Filtration media and methods of making same

Abstract

The invention relates to a filter medium comprising an antibacterial compound, to a method for producing the filter medium, to a filter element, to a filter system, and to the use of the filter medium for water filtration in a combustion chamber of an internal combustion engine.

Description

Technical Field

[0001] The present invention relates to a filter medium containing an antimicrobial compound, a method for preparing the filter medium, a filter element, a filter system, and the use of the filter medium for filtering water in a combustion chamber of an internal combustion engine. Background Art

[0002] In the development of new engine generations, increasing attention is being paid to reducing polluting exhaust gas emissions such as nitrogen oxides (NOx). One possible technical solution to reduce NOx in the exhaust gas is to spray water into the gas / air mixture in the engine combustion chamber. Spraying water into the combustion chamber does reduce the exhaust gas temperature and reduces pre-ignition. However, the use of water also brings some problems related to impurities in the water. These impurities can cause damage to components in the cylinder and, in addition, can promote the growth of microbial populations such as bacteria, algae, fungi or other microorganisms.

[0003] In patent application DE102017006462A1 (hereinafter referred to as DE'462), a filter medium is proposed, which includes a mesh as a support layer and a meltblown layer as a filter layer, wherein the mesh and the meltblown layer are impregnated or coated with an antibacterial material. However, this medium has some disadvantages. First, the presence of the mesh leads to an increase in the cost of the medium. In addition, the meltblown layer needs to have a higher weight and thickness, which not only leads to higher costs, but also reduces the number of pleats of the filter. It is well known that the number of pleats affects the filter area, which in turn affects the service life, dust holding capacity and pressure difference of the filter medium.

[0004] Therefore, there is still a need for a filter medium that excels in filtration efficiency, dust holding capacity, strength, service life, and antimicrobial activity for filtering water to be injected into a combustion chamber. In addition, there is still a need for a filter medium for filtering water in a combustion chamber of an internal combustion engine that is less expensive than existing filter media. Summary of the invention

[0005] One object of the present invention is to provide a filter medium which is excellent in filtration efficiency, dust holding capacity, strength, pressure difference and service life and has antibacterial activity. Another object of the present invention is to provide a filter medium for filtering water in a combustion chamber of an internal combustion engine, which filter medium is less expensive than existing filter media.

[0006] The filter medium of the present invention is particularly suitable for filtering water in the combustion chamber of an internal combustion engine.

[0007] The filter medium of the present invention comprises:

[0008] i) a first meltblown layer, and

[0009] ii) a second spunbond layer,

[0010] At least one of the first layer and the second layer contains at least an antimicrobial compound.

[0011] The first meltblown layer can be manufactured according to known manufacturing methods. Suitable polymers for the first meltblown layer include, for example, polyolefins (such as polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate) and polyamides. Preferably, the meltblown layer includes polybutylene terephthalate (PBT). Additives such as crystallization accelerators and dyes can also be mixed into the polymer.

[0012] The average fiber diameter of the first meltblown layer is 0.5-10 μm, preferably 0.5-5 μm, more preferably 0.5-2 μm, and particularly preferably fibers with an average fiber diameter of 0.8-1.4 μm.

[0013] The basis weight of the first meltblown layer is 30-95 g / m 2 , preferably 40-90g / m 2 , more preferably 45-80g / m 2 .

[0014] The thickness of the first meltblown layer is 0.05-0.80 mm, preferably 0.1-0.6 mm, more preferably 0.2-0.5 mm (according to DIN EN ISO 534:2012; 0.1 bar pressure).

[0015] Additional meltblown layers may also be present in the filter media. These additional meltblown layers may be the same as the first meltblown layer, or may have different properties in terms of polymer composition, thickness, fiber diameter, and basis weight.

[0016] The second spunbond layer can be manufactured according to known manufacturing methods. Suitable polymers include polyolefins (such as polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyamides or mixtures thereof. Preferred polymers are polyesters, such as polybutylene terephthalate (PBT) and polyethylene terephthalate (PET).

[0017] Preferably, the second spunbond layer comprises bicomponent fibers.An example of a preferred multicomponent fiber is a PET / CoPET bicomponent fiber having a core-sheath structure.

[0018] The average fiber diameter of the second spunbond layer is 5-40 μm, preferably 10-30 μm, and more preferably 15-20 μm.

[0019] The basis weight of the second spunbond layer is 40-130 g / m 2 , preferably 50-110g / m 2, more preferably 60-90g / m 2 .

