TECHNICAL FIELD

The present invention generally relates to a composite filtering material, preferably an active composite filtering material, for making textiles and to a manufacturing process of such a material. In particular, the present invention relates to a composite material comprising at least one layer with added nanomaterials.

BACKGROUND

In the prior art filters are known which are capable of trapping pathogens - such as viruses, bacteria and spores - as well as dust or allergens, by applying a layer of nanofibres on a breathable substrate, thereby creating a composite filtering material. The nanofibres defining the layer are arranged so as to define inter-spaces of nanometric dimensions, which are therefore small enough to retain the particles to be filtered. The filtration efficiency of these materials is extremely high and the filtration principle is mechanical. The particles in the fluid are larger than the pores in the nanofibre network, but the molecules forming the fluid, such as liquids, gases and vapours, can pass through them with limited pressure losses. Thereby, the substrate retains its breathable properties.

The nanofibres used consist of filaments of flexible material, typically polymeric, which can be of natural or synthetic origin. Examples of natural polymers include collagen, cellulose, silk fibroin, keratin, gelatin and polysaccharides such as chitosan and alginate. Examples of synthetic polymers include poly(lactic acid) (PLA), polycaprolactone (PCL), polyurethane (PU), poly(lactic-co-glycolic) acid (PLGA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(ethylene-co- vinylacetate) (PEVA) and polyvinyldenfluoride (PVDF).

Several methods are known in the prior art for producing nanofibres, the most commonly used of which is electrospinning. Among other things, electrospinning makes it possible to generate ultra-thin fibres with controllable diameters, compositions and orientations.

Nanofibres are also extremely flexible with respect to their functionalisation. It is therefore known to functionalise the nanofibre layer with chemical additives, also of nanometric dimensions, such as ceramic or metallic nanoparticles - for example copper or silver, to give the composite material germicidal properties. Such particles are capable of oxidatively degrading and inactivating cell membranes.

Of particular interest is the application in which an oxidative catalyst is used as a chemical additive to maintain its germicidal action unaltered over time. If properly activated, the oxidative catalyst promotes the oxidation of the pathogen on the one hand and is capable of regeneration on the other. Among the oxidative catalysts, the use of light-activated catalysts (photocatalysts) is widespread, particularly titanium dioxide (TiC ), which is activated by ultraviolet radiation. Of particular interest is the fact that the photocatalytic action of the titanium dioxide nanoparticles makes it possible to decompose volatile organic compounds (VOCs), which are the main culprits of bad odours within closed environments.

The Applicant has noted that the nanofibre filter layer of the composite material is particularly delicate. Such a filtering layer generally adheres to the substrate in a precarious manner, being able to detach from the substrate or release the nanofibres in the event of abrasion. This not only leads to the degradation of the filtering layer, but also generates nanopowders that can be particularly harmful if inhaled.

With particular reference to titanium dioxide nanoparticles, the Applicant also observed that such nanoparticles are fixed to the layers of nanofibres by coating them with a dispersion of resins and nanoparticles. However, such a coating offers little resistance to washing and abrasion, operations that generally cause the resin to be removed from the nanofibre layer, and the constraining photocatalytic nanoparticles therewith.

Such a composite filtering material is known to be used in combination with breathable fabric layers for air filtration applications, for example in oral-nasal protection devices. In particular, the oral-nasal protection devices consisting of two layers of fabric generally include a pocket through which the composite material can be inserted to place it between the two layers of fabric. In such devices, the fabric layers must necessarily be thin enough to allow the passage of air, to ensure breathability, and possibly light to activate a possible photocatalyst.

In these devices, the pathogen generally passes through a first layer of breathable fabric and is blocked by the nanofibres present on the composite material for a sufficient time to be inactivated by the oxidative action, possibly supported by a photocatalytic effect.

The Applicant has noted that due to the sensitivity of the nanofibre layer of the composite filtering material set out above, already the operations of inserting such composite material between the two layers of fabric generally lead to a partial degradation of the filtering effect and/or of the germicidal effect which are added to the deterioration generated by normal use.

In fact, the Applicant has highlighted that the device resulting from the set of the composite filtering material inserted between the two fabric layers cannot be subjected to the traditional maintenance operations of a traditional fabric, without thereby suffering deterioration. In fact, the rubbing of the composite material against the two fabric layers due for example to washing or ironing operations leads to a natural detachment of the nanomaterials present in the filtering layer of the composite material, thus making it no longer effective either in terms of its filtering action or in terms of its possible further germicidal action.

