Filter medium, method for producing same, and use of the filter medium in a filter element

Abstract

A filter medium has a substrate layer and a nanofiber layer arranged on the substrate layer. Adhesive fibers are laid onto the nanofiber layer and connect the nanofiber layer with the substrate layer. The nanofiber layer is located between the substrate layer and the adhesive fibers.

Claims

1. A filter medium comprising: a substrate layer, wherein the substrate layer is nonwoven fiber layer comprising at least 90 wt % of cellulose fibers; at least 90 wt % of synthetic fibers; or at least 90 wt % of cellulose fibers and synthetic fibers, wherein the substrate layer has a first flow side, wherein the first flow side is either an inflow side or an outflow side of the substrate layer; a nanofiber layer having a first side arranged directly on the first flow side of the substrate layer, the nanofiber layer comprising synthetic nanofibers having diameters in a range of 50 nm to 500 n m; a hot-melt adhesive fiber layer arranged on a second side of the nanofiber layer such that the nanofiber layer is arranged between the substrate layer and the hot melt adhesive fiber layer, wherein the a hot-melt adhesive fiber layer is made of a different material than both the nanofiber layer and the substrate layer; wherein the hot-melt adhesive layer is a separate layer from the nanofiber layer and the substrate layer, the hot-melt adhesive layer is applied onto the second side of the nanofiber layer, wherein the second site is opposite the first side of the nanofiber layer which is arranged directly on the substrate layer; wherein the hot-melt adhesive fiber layer is applied while wet onto the second side of the nanofiber layer, such that the material of the hot melt adhesive fibers of the hot-melt adhesive fiber layer wet or enclose the synthetic nanofibers of the nanofiber layer, the material of the hot-melt adhesive fibers of the hot-melt adhesive fiber enclose the synthetic nanofibers thereby connecting and fixing the nanofiber layer onto the substrate layer; wherein the material of the hot melt adhesive fibers consists of one or more compounds selected from the group consisting of polyurethane, amorphous polyalphaolefins, poly(ethylene-co-vinyl acetate) polymers (PEVA), polyester elastomers (TPE-E), polyurethane elastomers (TPE-U), copolyamide elastomers (TPE-A), and vinyl pyrrolidone/vinyl, acetate copolymers wherein nanofibers of the nanofiber layer and the substrate layer each comprise connecting regions with the hot-melt adhesive fibers, wherein in the connecting regions a material fusion between the hot-melt adhesive fibers and the nanofibers of the nanofiber layer or the substrate layer exists.

2. The filter medium according to claim 1, wherein the hot-melt adhesive fibers are applied onto the nanofiber layer with a mass application in a range from 1 g/m.sup.2 to 10 g/m.sup.2.

3. The filter medium according to claim 2, wherein the mass application is in a range from 4 g/m.sup.2 to 6 g/m2.

4. The filter medium according to claim 1, wherein the substrate layer is carded nonwoven; a spunbonded nonwoven; or a carded nonwoven and a spunbonded nonwoven.

5. The filter medium according to claim 1, wherein the hot-melt adhesive fibers comprise a cross-sectional area which is at least three times that of a cross-sectional area of nanofibers of the nanofiber layer.

6. The filter medium according to claim 5, wherein the cross-sectional area of the hot-melt adhesive fibers is at least eight times that of the cross-sectional area of the nanofibers of the nanofiber layer.

7. The filter medium according to claim 1, wherein the nanofibers of the nanofiber layer have a melting point temperature; wherein the hot-melt adhesive fibers have a different melting point temperature that is less than the melting point temperature of the nanofibers of the nanofiber layer.

8. The filter medium according to claim 1, wherein the hot-melt adhesive fibers delimiting a window comprising an average window size of a surface section that amounts to at least 500 Φm5 per cm2.

9. The filter medium according to claim 1, wherein the filter medium is comprised exclusively of the substrate layer, the nanofiber layer, and the hot-melt adhesive fibers.

10. The filter medium according to claim 1, wherein more than 70% of a surface of the nanofiber layer is arranged at an inflow side or an outflow side of the substrate layer and is not covered.

11. The filter medium according to claim 10, wherein said more than 70% of the surface of the nanofiber layer is not covered by the hot-melt adhesive fibers.

