Glass-free filter media with a dense layer made of synthetic fibers

Abstract

The present invention relates to a multilayer filter medium having a dense layer made of synthetic fibers, as well as its use and production method.

Description

Technical Field

[0001] This invention relates to multilayer filter media having a dense layer made of synthetic fibers, as well as their uses and production methods. Background Technology

[0002] Filter media are used in various systems to remove unwanted substances (i.e., particles) from liquids or gases by passing the liquid through the filter media.

[0003] In many filtration fields, the requirements for the purity of filtered liquids are becoming increasingly stringent. This applies to liquids used in industry, such as lubricating oils, hydraulic oils, or internal combustion engine fuels, as well as liquids used in the food sector and medical or pharmaceutical applications. For example, in the filtration of diesel fuel for internal combustion engines, the ISO 19438:2003 requirement for the separation efficiency of 4μm large particles has been continuously increasing over the past 15 years. For this reason, significant efforts have been made in the past to continuously improve the separation efficiency of the filter materials used, while maintaining their dust holding capacity and thus keeping the filter's service life at least unchanged.

[0004] Filter media containing glass fibers are widely used fuel filter materials. These filter media achieve very high removal efficiency for particles ≥99.5%. However, the abrasive effect of glass fibers (which can be washed out of the filter media) can damage equipment located downstream of the filter, such as the fine nozzles of a fuel injection system.

[0005] In fact, during the processing of filter media, glass fibers may break into smaller fragments under mechanical stress. These small glass particles are also loosely present in the filter media material and can be washed away from the media. Furthermore, loosely bound glass fibers in the media can be washed away by the fuel in the media.

[0006] Due to the abrasive properties of glass fibers / particles, this so-called glass fiber shedding can damage the working parts behind the filter element. This is why the use of glass fibers in high-efficiency fuel media always presents a potential risk in applications.

[0007] EP 1133342 B1 and US 7,137,510 B1 disclose multilayer filter media comprising meltblown nonwoven fabric as the main filter layer, wherein the meltblown nonwoven fabric is made of PP (polypropylene) or PES (polyethersulfone).

[0008] US 9,149,748 B2 discloses a filter medium comprising a first layer, a second layer, and a third layer, wherein the second layer is located between the first and third layers and comprises a large number of fibers formed by a melt-blown process, and wherein the air permeability and / or average flow pore size of the first and third layers are greater than that of the second layer.

[0009] DE 102012010307 A1 discloses a multilayer filter material comprising, in the flow direction, a first layer containing a wet-laid nonwoven fabric, a second layer containing a wet-laid nonwoven fabric made of cellulose or synthetic fibers or mixtures thereof, and a third layer containing a calendered meltblown nonwoven fabric. Using this filter material, an efficiency of 99.3% is achieved according to ISO 19348.

[0010] It is still necessary to provide fiber-free filter media that still have very high removal efficiency for particles with a diameter ≥4μm. Summary of the Invention

[0011] Therefore, the object of the present invention is to provide a filter medium with high separation efficiency (i.e., ≥99.3% for 4μm particles) that does not use glass fibers.

[0012] This objective is achieved through a filter medium, which includes:

[0013] a) First layer,

[0014] b) The second layer, and

[0015] c) The third layer can be chosen arbitrarily.

[0016] Specifically, this objective is achieved through a filter medium, which includes:

[0017] a) First layer,

[0018] b) A porous second layer with a diameter of 4-13 μm, and

[0019] c) The third layer can be chosen arbitrarily.

[0020] In the context of this invention, the diameter of a "pore" is the diameter of pores uniformly distributed within the layer. This characteristic can be determined according to the method defined below.

[0021] Preferably, the filter medium includes a third layer. More preferably, the second layer is located between the first and third layers.

[0022] The first layer can be any layer selected from the group consisting of wet-laid nonwoven fabric, dry-laid nonwoven fabric, or synthetic mesh.

[0023] Within the meaning of this invention, wet-laid nonwoven fabric refers to any nonwoven fabric that can be produced using wet-laid processes known to those skilled in the art for manufacturing filter media.

[0024] The first layer of wet-laid nonwoven fabric comprises natural fibers, synthetic fibers, or mixtures thereof. Examples of natural fibers include cellulose, cotton, wool, hemp, regenerated cellulose, and fibrillated cellulose. Preferably, the first layer comprises at least 70% natural fibers.