In order to overcome such problems, it has been considered to load the composite material with many more nanomaterials than would actually be needed to have a good filtering and/or germicidal action. In fact, the loss of some of the nanomaterials (nanofibres and nanoparticles) as a result of handling the device would be compensated for by the higher amount included at the outset.

However, such a solution involves higher costs than those actually necessary. Furthermore, even with large quantities of nanomaterials, it cannot be excluded that degradation will sooner or later permanently compromise the filtering and/or germicidal effects of the material.

Last but not least, a higher amount of nanomaterials in the filtering layer of the composite material introduces a greater pressure drop when the fluid passes through, making the use of such a composite material inside an oral-nasal protection device uncomfortable, for example.

OBJECTS AND SUMMARY OF THE INVENTION

In view of the foregoing, the problem underlying the present invention is to devise a composite filtering material which is sufficiently robust so as not to be substantially subject to degradation under normal processing, use and maintenance thereof.

In the context of such a problem, an object of the present invention is to make a composite filtering material capable of maintaining its filtering effect substantially unchanged over time, regardless of the type of use made thereof.

A further object of the present invention is to produce a composite filtering material that requires a minimum amount of nanomaterials to exert its filtering and germicidal effects over time.

Another object of the present invention is to obtain a composite filtering material that essentially does not release nanopowders during its use.

According to its first aspect, the invention thus relates to a composite filtering material comprising at least one intermediate layer in nanomaterials coupled with layers in breathable material and in interposition therebetween, the intermediate layer and the layers in breathable material being mutually constrained by a plurality of micrometric constraints made along an overlapping surface of the layers, in which the micrometric constraints have dimensions measurable in terms of a diameter of a circumference inscribing each constraint, with the diameter d of such a circumference being less than or equal to 0.5 mm. The Applicant has found that by creating micrometric constraints, such as microwelds or micro bonding points, with appropriate micrometric dimensions, it is possible to constrain the layers to each other, maintaining the filtering features of the composite material and at the same time eliminating the mechanical stresses on the intermediate layer, which are discharged by the constraint points.

Furthermore, the presence of micrometric constraints makes it possible to prevent the detachment from the breathable layers, which would lead to a loss of the filtering effect, without however being detectable by visual inspection of the composite material, as it is concealed by the breathable material itself.

In essence, the presence of the micrometric constraints makes it possible to overcome the degradation of the intermediate layer in nanomaterials.

According to a second aspect of the invention, the invention relates to a process for manufacturing a composite filtering material comprising the steps consisting of:

- making a layer in nanomaterials;

- constraining the nanomaterial layer between two layers of breathable material and therebetween by means of micrometric constraints distributed along an overlapping surface of the layers, where the micrometric constraints have dimensions measurable in terms of a diameter of a circumference inscribing each constraint, with the diameter d of such a circumference less than or equal to 0.5 mm.

Advantageously, the manufacturing process of a composite filtering material thus configured allows to achieve the same advantages as described with reference to the composite filtering material according to the invention.

The present invention may have at least one of the preferred following features; the latter may in particular be combined with one another as desired in order to meet specific application needs.

Preferably, the micrometric constraints have dimensions which can be measured in terms of a diameter of a circumference inscribing each constraint, with the diameter d of such a circumference being less than or equal to 0.2 mm.

Preferably, the micrometric constraints are distributed over at least one portion of the overlapping surface of the layers with a surface distribution of at least 1 constraint/cm ² , preferably at least 5 constraints/cm ² , more preferably at least 25 constraints/cm ² .

Preferably, the micrometric constraints are distributed over at least one portion of the overlapping surface of the layers according to a random distribution, i.e., a distribution in which no repeating pattern is identifiable. More preferably, the at least one portion of the overlapping surface of the layers in which the micrometric constraints are distributed according to a random distribution is a portion having an area equal to 1 cm ² .

Advantageously, a random distribution of micrometric constraints allows for an aesthetic finish of the composite material which essentially lacks texture. Furthermore, a random distribution of micrometric constraints allows the mechanical stresses to be evenly distributed in any transition areas between areas with different constraint densities.

In an alternative embodiment, particularly suitable for areas of the overlapping surface intended to be subjected to more intense mechanical stresses, the micrometric constraints are distributed over at least one portion of the overlapping surface of the layers with a surface distribution of at least 45 constraints/cm ² , preferably at least 70 constraints/cm ² , more preferably at least 160 constraints/cm ² .

In a preferred embodiment, the micrometric constraints are made so as to define at least two areas within the overlapping surface with different micrometric constraint surface distributions.