12. The filter medium according to claim 10, wherein more than 90% of the surface of the nanofiber layer arranged at the inflow side or the outflow side of the substrate layer is not covered by the hot-melt adhesive fibers.

13. A filter element comprising a filter medium according to claim 1, wherein the filter medium is in a folded, embossed, and/or wound form; or the filter element comprising a wrapping of one or more layers about an exterior of the filter element, the wrapping comprised of the filter medium according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention will be explained in more detail based on an embodiment with the aid of several Figures.

(2) FIG. 1 is a schematic illustration of a filter medium according to the invention.

(3) FIG. 2 is an enlarged microscopic plan view of the filter medium according to the invention in inflow direction.

(4) FIG. 3 shows FIG. 2 in a monochrome view.

(5) FIG. 4 is a sectional image of the filter medium according to the invention.

(6) FIG. 5 shows FIG. 4 in monochrome view.

(7) FIG. 6 is a microscopic plan view of the filter medium according to the invention in inflow direction.

(8) FIG. 7 shows FIG. 6 in monochrome view.

(9) FIG. 8 is a microscopic plan view of a filter medium with a substrate layer and a nanofiber layer after mechanical loading.

(10) FIG. 9 is a microscopic plan 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.

(11) FIG. 10 is a schematic sequence of a manufacturing process illustrated in a simplified way.

(12) The Figures show only examples and are not to be understood as limiting.

DESCRIPTION OF PREFERRED EMBODIMENTS

(13) FIG. 1 shows an embodiment of a filter medium 1 according to the invention with a substrate layer 2 that is preferably embodied as first fiber layer and with at least one nanofiber layer 3 arranged at the inflow side or outflow side on the substrate layer and embodied as a second fiber layer.

(14) The substrate layer 2 can be preferably embodied as a nonwoven layer and particularly preferred as a carded nonwoven or spunbonded nonwoven. It comprises preferably fibers 2a with an average fiber diameter of preferably more than 1 Φm, in particular in a range from 3 Φm to 50 Φm.

(15) The substrate layer 2 in a preferred embodiment variant can comprise more than 90 wt % synthetic fibers and/or cellulose fibers. The remaining wt % up to 100 wt % comprise impregnation additives for mechanical and chemical stabilization and binding agents. The substrate layer 2 itself must not exhibit an essential filter function but can serve mainly for stabilizing the filter medium, in particular the additional fiber layer which is arranged thereon. Alternatively, the substrate layer can also be designed as a prefilter layer which in particular filters out coarser particles from the medium flow.

(16) The substrate layer 2 can be embodied preferably as a carrier layer for a nanofiber layer 3 that is arranged preferably immediately adjacent thereto. The individual fibers of the nanofiber layer 3 comprise an extremely minimal fiber diameter and the applied layer is structurally comparable to a fine spider web. A correspondingly high tendency for destruction of the nanofiber layer 3 therefore exists and this tendency is to be counteracted.

(17) The fibers 3a of the nanofiber layer 3 comprise preferably an average fiber diameter in a range from 50 nm to 500 nm, preferably in a range from 70 nm to 150 nm. The average fiber diameter can be determined according to DIN 53811:1970-07.

(18) The nanofiber layer 3 can be arranged, for example, at the inflow side or outflow side relative to the substrate layer 2. In this way, an advantageous stabilization by the hot-melt fibers can be achieved.

(19) When the nanofiber layer 3 is arranged at the outflow side relative to the substrate layer 2, the substrate layer 2 is preferably embodied as a filter layer, in particular as a nonwoven layer for filtration. The nanofiber layer 3 serves in this context for fine filtration of the medium.

(20) When the nanofiber layer 3 is arranged at the inflow side relative to the substrate layer 2, then the nanofiber layer 3 serves for surface filtration. The substrate layer 2 arranged at the outflow side relative to the nanofiber layer 3 must have hardly any filtration properties in this embodiment variant.

(21) The nanofiber layer 3 and the substrate layer 2 are connected to each other by adhesive fibers and/or hot-melt adhesive fibers 4. The adhesive fibers and/or hot-melt adhesive fibers 4 can be embodied individually or preferably as a complete fiber layer.

(22) The adhesive fibers and/or hot-melt adhesive fibers are applied with a mass application in a range from 1 g/m5 to 10 g/m5, preferably 4 g/m5 to 6 g/m5, onto the substrate layer 2 or onto the sequence of substrate and nanofiber layers 2 and 3.

