Filter media containing a fine fiber layer

Abstract

The present disclosure describes a filter medium that minimizes the adverse effects of flow rate fluctuations on filter medium efficiency without a corresponding increase in pressure drop. The filter medium includes a support layer, a continuous fine fiber layer, and an efficiency layer. The continuous fine fiber layer includes continuous fine fibers having a diameter of up to 10 micrometers and disposed downstream of the efficiency layer.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 912,456, filed October 8, 2019; U.S. Provisional Patent Application No. 62 / 947,998, filed December 13, 2019; U.S. Provisional Patent Application No. 62 / 952,979, filed December 23, 2019; U.S. Provisional Patent Application No. 62 / 992,003, filed March 19, 2020; and U.S. Provisional Patent Application No. 63 / 004,602, filed April 3, 2020, the entire disclosures of which are incorporated herein by reference. [Background technology]

[0002] Filter media for use in hydraulic applications are typically tested at a constant flow rate. However, in many hydraulic applications, the flow rate changes during use. Fluctuations in flow rate, including, for example, circulating or other dynamic flow conditions, can adversely affect the performance of the filter media, particularly its efficiency, by providing multiple opportunities for particles to pass through the interstices of the media. Summary of the Invention [Means for solving the problem]

[0003] The present disclosure describes a filter medium that minimizes the adverse effect of flow rate fluctuations on the efficiency of the filter medium without a corresponding increase in pressure drop, i.e., an increase in the pressure required to force the fluid through the filter medium. At the time of the present invention, it was known that the effect of flow rate fluctuations on the performance of the filter medium could be minimized by increasing the efficiency of the filter medium, but the measures used to increase the efficiency of the filter medium also resulted in a corresponding increase in pressure drop. Such an increase in pressure drop increases the chance that the filter will be bypassed (for example, via a bypass valve), increasing energy consumption and shortening the filter's lifespan. In contrast, the filter medium described herein achieves high efficiency without worsening pressure drop.

[0004] In one aspect, the present disclosure describes a filter medium comprising a support layer; a continuous fine fiber layer having a thickness of at most 50 μm; and an efficiency layer. The composite comprising the support layer and the continuous fine fiber layer has a P95 / P50 ratio of at most 1.8, at most 1.9, or at most 2. The efficiency layer has a P95 / P50 ratio of at least 1.8, at least 1.9, or at least 2. Additionally, the P95 value of the composite is within the range provided by the P5 and P50 values ​​of the efficiency layer.

[0005] In some embodiments, the composite has a P95 / P50 ratio greater than one.

[0006] In some embodiments, the continuous fine fiber layer has a thickness of at least 2 μm. In some embodiments, the continuous fine fiber layer is disposed between the efficiency layer and the support layer. In some embodiments, the continuous fine fiber layer comprises fibers having a diameter of at most 10 micrometers (μm). In some embodiments, the continuous fine fiber layer comprises fibers having an elliptical shape. In some embodiments, the continuous fine fiber layer comprises fibers having a diameter of at least 1 micrometer (μm).

[0007] In some embodiments, the continuous fine fiber layer comprises a mixture of fibers of different diameters. The fibers of different diameters may be mixed within a single layer of the continuous fine fiber layer. Additionally or alternatively, the fibers of different diameters may form different layers in the continuous fine fiber layer.

[0008] In some embodiments, the efficiency layer has a P95 / P50 ratio of at most 10, at most 15, or at most 20. In some embodiments, the efficiency layer is positioned upstream of the filter media.

[0009] In some embodiments, the filter media further comprises a second efficiency layer, which may be positioned adjacent to and upstream of the efficiency layer.

[0010] In some embodiments, the efficiency layer comprises bicomponent fibers and efficiency fibers, the efficiency fibers having a smaller diameter than the bicomponent fibers. The efficiency fibers may comprise glass fibers. In some embodiments, the efficiency layer comprises microfibrillated cellulose fibers.

[0011] In some embodiments, the support layer may include a spunbond layer.

[0012] In another aspect, the present disclosure describes a filter element comprising the filter media described herein. In some embodiments, the wire support can be positioned downstream of the support layer.

[0013] As used herein, "fibers" have an average fiber diameter of at most 100 micrometers.

[0014] As used herein, a fiber having an "average" diameter means that in a sample of multiple fibers, the average fiber diameter of the population of fibers in the sample has the stated average fiber diameter. The population of fibers includes fibers having diameters within 25% of the average fiber diameter. For example, a population of fibers having an average diameter of 1000 nm includes fibers having diameters of at least 750 nm and at most 1250 nm. In another example, a population of fibers having an average diameter of 250 nm includes fibers having diameters of at least 188 nm and at most 313 nm. In a further example, a population of fibers having an average diameter of 500 nm includes fibers having diameters of at least 375 nm and at most 625 nm. In yet another example, a population of fibers having an average diameter of 1400 nm includes fibers having diameters of at least 1050 nm and at most 1750 nm.

[0015] Fiber diameter can be measured using top-down SEM images. The sample can be sputter coated. A useful sputter coater can be a mixture of gold and palladium, including a 60:40 Au:Pd mixture. Measuring the fiber diameter at at least 30 locations within the sample can provide a more accurate measurement of fiber diameter. Software such as Trainable Weka Segmentation (ImageJ plugin) can be useful for analyzing fiber diameter.

[0016] As used herein, "fine fibers" refer to fibers having a diameter of at most 10 micrometers (μm). In some embodiments, fine fibers have a diameter of at least 50 nm or at least 100 nm.

[0017] The term "diameter" refers to either the diameter of a circular cross-section of a fiber or the largest cross-sectional dimension of a non-circular cross-section of a fiber.

[0018] As used herein, the term "particle size" refers to the diameter of a particle as determined as described in ISO 11171:2016.

[0019] As used herein, "continuous fine fibers" refer to fine fibers having an aspect ratio (i.e., the ratio of the length to the width dimensions) of at least 5,000, or more preferably at least 10,000. Reference herein to a continuous fine fiber layer refers to a layer comprising continuous fine fibers (as opposed to short-cut fine fibers). A continuous fine fiber layer is preferably formed by a fiber-forming process that produces continuous fine fibers, although the resulting layer may or may not contain only one continuous fine fiber. That is, a continuous fine fiber layer may comprise one or more fine fibers having an aspect ratio of at least 5,000, or more preferably at least 10,000.

[0020] As used herein, "short cut microfibers" refer to microfibers having an aspect ratio (i.e., the ratio of the length to the width dimension) of less than 5000, less than 2500, or less than 1,000. Typically, short cut microfibers may have an aspect ratio of at least 10 and up to 5,000.

[0021] As used herein, "mixed" fibers or "mixed fiber structure" refers to fibers having at least two different diameters, where fibers having a first average diameter are mixed with fibers having a second average diameter, i.e., fibers are intermingled within the same layer (or tier) of a media structure, either as a result of the fibers being formed or deposited simultaneously or by using very short (e.g., up to 10 seconds, up to 20 seconds, or up to 30 seconds) pulses of each polymer solution. When visualized using top-down SEM imaging, the fibers having the first average diameter can be seen as being located both below and above the fibers having the second average diameter.

[0022] As used herein, "layered" fibers or "layered fiber structure" refers to fibers having at least two different diameters, wherein the fibers having a first average diameter are substantially unentangled with the fibers having a second average diameter as a result of the fibers of different diameters being applied to a substrate in an alternating manner.

[0023] As used herein, unless otherwise specified, pore sizes (e.g., P5, P50, and P95) and pore size ratios (e.g., P95 / P50) are determined using capillary flow porometry. Capillary flow porometry can be performed using a continuous pressure scan mode. It can be useful to use silicone oil, which has a surface tension of 20.1 dynes / cm and a wetting contact angle of 0, as the wetting liquid. The sample is first tested in a dry state, varying from low to high pressure, and then in a wet state, also varying from low to high pressure. Testing is typically performed at ambient temperature conditions (e.g., 20°C to 25°C). 256 data points can be collected across the entire pressure scan range for both the wetting and drying curves. Typically, tortuosity and / or shape factors are not used (i.e., factors equal to 1 can be used for comparison with other test methods that use adjustment factors).

[0024] As used herein, the value P(x%) is the calculated pore size where the wetting curve is equal to (100-x)% of the drying curve, as determined using the methods described herein. Although a calculated value, it can be understood to represent the point where x% of the total flow through the bed passes through pores of that pore size or smaller. For example, P50 (mid-flow pore size) represents the point where the wetting curve is equal to half the drying curve and can be considered the pore size where 50% of the total flow through the bed passes through pores of that pore size or smaller.

[0025] The average pore size (e.g., average maximum pore size) can be calculated from the median of at least three measurements (taken from at least three different sample locations). Individual measurements of maximum pore size (also called P100) can be found at the bubble point, which is identified after fluid begins to pass through the sample, three consecutive measurements show an increase of at least 1%, and 256 data points are collected across the scan at a rate of approximately 17 data points / minute.