[0020] The thickness of the second spunbond layer (according to DIN EN ISO 534:2012; 0.1 bar pressure) is 0.09-0.70 mm, preferably 0.10-0.50 mm, more preferably 0.18-0.40 mm.

[0021] The filter medium of the present invention may further include a third spunbond layer, wherein the polymer type and average fiber diameter used in the third spunbond layer are the same as those described above for the second spunbond layer.

[0022] The basis weight of the third spunbond layer is 5-40 g / m 2 , preferably 10-30g / m 2 , more preferably 15-25g / m 2 .

[0023] The thickness of the third spunbond layer (according to DIN EN ISO 534:2012, 0.1 bar pressure) may be 0.08-0.40 mm, preferably 0.09-0.30 mm, more preferably 0.10-0.20 mm.

[0024] When the third spunbond layer is present, it is placed on the side of the meltblown layer opposite to the second spunbond layer. The third spunbond layer will serve as a protective layer for the meltblown layer.

[0025] When the filter medium is used in a filter element, it is installed in such a way that the flow direction of the fluid to be passed through the filter medium is through the first meltblown layer or the third spunbond layer (if present), and the outflow side is the second spunbond layer.

[0026] At least one layer of the filter medium contains an antimicrobial compound. "Antibacterial compound" refers to any compound that can inhibit the growth of microbial populations (such as bacteria, algae and / or fungi). The at least one antimicrobial compound can be selected from the group consisting of metals, metal salts of pyrithione, quaternary ammonium salts, polyelectrolytes, polymeric biguanide derivatives or mixtures thereof. The metal and the metal in the metal salt of pyrithione are selected from the group consisting of copper, zinc, silver or mixtures thereof. The metal can be used in the form of nanoparticles, preferably silver nanoparticles. The quaternary ammonium salt is selected from the group consisting of benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetalkonium chloride, cetylpyridinium chloride, cetyltrimethylammonium, cetrimide, dofanium chloride, tetraethylammonium bromide, didecyldimethylammonium chloride and domiphen bromide. The antimicrobial compound may also be selected from polymers, such as polyelectrolytes (such as polycations or polyanions) and salts thereof, or from polymeric biguanide derivatives, such as poly(hexamethylene biguanide) hydrochloride. Preferably, the at least one antimicrobial compound comprises a biguanide derivative.

[0027] The at least one layer containing at least one antimicrobial compound can be impregnated or coated with the antimicrobial compound. Alternatively, the at least one antimicrobial compound can be added to the polymer material before the polymer material is processed into a meltblown layer and / or a spunbond layer.

[0028] The antimicrobial compound can be applied using known techniques, such as spraying, dipping, roller coating, foam coating or dusting. Saturated size presses or other conventional equipment, such as curtain coaters, metered press coaters, foam bonders, gravure rolls, dip and nip, doctorate transfer rolls, rod coaters and spray coaters can be used. When the antimicrobial compound is applied in liquid form (e.g., by dipping), the components need to be mixed in a solvent. Preferred solvents are water, organic solvents or mixtures thereof. Among organic solvents, alcohols such as methanol or ethanol can be mentioned. Preferably, the antimicrobial compound is applied by Foulard dipping technology.

[0029] Preferably, the layer comprising the antimicrobial compound is the first meltblown layer. More preferably, only the first meltblown layer comprises at least one antimicrobial compound. In a preferred embodiment, the first meltblown layer is coated with the at least one antimicrobial compound, and more preferably, the coated first meltblown layer is the only layer comprising the antimicrobial compound.

[0030] If more than one layer (e.g., more than one first meltblown layer) contains an antimicrobial compound, but multiple layers (depending on the type of filter medium, for example, two or three layers, such as a second spunbond layer and a third spunbond layer) contain such a compound, then these layers may differ in the type of antimicrobial compound used in the layers (i.e., the same antimicrobial compound is used in each layer, or different types of antimicrobial compounds are used), the amount applied, and the manner in which the antimicrobial compound is applied (e.g., coating, dispersion in the fibers within the layer, etc.).

[0031] The initial efficiency of the filter medium of the present invention for 4 μm particles is at least 85%, preferably at least 90%, and more preferably at least 95%. The initial efficiency of the filter medium is based on ISO 19438:2003 (E) standard, at an area of ​​200 cm 2 The measurement was performed on a flat plate using A3 intermediate test dust (ISO12103-1, PTI Powder Technology Inc.) at a flow rate of 0.71 L / min under the condition of BUGL 100.

