Field of invention

The technical solution relates to a filtration material intended for air filtering, the filtration material being based on a combination of spun bond (SB) and/or meltblown (MB) and electrospun (ES) non-woven textiles (NT). This material can be easily processed by welding or sewing to make filtering facepieces - face masks, respirators, half-masks, pocket filters, filters for automobile interiors and simple or folded partitions for mask filters, air-conditioning devices and similar protection applications for cleaning particle-contaminated air.

Description of the prior art

At present, for the above applications filtration materials made from non-woven textiles (NT) or fabrics are used, which, however, do not optimally meet the properties required by manufacturers of filtration products, i.e. maximum filtration efficiency at the minimum possible pressure drop.

The filtration materials are assessed according to EN 143, EN 149, EN 779 - 2011 European standards, which specify requirements for filtration efficiency (FE) and pressure drop (Ap) for filtered particles 400 nm in size, and according to EN 1822 - 2009 standard defining requirements for filtration efficiency (FE) at a place where the nanoparticles penetration is maximum one (maximum penetrating particle size - MPPS) - consequently, an extreme in the dependence of filtration efficiency on particle size (a V-shaped curve). The most significant mechanism of eliminating fine particles from air with ES filters is that of particle capture (see Fig. 1).

A disadvantage of the currently used filtration materials based on meltblown (MB) non- woven textiles is a lower capture of very fine particles (10 - 400 nm in size). In order to improve the fine particle capture capacity it is necessary to increase the content of the meltblown (MB) fibrous material in the filter. However, an increase in the content of the meltblown (MB) fibrous material results in an excessive increase of the filter pressure drop. Nature of the technical solution

The shortcomings described above can be eliminated to a great extent with the filtration material for air filtering in compliance with the technical solution submitted here. The nature of the solution consists in the fact that the multilayer structure of this material comprises

- at least one layer of spun bond (SB) and/or meltblown (MB) non-woven textile having a mass per unit surface area of 15 to 100 g/ m ² , a distribution of fibre diameters of 200 nm to 8000 nm and a mean pore size greater than 1200 nm and

- at least one layer of electrospun (ES) non-woven nanotextile having a mass per unit surface area of 0.05 to 4 g/ m ² , a distribution of fibre diameters in the range of 40 nm to 400 nm and a mean pore size of 200 to 1800 nm.

The spun bond (SB) and/or meltblown (MB) non-woven textile is made advantageously from fibres based on a polymer selected from a group of polymers including polypropylene (PP), polyethylene terephthalate (PET), polyurethanes (PU), polylactic acid (PLA) and polyamide 6 (PA6).

The layer of the electrospun (ES) non-woven nanotextile is made advantageously from nanofibres based on a polymer from a group of polymers comprising polyvinylidene fluoride (PVDF), polyurethanes (PU), polylactic acid (PLA), polyamide 6 (PA6), polyacrylonitrile (PAN), cellulose acetate (CA), polystyrene (PS), polyether sulphone (PESU) and polyvinyl butyral (PVB).

Several preferred multilayer structures of the filtration material have been produced with respect to the specific composition of the layers, namely:

a) a multilayer structure containing a non-woven textile based on a combination of a meltblown (MB) polypropylene (PP) layer deposited onto a spun-bond (SB) polypropylene substrate and an electrospun (ES) non-woven nanotextile made from polyvinylidene fluoride (PVDF) nanofibers;

b) a multilayer structure containing a double-layer of meltblown (MB) and spun bond (SB) non-woven textiles from polypropylene (PP) microfibers joined with an electrospun (ES) non-woven nano textile made from polyvinylidene fluoride (PVDF) nanofibers, the multilayer structure lying on a viscose substrate;

c) a multilayer structure containing a combination of meltblown (MB) non-woven textile made from a blend of polypropylene (PP) and polyethylene terephthalate (PET) staple fibres, and electrospun (ES) non-woven nanotextile made from polyvinylidene fluoride (PVDF) nanofibers;

d) the multilayer structure created as a sandwich, the layer composition being a spunbond (SB) polypropylene (PP) layer - meltblown (MB) polypropylene (PP) layer - non-woven nanotextile made from polyvinylidene fluoride (PVDF) nanofibers - meltblown (MB) polypropylene (PP) layer - spunbond (SB) polypropylene (PP) layer.