[0025] The average fiber diameter of natural fibers can be 10-50μm, preferably 15-40μm, or even more preferably 20-35μm.

[0026] Synthetic fibers include polyester fibers, polypropylene fibers, multicomponent fibers with different melting points for individual components, polyamide fibers, and acrylic fibers.

[0027] Examples of polyester fibers are polybutylene terephthalate (PBT) fibers, polyethylene terephthalate (PET) fibers, and polylactic acid (PLA) fibers. Preferred examples of multicomponent fibers are PET / CoPET bicomponent fibers with a core-sheath structure.

[0028] The average fiber diameter of synthetic fibers is typically 3-30 μm, preferably 5-15 μm, and the cutting length is typically 3-60 mm, preferably 4-12 mm.

[0029] The first layer may be composed of 100% natural fibers or 100% synthetic fibers. Preferably, the first layer is composed of 100% natural fibers.

[0030] Dry-laid nonwovens include, for example, spunlaid nonwovens, which can be produced according to any manufacturing method.

[0031] Suitable polymers for spun web nonwovens are, for example, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyolefins such as polypropylene and polyurethane, or mixtures thereof. In many applications, spun web nonwovens comprising bicomponent fibers may be particularly advantageous. Preferred examples of multicomponent fibers are PET / CoPET bicomponent fibers with a core-sheath structure. Typical average fiber diameters for spun web nonwovens are 5-30 μm, preferably 10-20 μm, and even more preferably 12-17 μm.

[0032] For liquid applications, such as fuel filtration, it may be particularly suitable for the first layer to consist of at least 70% natural fibers, based on the total weight of the fibers in the first layer.

[0033] When the first layer comprises at least 70% natural fibers, it is preferably impregnated with an adhesive resin. Any known resin adhesive composition can be used.

[0034] The thickness of the first layer can be selected as needed. Preferably, the first layer may have a thickness greater than or equal to 0.15 mm, more preferably greater than or equal to 0.20 mm, or most preferably greater than or equal to 0.40 mm. The first layer may have a thickness less than or equal to 2.00 mm, more preferably less than or equal to 1.60 mm, or most preferably less than or equal to 1.20 mm. Combinations of the above ranges are also possible, preferably greater than or equal to 0.15 mm and less than or equal to about 1.00 mm. The thickness can be determined according to standard ISO 534:2012-02 using a test plate pressure of 0.1 bar.

[0035] Preferably, the porosity of the first filter layer is 60-90%, more preferably 70-80%.

[0036] The first layer can also be a grid made of thermoplastic polymer or a printed polymer pattern. The polymer for the printed polymer pattern is preferably a hot melt adhesive. The base material of the polymer or hot melt adhesive for the printed polymer pattern can be selected from the group consisting of: ethylene-vinyl acetate (EVA) copolymers; polyolefins (PO), such as polyethylene (typically low-density polyethylene (LDPE), but also high-density polyethylene (HDPE), which has a higher melting point and better temperature resistance), polypropylene (PP), atactic polypropylene (APP), polybutene-1, oxidized polyethylene, etc.; polyamides (PA) and copolyamides (CoPA); polyesters (PES), copolyesters (CoPES), such as polyethylene terephthalate (PET), PET copolymers (CoPET), polybutylene terephthalate (PBT) and PBT copolymers (CoPBt); thermoplastic polyurethane (TPU); styrene block copolymers (SBS); and mixtures thereof. When a printed polymer pattern is selected as the first layer, the polymer pattern is printed directly onto the second layer. Patent application EP 19166533 describes the advantages and production methods of printed polymer patterns.

[0037] The second layer comprises a porous nonwoven fabric layer with a diameter of 4-13 μm, preferably 5-11 μm.

[0038] Preferably, the maximum pore size (diameter) of the second layer is 5-17 μm, more preferably 6-16 μm.

[0039] High initial efficiency can be achieved when the second layer has porosity within the range described above.

[0040] The second layer can be any layer selected from the group consisting of spunbond nonwoven fabric, meltblown nonwoven fabric, and combinations of spunbond nonwoven fabric and meltblown nonwoven fabric, provided that the diameter of the pores in the second layer is within the range described above.

