Air filter unit and use of an air filter unit in a motor vehicle

Abstract

The invention relates to an air filter unit and to the use of an air filter unit in a motor vehicle. The invention relates to an air filter unit, comprising:-at least one ionization unit, and-at least one filter medium, the at least one ionization unit having at least one discharge electrode, at least one counter electrode, and at least one voltage source, and the at least one filter medium being located downstream of the ionization unit, at least one outer electret layer, followed by at least one mechanical separation layer, followed by at least one inner electret layer, and followed by at least one electrically conductive layer, are arranged in the direction from the inflow side to the outflow side. The invention further relates to the use of such an air filter unit in a motor vehicle.

Description

Field of the Invention

[0001] The present invention relates to an air filtration unit, in particular an air filtration unit for a motor vehicle. The present invention also relates to the use of such an air filtration unit in a motor vehicle. Background Art

[0002] In order to achieve a comfortable and healthy air quality in the passenger compartment of a motor vehicle, it is necessary to purify particulate matter (such as fine dust particles) and harmful gases (such as volatile hydrocarbons, nitrogen oxides, ammonia, ozone or hydrogen sulfide) from the fresh air introduced from the outside. In particular, in urban areas, the outdoor air is often heavily loaded with fine dust. For example, the fine dust load in large cities often exceeds the daily average of PM2.5 of 15 μg / m 3 specified by the World Health Organization (WHO) on a daily average basis. This can pose significant health risks.

[0003] In the prior art, the dust that would otherwise be introduced into the passenger compartment via the air conditioning device is usually separated by a filter element installed in the air conditioning device and having a fiber filter layer for separating out particulate matter. However, the space available in such an air conditioning device is limited. At the same time, minimum safety requirements must also be observed, for example, to avoid window fogging, which requires sufficient air delivery. To ensure sufficient air flow, the filter element needs to have a low flow resistance or low pressure loss. The resulting disadvantage is that the filter fiber layer used for particulate separation typically has to be implemented very porous. As a result, the mechanical dust separation rate is usually very low.

[0004] To overcome this problem, in the prior art, filter media that attract electrostatically charged particles are usually proposed. For this purpose, for example, the filter media are electrostatically charged during the production process, or filter media that exhibit a certain degree of electrostatic charge even without a special charging method during the production process are used. This results in that during the operation of using electrostatically charged filter media, dust particles that are usually also electrostatically charged, even extremely small particles with a diameter of < 0.3 µm, can be separated well first. In this way, the flow resistance of the filter does not necessarily increase. For example, EP 3056364 A1 describes the application of a dielectric material (such as polypropylene) as a filter media.

[0005] However, for example, the electrostatic charge loaded during the production process rapidly decreases with the aging of the filter media and the increase in dust load during driving operation. This means that the electrostatic attraction of the filter media is only effective at the beginning of the life cycle of the filter, and depending on the degree of external air pollution, the electrostatic attraction often significantly fails after a few weeks or months. As a result, vehicle passengers are already exposed to a significantly increased particle concentration at a certain point before the replacement interval of the filter media. Summary of the invention

[0006] The problem underlying the invention is to specify a filter system for purifying external air fed into the passenger compartment, with which filter system an adequate filtering effect can be achieved even with large air flows and over longer periods of use.

[0007] This problem is solved according to the invention by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0008] According to the invention, an air filter unit is provided which has at least one ionization unit and at least one filter medium, wherein the at least one ionization unit has at least one discharge electrode, at least one counter electrode and at least one voltage source, and wherein the at least one filter medium is located downstream of the ionization unit and, viewed from the inlet side in the direction toward the outlet side, has: first at least one outer electret layer, then at least one mechanical separation layer, then at least one inner electret layer, and then at least one electrically conductive layer.

[0009] The air filter unit according to the invention having the features of independent patent claim 1 has the significant advantage over the prior art that a high particle separation rate is achieved over the entire service life of the filter medium. This is primarily caused by the fact that the electrostatic separation effect of the air filter unit can be maintained during the service life of the filter medium.

[0010] This results in the further significant advantage that the air filter unit provides a good separation rate with low pressure losses over the entire service life of the filter medium, thus resulting in a significantly lower particle load being experienced by the vehicle occupants. At the same time, the flow resistance of the system is low and is similar, for example, to a conventional interior air filter, which however has a significantly lower particle separation rate.

[0011] This object can be achieved in particular by a combination of at least one ionization unit and at least one filter medium, wherein the at least one filter medium, viewed from the inlet side in the direction of the outlet side, comprises first at least one outer electret layer, then at least one mechanical separation layer, then at least one inner electret layer and then at least one electrically conductive layer.

[0012] Hereinafter, the air filter unit according to the present invention will be explained in detail.

[0013] The present invention is based on the following general idea, namely, designing at least one filter medium for purifying the air guided from the outside into the passenger compartment and combining it with at least one ionization unit, so that the conveyed air can be purified efficiently.

[0014] Accordingly, an air filtration unit is proposed, for example, an air filtration unit for a vehicle air conditioning device, for a vehicle ventilation system, for a vehicle heating system, or for a combined heating, ventilation, and air conditioning system (HVAC system). The flow path of the air flow is guided through the air filtration unit. The air flow is the air flow that guides air from the outside into the vehicle interior, especially into the passenger compartment. Therefore, the inflow side is understood as the side where the air flow is conveyed from the outside. The air filtration unit has at least one ionization unit arranged in the flow path and at least one filter medium arranged downstream of the ionization unit in the flow path.

[0015] This means that the air filtration unit can have one ionization unit arranged in the flow path and one filter medium arranged downstream of the ionization unit in the flow path. However, alternatively, it is also conceivable that the air filter has two or more ionization units arranged in the flow path and two or more filter media arranged downstream of their respective ionization units in the flow path. It has proven particularly advantageous that the air filtration unit has one ionization unit arranged in the flow path and one filter medium arranged downstream of the ionization unit in the flow path.

[0016] At least one ionization unit is used to ionize at least a part of the particles contained in the air conveyed from the outside. In principle, all ionization units known to those skilled in the art and suitable for this purpose can be considered. For example, the ionization unit is described in both US 2021 / 0021107 A1 and EP 3056364 A1.

