Composite filter media and method of production thereof

Abstract

A composite filtration medium comprising a precision fabric of the type having weft and warp yarns, on the surface of which nanofibres are deposited by electrospinning. A method for producing a composite filtration medium comprising an electrospinning step for forming nanofibres and a subsequent step of depositing said nanofibres on a base fabric; the method comprises injecting, through a nozzle, a material for forming nanofibres dissolved in a solvent or mixture of solvents, so as to spread it on an electrode; the method comprises applying a potential difference between the nozzle and the electrode; the nanofibres are formed as a result of the evaporation of the solvent or mixture of solvents due to the electric field and by virtue of the stretching of the polymer deposited on the electrode by the nozzle; the nanofibres thus formed are subsequently stretched and deposited on said base fabric.

Description

Background Technology

[0001] The subject of this invention is a composite filter medium and its production method.

[0002] The present invention particularly relates to composite filter media in the form of fabric, which are used as protective media for electroacoustic components in the field of consumer electronics, such as speakers, receivers, microphones, etc.

[0003] Different fabrics are known to be used to protect acoustic devices, with the aim of providing adequate protection against external factors while simultaneously providing sufficient acoustic performance.

[0004] Conventional composite fabrics used in the industries described above have the drawback of not being able to withstand temperatures up to 300°C. In conventional composite fabrics, the mesh is coated with a layer of nanofibers. In fact, the fibers forming the fabric tend to degrade due to heating and essentially do not have a thermal profile suitable for ensuring the required performance.

[0005] Another drawback of existing composite materials is represented by poor adhesion between nanofibers and monofilaments that form the mesh of the fabric. Summary of the Invention

[0006] The purpose of this invention is to provide a composite filter medium that is an improvement over filter media known to date and exhibits higher performance.

[0007] In particular, the object of the present invention is to provide a novel composite fabric with filtering function for electroacoustic components, which, by exhibiting filtering performance equivalent to or higher than that of composite fabrics according to the prior art, will be able to withstand temperatures up to 300°C.

[0008] Another object of the present invention is to provide composite fabrics of the type described above, which can provide improved adhesion between the filaments of the fabric mesh and the nanofibers of the covering layer even without the use of adhesive additives.

[0009] Of the above objectives, the object of the present invention is to provide a filter medium that will be particularly useful in the production of hearing aids and sound devices.

[0010] Another object of the present invention is to provide a filter medium that ensures sufficient characteristics, at least similar to those of conventional fabrics, but with improved protective capabilities.

[0011] Another object of the present invention is to provide a filter medium that can simultaneously ensure better acoustic performance and better protection against particulate intrusion.

[0012] Another object of the present invention is to provide a filter medium that can guarantee air permeability and acoustic impedance values ​​at least equal to those of conventional fabrics, but with a certain degree of protection against the intrusion of metal dust, textile dust, etc., which is superior to the protection of conventional fabrics against the intrusion of metal dust, textile dust, etc.

[0013] Another object of the present invention is to provide a filter medium that can be advantageously used to protect electroacoustic components in the field of consumer electronics, such as speakers, receivers, microphones, etc.

[0014] Another object of the present invention is to provide a filter medium that will ensure the greatest possible reliability and safety during use.

[0015] These and other objectives are achieved by composite filter media and methods of their production, as specified in the appended claims, and these objectives will become more apparent hereinafter. Attached Figure Description

[0016] Further features and advantages of the subject matter of the invention will become more apparent from the description of preferred, but not exclusive, embodiments of the invention, which are illustrated in the accompanying drawings by way of indicative and non-limiting examples.

[0017] Figure 1 A composite filter medium according to the present invention is shown, which is composed of a PEEK 71.35 monofilament base fabric, i.e., a weft and warp yarn with 71 threads in 1 cm of fabric, and a polyetheretherketone monofilament with a nominal diameter of 35 μm.

[0018] The substrate fabric has a coating layer of polyimide nanofibers deposited in solution by means of an electrospinning process. A suitable solvent is DMAc (dimethylacetamide) and NMP (N-methyl-2-pyrrolidone) in a weight ratio of 40:60. A solution of polyimide for forming nanofibers by electrospinning is prepared in this solvent mixture.

