The present invention relates to a method and a machine for yarn or fabric mercerization.

Mercerization is an industrial process to which yarns (and textile products in general) are subjected to provide them with improved mechanical, aesthetic and functional qualities.

In greater detail, mercerization is carried out by immersing and/or impregnating the yarns or fabrics in or with chemical solutions such as to give them improved aesthetic and/or mechanical characteristics.

Mercerization processes are known to be carried out using caustic soda solutions. This treatment facilitates subsequent dyeing, and also renders the colour more intense. It also gives the textile product optimal characteristics with reference to breathability.

In greater detail, mercerization treatment converts the crystalline structure of the yarn fibre cellulose from the natural form known as "cellulose I" to the regenerated form known as "cellulose II".

This irreversible modification is due to a change in the arrangement of the cellulose intramolecular bonds. In particular, some OH bonds of the cellulose II remain free and available to effect bonds with the H+OH water molecules present in the moisture of the air and/or in body sweat.

This modification results in an increase of up to about 20% of moisture restoration, without the fibres giving an impression of wetness. This represents a form of air moisture absorption and desorption which is particularly beneficial and comfortable for human body breathability.

Mercerization processes are also known using anhydrous liquid ammonia instead of the caustic soda solution. This treatment improves the fibre mechanical characteristics while at the same time obtaining an improved soft feel. The use of ammonia also enables more intense colour tones to be achieved on already dyed products, plus greater dimensional stability.

It should be noted that treatments with ammonia cannot be defined strictly as mercerization processes as they determine slightly different chemico-physical modifications. However, in the technical sector in question, it is common to define treatments for enhancing textile products with ammonia by the term "mercerization".

Hence within the scope of the present invention, the term "mercerization" will be applied to those enhancing treatments on textile products implemented with either caustic soda or ammonia without distinction.

In the known art, mercerization is carried out in dedicated machines comprising handling rollers on which the yarns or fabrics to be treated are disposed.

A tank is arranged to receive a working solution required for the treatment.

The tank is arranged such that the yarn or fabric can be immersed in the solution. In detail, the textile product, during its movement, is immersed in and extracted from the solution for a certain number of cycles.

Known machines also comprise a squeezing member to squeeze the skein leaving the solution, so eliminating the excess solution from the yarn or fabric. Further washing and squeezing phases of the yarn or fabric are carried out by dispensing water on the product under treatment.

As seen, known mercerization processes use chemical substances involving irritating fumes which can considerably prejudice the working environment.

In this respect, specific regulations require ventilation systems or general precautions to prevent damage to the workers' health.

In this context, the technical aim at the base of the present invention is to propose a yarn mercerization method and machine which overcome the aforestated drawback of the known art.

A particular object of the present invention is to provide a yarn mercerization method and machine which are more effective and reliable in terms of operator safety.

The stated technical aim and the specified object are substantially attained by a method and a machine for yarn or fabric mercerization comprising the technical characteristics highlighted in one or more of the accompanying claims.

Further characteristics and advantages of the present invention will be more apparent from the indicative and therefore non-limitative description of a preferred but non-exclusive embodiment of a method and a machine for yarn or fabric mercerization, as illustrated in the accompanying drawings, in which: Figure 1 is a schematic front view of a yarn mercerization machine in accordance with the present invention;

Figure 2 is a perspective view of the machine of Figure 1 with some elements removed to better highlight others;

Figures 3 and 4 are perspective views of a variant of the machine of Figure 1 in two different operative conditions.

With reference to the accompanying figures, the reference numeral 1 indicates overall a machine for yarn or fabric mercerization, in accordance with the present invention.

A yarn mercerization method in accordance with the present invention is, by way of example, implemented by the machine 1 .

The method is implemented by wetting the yarn F or fabric in a solvent fluid the purpose of which is to determine chemical-physical modifications of the yarn textile fibres in question. The yarn is then squeezed to eliminate any excess fluid quantity.

The step of wetting the yarn or fabric with the fluid takes place by spraying the fluid onto the moving yarn or fabric.

The excess fluid is collected in a tank 7 through which the moving yarn or fabric is made to transit. In this manner, the yarn or fabric is further impregnated with the fluid by immersing it therein.

In the case of yarns, these are wound into skeins which are subjected to movement.

The step of wetting the yarn or fabric terminates after a predetermined number of cycles of immersion into and extraction from the bath of the tank 7.

Having concluded this step, the squeezing step is carried out. The excess fluid is thus collected and removed to be recovered and made up to strength.

According to the invention, the steps of wetting and squeezing the yarn or fabric are carried out in a working environment which is hermetically sealed and isolated from the external atmosphere.