[0017] At least one ionization unit has at least one counter electrode. For example, it is conceivable that at least one counter electrode is present first on the inflow side in the air path. At least one counter electrode can be designed, for example, as a grid structure made of a conductive material, which is located in the air path and can be traversed by air. For example, such a grid structure can contain steel, especially stainless steel. In addition, at least one ionization unit has at least one discharge electrode. This means that the ionization unit has one or more discharge electrodes. It should be understood that at least one counter electrode and one or more discharge electrodes are arranged electrically separately. One or more discharge electrodes can be located at different positions in the flow path. For example, they are downstream of at least one counter electrode in the flow path and can be designed as electrode rods.

[0018] It has also been proven advantageous that at least one counter electrode on the inflow side in the air path is arranged at a spacing of at least approximately 15 mm to at most approximately 50 mm from one or more discharge electrodes. Furthermore, the ionization unit has a voltage source, in particular a high-voltage source, to which at least one counter electrode and one or more discharge electrodes are conductively connected.

[0019] For example, an electric field is generated between one or more discharge electrodes and at least one counter electrode in the flow path. Suitably, during operation of the air filtration unit, a first electric potential is applied or can be applied at one or more discharge electrodes, while a second electric potential different from the first electric potential is applied or can be applied at at least one counter electrode. It is conceivable, for example, that the first electric potential is the supply electric potential and the second electric potential is the counter electric potential. For example, the counter electric potential can be obtained by grounding at least one counter electrode. For example, the counter electric potential can be a zero electric potential. Suitably, a negative or positive potential difference is applied or can be applied between at least one counter electrode and one or more discharge electrodes during operation of the air filtration unit. For example, a negative potential difference in the range of at least approximately -5 kV to at most approximately -15 kV can be applied. In this case, a negative corona discharge can be generated at one or more discharge electrodes.

[0020] Thus, a negative or positive corona discharge can be generated by means of one or more discharge electrodes, and thereby gas molecules in the air are ionized. In principle, it is conceivable to generate a direct-current corona discharge, an alternating-current corona discharge or a pulsed corona discharge by means of the ionization unit. In principle, an electric potential with a negative polarity or an electric potential with a positive polarity can be applied to the discharge electrodes. It has been proven advantageous to apply a direct-current voltage with a negative polarity to the discharge electrodes for generating a corona discharge. Thereby, more ions are generated compared to the positive polarity. The obtained ionized gas molecules can then attach to the surfaces of the particles contained in the air conveyed from the outside, thereby causing the particles to acquire a net charge.

[0021] It is also conceivable that one or more additional counter electrodes are arranged additionally downstream of the discharge electrodes. For example, such an additional counter electrode can be conductively connected to a conductive surface filter coating of at least one filter medium, in particular at least one conductive layer. This will be discussed in detail later.

[0022] After the air flow is ionized in at least one ionization unit, the ionized air flow impinges on at least one filter medium. It should be understood that the ionized air flow herein refers, without further meaning, to at least some of the gas molecules of the air in the air flow and at least some of the pollutant particles carried by the air flow having a static electric charge. For example, it is conceivable that at least one filter medium and at least one ionization unit are arranged at a distance of at least about 1 mm to at most about 50 mm, preferably at a distance of at least about 5 mm to at most about 20 mm.

[0023] At least one filter medium according to the invention has at least one external electret layer on the inflow side. Herein, the inflow side is understood to mean that the air flow that has first been ionized by the ionization unit and is conveyed from the outside next first impinges on at least one external electret layer of the filter medium. For a person skilled in the art, an electret is understood to be an electrically insulating material that contains approximately permanently stored charges or approximately permanently oriented electric dipoles and thus generates an approximately permanent electric field in its surrounding environment or within it. The electret layer can, for example, be made of polymer fibers, such as fibers made of polypropylene or polyethylene terephthalate. At least one external electret layer has a static electric charge. Thus, the particle separation taking place on at least one external electret layer is mainly based on an electrostatic separation effect. The function of at least one external electret layer is to receive larger dust particles.

[0024] At least one mechanical separation layer is arranged on the outflow side of at least one external electret layer. It should be understood that the outflow side of at least one external electret layer is understood herein to mean that the ionized air flow conveyed from the outside first impinges on the external electret layer, where at least some of the particles with a static electric charge are separated out, and the air flow without these separated particles leaves on the opposite side of the external electret layer and from there impinges on at least one mechanical separation layer. At least one mechanical separation layer is protected by at least one external electret layer located in front of it, so that a large part of the larger particles are intercepted in at least one external electret layer, whereby the clogging of at least one mechanical separation layer and the resulting increase in flow resistance can be largely avoided or at least significantly delayed. At least one mechanical separation layer can, for example, be a non-woven fabric made of nanofibers, wherein the separation effect is based on the fact that at least one mechanical separation layer has intermediate spaces, the number and diameter of which are designed such that the inflowing air can pass through at least one mechanical separation layer, while the particles are largely intercepted therein. Thus, at least one mechanical separation layer is used to ensure a high mechanical separation rate for fine dust. Thereby, compared with at least one external electret layer, it causes a slightly higher flow resistance.

[0025] On the outflow side of at least one mechanical separation layer, at least one internal electret layer is also arranged. As already explained above in connection with the external electret layer, the electret layer can for example be made of polymer fibers, for example fibers made of polypropylene or polyethylene terephthalate. At least one internal electret layer has an electrostatic charge. Thus, the particle separation effected on at least one internal electret layer is mainly based on an electrostatic separation effect.

[0026] On the outflow side of at least one internal electret layer, at least one electrically conductive layer is also arranged. The electrically conductive layer can for example be a mesh made of metal (such as stainless steel). Alternatively, the electrically conductive layer can for example be a layer having at least one activated carbon coating.

[0027] At least one external electret layer, at least one mechanical separation layer, at least one internal electret layer and optionally at least one electrically conductive layer can for example be stacked successively and pressed and laminated, or for example be connected to one another or bonded to one another linearly at the cross-sectional edges and dotwise on the surface by means of ultrasonic welding or thermal welding. This also applies mutatis mutandis to other layers and coatings which will be explained in more detail in the present application.

[0028] Within the scope of the present application, a "layer" is understood as a continuous unit having a thickness extending in the flow direction. In the present context, such a layer can consist of a single coating. However, alternatively it is also possible that such a layer has a plurality, i.e. at least two successive coatings, where these coatings are for example different from one another in terms of their material composition.

