WO2025219876A1

WO2025219876A1 - Air filter

Info

Publication number: WO2025219876A1
Application number: PCT/IB2025/053945
Authority: WO
Inventors: Giorgio Girondi
Original assignee: UFI Innovation Center SRL
Current assignee: UFI Innovation Center SRL
Priority date: 2024-04-18
Filing date: 2025-04-15
Publication date: 2025-10-23
Anticipated expiration: 2026-10-18

Abstract

The invention is an air filter comprising a filtering medium (10) suitable for perform a particle filtration action on the air crossing it so as to identify a dirty side (I1) and a clean side (I2). The filtering medium (10) comprises: - a first layer (100), facing towards the dirty side (I1), suitable for performing a particle filtration and collection action, wherein said first layer (100) is a non-woven fabric comprising synthetic fibers made of a polymer material; - a second layer (200), facing towards the clean side (I2) and arranged downstream of the first layer (100) with respect to the air circulation direction, for the fine filtration of the particles, wherein said second layer (200) is made of non-woven fabric comprising synthetic fibers made of at least two distinct polymer materials. In particular, the first layer (100) is thicker than the second layer (200) and the first layer (100) has a lower filtering efficiency than the second layer (200). The filtering medium (10) has an overall filtering efficiency greater than or equal to 99.9%.

Description

"AIR FILTER"

DESCRIPTION

Field of application

[0001] The present invention relates to an air filter .

[0002] In particular, the present invention relates to a speci fic air filter to be enclosed in an air filtration system . In particular, the air filtration system comprising said air filter is also in turn the subj ect of the present invention .

[0003] According to an embodiment , said air filtration system is the air filtration system for supplying air to an internal combustion engine . According to an embodiment , said filtration system is the filtration system for supplying air to the cathode of a fuel cell . According to an embodiment , said air filtration system is the air filtration system for ventilating the passenger compartment of a vehicle , or generally of an environment . Background art

[0004] In the prior art , filtration systems for filtering air then used for speci fic operations by speci fic components of the vehicle are known .

[0005] Such systems conventionally comprise at least one air filter adapted, by means of appropriate filtering media enclosed therein, to filter the external air to avoid undesired elements from accessing the utility which uses the filtered air .

[0006] Solutions of filtering media are known, suitable for performing a particle filtration of solid contaminants , such as dust or dirt , in other words , fine dust , pollen and contaminating particles .

[0007] The primary application of said air filters is that of belonging to an air filtration system for supplying air to an internal combustion engine : such air filters have speci fic, particularly conclusive , dust collection and filtering ef ficiency requirements .

[0008] In the prior art , air filters , like those belonging to air filtration systems for supplying air to an internal combustion engine , have cellulose filtering media in order to meet the aforesaid requirements .

[0009] A conventional problem of said air filters is associated with the material of the cellulose-based filtering medium, which is less stable from a thermal and chemical point of view . Said cellulose is functionali zed with nanofiber coatings to reach high filtering ef ficiency values . Clearly, however, this results in a cost increase and increased complication of the production processes .

[0010] Filtering media solutions suitable for avoiding any microbes or bacteria from reaching the passenger compartment of the vehicle are also known . In such filtering medium solutions , indeed, the presence is provided of appropriate antibacterial agents suitable for avoiding the microbes reaching the filtering medium or formed in the filtering medium from reaching the passenger compartment .

[0011] Such filtering medium solutions are not particularly long-lasting, ef ficient or resistant , therefore requiring frequent maintenance actions .

Solution of the invention

[0012] Therefore , the need is strongly felt to have an air filter which solves the aforesaid problems encountered in the solutions of the prior art , i . e . , having an air filter exhibiting a mix of strong filtering features and at the same time increased duration over time .

[0013] Therefore , it is the obj ect of the present invention to provide an air filter which ful fil s such a need .

