Filter medium, method for its production and use of the filter medium in a filter element

Abstract

Filter medium (1) comprising a substrate layer (2) and a nanofiber layer (3), characterized in that the nanofiber layer (3) is connected to the substrate layer (2) by adhesive and / or hot melt adhesive fibers (4) deposited on the nanofiber layer, wherein the nanofiber layer (3) is located in the sequence of layers between the substrate layer (2) and the adhesive and / or hot melt adhesive fibers (4), characterized in that the nanofiber layer (3) is arranged directly adjacent to the substrate layer (2) and that the adhesive and / or hot melt adhesive fibers (4) have a fiber cross-sectional area which is at least three times, preferably at least eight times, the fiber cross-sectional area of ​​the nanofibers of the nanofiber layer (2), wherein the adhesive and / or hot melt adhesive fibers (4) are at least partially fused with the substrate layer (2), and wherein the nanofibers of the nanofiber layer (3) have melting points as connection points with the adhesive and / or hot melt adhesive fibers (4).and wherein the adhesive and / or hot melt adhesive fibers (4) penetrate the nanofiber layer (3).

Description

[0001] The invention relates to a filter medium according to the preamble of claim 1, as well as a method for its production and two uses of this filter medium.

[0002] From DE 102 49 998 B3, a combined particle and adsorption filter is known, comprising one particle filter layer and two adsorption layers, wherein the particle filter layer is arranged between and connected to the two adsorptive layers. Each adsorption layer has an adsorption layer on a support layer, and the two adsorption layers are connected to the particle filter layer such that the adsorption layers of the two adsorptive layers face each other and the particle filter layer, while the support layers of the two adsorption layers face away from the particle filter layer and from each other. The particle filter layer consists of an electrostatically charged spunbond nonwoven fabric coated on its two main surfaces facing away from each other with electrostatically charged micro- and / or nanofibers of opposite electrical polarity.

[0003] EP 1 985 349 A2 discloses a filter medium in which two nonwoven layers are bonded together by hot melt adhesive fibers. The hot melt adhesive fibers themselves are designed as nanofibers and serve to bond the two filter layers. This nanofiber layer does not perform a filtration function; rather, the small fiber diameter of this nanofiber layer in EP 1 985 349 A2 ensures that the adhesive bond is finely distributed and has a small contact area.

[0004] EP 2 006 009 A1 discloses a filter medium with multiple filter layers. The individual filter layers can consist, for example, of meltblown or nanofibers and are arranged on a support layer which incorporates hot melt adhesive fibers for bonding the filter layers. EP 2 006 009 A1 optionally includes an additional microfiber layer made of nanofibers and meltblown fibers. Thus, in EP 2 006 009 A1, the support layer possesses the material properties necessary for bonding the filter layers to the nanofibers. The disadvantage of using hot melt adhesive fibers in the support layer is that the nanofibers, if they form the outermost layer, can be damaged during further processing, e.g., by deflecting the filter web over rollers and cylinders, winding, embossing, and folding. Damage can also occur during manual handling of the finished filter element and its installation.Furthermore, an "external" nanofiber layer can be damaged under difficult filtration conditions, e.g., high volume flow, differential pressure, and / or high viscosity of the medium. Further prior art is described in DE 20 2010 009 671 U1 and CN 1 04 066 492 A.

[0005] Therefore, the object of the present invention is to protect the surface of the nanofibers from mechanical damage and at the same time to create a connection with a support layer adjacent to the nanofiber layer.

[0006] This problem is solved by a filter medium having the features of claim 1.

[0007] A filter medium according to the invention comprises a substrate layer and a nanofiber layer, wherein the nanofiber layer is connected to the substrate layer by adhesive and / or hot melt adhesive fibers, the nanofiber layer being located in the sequence of layers between the substrate layer and the adhesive and / or hot melt adhesive fibers. In contrast to EP 2 006 009 A1, these are applied to the nanofiber layer from the side opposite the substrate layer, resulting in a kind of framing of the nanofiber layer.

[0008] While in the prior art the nanofibers only sink slightly into the hot melt adhesive fibers of the substrate layer, thus providing no protection against mechanical damage, the hot melt adhesive fibers applied to the surface within the scope of the present invention, due to their protruding nature relative to the nanofibers, form effective protection, e.g., as a grip protection, i.e., as protection against abrasion of the nanofibers. In other words, the hot melt adhesive fibers ensure adhesion of the nanofiber layer to the substrate layer and additionally provide protection against abrasion of the nanofibers.

[0009] The hot melt adhesive fibers also touch the substrate layer, thus enabling a connection, in particular a material-bonded connection, between the nanofiber layer and the substrate layer.