[0041] Suitable polymers for the second layer are, for example, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyolefins such as polypropylene and polyurethane, or mixtures thereof. In many applications, the use of bicomponent fibers may be particularly advantageous. An example of a preferred multicomponent fiber is a PET / CoPET bicomponent fiber with a core-sheath structure.

[0042] The second layer is preferably a meltblown layer. More preferably, the meltblown layer comprises polyester fibers. The second layer may include both a meltblown layer and a spunbond layer. In this case, the meltblown layer and the spunbond layer constituting the second layer are densified together to obtain a second layer with a porous diameter as defined above.

[0043] Preferably, the second layer is a dense layer, and more preferably, a dense meltblown layer. The densification step ensures the desired diameter of the pores and the uniformity of the layer, which in turn leads to excellent performance.

[0044] The second layer can be produced using any known method for producing spunbond or meltblown products.

[0045] Preferably, the average fiber diameter (d1) of the fibers in the second layer (before calendering / densification) is 0.01 to 3 μm, more preferably 0.25 to 2.5 μm, and most preferably 0.5 to 2 μm.

[0046] Preferably, the average diameter (d1) of the fibers in the second layer (before densification, i.e., before calendering by a flatbed calender) is ≤1.8 μm, more preferably 0.6 μm ≤ d1 ≤ 1.8 μm, and particularly preferably 0.60 μm ≤ d1 ≤ 1.75 μm. In this layer, at least 20%, preferably 30%, of the fibers have a diameter (d) ≤1 μm, preferably 0.6 μm ≤ d ≤ 1 μm, and particularly preferably 0.60 ≤ d ≤ 0.95 μm. Preferably, at least 25%, particularly preferably at least 30%, of the fibers have a diameter of 0.60 ≤ d ≤ 0.90 μm. The proportion of fibers with a diameter of 0.6 ≤ d ≤ 0.85 μm is at least 25%, preferably at least 30%.

[0047] In this invention, a distinction is made between “average fiber diameter” (d1) and “diameter” (d). This difference is important because the average fiber diameter does not provide information about the number of fine fibers with a diameter (d) ≤ 1 μm.

[0048] When the second layer comprises a spunbond layer and a meltblown layer, it is important that at least one layer (i.e., only a spunbond layer, only a meltblown layer, or both) has a fiber diameter within the aforementioned range before calendering. For example, when the meltblown layer has a fiber diameter within the aforementioned range, the additional spunbond layer of the second layer may have: a thickness of 0.09 to 0.8 mm; and a fiber diameter of 10-40 g / m². 2 Basis weight and 30-3500 l / m 2 The breathability of s.

[0049] The second layer is densified by calendering with a flatbed burnishing machine. The thickness of the calendered second layer can be selected as needed. Preferably, the second layer may have a thickness greater than or equal to 0.09 mm, more preferably greater than or equal to 0.10 mm, or most preferably greater than or equal to 0.15 mm. The second layer may have a thickness less than or equal to 1.00 mm, more preferably less than or equal to 0.70 mm, or most preferably less than or equal to 0.50 mm. Combinations of the above ranges are also possible, preferably greater than or equal to 0.10 mm and less than or equal to about 0.50 mm. The thickness can be determined according to standard ISO 534:2012-02 using a plate pressing of 0.1 bar.

[0050] The total thickness of the filter media is preferably greater than or equal to 0.20 mm, more preferably greater than or equal to 0.30 mm, even more preferably greater than or equal to 0.50 mm, and most preferably greater than or equal to 0.80 mm. The total thickness of the filter media is preferably less than or equal to 2.00 mm, more preferably less than or equal to 1.5 mm, even more preferably less than or equal to 1.20 mm, and even more preferably less than or equal to 1.00 mm. Combinations of the above ranges are also possible; for example, a thickness greater than or equal to 0.50 mm and less than or equal to about 1.00 mm is preferred. The thickness can be determined according to standard ISO 534:2012-02 using a plate pressure of 0.1 bar.

[0051] Using meltblown nonwoven fabric as the second layer of the filter medium is highly advantageous because meltblown technology allows for the commercial production of nonwoven fabrics comprising very fine fibers with very small diameters, as described above. The combination of meltblown and nonwoven fiber webs containing these fine fibers results in an initial filtration efficiency of ≥99.3% according to ISO 19438:2003.