[0014] Such an obj ect is achieved by an air fi lter as claimed in claim 1 . Such an obj ect is also achieved by an engine air filtration system of a vehicle comprising said air filter according to claim 16 . Such an obj ect is also achieved by a cathode air filtration system of a fuel cell comprising said air filter according to claim 17 . Such an obj ect is also achieved by a ventilation air filtration system of an environment , in particular a vehicle passenger compartment , comprising said air filter according to claim 18 .

[0015] The claims dependent thereon show preferred constructional variants implying further advantageous aspects .

Description of the drawings

[0016] Further features and advantages of the invention will become apparent from the description below of preferred embodiments thereof , given by way of nonlimiting indication, with reference to the accompanying drawings , in which :

Figure 1 is a perspective view of an air filter according to the present invention, according to a first embodiment ;

- Figure 2 shows a section view of the air filter in Figure 1 ;

- Figure 2a shows an enlargement of a portion A of the air filter in Figure 2 ;

- Figures 3 ' and 3 ' ’ show two perspective views of an air filter according to the present invention, according to a second embodiment ;

- Figure 4 shows a section view of the air filter in Figure 3 ' ;

- Figures 4a and 4b show an enlargement of a portion A and a portion B of the air filter in Figure 4 ;

Figure 5 is a perspective view of an air filter according to the present invention, according to a third embodiment ;

- Figure 6 shows a section view of the air filter in Figure 5 ;

- Figures 6a and 6b show an enlargement of a portion A and a portion B of the air filter in Figure 6 ;

Figure 7 is a perspective view of an air filter according to the present invention, according to a fourth embodiment ;

- Figure 8 shows a section view of the air filter in Figure 7 ;

Figure 9 is a perspective view of an air filter according to the present invention, according to a fi fth embodiment ;

- Figure 10 shows a section view of the air filter in Figure 9 ;

- Figure 11 is a photo taken by an electronic microscope of a portion of a filtering medium enclosed in an air filter according to the present invention;

- Figure 12 is a table of the parameters and results of three tests performed on respective air filters made according to the present invention, with ISO "a2" type dust , ISO "a4" type dust , and ISO "al" type dust , respectively .

Detailed description [0017] In the accompanying drawings , reference numeral 1 indicates an air filter 1 according to the present invention .

[0018] The present invention also relates to an engine air filtration system of a vehicle , comprising said air filter 1 .

[0019] The present invention also relates to a cathode air filtration system of a fuel cell , comprising said air filter 1 .

[0020] According to the present invention, the air filter 1 comprises a filtering medium 10 suitable for performing a particle filtration action on the air cros sing it .

[0021] The filtering medium 10 is thus suitable for identi fying a dirty side 11 and a clean side 12 : the dirty side 11 is reached by air to be filtered, and the clean side 12 is crossed by filtered air .

[0022] According to the present invention, the filtering medium 10 is made of synthetic material in its entirety .

[0023] The filtering medium 10 comprises a first layer 100 and a second layer 200 .

[0024] The first layer 100 is faced towards the dirty layer 11 .

[0025] According to a preferred embodiment , the first layer 100 corresponds with the inlet face of the filtering medium 10 reached by the air to be fi ltered . [0026] The first layer 100 is suitable for performing a particle filtration and collection action . In other words , the first layer 100 is suitable for collecting the particles , dust in particular, in the volume thereof .

[0027] The first layer 100 is a non-woven fabric made of synthetic fibers . Said synthetic fibers are made of polymer material .

[0028] The second layer 200 is designed to perform a fine filtration action of the air .

[0029] The second layer 200 is faced towards the clean side 12 .

[0030] In other words , the second layer 200 is arranged downstream of the first layer 100 with respect to the air circulation direction .

[0031] According to a preferred embodiment , the second layer 200 corresponds to the outlet face of the filtering medium 10 from which filtered air exits .

[0032] According to the present invention, said second layer 200 is a non-woven fabric comprising synthetic fibers made of at least two distinct polymer materials .

[0033] According to the present invention, the filtering medium comprises a first layer 100 and a second layer 200 , both free from the presence of nanofibers .

