WO2021255601A1

WO2021255601A1 - Filter material for mask for sanitary use

Info

Publication number: WO2021255601A1
Application number: PCT/IB2021/055164
Authority: WO
Inventors: Fabio Di Berardino; Renzo Marcello Odoardi; Alessandro Gagliardini; Carmine Cimini
Original assignee: Texol S.R.L.
Priority date: 2020-06-15
Filing date: 2021-06-11
Publication date: 2021-12-23
Also published as: IT202000014191A1

Abstract

The present invention relates to a process for the preparation of a filter material to block harmful particles, in particular viral, bacterial and/or toxic particles, suitable for being incorporated into a sanitary article, as well as a filter material obtainable by means of said process and an individual health protection mask comprising said filter material.

Description

"Filter material for mask for sanitary use"

FIELD OF THE INVENTION

The present invention relates to a process for the preparation of a filter material to block harmful particles, in particular viral, bacterial and/or toxic particles, suitable for being incorporated into a sanitary article, as well as to a filter material obtainable by means of said process, and to an individual health protection mask comprising said material.

STATE OF ART With the global sanitary emergency due to COVID-19 all over the world has recorded a significative increase in the request for individual protection devices and, as a consequence, an increase in the need for availability on the market of effective and low-cost materials suitable to protect from airborne biological agents, such as viral or bacterial particles.

The main requisites of the individual protection face masks of medical type, based upon UNI EN 14683:2019 standard, are summarized in the following Table 1:

Table 1: Requisites for health masks

The bacterial filtration efficiency (BFE) parameters are particularly important, which efficiency must reach values at least equal to 95% in case of common masks of Type-1, and differential pressure (DP) parameters, which pressure represents a measurement of the breathability levels guaranteed by the protection mask. Most masks currently available on the market are implemented with materials made of non-woven fabric obtained by means of “spunbond” technology. Generally, said materials are characterized by bacterial filtration efficiency values around 50-60%. A weight increase, for example through the insertion in the mask of several layers of filter material, allows to increase the filtering capability of the mask itself, however often in a limited way, not allowing to reach values of BFE required by the standard.

An excessive increase in the layers of filter material often can further involve an insufficient breathability, by making necessary the use of valves inside the masks which could make easier breathing. In such context, the possibility of developing new procedures for the preparation of filtering devices capable of conjugating a greater filtration efficiency of dangerous particles and high breathability, that is low differential pressure, represents one of the needs and even one of the main challenges in the field.

SUMMARY OF THE INVENTION The object of the present invention is to obviate the problems found in the known art and to fulfil the need for availability of filtering protection devices which are capable of conjugating a high filtration efficiency to high breathability, by providing as solution a process for the preparation of a filter material particularly suitable to block aerosol comprising viral or bacterial pathogen agents and/or toxic particles. In particular, the process for manufacturing the filter material, the invention relates to, provides the implementation of non-woven fabric, apt to be incorporated in a health protection mask, formed by three layers, wherein the external layers are implemented by using the “spunlace” technology, whereas the central layer is implemented by means of “air-laid” technology. Said filter material preferably consists of a non-woven fabric comprising cellulosic fibers, such as cellulose pulp, rayon- viscose and cotton.

When inserted inside a health mask, the filter material object of the present invention, allows to reach levels of bacterial filtration even higher than 99%. Moreover, as clearly shown in the differential pressure (DP) tests shown in the experimental section, the finding of the present invention is surprisingly capable of guaranteeing a much higher breathability (< 18 Pa/cm²) than the conventional filtering masks even if characterized by comparable bacterial filtration efficiencies. In fact, at such filtration levels, the known health masks generally have differential pressure values near to the standard limit (49 Pa/cm²) and then require suitable valves to ease breathing. The BFE/DP ratio of the filter material developed by the inventors instead results to be surprisingly advantageous with respect to what reported for filtering materials known in the field, such as, for example, the microfiber- based filtering agents obtained by means of “meltblown” technology.