[0019] Figure 2 This is a graph showing the Rub & Buzz analysis of standard composite fabrics (Aethex 25), PROTO 1, and Acoustex 025 (Ac 025) fabrics, where:

[0020] -RUB&Buzz analysis is the analysis of sound types on the undesirable effects of irregular nonlinear distortion;

[0021] -Aethex 25 is a composite fabric based on existing technology that is not suitable for withstanding high temperatures (nano mesh with acoustic impedance of 25 MKS Rayleigh).

[0022] -PROTO 1 is a composite fabric according to the present invention, which also has an acoustic impedance of 25 MKS Rayleigh;

[0023] Acoustex 025 is a non-composite fabric, meaning it has no nanofiber coating, and it also has an acoustic impedance of 25 MKS Rayleigh.

[0024] Figure 3 The preparation Figure 1 The untreated PEEK 71.35 base fabric used in the composite.

[0025] Figure 4 The figure shows Figure 3 A view of the surface of the PEEK monofilaments on the PEEK 71.35 base fabric during electrospinning treatment using only DMAc-NMP solvent at a weight percentage of 40:60 without the use of nanofibers.

[0026] Figure 5 The figure shows a fabric according to the prior art, which, unlike the filter medium according to the invention, does not show any swelling portions.

[0027] Figure 6 The figure shows Figure 1 The composite filter media, viewed on the surface of the PEEK monofilament of the base fabric before (A) and after (BF) various thermal cycles during electrospinning treatment with DMAc-NMP solvent and polyimide nanofibers in a weight percentage ratio of 40:60, wherein:

[0028] -B: 260℃_1min_2 reflux cycles per cycle;

[0029] -C: 260℃_10min_2 reflux cycles each time;

[0030] -D: 260℃_30min_2 reflux cycles each time;

[0031] -E: 260℃ for 1 hour, 2 reflux cycles per cycle;

[0032] -F: 260℃ for 2 hours, 2 reflux cycles per cycle;

[0033] Figure 7 The energy required to completely remove oil from the composite fabric according to the invention was compared with the energy required to remove oil from a filter medium with comparable air permeability according to the prior art, wherein:

[0034] PROTO 1, PROTO 2, and PROTO 3 each have a capacity of 4500 (l / m) 2 s -1 200Pa, 2350 (l / m 2 s -1 200Pa and 980 (l / m 2 s -1 The composite fabric according to the invention has an air permeability of 200 Pa;

[0035] -Aethex 25, Aethex 70 and Aethex 160 have 4500 (l / m) respectively 2 s -1 200Pa, 2350 (l / m 2 s -1 200Pa and 980 (l / m 2 s -1 Air permeability of 200 Pa according to existing technology filter media. Detailed Implementation

[0036] Referring specifically to the figures presented in the foregoing figures, the composite filter medium 1 according to the invention comprises a fabric having weft and warp yarns, preferably PEEK yarn or monofilament 2, on which polyimide nanofibers 3 are deposited by electrospinning. According to the invention, the monofilament 2 can be replaced by a different type of yarn formed from polymers suitable for withstanding high temperatures, such as fabrics made of glass fiber, poly(p-phenylene sulfide), polyimide, polyethersulfone, and sulfonated polyarylethersulfone. Furthermore, the nanofibers themselves can be made of materials different from polyimide and resistant to high temperatures, such as polybenzimidazole, sulfonated polyetheretherketone, polyethersulfone, and sulfonated polyarylethersulfone.

[0037] The present invention applies to monofilaments and nanofibers characterized by good thermal resistance properties, which are expressed in terms of melting temperature and / or glass transition temperature having a thermal range from room temperature to up to 300°C.

[0038] The base fabric used in preparing the composite filter medium according to the invention is selected from synthetic monofilament fabrics that typically have a wide range of diameters from 3 threads / cm to 200 threads / cm and from 24 μm to 600 μm, and the synthetic monofilament fabric has different chemical properties from the monofilaments used for weaving.