[0052] To achieve high separation through overall arrangement even in the initial stage of using the filter media, it is advantageous to use a layer comprising cellulose as the first layer (outflow side layer). This material exhibits high separation of particles to be filtered out, even in the initial stage, but its storage capacity is lower than that of meltblown nonwoven fabric.

[0053] Advantageously, in the filter layer according to the invention, foldability, support for other (synthetic) layers, and very fine filtration are integrated into the cellulose layer as a first layer. Preferably, the first layer is located on the outflow side.

[0054] Polyester fibers, such as PBT fibers, are preferred for the second layer because they exhibit good heat resistance, making them highly suitable for processes involving calendering. Due to this good heat resistance, temperature conditions during calendering can be adjusted as needed, resulting in a filter medium with the desired uniform distribution and pore size uniformity (i.e., porosity). Furthermore, using fibers with good heat resistance avoids the problem of small fibers completely melting during the calendering step, which would lead to an undesirable foil-like property in the second layer.

[0055] Because the filter medium of the present invention does not contain glass fibers, damage to the equipment located after the filter is avoided due to the abrasive effect of glass fibers, which can be washed out from the filter medium.

[0056] The filter media may include a third layer, which may be selected from the group consisting of a spunbond layer and a meltblown layer. Preferably, the third layer is a meltblown layer. Preferably, the third layer comprises polyester fibers, such as PBT, PET, or PET / CoPET bicomponent fibers.

[0057] More preferably, the polyester fibers included in the second and third layers are polybutylene terephthalate (PBT) fibers.

[0058] The average fiber diameter of the third layer fibers (e.g., polyester fibers) is 0.01 to 10 μm, more preferably 0.5 to 7 μm, and most preferably 1 to 5 μm.

[0059] The thickness of the third layer can be selected as needed. Preferably, the third layer may have a thickness greater than or equal to 0.09 mm, more preferably greater than or equal to 0.10 mm, or most preferably greater than or equal to 0.15 mm. The third layer may have a thickness less than or equal to 1.00 mm, more preferably less than or equal to 0.80 mm, or most preferably less than or equal to 0.50 mm. Combinations of the above ranges are also possible, for example, preferably greater than or equal to 0.15 mm and less than or equal to about 0.50 mm. The thickness can be determined according to standard ISO 534:2012-02 using a test plate pressure of 0.1 bar.

[0060] Preferably, the second layer is a dense meltblown nonwoven fabric, wherein densification is preferably achieved by calendering. In the context of this invention, the densified meltblown nonwoven fabric is produced using flat rollers via calendering, such that the entire surface of the meltblown nonwoven fabric, i.e., all the fibers on the surface, is partially melted to obtain the desired diameter of the pores. This calendering step must be distinguished from the calendering step used to join two or more layers, where the calendering roller has a specific design (or pattern), typically in the form of dots, protruding from the surface of the roller, and bonding is achieved by initiating the melting of the polymer fibers only in the protruding areas of the roller through heating. This calendering step used to join two or more layers does not significantly affect the diameter of the pores in the filter layer. Conversely, in the calendering step of producing dense meltblown nonwoven fabric using flat rollers, the meltblown nonwoven fabric is compressed, resulting in a specific pore size (i.e., the diameter of the pores). In particular, the pore size distribution of the layer becomes uniform. Preferably, the second layer consists solely of this dense meltblown nonwoven fabric. Preferably, the second layer consists of a co-densified meltblown layer and a spunbond layer. More preferably, the second layer consists of PBT (polybutylene terephthalate) fibers. Preferably, based on the total weight of the fibers in the second layer, the second layer comprises at least 50% by weight, more preferably at least 60% by weight, more preferably at least 70% by weight, more preferably at least 80% by weight, more preferably at least 90% by weight, and most preferably at least 95% by weight of PBT fibers. The second layer can be densified (i.e., calendered) between two hot calendering rollers at 40°C-180°C using a linear pressure of 5 N / mm-450 N / mm. As a result, the separation efficiency of the filter material according to the invention is significantly increased.