[0010] Alternatively, adhesive fibers, i.e., fibers with which bonds can be created due to their dissolving or melting properties, can also be used, whereby these can be chemically or physically curing, and / or the aforementioned hot melt adhesive fibers, i.e., hot melt adhesives (also called hot melts) in fiber form, wherein the hot melt adhesive fibers are thermally meltable adhesive systems that develop cohesion (internal strength) upon cooling, can be used within the scope of the present invention. Hot melt adhesive fibers can be thermoplastic or reactive. Thermoplastic hot melt adhesives can be reversibly melted. Reactive hot melt adhesives exhibit chemical crosslinking reactions during or after cooling.Suitable base polymers for hot melt adhesives include polyamides (PA), polyethylene (PE), amorphous polyalphaolefins, ethylene vinyl acetate (co)polymers (EVAC), polyester elastomers (TPE-E), polyurethane elastomers (TPE-U), copolyamide elastomers (TPE-A), and vinylpyrrolidone / vinyl acetate copolymers. According to the invention, the nanofiber layer is located in the layer sequence between the substrate layer (2) and the adhesive and / or hot melt fibers. In other words, the adhesive and / or hot melt fibers are located in the layer arrangement on an existing composite of substrate layer and nanofiber layer, such that, according to the invention, the hot melt fiber layer is always arranged on an outer surface of the filter medium.

[0011] The hot melt adhesive fibers can be arranged randomly or in an ordered manner, e.g., as continuous fibers with a network structure on the nanofibers. In some cases, the hot melt adhesive fibers can be bonded to the substrate layer.

[0012] Advantageous embodiments of the invention are the subject of the dependent claims.

[0013] In contrast to EP 1 985 349 A2, the nanofiber layer of the filter medium can be used for fine filtration of a medium, particularly following filtration through the substrate layer, provided the nanofiber layer is arranged downstream of the substrate layer. Alternatively, the nanofiber layer can be used for surface filtration, provided the nanofiber layer is arranged upstream of the substrate layer and the substrate layer is a closed, sheet-like medium without a filter function.

[0014] The nanofibers of the nanofiber layer can advantageously have a mean fiber diameter between 50 and 500 nm, preferably between 70 and 150 nm. This fiber diameter is particularly advantageous for filtering very fine particles from a medium to be filtered.

[0015] One advantageous type of nanofiber is polyamide nanofiber.

[0016] The substrate layer can advantageously be designed as a nonwoven layer comprising at least 90 wt.% cellulose and / or synthetic fibers. In this case, the substrate layer can also provide a filter function. For processing the filter medium, it is particularly advantageous if the substrate layer is designed as a carded nonwoven and / or spunbond nonwoven.

[0017] The adhesive and / or hot melt adhesive fibers can advantageously have a melting point that is at least 30°C below the melting point of the nanofibers in the nanofiber layer. This prevents the formation of a large melting area when the hot melt adhesive fibers are applied in a partially liquefied state, due to the simultaneous melting of the nanofibers, which would reduce the filter performance of the nanofiber layer.

[0018] Advantageously, the maximum melting point of the melt fibers is 220°C. In contrast, the melting point of a conventional polyamide nanofiber is 240°C.

[0019] To provide a large filtration area while simultaneously offering sufficient protection against mechanical stresses, more than 70%, preferably more than 90%, of the surface of the nanofiber layer can be left uncovered on the upstream or downstream side of the substrate layer.

[0020] This is also a further distinguishing feature compared to the design variant described in EP 1 985 349 A2, in which the nanofiber layer is completely covered on both sides, i.e. on both surfaces, by another nonwoven layer.

[0021] The adhesive and / or hot melt adhesive fibers had a fiber cross-sectional area, i.e., the perpendicular cross-sectional area through a fiber, which was at least three times, preferably at least eight times, the fiber cross-sectional area of ​​the nanofibers in the nanofiber layer. This enabled a wide framing for particularly good mechanical protection.

[0022] The adhesive and / or hot melt adhesive fibers can be made of a thermoplastic material or, more preferably, consist of a thermoplastic material, so that the bonding of the substrate layer and the nanofiber layer is primarily achieved by melting the fibers.

[0023] The thermoplastic polymer of the adhesive and / or hot melt adhesive fibers can advantageously be selected from one or more polyolefin compounds, polyester compounds, polyurethane compounds, and / or polyamide compounds. Suitable base polymers for hot melt adhesives include polyamides (PA), polyethylene (PE), amorphous polyalphaolefins, ethylene vinyl acetate (co)polymers (EVAC), polyester elastomers (TPE-E), polyurethane elastomers (TPE-U), copolyamide elastomers (TPE-A), and vinylpyrrolidone / vinyl acetate copolymers.