In a variant of the invention, the micrometric constraints have a substantially grid-shaped distribution with an inter-spacing pitch p between 0.4 mm and 10 mm.

More preferably, the inter-spacing pitch p is between 0.6 mm and 5 mm.

Even more preferably, the inter-spacing pitch p is between 0.8 mm and 2 mm.

In a variant of the invention, the nanomaterial layer has a thickness, measured in nanomaterial density, between 1 g/m ² and 10 g/m ² .

Preferably, the nanomaterial layer has a thickness, measured in nanomaterial density, between 1.2 g/m ² and 5 g/m ² .

More preferably, the nanomaterial layer has a thickness, measured in nanomaterial density, between 1.5 g/m ² and 3 g/m ² .

In a variant of the invention, the nanomaterials forming the intermediate layer comprise nanofibres made of flexible material, typically polymeric of natural or synthetic origin.

Preferably, the nanomaterials forming the intermediate layer comprise chemical additives with a germicidal effect in the form of nanoparticles.

More preferably, the nanoparticles of chemical additives with a germicidal effect comprise nanoparticles of at least one among:

- Copper (Cu), - Silver (Ag)

- Nitrogen-doped titanium dioxide (N-TiC ),

- Zinc oxide (ZnO), and

- Silica (S1O2).

In a preferred variation of the invention, the nanomaterials forming the intermediate layer comprise nanoparticles of chemical additives that can be activated by electromagnetic radiation with wavelength l comprised in the ultraviolet spectrum or the visible spectrum.

Preferably, the nanoparticles of chemical additives that can be activated by electromagnetic radiation with a wavelength l comprised in the ultraviolet spectrum or the visible spectrum comprise nanoparticles of at least one among:

- nitrogen-doped titanium dioxide (N-T1O2),

- zinc oxide (ZnO), and

- silica (S1O2).

Preferably, the nanomaterial layer has a filtering capacity of at least FFP1 as defined in EN 149:2009 or equivalent.

More preferably, the nanomaterial layer has a filtering capacity of at least FFP2 as defined in EN 149:2009 or equivalent.

Preferably, at least one of the two layers of breathable material is made of fabric, non-woven fabric or cloth.

Preferably, at least one of the two layers of breathable material is made of fabric, non-woven fabric or cloth that is light enough to allow light to pass therethrough, in particular the passage of sunlight.

Preferably, at least one of the two layers of breathable material is made of muslin, jersey or other textile material used in the manufacture of clothing, furniture and linen.

Preferably, the micrometric constraints are microwelded and the breathable material layers are made of thermoplastic materials.

More preferably, the microwelds are made as ultrasonic microwelds, thermal microwelds and/or laser micro welds.

Alternatively, the micrometric constraints are micrometric points of adhesive material.

In a variant of the invention, the step of making a nanomaterial layer comprises functionalising the microfibres by means of a germicidal chemical agent, preferably a photocatalytic germicidal chemical agent, more preferably a photocatalytic germicidal chemical agent activated by electromagnetic radiation with wavelength l comprised in the visible spectrum.

In a variant of the invention, the manufacturing process comprises a step of converting the composite filtering material comprising making cuts, seams and finishes.

Advantageously, starting from the composite filtering material according to the invention, it is possible to make textile products such as tablecloths, curtains, upholstery, clothing or even oral- nasal protection devices which are essentially capable of sanitising themselves within a few seconds of exposure to light. Moreover, by virtue of the decomposition property of volatile organic compounds (VOCs) of the nanoparticles activated by electromagnetic radiation with a wavelength l comprised in the ultraviolet or visible spectrum, it is possible to make textiles capable of in fact not absorbing bad odours present in the environment in which they are placed and contributing to eliminating them from the environment itself.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will be more evident from the following detailed description of certain preferred embodiments thereof made with reference to the appended drawings.

The different features in the individual configurations may be combined with one another as desired according to the preceding description, should there be advantages specifically resulting from a specific combination.

In such drawings,

- figure 1 is a perspective, cutaway and enlarged view of a portion of a composite filtering material according to a first embodiment of the present invention;

- figure 2 is a detailed diagram illustrating the micro-constraints applied to the composite filtering material in accordance with a second embodiment of the present invention;

- figures 3a and 3b are enlarged schematic depictions of a composite filtering material according to a third and fourth embodiment of the present invention, respectively;

- figure 4 is a block diagram of the manufacturing process of a composite filtering material according to the present invention; and

- figure 5 is an enlarged schematic view of a nanofibre functionalised with chemical additives in the form of nanoparticles.