[0026] As used herein, the "β ratio" (also referred to herein as "β" or "beta ratio") is the ratio of upstream particles to downstream particles. The more efficient the filter, the higher the β ratio. The β ratio is defined as follows:

number

[0027] As used herein, "overall β ratio" or "overall β" is the ratio of the sum of all upstream particles over the course of an assay to the sum of all downstream particles over the course of the test (the test is conducted at a pressure of 25 psi (172 kPa)).

number

[0028] As used herein, "β100" is the particle size where the overall β is 100.

[0029] "Filtration efficiency" or "efficiency" as used herein refers to the percentage of contaminants removed by a filter, calculated as follows:

number

[0030] As used herein, "pressure drop" (also referred to herein as "dP" or "ΔP") relates to the pressure (applied by a pump) required to force a fluid (before the addition of contaminants) through a filter or filter medium at a particular fluid velocity. Unless otherwise specified, pressure drop is measured as described in ISO 3968:2017.

[0031] The terms "comprises" and their derivatives do not have a limiting meaning when these terms appear in the specification and claims. Such terms are understood to mean the inclusion of the stated step or element or group of steps or elements, but not the exclusion of other steps or elements or group of steps or elements. "Consisting of" means inclusive of and limited to everything that follows the phrase "consisting of." Thus, the phrase "consisting of" indicates that the recited elements are necessary or essential, and that no other elements may be present. "Consisting essentially of" means including the elements recited after the phrase, and is limited to other elements that do not interfere with or contribute to the activity or function specified in this disclosure for the recited elements. Thus, the phrase "consisting essentially of" indicates that the recited elements are necessary or essential, but that other elements are optional and may or may not be present depending on whether they materially affect the activity or function of the recited elements.

[0032] The words "preferred" and "preferred" refer to embodiments of the invention that may offer certain benefits, under particular circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the listing of one or more preferred embodiments does not imply that other embodiments are not useful, or is intended to exclude other embodiments from the scope of the invention.

[0033] Unless otherwise stated, "a," "an," "the," and "at least one" are used interchangeably to mean one or more. The phrases "at least one" and "including at least one" followed by a list refer to any one of the listed items and any combination of two or more of the listed items.

[0034] As used herein, the term "or" is generally used in its ordinary sense, including "and / or," unless the context clearly dictates otherwise. The term "and / or" refers to one or all of the listed elements or a combination of any two or more of the listed elements.

[0035] As used herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). As used herein, the recitations of "up to" a number (e.g., up to 50) include that number (e.g., 50).

[0036] In any method disclosed herein that includes separate steps, the steps can be performed in any practicable order, and, where appropriate, any combination of two or more steps can be performed simultaneously.

[0037] Throughout this specification, references to "one embodiment," "embodiment," "particular embodiment," or "some embodiments" mean that a particular feature, configuration, composition, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Thus, the appearances of such phrases in various places throughout this specification do not necessarily refer to the same embodiment of the present disclosure. Furthermore, particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more embodiments.

[0038] References to standard methods (e.g., ASTM, TAPPI, AATCC, etc.) refer to the most current method available at the time of filing this disclosure, unless otherwise specified.

[0039] Unless otherwise indicated, all numbers expressing quantities, molecular weights, and the like of ingredients used in the specification and claims should be understood in all instances to be modified by the term "about." The term "about," as used herein in connection with a measured quantity, refers to the variation in that measured quantity that is expected by one of ordinary skill in the art making the measurement and exercising a level of care commensurate with the purpose of the measurement and the precision of the measuring device used. Accordingly, unless specifically indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0040] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible, however, all numerical values ​​inherently contain a range necessarily resulting from the standard deviation found in their respective testing measurements.

[0041] All headings are for the convenience of the reader and should not be used to limit the meaning of the text that follows the heading, unless specifically stated.

[0042] The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The following description more particularly exemplifies exemplary embodiments. In several places throughout the specification, guidance is provided by lists of examples that can be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list. [Brief explanation of the drawings]

[0043] [Figure 1A]1 illustrates exemplary filter media and filter element structures as further described herein. [Figure 1B] 1 illustrates exemplary filter media and filter element structures as further described herein. [Figure 2A] 1 shows a schematic diagram of an exemplary embodiment of a continuous fine fiber layer of a filter media described herein, comprising a mixture of fibers of different diameters in different levels of the continuous fine fiber layer. [Figure 2B] Exemplary images of a continuous fine fiber layer including a fine fiber layer deposited on a nylon scrim are shown at 500x magnification (top panel) and 2000x magnification (bottom panel), where an efficiency layer, not shown, would typically be placed upstream of the media. [Figure 2C] 1 shows an exemplary SEM image (1000x magnification) of a sample prepared as described in Example 3 (a continuous fine fiber layer comprising fine fine fibers resting directly on a scrim). [Figure 2D] 1 shows an exemplary SEM image (1000x magnification) of a sample made as described in Example 3 (a continuous fibril layer comprising thin fibrils overlaid on thick fibrils). [Figure 2E] 1 shows exemplary SEM images (1000x magnification) of continuous fine fiber layer samples made as described in Example 4 using Solution 1 to achieve thin fine fibers (left panel), Solution 1 and Solution 2 to achieve mixed diameter (small and large) fine fibers (middle panel), and Solution 2 to achieve thick fine fibers (right panel). [Figure 2F] 1 shows a schematic diagram of a sample made as described in Example 3 (thin fine fibers laid directly on a scrim). [Figure 2G] 1 shows a schematic of a continuous fine fiber layer sample made as described in Example 3 (thin fine fibers laminated to thick fine fibers, thick fine fibers resting directly on a scrim). [Figure 2H]1A-1C show schematic diagrams of exemplary media structures. In each structure, a support layer is not shown, but would typically be located downstream of the media. In each structure, an efficiency layer is not shown, but would typically be located upstream of the media. [Figure 2I] 1A-1C show schematic diagrams of exemplary media structures. In each structure, a support layer is not shown, but would typically be located downstream of the media. In each structure, an efficiency layer is not shown, but would typically be located upstream of the media. [Figure 2J] 1A-1C show schematic diagrams of exemplary media structures. In each structure, a support layer is not shown, but would typically be located downstream of the media. In each structure, an efficiency layer is not shown, but would typically be located upstream of the media. [Figure 2K] 1A-1C show schematic diagrams of exemplary media structures. In each structure, a support layer is not shown, but would typically be located downstream of the media. In each structure, an efficiency layer is not shown, but would typically be located upstream of the media. [Figure 2L] 1A-1C show schematic diagrams of exemplary media structures. In each structure, a support layer is not shown, but would typically be located downstream of the media. In each structure, an efficiency layer is not shown, but would typically be located upstream of the media. [Figure 2M] 1A-1C show schematic diagrams of exemplary media structures. In each structure, a support layer is not shown, but would typically be located downstream of the media. In each structure, an efficiency layer is not shown, but would typically be located upstream of the media. [Figure 3A]The β ratio versus particle size is shown for three different media under circulating flow conditions (blue) or steady flow conditions (red). Left panel: Donaldson Synteq XP™ synthetic liquid media with an efficiency rating of 10 microns (μm). Center panel: Donaldson Synteq XP™ synthetic liquid media with an efficiency rating of 5 microns. Right panel: Filter media (XP / fine fiber / scrim) described in Example 1 (efficiency layer (Donaldson Synteq XP™ synthetic liquid media with an efficiency rating of 10 microns), continuous fine fiber layer, and support layer (scrim)). [Figure 3B] Figure 3A shows the pressure drop for the same media tested. [Figure 4]

[0023] Figure 1 shows the particle size-to-beta ratio under steady-state flow conditions for filter elements including Donaldson Synteq XP™ synthetic liquid media with a 10 micron efficiency rating (top) or the filter media described in Example 2 (efficiency layer (Donaldson Synteq XP™ synthetic liquid media with a 10 micron efficiency rating), continuous fine fiber layer, and support layer). The beta ratio was measured as described in the steady-state flow condition test in the Examples. The three numbers separated by slashes indicate the International Organization for Standardization (ISO) cleanliness code, measured and defined as described in ISO 4406:2017. [Figure 5]