[0039] Specifically, the present invention is applicable to substrate fabrics that can withstand high process temperatures (up to 300°C) both in a single-step thermal process and in a thermal recirculation or reflux process, i.e., in a process involving multiple consecutive cooling / heating cycles.

[0040] In addition to metallization, for finishing operations and other surface treatments, fabrics selected from the following are used: washed and heat-set "white" fabrics, colored fabrics, and fabrics that have undergone plasma treatment, hydrophobic treatment, hydrophilic treatment, antibacterial treatment, antistatic treatment, etc.

[0041] The preferred embodiment of this invention is a monofilament fabric made of polyetheretherketone (PEEK), which has 71 threads / cm, a diameter of 35μm, a base fabric mesh size of 102μm, and a density of 20g / m². 2 The weight of the woven fabric and its thickness of 65μm.

[0042] The present invention is applicable to polymer nanofibers that can withstand high process temperatures of up to 300°C in both one-step thermal processes and reflux cycles, with the diameter of the nanofibers ranging from 50 nm to 500 nm.

[0043] The present invention preferably comprises polyimide (PI) nanofibers having a diameter between 100 nm and 220 nm.

[0044] The electrospinning process for forming nanofibers and subsequently depositing them onto a substrate fabric involves injecting a material for forming nanofibers dissolved in a suitable solvent or mixture of solvents through a nozzle to spread it onto an electrode.

[0045] Nanofibers are formed as a result of the evaporation of the solvent or solvent mixture due to the electric field caused by the potential difference between the nozzle and the electrode, and by stretching the polymer deposited on the electrode through the nozzle.

[0046] The nanofibers formed are then stretched and subsequently deposited onto a substrate fabric.

[0047] Furthermore, compared to existing technologies, the nanofibers 3 thus formed in an innovative manner not only deposit on the substrate fabric but also adhere firmly to it using some process parameters that will be explained below, without the need for glue and / or adhesives applied to the substrate fabric and / or nanofiber layer. These process parameters facilitate the formation of the thread 2 portion and the surface swelling portion 4 of the substrate fabric.

[0048] The swelling portion 4 of the base line 2, which does not affect the structural properties of the base fabric, facilitates the strong adhesion of the nanofibers 3 arranged on the base line 2, enabling the formation of a more stable product from the perspective of the integrity of the adhesion between the base fabric and the nanofibers during various processing techniques of the filter media.

[0049] According to the present invention, this result is achieved by subjecting a solution of polyimide in a mixture of dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP) solvent (NMP in excess) to an electrospinning process to form nanofibers 3. During the electrospinning process, polyimide nanofibers are thus obtained deposited on a thread 2 made of polyetheretherketone (PEEK). During this deposition step, the solution of the aforementioned solvent, still carried by the nanofibers 3, wets the thread 2 on the surface where it contacts the nanofibers, thereby forming softened portions and swollen portions 4 on the surface itself. These softened portions and swollen portions 4 are incorporated into a portion of the nanofibers 3 during the electrospinning process, thereby facilitating their adhesion or anchoring to the thread 2. Figure 1 ).

[0050] Therefore, according to the present invention, during the electrospinning process, nanofibers 3 not only deposit on monofilaments 2, but also exhibit adhesion or relative fixation between the monofilaments and the monofilaments, a phenomenon that contributes to the stability of the composite fabric 1. A suitable solvent for this purpose is a mixture of DMAc and NMP in a 40:60 ratio, wherein NMP is present in excess, particularly in a mixture of solvents at a concentration greater than or equal to 50% by weight. Thus, in this manner, adhesion of the nanofibers is facilitated without impairing the structural properties of the base fabric. Figure 1 , Figure 3 and Figure 4 This is an SEM image that explains the phenomenon just described.

[0051] Table 1 provides a comparison of the percentage change (Δ% of AP) in thermal resistance properties versus air permeability before and after one or more recirculation cycles between the filter media according to the present invention and prior art filter media at different temperatures and different usage times, specifically 130°C for 120 hours (the temperature and usage time typically required for filter media according to the prior art); and 260°C for a time range from 1 minute to 2 hours (the temperature and usage time typically required for filter media operating at high temperatures).