Apart from the already illustrated advantages, literature data have shown that the SARS viruses survive only few hours on materials implemented with cellulosic fibers, whereas they are capable to survive for a period of time even longer than seven days on common health masks based upon plastic materials such as polypropylene. The process object of the present invention, allows to implement filtering materials even wholly consisted of cellulosic fibers, and therefore results to be particularly suitable to implement highly re-usable protective masks, effective against SARS viral particles.

Therefore, a first aspect of the present invention relates to a process for the preparation of a filter material to block harmful particles, in particular viral, bacterial and/or toxic particles, suitable for being incorporated into a sanitary article, comprising the following steps:

(i) preparing a first layer of non-woven fabric by using spunlace technology;

(ii) preparing a second layer of non-woven fabric by using air-laid technology;

(iii) preparing a third layer of non-woven fabric by using spunlace technology;

(iv) welding together the layers obtained in said steps (i), (ii) and (iii).

A second aspect of the present invention is the filter material obtainable from the process of the present invention.

A third aspect of the present invention is a health protection mask (5) comprising the filter material of the present invention.

Other advantages and features of the present invention will result evident from the following detailed description. BRIEF DESCRIPTION OF FIGURES

Figure 1 - Schematic representation of an embodiment of the filter material according to the invention seen in the version disassembled in the several constituting layers.

Figure 2 - A top plan view schematic representation of an embodiment of a health protection mask according to the invention.

In the above-mentioned figures, the sizes will be meant as purely exemplifying and not necessarily with components shown in proportion.

DETAILED DESCRIPTION OF THE INVENTION

GLOSSARY

The terms used in the present description are as generally understood by the person skilled in the art, except where differently indicated.

The term “non-woven fabric” is used according to the meaning commonly known in the art, that is to designate a material similar to a fabric but obtained with processes different from weaving or knitting, characterized by fibers arranged in layers or crossed, joined together mechanically, with adhesive, or with thermal processes.

Where specified, the unit of measure “decitex”, abbreviated “dtex”, represents the unit of measure for the linear density used in the textile field for titration of textile fibers, corresponding to 1 gram on 10 kilometres.

The unit of measure gram/m² also abbreviated “gms”, in the present invention designates the mass in grams of the material made of non-woven fabric calculated on square meter.

As already mentioned, the present invention relates to a process for the implementation of a filter material, apt to be incorporated in a health mask, for the implementation of an individual protection device capable of conjugating high bacterial filtration efficiency, high breathability and higher re usability.

By firstly referring to Figure 1, a filter material according to a preferred embodiment of the invention is designated as a whole with (1).

Therefore, a first aspect of the invention relates to a process for the preparation of a filter material (1) to block harmful particles, in particular viral, bacterial and/or toxic particles, suitable for being incorporated into a sanitary article, comprising the following steps:

(i) preparing a first layer (2) of non-woven fabric by using spunlace technology;

(ii) preparing a second layer (3) of non-woven fabric by using air-laid technology;

(iii) preparing a third layer (4) of non-woven fabric by using spunlace technology;

(iv) welding together the layers obtained in said steps (i), (ii) and (iii).

The process described in the present invention could be used for the realizationof filtering materials with different degree of stratification, but comprising at least three layers obtained by means of the above-mentioned technologies, on condition that the functionality requirements are met.

Therefore, a preferred embodiment version relates to a process for the implementation of a three layered filter material, wherein the two external layers are prepared by means of “spunlace” technology, whereas the central layer is implemented with “air-laid” technology.

Based upon the “spunlace” technology, the fibers of the material made of non-woven fabric are sent to a “carder” insider thereof they are oriented by producing a carded fabric. Said carded fabric is then subjected to a welding, or “interlacing”, process through the application of very thin under pressure water jets (h ydro-entanglemen . Generally, the “spunlace” process uses staple fibers, typically with linear density comprised between 1 and 10 dtex and a length approximatively around 40 mm.