[0023] Figure 1 shows the particle size-to-particle size beta ratio under recirculating flow conditions for filter elements including Donaldson Synteq XP™ synthetic liquid media with a 10 micron efficiency rating (top) or the filter media described in Example 2 (efficiency layer (Donaldson Synteq XP™ synthetic liquid media with a 10 micron efficiency rating), continuous fine fiber layer, and support layer). The beta ratio was measured as described in the recirculating flow conditions test in the Examples. The three numbers separated by slashes indicate the International Organization for Standardization (ISO) cleanliness code, measured and defined as described in ISO 4406:2017. [Figure 6A]Figure 6A shows the initial pressure drop plotted against the maximum composite pore size (Figure 6A) or the intermediate flow pore size (Figure 6B) for composites including one or more continuous fine fiber layers and a support layer, as further described in Example 5. Triangles represent samples that maintained the structural integrity of the fine fibers throughout the test. Squares represent samples in which the fine fibers were blown off during the test. [Figure 6B] Figure 6A shows the initial pressure drop plotted against the maximum composite pore size (Figure 6A) or the intermediate flow pore size (Figure 6B) for composites including one or more continuous fine fiber layers and a support layer, as further described in Example 5. Triangles represent samples that maintained the structural integrity of the fine fibers throughout the test. Squares represent samples in which the fine fibers were blown off during the test. [Figure 7] 1 shows the cumulative flow pore size distribution of the samples described in Example 6. [Figure 8A] 1 shows an exemplary cross-sectional image of a continuous fine fiber layer on a support layer. [Figure 8B] 1 shows exemplary images of a method for measuring the thickness of a continuous fine fiber layer, as further described in the Examples. [Figure 8C] 1 shows exemplary images of a method for measuring the thickness of a continuous fine fiber layer, as further described in the Examples. [Figure 8D] 1 shows exemplary images of a method for measuring the thickness of a continuous fine fiber layer, as further described in the Examples. DETAILED DESCRIPTION OF THE INVENTION

[0044] The present disclosure describes a filter medium that minimizes the adverse effects of fluctuations in flow rate (e.g., occurring during dynamic flow conditions) on filter medium efficiency without a corresponding increase in pressure drop, i.e., the increase in pressure required to force fluid through the filter medium. The present disclosure further describes methods of forming the filter medium.

[0045] Challenges in designing filter media for dynamic flow conditions The present disclosure describes a filter medium that minimizes the adverse effects of flow rate fluctuations on filter medium efficiency without a corresponding increase in pressure drop. These flow rate fluctuations may occur, for example, during dynamic flow conditions. Dynamic flow conditions include, for example, circulating flow conditions. However, as discussed further herein, the filter medium design can also be used to improve performance in other liquid applications.

[0046] If a filter were designed with efficiency as the only performance criterion, it would easily solve all filtration needs. However, in most applications, pressure and filter life must also be considered and balanced against the desired efficiency.

[0047] For example, it would be simple to design a filter that could remove 100% of all particles larger than 0.5 μm, but such a filter design would be impractical if the pressure required to force fluid through the filter was unreasonably high or if the filter needed to be replaced at impractically short intervals. In a more specific example of a filter, even if a car's oil filter could keep the engine perfectly clean, if that filter required a large portion of the engine's power to force fluid through the filter and needed to be replaced every time the vehicle was refueled, it would be virtually commercially unfeasible.

[0048] To illustrate how the filter media described herein improve efficiency performance, it is useful to first explain how the filter media collects contaminants and how that collection affects the pressure on the filter media as fluid flows through it.

[0049] Filter media contain spaces between their components and can collect contaminants on their top surface. As contaminants collect in the spaces in or above the filter media, the spaces for fluid flow become smaller and fewer in number, increasing the pressure required to force the fluid through the filter media. The lifespan of a working liquid filter media (especially hydraulic) is typically defined by the maximum pressure generated when a particular liquid flows through the filter media. Thus, as contaminants collect, the pressure drop increases and the porosity of the filter media (the ratio of the volume of voids in the porous media to the total volume of the porous media) decreases.

[0050] Reduced porosity is the primary cause of pressure drop and is therefore the primary parameter defining the lifespan of a liquid filter. Therefore, to achieve a longer lifespan for hydraulic filter media, it is desirable to manage how contaminants are collected by the filter media. Distributing the locations where contaminants are collected (e.g., by making more space available throughout the depth of the media) rather than collecting contaminants in a single location (e.g., on the surface of the media) maintains the porosity of the media longer, reduces the pressure required to move the liquid through the media, and extends the lifespan of the media. Media designs that distribute the locations where contaminants are collected throughout the depth of the media are referred to as depth-loading media.

[0051] Higher porosity throughout the depth of the filter media allows more space for contaminants to collect during use. Hypothetically, the longest-lasting filter media is one with 100% porosity. However, this advantage is merely hypothetical, since some of the volume must be occupied by something to capture and retain contaminants. Therefore, it is desirable to have as high a porosity as possible while still providing the filter media with the necessary properties to achieve the desired efficiency and strength.

[0052] In hydraulic filtration, the primary filtration mechanism is size exclusion. During size exclusion, contaminants are trapped by the filter media when they are trapped in pores of a smaller size than the contaminant. A wide distribution of pore sizes throughout the depth of the filter media allows for distribution of contaminants within the thickness of the filter media. The pores may be randomly spaced or may form a gradient or other pattern structure. Regardless of the pattern (or lack thereof), the desired effect is to distribute the contaminants as much as possible throughout the depth of the filter media.

[0053] Filter media designed for size exclusion collection have been shown in clinical trials to perform well under steady-state flow conditions. However, in most hydraulic flow applications, the flow rate through the filter media can be variable and have a cyclical flow pattern. Under these fluctuating flow conditions, changing forces, more commonly referred to as dynamic forces, are exerted on both the filter media structure and the contaminants captured by the filter media. These dynamic forces change the way the filter media captures contaminants, reducing overall efficiency.

[0054] Without wishing to be bound by theory, it is believed that the overall decrease in efficiency observed during fluctuating flow conditions is due to contaminants previously trapped in pores with dimensions smaller than those of the contaminants being re-released when a different force is applied to the filter media.

[0055] As a result, filters rated for a particular efficiency performance under steady-state flow conditions often perform poorly under variable (e.g., cyclic) flow conditions, causing more contaminants to pass through the filter and reach the downstream output. Increased contaminants downstream of the filter can increase wear on the hydraulic system and / or shorten the life of critical hydraulic components.

[0056] Therefore, it is desirable for users of these hydraulic systems to use hydraulic filter media that are designed to perform reliably under varying flow conditions.

[0057] One way to increase the efficiency of media under fluctuating flow conditions is to increase the thickness of the filter media. Increasing the thickness (or depth) increases the chances of capturing certain contaminants. However, if the filter media becomes too thick, it becomes difficult to pack into a limited space, such as a traditional pleated structure. Furthermore, even if increasing the thickness improves the chances of capturing certain contaminants, contaminants may still pass through the media.

[0058] Another way to increase the efficiency of media under fluctuating flow conditions is to reduce the pore size of the filter material. However, as mentioned above, reducing the pore size will cause the filter material to reach its capacity limit more quickly. Furthermore, smaller pore sizes may require more pressure to force the liquid through the media before contaminants are captured, and certainly more pressure will be required to force the liquid through the media after a certain amount of contaminants has been captured.

[0059] The filter media described herein attempt to overcome these limitations by providing a multi-layer structure. While each layer individually would degrade performance, the combination of layers improves performance under fluctuating flow conditions (including, for example, circulating flow conditions).

[0060] filter medium In one aspect, the present disclosure describes a filter medium including a support layer, a continuous fine fiber layer, and an efficiency layer. In some embodiments, the continuous fine fiber layer is disposed between the efficiency layer and the support layer, and the efficiency layer is disposed upstream of the filter medium. In some embodiments, the continuous fine fiber layer functions as a surface loading layer. In some embodiments, the efficiency layer functions as a depth loading layer.

[0061] As noted above, a depth-loading layer alone has low solidity and a wide pore size distribution, resulting in low efficiency under fluctuating flow conditions. A continuous fine fiber layer alone, when functioning as a surface-loading layer, would have a very short lifespan under fluctuating flow conditions because the pressure required to force liquid through the filter medium begins to increase almost immediately as contaminants are collected. Also, a support layer alone would be unsuitable for use as a filter medium under fluctuating flow conditions because its efficiency is virtually nonexistent.

[0062] However, in combination with selected features described further herein, the support layer, continuous fine fiber layer, and efficiency layer minimize the adverse effects of fluctuating flow conditions on filter media efficiency and provide a filter media that does not exhibit commercially practically unviable increases in pressure drop.

[0063] For example, as described further herein, a continuous fine fiber layer acting as a surface loading layer prevents particles from passing through the filter media. Additionally, because the continuous fine fiber layer is very thin, it does not increase the pressure drop as much as a thicker media. Furthermore, combining a continuous fine fiber layer with an appropriate low solidity layer (i.e., an efficiency layer that functions as a depth loading layer) can extend the life of the filter media.

[0064] Additional optional construction of filter media As described above, the filter medium includes a continuous fine fiber layer and an efficiency layer. However, in some embodiments, the filter medium may include multiple continuous fine fiber layers and multiple efficiency layers. For example, in one embodiment, the filter medium may include a first efficiency layer disposed upstream of the filter medium, a first continuous fine fiber layer disposed downstream of the first efficiency layer, a second efficiency layer disposed downstream of the first continuous fine fiber layer, and a second fine fiber layer disposed downstream of the second efficiency layer. A support layer is typically disposed downstream of the most downstream continuous fine fiber layer (see the left panel of Figure 1B).