[0061] The individual layers of the filter media can be produced separately and then combined; or each layer can be formed directly on the surface of the underlying layer; or both methods can be combined. The combination of individual layers can be achieved by stacking and optionally by bonding, sintering, or calendering. As mentioned above, if a calendering step is performed to achieve bonding of the different layers, this will not include the use of a flatbed calender.

[0062] Preferably, the first layer and the second layer are bonded together by adhesive.

[0063] Preferably, the first and second layers, which are pre-connected together, are bonded to the third layer by adhesive.

[0064] Preferably, the base weight increases from the second layer to the first layer and optionally from the third layer to the first layer.

[0065] The preferred base weight for the first layer is 100-350 g / m³. 2 More preferably 125-300g / m 2 More preferably 175-250g / m 2 .

[0066] The preferred base weight for the second layer is 10-200 g / m³. 2 More preferably 25-150g / m 2 More preferably 50-100g / m 2 .

[0067] The preferred base weight of the third layer is 10-175 g / m³. 2 More preferably 15-150g / m 2 More preferably 20-90g / m 2 .

[0068] The preferred total basis weight of the filter media is 150-700 g / m³. 2 More preferably 200-500g / m 2 More preferably 250-450g / m 2 The optimal value is 300-400g / m³. 2 .

[0069] Preferably, the basis weight increases from the second layer of the filter medium used to the first layer and optionally from the third layer to the first layer.

[0070] Preferably, breathability increases from the first layer to the second layer and optionally from the second layer to the third layer.

[0071] Preferably, the air permeability decreases from the third layer to the first layer.

[0072] The permeability of the first layer can be lower than that of any other layer in the filter medium.

[0073] The first layer is preferably greater than or equal to 1 L / m 2 s, greater than or equal to 2L / m 2 s, or greater than or equal to 3L / m 2 The breathability of s.

[0074] Preferably, the first layer may have a concentration of less than or equal to 20 L / m³. 2 s, less than or equal to 16 L / m 2 s, less than or equal to 12L / m 2 The breathability of s. Combinations of the above ranges are also possible. For example, breathability may preferably be greater than or equal to 1 L / m. 2 s and less than or equal to 20 L / m 2 s. Air permeability can be determined according to standard EN / ISO 9237 (1995) (where the area measured at a pressure difference of 2 mbar is 20 cm²). 2 ).

[0075] Preferably, the second layer can have a concentration greater than or equal to 5 L / m 2 s, greater than or equal to 10 L / m2 s, greater than or equal to 15 L / m 2 The second layer has a breathability of s. Preferably, the second layer can have a breathability of less than or equal to 70 L / m. 2 s, less than or equal to 60 L / m 2 s, less than or equal to 40 L / m 2 The breathability of s. Combinations of the above ranges are also possible. For example, breathability may preferably be greater than or equal to 5 L / m. 2 s and less than or equal to 70 L / m 2 s, more preferably greater than or equal to 10 L / m 2 s and less than or equal to 60 L / m 2 s, the optimal value is greater than or equal to 15 L / m 2 s and less than or equal to 40 L / m 2 s. Air permeability can be determined according to standard EN / ISO 9237 (1995) (where the area measured at a pressure difference of 2 mbar is 20 cm²). 2 ).

[0076] Preferably, the third layer can have a concentration greater than or equal to 75 L / m³. 2 s, greater than or equal to 100 L / m 2 s, greater than or equal to 125

[0077] L / m 2 The third layer has a breathability of s. Preferably, the third layer can have a breathability of less than or equal to 400 L / m. 2 s, less than or equal to 300 L / m 2 s, less than or equal to 200 L / m 2 The breathability of s. Combinations of the above ranges are also possible. For example, breathability may preferably be greater than or equal to 75 L / m. 2 s and less than or equal to 250 L / m 2 s. Air permeability can be determined according to standard EN / ISO 9237 (1995) (where the area measured is 20 cm² under a pressure difference of 2 mbar). 2 ).

[0078] The overall air permeability of the filter media is preferably between 0.5 and 20 L / m³. 2 Within the range of s, more preferably 0.5 to 15 L / m 2 s, optimal value is 1 to 10 L / m 2 s.

[0079] Furthermore, the present invention relates to its use as a filter medium for liquid filtration, comprising a) a first layer, b) a second layer, and c) an optional third layer, wherein during filtration, the flow direction of the liquid is from the second layer to the first layer, and optionally from the third layer to the first layer.

