Filter Medium for Fluid Filtration, a Method for Manufacturing a Filter Medium and a Fluid Filter

Abstract

A filter medium for fluid filtration, said filter medium having two layers, including at least one coarse filter layer and a fine filter layer which is arranged downstream of the coarse filter layer in the through-flow direction. The coarse filter layer and the fine filter layer are connected to one another without the use of chemical binding agents. The coarse filter layer and the fine filter layer are each a polymer non-woven of thermoplastic polymer fibres. The fibre fineness of the thermoplastic polymer fibres in the fine filter layer is greater than the fibre fineness of the thermoplastic polymer fibres in the coarse filter layer. The thermoplastic fibres of the coarse filter layer as well as the thermoplastic layers of the fine filter layer are melt-blown fibres.

Claims

1. A filter medium for fluid filtration, said filter medium comprising two layers, comprising at least one coarse filter layer and a fine filter layer which is arranged downstream of the coarse filter layer in a through-flow direction, wherein the coarse filter layer and the fine filter layer are connected to one another without the use of chemical binding agents, wherein the coarse filter layer and the fine filter layer are each a polymer non-woven of thermoplastic polymer fibres, wherein the fibre fineness of the thermoplastic polymer fibres in the fine filter layer is greater than the fibre fineness of the thermoplastic polymer fibres in the coarse filter layer, and wherein the thermoplastic fibres of the coarse filter layer as well as the thermoplastic layers of the fine filter layer are melt-blown fibres.

2. A filter medium according to claim 1, wherein the fibre diameter of the melt-blown fibres in the coarse filter layer is in the range of 0.8 μm to 5.0 μm.

3. A filter medium according to claim 1, wherein the fibre diameter of the melt-blown fibres in the fine filter layer is in a range of 100 μm to 500 μm.

4. A filter medium according to claim 1, wherein the melt-blown fibres of the coarse filter layer and/or fine filter layer are polyester fibres.

5. A filter medium according to claim 4, wherein the polyester fibres are polyterephthalate fibres.

6. A filter medium according to claim 1, wherein the fibre diameter distribution of the melt-blown fibres in the coarse filter layer and/or fine filter layer is uniform.

7. A filter medium according to claim 1, wherein the fibre diameter distribution of the melt-blown fibres in the coarse filter layer and/or fine filter layer have a gradient, wherein the fibre diameter continuously reduces in the through-flow direction.

8. A filter medium according to claim 1, wherein a protective layer of non-woven material which is arranged upstream of the coarse filter layer in the through-flow direction and is connected to this without the application of chemical binding agents is provided, wherein the fibres of the non-woven material of the protective layer are thermoplastic polymer fibres.

9. A filter medium according to claim 1, wherein the fine filter layer comprises a plurality of filter plies of melt-blown non-woven which are connected to one another without the use of a chemical binding agent, wherein the average of the geometric pore sizes of the melt-blown non-wovens reduces in the through-flow direction from filter ply to filter ply.

10. A filter medium according to claim 9, wherein the fine filter layer comprises a pre-separation ply of melt-blown non-woven with pores with a pore size of 5 μm to 15 μm.

11. A filter medium according to claim 9, wherein the fine filter layer comprises a main separation ply of a melt-blown non-woven with pores with a pore size of 1 μm to 8 μm.

12. A filter medium according to claim 1, wherein a support layer of non-woven material which is arranged downstream of the fine filter layer in the through-flow direction and is connected to this without the use of chemical binding agent is provided, wherein the fibres of the non-woven material of the support layer are thermoplastic polymer fibres.

13. A filter medium according to claim 12, wherein the support layer comprises a pleating.

14. A method for manufacturing a filter medium according to claim 1, comprising the following steps: arranging the at least one coarse filter layer and the at least one fine filter layer over one another, bringing energy into the loose composite of coarse filter layer and fine filter layer in a manner such that the melt-blown fibres partly melt and the coarse filter layer and fine filter layer are connected to one another, wherein the connecting of the coarse filter layer and the fine filter layer is effected without the application of chemical binding agents.