[0029] It is also conceivable, for example, that at least one filter medium is inserted into a frame contained in an air filtration unit. Thereby, better stability of the structure can be achieved. All frames known to the person skilled in the art for filter media are applicable. Such a frame can for example be made of metal or plastic. For example, the frame can be made of a thermoplastic, a thermoset or an elastomer. It is expedient that the frame is made of a thermoplastic. For example, the frame is made of PA6, PA6.6, polypropylene, polyethylene, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate or polyetheretherketone. It is to be understood that the frame can additionally contain other auxiliaries, such as binders, crosslinking agents and additives. It is particularly expedient that the frame is glass fiber reinforced. For example, the frame can be made of PA6.6 GF30. It is furthermore to be understood that it is also conceivable to install a sealing element between the filter medium and the frame.

[0030] It has been proven advantageous for at least one electrically conductive layer to be in electrical contact with the counter electrode of the ionization unit. It should be understood that the electrical contact of at least one electrically conductive layer with the counter electrode of the ionization unit is advantageously achieved via an electrically conductive planar coating. For example, a planar coating having activated carbon or consisting of activated carbon is suitable for this purpose. This type of electrical contact is particularly advantageous because it enables the reactivation of the filter medium in terms of the function of its electret coating. This in turn advantageously leads to a significant increase in the separation efficiency with respect to fine dust or other particles.

[0031] For example, it has been proven suitable that, during the operation of the air filtration unit, on the one hand, a first electrical potential is applied or can be applied to one or more discharge electrodes, and on the other hand, a second electrical potential different from the first electrical potential is applied or can be applied to at least one counter electrode and at least one electrically conductive layer. Reference is made to the previous statements regarding the design of the first electrical potential and the second electrical potential different from the first electrical potential. For the preferred case where a negative corona discharge should occur on one or more discharge electrodes, during the operation of the air filtration unit, it is suitable to apply or be able to apply a negative potential difference between, on the one hand, one or more discharge electrodes and, on the other hand, at least one counter electrode and at least one electrically conductive layer. Thereby, at least some of the particles separated out in at least one external electret layer are provided with a negative net charge in the air flow conveyed from the outside, and thereby a polarization effect can be formed between at least one external electret layer loaded with negatively polarized particles and at least one electrically conductive layer. However, alternatively, it is also conceivable that the air filtration unit is configured and operated to cause a positive corona discharge on one or more discharge electrodes.

[0032] Furthermore, it has been proven advantageous for the electrical contact of at least one electrically conductive layer with the counter electrode of the ionization unit to be controllable in time such that the at least one electrically conductive layer is electrically separated from the counter electrode after the expiration of a predetermined polarization time and is electrically reconnected to the counter electrode after the expiration of a predetermined depolarization time.

[0033] Electrical switches for controllably separating and contacting in time are known per se to those skilled in the art. For example, an electromechanical relay can be used for this purpose. Alternatively, the switch can be implemented purely electrically, for example. For this purpose, an insulated-gate bipolar transistor (IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET) can be used.

[0034] This means that at least one electrically conductive layer is preferably only connected to the mating potential for a predetermined polarization time. It should be understood that this predetermined polarization time depends on the desired polarization value. This measure is based on the knowledge that after the at least one electrically conductive layer has been polarized, especially when the at least one electrically conductive layer is a layer containing activated carbon, the filtration efficiency of the filter medium only decreases slowly, so that electrical power can be saved by a time-controlled electrical separation of the at least one electrically conductive layer.

[0035] After the expiration of the predetermined depolarization time, the at least one electrically conductive layer can be reconnected to the mating potential (i.e., to the mating electrode of the ionization unit). The polarization time and the depolarization time depend on the application case and the design of the air filtration unit, for example on the specifications of the filter medium and the amount of air to be filtered.

[0036] Furthermore, it has proven to be advantageous for at least one filter medium to also have a carrier layer on the outflow side of the at least one electrically conductive layer. This is used to stabilize the filter medium. For example, it has proven to be advantageous for the carrier layer to have polyester fibers (such as fibers made of polyethylene terephthalate) or polyolefin fibers (such as fibers made of polypropylene). For example, the carrier layer can be a non-woven fabric made of a spunbond non-woven fabric, where the non-woven fabric, for example, has polyester fibers or polyolefin fibers.

[0037] For example, it is also conceivable that the carrier layer is a spunbond non-woven fabric made of polymer fibers, where the fibers are made of two polymers, namely so-called "BiCo" fibers. Such "BiCo" fibers are known to the person skilled in the art, for example, by the Delta® BiCo technology. Typically, different polymer materials than those of the fiber sheath are used in the core of the fiber for BiCo fibers. Typically, these BiCo fibers are produced as continuous fibers, from which non-woven fabrics can then be produced. For example, it is conceivable that the fiber has a core made of polyethylene terephthalate and a sheath made of polybutylene terephthalate.

[0038] Spunbond non-woven fabrics are known to the person skilled in the art. Typically, such spunbond non-woven fabrics are obtained by extruding the polymer into fine, continuous fibers that are then drawn out while being wound around each other. Preferably, the spunbond non-woven fabric used has a grammage of at least approximately 40 g / m 2 to a maximum of approximately 100 g / m 2 and more preferably, the spunbond non-woven fabric used has a grammage of at least approximately 65 g / m 2 to a maximum of approximately 75 g / m 2 and preferably, the spunbond non-woven fabric used also has a minimum of approximately 3500 l / (m2 s) to a maximum of about 10,000 l / (m 2 s) of air throughput (LD). More preferably, the spunbond nonwoven fabric used has a minimum of about 5500 l / (m 2 s) to a maximum of about 6500 l / (m 2 s) of air throughput (LD). The air throughput can be determined according to the DIN EN 9237:1995 standard.

[0039] In addition, the spunbond nonwoven fabric used has fibers with a fiber thickness of at least about 20 μm to a maximum of about 80 μm.

[0040] Of course, it is conceivable that the carrier layer contains additional auxiliaries such as binders, crosslinking agents, and additives. Examples of binders are acrylates and melamine formaldehyde. Examples of additives are polyurethanes. For example, the weight percentage of the additional auxiliaries contained in the carrier layer is small. In particular, each of the auxiliaries contained therein is less than 2 weight percent.