DETAILED DESCRIPTION OF THE INVENTION

For the illustration of the drawings, use is made in the following description of identical numerals or symbols to indicate construction elements with the same function. Moreover, for clarity of illustration, certain references may not be repeated in all drawings.

While the invention is susceptible to various modifications and alternative constructions, certain preferred embodiments are shown in the drawings and are described hereinbelow in detail. It is in any case to be noted that there is no intention to limit the invention to the specific embodiment illustrated rather on the contrary, the invention intends covering all the modifications, alternative and equivalent constructions that fall within the scope of the invention as defined in the claims.

The use of “for example”, “etc.”, “or” indicates non-exclusive alternatives without limitation, unless otherwise indicated. The use of “comprises” and “includes” means “comprises or includes, but not limited to”, unless otherwise indicated.

With reference to Fig. 1 , a preferred embodiment of a composite filtering material according to the present invention is illustrated, collectively referred to as 10.

The composite filtering material 10 comprises at least one intermediate layer 11 of nanofibres coupled with two contiguous layers of breathable material 12,13. The nanofibres are preferably made of flexible material, typically polymeric, which can be of natural or synthetic origin.

The breathable material layers 12,13 are made from any type of fibre and in the form of fabric, non-woven fabric or cloth. Fibres suitable for the manufacture of the breathable layers 12,13 are for example natural fibres such as cotton, silk, wool, etc., man-made fibres such as viscose, lyocell, modal, etc. or synthetic fibres such as polyester (PS), polyethylene (PE), polypropylene (PP), etc.

At least one of the two layers of breathable material 12,13 is further made of a fabric or cloth light enough to allow light to pass therethrough, in particular the passage of sunlight. An example of a fabric suitable for allowing light to pass through is muslin; an example of a cloth suitable for allowing light to pass through is jersey. An example of a non-woven fabric suitable for allowing light to pass through is a sufficiently thin microfibre cloth.

As better illustrated in Fig. 2, the at least one intermediate layer 11 made of nanofibres is constrained to the two layers made of breathable material 12, 13 by micrometric constraints made along an overlapping surface of the layers 11, 12, 13. Each constraint has dimensions that can be measured in terms of a diameter of a circumference inscribing the constraint, having a diameter d of less than or equal to 1.0 mm, preferably less than or equal to 0.5 mm, more preferably less than or equal to 0.2 mm.

The micrometric constraints are also distributed over the surface of the sandwich 11,12,13 with a surface distribution of at least 1 constraint/cm ² , preferably at least 5 constraints/cm ² , more preferably 25 constraints/cm ² .

In particular, the micrometric constraints are distributed over the surface of the sandwich 11,12,13 with surface distributions chosen as a function of the mechanical stresses to which a particular area of the surface can be subjected.

For example, in the event of a composite material 10 intended for use as an oral-nasal protection device, such as that illustrated in Fig. 3a, a central area Ai is identifiable in which a greater surface distribution, e.g., 280 constraints/cm ² , is included, with respect to a surface distribution in a peripheral area A2, e.g., 10 constraints/cm ² . In the embodiment of Fig. 3a, the micro constraints are made according to a random distribution.

However, in the event of a composite material 10 intended for use as a tablecloth for example, such as that illustrated in Fig. 3b, a central area Ai is identifiable in which a lower surface distribution is included, e.g., 5 constraints/cm ² , with respect to a surface distribution of a peripheral area A2, e.g., 160 constraints/cm ² . In the embodiment of Fig. 3b, the micro-constraints are made according to a regular grid-shaped distribution.

In the event of a regular grid-shaped distribution, the micrometric constraints are preferably spaced by an inter-spacing pitch p between 0.4 mm and 10 mm, preferably between 0.6 mm and 5 mm, more preferably between 0.8 mm and 2 mm.

Preferably, the micrometric constraints are microwelds if the breathable material layers 12,13 are made of thermoplastic materials, or alternatively, micrometric bonding points.

The intermediate layer 11 is configured not to be an obstacle to heat-sealing or bonding and is therefore thin enough to allow the interpenetration of the layers of breathable material 12,13 in the points of melting or the passage of the adhesive.

At the same time, the intermediate layer 11 comprises a thickness and degree of uniformity sufficient to ensure a filtering capacity of at least FFP1 with the filtering capacity measured according to EN 149:2009 or equivalent.

