according to the present invention can also be carried out with solubilized dyes such as naphthol and sulfur dyes, but also with anionic or metallized dyes.

In an embodiment of the invention, the at least one powdered dye used has a particle size between 0.1 μm to 100 μm, preferably between 0.5 to 60 μm, more preferably between 0.5 to 20 μm

The quantity of dye scattered on the matter to be dyed depends on the color to be obtained. For example, one can deposit between 0.1 to 50% powdered dye on the matter to be dyed, preferably between 0.5 and 30 % and more preferably between 0.9 and 10 %. The process of the invention allows a homogeneous application of the dyes because of a uniform scattering. The problems of evenness observed in the prior art for example during a nonhomogeneous padding, are removed thanks to the process of the present invention. This advantage is of primary importance because to take up again a dyeing, either by stripping or by clearing, is expensive and takes a long time. In a preferred embodiment of the present invention, the powdered dye is preferably homogenized and/or mixed by means of an alternating electric field. An embodiment for implementing this preliminary step is illustrated on figure 2, in which the dye is scattered on the conveying belt. In this assembly the powdered dye 2 is stored in the hopper 10 of a scattering device before being scattered thanks to the rotation of an engraved or needle cylinder 11. A brush 12 flakes off and separates the dye grains which fall then by gravity on the conveying belt 16. In this assembly the homogenization process uses two plate electrodes each composed of a metal part 14 and of an insulator 15 and connected to a high-voltage AC generator 13. This device is used to disperse and homogenize the powdered dye 2 on the surface of the conveying belt 16 fed by means of a motorized device 17. The powder thus dispersed and homogenized on the surface of the conveying belt is then covered with the matter to be dyed 1 so as to be impregnated/dyed by the process according to the invention, for which an embodiment thereof is illustrated on figure 1. In the assembly of figure 3 the operating mode is identical to that of figure 2, with the difference that the powdered dye distributed on the belt 16 is transferred on the top of the matter to be dyed 1 which is fed on another belt 18 moving by means of a device 19. This assembly allows depositing the powdered dye on the matter to be dyed without having to have a subsequent homogenization step. The matter to be dyed on which the dye was deposited can be then subjected to the dry dyeing process of the invention.

In the assembly of figure 4, the operation is identical to that described above with the difference that the device for homogenization by the alternating electric field is directly positioned under the infeed cylinder of the scattering device 11. In this case, the alternating electric field is applied to the powdered dye 2 by the electrodes 14 which are covered with dielectric plates 15 and connected to the high-voltage AC generator 13, the electrodes being arranged vertically.

In this embodiment, the powdered dye 2 is distributed on the belt 16. The flow of operation is not shown, the powdered dye dispersed and homogenized on the surface of the conveying belt is then covered with the matter to be dyed 1 which will be impregnated/dyed by the process according to the invention, for which an embodiment thereof is illustrated on figure 1. In the assembly of figure 5, the operation is identical to that of figure 4. In this case, the alternating electric field is applied to the powdered dye 2 by the electrodes 14 covered with the dielectric plates 15 and connected to the high-voltage AC generator 13, the electrodes being arranged vertically. In this embodiment, the powdered dye 2 is directly scattered on the top of the matter to be dyed 1 fed on a belt 16 moving by means of device 17. This assembly allows depositing the powdered dye on the matter to be dyed without having to have a subsequent homogenization step. The matter to be dyed on which the dye was deposited can be then subjected to the dry dyeing process according to the invention. The process of the invention is flexible and allows modifying the dyeing conditions during the production. For example, if when starting the production, the color obtained does not appear adequate, the scattering device is adjusted again so as to obtain the desired color. This operation is fast, simple and allows not losing too much raw material. Thanks to the process of the invention, the sublimation of the uniformly distributed dye in the fiber will take place within the fiber. The transfer is thus very effective and shorter compared to the padding/thermosoling process. The process of the present invention allows energy savings compared to the processes of the prior art by avoiding the use of heated baths, and by removing the drying step since the dye is directly impregnated in its solid form. That allows making savings on the cost of the heating and drying machines, and on the cost of the energy needed for said drying and heating. The process also allows a significant water savings and avoids the very expensive problem of processing the colored liquid waste left after bathing and padding. It also permits to avoid the disposal of these effluents. Using the process according to the invention allows moreover another significant financial saving thanks to the reduction of the costs of raw materials and logistics. The process of the invention avoids using auxiliary dyeing products and does not produce polluting liquid waste, contrarily to the processes of the prior art. All the textile matters likely to be dyed with dyes which sublimate can be used in the process of the invention. The matter to be dyed can be in the form of fiber, thread, set of yarns, variable length lap, mat, strand, and preferably woven fabrics, knitted fabric, braid, non-woven materials, whatever their thickness. The thickness of the textile matter which can be used in the present invention can vary 0.1 μm to 190 mm. The process of the invention is particularly adapted to the dyeing of all natural, synthetic or artificial fibers of organic nature chemically modified or not or a blend thereof. The invention is particularly adapted to the dyeing of fibers or thread of polyester, polyamide, aramide, acetate and polyacetate fibers such as the triacetate, chlorofibers, acrylic fibers, polypropylene, polyurethanes, polyamide-imides, PVC fibers, polyvinyl fibers, polyacrylonitrile fibers, cotton, wool, flax, silk, and any blend thereof, as well as all other synthetic, natural or artificial fibers of organic nature which can be chemically modified or not, and blends thereof. In an embodiment of the invention, one will use polyester of the type PET, PBT, PTT and copolyester or any other polymer of similar chemical nature. These polyester fibers are preferably dyed with disperse dyes. Non-limiting examples of polyester suitable for the process of the present invention comprise amongst other things polyethylene terephtalate, polycarbonates, and the like. In another embodiment, one will use polyamide or any polymer of close chemical nature such as copolyamide. The polyamide can be dyed using the process of the invention with dyes of the anionic or metallized type but also with disperse dyes, which are particularly interesting from an economical point of view for certain applicability such as stockings and pantyhose. The disperse dyes migrate very well and, taking into account their fixation mode, cover the irregularities well. The acetate and triacetate fibers or threads, fibers such as the chlorofibers, acrylic resin, polyurethanes and the polyamide-imides can be dyed according to the process of the invention with disperse dyes.