In a preferred embodiment of the process of the invention, the fibers of the first external material (2) are then carded and “interlaced” with high-pressure water jets and, on such first layer (2) the layer obtained by means of air-laid process (3) is deposited. At last, above such layer (3) the second “spunlace” carded external layer (4) is deposited.

During step (iv), the layers obtained in steps (i), (ii) and (iii) are overlapped and are then interlaced and welded to each other to form an apparently homogeneous and perfectly cohesive filter material. Said welding (iv), or “cohesion”, process of the obtained layers can be performed with methods known in the state of art, for example by welding with high-pressure water jets, thermowelding, or ultrasound welding.

According to an aspect of the invention, the process can even comprise one or more intermediate steps wherein each obtained layer made of non-woven fabric is subjected to drying in oven. According to an additional aspect of the invention, the process for the implementation of said filter material may comprise a step (v), wherein the multilayer material obtained directly in step (iv) has passed in oven for drying.

At the end of any one of the described drying passages, the material obtained in one of the various embodiments can even be wound in coils which can be subjected to cutting or winding procedures.

The composition of the layers of the filter material realizable by the process of the present invention can be varied both in terms of nature of fibers and in terms of weight.

In an aspect of the invention, the fibers of said first layer (2), for example, can be hydrophobic fibers, whereas the fibers of said third layer (4) can be hydrophilic fibers, or vice versa.

In particular, according to an aspect of the invention, the fibers of said first layer (2) and the fibers of said third layer (4) can be selected from synthetic fibers, such as polypropylene or polyester, or cellulosic fibers, such as rayon-viscose, cotton, lyocell, or cellulose pulp.

Suitable fibers for the realization of said first (2) and/or third layer (4) according to the process of the present invention, include fibers characterized by a linear density comprised between 1 and 10 dtex, which have a length comprised between 20 and 80 mm, preferably comprised between 30 and 60 mm and still more preferably between 34 and 50 mm.

Alternatively, in order to increase the filtering power of the material, in particular against aerosol with sizes smaller than 3 microns or other polluting microparticles, it is possible to use fibers with linear density lower than 1 dtex, but still compatible with the carding processes. These fibres include, for example, Lyocell micro fibres with linear density of 0.9 dtex and length of 34 mm produced by the firm Lenzing (Austria), or even microfine viscose fibres with linear density of 0.5 dtex and length of 40 m produced by the firm Kelheim fibres (Germany).

Therefore, according to an aspect of the present invention, the fibers of said first layer (2) and/or the fibers of said third layer (4) have a linear density comprised between 0.5 and 10 dtex, preferably comprised between 0.5 and 2.2 dtex and still more preferably between 0.9 and 1.7 dtex.

In a preferred embodiment, the fibers used for the implementation of said first (2) and/or third layer (4) have a diameter comprised between 1 and 30 microns, more preferably between 5 and 20 microns and still more preferably between 7 and 15 microns.

Not limiting examples of commercially available fibres which can be used for the preparation of said first (2) and/or third layer (4) according to the steps (i) and/or (iii) of the herein described process, include viscose fibres with linear density of 1.7 dtex and length of 40 mm, produced by the firm Lenzing (Austria), fibers made of polyester with linear density 1.5 dtex and length of 38 mm, produced by the firm Tainan spinning Co (Taiwan), or fibers made of polypropylene with linear density 1.5 dtex and length of 38 mm, produced by the firm Kolon industries (Republic of Korea).

As far as the weight of said first layer (2) and/or said third layer (4) is concerned, according to an aspect of the invention, this can vary in a range of 30-60 grams/m².

According to a particularly preferred embodiment of the invention, the second layer (3) prepared by means of “air-laid” technology in step (ii) of the herein described process, comprises or consists of cellulose pulp fibers.