Drawings

Fig. 1 - An image of electrospun (ES) nanostructure containing captured particles 20 - 400 nm in size; magnification: lOOOOx;

Fig. 2 - A scanning electron microscope (SEM) image of the meltblown (MB) structure, magnification: 4000x;

Fig. 3 - An image of an electrospun (ES) nanostructure, magnification: 40000x;

Fig. 4 - 3D models: (a) meltblown (MB) structure (b), electrospun (ES) nanostructure, (c) combination of meltblown (MB) structure and electrospun (ES) nanostructure;

Fig. 5 - Experimental data for filtration materials based on meltblown (MB) structure, electrospun (ES) nanostructure and a combination of meltblown (MB) structure and electrospun (ES) nanostructure.

Examples of implemented technical solution (embodiments)

Example 1

The multilayer structure of the filtration material in the exemplary embodiment (see Fig. 4c) contains a combination of a non-woven textile comprising an MB layer from PP (see Figs 2 and 4a) deposited onto a SB substrate made from PP with an ES non-woven nanotextile (see Figs. 3 and 4b) made from PVDF nanofibers. The MB PP layer has a mass per unit surface area of 25 g / m ² , a fibre diameter distribution of 500 nm to 5000 nm and a mean pore size of 1900 nm. The MB PP layer was deposited onto the SB PP substrate having a mass per unit surface area of 17 g/m ² . ES non-woven nanotextile made from PVDF nanofibers has a mass per unit surface area of 0.2 g / m ² , a fibre diameter distribution ranging from 40 to 400 nm and a mean pore size of 1100 nm.

Filtration effects of the material according to Example 1 are illustrated in a clear manner in Fig. 5. As it is obvious here, in case of particles approximately 103 nm in size, the MB PP structure alone (according to Fig. 4a) deposited onto the SB PP substrate exhibits a filtration efficiency of 55% and a pressure drop of Dr = 42 Pa. The ES non- woven nanotextile (according to Fig. 4b) made from PVDF nano fibers has a filtration efficiency FE = 65% and a pressure drop Dr of 20 Pa only. A combination of the MB and ES structures described (according to Fig. 4c) results in a filtration material having a filtration efficiency FE = 82% for particles 40 nm in size and a pressure drop Dr of 61 Pa only. Hence it results in a material corresponding already to almost E 10 filtration class (according to EN 1822 standard) while exhibiting a lower pressure drop, as measured at the front speed of 5.7 cm/s, which corresponds to an air flow rate of 30 1/min.

Example 2

Another example of a filtration material intended for making half-masks features a multilayer structure comprising a combination of MB and SB non-woven textiles made from PP microfibers and an ES non-woven nanotextile made from PVDF nanofibers, the multilayer structure lying on a viscose (VS) substrate. The microfibre material made from PP microfibres is produced by joining SB and MB non-woven textiles having a mass per unit surface areas of 17 and 25 g/m ² , consequently, a total mass per unit surface area of 42 g/m ² , an MB fibre diameter distribution ranging from 500 to 1500 nm and a mean pore size of 1900 nm. ES non- woven nanotextile made from PVDF nanofibres having a mass per unit surface area of 0.5 g/m ² , a fibre diameter distribution ranging from 40 to 400 nm and a mean pore size of 800 nm is deposited onto a non-woven VS substrate having a mass per unit surface area of 55 g/m ² .

The example documents an improvement of filtration properties of the materials for half-masks evaluated in compliance with EN 149 standard, which makes use of aerosol having an average particle size of 400 nm for evaluation of the filtration capacity. The material from PP microfibres produced by joining two SB/MB non-woven textiles features an inhalation resistance of Dr = 229 Pa and a filtration efficiency FE = 94 %, as measured with paraffin oil at an air flow rate of 95 1/min. and corresponds to FFP2 class. Corresponding minimum requirements specified in EN 149 standard for class 2 under the above given conditions of the test using the paraffin aerosol are Dr = 240 Pa and filtration efficiency FE = 94%. A material having approximately the same pressure resistance of Dr = 213 Pa can be produced by combining SB/MB non-woven textiles having mass per unit surface areas of 17/25 g/m ² with a material produced by applying 0.5 g/m ² PVDF nanofibres onto a VS substrate having a mass per unit surface area of 55 g/m ² . The filtration efficiency of such a combination, in comparison with the original SB/MB material containing no nanofibers, increases markedly up to FE = 99.6%. Consequently, the material features a FFP3 filtration class, the minimum requirements at a flow rate of 95 1/min being Dr < 300 Pa and filtration efficiency FE > 99,0 %.

Example 3

The composition of the multilayer material is identical with that given in Example 2, the difference consisting in the fact that the ES non-woven textile has a mass per unit surface area of 2.3 g/m ² , a fibre diameter distribution ranging from 40 to 400 nm and a mean pore size of 255 nm. This material was used for production of folded filters for HEPA filtration in air- conditioning units. A positive effect of the combination of MB and ES non-woven textile was demonstrated in two tests where the material described was subjected to identical flow of contaminated air from the side of the VS SB material as well as from the opposite side of PP MB non-woven textile. In case of filtration from the side of the MB non-woven textile the filter capacity increased by 32% due to a more efficient prefiltration.