[0032] The filter medium of the present invention has a dust holding capacity of at least 1.3 g / 200 cm at a pressure drop of 0.7 bar (measured on a flat plate according to ISO 19438:2003).2 , preferably at least 1.5 g / 200 cm 2 , more preferably at least 1.8 g / 200 cm 2 .

[0033] The initial efficiency of the filter element has also been tested in accordance with ISO 19438:2003(E). The filter element has an initial efficiency level of at least 85% for 4 μm particles, at least 90% for 5 μm particles, at least 99.9% for 10 μm particles and at least 99.95% for 20 μm particles. The same efficiency levels are achieved when the filter element is tested in accordance with ISO 19438:2003(E) but microfiltrated water is used instead of the test fluid specified in that standard. The specific dust holding capacity is at least 75 g / m at a pressure drop of 0.3 bar in accordance with ISO 19438:2003(E). 2 .

[0034] Preferably, the "pores" of the filter medium have a diameter of 5-30 μm, preferably 10-25 μm, according to the pore size measurement method described below. More preferably, the diameter (size) of the "pores" is about 7-15 μm.

[0035] Preferably, the maximum pore size (diameter) is 15 to 40 μm, more preferably 15 to 30 μm.

[0036] Surprisingly, it has been found that the antimicrobial compounds in the filter medium not only have an outstanding antimicrobial activity but are also very stable over a long period of time and are therefore particularly suitable for water filtration in the combustion chamber of an internal combustion engine.

[0037] The antimicrobial activity of the filter medium has been tested in accordance with the DIN EN ISO 20743:2013 standard. To adapt this standard to the purposes of these studies and to deviate from it, Pseudomonas aeruginosa and Stenotrophomonas maltophilia were used as microorganisms. Over a 24-hour incubation period, the filter medium has an antimicrobial activity of at least 2 log, preferably at least 4 log (i.e. logarithmic reduction factor (LRF)>2, more preferably LRF>4), which means that its inactivation rate is greater than 99.99%.

[0038] The effects of pH (i.e., pH 5, 7, and 9) and temperature (5°C, 30°C, 80°C) on the release properties of the coating were also tested. The results showed that even after 3 months, the filter medium remained stable at different pH values ​​and temperatures, and no significant release from the coating was detected. For example, the silver ion release from the silver ion-containing coating was less than 60 μg / L at temperatures of 5°C, 30°C, and 80°C and at pH values ​​of 5, 7, and 9. The release of ammonium ions was less than 0.643 mg / L at 5°C and 30°C. Bacteria had no effect on the release behavior. The test conditions are described in the corresponding section.

[0039] Depending on the size of the filter element, the filter medium can be folded into a filter element with different pleats.

[0040] The amount of the at least one antimicrobial compound in the filter medium is generally 0.0001 wt % to 2.0000 wt %, preferably 0.001 wt % to 1.8000 wt %, more preferably 0.01 wt % to 1.5 wt %, based on the total weight of the filter medium.

[0041] The hydrophobicity of the filter medium is 0. Hydrophobic materials are water-repellent. Even after a long time, water remains on the surface of the material in the form of droplets. For this measurement, the water absorption capacity of the substrate is determined. The hydrophobicity can be determined by dripping liquids with different surface tensions. Take a drop of the test liquid from a dropper bottle and drip it on the material to be tested. After standing for one minute, observe which test liquid mixture still remains on the material in the form of droplets without penetrating. The test liquids are applied in increasing order. The number of the liquid that allows the droplet to remain on the material for one minute without penetrating is used as the measurement result. In the present case, the test liquid is water (i.e. numbered 0).

[0042] The filter medium can be prepared by bonding a spunbond layer to a meltblown layer. Any known bonding method can be used, such as needle punching, sputtering, thermal processing (i.e., calendering, ultrasonic welding) and chemical processes (i.e., using adhesives). Preferably, the meltblown layer and the spunbond layer are connected by a point calender.

[0043] The present invention also relates to a filter element and a filter system comprising the filter medium of the present invention. The filter element may include a first end plate and a second end plate, and the filter medium is arranged between the two end plates. For example, the filter medium can be folded into a zigzag shape and arranged between the two end plates. The filter element can flow radially from the outside to the inside or from the inside to the outside. In addition, the filter element may be provided with at least one check valve so that the filtered water will not flow back through the filter element. The present invention also provides a filter system, which includes at least one filter element, a filter element shell and a filter shell cover. The filter element is located in the filter element shell. When the filter element is correctly installed in the shell, the raw water side and the pure water side will be isolated by the filter element, so that the liquid must be filtered through the filter medium of the filter element.