[0065] For example, in another embodiment, the filter media includes a first efficiency layer disposed upstream of the filter media, a first continuous fine fiber layer disposed downstream of the first efficiency layer, a second efficiency layer disposed downstream of the first continuous fine fiber layer, a second fine fiber layer disposed downstream of the second efficiency layer, a third efficiency layer disposed downstream of the first continuous fine fiber layer, and a third continuous fine fiber layer disposed downstream of the third efficiency layer. A support layer is typically disposed downstream of the most downstream continuous fine fiber layer (see the middle panel of FIG. 1B).

[0066] In some embodiments, the filter media may include two or more efficiency layers disposed upstream of the filter media and a continuous fine fiber layer disposed downstream of the efficiency layer (see right panel of FIG. 1B). Additional efficiency layers may be used, for example, to extend the filter media's throughput limit (and thus lifespan) or improve pressure drop. Such additional efficiency layers may also be referred to as load layers. An exemplary embodiment of a filter media including a support layer, a continuous fine fiber layer, an efficiency layer, and a second efficiency layer (or load layer) is described and characterized in Example 6.

[0067] Characteristics of filter media In some embodiments, the filter media described herein achieve increased efficiency compared to media that do not include one or more continuous fine fiber layers that do not worsen the pressure drop, i.e., the pressure drop of the filter media described herein is within 150%, within 100%, within 50%, within 20%, within 15%, or within 10% of the pressure drop of a filter media that does not include one or more continuous fine fiber layers.

[0068] In some embodiments, the filter media described herein achieve increased efficiency compared to media that do not include one or more continuous fine fiber layers or one or more support layers that do not exacerbate the pressure drop, i.e., the pressure drop of the filter media described herein is within 150%, within 100%, within 50%, within 20%, within 15%, or within 10% of the pressure drop of a filter media that does not include one or more continuous fine fiber layers or support layers.

[0069] For example, in exemplary embodiments, the pressure drop of the filter media is within 50% to 150% of the pressure drop observed with one or more efficiency layers alone (i.e., the pressure drop of a filter media that does not include one or more continuous fine fiber layers or a support layer).

[0070] In some embodiments, the filter media described herein achieve equivalent efficiency under circulating flow conditions compared to media that do not include a continuous fine fiber layer under steady-state flow conditions. Preferably, this efficiency is achieved without a significant pressure drop penalty. For example, the pressure drop is within 150%, 100%, 50%, 20%, 15%, or 10% of the pressure drop of a filter media that does not include one or more continuous fine fiber layers or a support layer.

[0071] In some embodiments, the filter media described herein have an overall β of at least 5, at least 7, or at least 10 under circulating flow conditions. 10μm The filter media has an overall β of at most 50, at most 100, at most 200, at most 300, at most 500, at most 1000, at most 1500 or at most 2000. 10μm For example, the overall β 10μm can be in the range of 5 to 2000, in the range of 5 to 200, or in the range of 5 to 100.

[0072] Circulating flow conditions can be evaluated using ISO / CD 23369 Edition 1, except when testing flat sheet performance. Testing should be performed in single-pass mode and at 25°C. Flow velocities through the medium can be circulated at 5 mm / s to 1.25 mm / s for a 10-second cycle. ISO 12103-1, Medium Test Dust, can be useful as a particle detector. An upstream particle concentration of 10 mg / L can be used. Continuous particle concentration measurements can be collected every 6 seconds. It can be useful to control the fluid conductivity in the range of 1000 picosiemens per meter (pS / m) to 1500 pS / m.

[0073] In some embodiments, one or more fibers of the filter media can be selected or treated to modify the electrostatic charge of the filter media. The charge typically includes a layer of positive or negative charge trapped at or near the surface of the polymer or a charge cloud accumulated in the bulk of the polymer. The charge can also include a polarization charge frozen in the alignment of molecular dipoles. Methods for exposing materials to an electric charge are well known to those skilled in the art. These methods include, for example, thermal methods, liquid contact methods, electron beam methods, plasma methods, and corona discharge methods.

[0074] Average maximum pore size and average intermediate flow pore size of the composite material of the support layer and continuous fine fiber layer As described above, the filter media includes a support layer and a continuous fine fiber layer. In some embodiments, the continuous fine fiber layer can include multiple continuous fine fiber layers. The support layer and one or more continuous fine fiber layers can form a composite. The composite includes at least one continuous fine fiber layer.

[0075] In some embodiments, the filter medium has an average maximum composite pore size of at most 20 μm, preferably at most 15 μm, and more preferably at most 14 μm. In some embodiments, the filter medium has a composite maximum pore size of at least 0.1 μm. As used herein, "average maximum composite pore size" refers to the average maximum composite pore size including the support layer and any continuous fine fiber layers present in layers adjacent to the support layer.

[0076] In some embodiments, the filter media has a composite mean mean flow pore size or P50 of at most 11 μm, preferably at most 9 μm, and more preferably at most 6 μm. In some embodiments, the filter media has a composite mean mean flow pore size or P50 of at least 0.1 μm. As used herein, "composite mean mean flow pore size" refers to the mean mean flow pore size of the composite, including the support layer and any continuous fine fiber layers present in layers adjacent to the support layer.

[0077] In some embodiments, the average maximum pore size of the composite and / or the average intermediate flow pore size of the composite are preferably determined using capillary flow porometry.

[0078] Without wishing to be bound by theory, it is believed that the average maximum pore size of the composite and the average intermediate flow pore size of the composite depend, among other factors, on the diameter of the fine fibers, the relative amounts of fine and coarse fibers, and the composite morphology (layered, mixed, etc.).

[0079] In some embodiments, the composite may have a median flow pore size similar to that of the efficiency layer. For example, in some embodiments, the median flow pore size (P50) of the composite may be within 1%, 2%, 3%, 5%, 10%, 20%, 30%, 50%, 100%, or 200% of the median flow pore size (P50) of the adjacent efficiency layer.

[0080] As described in Example 5, the average maximum pore size of a filter media composite can be correlated to the filter media's ability to withstand a pressure drop of at least 20 psi during liquid filtration, demonstrating superior filtration performance over filter media that cannot withstand the same conditions.

[0081] The average maximum pore size of a filter media composite can be correlated to the filter media's ability to withstand a pressure drop of at least 20 psi during liquid filtration, and the average maximum pore size of a composite can sometimes provide inconsistent values ​​if the media contains defects or abnormally large maximum pores. Therefore, to better understand the pore size range and pore size distribution of a composite, additional values ​​were also examined, as described below.

[0082] P95 / P50 ratio of composites containing a support layer and a continuous fine fiber layer In some embodiments, the composite formed from the support layer and the continuous fine fiber layer has a P95 / P50 ratio of at most 1.8, at most 1.9, or at most 2.

[0083] While the pore size of the fine fiber layer largely controls the value of the composite's P95 / P50 ratio, interactions between the support layer and the continuous fine fiber layer also affect performance. Without wishing to be bound by theory, it is believed that these interactions make measuring the pore size of a composite more informative than measuring the pore size of the fine fiber layer alone.

[0084] The P50 value reflects the pore diameter below which 50% of the fluid flows, the P95 value reflects the pore diameter below which 95% of the fluid flows, and a larger ratio of P95 / P50 generally reflects a wider range of pore sizes over which relatively large pores exist.

[0085] Without wishing to be bound by theory, it is believed that composites having a P95 / P50 ratio greater than 2 do not provide sufficient efficiency under circulatory flow. A P95 / P50 ratio less than 2 increases the pressure drop (due to increased solidity), but the continuous fine fiber layer is so thin (e.g., less than 50 μm) that the corresponding pressure drop can be kept within an acceptable range.

[0086] In some embodiments, the composite has a P95 / P50 ratio of at least 1.

[0087] P95 / P50 ratio of the efficiency layer adjacent to the fine fiber layer In some embodiments, the efficiency layer has a P95 / P50 ratio of at least 1.8, at least 1.9, or at least 2.

[0088] Without wishing to be bound by theory, it is believed that composites having a P95 / P50 ratio less than 1.8 exhibit a range of solidity that would be expected to result in undesirably high pressure drops. Additionally, as the P95 / P50 decreases, the solidity increases, and therefore the number of particles that can be trapped by the composite also decreases.

[0089] In some embodiments, the efficiency layer has a P95 / P50 ratio of at most 2.5, at most 3, at most 4, at most 5, at most 10, at most 15, or at most 20.

[0090] Without wishing to be bound by theory, a P95 / P50 ratio greater than 20 is expected to result in a media layer with larger pore sizes and therefore too few pores of the size required to capture the desired particle size (e.g., particle sizes in the range of 1 μm to 100 μm).

[0091] For example, the efficiency layer has a P95 / P50 ratio in the range of 1.8-20, in the range of 2-10, or in the range of 2-5.

[0092] In some embodiments, the maximum value of the range including the P95 / P50 ratio of the composite is preferably less than or equal to the minimum value of the range including the P95 / P50 ratio of the efficiency layer. In some embodiments, the P95 / P50 ratio of the composite is preferably less than or equal to the P95 / P50 ratio of the efficiency layer.