[0052] Specifically:

[0053] -Aethex 25 is a composite fabric (nano-mesh with an acoustic impedance of 25 MKS Rayleigh) that is unsuitable for high temperatures according to existing technology; and

[0054] PROTO 1 is a composite fabric according to the invention formed from a PEEK 71.35 base fabric with a polyimide nanofiber coating layer, obtained by electrospinning the polyimide in a solution of DMAc / NMP in a 40:60 ratio, and the composite fabric also has an acoustic impedance of 25 MKS Rayleigh.

[0055] Table 1 then provides a comparison of the percentage differences in air permeability measured before and after one or more recirculation cycles from 25°C to 130°C and from 25°C to 260°C, between the filter media PROTO 1 according to the invention and the filter media Aethex 25 according to the prior art. (The data is presented in l / m² at a pressure of 200 Pa.) 2 s -1 Measure air permeability.

[0056] As shown in this table, within a thermal range of 25°C to 130°C and for a typical time using filter media according to the prior art, the filter media according to the invention have the same filtration capacity as filter media according to the prior art, and only the filter media according to the invention can be used at high temperatures, for varying durations, and in numerous recirculation cycles. For this reason, data measured at 260°C cannot be used for composite fabrics Aethex 25, as they are not measurable. It is known that an indicator of damage to the filter media during or after its use is its increased or decreased air permeability compared to its unused initial state, expressed as a percentage of tolerance higher than the physiological tolerance percentage of the process, generally considered acceptable within 8%, as this property implies the possible morphological damage to the filter media during its use. Conversely, excessive or defective changes in air permeability, including within the tolerance range of the process itself, relative to its unused initial state, are an indication that the protective capacity of the filter media remains unchanged during its use. In specific cases, a decrease in the air permeability of the filter media, including within the tolerance range of the process, i.e., less than 5%, can be noted, which confirms the filtration capacity of the composite media according to the invention.

[0057] Table 1

[0058]

[0059] NA = Not obtained

[0060] Figure 6 The figures illustrate views of the surface of PEEK monofilaments of a substrate fabric electrospun with DMAc-NMP solvent and polyimide nanofibers in a 40:60 weight percentage ratio according to the composite filter media of the present invention before (A) and after (BF) various thermal recycles, wherein specifically:

[0061] -B: 260℃_1min_2 reflux cycles per cycle;

[0062] -C: 260℃_10min_2 reflux cycles each time;

[0063] -D: 260℃_30min_2 reflux cycles each time;

[0064] -E: 260℃ for 1 hour, 2 reflux cycles per cycle;

[0065] -F: 260℃ for 2 hours, 2 reflux cycles each time.

[0066] As can be seen from the presented images, in all the study cases of thermal recycling from B to F, due to the formation of swollen portions on the surface of the fabric itself described above, the uniformity of the mesh-like coating layer of the filter media according to the invention and the morphological appearance of the adhesion of the polyimide nanofibers to the PEEK fabric remain unchanged compared to the morphological appearance of the filter media itself before its use, confirming the thermal resistance of the filter media according to the invention in the thermal recycling tests conducted.

[0067] Table 2 below shows a comparison of the air permeability, pore size and acoustic impedance properties of various prototype filter media according to the present invention with the corresponding properties of a standalone PEEK 71.35 substrate fabric, i.e., a PEEK 71.35 substrate fabric without a nanofiber coating.

[0068] In this table, pores are defined as a combination of pores present in the base fabric and pores formed in the nanofiber coating layer. At a pressure of 200 Pa, the pores are expressed in l / m³. 2 s -1 Measure air permeability.

[0069] also:

[0070] -PEEK 71.35 is a mesh with a base fabric of 71 threads / cm, a diameter of 35μm, and a mesh size of 102μm, and a weight of 20g / m². 2 The weight of the woven fabric and the thickness of the base fabric according to the invention are 65 μm;

[0071] -PROTO 1 is a composite fabric according to the invention, which is formed from a PEEK 71.35 base fabric having a polyimide nanofiber coating layer obtained by electrospinning polyimide in a solution of DMAc / NMP in a 40 / 60 ratio.