[0044] The filter medium of the present invention can be used for filtering water in the combustion chamber of an internal combustion engine.

[0045] With full consideration of the above, the present invention particularly provides the following preferred embodiments:

[0046] Ⅰ. A filter medium comprising:

[0047] i) a first meltblown layer, and

[0048] ii) a second spunbond layer,

[0049] At least one of the first layer and the second layer contains at least one antimicrobial compound.

[0050] II. The filter medium according to I, wherein the at least one antimicrobial compound is selected from the group consisting of metals, copper pyrithione metal salts, quaternary ammonium salts, polyelectrolytes, polymeric biguanide derivatives or mixtures thereof.

[0051] III. The filter medium according to any one of I-II, wherein only the meltblown layer contains the at least one antimicrobial compound.

[0052] IV. A filter medium according to any one of I-III, wherein both the first meltblown layer and the second spunbond layer contain the at least one antimicrobial compound. The antimicrobial compounds in the two layers may be the same or different. If the same antimicrobial compound is used, the two layers may differ in the amount of antimicrobial compound applied, the manner in which the antimicrobial compound is provided in the layer, etc.

[0053] V. The filter media according to any one of I-IV, further comprising a third spunbond layer.

[0054] VI. The filter medium according to any one of IV, wherein the first meltblown layer, the second spunbond layer and the third spunbond layer all contain the at least one antimicrobial compound. The antimicrobial compounds in the three layers may be the same or different. If the same antimicrobial compound is used, the layers may differ in the amount of the antimicrobial compound applied, the manner in which the antimicrobial compound is provided in the layer, etc.

[0055] VII. The filter medium according to any one of I-VI, wherein the first meltblown layer, the second spunbond layer, and the third spunbond layer are all coated with the at least one antimicrobial compound.

[0056] VIII. The filter medium according to any one of I-VII, wherein the meltblown layer comprises polyester fibers.

[0057] IX. The filter medium according to any one of I-VIII, wherein the at least one antimicrobial compound is selected from the group consisting of quaternary ammonium salts and polymeric biguanide derivatives.

[0058] X. The filter medium according to any one of I-IX, wherein the amount of the at least one antimicrobial compound is 0.0001 wt % to 2.0000 wt % based on the total weight of the filter medium.

[0059] XI. The filter medium according to any one of I-X, wherein the thickness of the first meltblown layer is 0.05-0.8 mm.

[0060] XII. The filter medium according to any one of I-XI, wherein the at least one antimicrobial compound is selected from zinc pyrithione, silver nanoparticles, quaternary ammonium salts and polyhexamethylene biguanide hydrochloride.

[0061] ⅩⅢ. The filter medium according to any one of I-XII, wherein the at least one antimicrobial compound comprises or consists of a quaternary ammonium salt and polyhexamethylene biguanide hydrochloride.

[0062] ⅩⅣ. A filter element comprising the filter medium as described in any one of I-XIII.

[0063] XV. The filter element according to XIV, comprising a first end plate, a second end plate and a filter medium through which radial flow can pass.

[0064] XVI. Filter element according to XIV or XV, comprising at least one valve, in particular a non-return valve.

[0065] XVII. A filter system comprising the filter element, filter element housing and filter housing cover as described in XIV to XVI.

[0066] XVIII. Use of a filter medium according to any one of I to XIII for filtering water in a chamber of an internal combustion engine.

[0067] Test Method

[0068] Aperture: The pore size measurement is carried out in accordance with DIN ISO 4003:1990. The sample is placed between a gas-tight clamp above an orifice equipped with an air supply and connected to a pressure gauge (U-tube with mm scale indication). Each sample is tested with its upper surface facing upwards. Denatured ethanol (100% ethanol with 1% MEK (methyl ethyl ketone) as denaturant) is poured over the edge of the upper sample clamp (do not spray directly on the sample, liquid depth is about 4 mm) so that a slight air overpressure is generated above the liquid. The air pressure is increased slowly (approx. 5 mm water gague / sec) until the first bubbles appear. The required air pressure value (in mm water column) is read from the pressure gauge. With the help of the surface tension of the ethanol (at 23°C), the maximum pore size ("largest pore", "maximum pore size", "maximum pore diameter") can be calculated.

[0069] The air pressure is then increased further until the air passes through the entire surface of the sample (10 cm 2 ) and produce evenly distributed bubbles but no foam, to determine the value of "Porosity". Read the air pressure value again and calculate the relative pore size, which is the diameter of the "Porosity".