[0034] In a further preferred embodiment , the filtering medium 10 comprises a third layer with active carbons . [0035] Preferably, said third layer with active carbons is positioned downstream of the second layer 200 with respect to the air circulation direction. In such an embodiment, the second layer 200 is between the first layer 100 and the third layer.

[0036] According to a preferred embodiment, the air filter 1 comprises a support element 50 suitable for providing the filtering medium 10 with structural support.

[0037] Preferably, the support element 50 is arranged around the perimeter.

[0038] Preferably, the support element 50 extends from the dirty side 11 to the clean side 12.

[0039] Preferably, the support element 50 is arranged at the ends of the filtering medium 10, for example, the support element 50 comprises one or two end plates.

[0040] According to the present invention, the first layer 100 is thicker than the second layer 200.

[0041] Moreover, according to the present invention, the first layer 100 has a lower filtering efficiency than the second layer 200.

[0042] According to a preferred embodiment, the first layer 100 has a thickness greater than 1.5 millimeters, preferably between 2.2 millimeters and 3.4 millimeters.

[0043] According to a preferred embodiment, the second layer 200 has a thickness less than 1.5 millimeters, preferably between 0 . 5 millimeters and 1 millimeter .

[0044] In particular, the value of "thickness" is measured according to DIN EN ISO 9073-2 standard .

[0045] Again according to the present invention, the filtering medium 10 has an overall filtering ef ficiency greater than or equal to 99 . 9% .

[0046] According to the present invention, the presence of the two layers , with the aforesaid features , is such as to allow achieving the preset obj ect .

[0047] According to a preferred embodiment , the first layer 100 comprises synthetic fibers selected from polyethylene terephthalate , polybutylene terephthalate and polypropylene .

[0048] Preferably, the first layer 100 consists of polyethylene terephthalate fibers in its entirety .

[0049] Preferably, in the first layer 100 , said synthetic fibers have an arrangement such as to form a varying structure in the thickness . This means that in the first layer 100 , said synthetic fibers are arranged so as to form a gradient structure in the thickness of said first layer .

[0050] According to a preferred embodiment , said synthetic fibers , preferably made of polyethylene terephthalate , have a varying structure arrangement in the thickness thereof having greater filtering ef ficiency close to the second layer 200 .

[0051] According to a preferred embodiment , said synthetic fibers , preferably made of polyethylene terephthalate , have a varying structure arrangement in the thickness thereof having less permeability close to the second layer 200 .

[0052] According to a preferred embodiment , said synthetic fibers , preferably made of polyethylene terephthalate , have a varying structure arrangement in the thickness thereof having less dust retaining capacity per area unit close to the second layer 200 .

[0053] According to a preferred embodiment , said synthetic fibers , preferably made of polyethylene terephthalate , have a varying structure arrangement in the thickness thereof having greater basis weight close to the second layer 200 .

[0054] According to a preferred embodiment , said synthetic fibers , preferably made of polyethylene terephthalate , have a varying structure arrangement in the thickness thereof having a greater solid fraction close to the second layer 200 .

[0055] According to a preferred embodiment , the first layer 100 is a single layer .

[0056] According to a preferred embodiment , in the manufacturing operations , the first layer 100 is made so as to have the aforesaid gradient .

[0057] According to a further preferred embodiment , the first layer 100 comprises a first inlet substrate 110 and a first outlet substrate 120 .

[0058] Preferably, the first inlet substrate 110 is a nonwoven fabric made of synthetic fibers , preferably of polyethylene terephthalate .

[0059] Preferably, the first outlet substrate 120 is a nonwoven fabric made of synthetic fibers , preferably of polyethylene terephthalate .

[0060] According to a preferred embodiment , in the manufacturing operations , the first layer 100 is made so as to identi fy said substrates .

[0061] According to a preferred embodiment , in the manufacturing operations , the first layer 100 is made by coupling said two speci fically made substrates 110 , 120 .

[0062] According to a preferred embodiment , the second layer 200 comprises polypropylene fibers and polyethylene terephthalate fibers .

[0063] According to a preferred embodiment , the second layer 200 is a single layer .