[0041] The carrier layer preferably has a thickness of at least about 80 μm to a maximum of about 2 mm, and more preferably, the carrier layer has a thickness of 300 μm to a maximum of about 1 mm.

[0042] The determination of the thickness of such a layer is known to those skilled in the art and can be achieved, for example, according to the DINEN ISO 9073-02:1997 standard.

[0043] Furthermore, it has proven advantageous that the filter medium has a covering nonwoven fabric on the inflow side in front of at least one external electret layer. This covering nonwoven fabric is preferably designed as a lightweight, open covering nonwoven fabric, which has a weight per unit area of about < 50 g / m 2 、particularly preferably about 20 g / m 2 and is used to intercept the largest dust particles and thus relieve the burden on the subsequent layers without a significant increase in flow resistance. In addition, it can prevent fibers from peeling off from the subsequent layers. For example, the covering nonwoven fabric can be made of polypropylene fibers or polyester fibers (such as polyethylene terephthalate), and its weight per unit area is less than about 50 g / m 2 、particularly preferably about 20 g / m 2 .

[0044] Regarding the optional auxiliaries contained in the covering nonwoven fabric, such as binders, crosslinking agents, and additives, reference is made to the foregoing content in connection with the carrier layer.

[0045] For at least one external electret layer, in principle, one or more coatings made of all non-woven fabrics, textiles, knitted fabrics or woven fabrics that can have a static charge or can be electrostatically charged can be used. For example, the respective coatings of at least one external electret layer can include, for example, melt-blow or spun-bond continuous polymer fibers, especially polyolefin fibers, which are processed, for example, in the form of non-woven fabrics. Melt-blow fibers can be obtained by extruding a molten polymer through an extrusion molding machine with small capillaries, and the fibers emerging from the capillaries are blown with hot air in one direction, pulled in length and then thermally joined.

[0046] At least one external electret layer typically has a thickness of at least about 300 μm to at most about 10 mm. In addition, at least one external electret layer is also designed with an intermediate space. It should be understood that the intermediate space is typically designed as an open intermediate space to ensure the flow-through of the air to be purified, even if, at the same time, it does not exclude that at least one external electret layer additionally includes a closed intermediate space for production reasons. Preferably, at least one external electret layer also has a minimum of about 300 l / (m 2 s) to a maximum of about 1500 l / (m 2 s) of air flow rate (LD) at 200 Pa.

[0047] At least one mechanical separation layer is efficiently protected by at least one external electret layer from being blocked by dust particles.

[0048] As described above, it is suitable to use one external electret layer, which can in turn have one or more coatings. However, alternatively, it is also conceivable to use two or more layers of external electret layers stacked on top of each other. At least one of these two or more layers of external electret layers can in turn have one or more coatings.

[0049] It has been proven suitable that at least one external electret layer has at least one external electret coating containing polyolefin fibers, wherein the at least one external electret coating containing polyolefin fibers is constructed from two different types of polymer fibers, and wherein the first type of polymer fiber is a polyolefin fiber and the second type of polymer fiber is a fiber made of a modified polyolefin. In this context, a modified polyolefin is understood to mean that the polyolefin has a substituent selected from the group consisting of, for example, -Cl, -F, -CN.

[0050] Preferably, the first type of polymer fiber is a fiber having polypropylene, and the second type of polymer fiber is a fiber having at least one polymer material selected from the group consisting of polyvinyl chloride, polytetrafluoroethylene, and modified polyacrylonitrile.

[0051] The term "modified polyacrylonitrile" is known to those skilled in the art. It can be understood as a fiber composed of acrylonitrile and one or more other components, where the other components can be, for example, vinyl chloride or vinylidene chloride. Typically, the weight fraction of acrylonitrile in such modified polyacrylonitrile fibers is from at least about 50% to at most about 85%.

[0052] Alternatively, the first type of polymer fiber is preferably a fiber having polypropylene. Additionally alternatively, the second type of polymer fiber is preferably a fiber having at least one polymer material selected from the group consisting of polyvinyl chloride, polytetrafluoroethylene, and modified polyacrylonitrile.

[0053] Preferably, at least one outer electret layer's at least one outer electret coating containing polyolefin fibers can be, for example, a non-woven fabric, where the non-woven fabric is constructed from two different types of polymer fibers, and the first type of polymer fiber is a fiber having polypropylene, while the second type of polymer fiber is a modified polyacrylonitrile fiber. Particularly preferably, the weight fraction ratio of the first type of polymer fiber to the second type of polymer fiber is 50:50.

[0054] Regarding the auxiliaries that may optionally be contained in at least one outer electret coating, reference is made, where meaningful, to the content described above in connection with the carrier layer.

[0055] Furthermore, it has proven advantageous that at least one outer electret coating containing polyolefin fibers has a grammage of less than about 200 g / m 2 and preferably about 100 g / m 2 .

[0056] Furthermore, it has proven advantageous that at least one outer electret layer additionally has at least one outer gradient coating on the inflow side of at least one outer electret coating containing polyolefin fibers. Preferably, at least one outer gradient coating has electrostatically charged fibers made of polyolefin. Particularly preferably, at least one outer gradient coating has electrostatically charged fibers made of polypropylene.

[0057] Furthermore, it has proven advantageous that at least one outer gradient coating of at least one outer electret layer has a grammage of less than about 150 g / m 2 and preferably about 50 g / m 2 .

[0058] Preferably, at least one outer electret coating has a thickness of at least about 300 μm to at most about 5 mm. In the case where at least one outer electret layer further has at least one outer gradient coating, preferably, the outer electret layer has a thickness of at least about 600 μm to at most about 10 mm, which is composed of the thickness of at least one outer electret coating of at least about 300 μm to at most about 5 mm and the thickness of at least one outer gradient coating of at least about 300 μm to at most about 5 mm.

[0059] In addition, in principle, at least one mechanical separation layer may have one or more coatings. In addition, in principle, all non-woven fabrics, textiles, knitted fabrics or woven fabrics that can achieve mechanical separation of particles can be used for one or more coatings of at least one mechanical separation layer.

[0060] However, it has been proven to be particularly advantageous that at least one mechanical separation layer has nanofibers, wherein the diameter of the nanofibers is at least about 10 nm to at most about 800 nm, preferably, the diameter of the nanofibers is at least about 90 nm to at most about 500 nm. In particular, it has been proven to be advantageous that the diameter of the nanofibers is at least about 90 nm to at most about 120 nm.