[0070] The "maximum pore size" and "porosity" can be calculated using the above method using the following formula:

[0071]

[0072] d = pore diameter (μm);

[0073] p = air pressure (mN / m 2 );

[0074] σ = surface tension of the test liquid (e.g. ethanol), [at 23°C, σ for ethanol = 21.330225 mN / m];

[0075] α = contact angle between liquid and sample;

[0076] (Conversion relationship: 1 mm water column = 98.07 mN / m 2 ).

[0077] thickness: The thickness stated in this application is measured in accordance with DIN EN ISO 534:2012-02, but using a test pressure of 0.1 bar.

[0078] Basis Weight: According to DIN EN ISO 536:2012-1.

[0079] Initial efficiency and dust holding capacity of flat plate It is measured according to ISO 19438:2003(E) (ISO12103-1, A3 intermediate test dust, PTIPowder Technology Inc.), with a sample size of 200 cm 2 , flow rate is 0.71L / min, BUGL100).

[0080] The initial efficiency and dust holding capacity of the filter elements are determined according to ISO 19438:2003(E).

[0081] Filter element pressure drop, According to ISO 4020:2001: The pressure drop depends on the geometry of the filter element, according to ISO 4020:2001, at 120 L / h and 4 cSt, the pressure drop is less than 25 mbar. The same results were obtained in distilled water (this is a deviation from ISO 4020:2001).

[0082] Average fiber diameter: The determination is performed using a scanning electron microscope (eg Phenom Fei) in conjunction with software capable of measuring diameter (eg Fibermetric V2 software).

[0083] Sampling: For nonwoven fabrics, select at least 5 points in the width direction for analysis.

[0084] Record:

[0085] 1. Sample sputtering

[0086] 2. Based on random images of the optical image (no magnification), selected areas were rasterized at a magnification of at least 500 times (magnification depends on the sample to ensure that fibers can be identified).

[0087] 3. The fiber diameter is determined by the "one click" method. Each fiber must be tested once. The measurement points where the fiber intersections are detected do not represent the fiber diameter and must be removed manually.

[0088] 7. Calculation

[0089] The average values ​​and fiber diameter distribution were evaluated using Excel spreadsheets from the data acquired from Fibermetric V2 software.

[0090] For each point, the diameters of at least 100 fibers are recorded and their average value is calculated. These five average values ​​are then combined to form an average value, which is the average fiber diameter of the nonwoven. The average fiber diameter of the nonwoven is therefore calculated based on at least 500 fibers.

[0091] Antimicrobial Testing: The test was carried out in accordance with DIN EN ISO 20743:2013. In order to comply with this standard and to deviate from the objectives of the present invention, the microorganisms Stenotrophomonas maltophilia and Pseudomonas aeruginosa were used.

[0092] Preparation of the inoculum: Inoculation is carried out in a preculture. The preculture is prepared before the start of the experiment. For this purpose, one or two growing colonies of the bacterial strain are transferred from the agar plate to 40 mL of culture medium in a 250 mL Erlenmeyer flask with baffles, which is incubated overnight at 30°C. Based on the optical density of the overnight culture, the cell number is determined using a calibration curve between the number of cells and the optical density. Depending on the target concentration in the test batch, a dilution is prepared from it and used to inoculate the test batch. To investigate the antimicrobial properties, each test batch starts with a microbial concentration of approximately 10 6 -10 7 CFU / mL.

[0093] According to the standard, the mass of the test sample is 0.4 g. Before testing, the sample is irradiated with UV light for at least 2 hours. Subsequently, four samples of the sterilized filter medium are placed in a 50 mL centrifuge tube. Next, 50 μL of inoculum is applied to each sample, so that 4 samples inoculated with 0.2 mL of inoculum are contained in the centrifuge tube.

[0094] For hydrophobic samples, it is not possible to apply the microorganisms as described above, since the droplets would remain on the filter surface. Therefore, the reference filter piece was immersed in water ("wetted") before testing. Furthermore, the microorganisms could only be applied dropwise and left to dry for 3-4 hours.

[0095] The tube containing the t0 sample is reopened immediately after closing to add 20 ml of SCDLP medium. The tube is then vortexed 5 times for 5 seconds each time and then shaken for 30 seconds at an arc of 30 cm. Next, the medium is poured out and stored on ice. The solution containing the shaken microorganisms obtained in this way is then diluted, spread on LB medium, and evaluated by the plate count method.