All synthetic, natural or artificial fibers of organic nature which can be chemically modified or not, can be dyed according to the process of the present invention, even if fastness to dyeing of the dyes which sublimate is not satisfactory; this effect can be sought by the dyer.

In a preferred embodiment of the invention, the matter to be dyed is selected from the group comprising polyester, blends based on polyester and on other fibers comprising acetate and poly-acetate, polyamide, PVC and comprising cotton, wool, silk, flax or other natural fibers.

The present invention encompasses also any dyed textile matter which will have been obtained by a dyeing process according to the process of the invention. The following examples illustrate some features of the present invention, without, however, limiting the scope of the application. Examples: Example 1: The tests were performed with a commercial blue dye of the disperse type having small molecules. The matter to be dyed used in the process of the present invention is a polyester woven fabric (polyethylene terephtalate) of 150 g/m² and a twill weave. The impregnation tests were performed with electrode plates under a 35 kV voltage during 30 seconds. Thermal fixation was performed either in a hot-flue dryer with dry heat at 210 °C or in a steamer at 210 °C and 100 % relative humidity. The tests allowed obtaining very good results in term of color and homogeneity. The particle size of the dye is an important factor; apart from the quality of the dispersion which depends on the particle size, thermal fixation duration is strongly related also to the size of the aggregates present at the surface of the fabric, which conditions the kinetics of sublimation of the dye. The thermal fixation tests in wet heat (steamer) give good results in term of evenness quality and can be preferred to thermal fixation in hot-flue dryer. Example 2: Complementary test with calendering fixation. The tests of this example were carried out with a commercial red dye of the disperse type with middle size molecules. The matter to be dyed used in the process of the invention is a polyester fabric (polyethylene terephtalate) of 150 g/m² and twill weave. The impregnation tests were performed with electrode plates under a 35 kV voltage during 30 seconds. Thermal fixation of the impregnated dyes was performed on a printing transfer calender adjusted at 200 °C. The dyeing results were very good in term of color and evenness and allowed to obtain a red woven fabric of an equivalent quality than the one obtained with the Pad-Thermosol process of reference.

Example 3: Comparative tests: influence of the process according to the invention

Tests were carried out by using the process according to an embodiment of the present invention, and as a comparative test, a simple scattering without using the impregnation module according to the invention. The tests were performed with a commercial blue dye of the disperse type having small molecules. The matter to be dyed used in the process of

Claims

the present invention is a polyester woven fabric (polyethylene terephtalate) of 150 g/m² and a twill weave. The conditions used during the dyeing according to the invention were the followings: Dye rate about 3%. Impregnation 35 kV, 30 s, Thermal fixation: 210°C, 6 minutes. The conditions of the comparative example for which the process according to the invention was not used were as follows: Dye rate about 3%. Thermal fixation: 210°C, 6 minutes. In the case where the sample was not treated by the process of the invention a less good evenness of the dye was obtained resulting in a significant spotty effect. Moreover, the dye did not go through the fabric and consequently only one side of the fabric was dyed. It is thus noted that the impregnation and the dyeing by means of the process of the invention allows the dispersion of the grains of dye in a much more uniform manner thereby allowing obtaining good evenness. In the case of an impregnation according to the invention, the dyeing phenomenon is identical on both sides of the fabric although the scattering was carried out only on one side. Example 4:

The tests of this example were carried out with a commercial red dye of the disperse type having a good lightfastness (dye for the automotive industries). The matter to be dyed used in the process of the invention is a polyester fabric (polyethylene terephtalate) of 300 g/m². The dyeing was performed with 2% dye per fabric weight. The impregnation tests were performed with electrode plates under a 35 kV voltage during 30 seconds. Thermal fixation of the impregnated dyes was performed on a printing transfer calender adjusted at 200 °C.