[0072] PROTO 2-PROTO 5 are composite fabrics according to the present invention, similar to PROTO 1, and obtained by electrospinning processes with different parameters.

[0073] Table 2

[0074]

[0075] Table 2. Air permeability and pore size properties of some prototypes of the substrate fabric and filter media according to the present invention.

[0076] As can be seen from Table 2 above, in terms of air permeability, in the electrospinning process used to prepare PROTO 1 to PROTO 5 according to the present invention, the PEEK fabric web is covered with nanofibers in a gradually increasing manner, thereby obtaining a reduced pore size and an increased acoustic impedance.

[0077] Conversely, Table 3 below shows the air permeability properties of standard fabrics (if available) with pore sizes comparable to those of various prototypes according to the invention, wherein:

[0078] -PES 38 / 20 and PES15 / 09 have mesh sizes of 38μm and 15μm respectively, and a mesh size of 1cm. 2 The fabrics contain 20% and 9% polyester with free surface area, respectively.

[0079] Table 3

[0080]

[0081] NA = Not obtained

[0082] Table 3. Air permeability and pore size properties of some prototypes of the substrate fabric and filter media according to the present invention.

[0083] Table 3 emphasizes that, with comparable pore sizes, the air permeability in the cases of PROTO 1 and PROTO 2 is significantly greater than that in the case of the fabric, thus ensuring better acoustic performance. Conversely, since no standard reference fabric is available for comparison with PROTO 3 and PROTO 4, it is evident that only the composite fabric according to the invention can ensure the described air permeability properties and particle protection.

[0084] Finally, another objective of the present invention is to provide a novel composite fabric that has a filtering effect on electroacoustic components, which, in addition to being able to withstand temperatures up to 300°C, also has filtering performance equivalent to or higher than that of existing composite fabrics.

[0085] Under inspection, different prototypes with the same air permeability as the composite fabrics according to the prior art have been prepared, and filter media with pore sizes comparable to or smaller than the corresponding composite fabrics according to the prior art have been obtained, given the same properties of air filtration.

[0086] By adding plasma treatment to the filter medium according to the invention, in combination with polyimide nanofibers 3, the energy required to remove oil deposited on the surface of the filter medium is significantly reduced compared to the energy required by filter media according to known technology, except for increasing the water-column resistance known in the case of filter media belonging to the prior art, thereby obtaining better protective performance than the latter.

[0087] Figure 7 The paper presents the pressure required to completely remove oil deposited on the surface of filter media according to the prior art and filter media according to the invention, the filter media according to the prior art having air permeability comparable to that of various prototypes according to the invention.

[0088] exist Figure 7 middle:

[0089] Aethex 25 and PROTO 1 are composite fabrics according to the prior art and the present invention, respectively. Aethex 25 and PROTO 1 have pore sizes of 60 μm and 36 μm, respectively, and a density of approximately 4500 l / m. 2 s -1 200Pa of permeability;

[0090] Aethex 70 and PROTO 2 are composite fabrics according to the prior art and the present invention, respectively. Aethex 70 and PROTO 2 have pore sizes of 12 μm and 19 μm, respectively, and a density of approximately 2350 l / m. 2 s -1 200Pa of permeability;

[0091] Aethex 160 and PROTO 3 are composite fabrics according to the prior art and the present invention, respectively. Aethex 160 and PROTO 3 have pore sizes of 14 μm and 5 μm, respectively, and a density of approximately 980 l / m. 2 s -1 )200Pa of permeability.

[0092] from Figure 7 The invention specifically demonstrates that, for composite fabrics according to the invention, the pressure required to completely remove oil from the composite fabric is lower than that required for composite fabrics of the prior art, making the cleaning of the fabric simpler and faster.

[0093] This invention has a wide range of advantageous applications.

[0094] One example of the practical application of this invention relates to filtration, even at high temperatures.

[0095] Compared to conventional types of nanomesh, filter media made of PEEK and polyimide can also be used in several other applications; for example, it can be used in applications where the filter media will be subjected to high process temperatures, and it is necessary for its properties to remain unchanged, i.e., the fabric and nanofibers do not undergo any changes due to temperature.

