The present invention relates to a device for the dosage and chemical reduction, in a continuous cycle, of dyes in powder form, as microbeads or aqueous dispersion, such as indigo, for example, used in dyeing processes to which the yarn chains of warp for fabrics are subjected in a continuous cycle. In particular, the invention relates to a device which can be used in continuous-cycle machines and/or dyeing plants, which must operate with reduction baths .

A typical application of this dyeing technology is continuous-cycle dyeing with indigo of the chains of warp for denim fabrics.

Denim is the fabric normally used for the manufacturing of jeans and sportswear articles in general and is the fabric which is quantitatively most widely produced in the world and indigo is consequently the most widely-used dye in the world. Classic denim is produced for the weaving of predyed cotton threads . In particular, only the warp is dyed in continuous, whereas the weft is used untreated.

Typically and traditionally, the dying of chains of warp for denim fabrics is effected by means of the so- called "ring-spun" or "open-end" system, in open tanks, at low temperature, using indigo as dye. Indigo is an ancient natural dye, produced by synthesis for over 100 years, in the commercial forms of powder, microbeads, or in aqueous dispersion and, for the last ten years or so, also in concentrated aqueous solution (leuco) .

Indigo dye requires a characteristic dyeing process for its application to cotton yarn. This dye, in fact, having a relatively small molecule and a low affinity for cellulose fibres, requires for its application to said fibres, not only that it be chemically reduced into an alkaline solution (in leuco form) but also a plurality of impregnations interspersed by squeezing and subsequent air oxidation.

In order to obtain a "blue denim" with a medium or dark colour intensity, the yarn must therefore be subjected to a first dyeing (subdivided into impregnation, squeezing and oxidation phases) immediately followed by various over-dyeings, the darker the shades and higher the solidity requested, the more numerous these will be.

The above-mentioned dyeing process is at present applied in all continuous-cycle dyeing machines and plants with indigo of chains warp, both in the "ring- spun" and "open-end" system. More specifically, the above machines normally consist of two or more pre- treatment tanks, six or more dyeing tanks, equipped with the relative squeezing and oxidation group, followed by three or more final washing units.

The dyeing tanks are connected, in both operative systems, by means of a pump and piping system, to a mixing/circulation tank, which is normally absent in the ring- spun system in which the circulating dyeing bath is filtered, thermo-regulated and with the continuous addition of suitable amounts of sodium hydroxide and sodium hydrosulfite, and also with the concentrated indigo bath previously reduced to the leuco state, in the necessary amount, on the basis of the concentration, in order to obtain the required colour shade .

It is known that in these machines dyeing is effected in an alkaline environment and with a calculated excess of sodium hydrosulfite, and that said sodium hydrosulfite, depending on the bath/air contact, reacts with the oxygen of the air losing its reducing capacity towards indigo. Due to this easy oxidizability of sodium hydrosulfite, it is necessary to add dosed quantities of hydrosulfite to the dyeing bath in order to compensate this loss. These reintegrations of sodium hydrosulfite, with a stoichiometrically corresponding quantity of sodium hydroxide, must be effected regularly and with high precision in order to keep the dyeing capacity of the bath unchanged, and guarantee constant and reproducible results.

The document US-A-2630002 , for example, relates to an automatic device capable of effecting the continuous-cycle dosage of sodium hydrosulfite, with possible mixing with a liquid component of the dyeing bath. The document WO 2008/056256 Al relates to a continuous-cycle dyeing device, hermetically sealed and in an inert environment, so as to allow a drastic reduction in the consumptions of sodium hydroxide and sodium hydrosulfite . The document US-A-2221780 relates to a dyeing plant equipped with a dosage system of the sodium hydrosulfite whose objective is to maintain the dyeing bath constantly in reduction.

Whereas the reintegrations of sodium hydroxide and sodium hydrosulfite are effected by direct dosage of the commercial product, this is not possible with indigo dye in the form of powder, microbeads or in aqueous solution (the most widely-used commercial forms worldwide and economically the most advantageous) , as this dye is not directly soluble in water.

The dosage of the reinforcing indigo bath can only be effected after being chemically reduced in an alkaline solution (in leuco form) , in a suitable container, an operation which can be carried out in all concentrations up to the maximum possible of 90 grams/litre due to its solubility limit.