[0064] According to a preferred embodiment , in the manufacturing operations , the second layer 200 is made by interlacing said distinct polypropylene and polyethylene terephthalate fibers . [0065] According to a preferred embodiment , in the manufacturing operations , the second layer 200 is made by randomly interlacing said distinct polypropylene and polyethylene terephthalate fibers to form a second layer 200 made of a non-woven fabric .

[0066] According to a preferred embodiment , the second layer 200 comprises a second inlet substrate 210 and a second outlet substrate 220 formed from di f ferent types of synthetic fibers , respectively .

[0067] According to a preferred embodiment , the second layer 200 comprises a second inlet substrate 210 comprising polypropylene fibers and a second outlet substrate 220 comprising polyethylene terephthalate fibers .

[0068] According to a preferred embodiment , the second layer 200 comprises a second inlet substrate 210 comprising polypropylene terephthalate fibers and a second outlet substrate 220 comprising polypropylene fibers .

[0069] According to a preferred embodiment , the second inlet substrate 210 is a non-woven fabric comprising exclusively three polypropylene fibers .

[0070] According to a preferred embodiment , the second outlet substrate 220 is a non-woven fabric comprising exclusively polyethylene terephthalate fibers . [0071] According to a preferred embodiment , the polyethylene terephthalate fibers of the first layer 100 have an average diameter between 5 and 30 micrometers .

[0072] According to a preferred embodiment , the polyethylene terephthalate fibers of the second layer 200 have an average diameter between 20 micrometers and 30 micrometers , preferably between 25 and 30 micrometers .

[0073] According to a preferred embodiment , the synthetic fibers of the first layer 100 , preferably made of polyethylene terephthalate , have a varying structure arrangement in the thickness thereof having fibers with a smaller average diameter close to the second layer 200 .

[0074] Preferably, the synthetic fibers of the first layer 100 , preferably made of polyethylene terephthalate , have a varying structure arrangement in the thickness thereof having fibers with a smaller diameter close to the second layer 200 and with a greater solid fraction at the second layer 200 .

[0075] According to a preferred embodiment , the synthetic fibers of the first layer 100 , preferably made of polyethylene terephthalate , have a varying structure arrangement in the thickness thereof having a first outlet substrate 120 with synthetic fibers having a smaller average diameter than the average diameter of the synthetic fibers of the first inlet substrate 110 . [0076] According to a preferred embodiment , the synthetic fibers of the first layer 100 , preferably made of polyethylene terephthalate , have a varying structure arrangement in the thickness thereof having a first outlet substrate 120 with synthetic fibers having a smaller average diameter than the average diameter of the synthetic fibers of the first inlet substrate 110 and where the solid fraction of the first outlet substrate 120 is greater than the solid fraction of the first inlet substrate 110 .

[0077] According to a preferred embodiment , the synthetic fibers of the first layer 100 , preferably made of polyethylene terephthalate , have a varying structure arrangement in the thickness thereof having a first outlet substrate 120 with synthetic fibers having a smaller average diameter than the average diameter of the synthetic fibers of the first inlet substrate 110 , where the solid fraction of the first outlet substrate 120 is greater than the solid fraction of the first inlet substrate 110 , and where the basis weight of the first outlet substrate 120 is greater than the basis weight of the first inlet substrate 120 .

[0078] According to a preferred embodiment , the synthetic fibers of the second layer 200 have an average diameter between 1 micrometer and 30 micrometers . [0079] According to a preferred embodiment , the second layer 200 comprises synthetic fibers made of at least two distinct polymer materials where the fibers of the first polymer material , polypropylene fibers , for example , have a di f ferent average diameter with respect to the fibers of the second polymer material , polyethylene terephthalate fibers , for example .

[0080] According to a preferred embodiment , the polypropylene fibers of the second layer 200 have a smaller average diameter than the synthetic fibers of the first layer 100 .

[0081] According to a preferred embodiment , the polypropylene fibers of the second layer 200 have a smaller average diameter than the average diameter of the synthetic fibers of the first inlet substrate 110 and the first outlet substrate 120 .