(23) The adhesive fibers and/or hot-melt adhesive fibers 4 can be applied by a hot injection process or spraying process onto the substrate layer 2 prior to application of the nanofiber layer 3 or alternatively after application of the nanofiber layer 3 onto the entirety of the two material layers 2 and 3.

(24) Preferably, the adhesive fibers and/or hot-melt adhesive fibers comprise at least 20 wt %, preferably more than 65 wt %, of a thermoplastic synthetic material or an adhesively acting fiber material. Particularly preferred, this can be a polyolefin, a polyester and/or a polyamide. The average fiber diameter of the adhesive fibers and/or hot-melt adhesive fibers can amount to preferably 5 Φm to 50 Φm, particularly preferred 7 Φm to 14 Φm. The remaining wt % up to 100 wt % encompass in particular fillers such as, for example, calcium carbonate.

(25) As adhesively acting fiber material, e.g. a fiber material can be used that is partially dissolved, e.g., by using a solvent-containing adhesive. Alternatively or additionally, the adhesive fibers 4 themselves can be comprised of an adhesively acting material or can be provided with an adhesively acting coating.

(26) The application of adhesive fibers and/or hot-melt adhesive fibers 4 onto the surface of the substrate layer 2 and nanofiber layer 3 enables, as a first layer at the inflow side, a protection (e.g., handling protection) of the nanofiber layer 3 because the adhesive fibers and/or hot-melt adhesive fibers 4, due to their multiple times greater diameter are mechanically significantly more stable than the nanofibers of the nanofiber layer 3.

(27) The filter medium 1 with the different material layers 2, 3, and 4 is foldable and can be embodied as a folded filter.

(28) 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.

(29) In a further preferred embodiment variant, the nanofiber layer 3 is arranged to immediately adjoin the substrate layer 2.

(30) The hot-melt adhesive fibers 4 in a further preferred embodiment variant are fused with the substrate layer 2 at least in sections. Also, the nanofibers of the nanofiber layer 3 comprise fused spots with the hot-melt adhesive fibers 4 as connecting points.

(31) The weight per surface area of the filter medium 1 is in a range from 50 g/m5 to 250 g/m5.

(32) In a preferred embodiment variant, the connection is realized without additional binders exclusively by means of the adhesive fibers and/or hot-melt adhesive fibers 4.

(33) The average surface area of a window in the aforementioned defined surface section, which is delimited by the respective adhesive fibers and/or hot-melt adhesive fibers, preferably amounts to at least 500 Φm5.

(34) The filter medium 1 according to the invention is suitable for use in industrial filters or for filtration of engine intake air of internal combustion engines. Alternatively, the filter medium 1 can also be used in eroding machines, as air filter in driver cabins or as liquid filter. Also, a use in fuel or oil filters is conceivable with properly selected material.

(35) Provided that the nanofiber layer 3 and the adhesive fibers and/or hot-melt adhesive fibers 4 are located at the inflow side relative to the substrate layer 2, a handling protection or a protection against mechanical damage of the nanofiber layer 3 is achieved which was not ensured in the past with conventional filter media.

(36) Provided that the nanofiber layer 3 and the adhesive fibers and/or hot-melt adhesive fibers 4 are located at the outflow side relative to the substrate layer 2, the adhesive force of the nanofibers on the substrate layer 2 is significantly increased. A good mechanical support and a stable connection of the nanofiber layer 3 to the substrate layer 2 is enabled. As a result, the filtration performance of the filter medium 1 is increased or certain applications become even possible in the first place with this configuration of the filter medium 1. This concerns filtration applications with high volume flows, e.g., secondary air filter elements, or applications in which a high differential pressure may occur, e.g., liquid filter elements.

(37) The nanofiber layer 3 moreover is protected during processing of the filter medium 1 for its use in filter elements against mechanical damage. Typical processing steps are e.g. winding, embossing, folding, wrapping, and handling of the correspondingly treated medium, e.g., insertion into a filter housing of the filter element. A corresponding filter element with a filter medium embodied as a folded bellows is disclosed, for example, in DE 10 2012 019 862 A1.

(38) By protecting the nanofiber layer 3, the filtration performance in comparison to standard nanofiber media can be increased.