[0080] Preferably, the filter medium of the present invention is used for liquid filtration.

[0081] According to ISO 19438:2003, the initial efficiency of the second layer for particles ≥4.0 μm is at least 99.3%, preferably 99.5% for particles ≥4 μm in diameter (see Methods below).

[0082] According to ISO 19438:2003, the initial efficiency of the total filter media for particles ≥4.0 μm is even more preferably at least 99.7%.

[0083] Methods for producing filter media

[0084] The filter medium of the present invention can be produced using any technology known in the art. For example, the filter medium of the present invention can be prepared by a method comprising the following steps:

[0085] a) Provides a first layer, a second layer, and an optional third layer.

[0086] b) Attach the second layer to the first layer by burnishing or gluing, and

[0087] c) Optionally, the third layer is attached to the free surface of the second layer by burnishing or gluing.

[0088] Preferably, step a) includes densifying the second layer by burnishing. More preferably, step a) includes densifying the second layer by burnishing using a flat burnishing roller.

[0089] When the first layer is a printed polymer pattern, a second layer is first provided and densified. The first layer is then printed directly onto the densified second layer. Subsequently, if a third layer is present, it is bonded to the other side of the second layer.

[0090] Filter

[0091] The filter medium of the present invention may be included in a filter element. Preferably, the filter element includes at least one filter medium as described above and an optional additional layer.

[0092] The filter media in the appended claims can be used in many applications. Filters made from the media of the present invention are particularly suitable for liquid filtration, such as fuel filtration (e.g., gasoline or diesel), oil filtration (e.g., lubricating oil and hydraulic oil), and water.

[0093] Preferred implementation scheme:

[0094] 1. A filter medium comprising (or consisting of): a) a first layer, b) a second layer having pores with a diameter of 4-13 μm, and c) an optional third layer.

[0095] 2. The filter medium according to claim 1, wherein the second layer comprises a dry-laid nonwoven fabric.

[0096] 3. The filter medium according to any one of 1 to 2, wherein the second layer is selected from the group consisting of a spunbond layer, a meltblown layer, and a combination of a spunbond layer and a meltblown layer.

[0097] 4. The filter medium according to any one of 1 to 3, wherein the second layer comprises a meltblown layer.

[0098] 5. The filter medium according to any one of 1 to 4, wherein the first layer comprises cellulose.

[0099] 6. The filter medium according to any one of 1 to 5, wherein the filter medium comprises a third layer.

[0100] 7. The filter medium according to any one of 1 to 6, wherein the second layer comprises a spunbond layer and a meltblown layer.

[0101] 8. The filter medium according to any one of 1 to 7, wherein the second layer consists of a spunbond layer and a meltblown layer.

[0102] 8. The filter medium according to any one of 1 to 7, wherein the second layer is densified.

[0103] 9. The filter medium according to any one of 1 to 8, wherein the second layer comprises or is composed of polyester fibers.

[0104] 10. The filter medium according to any one of 1 to 9, wherein air permeability increases from the first layer to the second layer and optionally from the second layer to the third layer.

[0105] 11. The filter medium according to any one of 1 to 10, wherein the basis weight increases from the second layer to the first layer and optionally from the third layer to the first layer.

[0106] 12. The filter medium according to any one of 1 to 4 and 6 to 11, wherein the first layer is a grid or printed polymer pattern.

[0107] 13. Use of the filter medium according to any one of 1 to 12 for filtering liquids.

[0108] 14. The use according to 13, wherein during filtration, the direction of liquid flow is from the second layer to the first layer, and optionally from the third layer to the first layer.

[0109] 15. The use according to any one of 13 to 14, wherein the liquid is selected from the group consisting of fuel, oil and water.

[0110] 16. A method for producing a filter medium according to any one of 1 to 12, comprising the following steps:

[0111] a) Provide a first layer, a second layer, and optionally a third layer.

[0112] b) Densify the second layer.

[0113] c) Connect the first layer, the second layer, and optionally connect the third layer.

[0114] 17. A method for producing a filter medium according to any one of 1 to 12, comprising the following steps:

[0115] a) Provide a second and third layer;

[0116] b) Densify the second layer;

[0117] c) Print the polymer pattern on the second layer (i.e., the first layer);

[0118] d) Connect the second layer and the third layer in step c).