[0093] For example, in an exemplary embodiment, the P95 / P50 ratio of the composite is at most 1.8 and the P95 / P50 ratio of the efficiency layer is at least 1.8. In another exemplary embodiment, the P95 / P50 ratio of the composite is at most 1.9 and the P95 / P50 ratio of the efficiency layer is at least 1.9. In yet another exemplary embodiment, the P95 / P50 ratio of the composite is at most 2 and the P95 / P50 ratio of the efficiency layer is at least 2.

[0094] In some embodiments, it is preferred that the maximum P95 / P50 ratio of the composite be less than the minimum P95 / P50 ratio of the efficiency layer. For example, in an exemplary embodiment, the P95 / P50 ratio of the composite is at most 1.8 and the P95 / P50 ratio of the efficiency layer is at least 2. In another exemplary embodiment, the P95 / P50 ratio of the composite is at most 1.9 and the P95 / P50 ratio of the efficiency layer is at least 2.

[0095] For example, in some embodiments, the efficiency layer adjacent to the fine fiber layer may have a P95 / P50 ratio that is at most 1.5 times, at most 2 times, at most 3 times, at most 4 times, at most 5 times, at most 6 times, at most 7 times, at most 8 times, at most 9 times, or at most 10 times greater than the P95 / P50 ratio of the composite.

[0096] Pore ​​size distribution overlap In some embodiments, the pore size distribution of the efficiency layer overlaps with the pore size distribution of the composite (including the support layer and fine fiber layer). When the filter media includes more than one efficiency layer, the pore size distribution of the efficiency layer adjacent to the fine fiber layer overlaps with the pore size distribution of the composite (including the support layer and fine fiber layer). Without wishing to be bound by theory, it is believed that this overlap in pore size distributions extends the life of the filter.

[0097] If the pore size distribution of the efficiency layer and the pore size distribution of the composite do not overlap because the pore size of the composite is smaller than that of the efficiency layer, the fine fiber layer will trap particles of a size that is not trapped by the efficiency layer. This trapping increases the pressure drop and results in reduced media life.

[0098] If the pore size of the composite is larger than the pore size of the efficiency layer and there is no overlap between the pore size of the efficiency layer and the pore size of the composite, the fine fiber layer will not provide the desired efficiency improvement.

[0099] Similarly, if the pore sizes of the efficiency layer and the composite overlap over their entire range, the fine fiber layer is unlikely to provide the desired efficiency improvement.

[0100] Thus, in some embodiments, the P95 of the composite preferably falls within the range provided by the P5 and P50 values ​​of the efficiency layer.

[0101] As shown in Example 6, when the P95 of the composite falls below the range provided by the P5 and P50 values ​​of the efficiency layer adjacent to the fine fiber layer, the resulting pressure drop of the filter medium is large (23.2 kPa), exceeding 150% of the pressure drop of a filter medium that does not include a fine fiber layer and a support layer.

[0102] Without wishing to be bound by theory, it is believed that using a composite having a P95 within the range provided by the P5 and P50 values ​​of the adjacent efficiency layer allows the resulting filter media to take advantage of both the depth loading characteristics of the efficiency layer and the surface loading characteristics of the continuous fine fiber layer of the composite. The loss of efficiency during dynamic flow conditions observed when using only the efficiency layer is not observed with the claimed media due to the higher solidity and smaller pore size of the continuous fine fiber layer. However, the high pressure drop that would be observed if the desired efficiency were achieved using only the continuous fine fiber layer is avoided.

[0103] filter element In some embodiments, the filter media disclosed herein can be included in a filter element that includes a wire support. The wire support can be positioned downstream of the support layer.

[0104] In some embodiments, the filter media, including, for example, the filter media contained in the filter element, is pleated.

[0105] Exemplary filter elements include flat panel filters, cartridge filters, or other filtering components. Examples of such filter elements are described in U.S. Patent Nos. 6,746,517; 6,673,136; 6,800,117; 6,875,256; 6,716,274; and 7,316,723.

[0106] How to use In some embodiments, the filter media of the present disclosure can be used to filter fluids, including, for example, fluid streams. Fluids include air, gases, and liquids. In some embodiments, the filter media of the present disclosure can be used to remove particles from the fluid stream.

[0107] In some embodiments, the filter media of the present disclosure can be used to filter air. In some embodiments, including when the filter media of the present disclosure is used to filter air, the filter media can be positioned upstream of other layers within the filter element.

[0108] In some embodiments, the filter media of the present disclosure can be used to filter gases. The gaseous stream can include, for example, air and / or industrial waste gases. In an exemplary embodiment, the filter media of the present disclosure can be used to filter blow-by gases from the crankcase of a diesel engine, which carries a significant amount of entrained oil as aerosols. In a further exemplary embodiment, the filter media of the present disclosure can be used in a gas turbine.

[0109] In some embodiments, the filter media of the present disclosure can be used to filter liquids. In some embodiments, including when the filter media of the present disclosure are used to filter liquids, the filter media can be positioned downstream of other layers within the filter element. Exemplary liquids can include, for example, aqueous liquids, hydraulic fluids, oils, fuels, lubricants, etc. Aqueous liquids can include natural and man-made streams such as wastewater, cooling water, and process water.

[0110] In some embodiments, the filter media of the present disclosure may be particularly well suited for use in applications where flow rates fluctuate, including, for example, hydraulic applications. Fluctuations in flow rates, including, for example, circulating flow conditions, can adversely affect the performance of the filter media, particularly its efficiency, as particles have multiple opportunities to pass through the openings in the media.

[0111] At the time of the present invention, the influence of flow rate fluctuations on filter performance has typically been minimized by increasing the efficiency of filter media, but increasing filter media efficiency also results in a corresponding increase in pressure drop, i.e., the pressure required to force fluid through filter media.This increase in pressure drop increases the chance of filter being bypassed (for example, via bypass valve), which increases energy consumption and shortens filter life.In contrast, the filter media of the present disclosure can achieve improved efficiency under circulating flow conditions without worsening pressure drop.

[0112] Continuous fine fiber layer The continuous fine fiber layer comprises continuous fine fibers having a diameter of at most 10 micrometers (μm). In some embodiments, the continuous fine fiber layer comprises a single layer. In some embodiments, the continuous fine fiber layer comprises multiple continuous fine fiber layers. In some embodiments, when the continuous fine fiber layer comprises multiple layers, the multiple layers may comprise fine fibers of different diameters. In some embodiments, when the continuous fine fiber layer comprises multiple layers, one or more layers may comprise continuous fine fibers having different diameters within the layer. In some embodiments, when the continuous fine fiber layer comprises multiple layers, each layer may comprise a different combination of continuous fine fibers having different diameters.

[0113] In some embodiments, the continuous fine fiber layer functions as a surface loading layer.

[0114] In some embodiments, the continuous fine fiber layer may include fibers having a diameter of at least 0.05 μm, at least 0.1 μm, at least 0.2 μm, at least 0.5 μm, or at least 1 μm.

[0115] In some embodiments, the continuous fine fiber layer may comprise fibers having a diameter of at most 1.5 μm, at most 2 μm, at most 3 μm, at most 4 μm, at most 5 μm, at most 6 μm, at most 7 μm, at most 8 μm, at most 9 μm, or at most 10 μm. For example, in exemplary embodiments, the continuous fine fiber layer comprises fibers having a diameter in the range of 0.1 μm to 5 μm, 0.5 μm to 5 μm, 1 μm to 5 μm, or 1 μm to 2 μm. For example, in some embodiments, including those in which the continuous fine fibers have an elliptical shape, the continuous fine fibers may preferably comprise fibers having a diameter in the range of 1 μm to 5 μm. For example, in some embodiments, including those in which the continuous fine fibers do not comprise a mixture of fibers of different diameters, the continuous fine fibers may comprise fibers having a diameter in the range of 0.2 μm to 1.5 μm.

[0116] In some embodiments, the continuous fine fiber layer can include fibers having an oval (including circular) shape. For example, the fibers can have a cross-sectional major axis (width):cross-sectional minor axis (height) ratio of at least 2:1 (e.g., fettuccine-like) to 1:1 (e.g., spaghetti-like).

[0117] In some embodiments, the continuous fine fiber layer may preferably comprise fibers having a diameter in the range of 1 μm to 5 μm and a cross-sectional major axis (width):cross-sectional minor axis (height) ratio of at least 1.5:1 to 1:1.

[0118] In some embodiments, the continuous fine fiber layer has a solidity of at least 10%, at least 11%, at least 12%, at least 13%, at least 14%, at least 15%, at least 20%, or at least 25%. In some embodiments, the continuous fine fiber layer has a solidity of at most 15%, at most 20%, at most 25%, at most 30%, at most 35%, or at most 40%. In exemplary embodiments, the continuous fine fiber layer has a solidity in the range of 15% to 30%.