[0096] The innovative application of the filter media according to the present invention is related to MEMS (Micro-Electro-Mechanical Systems) technology.

[0097] Specifically, the MEMS device is characterized by two vents, one inside the MEMS device, which involves the use of a protective filter medium that is not necessarily post-processed by die-cutting, and one outside the device itself, which involves the use of a protective filter medium that must be post-processed by die-cutting. This overcomes the problems of overheating and pressure equalization of electronic components during their use.

[0098] This makes it possible to withstand very high process temperatures (even close to 300°C) during multiple steps of assembly and use, which facilitates the passage of air between the inside and outside of the MEMS device.

[0099] The need to protect these two exhaust ports with a protective film that is permeable to air and can withstand temperatures close to 300°C is essential to prevent contamination by moisture, particles, dust, oil, etc., and more generally to prevent degradation of sound transmission performance, to enable airflow recirculation, and finally, because their high-temperature resistance facilitates the assembly of MEMS devices with previously integrated protective layers. This technology choice is beneficial to the production of MEMS devices and makes the production of MEMS devices more economical. If a MEMS device is assembled without protective exhaust ports, the MEMS device may be damaged during the assembly process.

[0100] In the current technology, the protection of internal and external vents of MEMS devices is achieved in two ways: i) no protective layer is applied, resulting in a very short service life of the device; ii) protective adhesive tape is applied.

[0101] Choosing to apply protective adhesive tape is not considered satisfactory compared to not protecting the exhaust port itself, because these tapes are not permeable to air, and therefore, although they protect the device from several contaminants, they cannot allow for adequate air recirculation, which leads to problems such as MEMS overheating and internal pressure imbalance.

[0102] Therefore, the use of a filter medium made of a known type of nanomesh, along with the additional advantage of thermal resistance according to the invention, represents an advancement relative to the existing level of MEMS technology, for both internal and external protection of MEMS devices.

[0103] In acoustic applications, this invention can be used in cases where filter media are co-molded with high-melting-point polymers, thereby ensuring thermal resistance during the process.

[0104] In addition to its use in applications involving high temperatures (where conventional nanonets cannot be used due to obvious physical limitations), a second advantage of this invention is the improved and tighter adhesion between the support fabric and the nanofibers.

[0105] In this case, this property can actually be achieved:

[0106] - Post-processing of materials to prevent damage to them and thus potential deterioration of their performance (see typical die-cutting processes for providing nanomesh portions of encapsulation assembled with adhesive layers);

[0107] - A major advantage in terms of acoustic properties; in fact, in cases where the adhesion between nanofibers and standard fabrics is not strong, the passage of sound, i.e., the passage of airflow at a given rate, can cause possible micro-vibrations in the nanofiber layer on the substrate, resulting in sound distortion or undesirable noise.

[0108] With the nanofibers firmly adhered to the substrate, the vibration problem just described disappeared, and the sound became clearer.

[0109] Typically, the onset of sound distortion or undesirable noise caused by micro-vibrations induced by a nanofiber layer electrospun on a substrate can be studied through acoustic analysis known as “Rub & Buzz”.

[0110] Figure 2 A graph showing Rub & Buzz analysis of a standard nanomesh sample (Aethex 25), a sample of PROTO 1 (i.e., the filter media according to the invention), and a sample of fabric Acoustex 025 with the same acoustic impedance as Aethex 25 and PROTO 1 is presented.

[0111] from Figure 2 The charts presented typically show that, for all measured samples—Aethex 25, PROTO 1, Acoustex 025—the percentage of vibration caused by the filter media is less than 0.8% (a reference target for commercial acoustic equipment).

[0112] Furthermore, by comparing PROTO 1 with two reference samples, it can be noted that all samples of PROTO 1 have lower percentage values ​​of Rub & Buzz and are therefore improved compared to Aethex 25 and Acoustex025 due to better adhesion of the nanofiber layer to the substrate fabric.