[0119] definition

[0120] In this document, the term "filter element" refers to any device that can be used in a filtration process, which is a mechanical or physical process for separating one substance from another (e.g., solids, liquids, and gases) by means of an inserted filter medium.

[0121] In this article, the term "filter media" refers to the material used in filters to separate particles from their suspension in air or liquid.

[0122] In this article, the term "inflow side" refers to one side of the filter medium through which the material to be filtered enters the filter medium.

[0123] In this article, the term "outflow side" refers to one side of the filter medium through which the material to be filtered exits the filter medium.

[0124] In this paper, the term "flow direction" refers to the direction in which the material to be filtered flows through the filter medium, that is, the flow direction is from the inflow side to the outflow side of the filter medium.

[0125] In this article, the term "layer" refers to a thin sheet of any material used for filter media.

[0126] In this document, the term "surface" refers to any interface between the filter media layer and its surrounding environment or any interface between the filter media and its surrounding environment.

[0127] In this document, the term "liquid" refers to fuels, such as fuels used in internal combustion engines, such as gasoline or diesel; oils, such as lubricating oil and hydraulic oil; or water.

[0128] In this document, the term "meltblown nonwoven fabric" refers to all nonwoven fabrics that can be produced using meltblown processes known to those skilled in the art for manufacturing filter media, wherein the meltblown process is a process in which molten polymer is extruded into a high-speed hot gas stream, thereby transforming the molten polymer into fibers.

[0129] In this document, the term "cellulose" refers to any material made from plants that produce fibrous products based on cellulose molecular polymers as well as regenerated cellulose. Cotton plants produce individual cellulose fibers, while wood pulp is made by mechanically and / or chemically separating wood fibers. Other sources of cellulose are fibers such as flax, Manila hemp, ramie, and jute. Regenerated cellulose (rayon) is made by dissolving wood pulp in a solution and extruding that solution through a spinneret into a chemical bath that regenerates the fibers.

[0130] Test methods

[0131] Fiber diameter Measure as follows:

[0132] Apparatus: Scanning electron microscope (SEM) "Phenom Fei" and related software Fibermetric V2.

[0133] Sampling: Five different regions of the filter media will be analyzed across the width of the paper.

[0134] Sample sputtering: Optical images are randomly recorded, and these areas are scanned at 1000x magnification.

[0135] The fiber diameter is determined by the "one-click" method, which requires recording each fiber once; the measurement point is detected at the fiber intersection, so it does not mean that the fiber diameter was manually removed.

[0136] Using data obtained from Fibermetric using Excel, the average fiber diameter and the percentage of fibers with a specific fiber diameter are evaluated.

[0137] Therefore, the average fiber diameter of each sample is recorded at at least 5 points, and these 5 averages are combined into a single average. This value is called the average fiber diameter of the sample.

[0138] A total of at least 500 fibers must be evaluated.

[0139] The percentage of fibers with a specific diameter was also recorded.

[0140] First, second and third layers Layer thicknessand total filter media thickness Measured using a plate pressure of 0.1 bar according to DIN EN ISO 534 2012-02.

[0141] breathability According to DIN EN ISO 9237 (1995), the pressure difference at 200 Pa and 20 cm 2 At the sample size, using a 20cm... 2 Measurements were taken using a Textest FX3300 instrument with a test head.

[0142] Basis weight Measured according to DIN EN ISO 536 (2012-11).

[0143] efficiency According to ISO 19438 (2003), at 200cm 2 Initial separation and dust storage capacity were measured using A3 medium test dust (ISO 12103-1, PTI Powder Technology) on a plate with a sample area, an upstream concentration of 100 mg / L, and a flow rate of 0.71 L / min. The test ended when the pressure differential increased by 0.7 bar.

[0144] Maximum pore diameter and pore size Measured in accordance with DIN ISO 4003:1990.