[0082] According to a preferred embodiment , the polypropylene fibers of the second layer 200 have a smaller average diameter than the average diameter of the polyethylene terephthalate fibers of the second layer 200 .

[0083] According to a preferred embodiment , the synthetic fibers of the second inlet substrate 210 have a smaller average diameter than the average diameter of the synthetic fibers of the second outlet substrate 220 . [0084] According to a preferred embodiment , the polyethylene terephthalate fibers of the second inlet substrate 210 have a smaller average diameter than the average diameter of the polypropylene fibers of the second outlet substrate 220 .

[0085] According to a preferred embodiment , the polypropylene fibers of the second inlet substrate 210 have a smaller average diameter than the average diameter of the polyethylene terephthalate fibers of the second outlet substrate 220 .

[0086] According to a preferred embodiment , the polypropylene fibers have a smaller average diameter than the average diameter of the polyethylene terephthalate fibers used in the first layer 100 and the second layer 200 , respectively .

[0087] According to a preferred embodiment , the polypropylene fibers have an average diameter between 1 micrometer and 10 micrometers , preferably between 2 micrometers and 7 micrometers , preferably between 3 and 5 micrometers .

[0088] According to the present invention, the presence of distinct polypropylene fibers and polyethylene terephthalate fibers in said second layer 200 generates an electrostatic charge due to the rubbing of polymer materials having di f ferent chemical nature caused by the passage of the air under filtration through said second layer 200.

[0089] According to a preferred embodiment, the first layer 100 has a filtering efficiency greater than 99% and the second layer 200 has a filtering efficiency greater than or equal to 99.8%.

[0090] According to the present invention, the "filtering efficiency" value is measured according to ISO 5011 standard with "a2" type dust (ISO FINE) , face velocity of 20 ± 5 cm/s, and differential pressure increase equal to 2.5 kPa .

[0091] According to a preferred embodiment, the first layer 100 has a greater permeability than the second layer 200. [0092] Preferably, the first layer 100 has a permeability equal to or greater than 750 mm/s, and the second layer 200 has a permeability less than 750 mm/s.

[0093] Preferably, the first layer 100 has a permeability greater than 850 mm/s, in particular between 900 mm/s and 1200 mm/ s .

[0094] Preferably, the first layer has a permeability equal to about 1150 mm/s.

[0095] Preferably, the second layer 200 has a permeability between 750 mm/s and 500 mm/s.

[0096] Preferably, the second layer 200 has a permeability equal to about 700 mm/s. [0097] In particular, the "permeability" value is measured at 200Pa according to DIN EN ISO 9237 standard .

[0098] According to a preferred embodiment , the first layer 100 has a dust collection capacity per area unit greater than the dust collection capacity per area unit of the second layer 200 .

[0099] According to the present invention, the filtering medium 10 has a dust collection capacity per overall area unit greater than 700 g/m^A2 .

[00100] Preferably, the first layer 100 has a dust collection capacity per area unit greater than 750 g/m^A2 , preferably greater than 800 g/m^A2 , and the second layer 200 has a dust collection capacity per area unit less than 150 g/m^A2 , preferably less than 100 g/m^A2 .

[00101] In particular, the "dust collection capacity per area unit" value is measured according to ISO 5011 standard implemented with "a2" type ( ISO FINE ) dust , with medium face velocity of 20 ± 5 cm/ s , and di f ferential pressure increase equal to 2 . 5 kPa .

[00102] According to a preferred embodiment , the first layer 100 has a basis weight greater than the basis weight of the second layer 200 .

[00103] According to a preferred embodiment , the first layer 100 has a basis weight greater than 150 g/m^A2 , preferably between 220 g/m^A2 and 240 g/m^A2 , and the second layer 200 has a basis weight less than 150 g/m^A2 , preferably between 100 g/m^A2 and 85 g/m^A2 .

[00104] In particular, the "basis weight" value of the first layer 100 and second layer 200 is measured according to DIN EN ISO 29073- 1 standard .