[0119] The solidity (c) of the continuous fine fiber layer is calculated by the following formula: F * 1.0 =4.3548e 8.8822cUsing the dimensionless fiber resistance parameter F * 1.0 It can be calculated from F * 1.0 can be calculated from the modified Kirsch-Fuchs equation, as further explained in the Examples.

[0120] Mixed diameter fine fibers In some embodiments, the continuous fine fiber layer may include a mixture of fibers of different diameters.

[0121] In some embodiments, the continuous fine fiber layer may include fibers of two different diameters. When the continuous fine fiber layer includes fibers of two different diameters, the ratio of the average diameter of the "small" fiber diameter fine fibers to the average diameter of the "large" fiber diameter fine fibers (thin fine fiber diameter:thick fine fiber diameter) may be at least 1:3 (i.e., the average fiber diameter of the thick fine fibers is three times the average fiber diameter of the thin fine fibers).

[0122] In some embodiments, the ratio of the average diameter of the "small" fiber diameter fibers to the average diameter of the "large" fiber diameter fibers (small fiber diameter:large fiber diameter) can be in the range of 1:3 to 1:6. For example, in an exemplary embodiment, the continuous fine fibers can include first fine fibers having an average diameter in the range of 0.2 μm to 0.3 μm and second fine fibers having an average diameter in the range of 0.9 μm to 1.1 μm. In another example, the average diameter of the first fine fibers can be 0.25 μm and the average diameter of the second fine fibers can be 1 μm. In yet another example, the average diameter of the first fine fibers can be 0.25 μm and the average diameter of the second fine fibers can be 1.4 μm.

[0123] In embodiments where the continuous fine fiber layer comprises a mixture of fibers of different diameters, the fibers of different diameters can be mixed or intermixed together within a single layer of the continuous fine fiber layer.

[0124] In embodiments where the continuous fine fiber layer comprises a mixture of fibers of different diameters, the fibers of different diameters can form different layers in the continuous fine fiber layer. When fibers of different diameters form different layers in the continuous fine fiber layer, the thicker fibers can be deposited on the support before the deposition of the thinner fibers to create a gradient (including, for example, a gradient of pore size and solidity) within the continuous fine fiber layer. Additionally or alternatively, when fibers of different diameters form different layers in the continuous fine fiber layer, the thicker and thinner fibers can be deposited to form multiple layers with different characteristics. Exemplary embodiments of such structures are shown in Figures 2A and 2H-2M. Further exemplary embodiments of continuous fine fiber layers comprising a mixture of fibers of different diameters are described in a co-pending application entitled "FILTER MEDIA LAYERS INCLUDING MIXED DIAMETER FINE FIBERS," filed on even date herewith, and having attorney docket number 0444.000110WO01.

[0125] In some embodiments, "thick" fine fibers have an average diameter of at least 0.6 μm, more preferably greater than 0.6 μm. In some embodiments, "thick" fine fibers have an average diameter of at least 0.7 μm, at least 0.8 μm, or at least 0.9 μm. In some embodiments, "thick" fine fibers preferably have an average diameter of at least 1 μm or greater. "Thick" fine fibers may have an average diameter of at most 1.1 μm, at most 1.2 μm, at most 1.3 μm, at most 1.4 μm, at most 1.5 μm, at most 2 μm, at most 3 μm, at most 4 μm, at most 5 μm, or at most 10 μm. An exemplary image of a continuous fine fiber layer comprising thick fine fibers deposited on a support layer is shown in FIG. 2B.

[0126] In embodiments where the continuous fine fiber layer comprises "thick" and "thin" fine fibers, the thick fine fibers may have an average diameter at least three times the average fiber diameter of the thin fine fibers. In such embodiments, the thin fine fibers may have an average diameter of at most 0.3 μm, at most 0.4 μm, at most 0.5 μm, or at most 0.6 μm. In some embodiments, the thin fine fibers of the continuous fine fiber layer may have an average fiber diameter of at least 0.2 μm.

[0127] In some embodiments, the thick fibrils may have a diameter at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the diameter of the thin fibrils. As noted above, even if the average fiber diameter of the thick fibrils is three times the average fiber diameter of the thin fibrils, either or both of the thick fibrils and the thin fibrils may comprise fibers of various sizes that provide the average diameter. For example, if the thick fibrils and the thin fibrils have a size distribution, the diameter of the smallest diameter thick fibrils will be at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the diameter of the largest diameter thin fibrils. In some such embodiments, the thick fibrils and the thin fibrils may form a bimodal distribution. In some embodiments, the thick fibrils may have a diameter at most 1 μm, at most 2 μm, or at most 3 μm larger than the diameter of the thin fibrils.

[0128] In some embodiments where the continuous fine fiber layer comprises "thick" and "thin" fine fibers, the continuous fine fiber layer may comprise at least 0.5% to 20% thick fine fibers, more preferably at least 1% to 10% thick fine fibers, or even more preferably at least 5% to 7% thick fine fibers. Additional ranges may also be useful, including, for example, at least 3% to 9% thick fine fibers or at least 4% to 8% thick fine fibers. Without wishing to be bound by theory, it is believed that optimizing the proportion of thick fine fibers in the second layer of fine fibers provides support for the thin fine fibers without disrupting the structure of the thin fine fibers or resulting in a corresponding loss of efficiency.

[0129] In some embodiments, the continuous fine fiber layer may include "thick" fine fibers and "thin" fine fibers, and the continuous fine fiber layer may include multiple layers. In an exemplary embodiment, the continuous fine fiber layer includes a first layer of fine fibers including thick fine fibers and a second layer of fine fibers including thin fine fibers. In another exemplary embodiment, the continuous fine fiber layer includes a first layer of fine fibers including thick fine fibers and a second layer of fine fibers including thick and thin fine fibers. In some embodiments, the first layer of fine fibers can be deposited on a support layer, and the second layer of fine fibers can be deposited on the first layer of fine fibers.

[0130] Characteristics of the continuous fine fiber layer In some embodiments, the continuous fine fiber layer preferably has a narrow pore size distribution.

[0131] In some embodiments, the continuous fine fiber layer has a fiber density of at least 0.005 g / m 2 , at least 0.01 g / m 2 , at least 0.05 g / m 2 , at least 0.1 g / m 2 , at least 0.5g / m 2 , at least 1 g / m 2 , at least 1.5g / m 2 , at least 2 g / m 2 or at least 2.5 g / m 2 In some embodiments, the continuous fine fiber layer has a basis weight of at most 1.5 g / m 2 , up to 2 g / m 2 , up to 2.5g / m 2 , up to 3 g / m 2 , up to 3.5g, / m 2 , up to 4g / m 2 , up to 4.5g / m 2 , up to 5g / m 2 , up to 10 g / m 2 , up to 15g / m 2 , up to 20 g / m 2 , up to 25g / m 2 , up to 50g / m 2 In an exemplary embodiment, the continuous fine fiber layer has a basis weight of at least 0.1 g / m 2~20g / m 2 In another exemplary embodiment, the continuous fine fiber layer has a basis weight of at least 0.1 g / m 2 ~1g / m 2 In a further exemplary embodiment, the continuous fine fiber layer has a basis weight of 0.43 g / m 2 When fibers of different diameters are layered, the basis weights of the continuous fine fiber layers are additive.

[0132] The basis weight of the fine fibers can be calculated from the mass of the fine fibers and the area of ​​the scrim according to the following formula: Total basis weight of the fine fiber layer = (mass of fine fibers) / (area of ​​scrim). The mass of the fine fibers can be calculated from the polymer and spinning conditions used to make the fine fibers according to the following formula: Mass of fine fibers = (% (w / v) of polymer in solution) x (pump speed) x (spinning time).

[0133] In some embodiments, the continuous fine fiber layer has a thickness of at least the average diameter of its largest fibers, ie, at least 0.2 μm, at least 0.3 μm, at least 0.4 μm, at least 0.5 μm, at least 0.6 μm, at least 0.7 μm, at least 0.8 μm, at least 0.9 μm, or at least 1 μm.

[0134] In some embodiments, the continuous fine fiber layer has a thickness that is the thickness of several fibers having the average diameter of their largest fibers. For example, the continuous fine fiber layer can have a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm.

[0135] In some embodiments, the continuous fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm.

[0136] In some embodiments, the total thickness of the continuous fine fiber layer can be measured using scanning electron microscopy (SEM). For example, a sample including at least the continuous fine fiber layer and the support layer can be prepared for SEM by cross-sectioning the sample while frozen (e.g., in liquid nitrogen). It may be useful to cross-section the sample, positioning it so that the support layer is cut before the fine fiber layer. It may be even more useful to cross-section the sample while it is submerged in liquid nitrogen. An exemplary magnification that can be used is 1000x. It may be useful to use software to outline the fine fiber portions in the SEM image and allow for reshading to facilitate the determination of the sample's thickness. The reshaded image can then be used to determine the maximum thickness of the fine fiber portions in the image. In some embodiments, the total thickness of the fine fiber layer can be determined by averaging at least five maximum thicknesses of five separate images of the same sample.