Under normal conditions of use, the concentration of 90 grams/litre, due to the low bath adsorption on the part of the yarn, limits the application of indigo dye on the fibre to a maximum of 2-2.5%, consequently not allowing dark dyeing, i.e. with much higher dye percentages on the fibre, increasingly requested by the market and fashion. These dyeings are only possible by overfeeding the dosage of the reinforcing bath, followed however by an increase in the level of the dyeing tanks and therefore their overflow.

The laboriousness of the above solubilization operation and the maximum concentration limit of 90 grams/litre has therefore forced indigo dye producers to study alternative solutions.

Only two producers throughout the world, and therefore practically under a monopoly regime, are at present able to offer indigo dye in aqueous solution (leuco) in concentrations of 30% and 40%. In other words, due to the relative higher specific gravity, concentrations respectively equal to 360 grams/litre and 480 grams/litre have been obtained, thus eliminating some of the above problems.

The availability of indigo dye in aqueous solution at a high concentration has therefore solved the above problems but, at the same time, has created numerous others. Said aqueous solution, in fact, for the reasons already discussed and also because it is at a high concentration, cannot be put in contact with air. Contact with air causes immediate oxidation, i.e. the return of indigo to the insoluble form, which can no longer be dosed, and consequently both the transportation and transfer and storage of the aqueous solution (leuco) must be carried out in an inert environment, normally under nitrogen.

Consequently, the final user must avail of a costly and special distribution plant, in a closed circuit, to the dyeing machines. A plant of this kind comprises at least two large tanks, one functioning and the other as reserve, situated for safety reasons in an adequate containment tank, which can be filled by means of tank trucks. The variations in the level of these tanks must be constantly compensated by nitrogen and this condition is ensured by a container with liquid nitrogen or various nitrogen cylinders with special supply, control and monitoring equipment.

If, in addition to what is specified above, there is also the fact that indigo dye in aqueous solution (leuco) has a purchase and transport cost which is significantly higher than that of the dye in other commercial forms, and that the distribution of this dye in aqueous solution is not universally ensured, it is evident that another solution to the problem must be found.

In the light of the above, the necessity is evident of availing of a device which makes it possible to operate with indigo dye in powder form, in microbeads or aqueous dispersion, as widespread and economically as possible, without having to previously subject it to chemical reduction, and also to be able to dose this dye directly in such a quantity as to be able to effect the dyeings of very dark shades, without any expedients .

An objective of the present invention is to provide a device for the dosage and chemical reduction, in a continuous cycle, of a dye in the form of powder, in microbeads or aqueous dispersion, in particular indigo, which can be used on continuous-cycle machines and dyeing plants, with indigo, new or already existing, and which allows the indigo to be dosed directly in its commercial form, eliminating the necessity of its previous chemical reduction, as is normally the case in the known art, with relative and consequent economical advantages .

Another objective of the invention is to provide a device for the dosage and chemical reduction, in a continuous cycle, of a dye, in the form of powder, in microbeads or aqueous dispersion which allows a quantity of dye to be chemically reduced, in a continuous cycle, so as to obtain dyeings of very dark shades, with a significant reduction in the production costs, simplification of the plant design in addition to universal availability and free choice of the supplier.

This and other objectives according to the present invention, are achieved by providing a device for the dosage and chemical reduction, through a continuous cycle, of a dye in the form of powder, microbeads or aqueous dispersion, in particular indigo, as specified in claim 1.

Further characteristics of the invention are evident from the dependent claims which represent an integral part of the present description.

The characteristics and advantages of a device for the dosage and chemical reduction, through a continuous cycle, of a dye in the form of powder, microbeads or in aqueous dispersion, according to the present invention, will appear more evident from the following illustrative and non-limiting description, referring to the enclosed schematic drawings, in which: figure 1 shows, with a simplified functional hydraulic scheme, the current state of the art relating to the circulation and dosage system of a classical continuous-cycle open end dyeing machine or plant with feeding of the reinforcing indigo bath, pre-reduced, prepared starting from the dye in the form of powder, microbeads or in aqueous dispersion, of warp yarns for denim fabrics;

figure 2 shows the same hydraulic scheme as figure 1, integrated and completed by the device for the dosage and chemical reduction, through a continuous cycle, of a dye in the form of powder, or in microbeads, according to the present invention; and

figure 3 shows the same hydraulic scheme as figure 1, integrated and completed by the device for the dosage and chemical reduction, through a continuous cycle, of a dye in aqueous dispersion, according to the present invention.

For the sake of descriptive clarity, reference will be made hereunder to an open-end dyeing machine or plant only, to warp yarn chains only and the colour indigo alone, even if what is specified obviously also refers to ring spun dyeing machines which procedurally differ in the absence of a mixing/circulation tank, for fabrics and other reduced dyes in the form of powder, microbeads or in aqueous dispersion.