[0024] The hot melt adhesive fibers can advantageously define a window or a frame opening, wherein the average window size of a surface section is preferably at least 500 µm. 2 per cm 2 amounts.

[0025] The filter medium can consist solely of the substrate layer, the nanofiber layer, and the hot-melt adhesive fibers. No further material layers are included in this advantageous design variant, thus ensuring good foldability of the filter medium.

[0026] The hot melt adhesive fibers are at least partially fused to the substrate layer. Similarly, the nanofibers of the nanofiber layer and the hot melt adhesive fibers share fusion points. The hot melt adhesive fibers penetrate the nanofiber layer, ensuring a particularly advantageous bond between the nanofiber layer and the substrate, and additionally providing protection against abrasion of the nanofibers.

[0027] The nanofibers of the nanofiber layer and the substrate layer can each have connection areas with the adhesive and / or hot melt adhesive fibers, in which a material bond is formed between the adhesive and / or hot melt adhesive fibers and the nanofibers of the nanofiber layer or the substrate layer.

[0028] A method for producing a filter medium according to any of the preceding claims comprises at least the following steps: A. Providing a substrate layer; B. Arrangement of a nanofiber layer on the substrate layer and C Arrangement of adhesive and / or hot melt adhesive fibers on the nanofiber layer, forming a connection between the substrate layer and the nanofiber layer.

[0029] The filter medium according to the invention can particularly preferably be used in a folded, embossed and / or wound form within a filter element or as a wrapping around a filter element. Preferred areas of application are industrial filters and filters in internal combustion engines, e.g., in vehicles, ships, and stationary machines.

[0030] The invention will now be explained in more detail using an exemplary embodiment and several figures. These show: Fig. 1 Schematic representation of a filter medium according to the invention; Fig. 2 Microscopic top view of the filter medium according to the invention in the direction of flow; Fig. 3 Fig. 2 in monochrome view; Fig. 4 Enlarged microscopic top view of the filter medium according to the invention in the direction of flow; Fig. 5 Fig. 4 in monochrome view; Fig. 6 Cross-sectional view of the filter medium according to the invention; Fig. 7 Fig. 6 in monochrome view; Fig. 8 Microscopic top view of a filter medium with a substrate layer and a nanofiber layer after mechanical stress; Fig. 9 Microscopic top view of a filter medium according to the invention with a substrate layer and a nanofiber layer on which hot melt adhesive fibers are arranged; and Fig. 10 Schematic sequence of a simplified manufacturing process.

[0031] The figures merely show examples and are not to be understood as limiting.

[0032] Fig. Figure 1 shows an embodiment of a filter medium 1 according to the invention with a substrate layer 2, which is preferably designed as a first fiber layer, and with at least one nanofiber layer 3 arranged on the upstream or downstream side of the substrate layer, which is designed as a second fiber layer.

[0033] The substrate layer 2 can preferably be designed as a nonwoven layer and particularly preferably as a carded or spunbond nonwoven. It preferably comprises fibers 2a with a mean fiber diameter of preferably more than 1 µm, in particular between 3 µm and 50 µm.

[0034] In a preferred embodiment, substrate layer 2 can comprise more than 90 wt.% plastic fibers and / or cellulose fibers. The remaining wt.% up to 100 wt.% comprises impregnation additives for mechanical and chemical stabilization and binders. Substrate layer 2 itself need not have a significant filtering function; rather, it can primarily serve to stabilize the filter medium, particularly the subsequent fiber layer arranged upon it. Alternatively, the substrate layer can also be designed as a pre-filter layer, which filters out larger particles from the medium flow.

[0035] The substrate layer 2 can preferably be configured as a support layer for a nanofiber layer 3, which is preferably arranged directly adjacent to it. The individual fibers of the nanofiber layer 3 have an extremely small fiber diameter, and the applied layer is structurally comparable to a fine spider web. There is a correspondingly high tendency for the nanofiber layer 3 to degrade, and this tendency is to be counteracted.

[0036] The fibers 3a of the nanofiber layer 3 preferably have a mean fiber diameter between 50 and 500 nm, preferably between 70 and 150 nm. The mean fiber diameter can be determined according to DIN 53811: 1970-07.

[0037] The nanofiber layer 3 can, for example, be arranged on the upstream or downstream side of the substrate layer 2. This allows for advantageous stabilization by the melt fibers.

