Description Technical field The present invention relates to a process for treating textile materials, in particular pieces of fabric or yarns, with ammonia. This type of process is commonly known as mercerizing. More specifically, the invention relates to a process for treating textile articles or materials with liquids at low condensation temperature, or at high vapor pressure. The invention also relates to a system for treating textile materials.

State of the Art

Mercerization is a typical treatment for fabrics and yarns made of all cellulosic fibers, in particular for cotton, which offers the material a series of advantages, such as: - increased luster and water absorption properties

- increased dimensional stability, -- increased affinity for dyes,

- improvement and enhancement of subsequent finishing treatments (i.e. anti- crease treatments). Currently, the mercerization process is implemented with the use of alkalis, generally caustic soda, which determines:

- shortening and swelling of the fiber,

- increased tensile strength,

- lower bending and torsional strength. The section of the fiber changes from elliptical to circular, thereby allowing greater reflection of light resulting in an increase in luster. Alternatively, liquid ammonia can be used as chemical mercerization agent.

Treatment of cotton fabrics with liquid ammonia is a finishing process that influences the technological textile properties of the fabric through deep-rooted structural changes in the fiber. This process has considerable potential for development, as extremely short contact times are required to perform mercerization by immersion in liquid ammonia (often below one second). During this type of treatment the fabric is impregnated with liquid ammonia in

percentages generally no less than 100% in weight and dried rapidly to limit the consequent extremely rapid shrinking process before this becomes unacceptable.

From the state of the art of research performed by various research institutes, it is known that treatment with liquid ammonia allows special mercerization effects to be obtained which are impossible with conventional mercerization methods using caustic soda and improves the quality of the dyeing and finishing processes (anti-crease power, increase in mechanical strength, swelling of the fiber and luster), obtaining an increase both in comfort and in the functional and aesthetic performance of the end product. An example of mercerization system with ammonia is described in US-A-

3980429. In these systems, the fabric is fed continuously and passes through a chamber in which an impregnation bath is provided, in which the fabric is immersed to be impregnated with ammonia. Arranged downstream of the impregnation bath are drying means, typically in the form of heated rollers, which cause the ammonia to evaporate from the fabric. Before passing over the heated rollers the fabric can be squeezed to eliminate part of the impregnated ammonia. A complex system is then provided for recovery and subsequent liquefaction of the gaseous ammonia to return the liquefied ammonia to the bath.

There are very few systems employing this technology, due to the difficulty related to the use of liquid ammonia, which at atmospheric pressure evaporates at -33°C. This involves machinery of complex construction, problems related to safety and to disposal of processing waste, resulting in a very complex system with high costs.

Recently, discontinuous mercerization systems have also be proposed. In these systems a piece of fabric wound on a roller is arranged in a closed chamber, where it is gradually unwound, immersed in an impregnation bath containing liquid ammonia, dried and rewound on a collection roller. An example of a discontinuous system of this type is described by C. Meyer, «Nuovo procedimento di trattamento discontinuo con ammoniaca>-> (New discontinuous treatment process with ammonia), in ITB, International Textile Bulletin 6/99, pages 48 and ff.

The need to recover and liquefy gaseous ammonia is also present in discontinuous systems.

The high toxicity and flammability of ammonia makes its recovery and the liquefaction processes particularly complex and critical. Objects and Summary of the Invention

The object of the present invention is to produce a method and a system, which overcome or reduce the aforesaid drawbacks. More specifically, the object of the present invention is to produce a method, which makes the mercerization process with ammonia, and more generally a process in which a textile article is impregnated with products, which at ambient pressure condense at low temperature, more simple and more economic, as well as intrinsically safer. The object of the present invention is to produce a system that is simpler and easier to manage, as well as more economic and safer, for mercerization with ammonia or for other treatments involving the impregnation of textile materials with products, which at ambient pressure condense at low temperature.

According to a first aspect, the invention relates to a method for treating a textile article with a product at low condensation temperature, including the steps of wetting the article with said product in liquid state and making the liquid product act on the fibers of the article; characterized in that the textile article is cooled by a cryogenic fluid and the article is subsequently impregnated with said product. In practice, the treatment product can be ammonia (for a mercerization treatment) or another product which requires analogous treatment conditions, or which has analogous problems from the viewpoint of management of the system and environmental pollution.

