METHOD FOR DYEING AND FINISHING TEXTILE MATERIAL AND CORRESPONDING APPARATUS

FIELD OF THE INVENTION

The present invention concerns a method and the corresponding apparatus for carrying out dyeing and finishing treatments using a solution of dyes dissolved in liquid ammonia.

The invention is applied on fabrics, non-woven fabrics, knitwear and yarns, to dye and in general to improve the characteristics of the product.

BACKGROUND OF THE INVENTION

In finishing treatments intended to improve the product characteristics of a textile article made of cellulose fiber, for a long time a process has been studied and applied that uses baths of liquid ammonia. In this process, a fabric is impregnated with liquid ammonia for a time that normally varies from 1 to 30 seconds and at a temperature of -34°C, that is, the temperature at which ammonia liquefies at atmospheric pressure.

The quality of the fabrics is improved due to the fact that ammonia exerts a swelling effect on the cellulose fibers, with a crystalline orientation of the cellulose, without causing damage to the structure of the fiber.

When the cellulose fiber is impregnated, the small molecule of liquid ammonia does not only penetrate into the amorphous zones, but also into the crystalline zones of the cellulose, breaking the hydrogen bonds so that the fiber can swell entirely. In the subsequent evaporation stage, with the creation of new hydrogen bonds, the cellulose which was originally type I transforms, in a certain percentage, into type III cellulose.

In particular, the conversion of the cellulose from type I to type III occurs in a progressively bigger percentage in proportion with an increased impregnation time in liquid ammonia.

The main benefits conferred on cellulose fabrics by this finishing treatment are:

• silky shine;
• better dimensional stability;
• increase in mechanical resistance;
• great improvement in wash-and-wear properties;
• improved look;
• the fabric looks "new" even after repeated washing;
• soft to touch;
• increased affinity to the dyes;
• uniform dyeing.

It has been shown that in the textile industry, liquefied ammonia can be used and recycled without any problems. On the other hand, regulations protecting the environment are becoming stricter and stricter, and this is a good reason to think about using liquid ammonia as a solvent also in dyeing treatments.

Many of the dyes used in dyeing textiles in a water medium are dissolved in liquid ammonia and therefore the method can be used to dye many categories of fibers.

The method of dyeing with dyes dissolved in liquid ammonia has the advantage that it eliminates all the problems correlated to the quality of the water, its consumption and subsequent purification. The method also eliminates numerous auxiliary products and chemical products such as wetting agents, electrolytes, softeners, carriers, retardants and equalizers.

Document US 3 824 076 describes a dyeing method in which reference is made to trials carried out in the laboratory on extremely small samples of fabric. In this document, the textile material is dyed with an ammonia solution mainly consisting of liquid ammonia, dyes, caustic soda and water. The dyeing recipes described in the document can be valid in trials carried out on small samples of fabric or knitwear, but cannot be applied industrially for dyeing big quantities of textiles.

This is because, often, the fabrics treated in industrial applications have a humidity that is not homogeneously distributed, and they can have irregular shrinkages in the various zones of the textile, so that the colors obtained would not be uniform, and also the dyes would not be sufficiently fixed to the fibers.

Purpose of the present invention is to obtain an industrial method for dyeing textile materials, and a corresponding apparatus, in which the dyeing is carried out with an ammonia solution containing the dyes; the method combines the benefits of fixing guaranteed by the liquid ammonia with a drastic saving in dyes, auxiliaries, water and steam of the dyeing process.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

The method for dyeing and simultaneously finishing textile material with an ammonia solution containing dyes dissolved therein, according to the present invention, provides the following steps:

• preparing the ammonia solution containing the dyes and sending said solution to a machine for processing the textile material; advantageously, the step of preparing the ammonia solution also comprises a control of the percentage of water with respect to the total weight of the solution containing liquid ammonia and water;
• adjusting the percentage of water present in the textile material with respect to its dry weight before said textile material enters into the processing machine;
• entry of the textile material into the machine through safety seals;
• impregnating the textile material with the ammonia solution for at least a few seconds, the textile material being kept mechanically constrained to prevent unwanted shrinkage;
• squeezing out the excess ammonia solution from the textile material, still kept mechanically constrained, in order to obtain an adjustable pick-up of about 80 - 100% with respect to the dry weight of the textile material;
• total evaporation of the ammonia from the textile material, still kept mechanically constrained, inside the processing machine;
• exit of the textile material, dyed and dried, from the processing machine through safety seals.

In one form of embodiment, upon exit from the processing machine, the textile material is subjected to a steaming cycle.

If performed, steaming can be carried out at atmospheric pressure, or high pressure in a pad steam steamer, with saturated or superheated water vapor, to fix the dyes to the textile fibers definitively.