It should also be specified that the dye in powder form can have various particle-sizes (gross, fine, very fine, in Colloisol ^® format, etc.). The term "microbeads" indicates an aggregation form of the powders mentioned above, in order to facilitate their manipulation and eliminate their dispersion into the environment to protect the health of the operators. Finally, the reduced dye in the form of aqueous dispersion, preferred for its facility of use and dosage, is composed of very fine powders of dye distributed in an aqueous-based liquid, non- solvent, to which suitable products have been added (dispersant, antifreeze agent, etc.) to guarantee the stability of the powders themselves.

Finally the term " leuco" indicates the aqueous solution of dye, after chemical transformation (reduction) of its initial form, which is insoluble, to the soluble state. The physical state of the leuco solution is completely different from that of the dye in aqueous dispersion, in which the same dye is in an insoluble state.

With reference to figure 1, this shows the dyeing group of a classical open-end continuous-cycle dyeing machine of yarns with indigo, with dosed feeding of the pre-reduced reinforcing bath starting from the dye in powder form or in microbeads, said dyeing group being indicated as a whole with the reference number 10. The dyeing group 10 comprises a plurality of - dyeing..tanks _

11 connected, by means of a piping system 12 equipped with a feeding pump 13 of the centrifugal type, to a mixing/circulation tank 14 of the dyeing bath.

One or more filters 15, one or more thermoregulation coils 16, a probe 17 for the temperature control and an automatic level regulator 18, are present, in a known way, inside the mixing/circulation tank 14 of the dyeing bath. On the water piping at the inlet of said tank 14, there is therefore a feeding valve 19 of the same water for reintegrating the level together with a measurer 20 of the quantity of water added. A volumetric doser 21a of sodium hydrosulfite, a container 22 for the feeding, by means of a relative dosage pump 23, of the process sodium hydroxide and a container 24 for the feeding, again by means of a relative dosage pump 25, of the concentrated indigo leuco bath and suitable auxiliary products for reinforcing the dyeing bath circulating in the dyeing tanks 11 and in relative piping system 12, are also connected to the tank 14.

With reference to figure 2, this illustrates the same dyeing group 10 for an open-end dyeing machine of yarns according to figure 1, to which a device is applied for the dosage and chemical reduction, in a continuous cycle, of indigo dye in the form of powder or in microbeads according to the invention. The container 24 and relative dosage pump 25, previously destined for the feeding of the concentrated indigo leuco bath for reinforcing the dyeing bath circulating in the dyeing tanks 11 and in relative piping system 12, are now converted for the feeding of auxiliary products which were previously an integral part of the concentrated indigo leuco bath. The device according to the invention envisages the presence of a dosage group 26, preferably of the ponderal type, of indigo dye in the form of powder or microbeads, and a dosage group 21b, preferably ponderal, of sodium hydrosulfite . The device according to the invention therefore envisages the presence of a first dissolving device 27, for example of the labyrinth type, fed by a centrifugal pump 28 which directly sucks the exhausted dyeing bath from the piping system 12 of the dyeing group 10. A heat exchanger 29 can be interposed between the dissolving device 27 and relative centrifugal pump 28.

The device according to the invention can also comprise an ultrasound reactor 30, fed by a centrifugal pump 31, and a second dissolving device 32, again of the labyrinth type and fed by a respective centrifugal pump 33. The second dissolving device 32 is in turn connected, in the supply and by means of a further centrifugal pump 34, to the mixing/circulation tank 14 of the dyeing bath, with the interpositioning or not of a heat exchanger 35.

A predefined quantity of the exhausted dyeing bath leaving the tanks 11 is advantageously, according to the present invention, collected in continuous by the piping system 12 for the circulation of the bath. This predefined quantity of the exhausted dyeing bath, possibly heated through the heat exchanger 29, is sent to the dissolving device 27 where, before entering the labyrinth path of the dissolving device 27 itself, the following are added, again in a continuous cycle:

- the required quantity of indigo dye in powder form or in microbeads, by means of the ponderal dosage group 26 of the dye;

- the quantity of sodium hydrosulfite necessary for the chemical reduction of said dye, in addition to the quantity normally used for compensating oxidation losses, by means of the ponderal dosage group 21b of sodium hydrosulfite;

- the corresponding stoichiometric quantity of sodium hydroxide, by means of the container 22 and relative dosage pump 23; and

the necessary quantity of auxiliary products, collected from a specific container 36, by means of a dosage pump 37.

