Filter media comprising pre-filter layer

Abstract

Filter media including pre-filter layers, and related components, systems, and methods related thereto, are provided. In some embodiments, the pre-filter layer may be designed to impart desired characteristics (e.g., high gamma and / or long service life) to the filter media while having a relatively minimal or no adverse effect on another characteristic of the filter media that is important for a given application. For example, a pre-filtration layer may be used to improve upstream removal of particulate matter, which may clog a downstream efficiency layer comprising submicron fibers and reduce filtration performance. The pre-filter layer may be configured to increase the useful life of the filter media and / or increase gamma of the filter media. The filter media as described herein may be particularly suited for applications involving filtering air, but the media may also be used in other applications.

Description

[0001] This application is a divisional application of the Chinese patent application entitled "Filter Medium Including Pre-Filter Layer" and application number 201580068500.1. Patent application 201580068500.1 is a national application entering the Chinese national phase based on the international application (PCT / US2015 / 066728) filed on December 18, 2015 under the Patent Cooperation Treaty, and the priority date of the application is December 19, 2014. Technical Field

[0002] Embodiments of the present invention generally relate to filter media including a pre-filter layer, and in particular, to filter media having enhanced performance characteristics. Background Art

[0003] A variety of filter media can be used to remove contaminants in a variety of applications. The filter media can be designed to have different performance characteristics depending on its desired use. For example, relatively low-efficiency filter media can be used for heating, ventilation, refrigeration, and air conditioning applications. For applications that require different performance characteristics (e.g., very high efficiency), such as for cleanroom or biomedical applications, high efficiency particulate air (HEPA) filters or ultra-low penetration air (ULPA) filters can be used.

[0004] The filter medium can be formed by one or more fiber nets. The fiber net provides a porous structure that allows fluid (e.g., gas, air) to flow through the filter medium. Contaminant particles contained in the fluid can be captured on or in the fiber net. The characteristics of the filter medium (e.g., surface area and basis weight) affect the performance of the filter, including filter efficiency, pressure drop, and resistance to fluid flow through the filter medium. Generally, higher filter efficiency may lead to higher fluid flow resistance, which results in a higher pressure drop across the filter medium for a given flow rate.

[0005] There is a need for filter media that can be used in a variety of applications and that have a balance of desirable properties including high efficiency and low resistance to fluid flow across the filter media, resulting in high gamma values. Summary of the invention

[0006] Filter media including a pre-filter layer and related components, systems and methods related thereto are provided. In some cases, the subject matter of the present application relates to related products, alternative solutions to specific problems and / or multiple different uses of structures and compositions.

[0007] In one set of embodiments, a series of filter media are provided. In one embodiment, the filter media includes a pre-filter layer comprising first fibers having a median diameter of less than or equal to about 2 microns. The pre-filter layer has a thickness of greater than or equal to about 20 microns and a basis weight of less than about 30 g / m 2 The filter media further comprises a second layer comprising second fibers having a median diameter of about 1 micron or less, wherein the second layer has an initial DOP efficiency of about 60% or greater, and the initial DOP efficiency of the second layer is greater than the pre-filter layer.

[0008] In another embodiment, the filter medium includes a pre-filter layer comprising first fibers having a median diameter of less than or equal to about 2 microns. The pre-filter layer has a thickness of greater than or equal to about 20 microns and a basis weight of less than about 30 g / m 2 , the initial DOP efficiency is less than or equal to about 90%. The filter medium also includes a polymer membrane having an initial DOP efficiency greater than or equal to about 60%, and wherein the initial DOP efficiency of the polymer membrane is greater than that of the pre-filtration layer.

[0009] When considered in conjunction with the accompanying drawings, other advantages and new features of the present invention will become apparent through the following detailed description of multiple non-limiting embodiments of the present invention. In the case where this specification and the documents incorporated by reference contain contradictory and / or inconsistent disclosures, this specification should be used as the standard. If two or more documents incorporated by reference contain contradictory and / or inconsistent disclosures relative to each other, the documents with a later effective date should be used as the standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, which are schematic and are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown is generally represented by a single numeral. For purposes of clarity, not every component is labeled, nor is every component of every embodiment of the present invention shown, when the illustration is not necessary for a person skilled in the art to understand the present invention. In the drawings:

[0011] Figures 1A to 1D shows a cross-section of a filter medium according to certain embodiments; and

[0012] Figure 2 Shown is a graph of pressure drop versus load time for certain filter media according to one set of embodiments. DETAILED DESCRIPTION

[0013] A filter medium including a pre-filter layer and related components, systems and methods related to the filter medium are provided. In some embodiments, the pre-filter layer can be designed to impart desired properties to the filter medium (e.g., high dust holding capacity and / or long service life) while having relatively minimal or no adverse effect on another property of the filter medium that is important for a given application. For example, the pre-filter layer can be used to improve the removal of upstream particulate matter (which may clog downstream layers (e.g., efficiency layers) and reduce filtration performance) without significantly reducing particulate efficiency (e.g., DOP efficiency) or increasing the pressure drop of the filter medium. The filter medium as described herein may be particularly suitable for applications involving filtering air, but the medium may also be used in other applications.

[0014] In some embodiments, the filter media may include a pre-filter layer including fibers having a median diameter of less than or equal to about 2 microns, and a second layer including fibers having a median diameter of less than or equal to about 1 micron (e.g., less than or equal to 0.5 microns). The particle efficiency of the second layer may be greater than the particle efficiency of the pre-filter layer. In some embodiments, the second layer may have a relatively high particle efficiency (e.g., greater than or equal to 60%, greater than or equal to 75%, greater than or equal to 90%). In some cases, the high particle efficiency of the second layer may be at least partially attributed to the relatively small median fiber diameter. The term "median" as used herein has its ordinary meaning and may refer to a value in an ordered set of values ​​where the number of values ​​below and above the value is equal, or if there is no middle number, the value is the arithmetic mean of the two middle values. The median fiber diameter may be determined by any suitable method (e.g., by SEM or by detecting using image processing software).

[0015] Many filtration applications require filter media to meet certain efficiency standards. For example, high efficiency particulate air (HEPA) filters or ultra-low penetration air (ULPA) filters are required to remove particles at efficiency levels greater than 99.95% and 99.9995, respectively, according to EN1822. In some existing filter media, the desired efficiency is achieved at the expense of other beneficial properties of the filter media. For example, changing the physical structure of the layer to increase its particle efficiency may adversely affect the pressure drop, the ability to keep particulate matter inside and / or the blocking tendency of the layer. For example, many existing filter media use efficiency layers including fibers of relatively small diameters, which impart high particle efficiency, but result in a pore structure that may be easily blocked and / or may not be able to keep dust particles inside. In such filter media, there may be a compromise between high particle efficiency and low pressure drop and / or long service life.

[0016] Some existing filter media have attempted to address this problem by using one or more pre-filter layers upstream of the efficiency layer. However, conventional pre-filter layers may not be able to capture certain particles and / or cannot be added without adversely affecting one or more beneficial filtration characteristics. Moreover, whether or not the pre-filter layer removes certain particles, adding a layer to the filter media may adversely affect one or more characteristics of the filter media. For example, the thickness and / or solidity of the pre-filter layer combined with other features of the filter media (e.g., the pore structure of the efficiency layer) can cause the pressure drop of the filter media to increase significantly. Therefore, there is a need for a filter media that can achieve the necessary particle efficiency for a given application while mitigating any negative impact on other desired filtration characteristics.

[0017] In some embodiments, the pre-filter is combined with a second layer to produce a filter medium having the necessary particle efficiency and having relatively minimal adverse effects or no adverse effects on other characteristics of the filter medium. A filter medium including such a pre-filter layer as described herein is not subject to one or more limitations of existing filter media and / or conventional pre-filter layers. As further described below, a pre-filter layer having specific structural features (e.g., low basis weight, median fiber diameter less than 2 microns) has sufficient particle efficiency and dust holding capacity to capture and retain small particles, otherwise the small particles will block one or more downstream layers (e.g., efficiency layers), resulting in a significant increase in pressure drop over time and ultimately reducing service life. The pre-filter layer may also have a sufficiently low basis weight so that adding a pre-filter layer to the filter medium does not significantly increase the total pressure drop of the filter or reduce γ. In addition, unlike some conventional pre-filter layers, the pre-filter layer described herein may contribute to the total particle efficiency of the filter medium and may therefore be combined with a second layer having a particle efficiency less than the standard but greater than the pre-filter layer to produce a filter medium having the necessary efficiency. Filter media including a pre-filter layer as described herein can be used to meet certain particle efficiency standards (e.g., ULPA, HEPA, masks) while also having desirable beneficial properties such as gamma, pressure drop, pressure drop change over time, dust holding capacity, and / or service life.

[0018] In some embodiments, the pre-filter layer has a relatively small median fiber diameter (e.g., less than or equal to about 2 microns), a low basis weight (e.g., less than or equal to about 30 g / m 2) and / or a particle efficiency of less than or equal to about 90% (e.g., about 10% to about 90%). The pre-filter layer can be combined with a second layer (e.g., an efficiency layer) having a particle efficiency greater than that of the pre-filter layer (e.g., a DOP efficiency greater than or equal to 60%) to form a filter medium having desired characteristics (e.g., a certain particle efficiency). In addition to one or more of the above-described structural features, the pre-filter layer can also be relatively thin (e.g., greater than or equal to about 20 microns and less than or equal to about 1 mm), have a high surface area (e.g., greater than or equal to 1.75 m 2 / g) and / or low solidity (e.g., greater than or equal to about 0.01% and less than or equal to about 25%). This combination of structural features can produce a pre-filter layer and resulting filter media with improved and unexpected filtration performance.

[0019] A non-limiting example of a filter medium including a pre-filter layer is Figures 1A to 1D In some embodiments, the filter medium 10 may include a pre-filter layer 15 and a second layer 20. In some embodiments, the pre-filter layer 15 may be directly adjacent to the second layer 20, such as Figure 1A to Figure 1B In other embodiments, layer 15 and layer 20 may be indirectly adjacent to each other, and one or more intermediate layers (e.g., a scrim) may separate the layers, such as Figure 1C to Figure 1D In some embodiments, filter media 10 may include one or more optional layers (e.g., scrim, backing layer) located upstream and / or downstream of layers 15 and 20, such as Figures 1B to 1D For example, Figure 1B As shown, in some embodiments, the filter medium may include a third layer 25 downstream of the pre-filter layer and the second layer. In some cases, the third layer may be directly adjacent to the second layer. In certain embodiments, layer 25 may be a scrim layer directly adjacent to the second layer. In other embodiments, layer 25 may be a backing layer (e.g., a pleated backing layer) directly adjacent to the pre-filter layer, as described in more detail below. In some cases, the backing layer (e.g., a pleated backing layer) may have a relatively high air permeability (e.g., greater than or equal to about 100 CFM) and a machine direction stiffness (e.g., greater than or equal to about 600 gu). In other embodiments, layer 20 may be indirectly adjacent to layer 25, and one or more intermediate layers may separate the layers.

[0020] Regardless of whether the filter medium includes layer 25, filter medium 10 may include layer 30 upstream of the second layer, such as Figure 1C In some cases, layer 30 may be directly adjacent to the pre-filter layer. In certain embodiments, layer 30 may be a backing layer (e.g., a pleated backing layer) that is directly adjacent to the pre-filter layer. In other embodiments, layer 15 and layer 30 may be indirectly adjacent to each other, with one or more intermediate layers separating the layers.

[0021] In some embodiments, the filter medium 10 may include a pre-filter layer 15, a second layer 20, a third layer 25, and a fourth layer 30, such as Figure 1D In other embodiments, the filter medium 10 may include a pre-filter layer 15, a second layer 20, and a third layer 25 or a fourth layer 30, respectively. Figure 1B and Figure 1C shown.

[0022] Generally, the one or more optional layers can be any suitable layer (eg, a scrim layer, a backing layer, a base layer, an efficiency layer, a capacity layer, a spacer layer, a support layer).

[0023] As used herein, when a layer is referred to as being "adjacent" another layer, it can be directly adjacent to the layer, or intervening layers may also be present. A layer being "directly adjacent" to another layer means that there are no intervening layers.

[0024] In some embodiments, one or more layers in the filter media can be designed to be independent of another layer. That is, fibers from one layer are not substantially intermixed (e.g., not intermixed at all) with fibers from another layer. For example, for Figures 1A to 1D In one set of embodiments, fibers from the pre-filter layer are not substantially intermixed with fibers from the second layer. The separate layers may be joined by any suitable process including, for example, lamination, thermal point bonding, calendering, sonication, or by an adhesive, as described in more detail below. However, it should be understood that certain embodiments may include one or more layers that are not independent of each other.

[0025] It should be understood that the configurations of layers shown in the drawings are examples only, and that in other embodiments, filter media containing layers of other configurations are possible. Figures 1A to 1D The first layer, the second layer, the optional third layer, and the optional fourth layer are shown in a specific order, but other configurations are possible. For example, the optional third layer may be disposed between the first layer and the second layer. It should be understood that the terms "second" layer, "third" layer, and "fourth" layer as used herein refer to different layers in the medium and are not meant to limit the specific position of the layer. In addition, in some embodiments, in addition to the layers shown in the figure, additional layers (e.g., a "fifth" layer, a "sixth" layer, or a "seventh" layer) may also be present. It should also be understood that in some embodiments, not all components shown in the figure need to be present.

[0026] The structural features of the pre-filter layer 15 can be balanced to produce a pre-filter layer that imparts beneficial properties to the filter media while having relatively minimal or no adverse effect on another property of the filter media that is important for a given application. For example, in some embodiments, the pre-filter layer can have a relatively small median fiber diameter that imparts sufficient dust holding capacity, surface area, and / or gamma at a relatively low basis weight and / or solidity. In some embodiments, the median fiber diameter of the pre-filter layer can be greater than or equal to about 0.1 microns, greater than or equal to about 0.2 microns, greater than or equal to about 0.3 microns, greater than or equal to about 0.4 microns, greater than or equal to about 0.5 microns, greater than or equal to about 0.8 microns, greater than or equal to about 1 micron, greater than or equal to about 1.2 microns, greater than or equal to about 1.5 microns, or greater than or equal to about 1.8 microns. In some cases, the median fiber diameter may be less than or equal to about 2 microns, less than or equal to about 1.8 microns, less than or equal to about 1.5 microns, less than or equal to about 1.2 microns, less than or equal to about 1 micron, less than or equal to about 0.8 microns, less than or equal to about 0.5 microns, less than or equal to about 0.4 microns, less than or equal to about 0.3 microns, or less than or equal to about 0.2 microns. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 0.5 microns and less than or equal to about 1 micron). Other values ​​of the median fiber diameter are also possible. In some embodiments, the average diameter of the fibers may fall within the above reference ranges for the median fiber diameter.

[0027] In certain embodiments, there may be a suitable range of median fiber diameters (e.g., greater than or equal to about 0.5 microns and less than or equal to about 1 micron) that allows the pre-filter layer to impart beneficial properties while minimizing negative side effects. For example, in some embodiments, a median fiber diameter above a suitable range may produce a desired dust holding capacity, but may only be able to achieve the required particle efficiency by increasing the basis weight of the pre-filter layer, which may increase the pressure drop. Conversely, in some embodiments, a median fiber diameter below a suitable range may produce the required particle efficiency and γ, but may lack sufficient dust holding capacity and / or be easily clogged, which may reduce the service life of the filter medium. In some embodiments, a suitable range may be greater than or equal to about 0.1 microns and less than or equal to about 2 microns, greater than or equal to about 0.1 microns and less than or equal to about 1 micron, or greater than or equal to about 0.5 microns and less than or equal to about 1 micron. It should be understood that in some cases, a suitable range of median fiber diameters may vary depending on the filtration application.