[00105] According to a preferred embodiment , the first inlet substrate 110 and the first outlet substrate 120 are made by means of the air laid technology .

[00106] Preferably, the first inlet substrate 110 and the first outlet substrate 120 are coupled and mutually j oined by hydroentanglement .

[00107] Preferably, the first inlet substrate 110 and the first outlet substrate 120 are rolled and mutually j oined by hydroentanglement .

[00108] According to a preferred embodiment , the second outlet substrate 220 is made by means of the spun-bond technology and the second inlet substrate 210 is deposited thereon by means of the melt blown technology .

[00109] Preferably, the first layer 100 and the second layer 200 thus obtained are coupled and then processed according to the shape with which the filtering medium according to the exemplary configurations shown below will be used .

[00110] According to a preferred embodiment , the filtering medium 10 is configured to operate in a pleated shape .

[00111] Preferably, the first layer 100 and the second layer 200 are coupled and subj ected to rolling operations to facilitate subsequent folding operations .

[00112] According to a preferred embodiment , the filtering medium 10 comprises a support net positioned upstream of the first layer 100 or downstream of the second layer 200 to facilitate folding operations , in particular in the configurations in which the two layers are not subj ected to rolling processing .

[00113] According to a preferred embodiment , the filtering medium 10 is configured to operate in a pleated shape of the panel type ( like that shown by way of example in accompanying Figures 1 , 3 ' , 3 ' ’ , 5 ) to be crossed by the fluid under filtration in the axial direction .

[00114] According to a preferred embodiment , the filtering medium 10 is configured to operate in a pleated shape of the cylinder or elliptical type ( like that shown by way of example in accompanying Figure 7 ) to be crossed by the fluid under filtration in the axial direction .

[00115] According to a preferred embodiment , the filtering medium 10 is configured to operate in a rolled shape of the tubular type , to be crossed by the fluid under filtration in the radial direction . [00116] According to a preferred embodiment , the air filter 1 further comprises separator elements 70 positioned between two adj acent folds of the filtering medium 10 in a pleated shape .

[00117] Preferably, said separator elements 70 are placed on the inlet side .

[00118] Preferably, said separator elements 70 are placed on the outlet side .

[00119] According to a preferred embodiment , the separator element 70 is a corrugated element made of a porous material .

[00120] According to a preferred embodiment , the separator element 70 is a corrugated element made of a non-porous material .

[00121] According to a preferred embodiment , the separator element 70 is a corrugated element made of paper and/or plastic .

[00122] According to a preferred embodiment , the separator element 70 is a net .

[00123] According to a preferred embodiment , the separator element 70 is a sponge .

[00124] According to a further embodiment , said separator elements 70 are adhesive seams positioned on the inlet side or the outlet side of the filtering medium

10 . [00125] According to a preferred embodiment , the folds of the filtering medium are crushed into an inlet region . Preferably, the intake pressure losses of air entering the air filter 1 are thus reduced .

[00126] According to a preferred embodiment , the filtering medium 10 is configured to operate in a flat shape of the type comprising a plurality of concentric pockets wrapped about a main axis , to be crossed by the fluid under filtration in the axial direction .

[00127] According to a preferred embodiment , the filtering medium 10 is configured to operate in a flat shape of the tubular type ( like that shown by way of example in accompanying Figure 9 ) to be crossed by the fluid under filtration in the radial direction .

[00128] Innovatively, the air filter of the present largely ful fills the aforesaid purpose , overcoming issues which are typical of the prior art .

[00129] Advantageously, the air filter has a filtering medium entirely made from synthetic fibers and speci fic dust collection capacity greater than 700 g/m^A2 and an overall filtering ef ficiency greater than or equal to 99 . 9% under the above-described testing conditions .

[00130] Advantageously, the air filter has dust collection properties per area unit and filter ef ficiency using stable and permeable filtering structures , minimi zing the impact on the pressure losses to the filtering system .

[00131] Advantageously, the filtering medium made from synthetic fibers combines collection and filtering ef ficiency properties with increased thermal stability as compared to cellulose-based filtering media .