15. A method according to claim 14, wherein the energy introduction is effected by pressing at an increased temperature and increased pressure.

16. A method according to claim 15, wherein the pressing at an increased temperature and increased pressure is effected by way of thermal calendering with the help of a thermo-calender.

17. A method according to claim 14, wherein the energy introduction is effected by way of ultrasound with the help of an ultrasound calender.

18. A fluid filter for the filtration of a fluid, comprising an onflow opening for raw fluid and a downstream opening for filtered pure fluid, wherein the at least one filter medium according to claim 1, through which fluid to be filtered can flow in a through-flow direction from the onflow opening to the downstream opening, is arranged between the onflow opening and the downstream opening.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0037] A preferred embodiment example of the invention is explained in more detail in the single FIGURE and is hereinafter described in more detail. The FIGURE shows: [0038] a section in the through-flow direction through a preferred embodiment example of the filter medium according to the invention, wherein the filter medium is only shown schematically.

DETAILED DESCRIPTION

[0039] The single FIGURE shows a preferred embodiment example of the filter medium 11 according to the invention. The filter medium 11 which is shown by way of example, in this case consists of five layers or plies. The filter medium can be manufactured in an almost arbitrary manner and can therefore be used as a filter material in a flat surface filter, bag filter, cartridge filter or depth filter for air filtration or as a belt filter, cartridge filter or drum filter for liquid filtration.

[0040] A fluid filter with such a filter medium 11 comprises at least one onflow opening (not represented), via which the raw fluid to be filtered enters into the fluid filter. The fluid can be a gaseous medium such as air or other gases to be filtered or alternatively liquids. The raw fluid to be filtered gets to the raw fluid side 12 of the filter medium 11 and flows through this in a through-flow direction 13 and filtered it exits the filter medium 11 at the pure fluid side 14.

[0041] Herein, the raw fluid to be filtered successively flows through the different function layers of the filter medium 11.

[0042] According to a preferred embodiment example, the raw fluid to be filtered firstly gets into an air-permeable protective layer 15 which is designed as a melt-blown non-woven and which protects the coarse filter layer 16 which lies therein from wear. The filtering effect in the relative thin protective layer is relative low. Expediently, the protective layer in the shown exemplary case consists of melt-blown fibres of polybutylene terephthalate or alternatively polyethylene terephthalate.

[0043] After the passage through the protective layer, the still practically unfiltered raw fluid gets into the coarse filter layer which can also be denoted as a particle and/or dust storage layer. Hereby, it is the case of a voluminous melt-blown ply, thus a melt-blown non-woven. In the described embodiment example, polybutylene terephthalate fibres or alternatively polyethylene terephthalate fibres are used as fibres for the melt-blown non-woven. The fibre diameter of the melt-blown fibres in the coarse filter layer in particular lies in the range of 1.0 μm to 3.0 μm. Since the coarse filter layer is a relatively voluminous melt-blown ply, it lends itself for the fibre fineness of the melt-blown fibres to have a gradient within this layer, wherein the fibre fineness becomes greater in the through-flow direction.

[0044] After the passage of the pre-filtered raw fluid, said raw fluid being freed of coarse particles which are held back in the coarse filter layer, the raw fluid enters into a fine filter layer 17.

[0045] The fine filter layer 17 consist of two plies, of pre-separation ply 17a of a melt-blown non-woven and a main separation ply 17b which is arranged downstream of the pre-separation ply in the through-flow direction 13 and which is likewise of a melt-blown non-woven. Polybutylene terephthalate fibres or alternatively polyethylene terephthalate fibres are applied as melt blown fibres of the pre-separation ply 17a as well as the main separation ply 17b. The fibre structure of the pre-separation ply 17a differs from the fibre structure of the main separation ply 17b. The melt-blown non-woven of the pre-separation ply 17a comprises pores with a pore size of 8 μm to 12 μm. The melt-blown non-woven of the main separation ply 17b in contrast comprises smaller pores, specifically those with a pore size of 3 μm to 6 μm.