[0028] In some embodiments, the pre-filter layer can have a relatively small basis weight. For example, in some embodiments, the basis weight of the filter media can be less than or equal to about 30 g / m 2 , less than or equal to about 25g / m 2 , less than or equal to about 20g / m2 , less than or equal to about 15g / m 2 , less than or equal to about 10 / m 2 , less than or equal to about 5g / m 2 , less than or equal to about 1g / m 2 , less than or equal to about 0.8g / m 2 or less than or equal to about 0.5 g / m 2 In some cases, the basis weight of the pre-filter layer can be greater than or equal to about 0.2 g / m 2 , greater than or equal to about 0.5 g / m 2 , greater than or equal to about 0.8 g / m 2 , greater than or equal to about 1g / m 2 , greater than or equal to about 5g / m 2 , greater than or equal to about 10g / m 2 , greater than or equal to about 15g / m 2 , greater than or equal to about 20g / m 2 , or greater than or equal to about 25g / m 2 Combinations of the above-referenced ranges are also possible (e.g., greater than or equal to about 0.5 g / m 2 and less than or equal to about 30 g / m 2 ). Other values ​​of basis weight are also possible. The basis weight can be determined according to standard ISO 536.

[0029] As described in more detail below, the pre-filter layer may include fiber types such as synthetic fibers, glass fibers and / or cellulose fibers. In some cases, the pre-filter layer may include a relatively high weight percentage of synthetic fibers (e.g., 100 weight %). For example, the pre-filter may include synthetic fibers formed by a meltblowing process, a melt spinning process, a centrifugal spinning process, or an electrospinning process. In some cases, as further described below, the synthetic fibers may be continuous. In some embodiments, the pre-filter layer may include relatively few glass fibers or no glass fibers. In other embodiments, the pre-filter layer may include a relatively high weight percentage of glass fibers (e.g., 100 weight %).

[0030] In some embodiments, the pre-filter layer can be relatively thin. For example, in some embodiments, the thickness of the pre-filter layer can be less than or equal to about 5 mm, less than or equal to about 4.5 mm, less than or equal to about 4 mm, less than or equal to about 3.5 mm, less than or equal to about 3 mm, less than or equal to about 2.5 mm, less than or equal to about 2 mm, less than or equal to about 1.5 mm, less than or equal to about 1 mm, less than or equal to about 0.5 mm, or less than or equal to about 0.1 mm. In some cases, the thickness of the pre-filter layer can be greater than or equal to about 0.02 mm, greater than or equal to about 0.05 mm, greater than or equal to about 0.08 mm, greater than or equal to about 0.1 mm, greater than or equal to about 0.5 mm, greater than or equal to about 1 mm, greater than or equal to about 1.5 mm, greater than or equal to about 2 mm, greater than or equal to about 2.5 mm, greater than or equal to about 3 mm, greater than or equal to about 3.5 mm, or greater than or equal to about 4 mm. Combinations of the above referenced ranges are also possible (e.g., greater than or equal to about 0.05 mm and less than or equal to about 5 mm, greater than or equal to about 0.1 mm and less than or equal to about 1 mm). Other values ​​of the average thickness are also possible. Thickness according to standard ISO 534 at 2.65 pounds per inch 2 In certain embodiments, very small thicknesses (eg, greater than or equal to about 0.02 mm) may be required to achieve certain beneficial filtration properties (eg, dust holding capacity).

[0031] In certain embodiments, the pre-filter layer described herein can have a relatively high surface area. For example, in some embodiments, the surface area of ​​the pre-filter layer can be greater than or equal to about 1.75 m 2 / g, greater than or equal to about 2.0m 2 / g, greater than or equal to about 2.5m 2 / g, greater than or equal to about 3m 2 / g, greater than or equal to about 3.5m 2 / g, greater than or equal to about 4m 2 / g, greater than or equal to about 4.5m 2 / g, greater than or equal to about 5m 2 / g, greater than or equal to about 10m 2 / g, greater than or equal to about 15m 2 / g, greater than or equal to about 20m 2 / g, greater than or equal to about 25m 2 / g, greater than or equal to about 30m 2 / g, greater than or equal to about 35m 2 / g, or greater than or equal to 40m 2 / g. In some cases, the surface area of ​​the pre-filter layer may be less than or equal to about 45m 2 / g, less than or equal to about 40m2 / g, less than or equal to about 35m 2 / g, less than or equal to about 30m 2 / g, less than or equal to about 25m 2 / g, less than or equal to about 20m 2 / g, less than or equal to about 15m 2 / g, less than or equal to about 10m 2 / g, less than or equal to about 5m 2 / g, less than or equal to about 4.5m 2 / g, less than or equal to about 4m 2 / g, less than or equal to about 3.5m 2 / g, or less than or equal to about 3m 2 It should be understood that combinations of the above reference ranges are possible (e.g., greater than or equal to about 1.75 m 2 / g and less than or equal to about 5.0m 2 / g, greater than or equal to about 5m 2 / g and less than or equal to about 45m 2 / g).

[0032] As defined herein, surface area is measured using a standard BET surface area measurement technique. BET surface area is measured according to the Battery Council International Standard BCIS-03A "Recommended Battery Materials Specifications Valve Regulated Recombinant Batteries", Section 10, "Standard Test Method for Surface Area of ​​Recombinant Battery Separator Mat". According to this technique, the BET surface area is measured via adsorption analysis using a BET surface analyzer (e.g., Micromeritics Gemini III 2375 surface area analyzer) with nitrogen; the sample amount is 0.5 to 0.6 grams in, for example, a 3 / 4" tube; and the sample is degassed at 75°C for at least 3 hours.

[0033] In certain embodiments, the pre-filter layer described herein may have a relatively low solidity. For example, in some embodiments, the solidity of the pre-filter layer may be less than or equal to about 50%, less than or equal to about 40%, less than or equal to about 30%, less than or equal to about 10%, less than or equal to about 5%, less than or equal to about 1%, less than or equal to about 0.5%, less than or equal to about 0.1%, or less than or equal to about 0.05%. In some cases, the solidity of the pre-filter layer may be greater than or equal to about 0.001%, greater than or equal to about 0.005%, greater than or equal to about 0.01%, greater than or equal to about 0.05%, greater than or equal to about 0.1%, greater than or equal to about 0.5%, greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, greater than or equal to about 15%, greater than or equal to about 20%, greater than or equal to about 25%, greater than or equal to about 30%, or greater than or equal to about 40%. It should be understood that combinations of the above reference ranges are possible (e.g., greater than or equal to about 0.001% and less than or equal to about 50%, greater than or equal to about 0.01% and less than or equal to about 25%). Solidity can be determined using the following formula: Solidity = [Basic Weight / (Fiber Density * Thickness)] * 100. Basis weight and thickness can be determined as described herein. Porosity can be derived from solidity according to the following equation: Solidity (%) = 100 - Porosity (%).

[0034] In some embodiments, the pre-filter layer may have a certain particle efficiency. The particle efficiency can be determined by measuring the penetration of certain particles through the layer and / or filter media. The penetration rate (usually expressed as a percentage) is defined as follows:

[0035] Pen=(C / C0)*100

[0036] Where C is the particle concentration after passing through the filter and C0 is the particle concentration before passing through the filter. A typical penetration test involves blowing dioctyl phthalate (DOP) or sodium chloride (NaCl) particles through a filter medium or layer and measuring the percentage of particles that penetrate the filter medium or layer. The penetration and pressure drop values ​​described herein are based on the EN1822:2009 standard for DOP particles and the ASTM D2 986-91 standard for NaCl particles, using an 8130 CertiTest from TSI, Inc. TMThe penetration rate is determined by an automatic filter test unit equipped with a dioctyl phthalate generator for DOP aerosol testing or a sodium chloride generator for NaCl aerosol testing. The average particle size produced by the DOP particle generator is about 0.3 microns in mass average diameter. The average particle size produced by the salt particle generator is 0.26 microns in mass average diameter. The instrument is based on an instantaneous measurement of the pressure drop across the fiber web and the resulting penetration value. The initial penetration rate is first obtained at the beginning of the test and can be used to determine the initial efficiency. All penetration rate values ​​described herein are determined as follows: a continuous load of DOP or NaCl particles is used and the fiber web is 100 cm 2 The upstream face of the layer was subjected to an airflow of 32 L / min over the face area, resulting in a media face velocity of 5.3 cm / sec. The media face velocity is the velocity of the air as it impacts the upstream side of the filter media.

[0037] Particle efficiency is defined as:

[0038] 100-Penetration%

[0039] Since it may be desirable to rate filter media or layers according to the relationship between penetration and pressure drop across the media, or particle efficiency as a function of pressure drop across a media or web, filters may be rated according to a value known as the gamma value. In general, higher gamma values ​​indicate better filtration performance, i.e., high particle efficiency as a function of pressure drop. The gamma value is expressed according to the following formula:

[0040] γ=(-log(initial DOP penetration % / 100) / pressure drop, Pa)×100×9.8, which is equivalent to

[0041] γ=(-log(initial DOP penetration % / 100) / pressure drop, mmH2O)×100

[0042] As described above, DOP penetration percentage is based on the percentage of particles that pass through the filter media or layer. In the case of reduced DOP penetration percentage (i.e., increased particle efficiency) (when particles are less able to pass through the filter media or layer), γ increases. In the case of reduced pressure drop (i.e., low resistance to fluid flow through the filter), γ increases. These general relationships between DOP penetration, pressure drop, and / or γ assume that other characteristics remain unchanged.

[0043] The particle efficiency of the pre-filter layer may be less than that of the second layer and may vary depending on the application. For example, in some embodiments, the initial DOP efficiency of the pre-filter layer may be greater than or equal to about 5%, greater than or equal to about 10%, greater than or equal to about 20%, greater than or equal to about 30%, greater than or equal to about 40%, greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 65%, greater than or equal to about 70%, greater than or equal to about 75%, greater than or equal to about 80%, greater than or equal to about 85%, or greater than or equal to about 90%. In some cases, the initial DOP efficiency of the pre-filter layer may be less than or equal to about 90%, less than or equal to about 85%, less than or equal to about 80%, less than or equal to about 75%, less than or equal to about 70%, less than or equal to about 65%, less than or equal to about 60%, less than or equal to about 50%, less than or equal to about 40%, less than or equal to about 30%, less than or equal to about 20%, or less than or equal to about 10%. It should be understood that combinations of the above reference ranges are possible. The initial DOP efficiency can be measured according to EN1822. In some embodiments, for certain applications (e.g., high efficiency, ultra-high efficiency, HEPA, ULPA), the initial DOP efficiency of the pre-filter layer may be greater than or equal to about 10% and less than or equal to about 90%, or greater than or equal to about 15% and less than or equal to about 85%. In other applications (e.g., low efficiency, HVAC), the initial DOP efficiency of the pre-filter layer may be greater than or equal to about 5% and less than or equal to about 85%, or greater than or equal to about 10% and less than or equal to about 60%.

[0044] In some embodiments, the range of the initial NaCl particle efficiency of the pre-filter layer can be as described above for the initial DOP efficiency of the pre-filter layer. For example, in some embodiments, the initial NaCl particle efficiency of the pre-filter layer can be greater than or equal to about 5%, greater than or equal to about 10%, greater than or equal to about 20%, greater than or equal to about 30%, greater than or equal to about 40%, greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 65%, greater than or equal to about 70%, greater than or equal to about 75%, greater than or equal to about 80%, greater than or equal to about 85%, or greater than or equal to about 90%. In some cases, the initial NaCl particle efficiency of the pre-filter layer may be less than or equal to about 90%, less than or equal to about 85%, less than or equal to about 80%, less than or equal to about 75%, less than or equal to about 70%, less than or equal to about 65%, less than or equal to about 60%, less than or equal to about 50%, less than or equal to about 40%, less than or equal to about 30%, less than or equal to about 20%, or less than or equal to about 10%. It should be understood that combinations of the above reference ranges are possible. In some embodiments, for certain applications (e.g., high efficiency, ultra-high efficiency, HEPA, ULPA), the initial NaCl particle efficiency of the pre-filter layer may be greater than or equal to about 10% and less than or equal to about 90%, or greater than or equal to about 15% and less than or equal to about 85%. In other applications (e.g., low efficiency, HVAC), the initial NaCl particle efficiency of the pre-filter layer may be greater than or equal to about 5% and less than or equal to about 85%, or greater than or equal to about 10% and less than or equal to about 60%. Initial NaCl particle efficiency can be determined using ASTM D2 986-91.

[0045] Generally, the pre-filter layer can be designed to produce a filter medium with a relatively high gamma. In some cases, the gamma of the pre-filter layer can be greater than or equal to about 3, greater than or equal to about 5, greater than or equal to about 8, greater than or equal to about 10, greater than or equal to about 12, greater than or equal to about 15, greater than or equal to about 20, greater than or equal to about 30, greater than or equal to about 40, greater than or equal to about 50, or greater than or equal to about 60. In some cases, the gamma of the pre-filter layer can be less than or equal to about 75, less than or equal to about 60, less than or equal to about 50, less than or equal to about 40, less than or equal to about 30, less than or equal to about 25, less than or equal to about 20, less than or equal to about 15, or less than or equal to about 10. It should be understood that combinations of the above referenced ranges are possible (e.g., greater than or equal to about 3 and less than or equal to about 75, greater than or equal to about 8 and less than or equal to about 75, greater than or equal to about 20 and less than or equal to about 75).

[0046] It should be understood that the gamma, DOP efficiency, and NaCl efficiency values ​​described herein can be obtained using uncharged layers such that particle separation is substantially or solely mechanical. For example, the layers or filter media can be discharged or otherwise treated such that only mechanical particle separation occurs. In other embodiments, the layers or filter media may be charged, and particle separation may not be substantially or solely mechanical particle separation.

[0047] In some embodiments, the pre-filter layer can have a relatively low pressure drop. For example, in some embodiments, the pressure drop can be less than or equal to about 35 mmH2O, less than or equal to about 30 mmH2O, less than or equal to about 25 mmH2O, less than or equal to about 20 mmH2O, less than or equal to about 15 mmH2O, less than or equal to about 10 mmH2O, less than or equal to about 5 mmH2O, less than or equal to about 1 mmH2O, or less than or equal to about 0.5 mmH2O. In some cases, the pressure drop can be greater than or equal to about 0.1 mmH2O, greater than or equal to about 0.3 mmH2O, greater than or equal to about 0.6 mmH2O, greater than or equal to about 1 mmH2O, greater than or equal to about 5 mmH2O, greater than or equal to about 10 mmH2O, greater than or equal to about 15 mmH2O, greater than or equal to about 20 mmH2O, or greater than or equal to about 25 mmH2O. It should be understood that all combinations of the above reference ranges are possible (e.g., greater than or equal to about 0.1 mm H2O and less than or equal to about 35 mm H2O, greater than or equal to about 0.6 mm H2O and less than or equal to about 15 mm H2O). Other ranges and values ​​of pressure drop are also possible. As used herein, pressure drop can be measured as described above.