[00132] Advantageously, the filtering medium made from synthetic fibers combines collection and filtering ef ficiency properties with increased stability and resistance towards moisture as compared to cellulose- based filtering media .

[00133] Advantageously, the filtering medium with synthetic fibers combines collection and filtering ef ficiency properties with increased chemical stability as compared to cellulose-base filtering media, particularly useful for cathode applications in which the filter must act ef fectively towards gaseous and chemically aggressive contaminants , such as NH3 and SO2 , for example , in addition to those of particle type .

[00134] Advantageously, the filtering medium with synthetic fibers collects the contaminant in the thickness of the material , reducing the amount of material to be used with respect to an air filter with cellulose-based filtering medium, the amount of dust collection per area unit being equal . [00135] Advantageously, the air filter is highly ef fective at filtering and collecting, being suitable for collecting high amounts of dust of a2 , a4 and al ISO FINE type . As a demonstration of the aforesaid advantage , note that the accompanying table in Figure 12 gathers the parameters and results obtained relating to three tests performed with the aforesaid three types o f dust .

[00136] Advantageously, the di f ferent features of first layer and second layer allow achieving important advantageous technical ef fects associated with the synergy of the two layers .

[00137] Advantageously, the presence of distinct polypropylene fibers and polyethylene terephthalate fibers in the second layer generates an electrostatic charge , following their mutual rubbing during the operation of the air filter, which contributes positively to the filtering ef ficiency properties of the second layer and the filtering medium in its entirety .

[00138] Advantageously, the presence of distinct polypropylene fibers and polyethylene terephthalate fibers in the second layer allows taking advantage of the ef fect of electrostatic charge induced by the mutual rubbing and increasing the overall ef ficiency of the system with a permeable filtering layer, minimi zing the ef fect on the pressure losses imposed on the filter system on which the air filter is used .

[00139] Advantageously, the presence of distinct polypropylene fibers and polyethylene terephthalate fibers in the second layer allows taking advantage of the mutual rubbing of fibers of di f ferent type to regenerate the electrostatic charge in the second layer due to the transit of air under filtration through the filtering medium . Advantageously, this solution provides a more ef fective and long-lasting solution as compared to those filtering materials subj ected to treatments suitable for imparting an electric charge to the filtering material , such as plasma treatments or treatments by means of corona "discharge" , for example , with which the material is not capable of regenerating the electrostatic charge once cancelled, for example under conditions of humid air or due to condensates .

[00140] Advantageously, the filtering medium achieves filtering ef ficiency properties greater than 99 . 9% without the use of nanofibers .

[00141] Advantageously, the filtering medium has a filtering ef ficiency greater than 99 . 9% under the conditions described above , thus also being use ful for air applications of the passenger compartment or household type , to prevent solid and bacterial contaminants from entering the environment to be conditioned .

[00142] Advantageously, the filtering medium has a filtering ef ficiency greater than 99 . 9% under the conditions described, allowing the blockage of the ingress of bacteria into the environment to be conditioned, avoiding the employment of antibacterial agents .

[00143] Advantageously, the filtering medium has a simpli fied shape and is simple to manufacture .

[00144] Advantageously, the engine air filtration system of a vehicle is suitable for having all the aforesaid contextuali zed advantages o f the air filter .

[00145] Advantageously, the cathode air filtration system of a fuel cell is suitable for having all the aforesaid contextuali zed advantages o f the air filter .

[00146] It is apparent that , in order to meet contingent needs , those skilled in the art may make changes to the invention as described above , all contained within the scope of protection as def ined by the following claims .