[0038] If the nanofiber layer 3 is located downstream of the substrate layer 2, the substrate layer 2 is preferably designed as a filter layer, in particular as a nonwoven layer for filtration. The nanofiber layer 3 then serves for fine filtration of the medium. If the nanofiber layer 3 is located upstream of the substrate layer 2, it serves for surface filtration. In this embodiment, the substrate layer 2, located downstream of the nanofiber layer 3, needs to exhibit virtually no filtration properties.

[0039] The nanofiber layer 3 and the substrate layer 2 are bonded together by adhesive and / or hot-melt adhesive fibers 4. The adhesive and / or hot-melt adhesive fibers 4 can be formed individually or, preferably, as a complete fiber layer.

[0040] The adhesive and / or hot melt adhesive fibers are applied with a mass deposition of between 1 and 10 g / m². 2 , preferably 4 to 6 g / m² 2, applied to substrate layer 2 or to the sequence of substrate and nanofiber layers 2 and 3.

[0041] The adhesive and / or hot melt adhesive fibers 4 can be applied to the substrate layer 2 by a hot spray or spray process before the application of the nanofiber layer 3, or alternatively, after the application of the nanofiber layer 3, to the entirety of the two material layers 2 and 3.

[0042] Preferably, the adhesive and / or hot melt adhesive fibers comprise at least 20 wt.%, and preferably more than 65 wt.%, of a thermoplastic polymer material or an adhesive fiber material. This is particularly preferably a polyolefin, a polyester, and / or a polyamide. The mean fiber diameter of the adhesive and / or hot melt adhesive fibers is preferably from 5 µm to 50 µm, and particularly preferably between 7 and 14 µm. The remaining wt.% up to 100 wt.% comprises, in particular, fillers such as calcium carbonate.

[0043] For example, a partially dissolved fiber material can be used as the adhesive material, e.g., through the use of a solvent-based adhesive. Alternatively or additionally, the adhesive fibers themselves can consist of an adhesive material or be provided with an adhesive coating.

[0044] The application of adhesive and / or hot melt adhesive fibers 4 to the surface of the substrate and / or nanofiber layer 2 and 3 enables, as the first layer on the upstream side, protection (e.g., grip protection) of the nanofiber layer 3, since the adhesive and / or hot melt adhesive fibers 4 are mechanically much more stable than the fibers of the nanofiber layer 3 due to their significantly larger diameter.

[0045] The filter medium 1 with the different material layers 2, 3, and 4 is foldable and can be designed as a pleated filter.

[0046] Preferably the filter medium 1 comprises three material layers, namely the substrate layer 2, the nanofiber layer 3 and the hot melt adhesive fibers 4 or the hot melt fiber layer.

[0047] Nanofiber layer 3 is arranged directly adjacent to substrate layer 2. The hot melt adhesive fibers 4 are at least partially fused to substrate layer 2. Likewise, the nanofibers of nanofiber layer 3 and the hot melt adhesive fibers 4 have melting points as connection points.

[0048] The basis weight of the filter medium 1 is between 50 and 250 g / m². 2 .

[0049] In a preferred embodiment, the connection is made without additional binders exclusively via the adhesive and / or hot melt adhesive fibers 4.

[0050] The average area of ​​a window in the aforementioned defined area section, which is bounded by the respective adhesive and / or hot melt adhesive fibers, is preferably at least 500 µm². 2 .

[0051] The filter medium 1 according to the invention is suitable for use in industrial filters or for filtering the intake air of internal combustion engines. Alternatively, the filter medium 1 can also be used in electrical discharge machines, as an air filter in driver's cabs, or as a liquid filter. With appropriate material selection, it can also be used in fuel or oil filters.

[0052] If the nanofiber layer 3 and the adhesive and / or hot melt adhesive fibers 4 are located on the upstream side of the substrate layer 2, a grip protection or protection against mechanical damage of the nanofiber layer 3 is achieved, which was not previously guaranteed with conventional filter media.

[0053] If the nanofiber layer 3 and the adhesive and / or hot melt adhesive fibers 4 are located on the downstream side of the substrate layer 2, the adhesive strength of the nanofibers on the substrate layer 2 is significantly increased. This ensures good mechanical support and a stable bond between the nanofiber layer 3 and the substrate layer 2. As a result, the filtration performance of the filter medium 1 is increased, or certain applications are only made possible by this filter medium 1 structure. This applies to filtration applications with high volume flows, e.g., secondary air filter elements, or applications in which a high differential pressure can occur, e.g., liquid filter elements.