According to an additional aspect of the invention, said step (ii) provides in particular the use of generally short fibers, such as cellulose pulp fibers with length preferably comprised between 1 and 4 mm. Based upon “air-laid” technology, the cellulose pulp fibers are dispersed in air current, transported through perforated rotating cylinders (or other distribution systems), and subsequently deposited above said perforated surface (or carpet), so as to form a “web”. Said step (ii) can use vacuum through said perforated surface so as to help and ease the process of depositing the fibers. An example of cellulose pulp fibers suitable to be used in the process according to the present invention, is represented by the cellulose fibers produced by the firm Georgia Pacific (USA), commercially known as “Golden Isles Fluffy Treated Fluff grade 4722”, characterized by an average length equal to at least 2.68 mm.

With the purpose of increasing the resistance thereof, it is also possible to mix said cellulose fibres to two-component synthetic fibers or, alternatively, to synthetic latexes capable of constituting additional bonds in the cellulose web which is formed during the “air-laid” process.

In case cellulose pulp in form of compact sheets or bands is used, the process of the present invention can even include an additional step upstream of the process (ii), wherein said sheets and/or cellulose bands can be sent to apparatuses such as, for example, a hammer mill, performing a break of the sheets to form discrete fibers which are then addressed by the air current according to the “air-laid” production process.

Still for the implementation of said second layer (3), the non-woven fabric can be characterized by a weight varying between 25 and 160 grams/m².

The total weight of the filter material obtained according to any one of the herein described process variants can then vary between 70 and 160 grams/m², whereas its total thickness can vary in a range of 0.3-1.2 mm, more preferably from 0.60 to 1.0 mm ed still more preferably from 0.75 to 0.90 mm. According to an additional aspect of the invention, the filter material obtained according to any one of the embodiment variants of the described process can have a water absorptive capacity at least equal to 600%, preferably higher than 600%.

As already mentioned, the materials consisting of cellulosic fibers are particularly suitable to realize sanitary articles to be used in the individual protection against viral pathogen agents since, contrary to plastic materials or materials consisting of synthetic fibers, they result to be more “unfavourable” to survival of viral particles, thus increasing the degree of re-usability of the product.

In a preferred meaning thereof, the filter material obtained from the process according to the present invention is characterized by a content of cellulosic fibers comprised between 5 and 100%, preferably equal to 60%.

In particular, in a preferred embodiment of the process according to the present invention, said first layer (2) consists of rayon-viscose fibers with a linear density equal to 1.7 dtex and length equal to 40 mm; said second layer (3) consists of cellulose pulp fibers with an average length of 2.68 mm; said third layer (4) is made of polyester fibers with a linear density equal to 1.5 dtex and length equal to 38 mm; and said filter material has a total weight equal to 95 grams/m².

As a whole, this preferred embodiment of the process allows then to obtain a filter material characterized by a viscose percentage equal to 35%, a cellulose pulp percentage equal to 25%, ed a polyester percentage equal to 40%, for a total of cellulosic fibers equal to 60% on the total weight of the material.

The present invention further relates to a filter material (1) to block harmful particles, in particular viral, bacterial and/or toxic particles, suitable for being incorporated into a sanitary article, comprising at least three layers made of non-woven fabric welded therebetween to form a homogeneous and perfectly cohesive material, wherein the central layer consists of cellulose pulp fibers, preferably cellulose pulp fibers having an average length of 2.68 mm. Not limiting examples of cellulose pulp fibers which can be used for the realization of said central layer of the filter material include the previously described examples, in particular cellulose fibers produced by the firm Georgia Pacific (USA), commercially known as “Golden Isles Fluffy Treated Fluff grade 4722”.

The composition of each one of the layers composing said filter material can vary both in terms of composition of the fibers, and in term of weight, according to any one of the already illustrated embodiments or variants.

In a preferred embodiment, said filter material (1) can be obtained by means of the process object of the invention, according to any one of the previously described embodiments. Also an object of the invention is a health protection mask, configured to be worn on the face of a user, comprising the filter material according to any one of the described embodiments.