[0061] In the case where at least one mechanical separation layer has one coating, it means that the coating preferably has nanofibers. In the case where at least one mechanical separation layer has multiple coatings, it means that at least one of these coatings preferably has nanofibers.

[0062] In addition, it has been proven to be advantageous that the nanofibers are obtained by electrospinning a polymer material. The process of electrospinning is known to those skilled in the art. Typically, a polymer solution is metered onto an electrode, where the polymer solution is accelerated away from the electrode due to an electric field. Thereby, continuous fibers are formed, and these continuous fibers are deposited as a non-woven fabric on a counter electrode.

[0063] In addition, preferably, each of one or more coatings of the mechanical separation layer containing nanofibers has a basis weight of at least about 0.5 g / m 2 to at most about 3 g / m 2 and preferably about 1 g / m 2 .

[0064] Preferably, one or more coatings of the mechanical separation layer containing nanofibers are each made of a non-woven fabric, which is made of polyamide fibers (especially fibers made of PA6.6), polypropylene fibers, polyester fibers (such as fibers made of polyethylene terephthalate), or polyvinyl alcohol. Particularly preferably, the fibers are made of polypropylene. It is conceivable here that the different coatings stacked one on top of the other are made of the same material, and it is also conceivable that at least one mechanical separation layer has two or more coatings made of different non-woven fabric materials, for example, one coating made of a polypropylene non-woven fabric and another coating made of a polyamide non-woven fabric.

[0065] Regarding the auxiliaries that at least one mechanical separation layer may optionally include, reference is made to the content described above in connection with the carrier layer for meaning.

[0066] At least one mechanical separation layer typically has a thickness of at least about 1 μm to at most about 0.5 mm. In addition, at least one mechanical separation layer is also designed with an intermediate space. It should be understood that the intermediate space is typically designed as an open intermediate space to ensure the flowability of the air to be purified, even if at the same time, but it does not exclude that at least one mechanical separation layer may additionally include a closed intermediate space for production reasons. Preferably, at least one mechanical separation layer also has a minimum of about 200 l / (m 2 s) to a maximum of about 600 l / (m 2 s) of air flow rate (LD) at 200 Pa.

[0067] In addition, it has been proven advantageous that at least one intermediate layer is also arranged between at least one mechanical separation layer and at least one internal electret layer. This intermediate layer serves as a carrier for at least one mechanical separation layer. The intermediate layer is, for example, a non-woven fabric containing polypropylene fibers or polyester fibers (such as fibers made of polyethylene terephthalate).

[0068] In addition, it is preferred that at least one intermediate layer has a grammage of less than about 50 g / m 2 、preferably about 20 g / m 2 .

[0069] For at least one internal electret layer, in principle, one or more coatings made of all non-woven fabrics, textiles, knitted fabrics or woven fabrics that can have static charges or can be electrostatically charged can be used. For example, the respective coatings of at least one internal electret layer can include, for example, melt-blow or spun-bond continuous polymer fibers, especially polyolefin fibers, which are processed, for example, in the form of non-woven fabrics. Melt-blow fibers can be obtained by extruding molten polymer through an extrusion molding machine with small capillaries, and the fibers emerging from the capillaries are blown with hot air in one direction, pulled in length and then thermally connected.

[0070] At least one internal electret layer typically has a thickness of at least about 300 μm to at most about 10 mm. In addition, at least one internal electret layer is also designed with intermediate spaces. It should be understood that the intermediate spaces are typically designed as open intermediate spaces to ensure the flowability of the air to be purified, even if at the same time but without excluding that at least one internal electret layer may additionally include closed intermediate spaces for production reasons. Preferably, at least one internal electret layer also has a minimum of about 300 l / (m 2 s) to a maximum of about 1500 l / (m 2 s) of air flow rate (LD).

[0071] As described above, it is suitable to use one internal electret layer, which can in turn have one or more coatings. However, alternatively, it is also conceivable to use at least one internal electret layer of two or more layers stacked one above the other. At least one external electret layer of these two or more layers can in turn have one or more coatings.

[0072] It has been proven suitable for at least one internal electret layer to have at least one internal electret coating containing polyolefin fibers, wherein the at least one internal electret coating containing polyolefin fibers is constructed from two different types of polymer fibers, and wherein the first type of polymer fiber is a polyolefin fiber and the second type of polymer fiber is a fiber made of modified polyolefin. In this context, modified polyolefin is understood to mean that the polyolefin has a substituent selected, for example, from the group consisting of -Cl, -F, -CN.

[0073] Preferably, the first type of polymer fiber is a fiber having polypropylene, and the second type of polymer fiber is a fiber having at least one polymer material selected from the group consisting of polyvinyl chloride, polytetrafluoroethylene, and modified polyacrylonitrile. Alternatively, the first type of polymer fiber is preferably a fiber having polypropylene. Additionally alternatively, the second type of polymer fiber is preferably a fiber having at least one polymer material selected from the group consisting of polyvinyl chloride, polytetrafluoroethylene, and modified polyacrylonitrile.

[0074] Preferably, at least one inner electret layer's at least one inner electret coating containing polyolefin fibers can be, for example, a non-woven fabric, wherein the non-woven fabric is constructed from two different types of polymer fibers, and the first type of polymer fiber includes fibers having polypropylene, while the second type of polymer fiber is modified polyacrylonitrile fiber. Particularly preferably, the weight fraction ratio of the first type of polymer fiber to the second type of polymer fiber is 50:50.

[0075] Regarding the auxiliaries that the at least one inner electret layer may optionally contain, reference is made in terms of meaning to the content described above in connection with the carrier layer.

[0076] Furthermore, it has been proven advantageous that at least one inner electret layer's at least one inner electret coating containing polyolefin fibers has a grammage of less than about 200 g / m 2 and preferably about 100 g / m 2 .

[0077] Furthermore, it has been proven advantageous that the inflow side of at least one inner electret layer's at least one inner electret coating containing polyolefin fibers additionally has at least one inner gradient coating. Preferably, at least one inner gradient coating has electrostatically charged fibers made of polyolefin. Particularly preferably, at least one inner gradient coating has electrostatically charged fibers made of polypropylene.