[0046] The pore sizes can be determined by the so-called bubble-point test. For this, the porous body to be characterised, in this case the pre-separation ply 17a and the main separation ply 17b is completely wetted with a test fluid whose surface tension is low and known. The sample is subsequently subjected to air at one side and the pressure is increased until the first bubble appears. This pressure is denoted as the bubble-point pressure. The apparently largest pore can be computed whilst taking into account the surface tension and the pressure necessary for opening the first pore, amid the assumption of circular pores, according to the following equation:

d.sub.x=4δ cos φ/Δp

d.sub.x: apparent pore diameter [m]
δ: surface tension [N/m]
cos φ: wetting angle
Δp pressure difference at the filter [Pa]

[0047] The diameter (d.sub.x) denotes a circularly round pore, whose area is equal to that of the real irregularly shaped pore.

[0048] Not only do melt-blown non-woven materials have discrete pore size, but a pore size spectrum. The pore size spectrum can be determined by way of an automated measuring device. For this, the materials are tested in accordance with the technical instruction of the DITF for non-wovens materials “Determining the pore size on the Coulter Porometer. Herein, Coulter Porofil is used as a test fluid. The samples are punched out to a diameter of 25 mm (4.9 cm.sup.2) before the measurement. The measurement range extends from 0.07 μm to 300 μm (theoretical pore size)

[0049] As already mentioned, the fibre unit of the fine filter layer, thus in the pre-separation ply 17a as well as in the main separation ply 17b is larger than the fibre fineness in the coarse filter layer. The fibre diameter of the melt-blown fibres in the fine filter layer lies in the range of 150 nm to 400 nm.

[0050] As is particularly shown in the single FIGURE, a protective layer 18 which in the exemplary case is a spun-bonded non-woven which consists of spun-bonded non-woven fibres is arranged downstream of the fine filter layer 17.

[0051] Of course, it is possible for the filter medium to also be constructed of more than five or less than five function layers. What is necessary are a coarse filter layer and a fine filter layer which is arranged downstream in the through-flow direction. For example, it is also possible for the coarse filter layer to comprise several plies which differ from one another with respect to fibre characteristics (fibre diameter, fibre fineness).

[0052] The manufacture of the filter medium according to the invention is effected by way of the melt-blow method. A characteristic melt-blow facility (not shown) comprises an extruder, in which plastic granulate is melted. In the exemplary case, polybutylene terephthalate granulate or alternatively polyethylene terephthalate granulate is melted here. The melted granulate is continuously fed to a spinnerette via a spin pump, said spinnerette comprising a melt distributor, a melt filter, various temperature and pressure measurement probes as well as at least one melt-blow nozzle. The polymer melt which is extruded from the nozzle, directly after the exit, is subjected to a converging temperature-regulated airflow of the so-called primary air which mixes with the surrounding air, the so-called secondary air, directly after the nozzle exit. The fibres which form here from the melt cool down on the way to deposition and are captured as intertwined fibres in the form of a non-woven. The depositing is mostly effected on an air-permeable structure such as a deposition belt or a screen drum which is additionally provided with a vacuum. This serves for holding the fibres on the deposit surface and leading away excess primary air.

[0053] In the specific exemplary case, it is firstly the fibres for the coarse filter layer which are deposited. Herein, exiting polybutylene terephthalate or alternatively polyethylene terephthalate is deposited in the previously described manner onto a previously manufactured or separately manufactured melt-blown non-woven which forms the protective layer. The loose composite which has arisen here is transported further and is moved to a second working station, at which the melt-blown non-woven of the fine filter layer 17 arises. Herein, it is firstly the polybutylene terephthalate or alternatively polyethylene terephthalate fibres for the pre-separation ply 17a which are applied onto the loose composite of the protective layer and coarse filter layer and subsequently the fibres for the melt-blown non-woven of the main separation ply 17b.