Textile material or article is intended as any semi-finished product of considerable length which can be fed along a treatment path. In particular, the article or textile material can be composed of a woven fabric, a knitted fabric, a non-woven fabric "or of a substantially tubular article made of woven or non- woven textile fibers. The article or textile material can also be a yarn with any structure.

As a rule, according to this first aspect of the invention, contact between the textile article and the product for the treatment thereof can also take place through conventional impregnation by immersing the textile article (i.e. a yarn or fabric) in a bath containing the treatment product in liquid state. The advantage attained by the invention in this case firstly consists in the fact that cooling o"f the

article greatly reduces evaporation of the liquid product contained in the impregnation bath. This simplifies the process, reduces consumption and increases productivity.

Moreover, according to an advantageous improved embod iment of the invention, the cryogenic cooling fluid can be in liquid state and can be contained in a bath which forms a barrier between a volume or chamber containing the impregnation bath and the outside. If the cryogenic liquid is devoid of polluting characteristics and can be released into the atmosphere, i.e. if it is composed of liquid nitrogen, a bath with an intermediate separating partition, which divides an inlet from an outlet, can form an effective barrier against dispersal into the environment of vapors of the product utilized for the treatment.

It would also be possible for the barrier to be formed of a cryogenic fluid in gaseous state. Cooling of the textile article can also take place, although this is less advantageous, by directing a jet of cryogenic gas against the article. According to an improved embodiment of the invention, impregnation of the textile product does not take place by immersion in a bath, but by condensation from gaseous state to liquid state of the treatment product on the textile article previously cooled with the cryogenic fluid. This can take place, for example, by feeding the textile article through an impregnation chamber containing gases or vapors of the treatment product, such as ammonia in a gaseous state.

In substance, in this preferred embodiment of the invention the fabric is subjected to controlled impregnation with liquid ammonia, whichi is made to condense from gaseous or vapor state directly on the fabric, previously cooled by the cryogenic fluid, in sufficient quantity to implement the process. In this case, cryogenic is intended as a fluid and more specifically as a liquid maintained at a sufficiently low temperature to cool the textile article by immersion to a temperature, which causes subsequent condensation of the treatment product. Specifically, the cryogenic liquid is a liquid with characteristics and thermodynamic conditions according to which the textile article made to emerge from the cryogenic liquid is cooled to the desired temperature, while the liquid evaporates rapidly from the textile article and does not interfere withi the action of the treatment product, which condenses on said textile article.

With this system the quantity of ammonia, which impregnates the fabric, can be reduced in a controlled way to any percentage value d esired. On the contrary, all systems currently in use perform impregnation by immersion or equivalent systems which contribute percentages much greater than 100% in weight to the fabric, if not followed by squeezing, or slightly below 100% if followed by squeezing, with the consequent need to remove very large quantities of this substance from the fabric.

It must be borne in mind that the fabrics involved by the treatment, which are in particular cotton, linen and hemp, absorb ammonia and spread it throughout all their fibers with great rapidity, but are much more reluctant to release it again. Repeated experiments and tests have shown that the percentages of ammonia required for treatment are considerably lower than the values currently in use in conventional systems, values which are simply the unavoidable result of the fact that in conventional systems and methods the fabric is immersed in and completely soaked with ammonia.

In practice, according to a possible embodiment of the invention, the process consists in rapid cooling of the fabric, by immersing it in a bath of cryogenic liquid, at a temperature which causes cooling sufficient to allow subsequent condensation of the ammonia or other product with characteristics compatible with this method. The pressure of the ammonia gas chosen to saturate the treatment chamber, which owing to environmental incompatibility must be isolated from the outside environment, also determines the temperature range to which the fabric must be taken to obtain condensation of the ammonia. Tests performed on various linen and cotton fabrics have shown that the same results are obtained both by immersing the fabric in liquid ammonia with a degree of impregnation ranging from 100% to 300% according to the conventional technique, and with the condensation process according to the present invention regulated in order to release into the fabric percentages of ammonia varying, for example, from 5% to 10%. In the above and in the description hereunder specific reference is made to the treatment of textile material using ammonia. In fact, in this application the method and the system according to the invention offer particula r and important advantages, as set forth above and as will be further explained hereunder.