[0113] It should be noted that plasma treatment can be added to the filter media according to the invention, thereby achieving benefits in two aspects:

[0114] - In the case of materials that are not particularly permeable, there is an increase in water column resistance; and

[0115] - Ensure the non-wetting property of the nanomesh in the case of highly permeable materials.

[0116] Furthermore, in the case of plasma treatment, the energy required to remove oil deposited on the surface of the filter media is reduced.

[0117] In practice, it has been found that the present invention has achieved the intended goals and objectives.

[0118] In fact, filter media composed of polymer nanofibers deposited on monofilament fabrics by electrospinning have been obtained.

[0119] During deposition, nanofibers are arranged on the lines, at the intersections between the lines, and in the web of the fabric; by being arranged in the web, the nanofibers reduce the average pore size and free surface of the fabric.

[0120] In this way, air permeability and acoustic impedance values ​​equal to those of standard fabrics can be obtained.

[0121] At equal permeability / resistance values, composite fabrics provide better protection against dust (metal dust, textile dust, etc.) than standard fabrics.

[0122] This is due to the random and three-dimensional structure of the nanofiber layers arranged in the mesh, which allows for a reduction in the surface area of ​​the channels, unlike fabrics that rely solely on their own mesh openings to reduce and / or prevent dust from passing through. The nanoscale size of the fibers also minimizes the percentage of closed or unfiltered volume.

[0123] In this way, by replacing the standard fabric with a composite fabric with equal permeability in a given application, it is possible to guarantee the same pressure drop under the same flow rate, thereby greatly improving protection against intrusion.

[0124] Therefore, in specific cases where composite fabrics are used as protective media for electroacoustic components (speakers, receivers, microphones) in consumer electronics, the same acoustic performance can be guaranteed compared to conventionally used fabrics, but with improved protection. In some cases, even better acoustic performance and better protection against particulate intrusion can be achieved simultaneously.

Claims

1. A method for producing a composite filter medium comprising a base fabric of the type having weft and warp yarns of polyetheretherketone (PEEK) yarns or monofilaments, characterized in that, The method includes an electrospinning step for forming polyimide (PI) nanofibers and a subsequent step of depositing the nanofibers onto the substrate fabric; the method includes injecting a material for forming the nanofibers dissolved in a mixture of dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP) through a nozzle to spread it onto an electrode, wherein the NMP solvent is in excess; the method includes applying a potential difference between the nozzle and the electrode; the nanofibers are formed as a result of the evaporation of the solvent mixture due to the electric field and by stretching the polymer deposited on the electrode using the nozzle; The nanofibers thus formed are then stretched and deposited on the base fabric; wherein the nanofibers are firmly adhered to the base fabric at the swollen portion of the thread in the base fabric without the need for glue and / or adhesive applied to the base fabric and / or the nanofiber layer, and the swollen portion is formed on the surface of the thread itself in contact with the nanofiber when the nanofibers are added.

2. A composite filter medium, obtained by the method according to claim 1, characterized in that, The wires or filaments have swelling portions on their surfaces that come into contact with the nanofibers, the swelling portions being incorporated into the nanofibers themselves, thus retaining the nanofibers on the surface of the wires or filaments themselves.

3. The composite filter medium according to claim 2, characterized in that, The fabric is selected from synthetic monofilament base fabrics having a diameter from 24 µm to 600 µm and a thread count from 3 threads / cm to 200 threads / cm.

4. The composite filter medium according to claim 3, characterized in that, In addition to metallization, for finishing and other surface treatments, fabrics selected from the following are used: washed and heat-set white fabrics, colored fabrics, and fabrics that have undergone plasma treatment, hydrophobic treatment, hydrophilic treatment, antibacterial treatment, or antistatic treatment.

5. The composite filter medium according to any one of claims 2-4, characterized in that, The fabric is a monofilament fabric made of polyetheretherketone (PEEK) with 71 threads / cm, a diameter of 35 µm, a mesh size of 102 µm in the base fabric, and 20 g / m². 2 The weight of the woven fabric and the thickness of 65 µm.

6. The composite filter medium according to claim 2, characterized in that, The nanofibers are polyimide (PI) nanofibers with diameters between 100 nm and 220 nm.

Images