[0048] In some embodiments, the air permeability of the pre-filter layer may be less than or equal to about 1,400 ft 3 / minute / foot 2In some cases, the air permeability of the pre-filter layer may be greater than or equal to about 2 CFM, greater than or equal to about 5 CFM, greater than or equal to about 8 CFM, greater than or equal to about 10 CFM, greater than or equal to about 25 CFM, greater than or equal to about 50 CFM, greater than or equal to about 100 CFM, greater than or equal to about 25 CFM, greater than or equal to about 50 CFM, greater than or equal to about 100 CFM, greater than or equal to about 250 CFM, greater than or equal to about 500 CFM, greater than or equal to about 750 CFM, greater than or equal to about 1,000 CFM, or greater than or equal to about 1,250 CFM. It is understood that all combinations of the above referenced ranges are possible (eg, greater than or equal to about 2 CFM and less than or equal to about 1,400 CFM, greater than or equal to about 8 CFM and less than or equal to about 300 CFM). Other ranges are also possible.

[0049] As used herein, air permeability is measured according to standard ASTM D737-75. In an air permeability test device, the sample is clamped at a pressure of at least 50 + / - 5 N (without deforming the sample and with minimal edge gaps) to provide a 38.3 cm 2 The test head (called the nozzle) is placed over a circular test area of ​​12.5 mm H2O. A steady stream of air is then supplied vertically to the sample test area, providing a pressure differential of 12.5 mm H2O across the material being tested. This pressure differential is recorded from a pressure gauge or manometer connected to the test head. A flow meter or volume counter is used to measure the pressure in feet. 3 / minute / foot 2 To measure the air permeability through the test area. The Frazier air permeability tester is an exemplary device for such measurement.

[0050] In some embodiments, the mean flow pore size of the pre-filter layer may be greater than or equal to about 0.5 microns, greater than or equal to about 1 micron, greater than or equal to about 5 microns, greater than or equal to about 10 microns, greater than or equal to about 20 microns, greater than or equal to about 30 microns, or greater than or equal to about 40 microns. In some cases, the mean flow pore size of the pre-filter layer may be less than or equal to about 50 microns, less than or equal to about 40 microns, less than or equal to about 30 microns, less than or equal to about 20 microns, less than or equal to about 10 microns, less than or equal to about 5 microns, less than or equal to about 2 microns, or less than or equal to about 1 micron. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 0.5 microns and less than or equal to about 50 microns, greater than or equal to about 1 micron and less than or equal to about 30 microns). Other values ​​of the mean flow pore size are also possible. The mean flow pore size can be determined according to standard ASTM F316-03.

[0051] In some embodiments, the pre-filter layer may be pleated. In some such embodiments, the pre-filter layer may have one or more of the mechanical properties (e.g., Mullenburst, elongation, tensile strength, stiffness) described below with respect to the backing layer (e.g., a pleated backing layer).

[0052] In some embodiments, the filter medium 10 may include a second layer 20. The second layer may be designed to improve the particle efficiency (e.g., initial DOP efficiency, initial NaCl efficiency) of the filter medium. In some such embodiments, the second layer may be a single layer or include multiple sublayers. For example, the second layer may include about 2 to about 10, about 2 to about 8, about 2 to about 6, or about 2 to about 4 sublayers. In certain embodiments, the second layer may include 2 or 3 sublayers. In some embodiments, one or more sublayers may be designed to be independent of another sublayer. In some cases, all sublayers in the second layer may be independent. In other embodiments, one or more sublayers may not be independent.

[0053] Whether the second layer is a single layer or includes multiple sub-layers, the second layer 20 (e.g., an efficiency layer) can have a relatively small median fiber diameter. In other embodiments, the second layer may not include fibers (e.g., when the second layer is a synthetic membrane layer). As described below, the second layer can have a greater particle efficiency than the pre-filter layer.

[0054] In some embodiments, the median fiber diameter of the second layer can be less than or equal to about 1 micron, less than or equal to about 0.8 microns, less than or equal to about 0.5 microns, less than or equal to about 0.2 microns, less than or equal to about 0.1 microns, less than or equal to about 0.08 microns, less than or equal to about 0.05 microns, less than or equal to about 0.04 microns, less than or equal to about 0.03 microns, or less than or equal to about 0.02 microns. In some cases, the median fiber diameter can be greater than or equal to about 0.01 microns, greater than or equal to about 0.03 microns, greater than or equal to about 0.05 microns, greater than or equal to about 0.07 microns, greater than or equal to about 0.1 microns, greater than or equal to about 0.2 microns, greater than or equal to about 0.3 microns, greater than or equal to about 0.4 microns, greater than or equal to about 0.5 microns, greater than or equal to about 0.8 microns, or greater than or equal to about 1 micron. Combinations of the above-referenced ranges are also possible (e.g., greater than or equal to about 0.1 microns and less than or equal to about 1 micron, greater than or equal to about 0.07 microns and less than or equal to about 0.5 microns). Other values ​​of the median fiber diameter are also possible. In some embodiments, the average diameter of the fibers may fall within the above-referenced ranges for the median fiber diameter.

[0055] As described in more detail below, the second layer (e.g., efficiency layer) can include fiber types such as synthetic fibers, glass fibers, and / or cellulose fibers. In some cases, the second layer can include a relatively high weight percentage of synthetic fibers (e.g., 100 weight %). In some such embodiments, the second layer can include relatively few or no glass fibers. In other embodiments, the second layer can include a relatively high weight percentage of glass fibers (e.g., 100 weight %).

[0056] Generally, the efficiency of the second layer is greater than that of the pre-filter layer and can vary depending on the application. For example, in some embodiments, the DOP efficiency of the second layer can be greater than or equal to about 10%, greater than or equal to about 20%, greater than or equal to about 35%, greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 70%, greater than or equal to about 80%, greater than or equal to about 90%, greater than or equal to about 95%, greater than or equal to about 97%, greater than or equal to about 99%, greater than or equal to about 99.5%, greater than or equal to about 99.9%, greater than or equal to about 99.95%, greater than or equal to about 99.99%, or greater than or equal to about 99.995%. In some cases, the initial DOP efficiency of the second layer may be less than or equal to about 99.99999%, less than or equal to about 99.999%, less than or equal to about 99.999%, less than or equal to about 99.997%, less than or equal to about 99.995%, less than or equal to about 99.9%, less than or equal to about 99.5%, less than or equal to about 99%, less than or equal to about 98%, less than or equal to about 97%, less than or equal to about 95%, less than or equal to about 90%, less than or equal to about 85%, less than or equal to about 75%, less than or equal to about 60%, less than or equal to about 50%, less than or equal to about 40%, less than or equal to about 30%, less than or equal to about 20%, or less than or equal to about 10%. It should be understood that combinations of the above referenced ranges are possible (e.g., greater than or equal to about 60% and less than or equal to about 99.99999%). Initial DOP efficiency may be measured according to EN1822 as described above.

[0057] In some embodiments, for certain applications, the initial DOP efficiency of the second layer may be greater than or equal to about 70% and less than or equal to about 99.99%, or greater than or equal to about 80% and less than or equal to about 99.99999%. In some applications, the initial DOP efficiency of the second layer may be greater than or equal to about 80% and less than or equal to about 99.99999%, or greater than or equal to about 90% and less than or equal to about 99.99999%. In certain applications (e.g., low particle efficiency, HVAC), the initial DOP efficiency of the second layer may be greater than or equal to about 10% and less than or equal to about 90%, or greater than or equal to about 35% and less than or equal to about 90%.

[0058] In some embodiments, the range of the NaCl particle efficiency of the second layer may be as described above with respect to the initial DOP efficiency of the second layer. Other ranges and values ​​of DOP and NaCl particle filtration particle efficiency are also possible. For example, in some embodiments, the initial NaCl efficiency of the second layer may be greater than or equal to about 10%, greater than or equal to about 20%, greater than or equal to about 35%, greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 70%, greater than or equal to about 80%, greater than or equal to about 90%, greater than or equal to about 95%, greater than or equal to about 97%, greater than or equal to about 99%, greater than or equal to about 99.5%, greater than or equal to about 99.9%, greater than or equal to about 99.95%, greater than or equal to about 99.99%, or greater than or equal to about 99.995%. In some cases, the initial NaCl efficiency of the second layer may be less than or equal to about 99.99999%, less than or equal to about 99.999%, less than or equal to about 99.999%, less than or equal to about 99.997%, less than or equal to about 99.995%, less than or equal to about 99.9%, less than or equal to about 99.5%, less than or equal to about 99%, less than or equal to about 98%, less than or equal to about 97%, less than or equal to about 95%, less than or equal to about 90%, less than or equal to about 85%, less than or equal to about 75%, less than or equal to about 60%, less than or equal to about 50%, less than or equal to about 40%, less than or equal to about 30%, less than or equal to about 20%, or less than or equal to about 10%. It should be understood that combinations of the above reference ranges are possible (e.g., greater than or equal to about 60% and less than or equal to about 99.99999%). The initial NaCl efficiency can be determined as described above.

[0059] Generally, the second layer can have a relatively high gamma. In some cases, the gamma of the second layer can be greater than or equal to about 7, greater than or equal to about 10, greater than or equal to about 12, greater than or equal to about 15, greater than or equal to about 20, greater than or equal to about 30, greater than or equal to about 40, greater than or equal to about 50, or greater than or equal to about 60. In some cases, the gamma of the second layer can be less than or equal to about 75, less than or equal to about 60, less than or equal to about 50, less than or equal to about 40, less than or equal to about 30, less than or equal to about 25, less than or equal to about 20, less than or equal to about 15, or less than or equal to about 10. It should be understood that combinations of the above referenced ranges are possible (e.g., greater than or equal to about 7 and less than or equal to about 75, greater than or equal to about 10 and less than or equal to about 75, greater than or equal to about 20 and less than or equal to about 75).

[0060] In some embodiments, the pressure drop of the second layer described herein may be greater than or equal to about 0.5 mm H2O, greater than or equal to about 1 mm H2O, greater than or equal to about 5 mm H2O, greater than or equal to about 10 mm H2O, greater than or equal to about 25 mm H2O, greater than or equal to about 50 mm H2O, greater than or equal to about 75 mm H2O, greater than or equal to about 100 mm H2O, or greater than or equal to about 125 mm H2O. In some cases, the pressure drop may be less than or equal to about 150 mm H2O, less than or equal to about 125 mm H2O, less than or equal to about 100 mm H2O, less than or equal to about 90 mm H2O, less than or equal to about 75 mm H2O, less than or equal to about 50 mm H2O, less than or equal to about 25 mm H2O, or less than or equal to about 10 mm H2O. It should be understood that combinations of the above reference ranges are also possible (e.g., greater than or equal to about 0.5 mmH2O and less than or equal to about 150 mmH2O, greater than or equal to about 1 mmH2O and less than or equal to about 90 mmH2O). Other ranges and values ​​of pressure drop are also possible. The pressure drop can be determined as described above.

[0061] In some embodiments, the basis weight of the second layer may be less than or equal to about 75 g / m 2 , less than or equal to about 50g / m 2 , less than or equal to about 35g / m 2 , less than or equal to about 25g / m 2 , less than or equal to about 20g / m 2 , less than or equal to about 15g / m 2 , less than or equal to about 10g / m 2 , less than or equal to about 5g / m 2 , less than or equal to about 1g / m 2 , less than or equal to about 0.8g / m 2 , less than or equal to about 0.5g / m 2 , less than or equal to about 0.1g / m 2 , less than or equal to about 0.05g / m 2 , or less than or equal to about 0.01 g / m 2 In some cases, the basis weight of the second layer can be greater than or equal to about 0.005 g / m 2 , greater than or equal to about 0.01 g / m 2 , greater than or equal to about 0.05 g / m 2 , greater than or equal to about 0.08 g / m 2 , greater than or equal to about 0.1 g / m 2 , greater than or equal to about 0.2g / m 2 , greater than or equal to about 0.5 g / m 2, greater than or equal to about 0.8 g / m 2 , greater than or equal to about 1g / m 2 , greater than or equal to about 5g / m 2 , greater than or equal to about 10g / m 2 , greater than or equal to about 15g / m 2 , greater than or equal to about 20g / m 2 , greater than or equal to about 30g / m 2 , greater than or equal to about 40g / m 2 , greater than or equal to about 50g / m 2 , or greater than or equal to about 60 g / m 2 Combinations of the above-referenced ranges are also possible (e.g., greater than or equal to about 0.005 g / m 2 and less than or equal to about 75g / m 2 , greater than or equal to about 0.01 g / m 2 and less than or equal to about 50g / m 2 ). Other values ​​of the basis weight are also possible. The basis weight is determined according to standard ISO 536.

[0062] In some embodiments, the thickness of the second layer may be less than or equal to about 5 mm, less than or equal to about 4.5 mm, less than or equal to about 4 mm, less than or equal to about 3.5 mm, less than or equal to about 3 mm, less than or equal to about 2.5 mm, less than or equal to about 2 mm, less than or equal to about 1.5 mm, less than or equal to about 1 mm, less than or equal to about 0.5 mm, less than or equal to about 0.1 mm, less than or equal to about 0.05 mm, or less than or equal to about 0.01 mm. In some cases, the thickness of the second layer may be greater than or equal to about 0.001 mm, greater than or equal to about 0.005 mm, greater than or equal to about 0.01 mm, greater than or equal to about 0.05 mm, greater than or equal to about 0.08 mm, greater than or equal to about 0.1 mm, greater than or equal to about 0.5 mm, greater than or equal to about 1 mm, greater than or equal to about 1.5 mm, greater than or equal to about 2 mm, greater than or equal to about 2.5 mm, greater than or equal to about 3 mm, greater than or equal to about 3.5 mm, or greater than or equal to about 4 mm. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 0.005 mm and less than or equal to about 5 mm, greater than or equal to about 0.01 mm and less than or equal to about 1 mm). Other values ​​of the average thickness are also possible. The thickness may be measured according to standard ISO 534 at 2.65 pounds per inch 2 Next measurement.

[0063] In some embodiments, the mean flow pore size of the second layer may be greater than or equal to about 0.05 microns, greater than or equal to about 0.1 microns, greater than or equal to about 0.15 microns, greater than or equal to about 0.2 microns, greater than or equal to about 0.5 microns, greater than or equal to about 1 micron, greater than or equal to about 10 microns, greater than or equal to about 20 microns, or greater than or equal to about 30 microns. In some cases, the mean flow pore size of the second layer may be less than or equal to about 40 microns, less than or equal to about 30 microns, less than or equal to about 20 microns, less than or equal to about 10 microns, less than or equal to about 5 microns, less than or equal to about 2 microns, or less than or equal to about 1 micron. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 0.05 microns and less than or equal to about 40 microns, greater than or equal to about 0.1 microns and less than or equal to about 30 microns). Other values ​​of the mean flow pore size are also possible. The mean flow pore size can be determined according to standard ASTM F316-03.

[0064] In some embodiments, the solidity of the second layer may be less than or equal to about 50%, less than or equal to about 40%, less than or equal to about 30%, less than or equal to about 10%, less than or equal to about 5%, less than or equal to about 1%, less than or equal to about 0.5%, less than or equal to about 0.1%, or less than or equal to about 0.05%. In some cases, the solidity of the second layer may be greater than or equal to about 0.001%, greater than or equal to about 0.005%, greater than or equal to about 0.01%, greater than or equal to about 0.05%, greater than or equal to about 0.1%, greater than or equal to about 0.5%, greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, greater than or equal to about 15%, greater than or equal to about 20%, greater than or equal to about 25%, greater than or equal to about 30%, or greater than or equal to about 40%. It will be understood that combinations of the above-referenced ranges are possible (eg, greater than or equal to about 0.001% and less than or equal to about 50%, greater than or equal to about 0.01% and less than or equal to about 25%). Solidity may be determined as described above.