In this respect, a hermetically sealed box enclosure 2 is provided defining the working environment.

Further details of the box enclosure 2 are provided hereinafter in describing the machine 1 .

The yarn F or fabric is hence inserted into the box enclosure 2 prior to the step of wetting it with the fluid.

As delivery of the solvent fluid takes place into the hermetically sealed working environment, there is no possibility of escape of fumes originating from the fluid.

In other words, advantageously, the complete isolation of the working environment from the external environment prevents any irritating and/or dangerous emergence of discharges deriving from the solvent fluid.

The method can also comprise a yarn or fabric wash step once the squeezing step is concluded.

This wash can be carried out by dispensing water or other liquid onto the treated yarn or fabric.

The method can also comprise a yarn or fabric drying step.

According to a first embodiment, the solvent fluid is an aqueous solution of caustic soda (sodium hydroxide).

In this case, advantageously, a vacuum is produced inside the box enclosure 2 by drawing out the air. Preferably, this step is implemented before the start of fluid delivery.

This enables the solution and the yarn to be degassed such that the solution diffuses into the fibres of the yarn F or of the fabric more deeply and more rapidly. By way of example, the pressure inside the working environment, i.e. inside the box enclosure 2, attains 40 mbar or less.

In this case, the caustic soda solution concentration is between 14 and 32 ^Q Be'. The wash step is carried out with water. This step enables mercerization to be completed, the water removing caustic soda from the fibres to cause them to swell.

In a second embodiment, the solvent fluid is anhydrous liquid ammonia.

The ammonia temperature is maintained less than -34 ^Q C to maintain the ammonia liquid.

Advantageously, the use of ammonia within the hermetically sealed working environment enables an effective mercerization process by preventing leakage of ammonia vapours which, as known, present considerable toxicity.

Preferably, no vacuum is generated in the working environment in order not to have to further lower the temperature of the ammonia to maintain it liquid.

However, in alternative embodiments, a vacuum is also generated in this case to improve fluid absorption into the yarn fibres. At the same time, the ammonia temperature is further lowered.

In this embodiment, a step of washing the working environment with nitrogen (or another inert gas) can be implemented to reduce or eliminate the oxygen present, in order to prevent violent ammonia oxidation reactions.

The yarn or fabric wash step is not indispensable in this embodiment. In this respect, the liquid ammonia evaporates once the yarn or fabric is returned to ambient temperature.

In any event, the water wash step can be provided to eliminate ammonia residues which could cause unpleasant product odours.

According to a third embodiment, the solvent fluid is a mixture of a sodium hydroxide solution and liquid ammonia.

Yarns or fabrics can hence be obtained presenting a considerable breathability and, at the same time, optimal characteristics regarding fabric dimensional stability and the mechanical strength of the fibres.

The overall solution obtained preferably has a density between 8 and 18 ^Q Be'.

In such a case, a vacuum can be produced inside the working environment to improve solvent fluid absorption.

Alternatively, the process can be implemented at constant pressure.

The water wash step is provided to complete the mercerization reaction.

According to a fourth embodiment, the caustic solvent fluid is composed of a water-alcohol and sodium hydroxide mixture.

Preferably, the alcohol used is ethyl alcohol. Alternatively, other alcohols such as isopropanol and isobutanol can be used.

As an alternative to sodium hydroxide, lithium hydroxide or other alkaline hydroxides suitable for the purpose can be used.

The alcohol lowers the surface tension of the yarn or fabric and enables the caustic soda to be carried into the textile fibres decidedly more rapidly and deeply.

The solution caustic soda concentration can therefore be lowered. By way of example, this concentration is between 3.5% and 8.6% of the solvent by weight. The wash step is implemented with water to complete the mercerization reaction.

In further embodiments, the wash is carried out in alcohol, chosen from the aforestated, to render the caustic soda removal extremely fast and effective. As stated, the described method can be implemented by the machine 1 comprising the hermetically sealed box enclosure 2.

The illustrated machine 1 is particularly suitable for the mercerization of yarns wound into skeins.

The box enclosure 2 comprises a lateral wall 3 of substantially cylindrical shape and a rear wall 1 1 which define a compartment. The box enclosure 2 also comprises a door 4 in a position opposite the rear wall 1 1 , to hermetically seal the compartment.

In other words, the box enclosure 2 presents a substantially barrel shape, in the preferred but non-binding embodiment.

As shown, the machine 1 comprises two box enclosures 2 each intended for treating a respective yarn skein, they both being sealed by the same door 4.

In general, the machine 1 can comprise any number of box enclosures 2.

Handling means 5 for the yarn skeins are disposed inside the compartments. As shown, the handling means 5 comprise, disposed in the respective box enclosures 2, at least two parallel rolls 6 about which the skeins are wrapped.