In one form of embodiment, at exit from the processing machine the textile material is subjected to a washing cycle with water and possibly with soaping to remove the minimal percentage of dyes not fixed to the fibers.

According to a variant, the ammonia solution with the dyes also comprises a quantity of caustic hydrate, chosen for example from sodium hydrate, potassium hydrate or lithium hydrate.

According to another variant, the ammonia solution with the dyes also comprises a quantity of sodium carbonate.

According to another variant, the ammonia solution with the dyes also comprises a quantity of distilled water.

In one form of embodiment, the ammonia solution, advantageously always kept cold, is prepared separately from the processing machine, in one or more tanks.

With the method described above, it is therefore possible to simultaneously dye and finish, with selected dyes dissolved in liquid ammonia, all cellulose fibers (cotton, linen, hemp, jute, ramie and others), a mixture of said fibers, a mixture of said fibers with synthetic fibers, artificial fibers (viscose, polynosic, modal, acetate, triacetate, cupro and others), a mixture of artificial fibers, a mixture of artificial fibers with cellulose fibers, a mixture of artificial fibers with synthetic fibers, fibers of animal origin (wool, cashmere, mohair, angora, goat hair, silk and others) and a mixture of the latter fibers with all those cited above.

Some synthetic fibers, such as polyamides, can also be dyed using the invention.

The process can be applied continuously or discontinuously with the medium kept at atmospheric pressure, or at an adjustable pressure lower than atmospheric pressure, or again at an adjustable pressure higher than atmospheric pressure.

The dyes used can be selected from the class of reactive dyes, direct dyes, dispersed dyes, and to a lesser extent the class of sulfur dyes, acid dyes, metalized acid dyes and also vat dyes if previously reduced.

The dyes used can be in the form of powder, or liquid form already dissolved in water.

It is known that the humidity rate in wool is 18.25%, in cotton 8.5%, in hemp 12%, in jute 13.75%, in linen 12%, in viscose 13%, in acetate 9% and in triacetate 7%.

The humidity can vary depending on the origin of the fiber, the count of the yarns, the weight and type of article and other parameters.

The humidity can also vary between the center and sides of a fabric, or between the start and end of the same piece. The humidity can also be distributed non-uniformly through the fabric.

If various fabrics of cotton with the same weight and morphology with the same pick-up, but which have different humidity rates, are impregnated with dyes dissolved in liquid ammonia, then these fabrics, after dyeing and drying, will have different intensities of color.

The ammonia molecule, penetrating inside the cellulose fiber, causes it to swell and consequently also to shorten.

For example, the almost total shrinkage (about 10% in the warp direction and 7% in the weft direction) of a cotton fabric weighing 120 g/m², combed yarns Ne 80, not mechanically constrained, impregnated with a pick-up of 150% liquid ammonia with respect to its dry weight, takes place in less than 4 seconds.

The almost total shrinkage of the same article, not mechanically constrained, impregnated with a pick-up of 100% with respect to its dry weight, takes place in less than 6 seconds.

The almost total shrinkage of the same article, not mechanically constrained, impregnated with a pick-up of 60% with respect to its dry weight, takes place in less than 12 seconds.

If a fabric with an established pick-up and not mechanically constrained is impregnated with dyes dissolved in liquid ammonia, after drying the dyed fabric can have different intensities of color between the center and the selvages, or between the start and end of the article, which phenomenon is due to the irregular thickening of the material, generated by non-homogeneous shrinkages in various points of the fabric.

In the method according to the present invention, the humidity is adjusted and distributed uniformly throughout the textile material, because with every variation thereof during the dyeing step, the concentration of the dyes dissolved in the liquid ammonia will vary directly on the fibers, so that then there will be a corresponding different intensity of color in different zones of the textile.

For this reason, according to the invention, before being impregnated with the ammonia solution, the textile material is dried so as to have a predetermined percentage of humidity, homogeneously distributed.

The textile material can be dried using a dryer installed opposite the dyeing machine or, alternatively, by using a rameuse. The percentage of water, monitored by a humidity detector, to be left on the textile material, is adjustable and can vary from article to article. In general, in cellulose fibers and fibers of animal origin, it has been found that a humidity of about 4-5% with respect to their dry weight is advantageous.

Removing the water from a cellulose textile material containing a lot of water, or water not distributed uniformly, so as to obtain a percentage of residual humidity of 4%-5% with respect to its dry weight, is a rapid and relatively simple process: on the contrary, the evaporation of the last percentage of water still present in the heart of the textile fibers is a process that takes time.

For this reason, for the purposes of the present invention, it is convenient to stop at the percentage indicated above, which is also uniformly distributed throughout the fabric or knitwear. In the case of synthetic fibers, the residual humidity will be about 0.5 - 1%, again with respect to the dry weight of the textile material.