[0065] In certain embodiments, the second layer described herein can have a relatively high surface area. For example, in some embodiments, the surface area of ​​the second layer can be greater than or equal to about 3 m 2 / g, greater than or equal to about 3.5m 2 / g, greater than or equal to about 4m 2 / g, greater than or equal to about 4.5m 2 / g, greater than or equal to about 5m 2 / g, greater than or equal to about 10m 2 / g, greater than or equal to about 15m 2 / g, greater than or equal to about 20m 2 / g, greater than or equal to about 25m2 / g, greater than or equal to about 30m 2 / g, greater than or equal to about 35m 2 / g, or greater than or equal to 40m 2 / g. In some cases, the surface area of ​​the second layer can be less than or equal to about 50m 2 / g, less than or equal to about 45m 2 / g, less than or equal to about 40m 2 / g, less than or equal to about 35m 2 / g, less than or equal to about 30m 2 / g, less than or equal to about 25m 2 / g, less than or equal to about 20m 2 / g, less than or equal to about 15m 2 / g, less than or equal to about 10m 2 / g, or less than or equal to about 5m 2 It should be understood that combinations of the above reference ranges are possible (e.g., greater than or equal to about 3 m 2 / g and less than or equal to about 50m 2 / g). The surface area can be determined as described above.

[0066] In some embodiments, the second layer can be a synthetic membrane layer. In these embodiments, the membrane layer can function as a filtration layer (e.g., an efficiency layer). It should be understood that although the description herein generally focuses on filter media that include a fibrous second layer, the description also applies to filter media that include a membranous second layer. For example, in Figures 1A to 1D In the embodiment shown, the second layer 20 may be a membrane filtration layer rather than a fibrous filtration layer as described above.

[0067] Generally, any suitable material can be used to form the membrane layer. Suitable materials include synthetic materials such as polytetrafluoroethylene (PTFE) (e.g., expanded or unexpanded), polyvinylidene fluoride (PVDF), polyethylene (e.g., linear low density polyethylene, ultra-high molecular weight polyethylene), polypropylene, polycarbonate, polyester, nitrocellulose mixed ester, polyether sulfone, cellulose acetate, polyimide, polyvinylidene fluoride, polyacrylonitrile, polysulfone, polyether sulfone and polyamide (e.g., nylon), etc. In some embodiments, the membrane may include a fluorinated polymer such as PVDF or PTFE.

[0068] The film layer can be a single layer film or a multilayer film. In the embodiment using a multilayer film, different layers can have different compositions. Generally, the film layer can be formed by suitable methods known in the art.

[0069] The membrane layer has a plurality of holes. The hole allows the fluid to pass through while the polluted particles are captured on the membrane. In some embodiments, the mean flow pore size of the membrane layer may be greater than or equal to about 0.1 micron, greater than or equal to about 0.15 micron, greater than or equal to about 0.2 micron, greater than or equal to about 0.5 micron, greater than or equal to about 1 micron, greater than or equal to about 10 microns, greater than or equal to about 20 microns, greater than or equal to about 30 microns, or greater than or equal to about 40 microns. In some cases, the mean flow pore size of the membrane may be less than or equal to about 50 microns, less than or equal to about 40 microns, less than or equal to about 30 microns, less than or equal to about 20 microns, less than or equal to about 10 microns, less than or equal to about 5 microns, less than or equal to about 2 microns, or less than or equal to about 1 micron. The combination of the above reference range is also possible (for example, greater than or equal to about 0.1 micron and less than or equal to about 50 microns, greater than or equal to about 0.5 micron and less than or equal to about 40 microns). Other values ​​of the mean pore size are also possible. The mean flow pore size can be determined according to standard ASTM F316-08 Method B, BS 6140.

[0070] In certain embodiments, the second layer (e.g., efficiency layer) may comprise a single layer. However, in other embodiments, the second layer may comprise more than one layer (i.e., sublayer) to form a multilayer structure. When the layer comprises more than one sublayer, the multiple sublayers may be different based on certain features (e.g., air permeability, basis weight, fiber type, and / or particle efficiency). In some cases, the multiple sublayers may be independent and combined by any suitable method (e.g., lamination, point bonding, or finishing). In some embodiments, the sublayers are substantially connected to each other (e.g., by lamination, point bonding, thermal point bonding, ultrasonic bonding, calendering, use of adhesives (e.g., glue nets) and / or co-pleating). In some cases, the sublayers may be formed as composite layers (e.g., by a wet-laid web process).

[0071] As described herein, the filter media may include a backing layer (e.g., a pleatable backing layer). In some embodiments, the backing layer may have certain enhanced mechanical properties, such as tensile strength, Mullen bursting strength, and tensile elongation. In some such embodiments, the backing layer (e.g., a pleatable backing layer) may be relatively strong and may facilitate pleating. For example, the backing layer may provide sufficient rigidity so that the filter media can be pleated into a configuration comprising sharp, well-defined peaks that can maintain a stable configuration during use.

[0072] In some embodiments, the tensile strength of the backing layer (e.g., a pleatable backing layer) in the machine direction (MD) may be greater than or equal to about 2 pounds / inch, greater than or equal to about 4 pounds / inch, greater than or equal to about 5 pounds / inch, greater than or equal to about 10 pounds / inch, greater than or equal to about 15 pounds / inch, greater than or equal to about 20 pounds / inch, greater than or equal to about 30 pounds / inch, greater than or equal to about 40 pounds / inch, greater than or equal to about 50 pounds / inch, or greater than or equal to about 60 pounds / inch. In some cases, the tensile strength in the machine direction may be less than or equal to about 70 pounds / inch, less than or equal to about 60 pounds / inch, less than or equal to about 50 pounds / inch, less than or equal to about 40 pounds / inch, less than or equal to about 30 pounds / inch, less than or equal to about 20 pounds / inch, less than or equal to about 10 pounds / inch, or less than or equal to about 5 pounds / inch. Combinations of the above referenced ranges are also possible (e.g., greater than or equal to about 2 pounds per inch and less than or equal to about 70 pounds per inch, greater than or equal to about 4 pounds per inch and less than or equal to about 60 pounds per inch). Other values ​​of tensile strength in the machine direction are also possible. The tensile strength in the machine direction can be determined according to standard T494 om-96 using a test span of 4 inches and a jaw separation speed of 1 inch per minute.

[0073] In some embodiments, the tensile strength of the backing layer (e.g., a pleatable backing layer) in the cross direction (CD) may be greater than or equal to about 1 lb / in, greater than or equal to about 2 lb / in, greater than or equal to about 5 lb / in, greater than or equal to about 10 lb / in, greater than or equal to about 15 lb / in, greater than or equal to about 1 lb / in, greater than or equal to about 20 lb / in, greater than or equal to about 30 lb / in, greater than or equal to about 40 lb / in, greater than or equal to about 50 lb / in, or greater than or equal to about 60 lb / in. In some cases, the tensile strength in the cross direction may be less than or equal to about 70 lb / in, less than or equal to about 60 lb / in, less than or equal to about 50 lb / in, less than or equal to about 40 lb / in, less than or equal to about 30 lb / in, less than or equal to about 20 lb / in, less than or equal to about 10 lb / in, or less than or equal to about 5 lb / in. Combinations of the above referenced ranges are also possible (e.g., greater than or equal to about 1 lb / inch and less than or equal to about 70 lb / inch, greater than or equal to about 2 lb / inch and less than or equal to about 40 lb / inch). Other values ​​of tensile strength in the transverse direction are also possible. The tensile strength in the transverse direction can be determined according to standard T494 om-96 using a 4 inch test span and a jaw separation speed of 1 inch / minute.

[0074] In some embodiments, the Mullen burst strength of the backing layer (e.g., a pleatable backing layer) may be greater than or equal to about 5 psi, greater than or equal to about 10 psi, greater than or equal to about 25 psi, greater than or equal to about 50 psi, greater than or equal to about 75 psi, greater than or equal to about 100 psi, greater than or equal to about 125 psi, greater than or equal to about 150 psi, greater than or equal to about 175 psi, greater than or equal to about 200 psi, greater than or equal to about 225 psi, greater than or equal to about 250 psi, or greater than or equal to about 275 psi. In some cases, the Mullen bursting strength may be less than or equal to about 300 psi, less than or equal to about 275 psi, less than or equal to about 250 psi, less than or equal to about 225 psi, less than or equal to about 200 psi, less than or equal to about 175 psi, less than or equal to about 150 psi, less than or equal to about 125 psi, less than or equal to about 100 psi, less than or equal to about 75 psi, less than or equal to about 50 psi, or less than or equal to about 25 psi. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 5 psi and less than or equal to about 300 psi, greater than or equal to about 10 psi and less than or equal to about 200 psi). Other values ​​of the Mullen bursting strength are also possible. The Mullen bursting strength can be determined according to standard T403 om-91.

[0075] In some embodiments, the tensile elongation at break of the backing layer (e.g., a pleatable backing layer) in the machine direction may be greater than or equal to about 0.1%, greater than or equal to about 0.3%, greater than or equal to about 0.5%, greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, greater than or equal to about 15%, or greater than or equal to about 18%. In some cases, the tensile elongation at break in the machine direction may be less than or equal to about 20%, less than or equal to about 18%, less than or equal to about 15%, less than or equal to about 10%, less than or equal to about 5%, less than or equal to about 1%, or less than or equal to about 0.5%. Combinations of the above referenced ranges are also possible (e.g., greater than or equal to about 0.1% and less than or equal to about 20%, greater than or equal to about 0.3% and less than or equal to about 5%). Other values ​​of the tensile elongation at break in the machine direction are also possible. Tensile elongation at break in the machine direction may be determined according to standard T494 om-96 using a test span of 4 inches and a nip separation speed of 1 inch / minute.

[0076] In some embodiments, the tensile elongation at break of the backing layer (e.g., a pleatable backing layer) in the transverse direction may be greater than or equal to about 0.1%, greater than or equal to about 0.3%, greater than or equal to about 0.5%, greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, greater than or equal to about 15%, or greater than or equal to about 18%. In some cases, the tensile elongation at break in the transverse direction may be less than or equal to about 20%, less than or equal to about 18%, less than or equal to about 15%, less than or equal to about 10%, less than or equal to about 5%, less than or equal to about 1%, or less than or equal to about 0.5%. Combinations of the above referenced ranges are also possible (e.g., greater than or equal to about 0.1% and less than or equal to about 20%, greater than or equal to about 0.3% and less than or equal to about 5%). Other values ​​of the tensile elongation at break in the transverse direction are also possible. The tensile elongation at break in the transverse direction may be determined according to standard T494 om-96 using a test span of 4 inches and a jaw separation speed of 1 inch / minute.

[0077] The backing layer (e.g., a pleated backing layer) may have a relatively high stiffness. For example, in some embodiments, the stiffness of the backing layer may be greater than or equal to about 400gu, greater than or equal to about 500gu, greater than or equal to about 750gu, greater than or equal to about 1,000gu, greater than or equal to about 1,500gu, greater than or equal to about 2,000gu, greater than or equal to about 2,500gu, greater than or equal to about 3,000gu, or greater than or equal to about 3,500gu. In some embodiments, the stiffness of the backing layer may be less than or equal to about 4,000gu, less than or equal to about 3,500gu, less than or equal to about 3,000gu, less than or equal to about 2,500gu, less than or equal to about 2,000gu, less than or equal to about 1,500gu, less than or equal to about 1,000gu, less than or equal to about 750gu, or less than or equal to about 500gu. Combinations of the above referenced ranges are also possible (e.g., greater than or equal to about 400 gu and less than or equal to about 4,000 gu, greater than or equal to about 500 gu and less than or equal to about 2,500 gu). Other values ​​of stiffness are also possible. Stiffness can be determined in accordance with TAPPI T543 om-94 based on the Gurley stiffness (bending resistance) of the filter media in the machine direction, which is reported in gu (equivalent to milligrams).

[0078] In some embodiments, the backing layer (e.g., a pleated backing layer) may include fibers having a relatively large diameter. For example, in some embodiments, the median fiber diameter of the backing layer (e.g., a pleated backing layer) may be greater than or equal to about 3 microns, greater than or equal to about 5 microns, greater than or equal to about 7 microns, greater than or equal to about 10 microns, greater than or equal to about 25 microns, greater than or equal to about 40 microns, greater than or equal to about 55 microns, greater than or equal to about 70 microns, or greater than or equal to about 85 microns. In some cases, the median fiber diameter may be less than or equal to about 100 microns, less than or equal to about 80 microns, less than or equal to about 60 microns, less than or equal to about 40 microns, less than or equal to about 20 microns, less than or equal to about 10 microns, or less than or equal to about 5 microns. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 3 microns and less than or equal to about 100 microns, greater than or equal to about 7 microns and less than or equal to about 60 microns). Other values ​​of the median fiber diameter are also possible. In some embodiments, the average diameter of the fibers may fall within the above referenced ranges for median fiber diameters.

[0079] The thickness of the backing layer (e.g., a pleated backing layer) can be selected as desired. For example, in some embodiments, the thickness of the backing layer can be greater than or equal to about 0.1 mm, greater than or equal to about 0.5 mm, greater than or equal to about 1 mm, greater than or equal to about 3 mm, greater than or equal to about 5 mm, greater than or equal to about 8 mm, greater than or equal to about 10 mm, or greater than or equal to about 12 mm. In some cases, the thickness of the backing layer can be less than or equal to about 15 mm, less than or equal to about 12 mm, less than or equal to about 10 mm, less than or equal to about 8 mm, less than or equal to about 5 mm, or less than or equal to about 2 mm. A combination of the above reference ranges is also possible (e.g., greater than or equal to about 0.1 mm and less than or equal to about 15 mm, greater than or equal to about 0.1 mm and less than or equal to about 5 mm). Other values ​​of average thickness are also possible. The thickness can be measured according to standard ISO 534 at 2.65 pounds per inch 2 Next confirm.

[0080] In some embodiments, the basis weight of the backing layer (eg, a pleatable backing layer) may be greater than or equal to about 20 g / m 2 , greater than or equal to about 30g / m 2 , greater than or equal to about 50g / m 2 , greater than or equal to about 75g / m 2 , greater than or equal to about 100g / m 2 , greater than or equal to about 125g / m 2 , greater than or equal to about 150g / m 2 , greater than or equal to about 175g / m 2, greater than or equal to about 200g / m 2 , greater than or equal to about 225g / m 2 , greater than or equal to about 250g / m 2 , or greater than or equal to about 275 g / m 2 In some cases, the basis weight of the backing layer can be less than or equal to about 300 g / m 2 , less than or equal to about 275g / m 2 , less than or equal to about 250g / m 2 , less than or equal to about 225g / m 2 , less than or equal to about 200g / m 2 , less than or equal to about 175g / m 2 , less than or equal to about 150 / m 2 , less than or equal to about 125g / m 2 , less than or equal to about 100g / m 2 , less than or equal to about 75g / m 2 , less than or equal to about 50g / m 2 , or less than or equal to about 25g / m 2 Combinations of the above-referenced ranges are also possible (e.g., greater than or equal to about 20 g / m 2 and less than or equal to about 300 g / m 2 , greater than or equal to about 50g / m 2 and less than or equal to about 150g / m 2 ). Other values ​​of basis weight are also possible. The basis weight can be determined according to standard ISO 536.