[0078] Furthermore, it has been proven advantageous that at least one inner electret layer's at least one inner gradient coating has a grammage of less than about 150 g / m 2 and preferably about 50 g / m 2 .

[0079] Preferably, at least one internal electret coating has a thickness of at least about 300 μm to at most about 5 mm. In the case where at least one internal electret layer further has at least one internal gradient coating, preferably, the internal electret layer has a thickness of at least about 600 μm to at most about 10 mm, which is composed of the thickness of at least one internal electret coating of at least about 300 μm to at most about 5 mm and the thickness of at least one internal gradient coating of at least about 300 μm to at most about 5 mm.

[0080] Furthermore, it has been proven advantageous that at least one electrically conductive layer is also a layer for gas adsorption. This means that at least one electrically conductive layer contains a material capable of gas adsorption or is composed of a material capable of gas adsorption, such as activated carbon. It is also conceivable that at least one electrically conductive layer contains other components capable of gas adsorption, such as zeolite.

[0081] Particularly advantageously, at least one electrically conductive layer has activated carbon.

[0082] For example, it is conceivable that at least one electrically conductive layer has at least two coatings, where at least one of the coatings has activated carbon. It is also conceivable that at least one electrically conductive layer has two or more coatings, and these coatings each have activated carbon respectively.

[0083] Alternatively, for example, it is conceivable that at least one electrically conductive layer has at least two coatings, where at least one of the coatings is formed of activated carbon. It is also conceivable that at least one electrically conductive layer has two or more coatings, and these coatings are each formed of activated carbon respectively.

[0084] For example, such a coating with activated carbon can have granular activated carbon. Alternatively, such a coating formed of or having activated carbon can also be formed of fibrous activated carbon or have fibrous activated carbon. In addition, such a coating formed of or having activated carbon can be composed of so-called spherical carbon or have spherical carbon. As another alternative, such a coating formed of or having activated carbon can be composed of granular and fibrous activated carbon or have granular and fibrous activated carbon. Additionally alternatively, such a coating formed of or having activated carbon can also be composed of spherical carbon and fibrous activated carbon or have spherical carbon and fibrous activated carbon.

[0085] Such a coating formed of or having activated carbon preferably also has a grammage of at least about 100 g / m 2 to at most about 750 g / m 2 and more preferably, such a coating formed of or having activated carbon has a grammage of at least about 300 g / m 2 to at most about 400 g / m2 grammage. Particularly preferably, such a coating formed of or having activated carbon has a grammage of about 350 g / m 2 grammage.

[0086] Furthermore, it has been found to be particularly advantageous that at least one electrically conductive layer has activated carbon and an ion exchanger.

[0087] For example, it is conceivable that at least one electrically conductive layer has at least two coatings, where at least one of the two coatings has an ion exchanger and activated carbon. Of course, it is also conceivable that at least one electrically conductive layer contains two coatings, where one of the two coatings contains activated carbon and the other of the two coatings contains an ion exchanger. For example, it is conceivable that at least one electrically conductive layer contains a coating composed of granules of a mixture (of activated carbon and an ion exchanger). Alternatively, it is also conceivable that at least one electrically conductive layer contains a coating composed of a fiber mixture (of activated carbon fibers and ion exchanger fibers).

[0088] For example, it is conceivable that at least one electrically conductive layer contains two coatings, where one of the two coatings contains activated carbon granules and has a grammage of at least about 100 g / m 2 to a maximum of about 600 g / m 2 grammage, and the other of the two coatings contains ion exchanger granules and has a grammage of at least about 100 g / m 2 to a maximum of about 390 g / m 2 grammage. Particularly preferably, at least one electrically conductive layer contains two coatings, where one of the two coatings contains activated carbon granules and has a grammage of about 300 g / m 2 grammage, and the other of the two coatings contains ion exchanger granules and has a grammage of about 220 g / m 2 grammage.

[0089] The ion exchanger can be not only a cation exchanger but also an anion exchanger or a mixed bed ion exchanger. However, it is also conceivable that the ion exchanger is only an anion exchanger or only a cation exchanger. Preferably, the ion exchanger is a cation exchanger.

[0090] Anion exchangers and cation exchangers are known to the person skilled in the art. For example, an anion exchanger can be a material having a secondary amine compound or a tertiary amine compound or a quaternary ammonium compound. For example, a suitable anion exchanger is a poly(styrene - divinylbenzene) bead functionalized with quaternary ammonium groups.

[0091] For example, the cation exchanger can be a material having sulfonic acid groups or carboxyl groups. For example, such a cation exchanger is a plastic resin, such as a polystyrene-based resin, which has sulfonic acid groups firmly bonded to the resin. Suitable cation exchangers are, for example, based on sulfonic acid group-functionalized poly(styrene-divinylbenzene) beads.

[0092] Furthermore, it is expedient that the activated carbon in the coating having activated carbon, the ion exchanger in the coating having an ion exchanger, or the activated carbon and the ion exchanger in the coating having activated carbon and an ion exchanger are fixed using an adhesive.

[0093] All common adhesive systems can be used for bonding. For example, a physically curable adhesive system selected from the group consisting of polyamide resins, saturated polyesters, ethylene-vinyl acetate copolymers, polyolefins, styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, and polyimides can be used, or a chemically curable adhesive system selected from the group consisting of epoxy resins, polyurethanes, phenolic resins, silicones, and cyanoacrylates can be used. It has been proven that it is advantageous to use an adhesive system selected from the group of polyolefins or an adhesive system selected from epoxy resins or polyurethanes. In particular, it has been proven that it is advantageous to use a physically curable adhesive system made of polypropylene. Typically, such a system is available as hot-melt polypropylene.

[0094] The coating containing an ion exchanger preferably also has a grammage of at least about 100 g / m 2 and at most about 390 g / m 2 and more preferably, such a coating containing an ion exchanger has a grammage of about 220 g / m 2

[0095] At least one electrically conductive layer preferably has a thickness of at least about 500 μm to at most about 5 mm, more preferably, at least one electrically conductive layer has a thickness of at least about 800 μm to at most about 3 mm. Particularly preferably, at least one electrically conductive layer has a thickness of about 2 mm.