However, it would also be possible to use the same method to treat textile articles with other products, which at the treatment pressure are made to condense by a saturated atmosphere, to be absorbed rapidly and in small quantities by the textile article. The cryogenic fluid utilized can advantageously by liquid n itrogen, which has temperature conditions suitable for the objects of the present method, evaporates almost instantly from the textile article when this is removed from the nitrogen, so that the article remains dry but at a sufficiently low temperature to cause condensation of the ammonia or other equivalent product by passing through an environment saturated with said product in gaseous state. Gaseous state is intended, within the scope of the present description and of the appended claims, also as vapor state.

As liquid nitrogen is a substance which, in the form of gas, is widely present in the air, it can be dispersed into the environment in unlimited amounts. This makes it useful in this process also to form a U seal, which allows passage of the fabric but prevents the ammonia from escaping, by that route, from the process chamber.

All in all, the impregnation process by condensation according to the invention differs from conventional methods according to two particularly relevant aspects:

1) the quantity of ammonia coming into play during the process i s considerably low, even 10 to 20 times lower than conventional methods, with consequent reduction in the dimensions and costs of the systems for drying and recovery of the ammonia; 2) it is not necessary to use liquid ammonia in the process, with consequent elimination of the burdensome system to compress and liquefy the ammonia recovered by the system to dry the fabric.

As a rule, the process can be a continuous process, with trie textile article fed through an open system, i.e. with an inlet and an outlet. Alternatively, however, the process and the system can be produced for discontinuous treatment, i.e. in which a piece of fabric or a reel of yarn or another textile article is unwound and rewound in a closed environment, from which the treated product is collected at the end of treatment after interrupting said treatment.

The invention also relates to a system for treating a textile article with a product in liquid phase at low condensation temperature, including: a path for the textile article; along said path impregnation means to impregnate the textile article with said product; means to remove the product from said article; characterized in that it has means to cool the textile article by immersion in a cryogenic fluid, said cooling means being disposed upstream of said impregnation means.

The impregnation means of the textile prod uct can include an impregnation system by immersion. More advantageously, as mentioned above, the systems has an impregnation chamber containing the treatment product in gaseous state and the textile article is taken to a temperature which causes impregnation by condensation of the treatment product on said article.

Further advantageous characteristics of the process and of the system according to the invention are indicated in the appended claims and will be described in greater detail with reference to non-limiting examples of embodiment of the invention.

Brief description of the drawings

The invention will now be better understood by following the description and accompanying drawing, which shows non-lirniting practical embodiments of the invention. More specifically, in the drawing: Figure 1 schematically shows a longitudinal section of a system according to the invention, in which impregnation of the textile article is implemented by condensation from the gaseous state of the treatment product; and

Figure 2 schematically shows a longitudinal section of a system in which impregnation is performed by immersion of the textile article in a bath containing the treatment product in liquid state.

Detailed description of preferred embodiments of the invention

With initial reference to the embodiment in Figure 1 , this initially shows a system for continuous treatment of a textile article, which is impregnated with ammonia by condensation from the gaseous state. The system is indicated generically with 1 and includes an unwinder 3 in which a reel B1 of fabric T to be treated is arranged, and a winder 5 in which the treated fabric is rewound on a reel B2. The fabric T is fed, guiding it around a roller 7, to a chamber 9 on the bottom of which is a bath 11 to contain a cryogenic

liquid L, typically liquid nitrogen. A second guide roller 13 immersed in the bath diverts the fabric T, which re-emerges from the cryogenic liquid L to enter an intermediate volume 15 above the free surface of the cryogenic liquid L. The intermediate volume 15 is separated by seals 17 (in the example show lip seals, but which could also have a different form) from an impregnation chamber 19.

In the impregnation chamber 19 there is an atmosphere rich in a product in gaseous state (also intending a possible vapor state) for treati ng the fabric T by impregnation. As the fabric T emerges from the cryogenic liquid L at a very low temperature, below the condensation temperature of the gaseous product contained in the impregnation chamber 19 at the pressure in force in the system, this product condenses on the fabric passing through the chamber 19 and impregnates it. Typically, the product with which the impregnation chamber is saturated 19 is ammonia in gaseous state.