[0081] In some embodiments, the backing layer (e.g., a pleated backing layer) can have a relatively low DOP efficiency. For example, in some embodiments, the backing layer can have a DOP efficiency of less than or equal to about 20%, a DOP efficiency of less than or equal to about 15%, a DOP efficiency of less than or equal to about 10%, a DOP efficiency of less than or equal to about 5%, a DOP efficiency of less than or equal to about 2%, or a DOP efficiency of less than or equal to about 1%. The DOP efficiency can be measured as described above.

[0082] In some embodiments, the backing layer (e.g., a pleated backing layer) can have a relatively high air permeability. For example, in some embodiments, the air permeability of the backing layer can be greater than or equal to about 50 ft3 / 32 in. 3 / minute / foot 2(CFM), about 75 CFM or more, about 100 CFM or more, about 250 CFM or more, about 500 CFM or more, about 1,000 CFM or more, about 1,250 CFM or more, about 1,500 CFM or more, or about 1,750 CFM or more. In some cases, the air permeability of the backing layer (e.g., a pleatable backing layer) may be less than or equal to about 2000 CFM, less than or equal to about 1,750 CFM, less than or equal to about 1500 CFM, less than or equal to about 1,250 CFM, less than or equal to about 1,000 CFM, less than or equal to about 750 CFM, less than or equal to about 500 CFM, less than or equal to about 250 CFM, less than or equal to about 100 CFM, or less than or equal to about 75 CFM. It should be understood that all combinations of the above referenced ranges are possible (e.g., greater than or equal to about 50 CFM and less than or equal to about 2000 CFM, greater than or equal to about 100 CFM and less than or equal to about 1,00 CFM). Other ranges are also possible. Air permeability can be determined according to ASTM D737-75 as described above.

[0083] As noted above, the filter media 10 described herein can be used in a wide range of applications that may require a certain level of particle efficiency. For example, the filter media can meet the highest EN1822 filter classification (e.g., ultra-high particle efficiency, ULPA), and thus can exhibit an efficiency of greater than or equal to about 99.9995%. Alternatively, the filter media can be suitable for HVAC applications, which are classified according to a particle efficiency of greater than or equal to about 15% and less than or equal to about 90%, or greater than or equal to about 35% and less than or equal to about 90%. For high particle efficiency applications (e.g., HEPA), the filter media exhibits a particle efficiency of greater than or equal to about 99.5% and less than or equal to about 99.995%.

[0084] In some embodiments, the particle filtration efficiency of the DOP of the filter media may be greater than or equal to about 15%, greater than or equal to about 20%, greater than or equal to about 35%, greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 70%, greater than or equal to about 80%, greater than or equal to about 90%, greater than or equal to about 95%, greater than or equal to about 97%, greater than or equal to about 99%, greater than or equal to about 99.5%, greater than or equal to about 99.9%, greater than or equal to about 99.95%, greater than or equal to about 99.99%, or greater than or equal to about 99.995%. In some cases, the DOP efficiency of the filter medium may be less than or equal to about 99.99999%, less than or equal to about 99.999%, less than or equal to about 99.999%, less than or equal to about 99.997%, less than or equal to about 99.995%, less than or equal to about 99.9%, less than or equal to about 99.5%, less than or equal to about 99%, less than or equal to about 98%, less than or equal to about 97%, less than or equal to about 95%, less than or equal to about 90%, less than or equal to about 85%, less than or equal to about 75%, less than or equal to about 60%, less than or equal to about 50%, less than or equal to about 40%, less than or equal to about 30%, less than or equal to about 20%, or less than or equal to about 10%. It should be understood that all combinations of the above reference ranges are possible. In some embodiments, the range of the NaCl particle efficiency of the filter medium may be as described above with respect to the DOP efficiency of the filter medium. Other ranges and values ​​of NaCl particle filtration efficiency are also possible. In some embodiments, DOP efficiency is determined as described herein.

[0085] Generally, the filter media can have a relatively high gamma. In some cases, the gamma of the filter media can be greater than or equal to about 7, greater than or equal to about 10, greater than or equal to about 12, greater than or equal to about 15, greater than or equal to about 20, greater than or equal to about 30, greater than or equal to about 40, greater than or equal to about 50, or greater than or equal to about 60. In some cases, the gamma of the filter media can be less than or equal to about 75, less than or equal to about 60, less than or equal to about 50, less than or equal to about 40, less than or equal to about 30, less than or equal to about 25, less than or equal to about 20, less than or equal to about 15, or less than or equal to about 10. It should be understood that all combinations of the above referenced ranges are possible (e.g., greater than or equal to about 7 and less than or equal to about 75, greater than or equal to about 10 and less than or equal to about 75, greater than or equal to about 20 and less than or equal to about 75). In some embodiments, gamma is determined as described herein.

[0086] In some embodiments, the filter media described herein including a pre-filter layer can have a relatively small change in pressure drop over time. For example, the change in pressure drop after 30 minutes of DOP loading can be less than or equal to about 350%, less than or equal to about 325%, less than or equal to about 300%, less than or equal to about 275%, less than or equal to about 250%, less than or equal to about 225%, less than or equal to about 200%, less than or equal to about 175%, less than or equal to about 150%, less than or equal to about 125%, less than or equal to about 100%, less than or equal to about 75%, less than or equal to about 50%, or less than or equal to about 25%.

[0087] In some embodiments, the change in pressure drop after 30 minutes of NaCl loading may be less than or equal to about 250%, less than or equal to about 225%, less than or equal to about 200%, less than or equal to about 175%, less than or equal to about 150%, less than or equal to about 125%, less than or equal to about 100%, less than or equal to about 75%, less than or equal to about 50%, or less than or equal to about 25%.

[0088] The change in pressure drop at 30 minutes using either DOP or NaCl pellets can be determined by comparing the pressure drop at 30 minutes to the first pressure drop reading at the beginning of the test. The pressure drop is determined as described above.

[0089] In some embodiments, the pre-filter layer may not significantly affect the pressure drop of the filter media, such that the total pressure drop of the filter media is similar to the air flow resistance of the efficiency layer. For example, in some embodiments, the pressure drop of the filter media may be greater than or equal to about 0.75 mm H2O, greater than or equal to about 1 mm H2O, greater than or equal to about 5 mm H2O, greater than or equal to about 10 mm H2O, greater than or equal to about 25 mm H2O, greater than or equal to about 50 mm H2O, greater than or equal to about 75 mm H2O, greater than or equal to about 100 mm H2O, or greater than or equal to about 125 mm H2O. In some cases, the pressure drop may be less than or equal to about 160 mm H2O, less than or equal to about 125 mm H2O, less than or equal to about 100 mm H2O, less than or equal to about 90 mm H2O, less than or equal to about 75 mm H2O, less than or equal to about 50 mm H2O, less than or equal to about 25 mm H2O, or less than or equal to about 10 mm H2O. It should be understood that combinations of the above reference ranges are possible (e.g., greater than or equal to about 0.75 mm H2O and less than or equal to about 160 mmH2O, greater than or equal to about 1 mm H2O and less than or equal to about 100 mmH2O). Other ranges and values ​​of pressure drop are also possible. In some embodiments, the pressure drop is determined as described herein.

[0090] Generally, structural characteristics may vary depending on the filtration application (eg, HEPA, ASHRAE, ULPA, face mask, etc.) and the materials used to form the filter media.

[0091] In some embodiments, the stiffness of the filter medium may be greater than or equal to about 400gu, greater than or equal to about 500gu, greater than or equal to about 700gu, greater than or equal to about 1,000gu, greater than or equal to about 1,500gu, greater than or equal to about 2,000gu, or greater than or equal to about 2,500gu. In some embodiments, the stiffness of the filter medium may be less than or equal to about 3,000gu, less than or equal to about 2,500gu, less than or equal to about 2,000gu, less than or equal to about 1,500gu, less than or equal to about 1,000gu, less than or equal to about 750gu, or less than or equal to about 500gu. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 400gu and less than or equal to about 3,000gu, greater than or equal to about 7000gu and less than or equal to about 2,000gu). Other values ​​of stiffness are also possible. In some embodiments, the stiffness is determined as described herein.

[0092] In some embodiments, the basis weight of the filter media may be greater than or equal to about 25 g / m 2 , greater than or equal to about 60g / m 2 , greater than or equal to about 100g / m 2 , greater than or equal to about 150g / m 2 , greater than or equal to about 200g / m 2 , greater than or equal to about 250g / m 2 , greater than or equal to about 300g / m 2 , greater than or equal to about 350g / m 2 , greater than or equal to about 400g / m 2 , greater than or equal to about 450g / m 2 , greater than or equal to about 500g / m 2 , or greater than or equal to about 550 g / m 2 In some cases, the basis weight of the filter media may be less than or equal to about 600 g / m 2 , less than or equal to about 550g / m 2 , less than or equal to about 500g / m 2 , less than or equal to about 450g / m 2 , less than or equal to about 400g / m 2 , less than or equal to about 350g / m 2 , less than or equal to about 300g / m 2 , less than or equal to about 250g / m 2 , less than or equal to about 200g / m2 , less than or equal to about 150g / m 2 , or less than or equal to about 100 g / m 2 Combinations of the above-referenced ranges are also possible (e.g., greater than or equal to about 60 g / m 2 and less than or equal to about 300 g / m 2 , greater than or equal to about 25g / m 2 and less than or equal to about 600 g / m 2 ). Other values ​​of basis weight are also possible. The basis weight can be determined according to standard ISO 536.

[0093] In some embodiments, the filter media may have a thickness of about 0.05 mm or more, about 0.01 mm or more, about 0.1 mm or more, about 0.5 mm or more, about 1 mm or more, about 5 mm or more, about 8 mm or more, about 10 mm or more, about 12 mm or more, about 15 mm or more, about 18 mm or more, or about 20 mm or more. In some cases, the filter media may have a thickness of about 25 mm or less, about 20 mm or less, about 18 mm or less, about 15 mm or less, about 12 mm or less, about 10 mm or less, about 8 mm or less, about 5 mm or less, or about 2 mm or less. Combinations of the above referenced ranges are also possible (e.g., about 0.05 mm or more and about 25 mm or less, about 0.1 mm or more and about 10 mm or less). Other values ​​of the average thickness are also possible. Thickness available according to ISO 534 at 2.65 lbs / in 2 Next confirm.

[0094] Generally, any layer in the filter media may contain any suitable fiber type. In some embodiments, one or more layers and / or the entire filter media may contain more than one type of fiber. For example, in certain embodiments, one or more layers and / or the entire filter media may contain one or more of synthetic fibers, cellulose fibers (e.g., regenerated cellulose fibers, lyocell, etc.) and / or glass fibers as described herein.

[0095] In some embodiments, the fibers in a layer (e.g., a pre-filter layer, a second layer) may also have an average length that may depend on the method by which the fibers are formed. For example, in some embodiments, fibers formed by a meltblowing process, a meltspinning process, an electrospinning process (e.g., solvent electrospinning, melt electrospinning), or a centrifugal spinning process may be continuous (e.g., greater than about 2 inches, greater than about 3 inches, greater than about 5 inches).

[0096] In some embodiments, filter media 10 may include synthetic fibers. For example, in some embodiments, pre-filter layer 15 and / or second layer 20 may include synthetic fibers. Synthetic fibers may have a relatively small median fiber diameter (e.g., less than or equal to about 2 microns). For example, the median diameter of the synthetic fibers in pre-filter layer 15 may be less than or equal to about 2 microns (e.g., about 0.5 microns to about 1.0 microns). The median diameter of the synthetic fibers in the second layer (e.g., efficiency layer) may be less than or equal to about 1 micron (e.g., about 0.1 microns to 0.5 microns). In embodiments where the second layer includes more than one sublayer, at least one sublayer may include synthetic fibers. For example, at least two sublayers (e.g., all sublayers) may include synthetic fibers. In some such embodiments, a sublayer including synthetic fibers may have a median fiber diameter that is substantially the same as or different from another sublayer. In some embodiments, the synthetic fibers in the pre-filter layer 15, the second layer 20, and / or the filter medium 10 may be continuous fibers formed by any suitable method (e.g., a melt-blowing process, a melt-spinning process, an electrospinning process (e.g., melt electrospinning, solvent electrospinning), or a centrifugal spinning process). In certain embodiments, the synthetic fibers may be formed by an electrospinning process. In other embodiments, the synthetic fibers may be discontinuous. In some embodiments, all fibers in the filter medium are synthetic fibers. In certain embodiments, all fibers in the pre-filter layer 15 and / or the second layer 20 are synthetic fibers.

[0097] Synthetic fiber can comprise any suitable type of synthetic polymer.The example of suitable synthetic fiber comprises polyester (for example, polyethylene terephthalate, polybutylene terephthalate), polycarbonate, polyamide (for example, various nylon polymers), polyaramid, polyimide, polyethylene, polypropylene, polyetheretherketone, polyolefin, acrylic, polyvinyl alcohol, regenerated cellulose (for example, synthetic cellulose, such as lyocell, rayon), polyacrylonitrile, polyvinylidene fluoride (PVDF), copolymer of polyethylene and PVDF, polyethersulfone and combination thereof.In some embodiments, synthetic fiber is organic polymer fiber.Synthetic fiber can also comprise multicomponent fiber (that is, fiber with multiple components, such as bicomponent fiber).In some cases, synthetic fiber can comprise meltblown fiber, melt-spun fiber, electrostatic spinning (for example, melt electrostatic spinning, solvent electrostatic spinning) fiber or centrifugal spinning fiber that can be formed by polymer (for example, polyester, polypropylene) as described herein.In some embodiments, synthetic fiber can be electrostatic spinning fiber.Each layer (or sublayer) in filter medium and filter medium can also comprise the combination of more than one type of synthetic fiber. It should be understood that other types of synthetic fibers may also be used.

[0098] In some embodiments, the median diameter of the synthetic fibers of one or more layers (e.g., pre-filter layer, second layer) and / or the entire filter media may be, for example, about 0.1 microns or more, about 0.3 microns or more, about 0.5 microns or more, about 1 micron or more, about 2 microns or more, about 3 microns or more, about 4 microns or more, about 5 microns or more, about 8 microns or more, about 10 microns or more, about 12 microns or more, about 15 microns or more, or about 20 microns or more. In some cases, the median diameter of the synthetic fibers may be less than or equal to about 30 microns, less than or equal to about 20 microns, less than or equal to about 15 microns, less than or equal to about 10 microns, less than or equal to about 7 microns, less than or equal to about 5 microns, less than or equal to about 4 microns, less than or equal to about 1.5 microns, less than or equal to about 1 micron, less than or equal to about 0.8 microns, or less than or equal to about 0.5 microns. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 1 micron and less than or equal to about 5 microns). Other values ​​of the median fiber diameter are also possible. In certain embodiments, the above ranges of median fiber diameters may apply to synthetic fibers of all media (e.g., all media may include synthetic fibers having a median fiber diameter within one or more of the above ranges). In some embodiments, the average diameter of the fibers may fall within the above reference ranges of median fiber diameters.