As shown in Figure 2, a health protection mask according to an embodiment of the invention is designated as a whole with (5). Said mask is characterized by a substantially flexible main body in form of strip or band. The main body has, plan viewed, a longitudinal direction L, corresponding to its length in a prevailing development direction, and a transversal direction T, orthogonal to L, and which defines the width thereof, further corresponding to the trace on the user’s face of the sagittal anatomical plane. Length and width can vary along the longitudinal or transversal extension of the mask (5).

The health mask (5) of the invention comprises a filtering central portion, apt to cover mouth and nose and configured to block harmful particles, in particular viral, bacterial and/or toxic particles, which filtering portion in turn comprises one or more layers of the filter material according to any one of the previously described embodiments. The filtering central portion of the mask (5) is configured to prevent that biological material coming from the user wearing the mask is released to contaminate the surrounding environment and/or that particles from outside reach the face of the user himself/herself.

In a preferred variant, said filtering central portion is characterized by a multi-layer configuration. In other terms, said central portion in turn comprises one or more central layers consisting of the filter material according to one of the previously described embodiments, and two external layers made

of non-woven fabric, a first external layer thereof being in contact with the user’s face and a second external layer being in contact with the environment.

The layer made of non-woven fabric in contact with the user’s face carries out a protective function, since it avoids that there is a direct contact of the skin with the central filter material. The composition of the two external layers even in this case can vary both in term of fibre nature and in terms of weight.

In a preferred embodiment variant, the two external layers are implemented with material obtained by means of “spunbond” technology. This material can be optionally modified with hydrophobic treatment. The fibers of non-woven fabric composing said spunbond material for example can be fibers of hydrophobic nature, in particular fibers of polypropylene. The presence of hydrophobic fibers made of non-woven fabric in the two external layers is important to guarantee that the health mask has a resistance to penetration of liquid “splashes”, known in the art as “splash resistance”, which is in conformity with the minimum values required for health protection masks. Not limiting examples of commercially available materials which can be used in the implementation of the two external layers of the mask central portion, include “spunbond” Texbond materials with weight equal to 27 or 35 grams/m², or “spunbond” Albis curaback materials with weight equal to 30 grams/m².

In an embodiment variant, said two external layers are prepared with material made of non-woven fabric obtained by means of “spunlace” technology. Advantageously, the “spunlace” non-woven fabric of these external layers can be obtained by using wholly cellulosic fibers. In particular, the first external layer, the one in contact with the user’s face, can be implemented with a “spunlace” material consisting of rayon-viscose fibers; the second external layer, facing towards the environment, can be implemented with a “spunlace” material consisting of rayon-viscose hydrophobic fibers, for example Olea fibers produced by the firm Kelheim fibers (Germany).

In a preferred embodiment variant, the central portion of said filtering mask consists of two external layers of “spunbond” Texbond material with weight equal to 27 grams/m² and of two central layers consisting of filter material having a weight equal to 95 grams/m², wherein each layer of said filter material consists of a first layer (2) consisting of rayon-viscose fibers with a linear density equal to 1.7 dtex and length equal to 40 m , a second layer (3) consisting of cellulose pulp fibers with an average length of 2.68 mm, and a third layer (4) consisting of polyester fibers with a linear density equal to 1.5 dtex and length equal to 38 mm.

The health mask (5) can further comprise a first and a second side portion, for example in form of under-strip or under-band of the main body and positioned at a respective right and left side with respect to the central portion of the same. Each side portion is apt to cover a respective side portion of the face substantially corresponding to a cheek and up to the ear attachment.

Advantageously, according to an aspect of the present invention, the health protection mask (5) according to any one of the previously described embodiments allows to reach bacterial filtration efficiency values at least equal to 95%, preferably higher than 99%.