In the labyrinth path of the dissolving device 27, the above substances and exhausted dyeing bath are amalgamated, the hydrosulfite dissolves and the chemical reduction of the indigo dye is initiated. The exhausted dyeing bath thus enriched is sent, by means of the pump 31, to the ultrasound reactor 30 which, when present, by accelerating the disaggregation of the particles of the dye, accelerates its reduction. The dyeing bath is then transferred, by means of the pump 33, to the second labyrinth dissolving device 32, where the chemical reduction is completed.

Finally, this predefined quantity of dyeing bath, enriched with the dye, dosed and chemically reduced, is sent by means of the pump 34, and possibly cooled through the heat exchanger 35, to the mixing/circulation tank 14, thus being added as reinforcement for the dyeing bath circulating in the piping system 12, with which it is mixed before the whole mixture is recirculated again through the pump 13 of the dyeing group 10.

With reference now to figure 3, this illustrates the same dyeing group 10 for an open-end dyeing machine of yarns according to figure 1, to which a device for the dosage and chemical reduction, through a continuous cycle, of an indigo dye in aqueous dispersion according to the present invention, is applied. The container 39 and relative dosage pump 38, previously destined for feeding the concentrated indigo leuco bath for reinforcing the dyeing bath circulating in the dyeing tanks 11 and in the relative piping system 12, are now converted for feeding the indigo in aqueous dispersion and relative auxiliary products .

The device of figure 3, with respect to that of figure 2, therefore envisages the elimination of the ponderal dosage group of indigo dye 26, whereas the operativeness of the system remains the same as that described for figure 2.

It should be pointed out that the chemical reduction, in a continuous cycle, of indigo dye described above is made possible by the use, as solubilization means instead of water, of the circulating dyeing bath, already in reduction, for enriching it only in the quantity of dye necessary for obtaining the intensity of the colour requested. It should be noted that the use or necessity of the ultrasound reactor 30 depends on the quantity of indigo dye to be reduced in the time unit, i.e. at the percentage of indigo to be applied to the fibre.

The heat exchanger 29, situated at the inlet of the device according to the invention and used for heating the predefined quantity of bath removed, in order to facilitate the reduction of the indigo dye which is added, is necessary if the dyeing is effected cold or at room temperature. The heat exchanger 35, situated at the outlet of the device according to the invention is consequently also necessary for cooling, with cold water, which can be re-used in the washing tanks, this predefined quantity of enriched bath before it enters the mixing/circulation tank 14, in order to maintain the thermal dyeing conditions unvaried.

It can thus be seen that the device for the dosage and chemical reduction, through a continuous cycle, of a dye in powder form, in microbeads or in aqueous dispersion, in particular indigo, according to the present invention, achieves the objectives specified above. Unlike the system so far used for the dosage of the concentrated reinforcing bath in dyeing processes with indigo in powder form, in microbeads or in aqueous dispersion, the device according to the invention allows dyeings of very dark shades, i.e. with a high percentage of dye on the fibre, which so far can only be obtained with the overflow expedient, or using the dye in a concentrated aqueous solution (leuco) .

The device according to the present invention therefore advantageously allows the use, for any colour intensity, of the universally available and more economical indigo dye in the form of powder, microbeads or in aqueous dispersion, eliminating the laborious preventive preparation of the reduced reinforcing bath and eliminating the complex and costly plant for the use of indigo in aqueous solution (leuco) , thus allowing a significant reduction in the production costs .

A further advantage is that the owners of dyeing plants do not need to be technically and commercially tied to any particular producer of dyes in aqueous solution (leuco) , with the advantage of being able to obtain the best offer for said dye in other commercial forms .

The device according to the present invention can be applied to any dyeing plant, traditional or special, open-end or ring-spun, in a continuous cycle with indigo. Finally, this device can obviously be equipped with all the necessary hydraulic, electric, electronic, driving, thermoregulation, control and monitoring equipment, and can be completed with various devices, not described as they are of the types known in the state of the art, for the automatic loading of hoppers of dosers and for any other operation necessary for the efficient functioning of the same device.

The device of the present invention thus conceived can in any case undergo numerous modifications and variants, all included in the same inventive concept; furthermore, all the details can be substituted by technically equivalent elements. In practice, the materials used, as also the forms and dimensions, can vary according to technical requirements .

The protection scope of the invention is therefore defined by the enclosed claims.