[0099] In some cases, the synthetic fibers can be continuous (e.g., meltblown fibers, spunbond fibers, electrospun fibers, centrifugal spun fibers, etc.). For example, the average length of the synthetic fibers can be at least about 5 cm, at least about 10 cm, at least about 15 cm, at least about 20 cm, at least about 50 cm, at least about 100 cm, at least about 200 cm, at least about 500 cm, at least about 700 cm, at least about 1000, at least about 1500 cm, at least about 2000 cm, at least about 2500 cm, at least about 5000 cm, at least about 10000 cm; and / or less than or equal to about 10000 cm, less than or equal to about 5000 cm, less than or equal to about 2500 cm, less than or equal to about 2000 cm, less than or equal to about 1000 cm, less than or equal to about 500 cm, or less than or equal to about 200 cm. Combinations of the above-referenced ranges are also possible (eg, greater than or equal to about 100 cm and less than or equal to about 2500 cm). Still other values ​​of the average fiber length are possible.

[0100] In some embodiments, the synthetic fibers are not continuous (e.g., staple fibers). Generally, non-continuous synthetic fibers may be characterized as being shorter than continuous synthetic fibers. For example, in some embodiments, the average length of the synthetic fibers in one or more layers of the filter media may be at least about 0.1 mm, at least about 0.5 mm, at least about 1.0 mm, at least about 1.5 mm, at least about 2.0 mm, at least about 3.0 mm, at least about 4.0 mm, at least about 5.0 mm, at least about 6.0 mm, at least about 7.0 mm, at least about 8.0 mm, at least about 9.0 mm, at least about 10.0 mm, at least about 12.0 mm, at least about 15.0 mm; and / or less than or equal to about 15.0 mm, less than or equal to about 12.0 mm, less than or equal to about 10.0 mm, less than or equal to about 5.0 mm, less than or equal to about 4.0 mm, less than or equal to about 1.0 mm, less than or equal to about 0.5 mm, or less than or equal to about 0.1 mm. Combinations of the above-referenced ranges are also possible (eg, at least about 1.0 mm and less than or equal to about 4.0 mm).Alternative values ​​of average fiber length are also possible.

[0101] In some embodiments where synthetic fibers are included in one or more layers and / or the entire filter medium, the weight percentage of synthetic fibers in one or more layers (e.g., pre-filter layer, second layer) and / or the entire filter medium may be greater than or equal to about 1%, greater than or equal to about 20%, greater than or equal to about 40%, greater than or equal to about 60%, greater than or equal to about 80%, greater than or equal to about 90%, or greater than or equal to about 95%. In some cases, the weight percentage of synthetic fibers in the second layer may be less than or equal to about 100%, less than or equal to about 98%, less than or equal to about 85%, less than or equal to about 75%, less than or equal to about 50%, or less than or equal to about 10%. Combinations of the above referenced ranges are also possible (e.g., greater than or equal to about 80% and less than or equal to about 100%). Other values ​​of the weight percentage of synthetic fibers are also possible. In some embodiments, one or more layers (e.g., pre-filter layer, second layer) and / or the entire filter medium contain 100% synthetic fibers. In other embodiments, one or more layers and / or the entire filter media may contain 0% synthetic fibers.

[0102] In one set of embodiments, one or more layers in the filter media may include bicomponent fibers. The bicomponent fibers may include thermoplastic polymers. The components of the bicomponent fibers may have different melting temperatures. For example, the fiber may include a core and a sheath, wherein the activation temperature of the sheath is lower than the melting temperature of the core. This causes the sheath to melt before the core, so that the sheath is bonded to other fibers in the layer, while the core maintains its structural integrity. The core / sheath bonded fibers may be coaxial or non-coaxial. Other exemplary bicomponent fibers may include split film fibers, side-by-side fibers, and / or "island-in-the-sea" fibers.

[0103] In some embodiments, the average length of the bicomponent fibers may be at least about 0.1 mm, at least about 0.5 mm, at least about 1.0 mm, at least about 1.5 mm, at least about 2.0 mm, at least about 3.0 mm, at least about 4.0 mm, at least about 5.0 mm, at least about 6.0 mm, at least about 7.0 mm, at least about 8.0 mm, at least about 9.0 mm, at least about 10.0 mm, at least about 12.0 mm, at least about 15.0 mm; and / or less than or equal to about 15.0 mm, less than or equal to about 12.0 mm, less than or equal to about 10.0 mm, less than or equal to about 5.0 mm, less than or equal to about 4.0 mm, less than or equal to about 1.0 mm, less than or equal to about 0.5 mm, or less than or equal to about 0.1 mm. Combinations of the above referenced ranges are also possible (e.g., at least about 1.0 mm and less than or equal to about 4.0 mm). Other values ​​of the average fiber length are also possible.

[0104] In some embodiments where bicomponent fibers are included in one or more layers (e.g., pre-filter layer, second layer) and / or the entire filter medium, the weight percentage of bicomponent fibers in one or more layers and / or the entire filter medium may be, for example, greater than or equal to about 1%, greater than or equal to about 2%, greater than or equal to about 3%, greater than or equal to about 5%, greater than or equal to about 10%, or greater than or equal to about 15%. In some cases, the weight percentage of bicomponent fibers in one or more layers and / or the entire filter medium may be less than or equal to about 20%, less than or equal to about 15%, less than or equal to about 10%, less than or equal to about 5%, less than or equal to about 4%, or less than or equal to about 2%. Combinations of the above referenced ranges are also possible (e.g., greater than or equal to about 1% and less than or equal to about 10%). Other values ​​of the weight percentage of bicomponent fibers are also possible. In other embodiments, one or more layers (e.g., pre-filter layer, second layer) and / or the entire filter medium may contain 0% bicomponent fibers.

[0105] In some embodiments, one or more layers in the filter media may include one or more cellulosic fibers, such as softwood fibers, hardwood fibers, mixtures of hardwood and softwood fibers, regenerated cellulose fibers, and mechanical pulp fibers (e.g., groundwood pulp, chemically treated mechanical pulp, and thermomechanical pulp).

[0106] The median diameter of the cellulose fibers in one or more layers (e.g., pre-filter layer, second layer) and / or the entire filter medium may be, for example, greater than or equal to about 1 micron, greater than or equal to about 2 microns, greater than or equal to about 3 microns, greater than or equal to about 4 microns, greater than or equal to about 5 microns, greater than or equal to about 8 microns, greater than or equal to about 10 microns, greater than or equal to about 15 microns, greater than or equal to about 20 microns, greater than or equal to about 30 microns, or greater than or equal to about 40 microns. In some cases, the median diameter of the cellulose fibers may be less than or equal to about 50 microns, less than or equal to about 40 microns, less than or equal to about 30 microns, less than or equal to about 20 microns, less than or equal to about 15 microns, less than or equal to about 10 microns, less than or equal to about 7 microns, less than or equal to about 5 microns, less than or equal to about 4 microns, or less than or equal to about 2 microns. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 1 micron and less than or equal to about 5 microns). Other values ​​of the median fiber diameter are also possible. In some embodiments, the average diameter of the fibers may fall within the above referenced ranges for median fiber diameters.

[0107] In some embodiments, the cellulose fibers may have an average length. For example, in some embodiments, the average length of the cellulose fibers may be greater than or equal to about 0.5 mm, greater than or equal to about 1 mm, greater than or equal to about 2 mm, greater than or equal to about 3 mm, greater than or equal to about 4 mm, greater than or equal to about 5 mm, greater than or equal to about 6 mm, or greater than or equal to about 8 mm. In some cases, the average length of the cellulose fibers may be less than or equal to about 10 mm, less than or equal to about 8 mm, less than or equal to about 6 mm, less than or equal to about 4 mm, less than or equal to about 2 mm, or less than or equal to about 1 mm. The combination of the above reference ranges is also possible (for example, greater than or equal to about 1 mm and less than or equal to about 3 mm). Other values ​​of average fiber length are also possible.

[0108] In certain embodiments, one or more layers and / or the entire filter medium may optionally contain cellulose fibers, such as regenerated cellulose (e.g., rayon, lyocell), fibrillated synthetic fibers, microfibrillated cellulose, and natural cellulose fibers (e.g., hardwood fibers, softwood fibers). For example, in some embodiments, the weight percentage of cellulose fibers in one or more layers and / or the entire filter medium may be greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, greater than or equal to about 15%, greater than or equal to about 45%, greater than or equal to about 65%, or greater than or equal to about 90%. In some cases, the weight percentage of cellulose fibers in the second layer may be less than or equal to about 100%, less than or equal to about 85%, less than or equal to about 55%, less than or equal to about 20%, less than or equal to about 10%, or less than or equal to about 2%. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 1% and less than or equal to about 20%). Other values ​​of the weight percentage of cellulose fibers in one or more layers and / or the entire filter medium are also possible. In some embodiments, one or more layers and / or the entire filter media comprises 100% cellulose fibers. In other embodiments, one or more layers and / or the entire filter media may comprise 0% cellulose fibers.

[0109] In some embodiments, one or more layers in the filter medium may include fibrillated fibers. As known to those of ordinary skill in the art, fibrillated fibers include parent fibers that branch into fibrils of smaller diameter (which in some cases can further branch out fibrils of even smaller diameter, and further branching is also possible). The branching properties of the fibrils result in layers and / or fiber webs with high surface areas, and can increase the number of contact points between the fibrillated fibers and other fibers in the web. The increase in such contact points between the fibrillated fibers of the web and other fibers and / or components contributes to the mechanical properties (e.g., flexibility, strength) and / or filtration performance characteristics of the reinforcing layers and / or fiber webs.

[0110] In some embodiments, the parent fiber may have a median diameter in the micron range. For example, the median diameter of the parent fiber may be greater than or equal to about 1 micron, greater than or equal to about 5 microns, greater than or equal to about 10 microns, greater than or equal to about 20 microns, greater than or equal to about 30 microns, greater than or equal to about 40 microns, greater than or equal to about 50 microns, greater than or equal to about 60 microns, or greater than or equal to about 70 microns. In some embodiments, the median diameter of the parent fiber may be less than or equal to about 75 microns, less than or equal to about 55 microns, less than or equal to about 35 microns, less than or equal to about 25 microns, less than or equal to about 15 microns, less than or equal to about 10 microns, or less than or equal to about 5 microns. The combination of the above reference ranges is also possible (for example, the median diameter of the parent fiber is greater than or equal to about 1 micron and less than or equal to about 25 microns). Other ranges are also possible. In some embodiments, the average diameter of the fiber may fall within the above reference range of the median fiber diameter.

[0111] In other embodiments, the parent fiber may have a median diameter in the nanometer range. For example, in some embodiments, the median diameter of the parent fiber may be less than about 1 micron, less than or equal to about 0.8 micron, less than or equal to about 0.5 micron, or less than or equal to about 0.1 micron. In some embodiments, the median diameter of the parent fiber may be greater than or equal to about 0.1 micron, or greater than or equal to about 0.5 micron. Combinations of the above reference ranges are also possible (for example, the median diameter of the parent fiber is greater than or equal to about 0.004 micron and less than or equal to about 0.02 micron). Other ranges are also possible. In some embodiments, the average diameter of the fiber may fall within the above reference range of the median fiber diameter.

[0112] The median diameter of protofibrils is generally less than the average diameter of parent fibers. According to the median diameter of parent fibers, in some embodiments, the median diameter of protofibrils may be less than or equal to about 25 microns, less than or equal to about 20 microns, less than or equal to about 10 microns, less than or equal to about 5 microns, less than or equal to about 1 micron, less than or equal to about 0.5 microns, less than or equal to about 0.1 micron, less than or equal to about 0.05 microns, or less than or equal to about 0.01 microns. In some embodiments, the median diameter of protofibrils may be greater than or equal to about 0.003 microns, greater than or equal to about 0.01 microns, greater than or equal to about 0.05 microns, greater than or equal to about 0.1 microns, greater than or equal to about 0.5 microns, greater than or equal to about 1 micron, greater than or equal to about 5 microns, greater than or equal to about 10 microns, or greater than or equal to about 20 microns. The combination of the above reference ranges is also possible (for example, the median diameter of protofibrils is greater than or equal to about 0.01 microns and less than or equal to about 20 microns). Other ranges are also possible.

[0113] In some embodiments, the average length of the fibrillated fibers may be less than or equal to about 10 mm, less than or equal to about 8 mm, less than or equal to about 6 mm, less than or equal to about 5 mm, less than or equal to about 4 mm, less than or equal to about 3 mm, or less than or equal to about 2 mm. In certain embodiments, the average length of the fibrillated fibers may be greater than or equal to about 1 mm, greater than or equal to about 2 mm, greater than or equal to about 4 mm, greater than or equal to about 5 mm, greater than or equal to about 6 mm, or greater than or equal to about 8 mm. Combinations of the above reference ranges are also possible (e.g., the average length of the fibrillated fibers is greater than or equal to about 4 mm and less than about 6 mm). Other ranges are also possible. The average length of the fibrillated fibers refers to the average length of the parent fibers from one end to the other end of the parent fibers. In some embodiments, the maximum average length of the fibrillated fibers falls within the above range. The maximum average length refers to the average value of the maximum dimension along one axis of the fibrillated fibers (including parent fibers and fibrils). It should be understood that in certain embodiments, fibers and fibrils may have sizes outside the above ranges.

[0114] The fibrillation level of fibrillated fibers can be measured according to any number of suitable methods. For example, the fibrillation level can be measured according to the Canadian Standard Freeness (CSF) test, which is specified by the freeness of TAPPI test method T 227om 09 pulp. The test can provide an average CSF value. In some embodiments, the average CSF value of fibrillated fibers can be about 10mL to about 750mL. In certain embodiments, the average CSF value of the fibrillated fibers used in the layer can be greater than or equal to about 10mL, greater than or equal to about 50mL, greater than or equal to about 100mL, greater than or equal to about 200mL, greater than or equal to about 400mL, greater than or equal to about 600mL, or greater than or equal to about 700mL. In some embodiments, the average CSF value of fibrillated fibers can be less than or equal to about 800mL, less than or equal to about 600mL, less than or equal to about 400mL, less than or equal to about 200mL, less than or equal to about 100mL, or less than or equal to about 50mL. Combinations of the above referenced ranges are also possible (e.g., the average CSF value of the fibrillated fibers is greater than or equal to about 10 mL and less than or equal to about 300 mL). Other ranges are also possible. The average CSF value of the fibrillated fibers can be based on one type of fibrillated fibers or more than one type of fibrillated fibers.

[0115] In certain embodiments, one or more layers may optionally include fibrillated fibers, such as fibrillated regenerated cellulose (e.g., rayon, lyocell), microfibrillated cellulose, fibrillated synthetic fibers, and fibrillated natural cellulose fibers (e.g., hardwood fibers, softwood fibers). For example, in some embodiments, the weight percentage of fibrillated fibers in one or more layers and / or the entire filter medium may be greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, greater than or equal to about 15%, greater than or equal to about 45%, greater than or equal to about 65%, or greater than or equal to about 90%. In some cases, the weight percentage of fibrillated fibers in the second layer may be less than or equal to about 100%, less than or equal to about 85%, less than or equal to about 55%, less than or equal to about 20%, less than or equal to about 10%, or less than or equal to about 2%. Combinations of the above reference ranges are also possible (e.g., greater than or equal to about 1% and less than or equal to about 20%). Other values ​​of the weight percentage of fibrillated fibers in the second layer are also possible. In some embodiments, one or more layers contain 100% fibrillated fibers. In other embodiments, one or more layers may contain 0% fibrillated fibers.

[0116] In some embodiments, one or more layers (e.g., pre-filter layer, second layer) and / or the entire filter media are substantially free of glass fibers (e.g., less than 1% by weight of glass fibers). For example, the pre-filter layer, second layer, and / or the entire filter media may contain 0% by weight of glass fibers. For certain applications where post-incineration filter media is preferred, filter media and arrangements that are substantially free of glass fibers may be advantageous. However, in other embodiments, one or more layers and / or the entire filter media may contain glass fibers (e.g., microglass fibers, chopped glass fibers, or combinations thereof).