At the same time, as it is evident from the experimental tests performed by the inventors, the health mask (5) according to any one of the previously mentioned embodiments is capable of providing differential pressure (DP) levels lower than 18 Pa/cm², preferably lower than 16 Pa/cm², thus by guaranteeing a high breathability.

EXAMPLES Some not limiting embodiment examples of the filter material according to the present invention are herein shown by way of illustration.

EXAMPLE 1 - Code SFP 85

A filter material made of non-woven fabric with total weight of 95 g/m² was implemented, consisting of the following fibers: External layer 1 (spunlace): viscose fibers with linear density of 1.7 dtex and length of 40 mm produced by the firm Lenzing (Austria).

Central layer (air-laid formation head): cellulose pulp fibers produced by the firm Georgia Pacific (USA) “golden isles fluffy treated fluff grade 4722. These fibers have an average length of 2.68 mm. External layer 2(spunlace): polyester fibers with linear density of 1.5 dtex and length of 38 mm produced by the firm Tainan spinning Co (Taiwan).

The proportions between the various fibers are: viscose 35 %, cellulose pulp 25 %, polyester 40% therefore the total of the cellulosic fibers is equal to 60 % by weight of the material.

The main features of the material are summarized in the herebelow Table 2:

Table 2

EXAMPLE 2 - Code 89015

Filter material consisting of three layers as in Example 1 but with following composition of the fibers: External layer 1: fibers made of polypropylene with linear density of 1.5 dtex and length 38 mm produced by the firm Kolon industries (Republic of Korea). Such layer has a weight of 30 g/m². Central layer (air-laid formation head): cellulose pulp produced by the firm Georgia Pacific (USA). Such layer has a weight of 90 g/m².

External layer 2: fibers made of polypropylene with linear density of 1.5 dtex and length 38 mm produced by the firm Kolon industries (Republic of Korea). Such layer has a weight of 30 g/m².

The total weight results to be of 150 g/m².

EXAMPLE 3 - Code 87013

Filter material consisting of three layers as in example 1 but with following composition of fibers: External layer 1: fibers made of polypropylene with linear density of 1.5 dtex and length 38 mm produced by the firm Kolon industries (Republic of Korea). Such layer has a weight of 30 g/m². Central layer (air-laid head): cellulose pulp produced by the firm Georgia Pacific (USA). Such layer has a weight of 70 g/m².

The total weight results to be of 130 g/m², whereas the thickness is equal to 0.87 mm. EXAMPLE 4 - Code 87014

Filter material consisting of three layers as in example 1 but with following composition of fibers: External layer 1: fibers made of polypropylene with linear density of 1.5 dtex and length 38 mm produced by the firm Kolon industries (Republic of Korea). Such layer has a weight of 30 g/m². Central layer (air-laid head): cellulose pulp produced by the firm Georgia Pacific (USA). Such layer has a weight of 80 g/m².

The total weight results to be of 140 g/m². EXAMPLE 5 - Code 87015

Filter material consisting of three layers as in example 1 but with following composition of fibers: External layer 1: fibers made of polypropylene with linear density of 1.5 dtex and length 38 mm produced by the firm Kolon industries (Republic of Korea). Such layer has a weight of 60 g/m². Central layer (air-laid head): cellulose pulp produced by the firm Georgia Pacific (USA). Such layer has a weight of 50 g/m².

External layer 2: fibers made of polypropylene with linear density of 1.5 dtex and length 38 mm produced by the firm Kolon industries (Republic of Korea). Such layer has a weight of 40 g/m².

The total weight results to be of 150 g/m². Determination of bacterial filtration efficiency (BFE) and of differential pressure (DP)

In order to verify the suitability of the invention as filter material, tests were performed aimed at determining the bacterial filtration efficiency and the differential pressure (DP) according to the UNI EN 14683:2019 standard.

In line with the above-mentioned standard, the filtration test was performed on an aerosol having sizes of 3 microns.