[0054] Furthermore, the nanofiber layer 3 is protected from mechanical damage during the processing of the filter medium 1 for its use in filter elements. Typical processing steps include, for example, winding, embossing, folding, wrapping, and handling the treated medium, e.g., its insertion into a filter housing of the filter element. A corresponding filter element with a filter medium designed as a bellows is known, for example, from DE 10 2012 019 862 A1.

[0055] By protecting the nanofiber layer 3, the filtration performance can be increased compared to standard nanofiber media.

[0056] In Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. Figure 7 shows an embodiment of a filter medium 1 according to the invention, photographically in black and white and in color with a recognizable light-dark contrast. Individual fibers 2a of the support layer, as well as the spiderweb-like fibers 3a of the nanofiber layer 3 and hot melt adhesive fibers 4, are visible. The support layer 2a can, for example, be made of polyester fleece and is visible in the background. The hot melt adhesive fibers 4 can, for example, comprise a polyolefin-based polymer and are visible in the foreground of the figures. Between the support layer 2a and the hot melt adhesive fibers 4 is the fine nanofiber layer 3, which is physically protected, in particular against abrasion, by the stable, coarser fibers, wherein the nanofibers 3a are, for example, a polyamide.

[0057] The Fig. 4 to Fig. 5 show the structure according to Fig. 2 and Fig. 3 in cross-section. Fig. 6 and Fig. Figure 7 shows an overview of the structure according to Fig. 2 and Fig. 3 with a smaller magnification to show the support position in the background more clearly.

[0058] From the Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. Figure 7 clearly shows the abrasion protection for the very thin nanofibers, which are thus optimally protected against mechanical stress during the processing process.

[0059] Fig. Figure 10 shows a manufacturing process for a filter medium 1 according to the invention. In step A, a substrate layer 2 is provided, for example by a roll of material.

[0060] As the substrate layer 2 passes through a first application station 5, nanofibers 3a are applied, deposited onto the substrate layer and forming a nanofiber layer 3 (step B). The substrate and nanofiber layers 2 and 3 then pass through a second application station 6. Application station 6 may, for example, be equipped with a heating station 7 to produce a polymer melt. The hot melt adhesive fibers 4, which are still partially liquid, are dispensed from application station 6 onto the nanofiber layer 3 (step C). The hot melt adhesive fibers 4 wet or encapsulate the nanofibers 3a and also partially wet the substrate layer 2, so that a bond is formed between the substrate layer 2 and the nanofiber layer 3 when the hot melt adhesive fibers 4 cool.

[0061] Finally, the hot melt adhesive fibers cool down and the filter medium 1 is formed, which can then be processed further.

[0062] A comparison of the improved mechanical resistance compared to conventional filter media during the embossing of the filter medium is presented in Fig. 8 and Fig. 9. A clear comparison between a conventional filter medium ( Fig. 8) and a filter medium according to the invention ( Fig. 9) shown.

[0063] Fig. 8 and Fig. 9 already appear different in the REM images. This is because, compared to the in Fig. 8 conventional filter medium shown in the filter medium according to the invention ( Fig. 9) The added layer of hot melt adhesive fibers changes the focal plane on the scanning electron microscope. Due to the different focal planes of the Fig. 8 and Fig. 9, can in Fig. 8. The nanofiber layer is displayed with significantly higher contrast. This representation is shown in Fig. 9. This is not possible due to the additional hot-melt adhesive fiber layer. Both filter media were embossed, a common processing step in which the filter medium is subjected to particularly high mechanical stress: When processing the filter medium into the finished element, the filter medium is wound multiple times and various structures are embossed using steel rollers to ensure the subsequent folding of the medium. This creates strong mechanical friction and shear on the fine fibers of the filter medium, especially on ultrafine fibers, such as nanofiber layers.

[0064] Fig. Figure 8 shows the conventional filter medium with a substrate layer (polyester fleece) and nanofibers (polyamide), but without hot melt adhesive fibers covering the nanofiber layer. Fig. Figure 8 clearly shows that the unprotected nanofibers on the surface were destroyed by the embossing, and thus their functionality in the filter medium is significantly restricted or destroyed during the embossing process. Fig. Figure 9 shows, in comparison, the filter medium according to the invention. Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. 7 with hot melt adhesive fibers 4 after embossing. The nanofibers 3a of the nanofiber layer 3 are not damaged and thus retain their functionality in the filter medium even after embossing. The fine nanofiber structure 3 under the hot melt adhesive fiber layer 4 is even present in the immediate edge areas of the embossing. Fig. 9 are still completely preserved. Fig. In contrast, 8 shows severe damage and abrasion of the nanofiber layer in the entire area of ​​the embossing and especially in the fold edge 10 after the same mechanical stress.

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