The dyeing results were very good in term of color and evenness and allowed to obtain a red woven fabric of the same quality than the one obtained with the Pad-Thermosol process of reference. Total energy consumption was strongly reduced as a result of using the dry process of the invention. The absence of residual dyeing baths and of auxiliary products reduced the pollution and the costs of dyeing. Claims 1. Process for the dyeing of textile matter, characterized in that the process uses an alternating electric field to impregnate at least one powdered dye in said textile matter.

2. Process for the dyeing of textile matter, comprising the following steps: (i) introducing a textile matter to be dyed in a device able to produce an alternating electric field (ii) providing at least one powdered dye in said device, (iii) producing an alternating electric field able to apply the powdered dye on the textile matter to be dyed, (iv) and optionally fixing the powdered dye in said matter thereby obtaining a dyed textile matter.

3. Process according to claim 1 or 2, wherein said alternating electric field is a low frequency alternating electric field in the range of 1 to 1000 Hertz.

4. Process according to any of claims 1 to 3, wherein the process comprises the steps of: (a) depositing at least one powdered dye on and/or underneath the matter to be dyed, (b) positioning said matter in an alternating electric field to impregnate said powdered dye in said matter to be dyed and (c) optionally fixing said powdered dye in said matter to obtain a dyed textile matter.

5. Process according to any of claims 1 to 4, wherein in a preliminary homogenizing step said powdered dye is first submitted to an alternating electric field.

6. Process according to claim 5, wherein said electric field is ranging from 0.1 to 20 kV/mm.

7. Process according to any of claims 1 to 6, wherein the matter to be dyed is positioned perpendicularly to the alternating electric field.

8. Process according to any of claims 1 to 7, wherein the alternating electric field used has a voltage of at least 0.1 kV/mm for a duration of at least 2 s, preferably between 5 kV/mm and 100 kV/mm for a duration between 5s and 100s, more preferably between 10 kV/mm and 50 kV/mm for a duration between 15 s and 50 s.

9. Process according to any of claims 1 to 8, wherein the dye impregnated in the matter is further fixed by means of a classical fixation technique.

10. Process according to claim 9, wherein the fixation technique is thermal fixation.

11. Process according to claim 10, wherein the thermal fixation is performed by a heat treatment, a steaming treatment, a steaming treatment at high temperature, a treatment by microwaves or radio frequency waves.

12. Process according to claim 10 or 11 , wherein said thermal fixation is performed at a temperature ranging from 70 to 240 °C.

13. Process according to any of claims 10 to 12, wherein the duration of the thermal fixation step is from 0.1 to 10 min.

14. Process according to any of claims 1 to 13, wherein said process is carried out in a continuous manner.

15. Process according to claim 14, wherein said dyeing and said thermal fixation are performed in a continuous manner.

16. Process according to any of claims 1 to 15, wherein said process is performed in a discontinuous manner.

17. Process according to any of claims 1 to 16, wherein the at least one powdered dye used is selected from the group comprising disperse dyes, plastosolubles, reactive dyes, vat dyes, solubilized dyes such as naphtol and sulfur dyes or a mixture thereof.

18. Process according to claim 17, wherein the at least one dye used is a disperse powdered dye.

19. Process according to any of claims 1 to 18, wherein the at least one powdered dye used has a particle size between 0.1 μm to 100 μm, preferably between 0.5 to 60 μm, more preferably between 0.5 to 20 μm.

20. Process according to any of claims 1 to 19, wherein between 0.1 to 50% of powdered dye is deposited on the matter to be dyed, preferably between 0.5 and 30 % and more preferably between 0.9 and 10 %.

21. Process according to any of claims 1 to 20, wherein the matter to be dyed is selected from the group comprising natural, synthetic or artificial fibers of organic nature which can be chemically modified or not or a blend thereof.

22. Process according to claim 21 , wherein said natural, synthetic or artificial fibers of organic nature are selected from the group comprising fibers or thread of polyester, polyamide, aramide, acetate and polyacetate fibers such as the triacetate, chlorofibers, acrylic fibers, polypropylene, polyurethanes, polyamide- imides, PVC fibers, polyvinyl fibers, polyacrylonitrile fibers, cotton, wool, flax, silk, and any blend thereof

23. Process according to any of claims 1 to 22, wherein the matter to be dyed is selected from the group comprising polyester, of blends based on polyester and other fibers comprising acetate and poly-acetate, polyamide, PVC and comprising cotton, wool, silk, flax or other natural fibers.

24. Process according to any of claims 1 to 23, wherein the textile matter to be dyed is selected from the group comprising fibers, threads, set of yarns, variable length laps, mat, strands, woven fabrics, knitted fabrics, braid and non-woven materials

25. Process according to any of claims 1 to 24, wherein the matter to be dyed has undergone beforehand a dyeing operation.

26. Process according to any of claims 1 to 25, for the printing of patterns, drawings, letters, continuously or discontinuously, using one or more colors, by depositing the powdered dye with a stencil system and the like.

27. Dyed textile matter obtained by the process as defined in any of claims 1 to 26.