The rolls 6 are disposed with their rotational axes coplanar with a substantially vertical plane.

At least one of the rollers 6 is motorized such as to rotate the skeins. Preferably, the motorized roll 6 is that positioned at a higher level. The roll 6 positioned at a lower level is idle.

Advantageously, the handling means 5 present a plurality of pairs of rolls 6 disposed in a corresponding plurality of box enclosures 2 to drive a corresponding plurality of yarn skeins F.

A fluid dispensing member 19 is disposed inside each box enclosure 2. It comprises a tube extending parallel to the rolls 6 and presenting a plurality of dispensing nozzles.

A tank 7 is disposed inside each box enclosure 2 to contain the solvent fluid originating from the dispensing member 19.

In particular, the tank 7 is disposed in proximity to the lower roll 6.

As shown in the drawings, the tank 7 is hinged to the box enclosure 2 such as to be able to rotate about an axis parallel to the rolls 6 to approach and/or withdraw from the lower roll 6.

In any event, the roll 6 positioned at a lower level is disposed such that the skein which transits in proximity to that roll 6 is immersed in the fluid collected in the tank 7.

A tensioning device 8 is associated with the handling means 5 to suitably tension the yarn and enable it to move.

In detail, the tensioning device 8 comprises a tensioning roller 9 movable between a non-operative position in which it is spaced from the skein and is not in contact therewith, and an operative position in which it is in contact with the skein and urges it to maintain it in tension.

The tensioning device 8 also comprises a crank 10 presenting a first end 10a fixed to the rear wall 1 1 of the box enclosure 2 and a second end 10b to which the tensioning roller 9 is projectingly fixed.

The crank 10 is rotated by a drive device (not shown) positioned outside the box enclosure 2, to reversibly bring the tensioning roller 9 from the non-operative position to the operative position.

A squeezing device 12 is associated with the handling means 5. The squeezing device 12 is also positioned inside the box enclosure 2 and, in accordance with that illustrated, is disposed in a position corresponding with the lower roll 6. The squeezing device 12 comprises a squeezing roller 13 movable between a non-operative position in which it is spaced from the skein and not in contact therewith, and an operative position in which it is in contact with the skein to urge it against the roll 6 in order to squeeze it and cause the excess solvent fluid to escape.

The squeezing device 12 also comprises a crank 14 presenting a first end 14a fixed to the rear wall 1 1 of the box enclosure 2 and a second end 14b to which the squeezing roller 13 is projectingly fixed.

The crank 14 is rotated by a drive device (not shown) positioned outside the box enclosure 2, to reversibly bring the squeezing roller 13 from the non-operative position to the operative position.

Preferably, a drying device 15 is associated with the handling means 5 and is functionally positioned downstream of the tank 7, with reference to the skein movement direction.

The drying device 15 is also positioned inside the box enclosure 2.

The drying device 2 comprises a drying roller 16 operatively disposed between the rolls 6.

The drying roller 16 is movable between a non-operative position in which it is spaced from the skein and not in contact therewith, and an operative position in which it is in contact with the skein.

The drying roller 16 is heated such that it can increase the skein temperature when in contact therewith, in order to dry it.

The drying device 15 also comprises a crank 17 presenting a first end 17a fixed to the rear wall 1 1 of the box enclosure 2 and a second end 17b to which the drying roller 16 is projectingly fixed. The crank 17 is rotated by a drive device (not shown) positioned outside the box enclosure 2, to reversibly bring the drying roller 16 from the non-operative position to the operative position.

According to a preferred embodiment, the lateral wall 3 and the rear wall 1 1 of the box enclosure 2 are fixed to a frame structure 18.

The door 4 is rotatably mounted on the lateral wall 3 in such a manner as to be able to be opened and closed.

In an alterative embodiment, the door 4 is rotatably fixed to the frame structure 18. In this case, the lateral wall 3 is slidingly associated with the frame structure 18 such that it separates from the rear wall 1 1 during opening. Comfortable access is hence made possible to the members contained inside the box enclosure 2 for maintenance operations.

Connection means (not shown) are operatively disposed between the door 4 and the lateral wall 3 of the box enclosure 2 such as to make the opening and closure of the door 4 simultaneous with the sliding of the lateral wall.

The described invention attains the proposed objects. In this respect, by confining the operations to the interior of a hermetically sealed working environment, not only are the steps involved in mercerization with traditional solvents made safer, but their effectiveness can also be increased by providing internal vacuum if considered desirable.

Moreover, different solvent products such as ammonia can be used which under normal conditions generate various problems because of toxic fumes.