(39) In FIGS. 2 to 7, an embodiment variant of a filter medium 1 according to the invention is illustrated photographically in black-and-white view and in a color view with recognizable light/dark contrast. One can recognize individual fibers 2a of the support layer as well as the spider web-like nanofibers 3a of the nanofiber layer 3 and hot-melt adhesive fibers 4. The support layer of the fibers 2a can be realized, for example, as a polyester nonwoven and can be seen in the background. The hot-melt adhesive fibers 4 can comprise, for example, a polyolefin basic polymer and can be seen in the foreground of the images. Between the support layer of the fibers 2a and the hot-melt adhesive fibers 4, the fine nanofiber layer 3 is located which is physically protected, in particular against abrasion, by the stable coarser fibers, wherein the nanofibers 3a, for example, are made of or comprise a polyamide.

(40) FIGS. 4 to 5 show the construction according to FIGS. 2 and 3 in cross section. FIGS. 6 and 7 show an overview photograph of the construction according to FIGS. 2 and 3 at a smaller magnification in order to show the carrier layer in the background more clearly once again.

(41) FIGS. 2 to 7 illustrate clearly the abrasion protection for the very thin nanofibers which are thus optimally protected in particular from mechanical loading during the manufacturing process.

(42) FIG. 10 shows a manufacturing process for a filter medium 1 according to the invention. In this context, a substrate layer 2 is provided in a step A, for example, as a material coil.

(43) When passing the substrate layer 2 through a first application station 5, the application of nanofibers 3a is realized which are laid onto the substrate layer and form a nanofiber layer 3 (step B). Subsequently, passage of the substrate layer 2 and nanofiber layer 3 through a second application station 6 is realized. The application station 6 may comprise, for example, a heating station 7 for producing a polymer melt. The hot-melt adhesive fibers 4 which are still partially in a liquid state are discharged by the application station 6 onto the nanofiber layer 3 (step C). In this context, the hot-melt adhesive fibers 4 wet or enclose the nanofibers 3a and at least also wet the substrate layer 2 in sections so that, upon cooling of the hot-melt adhesive fibers 4, a connection is produced between the substrate layer 2 and the nanofiber layer 3.

(44) Finally, the hot-melt adhesive fibers cool down and formation of the filter medium 1 is realized which can then be further processed.

(45) A comparison in regard to the mechanical resistance for embossment of the filter medium, improved relative to conventional filter media, is illustrated in FIGS. 8 and 9 by comparison of a conventional filter medium (FIG. 8) and a filter medium according to the invention (FIG. 9).

(46) FIGS. 8 and 9 appear already different in the SEM micrographs. This is so because the focal plane at the scanning electron microscope changes due to the hot-melt adhesive fiber layer which has been added in the filter medium according to the invention (FIG. 9) compared to the conventional filter medium shown in FIG. 8. Due to the different focal planes of FIGS. 8 and 9, in FIG. 8 the nanofiber layer can be represented with significantly better contrast. This representation is not possible in FIG. 9 due to the additional hot-melt adhesive fiber layer. Both filter media have been embossed, a conventional further processing step in which the filter medium is mechanically particularly strongly stressed. Upon processing of the filter medium to the finished element, the filter medium is wound multiple times and by means of steel rollers different structures are embossed in order to ensure the subsequent folding of the medium. In this context, a strong mechanical friction and shearing of the fine fibers of the filter medium is generated, in particular on finest fibers, such as nanofiber layers, for example.

(47) FIG. 8 shows the conventional filter medium with a substrate layer (polyester nonwoven) and nanofibers (polyamide) but without hot-melt adhesive fibers covering the nanofiber layer. In FIG. 8, it can be clearly seen that the thus unprotected nanofibers at the surface have been destroyed by the embossment and thus their functionality in the filter medium is already significantly limited or destroyed already during embossment. FIG. 9 shows in comparison the filter medium according to the invention according to FIGS. 2 to 7 with hot-melt adhesive fibers 4 after embossment. The nanofibers 3a of the nanofiber layer 3 are not destroyed and therefore maintain their functionality in the filter medium even after embossment. The fine nanofiber structure 3 underneath the hot-melt adhesive fiber layer 4 is still completely maintained even in the direct rim regions of embossment in FIG. 9. On the other hand, FIG. 8 shows, after identical mechanical loading, a great damage and abrasion of the nanofiber layer in the entire region of the embossment and in particular in the folding edge 10.