[0054] In the subsequent working step, the carrier non-woven of the support layer 18 is then yet deposited onto the loose composite.

[0055] The now arisen loose composite of the protective layer 15, coarse filter layer 16, fine filter layer 17 with the pre-separation ply 17a and the main separation ply 17b and the support layer 18 are subsequently connected to one another by way of thermal calendering.

[0056] For this, the loose composite is fed to a thermo-calender; herein the loose composite goes through calender rollers, of which at least one is a gravure roller. The distances of the individual connection points are to be selected such that one the one hand they lie sufficiently far apart for the filter-technological characteristics such as fluid permeability and particle storage capacity to remain largely uninfluenced. On the other hand however, the distances of the individual connection points to one another must turn out to be small enough for the downstream melt-blown to be able to expand a little, i.e. the danger of a bursting-open is minimised. For example, it is possible to provide calender gravures with a gravure depth of >1 mm and max. 3 mm. Expediently, the connection surface area (pressing area) does not lie above 25%, in order to ensure the air permeability of the composite. The connection surface area lies in the region of 12% to 18% with respect to the total filter surface.

[0057] A comparison of the technical data of a filter medium according to the invention with the known state of the art is given hereinafter.

[0058] The product according to the invention herein has the following construction:

Onflow Side (Coarse Filter Layer):

[0059] melt-blown non-woven with a weight of 100 g/m.sup.2 on polybutylene terephthalate deposited on a PET carrier ply [0060] the PBT melt-blown has an average fibre titre of approx. 1.8 dtex (decitex) [0061] the PET carrier ply is formed from a thermally calender-solidified carded non-woven from a bi-component staple fibre CoPET jacket and with a PET core. This fibre has a titre of approx. 4.4 dtex (decitex) and a staple length of 51 mm. The non-woven has a surface weight of approx. 20 g/m.sup.2. The solidification area is 100%.

Downstream Side (Fine Filter Layer):

[0062] melt-blown non-woven with a weight of 100 g/m.sup.2 on polybutylene terephthalate deposited on a PET carrier ply [0063] the PBT melt-blown has an average fibre titre of approx 1.0 dtex [0064] the PET carrier ply is formed by a thermally calender-solidified carded non-woven of a bi-component staple fibre CoPET jacket and with a PET core. This fibre has a titre of approx. 4.4 dtex and a staple length of 51 mm. The non-woven has a surface weight of approx. 20 g/m.sup.2. The solidification area is 100%.
Gravure: calender gravure with a pressing surface share of 6% with 6.9 points/cm.sup.2

Comparison Example According to the State of the Art

[0065] Onflow side (coarse filter layer): polybutylene terephthalate (PBT) melt-blown ply with a fibre distribution of 1.9 μm to 5.1 μm.
Downstream side (fine filter layer): bi-component ply based on polyamide (PA) on a PET carrier ply with a fibre distribution of 0.45 μm to 2.4 μm

TABLE-US-00001 TABLE comparison of technical data: material according to state of the the invention art separation efficiency >99.95% >99.95% (ISO 19438: 2003) dust retention capacity g/m.sup.2 140 g/m.sup.2 ca. 110 g/m.sup.2 (ISO 4020 6.4) air permeability at 200 Pa >6 I/m.sup.2/s 57 I/m.sup.2/s (DIN ISO 9237) largest pore 10 μm 9 μm

[0066] It is to be stated that the ply for the downstream side (fine filter layer) from the comparison example from the state of the art is manufactured by way of a so-called segmented-pie process which is more complicated and thus entails greater manufacturing costs in comparison to the described melt-blow method, with which the ply for the downstream side is manufactured.

[0067] Despite this, the material according to the invention in regard to the separation efficiency is on par with the state of the art. The dust retention capacity with the material according to the invention is increased compared to the state of the art.