As we said, in an advantageous solution, the ammonia dyeing solution can be prepared in one or more tanks serving the processing machine; the temperature of the solution must always be kept low, around its temperature of liquefaction of - 30°C/- 36°C, if working at atmospheric pressure, ready to be introduced, in the machine, into the zone where the textile is impregnated.

The ammonia dyeing solution, based on the dyes, can include:

• mainly liquid ammonia;
• a percentage in g/liter of powdered dyes dissolved in it, or a quantity in cc/liter of water solution containing the dyes;
• possibly, a minimum percentage of distilled water; in the case of dark colors, where it is necessary to increase the weight in grams/liter of the dyes to be dissolved, some powdered dyes can have problems of solubility in liquid ammonia alone, and therefore a percentage of water must be added to make them soluble; the percentage of water is variable from 3% to 10% with respect to the total weight of the solution containing liquid ammonia and water;
• possibly, a percentage variable from 0.5% to 2% with respect to the total of the solution of caustic hydrate concentrated to 50 Baumè; the caustic hydrate can be sodium hydrate, potassium hydrate or lithium hydrate;
• possibly, a minimum percentage of sodium carbonate or potassium carbonate.

So as not to inhibit the reaction of the liquid ammonia with the cellulose fiber, transformation from type I cellulose to type III cellulose, according to the present invention it is preferable that the overall percentage of water, that is, the humidity inside the fiber and the water in the ammonia dyeing solution (possible distilled water added to the solution, water in the possible dye and water in the caustic hydrate), should not exceed the maximum value of 20% with respect to the total weight of the solution containing liquid ammonia and water; the value, predetermined and monitored during the treatment cycle, is chosen as a function of the fibers and the dyes to be dissolved in the solution. The percentage of water in the solution can be monitored, for example, by an electronic densimeter; at atmospheric pressure, for example, 1 liter of water weighs 1 kilogram, while 1 liter of liquid ammonia weighs 0.682 kilograms.

In an alternative solution, before being dyed with the ammonia solution, the textile material is subjected to a treatment with a water solution containing caustic hydrate and possibly carbonate, before being subsequently dried, leaving on the textile the pre-set percentage of humidity containing the salts cited above.

To increase the dyeing yield, and to improve the characteristics of the cellulose fiber, the percentage of caustic hydrate at 50 Baumè can be increased to about 5-10% of the total solution.

In fact, by increasing the percentage an ammonia solution is formed containing the selected dyes and caustic hydrate, with the purpose of increasing the mercerization effect in the cellulose fiber compared with the treatment made with liquid ammonia alone.

If a woolen article is treated with the ammonia solution as described above, an optimum fixing of all the fibers is obtained.

With the present invention a plurality of advantages are obtained, such as:

• the cellulose fibers are finished;
• a uniform dyeing on the surface and in depth of the fibers;
• brilliant color;
• extremely high dyeing yield; in the case of reactive dyes, they react only with the cellulose hydroxyls, but not with the water hydroxyls as in the case of dyeing performed in a water medium;
• very high solidity of the color;
• elimination of nearly all the chemical auxiliaries present in dyeing in water medium;
• almost total elimination of water;
• drastic saving in heat energy;
• no unwanted shrinkage of the textile material;
• dyeing is carried out with almost zero pollution, since the ammonia is continuously recyclable and re-usable.

BRIEF DESCRIPTION OF THE DRAWINGS

We shall now refer in detail to one form of embodiment of the present invention, an example of which is shown in the attached drawing.

In particular, fig. 1 shows schematically a dyeing and finishing apparatus for textile articles according to the present invention.

DETAILED DESCRIPTION OF ONE FORM OF EMBODIMENT

We shall now give an example by way of illustration of the invention, which shall not be understood as a limitation thereof. For example, the characteristics shown or described insomuch as they are part of one form of embodiment can be adopted on, or in association with, other forms of embodiment to produce another form of embodiment. It is understood that the present invention shall include all such modifications and variants.

A dyeing and finishing apparatus for a textile article is indicated in general and in its entirety by the reference number 10 in the attached drawing.

It comprises a processing machine 11 in which, in this case, there is a vat 12 containing a solution of dyes dissolved in liquid ammonia, indicated by 13.

A textile material 14, prepared with a predetermined humidity, is introduced through safety seals 15 inside the processing machine 11, ready to be dyed by immersion in the solution of dyes and liquid ammonia.

Before it is introduced, the textile material 14 is dried by two heated cylinders 16a and 16b, and then cooled by a cooled cylinder 17, which lowers its temperature.

At exit from the cooled cylinder 17, the percentage of humidity still on the textile material 14 is monitored by a humidity detector 18; in the case of cellulose fibers, or fibers of animal origin, the residual humidity is advantageously kept at 4-5% with respect to the dry weight of the textile.

It is understood that for fibers of a different type, and/or according to the processing conditions, the value of residual humidity at exit from the drying unit can be different from the one indicated above.