[0117] The median diameter of the glass fiber may be, for example, less than or equal to about 30 microns, less than or equal to about 25 microns, less than or equal to about 15 microns, less than or equal to about 12 microns, less than or equal to about 10 microns, less than or equal to about 9 microns, less than or equal to about 7 microns, less than or equal to about 5 microns, less than or equal to about 3 microns, or less than or equal to about 1 micron. In some cases, the median fiber diameter of the glass fiber may be greater than or equal to about 0.1 microns, greater than or equal to about 0.3 microns, greater than or equal to about 1 micron, greater than or equal to about 3 microns, or greater than or equal to about 7 microns, greater than or equal to about 9 microns, greater than or equal to about 11 microns, or greater than or equal to about 20 microns. Combinations of the above referenced ranges are also possible (e.g., greater than or equal to about 0.1 microns and less than or equal to about 9 microns). Other values ​​of the median fiber diameter are also possible.

[0118] In some embodiments, the average length of the microglass fibers may be less than or equal to about 10 mm, less than or equal to about 8 mm, less than or equal to about 6 mm, less than or equal to about 5 mm, less than or equal to about 4 mm, less than or equal to about 3 mm, or less than or equal to about 2 mm. In certain embodiments, the average length of the microglass fibers may be greater than or equal to about 1 mm, greater than or equal to about 2 mm, greater than or equal to about 4 mm, greater than or equal to about 5 mm, greater than or equal to about 6 mm, or greater than or equal to about 8 mm. Combinations of the above-referenced ranges are also possible (e.g., the average length of the microglass fibers is greater than or equal to about 4 mm and less than about 6 mm). Other ranges are also possible.

[0119] Generally, the average fiber diameter of the chopped glass fibers may be greater than the diameter of the microglass fibers. In some embodiments, the length of the chopped glass fibers may be from about 0.125 inches to about 1 inch (e.g., about 0.25 inches or about 0.5 inches). In some embodiments, the average length of the chopped glass fibers may be less than or equal to about 1 inch, less than or equal to about 0.8 inches, less than or equal to about 0.6 inches, less than or equal to about 0.5 inches, less than or equal to about 0.4 inches, less than or equal to about 0.3 inches, or less than or equal to about 0.2 inches. In certain embodiments, the average length of the chopped glass fibers may be greater than or equal to about 0.125 inches, greater than or equal to about 0.2 inches, greater than or equal to about 0.4 inches, greater than or equal to about 0.5 inches, greater than or equal to about 0.6 inches, or greater than or equal to about 0.8 inches. Combinations of the above referenced ranges are also possible (e.g., the average length of the chopped glass fibers is greater than or equal to about 0.125 inches and less than about 1 inch). Other ranges are also possible.

[0120] In some embodiments, one or more layers (e.g., a pre-filter layer, a second layer) and / or the entire filter media may contain a relatively low content of glass fibers. For example, the second layer may contain less than or equal to about 10 wt %, less than or equal to about 5 wt %, less than or equal to about 2 wt %, or less than or equal to about 1 wt % glass fibers. In some cases, the pre-filter layer, the second layer, and / or the entire filter media may be substantially free of glass fibers (e.g., less than 1 wt % glass fibers, such as 0 wt % glass fibers).

[0121] In other embodiments, one or more layers (e.g., a pre-filter layer, a second layer) and / or the entire filter medium may optionally contain glass fibers (e.g., microglass fibers and / or chopped glass fibers). For example, in some embodiments, the weight percentage of glass fibers in one or more layers and / or the entire filter medium may be, for example, greater than or equal to about 0%, greater than or equal to about 10%, greater than or equal to about 25%, greater than or equal to about 50%, or greater than or equal to about 75%. In some cases, the weight percentage of glass fibers in one or more layers and / or the entire filter medium may be less than or equal to about 100%, less than or equal to about 75%, less than or equal to about 50%, less than or equal to about 25%, less than or equal to about 5%, or less than or equal to about 2%. Combinations of the above referenced ranges are also possible (e.g., greater than or equal to about 0% and less than or equal to about 2%). Other values ​​of the weight percentage of glass in one or more layers (e.g., a pre-filter layer, a second layer) and / or the entire filter medium are also possible. In some embodiments, one or more layers and / or the entire filter media comprises 100% glass fibers.

[0122] In some embodiments, in addition to the plurality of fibers, one or more layers and / or the entire filter media may also include other components, such as resins, surface treatments, and / or additives. Generally, any suitable resin may be used to achieve the desired properties. For example, the resin may be polymeric, water-based, solvent-based, dry strength, and / or wet strength. Typically, any additional components are present in limited amounts, such as less than 20% by weight of the resin, less than 10% by weight of the resin, less than 5% by weight of the resin.

[0123] In some embodiments, at least a portion of the fibers of one or more layers may be coated with a resin without substantially blocking the pores of the layer.In some embodiments, one or more layers or the entire filter media described herein comprise a resin.

[0124] In some embodiments, resin can be a binder resin.Binder resin is not in fiber form, and is different from the above-mentioned adhesive fibers (e.g., multicomponent fibers).Generally, binder resin can have any suitable composition.For example, binder resin can include thermoplastics (e.g., acrylic acid, polyvinyl acetate, polyester, polyamide), thermosetting plastics (e.g., epoxy resin, phenolic resin) or a combination thereof.In some cases, binder resin includes one or more of vinyl acetate resin, epoxy resin, polyester resin, copolyester resin, polyvinyl alcohol resin, acrylic resin (e.g., styrene acrylic resin) and phenolic resin.Other resins are also possible.

[0125] As further described below, the resin can be added to the fiber in any suitable manner (including, for example, in a wet state). In some embodiments, the resin coats the fiber and is used to bond the fibers to each other to promote bonding between the fibers. Any suitable method and equipment can be used to coat the fiber, for example, using curtain coating, gravure coating, melt coating, dip coating, knife roll coating or spin coating, etc. In some embodiments, the adhesive is precipitated when added to the fiber blend. When appropriate, any suitable precipitant (e.g., epichlorohydrin, fluorocarbon) can be provided to the fiber, for example, by injection into the blend. In some embodiments, when added to the fiber, the resin is added in a manner such that one or more layers or the entire filter medium is impregnated with resin (e.g., the resin permeates the entirety). In a multilayer net, the resin can be added to each layer separately before the layers are combined, or the resin can be added to the layer after the layers are combined. In some embodiments, the resin is added to the fiber in a dry state, for example, by spraying or saturated impregnation or any of the above methods. In other embodiments, the resin is added to the wet layer.

[0126] Filter media described herein can be produced using suitable processes, such as using wet-laid or non-wet-laid processes. In some embodiments, layers and / or filter media described herein can be produced using non-wet-laid processes (such as blow molding or spinning processes). In some embodiments, layers (e.g., pre-filter layers, second layers) and / or entire filter media can be formed by electrostatic spinning processes. In certain embodiments, layers (e.g., pre-filter layers, second layers) and / or entire filter media can be formed by melt-blown systems, such as the U.S. publication No. 2009 / 0120048 entitled "Meltblown Filter Medium" submitted on November 7, 2008 and the U.S. publication No. 2004-0152824 entitled "Fine FiberFilter Media and Processes" submitted on December 17, 2010, which are each incorporated herein by reference as a whole for all purposes. In certain embodiments, a layer (e.g., a pre-filter layer, a second layer) and / or the entire filter medium can be formed by a melt-spinning or centrifugal spinning process. In some embodiments, a non-wet-laid web process (e.g., an air-laid web process or a combing process) can be used to form one or more layers. For example, in an air-laid web process, synthetic fibers can be mixed while air is blown onto a conveyor. In a combing process, in some embodiments, the fibers are manipulated by a roller and an extension (e.g., a hook, a needle) connected to the roller. In some cases, forming a layer by a non-wet-laid web process may be more suitable for producing highly porous media. As described above, the layer may be impregnated (e.g., by saturation, spraying, etc.) with any suitable resin. In some embodiments, a non-wet-laid web process (e.g., melt-blown, electrostatic spinning) can be used to form a pre-filter layer, and a wet-laid web process can be used to form a second layer. The pre-filter layer and the second layer can be combined using any suitable process (e.g., lamination, co-pleating or finishing).

[0127] In some embodiments, the layers and / or filter media described herein can be produced using a wet-laid process. Generally, the wet-laid process includes mixing one or more types of fibers together; for example, one type of polymer staple fibers can be mixed with another type of polymer staple fibers and / or different types of fibers (e.g., synthetic fibers and / or glass fibers) to provide a fiber slurry. The slurry can be, for example, a water-based slurry. In certain embodiments, the fibers are optionally stored separately or in combination in different storage tanks before being mixed together.

[0128] For example, the first fibers may be mixed together and pulped in one container, and the second fibers may be mixed and pulped in a separate container. The first fibers and the second fibers are then combined together into a single fiber mixture. Before and / or after being mixed together, the appropriate fibers may be processed by a pulper. In some embodiments, before being mixed together, the combination of fibers is processed by a pulper and / or a storage tank. It is understood that other components may also be introduced into the mixture. In addition, it is understood that other combinations of fiber types, such as the fiber types described herein, may be used in the fiber mixture.

[0129] In certain embodiments, a medium comprising two or more layers (e.g., a pre-filter layer and a second layer) is formed by a wet-laid web process. For example, a first dispersion (e.g., pulp) containing fibers in a solvent (e.g., an aqueous solvent such as water) can be applied to a web conveyor in a paper machine (e.g., a Fourdrinier paper machine or a vacuum cylinder paper machine) to form a first layer supported by the web conveyor. A second dispersion (e.g., another pulp) containing fibers in a solvent (e.g., an aqueous solvent such as water) is applied to the first layer while the first layer is deposited on the web or subsequently. During the above process, a vacuum is continuously applied to the first and second dispersions of the fibers to remove the solvent from the fibers, thereby obtaining a product containing the first and second layers. The product thus formed is then dried and, if necessary, further processed (e.g., calendering) using known methods to form a multilayer filter medium. In some embodiments, such a process can result in a gradient of at least one characteristic across the thickness of two or more layers.

[0130] Any suitable method for producing the fiber slurry can be used. In some embodiments, additional additives are added to the slurry for ease of handling. The temperature can also be adjusted to a suitable range, e.g., 33°F to 100°F (e.g., 50°F to 85°F). In some cases, the temperature of the slurry is maintained. In some cases, the temperature is not actively adjusted.

[0131] In some embodiments, the wet-laid process uses equipment similar to conventional papermaking processes, such as a hydraulic pulper, a former or headbox, a dryer, and an optional converter. After the slurry is properly mixed in the pulper, the slurry can be pumped into the headbox, where it may or may not be combined with other slurries. Other additives may or may not be added. The slurry may also be diluted with additional water so that the final concentration of the fiber is within a suitable range, for example, about 0.1% to 0.5% by weight.

[0132] In some cases, the pH of the fiber slurry can be adjusted as desired. For example, the fibers of the slurry can generally be dispersed under neutral conditions.

[0133] Before the slurry is sent to the headbox, the slurry may optionally be passed through a centrifugal cleaner and / or a pressure screen to remove unfiberized material. The slurry may or may not be passed through additional equipment such as a refiner or a high-frequency deflaker to further enhance the dispersion of the fibers. For example, a high-frequency deflaker may be used to smooth or remove blocks or protrusions that may be generated at any point during the formation of the fiber slurry. The fibers may then be collected onto a screen or net at an appropriate speed using any suitable equipment (e.g., a Fourdrinier paper machine, a vacuum cylinder paper machine, a cylindrical paper machine, or a skew-wire Fourdrinier paper machine).

[0134] In some embodiments, resin is added to a layer (e.g., a preformed layer formed by a wet-laid web process). For example, when the layer passes along an appropriate screen or net, different components (e.g., polymer binder and / or other components) contained in the binder, which may be in the form of separate emulsions, are added to the fiber layer using suitable techniques. In some cases, each component of the resin is mixed into an emulsion before merging with other components and / or layers. The components contained in the resin can be pulled through the layer using, for example, gravity and / or vacuum. In some embodiments, one or more components contained in the binder resin can be diluted with demineralized water and pumped into the layer. In some embodiments, the resin can be applied to the fiber slurry before the slurry is introduced into the headbox. For example, the resin can be introduced (e.g., injected) into the fiber slurry and impregnated with fibers and / or precipitated on the fibers. In some embodiments, the resin can be added to the layer by a solvent saturation method.

[0135] During or after the formation of the filter media, the filter media can be further processed according to a variety of known techniques. For example, a coating method can be used to contain the resin in the filter media. Optionally, additional layers can be formed and / or added to the filter media using methods such as lamination, co-pleating, or finishing. For example, in some cases, two layers (e.g., a pre-filter layer and a second layer) are formed into a composite product by a wet-laid process as described above, and the composite product is then combined with a third layer by any suitable method (e.g., lamination, co-pleating, or finishing). It will be understood that the filter media or composite products formed by the methods described herein can be appropriately customized not only based on the components of each layer, but also based on the effect of using multiple layers with different properties in appropriate combinations to form a filter media having the characteristics described herein.

[0136] As described herein, in some embodiments, two or more layers of the filter media (e.g., a pre-filter layer and a second layer) can be formed separately and combined by any suitable method (e.g., lamination, finishing, or by using an adhesive). Two or more layers can be formed using different processes or the same process. For example, each layer can be independently formed by a non-wet-laid process (e.g., a melt-blown process, a melt-spinning process, a centrifugal spinning process, an electrospinning process, a dry-laid process, an air-laid process), a wet-laid process, or any other suitable process.

[0137] The different layers may be bonded together by any suitable method. For example, the layers may be bonded by adhesives and / or melt bonded to each other on either side. Lamination and calendering methods may also be used. In some embodiments, additional layers may be formed from any type of fiber or blend of fibers by an additional headbox or coater and appropriately adhered to another layer.

[0138] In some embodiments, further processing may include pleating the filter media. For example, two layers may be joined by a co-pleating process. In some cases, the filter media or its multiple layers may be suitably pleated by forming score lines at appropriate intervals from one another, so that the filter media is folded. In some cases, one layer may be wrapped around a pleated layer. It will be appreciated that any suitable pleating technique may be used.

[0139] In some embodiments, the filter media can be post-processed (eg, subjected to a corrugation process) to increase the surface area within the web. In other embodiments, the filter media can be embossed.

[0140] The filter media can include any suitable number of layers, such as at least 2, at least 3, at least 4, at least 5, at least 6, at least 7. In some embodiments, the filter media can include up to 20 layers.

[0141] The filter media described herein can be used for the entire filter arrangement or filter element. In some embodiments, the filter media comprises one or more additional layers or components. Non-limiting examples of additional layers (e.g., the third layer, the fourth layer) include meltblown layers, wet-laid layers, spunbond layers, carded layers, air-laid layers, spunlace layers, forcespun layers, or electrospun layers.

[0142] It should be understood that in addition to one or more layers described herein, the filter medium may include other parts. In some embodiments, further processing includes incorporating one or more structural features and / or reinforcing elements. For example, the filter medium can be combined with additional structural features such as polymer mesh and / or metal mesh. In one embodiment, a screen backing can be provided on the filter medium, thereby providing further rigidity. In some cases, the screen backing can help maintain a pleated structure. For example, the screen backing can be an extended metal mesh or an extruded plastic mesh.