[0096] The tubes containing the 24-hour samples were immediately placed in a 30°C incubator, and the same operation was performed after incubation at 30°C for 24 hours.

[0097] Colonies were counted after 24 hours and 2 days.

[0098] For evaluation, the number of cells at time 0 and at the time of sampling must be determined. To calculate the logarithmic reduction factor, the Log reduction factor is calculated based on the applied CFU (colony forming units) and the CFU shaken off immediately or 24 hours after application. 10 The evaluation is performed by presenting the log reduction factor (LRF).

[0099] Test conditions

[0100] -Cultivation temperature: 30℃

[0101] -Sample: Use 0.4g sample per batch, divided into 4 strips.

[0102] Evaluation: Log reduction factor (LRF) of each material (reference material and test material) was calculated by using the applied viable CFU (colony forming unit) and the viable CFU at 24 hours.

[0103] LRF=log(CFU 施加 / CFU t )

[0104] LRF=log CFU 施加 -log CFU t

[0105] CFU t is the CFU after incubation time t.

[0106] Coating Release Test:

[0107] 8 mL of water is taken from each batch and mixed with 2 test samples of 1 cm × 1.5 cm in a 15 mL centrifuge tube (Falcon tube). At the beginning of the experiment, the centrifuge tubes are prepared and provided for the samples, and the individual sample containers are no longer involved in subsequent experiments. The filter element test samples in water are incubated under different conditions and sampled, processed and measured after different test periods. The ion release is studied from the liquid phase at the beginning of the experiment and approximately 7 days, 28 days, 60 days and 90 days thereafter. The time course of possible dissolution should be recorded within 3 months. Analysis of anions is performed using ion chromatography (such as ICP-3000 or ICP-6000). Example

[0108] Examples 1 to 3

[0109] Prepare the filter media according to Table 1.

[0110] First meltblown layer Second spunbond layer The third spunbond layer Total medium polymer Polyester Polyester Polyester <![CDATA[Grammage (g / cm 2 )]]> 60 80 20 168 Thickness (0.1 bar) 0.35 0.30 0.15 0.97 Average fiber diameter (μm) 1.4 25 25 <![CDATA[Air permeability (L / m 2 s)]]> 66 Initial efficiency for 4μm* (%) 90 <![CDATA[Dust holding capacity (g / 200 cm 2 )*]]> 1.8

[0111] *Measured according to the test conditions described in this patent.

[0112] The media of the example was coated using the Foulard padding technique, with all three layers applied. Test pieces of the media were coated with the antimicrobial compounds listed in Table 2. The amount of antimicrobial compound in the example was 0.001 wt % based on the total weight of the filter media.

[0113] Table 2

[0114]

[0115]

[0116] As can be seen from Table 2, all filter media according to the present invention have very good antibacterial activity over a long period of time.

[0117] Comparative Example 1

[0118] Same as Example 1, but without coating. After 24 hours, both bacteria LRF had negative values.

Claims

1. A filter medium comprising: i) a first meltblown layer, and ii) a second spunbond layer, At least one of the first layer and the second layer contains at least an antimicrobial compound.

2. The filter medium according to claim 1, wherein: The at least one antimicrobial compound is selected from the group consisting of metals, copper pyrithione metal salts, quaternary ammonium salts, polyelectrolytes, polymeric biguanide derivatives or mixtures thereof.

3. The filter medium according to any one of claims 1 to 2, wherein: Only the meltblown layer contains at least one antimicrobial compound.

4. The filter media of any one of claims 1-3, further comprising a third spunbond layer.

5. The filter medium according to any one of claims 1 to 4, wherein: The meltblown layer includes polyester fibers.

6. The filter medium according to any one of claims 1 to 5, wherein: The at least one antimicrobial compound is selected from the group consisting of quaternary ammonium salts and polymeric biguanide derivatives.

7. The filter medium according to any one of claims 1 to 6, wherein: The at least one antimicrobial compound is present in an amount of 0.0001 wt % to 2.0000 wt % based on the total weight of the filter medium.

8. A filter element comprising the filter medium according to any one of claims 1 to 7. 9 . The filter element according to claim 8 , comprising a first end plate, a second end plate and a filter medium through which radial flow can pass.

10. Filter element according to claim 8 or 9, comprising at least one valve, in particular a non-return valve.

11. A filter system comprising the filter element, the filter element housing and the filter housing cover according to claims 8-10.

12. Use of the filter medium according to any one of claims 1 to 7 for filtering water in a chamber of an internal combustion engine.

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