[0145] The pore size is measured according to DIN ISO 4003:1990. Place the sample between the fitting of the airtight clamp and the pressure gauge (U-tube with a millimeter indicator), with the clamp positioned above the small orifice equipped with the air source. Test each sample with the top facing upwards. Pour denatured ethanol (100% ethanol containing 1% MEK (methyl ethyl ketone) denaturant) onto the edge of the upper sample holder (do not spray directly onto the sample / approximately 4 mm deep) to obtain a slight excess of air pressure on the liquid. Slowly increase the air pressure (approximately 5 mm water column / s) until the first bubble is seen. The necessary air pressure level will be read from the pressure gauge (millimeter water column gauge), and the diameter of the maximum pore size (“maximum pore size”, “maximum pore diameter”) can be calculated using the surface tension of ethanol (@23°C).

[0146] Then further increase the air pressure until the air covers the entire surface (10cm). 2 The air pressure is then read again, and the relative pore size is calculated, i.e., the diameter of the "pore", "pore size", "pore diameter", and "pore diameter".

[0147] The "maximum aperture" and the diameter of the "multiple pores" can be calculated as described above using the following formula:

[0148]

[0149] d = aperture [μm]

[0150] p = air pressure [mN / m] 2 ]

[0151] σ = Surface tension of the test liquid (e.g., ethanol)

[0152] [At 23℃, the σ of ethanol is 21.330225 mN / m]

[0153] α = Contact angle of the area where the liquid and sample meet

[0154] (Conversion: 1 mm water column = 98.07 mN / m) 2 )

[0155] The following formula is used to calculate the density of the filter media from its actual density and the average density of the fibers used. Porosity :

[0156] Porosity = (1 – density of filter medium [g / cm³]) 3 ] / Fiber density [g / cm 3 100% Example

[0157] General Embodiment 1

[0158] Exemplary embodiments of a three-layer arrangement are disclosed in Table 1. The first layer is a cellulose-impregnated base layer, followed by a dense meltblown layer based on PBT (polybutylene terephthalate). The densification step is performed using a flatbed calender. The third layer is a PBT-based meltblown layer.

[0159] Table 1

[0160]

[0161] Flow direction: Third layer (inflow side) – Second layer – First layer (outflow side)

[0162] Example 2

[0163] Compared to Example 1, the second layer includes the densified meltblown layer of Example 1 and an additional spunbond layer. The spunbond layer of the second layer comprises PBT fibers with a fiber diameter of 15 μm and a basis weight of 20 g / m³. 2 The thickness is 0.09 mm. The second layer, the meltblown layer and the spunbond layer, are densified together using a flatbed calender.

[0164] Flow direction: Third layer (inflow side) – Second layer – First layer (outflow side)

[0165] Comparative Examples 1 and 2

[0166] First layer: Cellulose-impregnated base layer, wet-laid web formation

[0167] The second layer: polyester meltblown fiber, densified through calendering.

[0168] Third layer: Meltblown layer

[0169] Flow direction: Third layer (inflow side) – Second layer – First layer (outflow side)

[0170] Table 2

[0171]

[0172] Examples 1, 2, Comparative Example 1, and Comparative Example 2 all include polyester meltblown fibers in the second layer.

[0173] As can be seen from Table 2, the filter media according to the present invention exhibits very good efficiency values, even though it does not contain glass fibers.

Claims

1. Filter medium comprising: a) a first layer, b) a second layer having pores with a diameter of 4-13 pm, and c) a third layer; wherein the second layer comprises a dry-laid nonwoven and is a densified layer; wherein the air permeability increases from the first layer to the second layer and from the second layer to the third layer.

2. Filter medium according to claim 1, wherein the second layer is selected from one of a spunbond layer, a meltblown layer and a combination of a spunbond layer and a meltblown layer.

3. Filter medium according to claim 1, wherein the first layer comprises cellulose.

4. Filter medium according to any one of claims 1 to 3, wherein the second layer comprises polyester fibers.

5. Filter medium according to any one of claims 1 to 3, wherein the second layer comprises a densified meltblown layer.

6. Filter medium according to any one of claims 1 to 3, wherein the basis weight increases from the second layer to the first layer and optionally from the third layer to the first layer.

7. Use of a filter medium according to any one of claims 1 to 6, wherein during filtration the flow direction of the liquid is from the second layer to the first layer and from the third layer to the first layer.

8. Use of a filter medium according to claim 7 for liquid filtration.

9. Method for producing a filter medium according to any one of claims 1 to 6, comprising the steps of: a) providing a first layer, a second layer and providing a third layer, b) densifying the second layer, c) connecting the first layer, the second layer and connecting the third layer.

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