[0137] Fiber properties of continuous fine fiber layer The continuous fine fiber layer comprises fine fibers. These fine fibers comprise a fiber-forming polymeric material. In some embodiments, the fine fibers can be produced by spinning only the fiber-forming polymeric material. In some embodiments, the fine fibers can be produced by spinning the fiber-forming polymeric material in combination with another substance.

[0138] Fine fiber technologies that contemplate polymeric materials mixed or blended with various other substances are disclosed in U.S. Patent No. 6,743,273 to Chung et al.; U.S. Patent No. 6,924,028 to Chung et al.; U.S. Patent No. 6,955,775 to Chung et al.; U.S. Patent No. 7,070,640 to Chung et al.; U.S. Patent No. 7,090,715 to Chung et al.; U.S. Patent Application Publication No. 2003 / 0106294 to Chung et al.; U.S. Patent No. 6,800,117 to Barris et al.; and U.S. Patent No. 6,673,136 to Gillingham et al. Additionally, in U.S. Patent No. 7,641,055 to Ferrer et al., a water-insoluble, high-strength polymeric material is produced by mixing or blending a polysulfone polymer with a polyvinylpyrrolidone polymer to produce a single-phase polymer alloy used in electrospun fine fiber materials.

[0139] The continuous fine fibers may comprise fibers made from any suitable polymer. In some embodiments, polyamides may be useful as the polymeric material for the continuous fine fibers. One useful class of polyamide condensation polymers is nylon materials. The term "nylon" is a generic term for all long-chain synthetic polyamides. Nylon nomenclature typically includes a series of numbers, such as nylon-6,6, indicating that the starting materials are a C6 diamine and a C6 diacid (the first number indicates the C6 diamine, and the second number indicates the C6 dicarboxylic acid compound). Another nylon can be produced by the polycondensation of ε-caprolactam in the presence of a small amount of water. This reaction forms nylon-6 (formed from a cyclic lactam, also known as ε-aminocaproic acid), a linear polyamide. Additionally, nylon copolymers are also contemplated. Exemplary nylon materials include nylon-6, nylon-6,6, nylon-6,10, and mixtures or copolymers thereof.

[0140] Copolymers can be made by combining various diamine compounds, various diacid compounds, and various cyclic lactam structures in a reaction mixture, then forming nylons with the monomer materials randomly arranged in a polyamide structure. For example, nylon-6, 6-6, 10 materials are nylons made from hexamethylenediamine and a blend of C6 and C10 diacids. Nylon-6, -6,6, -6,10 is made from ε-aminocaproic acid, hexamethylenediamine, and a blend of C6 and C10 diacids. 10 As used herein, the term "copolymer" includes polymers made from two or more different monomers, including terpolymers and the like.

[0141] In some embodiments, polysulfones may be useful as the polymeric material of the continuous fine fibers. Exemplary polysulfones include polysulfone (PS), polyethersulfone (PES), and polyphenylsulfone (PPSF), and mixtures thereof.

[0142] In some embodiments, polymeric materials comprising cellulose derivatives may be useful as continuous fiber polymeric materials. Examples of such polymers include ethyl cellulose, hydroxyethyl cellulose, cellulose acetate (including cellulose diacetate (DAC) and cellulose triacetate (TAC)), cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate phthalate, and mixtures thereof.

[0143] In some embodiments, the polymeric material of the continuous fine fibers may additionally or alternatively include polypropylene (PP), polyvinylpyrrolidone (PVP), poly(4-vinylpyridine) (P4VP), polyvinylidene fluoride (PVDF), or polytetrafluoroethene (PTFE, also known as Teflon), or mixtures thereof.

[0144] In some embodiments, resin aldehyde crosslinked polymers can be useful as continuous fine fiber polymeric materials, for example, as described in WO 2013 / 043987 A1.

[0145] In some embodiments, the continuous fine fiber layer has a higher solidity than one or more other layers in the filter media (including, for example, the support layer or the efficiency layer, or both). Without wishing to be bound by theory, it is believed that a layer with a higher solidity typically leads to an increased pressure drop, whereas providing a very thin continuous fine fiber layer helps provide increased efficiency without the corresponding pressure drop typically observed.

[0146] In some embodiments, the continuous fine fiber layer has a median flow pore size similar to that of the efficiency layer, hi some embodiments, the continuous fine fiber layer has a pore size distribution that is narrower than the pore size distribution of the efficiency layer.

[0147] In some embodiments, fine fibers can be produced by combining, for example, during the fiber formation process or a post-treatment process, a fiber-forming polymeric material with at least two reactive additives capable of reacting with one another, as further described in WO 2014 / 164130. The at least two reactive additives are optionally reactive with the fiber-forming polymer.

[0148] In some embodiments, fine fibers can be made by combining a fiber-forming polymeric material with a resin aldehyde composition, such as a melamine-formaldehyde resin.

[0149] In some embodiments, the resin aldehyde composition comprises a "polymer reactive resin aldehyde composition." The "polymer reactive resin aldehyde composition" comprises alkoxy groups, as further described in U.S. Pat. No. 9,587,328. In the final fiber, at least a portion of the polymer reactive resin aldehyde composition participates in crosslinking the polymer, and may optionally participate in self-crosslinking. The fiber-making polymer material also comprises reactive groups. In this context, "reactive" means that the polymer comprises one or more functional groups (e.g., active hydrogen groups) that can be crosslinked by the alkoxy groups of the polymer reactive resin aldehyde composition used to form the fine fibers.

[0150] In some embodiments, the resin aldehyde composition comprises a "polymer non-reactive resin aldehyde composition." The polymer non-reactive resin aldehyde composition comprises reactive groups for self-crosslinking, as further described in U.S. Pat. No. 9,435,056. In the final fiber, at least a portion of the polymer non-reactive resin aldehyde composition participates in self-crosslinking.

[0151] As used herein, "resin" or "resinous" refers to monomers, oligomers, and / or polymers that are capable of migrating to the surface of the fine fibers, especially during fiber formation. As used herein, the term "resin aldehyde composition" refers to the materials in the starting materials and the final fibers.

[0152] Method for forming a continuous fine fiber layer In another aspect, the present disclosure describes a method of forming a continuous fine fiber layer.

[0153] The continuous fine fiber layer can be formed by any suitable method. For example, the fine fibers of the present disclosure can be produced using a variety of techniques including electrospinning, force spinning, wet spinning, dry spinning, melt spinning, extrusion spinning, direct spinning, gel spinning, using the islands-in-the-sea process, and the like.

[0154] In some embodiments, the components of the continuous fine fiber layer can be combined in solution or in molten form. In certain embodiments, the fine fibers are electrospun from a solution or dispersion. For example, the polymeric material and resin aldehyde composition are dispersible or soluble in at least one common solvent or solvent blend suitable for electrospinning.

[0155] In some embodiments, a continuous fine fiber layer can be formed on a support layer. In some embodiments, a continuous fine fiber layer can be formed on an efficiency layer.

[0156] In some embodiments, where fibers of different diameters can form different tiers in a continuous fine fiber layer, the thicker fibers can be deposited on the support before the deposition of the thinner fibers. Additionally or alternatively, depending on the number of layers, the thinner fibers can be deposited on the support before the deposition of the thicker fibers.

[0157] In some embodiments, where fibers of different diameters can form the same layer in the continuous fine fiber layer, the fibers can be formed simultaneously.

[0158] The fine fibers are collected on a support layer, for example, during electrostatic or melt spinning, and are often heat-treated after fiber formation. Preferably, the continuous fine fiber layer is disposed as a layer of fibers on a first surface of a layer of permeable coarse fibrous media (i.e., a support layer).

[0159] Appropriate polymers and polymer concentrations can be selected by one of ordinary skill in the art, given the size and other properties desired for the continuous fine fiber layer. For example, in some embodiments, the fibers are preferably compatible with the fluid being filtered (e.g., hydraulic fluid, fuel, lubricant). Fibers are considered compatible with a fluid if they do not react with the fluid or other components and additives therein and are insoluble in the fluid (so that the fine fiber structure is not chemically or physically damaged by mere contact with the liquid). In an exemplary embodiment, the polymer solution comprises Solution 1, as described in the Examples. In an exemplary embodiment, the polymer solution comprises Solution 2, as described in the Examples.

[0160] In some embodiments, when fine fibers of different diameters are mixed, the fibers can be formed simultaneously. For example, when two (or more) fibers are formed by electrospinning, the fibers can be formed by simultaneous cospinning, including using two (or more) syringes, each containing a different polymer solution. Additionally or alternatively, each syringe can use a different syringe pump feed rate. In some embodiments, when fine fibers of different diameters are mixed, the fibers can be formed by alternating fiber formation, but using very short (e.g., up to 10 seconds, up to 20 seconds, or up to 30 seconds) pulses of each polymer solution.