The Applicant has identified that to allow the creation of the micro-constraints described above, the thickness - measured in nanofibre density - must be less than or at most equal to 10 g/m ² . On the other hand, in order to ensure a filtering capacity of FFP1 measured according to UNI EN 149:2009 - which implies a high degree of uniformity of the intermediate layer 11 substantially lacking clusters or bundles of fibres - the thickness of the intermediate layer 11 must be at least 1 g/m ² . Preferably, the thickness of the intermediate layer is between 1.2 g/m ² and 5 g/m ² , more preferably the thickness of the intermediate layer is between 1.5 g/m ² and 3 g/m ² .

According to a preferred embodiment, the intermediate layer comprises, in addition to the microfibres, at least one germicidal chemical additive in the form of nanoparticles. In the specific embodiment illustrated, the germicidal material is a photocatalytic chemical additive. Alternatively, non-photocatalytic chemical additives such as copper (Cu) or silver (Ag) can be used.

Among the photocatalytic chemical additives, chemical additives that can be activated by electromagnetic radiation with a wavelength l comprised in the visible spectrum (i.e., substantially 400 nm < l < 740 nm) or in the ultraviolet spectrum (i.e., substantially 100 nm < l < 400 nm) are particularly suitable. For example, known catalysts that can be activated by electromagnetic radiation with a wavelength l comprised in the visible or ultraviolet spectrum are nitrogen-doped titanium dioxide (N-TiC ), zinc oxide (ZnO) and silica (S1O2).

Advantageously, the chemical additives that can be activated by electromagnetic radiation with a wavelength l comprised in the visible or ultraviolet spectrum are very powerful catalysts which require less energy from the outside, as they can be activated by radiation generated by the sun alone or even by indoor lamps.

The manufacturing process of a composite filtering material 10 according to the present invention is schematically illustrated in Fig. 4.

A nanofibre layer 11 having a thickness - measured in nanofibre density - between 1 g/m ² and 10 g/m ² , preferably between 1.2 g/m ² and 5 g/m ² , more preferably between 1.5 g/m ² and 3 g/m ² is made (step 110).

The nanofibre layer 11 is preferably functionalised (step 115) by a germicidal chemical agent, in particular a photocatalytic germicidal chemical agent in the form of nanoparticles dispersed in the nanofibre matrix itself. Thereby, the high chemical reactivity and low probability of nanoparticle release following stresses are maintained. In fact, the nanoparticles 20 are embedded in the nanofibre 21, as illustrated in Fig. 5.

Preferably, the nanofibre layer 11 is functionalised by a germicidal chemical agent that can be activated by electromagnetic radiation with a wavelength l comprised in the visible spectrum.

The nanofibre layer 11 is thus constrained (step 120) between two layers of breathable material 12,13 by micrometric constraints distributed on the surface of the sandwich created by the three layers 11,12,13. Each constraint is made in a size which can be measured in terms of a diameter of a circumference inscribing the constraint, having a diameter d less than or equal to 1.0 mm, preferably less than or equal to 0.5 mm, more preferably less than or equal to 0.2 mm

The micrometric constraints are made on the surface of the sandwich 11,12,13 with a surface distribution of at least 1 constraint/cm ² , preferably at least 5 constraints/cm ² , more preferably 25 constraints/cm ² .

Preferably, the micrometric constraints are made so that at least two areas Ai, A2 are defined with different surface distribution.

According to a preferred embodiment, the micrometric constraints are made in a grid-shaped arrangement, preferably with an inter-spacing pitch p in the order of a millimetre. In particular, the pitch p is between 0.4 mm and 10 mm, preferably between 0.6 mm and 5 mm, more preferably between 0.8 mm and 2 mm.

In particular, the micrometric constraints are made by applying micrometric-sized spots of adhesive material. Such a technique is particularly suitable if the layers of breathable material 12,13 are made of natural or artificial fibres, even if they are different from each other.

Alternatively, in the event of layers of breathable material 12,13 made of synthetic fibres, the micrometric constraints are made by welding, e.g., ultrasonic, thermal or laser welding.

The resulting composite material 10 can then be processed (step 130) by cutting, stitching and finishing without causing the degradation of the nanomaterial layer 11. Such composite filtering material 10 can be used to make textiles such as tablecloths, curtains, upholstery, clothing or even oral-nasal protection devices that can essentially sanitise themselves within a few seconds of exposure to light, as well as possibly reduce volatile organic compounds (VOCs) present on the fabric and causing unpleasant odours.

Furthermore, the resulting composite fabrics and cloths can be treated, for example by washing and/or ironing, without degradation of the filtering capacity and possibly the germicidal and odour-reducing capacity of the nanomaterial layer 11.