The textile material 14 is then taken to be immersed in the vat 12, to be impregnated with the solution of dyes and liquid ammonia.

In the immersion and impregnation step, and during the whole of its passage inside the processing machine 11, the textile material 14 is kept mechanically constrained between a first tensioner roll 19, disposed inside the processing machine 11 in proximity to its entrance, and a second tensioner roll 23, disposed inside the processing machine 11 in proximity to its exit.

Between the rolls 19 and 23 the textile material 14 is therefore kept under tension with the desired degree of tensioning.

In the case shown here, a second roll 20 is partly immersed in the solution of dyes and liquid ammonia and determines the path of the textile material 14 inside the vat 12, and a third roll 21, motorized, disposed at exit from the vat 12, cooperates with a squeezer roll 22 to perform a first removal of the excess dyeing solution from the textile material 14.

During the impregnation step, the small molecule of ammonia penetrates quickly inside the amorphous zones and crystalline zones of the cellulose, carrying the dye and the hydrate with it; the penetration is further facilitated by the swelling of the fiber, due to the humidity still present inside the fiber. With the textile material 14 held mechanically constrained and at an adjustable tension between the rolls 19 and 23, impregnation takes place inside the vat 12 for a time that is generally about 2-3 seconds.

To guarantee an adjustable pick-up of about 80-100%, with respect to the dry weight of the textile material 14, of ammonia solution 13 to be left distributed homogeneously through the fibers, the article exiting from the impregnation vat 12 is immediately squeezed between the rolls 21 and 22.

The adjustable pick-up of about 80-100% of ammonia solution to be left uniformly distributed is an optimum value to prevent the deformation of the fibers which, during squeezing, are in a swollen and plastic condition.

In the solution shown here, at exit from the squeezing unit the textile material 14 is subjected to a drying cycle in which all the ammonia present is evaporated, so as to leave on the fibers only the dye, the caustic hydrate and a minimum quantity of water.

The total evaporation of the ammonia is obtained by direct contact of the textile material 14 against the surface of a series of heated cylinders 24 at a preset temperature and disposed one after the other, advantageously all in contact with each other.

In this step, as well as evaporating the ammonia, the percentage of water present in the fiber is also heated to a temperature of about 100°C, so that the dyes deposited on the textile material 14 are chemically pre-fixed or fixed to the fibers.

In fact, the fixing of the reactive dyes to the cellulose fibers, in the presence of the hydrate, is due to the raising of the temperature of the water present in the fibers and to the raising of the temperature of the dyes and fibers themselves.

The ammonia gases, and the possible water vapors taken in from the dryer by a plurality of suction units 25, can then be conveyed to a pre-condenser to be subsequently condensed, by a chiller unit, to the liquid state.

In a preferential solution, the ammonia gases can be subsequently condensed again to the liquid state in a known manner: the liquid ammonia thus obtained will be ready again for another use.

After the drying step, the textile material 14, dry and dyed, is made to exit from the processing machine through the safety seals 115.

The working pressure inside the processing machine 11 is preferably kept in a condition of slight depression, to prevent leakages of ammonia into the work place; in variant solutions, the pressure can also be kept at atmospheric pressure or in a condition of adjustable pressure higher than atmospheric pressure in the case of a discontinuous machine kept totally closed.

To guarantee or to complete the fixing of the dyes to the fibers, after exit from the processing machine the textile material 14 can be subjected to a steaming cycle, performed, in the solution shown, inside a steaming machine 26.

The steaming machine 26 can be the pad steam type, with saturated water vapor or superheated steam.

The steaming cycle can be carried out for a determinate time at atmospheric pressure or possibly under pressure conditions.

In an alternative dyeing process, after exit from the drying zone of the processing machine 11 the dyed textile material 14 is impregnated with a water solution containing the caustic hydrate and possibly carbonate, and is then steamed in the steamer where the dyes are fixed to the fibers.

At the end of steaming, the reduced percentage of dyes not fixed to the fibers are preferably removed by a washing cycle, performed in a washing machine 27 which in this case comprises a first washing machine 28 with hot water, and possibly soaping, then followed by the final washing in a second washing machine 29.

The washing time is short and the water consumption is extremely limited, even in the case of cellulose fibers dyed with reactive dyes, since the percentage of dyes not fixed to the fibers is minimal.

The dyeing of the yarns with an ammonia solution of dyes must be carried out from beam to beam, that is, from a beam that unwinds the textile disposed at entrance to the processing machine 11, to a beam that winds the dyed textile disposed at exit from the processing machine 11: that is to say, the yarns are kept adjacent and wound around suitably sized beams.

It is clear that modifications and/or additions of parts may be made to the method and apparatus as described heretofore, without departing from the field and scope of the present invention.