The impregnation chamber 19 is separated (but not sealingly isolated) from a successive drying chamber 21. In this chamber a higher temperature is in force than in the impregnation chamber 19, so that the ammonia (or other equivalent product) with which the fabric T was impregnated in the impregnation chamber 19, evaporates at least partly. Heating means, generically indicated with 23, are arranged inside the drying chamber 21. These can be composed of a fluid heat exchanger, of an electrical heating system, of a radio frequency, microwave or similar heating system. If a microwave system is used, the microwaves utilized will be at a frequency, which causes molecular resonance of the product (in this particular case ammonia) used to treat the fabric T.

A wash bath 25 containing a wash liquid, typically water, indicated with A, is arranged downstream of the drying chamber. The fabric is immersed in the bath 25 after having passed through the drying chamber 21

Seals 26 are arranged between the drying chamber 21 and the bath 25, to separate the two environments and prevent dispersal of the product, which is made to evaporate in the chamber 21 , towards the bath 25. The seals 27 can be lip seals or also of another type, for example produced with idle rollers in contact with the surface of the fabric T passing therethrough. In this way, the product which . is eliminated by evaporation from the fabric in the drying chamber 21 passes towards the impregnation chamber 19 through suitable apertures, such as

two openings adjacent to the guide roller 28 arranged between the two chambers 19 and 21 and around which the fabric T is guided, and is not dissolved in the water A contained in the bath 25 below.

To improve separation of the ammonia contained in the chamber 21 from the water contained in the bath 25, a flow of gaseous nitrogen, evaporated from the bath 11 , passes through a pipe 34 into the zone under the seal 26, to thus be interposed between the surface of the water and said seal.

Arranged inside the bath 25 is a guide roller 27, around which the textile article T is guided to re-emerge from the free surface of the water A and then be sent towards the winder 5. Squeezing and drying means, not shown, can be arranged along the path to the winder 5.

Operation of the system described above is as follows. The fabric to be treated is unwound from the reel B1 and fed substantially continuously and possibly at constant speed towards the chamber 9 and immersed in the cryogenic liquid L. From the bath 11 containing the cryogenic liquid L the fabric re-emerges to enter the intermediate volume 15 where the cryogenic liquid evaporates substantially completely from the fabric, which reaches the impregnation chamber 19 by passing through the seals 17, still in a cond ition of sufficiently low temperature to cause condensation of the ammonia gas or vapor present in the impregnation chamber 19. Consequently, the fabric T is impregnated with a limited quantity of ammonia.

The impregnated fabric is then guided around the roller 28 and enters the drying chamber 21 where the ammonia is made to evaporate more or less completely from the fabric. The bath 25 contains water and optionally chemical additives to cause precipitation of any ammonia residue contained in the fabric, which is immersed in said water, in the form of ammonia salts. The ammonia salts can subsequently be utilized as a by-product in other applications, for example as components for fertilizers for use in agriculture.

The water A contained in the bath 25 also acts as a physical barrier between the drying chamber 21 and the outside environment. The quantity of ammonia which may be dissolved in the water A and made to precipitate in the form of salts is extremely low and does not represent a problem from the viewpoint of disposal, also considering the possibility of using said salts.

Increasing the quantity of ammonia in the drying chamber 21 the ammonia passes in vapor or gaseous state from the chamber 22 back towards the chamber 19. In substance, there is continuous and automatic recirculation of the ammonia, which passes from the chamber 19 to the chamber 21 in the form of liquid ammonia, which impregnates the fabric, and vice versa, return of the ammonia from the chamber 21 to the chamber 19 in the form of gas or vapor.

Minimum quantities of ammonia which can be dispersed in the bath of water A can be suitably reintegrated through a pipe, not sh own, connecting with a stock tank. The diagram in Figure 1 also shows the presence of a pressure balancing system between the impregnation chamber 19 and 21 and the intermediate volumes 15 and 16. In the diagram illustrated this system is obtained by means of a series of pipes 31, 33, 34 and 36, which form a fluid connection of the chambers 19 and 21 and of the intermediate volumes 15 and 16 with a bath 35 containing an adequate head of water. The pressure in the intermediate volumes 15 and 16 and in the chambers 19 and 21 is therefore the same and determined by the head of water present in the bath 35.

The barrier of gaseous nitrogen, maintained at a constant pressure by the vents 31 and 36, which are positioned under both the seals 17 and 26, allows safe balancing of the pressures and confinement of the ammonia in the zone allocated for it, as said ammonia cannot exceed the pressure of the nitrogen barrier as a result of the vent pipe 33.