[0096] As described above, it is expedient to use an electrically conductive layer, in particular a layer containing activated carbon, which can in turn have one or more coatings. However, alternatively, it is also conceivable to use, for example, at least one electrically conductive layer of two or more layers stacked one on top of the other. This at least one electrically conductive layer of two or more layers can in turn have one or more coatings. However, it is particularly advantageous to use one electrically conductive layer.

[0097] ​Furthermore, it has been proven advantageous that the filter medium is designed to be pleated, i.e., the filter medium is in a pleated shape. Thereby, a larger filter surface can be provided without significantly increasing the flow resistance.

[0098] Furthermore, the present invention is also based on the general concept of providing an application of the above air filtration unit in a motor vehicle. In particular, the proposed air filtration unit is suitable for vehicle air conditioning equipment, vehicle ventilation systems, vehicle heating systems, or combined heating, ventilation, and air conditioning systems (HVAC systems).

[0099] Further important features and advantages of the present invention result from the dependent claims, the drawings, and the description of the accompanying drawings in connection with the drawings.

[0100] It should be understood that the above features and the features that will still be explained below can be used not only in the respectively described combinations, but also in other combinations or individually, without departing from the scope of protection of the present invention. Description of the Drawings

[0101] In which, respectively schematically:

[0102] Figure 1 A simplified perspective view of a preferred air filtration unit having an ionization unit and a filter medium is shown;

[0103] Figure 2 A simplified view of the filter medium is shown;

[0104] Figure 3 A simplified view of a filter medium having a plurality of coatings according to a preferred embodiment is shown. Detailed Description of the Invention

[0105] Figure 1 A very simplified perspective view of a preferred air filtration unit 100 is shown, which is preferably installed in a housing 105 of a vehicle air conditioning equipment (not shown). Figure 1 It also schematically indicates the air flow of the air transported from the outside in the inflow direction 103 and the air outflow 104 after passing through the ionization unit 101 and the filter medium 102. It should be understood that the air transported from the outside is outside air, which especially carries dust in an urban environment, and these dusts should be separated by means of the air filtration unit 100. The air thus purified is then especially transported to Figure 1 the passenger interior space not shown. Preferably, the air transported from the outside preferably flows completely through the air filtration unit. At least part of the gas molecules contained in the air flow are Figure 1The ionization unit 101 indicated in an extremely simplified illustration ionizes. The ionized gas molecules attach to the surfaces of the particles contained in the air, causing these particles to acquire a net charge. Thereby, an improved particle separation rate in the filter medium 102 can be achieved. The structure of the filter medium 102 will be discussed in detail in Figure 2 and Figure 3 still. Figure 1 The ionization unit 101 shown in Figure 1 has a plurality of electrodes 108 located in a plane, which are used to generate a corona discharge and are designed as so-called discharge electrodes made of, for example, stainless steel. These discharge electrodes are indicated by small triangles in Figure 1 . These discharge electrodes 108 are conductively connected to a high-voltage power supply 107 via electrical conductors 106. In addition, the ionization unit 101 also has counter electrodes 109, which are each constructed as hollow cylindrical counter electrode bodies that can be traversed by air in the embodiment shown in Figure 1 . The filter medium 102 is schematically indicated in Figure 1 with a corrugated design, but can alternatively be designed flat. The conductive layer of the filter medium 102 (not shown in Figure 1 ) can optionally be in electrical contact with the counter electrode via a further electrical conductor 110. During operation of the air filtration unit 100, it is now possible to apply a first electrical potential to the discharge electrodes 108 via the high-voltage power supply 107, while a second electrical potential different from the first electrical potential is applied to the counter electrodes 109 and optionally to the conductive layer of the filter medium 102.

[0106] Figure 2 shows the basic shape of the filter medium 102 in the air flow direction 204, which has an external electret layer 201a with a thickness of d 201a , a mechanical separation layer 202 with a thickness of d 202 , an internal electret layer 201b with a thickness of d 201b and a conductive layer 203 with a thickness of d 203 .

[0107] Figure 3 illustrates a preferred embodiment of the filter medium 102. The filter medium first has a covering nonwoven fabric 301 in the air flow direction 204. The covering nonwoven fabric 301 is a nonwoven fabric made of a spunbond nonwoven fabric, wherein the nonwoven fabric has polyester fibers. The grammage of the nonwoven fabric is approximately 70 g / m 2 . The fiber diameter of the polyester fibers is approximately 50 μm, and the thickness of the covering nonwoven fabric is approximately 300 μm. Following in the flow direction is the external electret layer 201a, which has an external gradient coating 305a and an external electret coating 304a containing polyolefin fibers. The thickness d of this external electret layer 201a201a is about 1 mm. The outer gradient coating 305a is an electrostatic coating made of polypropylene fibers, with a basis weight of about 50 g / m 2 . The outer electret coating 304a containing polyolefin fibers is preferably a non-woven fabric constructed from two different types of polymer fibers, where the first type of polymer fiber is a polyolefin fiber and the second type of polymer fiber is a modified polyacrylonitrile fiber. The weight fraction ratio of the first type of polymer fiber to the second type of polymer fiber is preferably 50:50. The basis weight of the outer electret coating 304a containing polyolefin fibers is approximately 100 g / m 2 .

[0108] Next is the mechanical separation layer 202. This is a non-woven fabric made of polypropylene nanofibers, and the diameter of the nanofibers is about 100 nm. The thickness d of the mechanical separation layer 202 202 is preferably about 200 μm.

[0109] This mechanical separation layer is separated from the subsequent inner electret layer 201b with an inner gradient coating 305b and an inner electret coating 304b containing polyolefin fibers by an intermediate layer 302. The thickness d of the inner electret layer 201b 201b is about 1 mm. The inner gradient coating 305b is an electrostatic coating made of polypropylene fibers, with a basis weight of about 50 g / m 2 . The inner electret coating 304b containing polyolefin fibers is preferably a non-woven fabric constructed from two different types of polymer fibers, where the first type of polymer fiber is a polyolefin fiber and the second type of polymer fiber is a modified polyacrylonitrile fiber. Particularly preferably, the weight fraction ratio of the first type of polymer fiber to the second type of polymer fiber is preferably 50:50. The basis weight of the inner electret coating 304b containing polyolefin fibers is approximately 100 g / m 2 .

[0110] Next is the conductive layer 203, which has two coatings 306 and 307. The thickness d of the conductive layer 203 203 is about 1 mm. Coating 306 contains activated carbon powder and has a basis weight of about 300 g / m 2 , while coating 307 contains ion exchange resin powder and has a basis weight of about 220 g / m 2 .