Test Nr.1 A filter mask was assembled, consisting of two external layers of spunbond T exbond material having each one a weight equal to 27 gsm, and of two central layers of the material with code SFP 85 described in Example 1. The results of BFE and DP obtained by an average of 5 measurements are the following:

BFE: 99.1 % +/- 0.6 Differential pressure: < 18 Pa/cm²

Test Nr.2

A filter mask was assembled, consisting of two external layers of spunbond Albis curaback material having each one a weight equal to 30 gsm, and of two layers of material with code SFP 85 described in Example 1. The results of BFE and DP obtained by an average of 5 measurements are the following:

BFE: 95.5 % +/-0.5 Differential pressure: < 18 Pa/cm²

Test Nr.3 A filter mask was assembled, consisting of two external layers of spunbond T exbond material having each one a weight equal to 35 gsm, and of one single layer of filter material with code SFP 85 described in Example 1. The results of BFE and DP obtained by an average of 5 measurements are the following: BFE: 99.3 % +/- 0.0

Differential pressure: < 16 Pa/cm2

Claims

1. A process for the preparation of a filter material (1) to block harmful particles, in particular viral, bacterial and/or toxic particles, suitable for being incorporated into a sanitary article, comprising the following steps:

(iv) welding together the layers obtained in said steps (i), (ii) and (iii).

2. The process according to claim 1 , wherein the fibers of said first layer (2) are hydrophobic fibers and the fibers of said third layer (4) are hydrophilic fibers, or vice versa.

3. The process according to claims 1 or 2, wherein the fibers of said first layer (2) and the fibers of said third layer (4) are selected from synthetic fibers, for example polypropylene or polyester, or cellulosic fibers, for example rayon-viscose, cotton, lyocell, or cellulose pulp.

4. The process according to any one of claims 1 to 3, wherein the fibers of said first layer (2) and/or the fibers of said third layer (4) have a linear density comprised between 0.5 and 10 dtex, preferably comprised between 0.5 and 2.2 dtex, and even more preferably comprised between 0.9 and 1.7 dtex.

5. The process according to any one of claims 1 to 4, wherein the fibers of said first layer (2) and/or the fibers of said third layer (4) have a length comprised between 20 and 80 mm, preferably comprised between 30 and 60 mm ed even more preferably comprised between 34 and 50 mm.

6. The process according to any one of claims 1 to 5, wherein said first layer (2) and/or said third layer (4) have a weight in a range of 30-60 grams/m².

7. The process according to any one of claims 1 to 6, wherein the fibers of said second layer (3) are cellulose pulp fibers.

8. The process according to claim 7, wherein said cellulose pulp fibers are mixed with synthetic fibers.

9. The process according to claims 7 or 8, wherein said cellulose pulp fibers have a length comprised between 1 and 4 mm.

10. The process according to any one of claims 1 to 9, wherein said second layer (3) has a weight between 25 and 160 grams/m².

11. The process according to any one of claims 1 to 10, wherein said filter material has a content of cellulosic fibers between 5 and 100%, preferably equal to 60%.

12. The process according to any one of claims 1 to 11 , wherein said filter material (1) has a variable total weight in the range of 70-160 grams/m².

13. The process according to any one of claims 1 to 12, wherein said first layer (2) consists of rayon-viscose fibers with a linear density equal to 1.7 dtex and length equal to 40 mm; said second layer (3) consists of cellulose pulp fibers with an average length of 2.68 mm; said third layer (4) is made of polyester fibers with a linear density equal to 1.5 dtex and length equal to 38 mm; wherein said filter material has a total weight equal to 95 grams/m².

14. The process according to any one of claims 1 to 13, wherein said step (iv) is carried out by means of high-pressure water jets.

15. The process according to any one of claims 1 to 14, comprising an additional step (v) of drying said obtained filter material in the oven.

16. The filter material (1) obtainable from the process according to any one of claims 1 to 15.

17. Health protection mask (5), configured to be worn on the face of a user, comprising the filter material according to claim 16.