The system 1 illustrated in Figure 1 allows continuous treatment of the entire fabric contained on the reel B1 , which can also be of considerable length and composed of several pieces stitched together.

A discontinuous system can be produced in an identical manner. Condensation conditions in. the chamber 19 and the feed speed of the fabric T can be controlled in order to obtain impregnation of the fabric with low percentages in weight of ammonia, typically and advantageously below 50% in weight of the dry fabric and preferably equal to or below 25%. In particular the article can be impregnated with a quantity ranging from 1% to 20% in weight, and preferably between 1% and 15% in weight, and even more preferably between 1% and 10% or between 1% and 8% in weight. ^•

As known to those skilled in the art, ammonia which is dissolved in water has no useful effect on the fabric. Considering that the fabric subjected to the treatment necessarily has a more or less relevant humidity content (typically in the region of 2-8%, although depending on the ambient humidity and on any pre- treatments of the article), it must be borne in mind that part of the ammonia absorbed by the fabric is neutralized by the water present in said fabric in the form of humidity. Water absorbs up to 40% in weight of ammonia. Therefore, if the fabric has, for example, a humidity percentage of 5% in weight with respect to the weight of the dry fabric, a quantity of 2% in weight of the dry fabric will be absorbed and neutralized by the water. To provide a quantity of useful ammonia of, for example, 3% in weight of the dry fabric, impregnation must take place with a total quantity of 5% in weight of ammonia, referred to the weight of the dry fabric.

Therefore, the percentages indicated above must be intended as useful or available percentages of ammonia. Useful percentage is intended as the percentage of ammonia, which remains available to perform its action on the textile fibers, after the water in the form of residual humidity in the fabric has been saturated by the ammonia.

Figure 2 shows an embodiment of a system in which impregnation of the textile article T takes place conventionally by immersion in a bath containing ammonia in liquid state, but which again uses some of the concepts described above to obtain part of the advantages mentioned.

The system in Figure 2 again has an unwinder 3 from which the fabric T is delivered, unwinding it from a reel B1. The number 11 indicates a bath containing cryogenic liquid L, typically liquid nitrogen. Arranged in the bath 11 is a guide roller 13 about which the fabric T is guided. The bath is divided, as in the example in Figure 1 , by a partition or wall, indicated here with 1 01 , which defines an inlet and an outlet of the bath 11. The partition 101 forms part of the wall to confine the volume 103 housing a bath 105 containing the ammonia A' in liquid state for treating the fabric T. The path of the fabric extends through the bath 11 and from this into the volume 103, in which the fabric is immersed in the bath 105 and guided around a guide roller 107. Positioned at the outlet of the impregnation bath 107 is a squeezing unit 109, composed of a pair of squeezing rollers which

eliminate part of the ammonia from the fabric.

Positioned downstream of the squeezing unit 109 is a drying system, indicated generically with 111 , inside which a drying drum or other means can be arranged to evaporate the residual ammonia from the fabric. The number 113 indicates an outlet from the drying system. The fabric thus dried is then optionally wet in water, or purified from residual ammonia by other systems, such as steam or the like.

In the system in Figure 2, impregnation of the fabric takes place conventionally, by means of the immersion bath 1O5, but contrary to known systems, the fabric T is previously cooled to a very low temperature, and reaches the volume 103 at, for example, a temperature of -80 ⁰ C, as in the case of the system in Figure 1. The fabric cooled to this temperature is immersed in the ammonia A ¹ contained in the bath 105 practically without any, except negligible, vaporization thereof. This drastically reduces the quantity of ammonia in gaseous state, which must be extracted from the volume 103 and recycled. At the same time, the bath 11 in which the cryogenic liquid L is contained forms an effective barrier between the volume or chamber 103 and the environment, preventing dispersal of ammonia into the environment. The cryogenic liquid is not reactive and does cause reactions with the ammonia. At the same time, it is entirely devoid of polluting effects and can therefore be discharged into the environment without particular measures, except those useful to reduce the consumption of nitrogen for questions related to economic management.

It is understood that the drawing only shows a possible example provided purely as a practical embodiment of the invention, which can vary in forms and arrangements without however departing from the scope of the concept on which the finding is based.