[0111] Subsequently is the carrier layer 303 with a thickness of d 303 . The carrier layer 303 is a non-woven fabric made of polypropylene fibers, with a basis weight of about 70 g / m 2, and the fiber diameter is about 50 μm. The thickness d of the carrier layer 303 is about 300 μm.

[0112] List of reference numerals

[0113] 100: Air filtration unit

[0114] 101: Ionization unit

[0115] 102: Filter medium

[0116] 103: Air flow in the inflow direction

[0117] 104: Air outflow

[0118] 105: Housing

[0119] 106: Electrical conductor for supplying power to the discharge electrode

[0120] 107: High-voltage power supply

[0121] 108: Discharge electrode

[0122] 109: Counter electrode

[0123] 110: Another electrical conductor connected to another counter electrode and having a conductive filter layer

[0124] 201a: External electret layer

[0125] 201b: Internal electret layer

[0126] 202: Mechanical separation layer

[0127] 203: Conductive layer

[0128] d 201a : Thickness of the external electret layer

[0129] d 201b : Thickness of the internal electret layer

[0130] d 202 : Thickness of the mechanical separation layer

[0131] d 203 : Thickness of the conductive layer

[0132] 204: Flow direction of the air flow

[0133] 301: Cover non-woven fabric

[0134] 302: Intermediate layer

[0135] 303: Carrier layer

[0136] 304a: External electret coating containing polyolefin fibers

[0137] 304b: Internal electret coating containing polyolefin fibers

[0138] 305a: External gradient coating

[0139] 305b: Internal gradient coating

[0140] 306: First coating of the electrically conductive layer

[0141] 307: Second coating of the electrically conductive layer

[0142] d 303 : Thickness of the carrier layer

Claims

1. An air filter unit (100), the air filter unit having - at least one ionization unit (101), and - at least one filter medium (102), wherein The at least one ionization unit comprises at least one discharge electrode (108), at least one counter electrode (109) and at least one voltage source (107), and wherein - The at least one filter medium (102) is located downstream of the ionization unit (101) and, viewed from the inflow side in the direction of the outflow side, comprises: firstly at least one outer electret layer (201a), then at least one mechanical separation layer (202), then at least one inner electret layer (201b), and then at least one electrically conductive layer (203).

2. The air filter unit (100) according to claim 1, characterized in that: The at least one electrically conductive layer (203) is in electrical contact with a counter-electrode of the ionization unit (101).

3. The air filter unit (100) according to claim 2, characterized in that: The electrical contact of the at least one electrically conductive layer (203) with the counter electrode of the ionization unit (101) can be controlled in time so that the at least one electrically conductive layer (203) is electrically separated from the counter electrode after a predetermined polarization time has expired and is electrically connected to the counter electrode again after a predetermined depolarization time has expired.

4. The air filter unit (100) according to any one of the preceding claims, It is characterized in that The at least one filter medium (102) further comprises a carrier layer (303) on the outflow side of the at least one electrically conductive layer (203).

5. The air filter unit (100) according to any one of the preceding claims, It is characterized in that The at least one filter medium (102) also has a covering nonwoven (301) on the inflow side upstream of the at least one outer electret layer (201a).

6. Air filter unit (100) according to any one of the preceding claims It is characterized in that The at least one outer electret layer (201a) has at least one outer electret coating (304a) containing polyolefin fibers, wherein the at least one outer electret coating containing polyolefin fibers is constructed from two polymer fibers of different types from one another, wherein a first polymer fiber type is a polyolefin fiber and a second polymer fiber type is a fiber made of a modified polyolefin, Preferably, said first polymer fiber type is a fiber comprising polypropylene, and / or The second polymer fiber type is a fiber having at least one polymer material selected from the group consisting of polyvinyl chloride, polytetrafluoroethylene, and modacrylic.

7. The air filter unit (100) according to any one of the preceding claims, characterized in that The at least one external electret layer (201a) also additionally has at least one external gradient coating (305a) on the inflow side of the at least one external electret coating (304a) containing polyolefin fibers, preferably the at least one external gradient coating having electrostatically charged fibers made of polyolefin.

8. The air filter unit (100) according to any one of the preceding claims, characterized in that The at least one mechanical separation layer (202) comprises nanofibers, The diameter of the nanofibers ranges from about 10 nm at the minimum to about 800 nm at the maximum. Preferably, the diameter of the nanofibers is a minimum of about 90 nm to a maximum of about 500 nm.

9. The air filter unit (100) according to any one of the preceding claims, It is characterized in that At least one intermediate layer (302) is also arranged between the at least one mechanical separation layer (202) and the at least one inner electret layer (201b).

10. The air filter unit (100) according to any one of the preceding claims, It is characterized in that The at least one inner electret layer (201b) has at least one inner electret coating (304b) containing polyolefin fibers, wherein the at least one inner electret coating containing polyolefin fibers is constructed from two polymer fibers of different types from one another, wherein a first polymer fiber type is a polyolefin fiber and a second polymer fiber type is a fiber made of a modified polyolefin, Preferably, said first polymer fiber type is a fiber comprising polypropylene, and / or The second polymer fiber type is a fiber having at least one polymer material selected from the group consisting of polyvinyl chloride, polytetrafluoroethylene, and modacrylic.

11. The air filter unit (100) according to any one of the preceding claims, It is characterized in that The at least one internal electret layer (201b) additionally has at least one internal gradient coating (305b) on the inflow side of the at least one internal electret coating containing polyolefin fibers, preferably the at least one internal gradient coating having electrostatically charged fibers made of polyolefin.

12. The air filter unit (100) according to any one of the preceding claims, characterized in that The at least one electrically conductive layer (203) is also a layer for gas adsorption.

13. The air filter unit (100) according to any one of the preceding claims, characterized in that The at least one electrically conductive layer (203) comprises activated carbon.

14. The air filter unit (100) according to any one of the preceding claims, characterized in that The at least one electrically conductive layer (203) comprises activated carbon and an ion exchanger.

15. The air filter unit (100) according to any one of the preceding claims, characterized in that The filter medium (102) is designed to be pleated.

16. Use of an air filter unit (100) according to any one of the preceding claims in a motor vehicle.

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