[0143] In some embodiments, the layer described herein may be a nonwoven web. The nonwoven web may include non-oriented fibers (e.g., fibers randomly arranged within the web). Examples of nonwoven webs include webs made by wet-laid or non-wet-laid processes as described herein. Nonwoven webs also include paper, such as cellulose-based webs.

[0144] Filter media can be incorporated into a variety of suitable filter elements for a variety of applications, including gas and liquid filtration. Filter media suitable for gas filtration can be used for HVAC, HEPA, masks and ULPA filtration applications. For example, filter media can be used in heating and air conditioning pipes. In another example, filter media can be used for respirators and mask applications (for example, surgical masks, industrial masks and industrial respirators). Filter element can have any suitable configuration as known in the art, including bag filters and plate filters. The filter assembly for filtering applications can include any one of a variety of filter media and / or filter elements. Filter element can include the above-mentioned filter media. The example of filter element includes gas turbine filter element, dust collection element, heavy air filter element, automobile air filter element, air filter element for large displacement gasoline engine (for example, SUV, pickup truck, truck), HVAC air filter element, HEPA filter element, ULPA filter element, vacuum bag filter element, fuel filter element and oil filter element (for example, lubricating oil filter element or heavy lubricating oil filter element).

[0145] The filter element can be incorporated into corresponding filtration systems (gas turbine filtration systems, heavy-duty air filtration systems, automotive air filtration systems, HVAC air filtration systems, HEPA filtration systems, ULPA filtration systems, vacuum bag filtration systems, fuel filtration systems, and oil filtration systems). The filter media can optionally be pleated into any of a variety of configurations (e.g., plates, cylinders).

[0146] The filter element may also be in any suitable form, such as a radial filter element, a plate filter element, or a channel flow element. The radial filter element may comprise a pleated filter medium confined within two open mesh screens of a cylindrical shape. During use, fluid may flow from the outside through the pleated medium to the inside of the radial element.

[0147] In some cases, the filter element comprises a housing that can be arranged around the filter medium. The housing can have a variety of configurations, and the configuration varies according to the intended application. In some embodiments, the housing can be formed by a frame arranged around the periphery of the filter medium. For example, the frame can be heat-sealed to the periphery. In some cases, the frame has a generally rectangular configuration that surrounds all four sides of the generally rectangular filter medium. The frame can be formed by a variety of materials, including any combination of, for example, cardboard, metal, polymer, or suitable material. The filter element may also include a variety of other features known in the art, such as stabilization features for stabilizing the filter medium relative to the frame, spacers, or any other suitable features.

[0148] As mentioned above, in some embodiments, filter medium can be incorporated into bag-type (or pocket-type) filter element.Bag-type filter element can be formed by any suitable method, for example, by placing two filter media together (or folding a single filter medium in half), and making three sides (or if folding, both sides) match each other so that only one side remains open, thereby forming a pocket in the filter.In some embodiments, a plurality of filter pockets can be attached to the frame to form a filter element.It should be understood that filter medium and filter element can have a variety of different structures, and specific structure depends on the application of filter medium and element used therein.In some cases, substrate can be added to filter medium.

[0149] The filter element may have the same property values ​​as those described above in connection with the filter media. For example, the gamma value, pressure drop, thickness and / or basis weight described above may also be found in the filter element.

[0150] During use, when a fluid (e.g., air) flows through the filter medium, the filter medium mechanically captures foreign particles onto the filter medium. The filter medium does not need to be charged to improve the capture of contaminants. Therefore, in some embodiments, the filter medium is not charged. However, in some embodiments, the filter medium may be charged.

[0151] Example 1

[0152] This example describes DOP loading of filter media with various pre-filter layers. The filter media had similar initial pressure drop, initial DOP penetration percentage, and gamma values, but differed in the median fiber diameter and basis weight of the pre-filter layer. The filter media without a pre-filter layer showed a very high increase in pressure drop due to pore plugging by aerosol. During DOP loading, the median fiber diameter was less than or equal to 2 microns and the basis weight was less than 30 g / m 2 The pressure drop of the filter media changes with time as little as possible. Figure 2 shown.

[0153] A filter media was formed containing a pre-filter layer, a HEPA efficiency layer, and a pleated backing layer. The pre-filter layer was upstream and directly adjacent to the HEPA efficiency layer, while the pleated backing layer was the most downstream layer. The HEPA efficiency layer was an electrospun nylon layer having a median fiber diameter of 250 nm. The HEPA efficiency layer had an initial DOP efficiency of 99.985% and an initial pressure drop of 25.5 mm H2O. The basis weight of the HEPA efficiency layer was 2.2 g / m 2 . During formation, the electrospun nylon fibers were collected onto a wet-laid pleatable backing layer, which was passed through the electrospinning line. The pleatable backing layer contained a blend of polyester fibers and an acrylate binder. The thickness of the pleatable backing layer was 0.6 mm and the air permeability was 265 CFM. Other properties of the pleatable backing layer are shown in Table 1. The pleatable backing layer with the efficiency layer and appropriate pre-filter layer was then hand-collated for DOP loading testing. Unless otherwise stated, the structural and performance properties of the layers and the entire filter were measured as described herein.

[0154] Table 1. Properties of the pleatable backing layer

[0155]

[0156] Three different polypropylene pre-filters were combined with an efficiency layer and a pleated backing layer. The pre-filter layers differed only in their median fiber diameter and basis weight. Pre-filter layers 1 and 2 had a median fiber diameter of less than 1 micron and a basis weight of less than 30 g / m 2 The median fiber diameter of the standard meltblown pre-filter layer is greater than 2 microns and the basis weight is greater than or equal to 30g / m 2 The standard meltblown pre-filter layer was formed using standard meltblowing technology. However, pre-filter layers 1 and 2 were formed using a meltblowing process to form meltblown fibers having relatively small diameters. The median fiber diameter of each pre-filter layer, the basis weight of each pre-filter layer, the initial pressure drop of each filter medium, the initial DOP penetration of each filter medium, and the percentage change in pressure drop of each filter medium after 30 minutes are shown in Table 2.

[0157] Table 2. Characteristics of filter media with various pre-filter layers

[0158]

[0159] As shown in Table 2, filter media including a pre-filter layer having a median fiber diameter less than or equal to 2 microns (i.e., pre-filter layer 1 or 2) had a lower increase in pressure drop than filter media lacking a pre-filter layer and filter media having a pre-filter layer having a median fiber diameter greater than 2 microns (i.e., standard meltblown). It is expected that filter media including a pre-filter layer having a median fiber diameter less than or equal to 2 microns will have a longer service life and lower energy consumption.

[0160] In addition, it is believed that the low pressure drop observed over time in pre-filter layers 1 and 2 is due to reduced clogging and the enhanced ability of pre-filter layers 1 and 2 to prevent DOP particles (which are oil particles) from forming a DOP oil film between pores during loading. Although the standard meltblown has a reduced pressure drop increase compared to the filter media without a pre-filter layer, the observed pressure drop increase for the standard meltblown is steeper and higher than that of the filter media containing pre-filter layers 1 or 2. The behavior of the filter media containing the standard meltblown may be due to the formation of a DOP oil film on at least a portion of the pores in the layer and / or the entire filter media, which is suppressed in the filter media containing pre-filter layers 1 or 2.

[0161] Having thus described several aspects of at least one embodiment of the present invention, it will be appreciated that a variety of changes, modifications and improvements will readily occur to those skilled in the art. These changes, modifications and improvements are intended to be a part of this disclosure and are intended to be within the spirit and scope of the present invention. Therefore, the above description and accompanying drawings are intended only as examples.

[0162] The present invention also provides the following technical solutions:

[0163] Note 1. A filter medium comprising:

[0164] A pre-filter layer, the pre-filter layer comprising first fibers having a median diameter of less than or equal to about 2 microns, the pre-filter layer having a thickness of greater than or equal to about 20 microns, wherein the basis weight of the pre-filter layer is less than about 30 g / m 2 , an initial DOP efficiency of less than or equal to about 90%; and

[0165] A second layer comprising second fibers having a median diameter less than or equal to about 1 micron, wherein the second layer has an initial DOP efficiency greater than or equal to about 60%, wherein the second layer has an initial DOP efficiency greater than the pre-filter layer.

[0166] Note 2. A filter medium comprising:

[0167] A pre-filter layer, the pre-filter layer comprising first fibers having a median diameter of less than or equal to about 2 microns, the pre-filter layer having a thickness of greater than or equal to about 20 microns, wherein the basis weight of the pre-filter layer is less than about 30 g / m 2 , an initial DOP efficiency of less than or equal to about 90%; and

[0168] A polymer membrane having an initial DOP efficiency of greater than or equal to about 60%, wherein the initial DOP efficiency of the polymer membrane is greater than that of the pre-filtration layer.

[0169] Note 3. The filter medium according to any of the preceding notes, wherein the surface area of ​​the pre-filter layer is greater than or equal to about 1.75 m 2 / g and less than or equal to about 45m 2 / g.

[0170] Note 4. The filter medium of any of the preceding notes, wherein the pre-filter layer has a thickness of less than or equal to about 1 mm.

[0171] Note 5. The filter media of any of the preceding notes, wherein the pre-filter layer has an initial DOP efficiency greater than or equal to about 10%.

[0172] Note 6. The filter media of any of the preceding notes, wherein the pre-filter layer has a solidity of less than or equal to about 25%.

[0173] Note 7. The filter medium of any of the preceding notes, wherein the pre-filter layer has a pressure drop of less than 35 mm H2O.

[0174] Note 8. The filter media of any of the preceding notes, wherein the first fibers have a median diameter less than or equal to about 1 micron.

[0175] Note 9. The filter media of any of the preceding notes, wherein the first fibers are continuous fibers.

[0176] Note 10. The filter medium of any of the preceding notes, wherein the first fibers are synthetic fibers.

[0177] Note 11. The filter media of any of Notes 1 or 3 to 10, wherein the second fibers have a median fiber diameter less than or equal to about 0.5 microns.

[0178] Note 12. The filter medium of any of Notes 1 or 3 to 11, wherein the first fibers have a median diameter greater than the second fibers have a median diameter.

[0179] Note 13. The filter medium of any of Notes 2 to 7 wherein the polymer membrane comprises a fluorinated polymer.

[0180] Note 14. The filter medium of any of the preceding notes, wherein the pre-filter has a gamma greater than or equal to about 7.

[0181] Note 15. A filter element comprising a filter medium according to any one of the preceding notes.

[0182] Note 16. The filter element of Note 15, wherein the filter element is a HEPA filter, a ULPA filter, an HVAC filter, or a mask.

[0183] Note 17. The filter media of any of Notes 1, 3-12, or 14-16, wherein the pre-filter layer comprises continuous fibers and the second layer comprises synthetic fibers.

[0184] Note 18. The filter media of any of Notes 1, 3-12, or 14-17, wherein the pre-filter layer and the second layer comprise synthetic fibers.

[0185] Note 19. The filter media of any of Notes 1, 3-12, or 14-17, wherein the pre-filter layer comprises synthetic fibers and the second layer comprises continuous fibers.

[0186] Note 20. The filter medium of any of Notes 1, 3 to 12, or 14 to 19, wherein the pre-filter layer and / or the second layer comprises electrospun fibers.

[0187] Note 21. The filter media of any of Notes 1, 3-12, or 14-19, wherein the pre-filter layer and / or the second layer comprises meltblown fibers.

[0188] Note 22. A method comprising:

[0189] A filter medium or a filter element according to any of the preceding notes is used to filter a fluid.

Claims

1. A filter medium comprising: a first layer, the first layer comprising first fibers, wherein the first fibers comprise synthetic fibers, wherein the synthetic fibers have a median diameter less than or equal to 4 microns, wherein the first layer has a thickness greater than or equal to 20 microns, wherein the first layer has an initial DOP efficiency less than or equal to 90% when in an uncharged state, and wherein the first layer has an air permeability greater than or equal to 10 CFM and less than or equal to 750 CFM; a second layer, the second layer comprising second fibers having a median diameter less than or equal to 1 micron, wherein the second layer has an initial DOP efficiency greater than or equal to 60%, and wherein the second layer has an initial DOP efficiency greater than the initial DOP efficiency of the first layer when the first layer is in an uncharged state; and The third layer has an air permeability greater than or equal to 75 CFM.

2. The filter media of claim 1, wherein the filter media comprises less than 1% by weight glass fibers.

3. The filter media of claim 1, wherein the filter media comprises 0 weight percent glass fibers.

4. The filter medium of any one of claims 1 to 3, wherein the third layer is a backing layer.

5. The filter medium according to any one of claims 1 to 3, wherein the basis weight of the first layer is less than or equal to 30 g / m 2 .

6. The filter media of any one of claims 1 to 3, wherein the first fibers have a median diameter less than or equal to 1 micron.

7. The filter media of any one of claims 1 to 3, wherein the synthetic fibers comprise meltblown fibers.

8. The filter media of any one of claims 1 to 3, wherein the second fibers comprise electrospun fibers.

9. The filter media of any one of claims 1 to 3, wherein the synthetic fibers have a median fiber diameter greater than or equal to 0.5 microns and less than or equal to 2 microns.

10. The filter medium according to any one of claims 1 to 3, wherein the surface area of ​​the first layer is less than or equal to 3 m 2 / g.

11. The filter medium of any one of claims 1 to 3, wherein the initial DOP efficiency of the first layer when in an uncharged state is greater than or equal to 30% and less than or equal to 80%.

12. The filter media of any one of claims 1 to 3, wherein the second fibers have a median fiber diameter less than or equal to 0.2 microns.

13. The filter media of any one of claims 1 to 3, wherein the air permeability of the third layer is greater than or equal to 75 CFM and less than or equal to 2,000 CFM.

14. The filter media of any one of claims 1 to 3, wherein the first layer is a pre-filter layer.

15. A method comprising filtering a fluid using the filter medium of any one of claims 1 to 3.

16. The filter media of any one of claims 1 to 3, wherein the first fibers have a median diameter less than or equal to 2 microns.

17. The filter media of any one of claims 1 to 3, further comprising a fourth layer.

18. The filter media of claim 17, further comprising a fifth layer.

19. The filter medium of claim 1, wherein: The first fibers include meltblown fibers; The second fiber comprises an electrospun fiber; The air permeability of the third layer is greater than or equal to 75 CFM and less than or equal to 2,000 CFM; and The filter medium has 0% by weight glass fibers.

20. The filter medium of claim 19, wherein: The first layer is a pre-filtration layer; The third layer is a backing layer; and The basis weight of the first layer is less than or equal to 30 g / m 2 .

21. A bicomponent fiber, wherein each component of the bicomponent fiber has a different melting temperature, the fiber comprising a core and a sheath, wherein the activation temperature of the sheath is lower than the melting temperature of the core, so that the sheath melts before the core, the sheath bonds to other fibers in the layer, and the core maintains its structural integrity.

22. A pleatable backing layer having a tensile strength in the machine direction (MD) greater than or equal to 2 pounds per inch, a tensile strength in the cross direction (CD) greater than or equal to 1 pound per inch, and a Mullen burst strength greater than or equal to 5 psi.

23. A membrane layer formed using a mixed ester of nitrocellulose, the membrane layer also comprising a fluorinated polymer; the membrane layer has a plurality of pores, the pores allowing fluid to pass through while contaminant particles are captured on the membrane, the average flow pore size of the membrane layer is greater than or equal to 0.5 microns and less than or equal to 40 microns.

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