List of reference signs :

[00147]

1 air filter

10 filtering medium

100 first layer 110 first inlet substrate

120 first outlet substrate

200 second layer

210 second inlet substrate 220 second outlet substrate

50 support element

70 separator element

11 clean side

12 dirty side

Claims

1. An air filter (1) , for example for an air filtration system, comprising a filtering medium (10) suitable for performing a particle filtration action on the air crossing it so as to identify a dirty side (II) and a clean side (12) , wherein the filtering medium (10) comprises : a first layer (100) , facing towards the dirty side

(11) , suitable for performing a particle filtration and collection action, wherein said first layer (100) is a non-woven fabric comprising synthetic fibers made of a polymer material;

- a second layer (200) , facing towards the clean side

(12) and arranged downstream of the first layer (100) with respect to the air circulation direction, for the fine filtration of the particles, wherein said second layer (200) is made of non-woven fabric comprising synthetic fibers made of at least two distinct polymer materials ; wherein the first layer (100) is thicker than the second layer (200) and wherein the first layer (100) has a lower filtering efficiency than the second layer (200) ; wherein the filtering medium (10) has an overall filtering efficiency greater than or equal to 99.9%.

2. Air filter (1) according to claim 1, wherein the first layer (100) has a filtering efficiency greater than 99% and the second layer (200) has a filtering efficiency greater than or equal to 99.8%.

3. Air filter (1) according to any one of the preceding claims, wherein the first layer (100) has a thickness greater than 1.5 millimeters, preferably between 2.2 millimeters and 3.4 millimeters, and the second layer

(200) has a thickness less than 1.5 millimeters, preferably between 0.5 millimeters and 1 millimeter.

4. Air filter (1) according to any one of the preceding claims, wherein the first layer (100) has a greater permeability than the second layer (200) .

5. Air filter (1) according to claim 4, wherein the first layer (100) has a permeability equal to or greater than 750 mm/s, and the second layer (200) has a permeability less than 750 mm/s.

6. Air filter (1) according to any one of the preceding claims, wherein the first layer (100) has a dust collection capacity per area unit greater than the dust collection capacity per area unit of the second layer (200) .

7. Air filter (1) according to claim 6, wherein the filtering medium (10) has a dust collection capacity per area unit greater than 700 g/m^A2.

8. Air filter (1) according to claim 6 or claim 7, wherein the first layer (100) has a dust collection capacity per area unit greater than 750 g/m^A2, preferably greater than 800 g/m^A2, and the second layer (200) has a dust collection capacity per area unit less than 150 g/m^A2.

9. Air filter (1) according to any one of the preceding claims, wherein the first layer (100) has a basis weight greater than the basis weight of the second layer (200) .

10. Air filter (1) according to claim 9, wherein the first layer (100) has a basis weight greater than 150 g/m^A2, preferably between 220 g/m^A2 and 240 g/m^A2, and the second layer (200) has a basis weight less than 150 g/m^A2, preferably between 100 g/m^A2 and 85 g/m^A2.

11. Ai r filter (1) according to any one of the preceding claims, wherein the first layer (100) comprises synthetic fibers, preferably made of polyethylene terephthalate, the varying structure arrangement of which in the thickness thereof has synthetic fibers of smaller average diameter close to the second layer (200) .

12. Air filter (1) according to claim 11, wherein the first layer (100) comprises a first inlet substrate (110) and a first outlet substrate (120) , wherein the first inlet substrate (110) comprises synthetic fibers of greater average diameter than the synthetic fibers of the first outlet substrate (120) and has a smaller solid fraction than the first outlet substrate (120) .

13. Ai r filter (1) according to any one of the preceding claims, wherein the second layer (200) comprises polypropylene fibers and polyethylene terephthalate fibers .

14. Ai r filter (1) according to any one of the preceding claims, wherein the second layer (200) comprises a second inlet substrate (210) comprising polypropylene fibers and a second outlet substrate (220) comprising polyethylene terephthalate fibers.

15. Ai r filter (1) according to any one of the preceding claims, comprising a support element (50) suitable for provide the filtering medium (10) with structural support .

16. An engine air filtration system of a vehicle, comprising an air filter (1) according to any one of claims 1 to 15.

17. A cathode air filtration system of a fuel cell, comprising an air filter (1) according to any one of claims 1 to 15.

18. A ventilation air filtration system of an environment, in particular a vehicle passenger compartment, comprising an air filter (1) according to any one of claims 1 to 15.