Example 4

The filtration material is analogical to that described in Example 2 but instead of a layer of nanofibres on VS a non-woven textile made from a blend of PP and PET staple fibres having a mass per unit surface area of 30 g/m ² was used as an underlying substrate. Filtration performance achieved under identical conditions was as follows: filtration efficiency FE > 99.5 % and pressure resistance Ap = 87 up to 98 Pa at an air flow rate of 30 1/min., or 257 up to 289 Pa at an air flow rate of 95 1/min. (as measured with the Lorenz 143 apparatus). Consequently, by combining MB non-woven textiles and ES non-woven nanotextile the filtration class of FFP3 was attained again.

Example 5

Another example of the filtration material intended for production of filtering facepieces features a multilayer structure created as a sandwich having the layer composition as follows: SB PP layer - MB PP layer - non-woven textile from PVDF nanofibres -MB PP layer - SB PP layer. The sandwich material has a total mass per unit surface area of 84.5 g/m ² , the non-woven nanotextile made from PVDF nanofibres has a mass per unit surface area of 0.48 g/m ² .

This example documents an improvement of filtration properties of the material for production of filters for particle filtering according to EN 143 standard, i. e. face masks, respirators, etc. This standard, similarly like EN 149, employs for evaluation of filtration capacities aerosol having a particle size of 400 nm. The sandwich material exhibited a pressure resistance Dr = 93 up to 109 Pa at a flow rate of 30 1/min. (requirement of the standard: < 120 Pa) and filtration efficiency FE = 99.96 - 99.99 % (requirement of the standard: > 99.95 %). Consequently, this material meets the requirements for materials of P3 class according to EN 143 standard. A similar material without any layer of non-woven textile, produced from SB/MB materials only and having identical pressure resistance, was able to capture particles 400 nm in size to about 90% only and the material meeting requirements for filtration efficiency of 99.95 % made from layers of SB/MB non-woven textile only and having a mass per unit surface area of 120 g/m ² , exhibited a pressure resistance of Dr = 184 Pa, as measured at a flow rate of 30 1/min.; therefore, it complied only with class 2 specified in EN 143 standard.

Example 6

The sixth example of the technical embodiment assesses a situation when the same non- woven nanotextile combined with either SB non-woven textile or MB non-woven textile is used in all cases. A comparison is made of sandwiches of VS SB non-woven textile - 0.2 g/m ² PVDF non-woven nanotextile - PP SB and VS SB non-woven textile - 0.2 g/m ² PVDF non-woven nanotextile - PP MB non-woven textile. In case of the material having no MB non-woven textile, the filtration class F9 decreased to class F8, as determined according to EN 779-2011 standard, which shows a positive effect of the MB non-woven textile and ES non-woven nano textile combination.

Example 7

A positive effect of combining a MB non-woven textile with a non-woven nanotextile became apparent also in manufacture of HEPA 15 filtration materials, when assessed in compliance with EN 1822-2009 standard. The sandwich of VS SB non-woven textile - 2.7 g/m ² PVDF non-woven nanotextile - PP MB non-woven textile exhibited a filtration efficiency FE = 99.9994 % at a pressure resistance of Dr = 234 Pa, while HEPA 15 filters made from glass microfibres exhibited a pressure resistance Dr up to 413 Pa at the corresponding filtration efficiency.

Example 8

MB non-woven textile in combination with ES nanofibres showed very desirable features also when employed for manufacture of filtration bags used in the food industry. Three- layer sandwiches comprising SB non-woven textile - non-woven nanotextile - SB non-woven textile + MB non-woven textile - non-woven nanotextile - SB non-woven textile contained an identical ES non-woven nanotextile made from polyurethane nanofibres having a mass per unit surface area of 1.4 g/m ² , a mean pore size of 320 nm and an identical filtration performance. When polluted air passed from the side of an MB non-woven textile, the filtration material containing the MB layer had a 41% longer lifetime than the material produced from SB non- woven textile only.

Example 9

Comparable results with the materials according to Examples 1 to 8 are obtained also with the materials containing a layer of SB and/or MB non-woven textile from the group of polymers including PET, PU, PLA and PA6 instead of the presented PP.

A similar case is that of a layer of ES non-woven nanotextile, which can alternatively be also produced from nanofibres based on a polymer from a group comprising PU, PLA, PA6, PAN, CA, PS, PESU and PVB while achieving results comparable with those attained when PVDF was used.