[0161] In some embodiments, when fibers of different diameters are layered, the fibers can be formed by alternating fiber formation. For example, when two (or more) fibers are formed by electrospinning, the fibers can be formed by alternating spinning of each fiber, including, for example, using two (or more) syringes, each syringe containing a different polymer solution. Additionally or alternatively, each syringe can use a different syringe pump feed rate. In some embodiments, when fibers of different diameters are layered, the fibers can be formed by alternating fiber formation using a pulse of each polymer solution for at least 30 seconds.

[0162] Any suitable method can be used to form a combination of thin and thick fine fiber layers. Exemplary methods that can be used to form layered fiber structures include one or more of the methods in Set A5, Set B, Set D5, Set E, Set I5, or Set J in Table 1. Exemplary methods that can be used to form mixed fiber structures include one or more of the methods in Set A6, Set D, Set D6, Set I, or Set L in Table 1. In some embodiments, a combination of layers can be formed that includes both layered and mixed fiber structures. Exemplary methods for forming such structures are described in the Examples.

[0163] Efficiency Layer The efficiency layer is a nonwoven filter medium.

[0164] In some embodiments, the efficiency layer preferably functions as a depth loading layer.

[0165] Exemplary nonwoven filter media include wet-laid resin-free media, wet-laid resin-bonded glass media, melt-blown media, wet-laid cellulosic media, and air-laid glass media.

[0166] Exemplary wet-laid resin-free media include Synteq XP™ Synthetic Liquid Media (Duramax P164378, Donaldson Company, Inc., Minneapolis, MN) with an efficiency rating of 10 microns and Synteq XP™ Synthetic Liquid Media (Duramax P165332, Donaldson Company, Inc., Minneapolis, MN) with an efficiency rating of 5 microns.

[0167] Exemplary wet-laid resin-bonded glass media include the Lydall LyPore family of media, such as LyPore XL Fluid Power 9104 (Lydall, Inc., Manchester, CT); the Ahlstrom Microglass family of media, such as MFPS1301 (Ahlstrom-Munksjoe, Helsinki, Finland); and H&V hydraulic media, such as Grade 1313 (Hollingsworth & Vose, East Walpole, MA).

[0168] Exemplary meltblown media include the Lydall LyPore MB family of media, such as LyPore MB9031 (Lydall, Inc., Manchester, CT); and the H&V meltblown family of media, grade PF23040 (Hollingsworth & Vose, East Walpole, MA).

[0169] Exemplary wet-laid cellulose media include media from the Ahlstrom fuel media family, such as grade 100P-68 (Ahlstrom-Munksjoe, Helsinki, Finland); and media from the H&V fuel media family, such as grade FS6314 (Hollingsworth & Vose, East Walpole, MA).

[0170] Exemplary airlaid media include media in air filtration media from Johns Manville, such as Everlith XLG-85 (Johns Manville, Denver, CO).

[0171] In some embodiments, the efficiency layer is preferably a wet laid media.

[0172] In some embodiments, the efficiency layer comprises bicomponent fibers and efficiency fibers, the efficiency fibers having a smaller diameter than the bicomponent fibers. In some embodiments, the efficiency layer may further comprise microfibrillated cellulose.

[0173] In some embodiments, the efficiency layer has a lower solidity than the solidity of the continuous fine fiber layer.

[0174] In some embodiments, the efficiency layer has a solidity of at least 3%, at least 4%, at least 5%, at least 6%, at least 7%, at least 8%, at least 9%, or at least 10%. In some embodiments, the efficiency layer has a solidity of at most 8%, at most 9%, at most 10%, at most 11%, at most 12%, at most 13%, at most 14%, or at most 15%. In exemplary embodiments, the efficiency layer has a solidity in the range of 7% to 12%. In some embodiments, the solidity of the efficiency layer is calculated using the following formula: c = BW / ρZ, where BW is the basis weight, ρ is the density of the fibers, and Z is the thickness of the media. If the efficiency layer includes different fibers, the mass ratio of the fibers can be used to determine the density (ρ). Basis weight can be measured according to TAPPI T410 om-08. Thickness can be measured according to TAPPI T411 om-15.

[0175] In some embodiments, the efficiency layer has a thickness of at least 0.05 mm, at least 0.1 mm, at least 0.2 mm, or at least 0.3 mm. In some embodiments, the efficiency layer has a thickness of at most 0.5 mm, at most 1 mm, at most 5 mm, at most 10 mm, at most 25 mm, or at most 50 mm. In some embodiments, the efficiency layer has a thickness in the range of 0.2 mm to 50 mm. In some embodiments, the efficiency layer has a thickness in the range of 0.2 mm to 1 mm. In some embodiments, the efficiency layer has a thickness in the range of 0.2 mm to 0.5 mm. Thickness can be measured according to TAPPI T411 om-15.

[0176] As noted above, in some embodiments, the continuous fine fiber layer has an intermediate flow pore size similar to that of the efficiency layer. Without wishing to be bound by theory, it is believed that if the intermediate flow pore size of the continuous fine fiber layer is much smaller than that of the efficiency layer, a large proportion of particles will be trapped by the continuous fine fiber layer, resulting in a shorter filter lifespan. On the other hand, if the intermediate flow pore size of the continuous fine fiber layer is much larger than that of the efficiency layer, the efficiency layer must have a high solids content, and the filter will similarly have a shorter lifespan due to lower throughput.

[0177] It will be appreciated that the intermediate flow pore size can be selected based on the desired efficiency of the filter media and the size of the particles to be filtered.

[0178] In exemplary embodiments, the efficiency layer has an intermediate flow pore size of at least 1 μm, at least 5 μm, at least 10 μm, at least 15 μm, or at least 20 μm. In exemplary embodiments, the efficiency layer has an intermediate flow pore size of at most 5 μm, at most 10 μm, at most 15 μm, at most 20 μm, at most 25 μm, at most 30 μm, or at most 35 μm. In certain exemplary embodiments, the fibers of the efficiency layer have an intermediate flow pore size range of 10 μm to 25 μm. In some embodiments, the intermediate flow pore size is preferably the average intermediate flow pore size determined using capillary flow porometry as described in the Examples.

[0179] In some embodiments, the efficiency layer has a pore size distribution that is broader than the pore size distribution of the adjacent continuous fine fiber layer.

[0180] As noted above, in some embodiments, the continuous fine fiber layer has a narrower pore size distribution than the pore size distribution of the adjacent efficiency layer.

[0181] In some embodiments, a resinous binder component is not necessary to provide sufficient strength to the efficiency layer, hi some embodiments, a resinous binder component is not included in the efficiency layer.

[0182] Bicomponent Fiber Bicomponent fibers can include any suitable bicomponent fiber or combination of bicomponent fibers. The term "bicomponent fiber" refers to a fiber having at least one thermoplastic binder polymer portion having a melting point and a second thermoplastic structural polymer portion having a higher melting point than the binder polymer portion. The physical configuration of these fibers is typically a "side-by-side" or "sheath-core" structure. In a side-by-side structure, two thermoplastic polymer resins are typically extruded into a connected side-by-side configuration. The low-melting point polymer functions as the binder, and the high-melting point polymer functions as the structural material. In a sheath-core structure, the core has a higher structural fiber melting point, and the sheath has a lower bonding layer melting point. In some embodiments, bicomponent fibers preferably have a sheath-core structure.

[0183] The low melting point polymer of the bicomponent fibers may have a melting point such that during the thermoforming process, the fibers are heated to a temperature at which the low melting point polymer fuses and bonds the fibers into an intact web. Typically, the high melting point polymer of the bicomponent fibers is a material that provides structural integrity to the web and does not melt at the thermal bonding or use temperatures.

[0184] For example, in one embodiment, the bicomponent fiber may include a low melting point polymer having a melting point of at least 100°C, at least 120°C, or at least 140°C. In some embodiments, the low melting point polymer has a melting point in the range of 140°C to 160°C. The bicomponent fiber may further include a high melting point polymer having a melting point of at least 235°C or at least 240°C. In some embodiments, the low melting point polymer has a melting point in the range of 240°C to 260°C.

[0185] In other embodiments, the bicomponent fibers may include a low melting point polymer having a melting point of at least 50°C, at least 60°C, or at least 70°C. In some embodiments, the low melting point polymer has a melting point in the range of 70°C to 115°C. The bicomponent fibers may further include a high melting point polymer having a melting point of at least 200°C, at least 220°C, or at least 240°C. In some embodiments, the high melting point polymer has a melting point in the range of 240°C to 260°C.

[0186] Without wishing to be bound by theory, it is believed that the relatively low melting point heavy polymer of the bicomponent fibers melts under the sheet, media, or filter-forming conditions and bonds the bicomponent fibers and other fibers present in the sheet, media, or filter-forming material into a mechanically stable sheet, media, or filter, while the high melting point polymer of the bicomponent fibers does not melt and consequently holds the other fibers in the web apart, thereby helping to maintain the less solid structure of the efficiency layer during the thermoforming process.

[0187] In some embodiments, the efficiency layer may include first bicomponent fibers and optional second bicomponent fibers. The inclusion of the second bicomponent fibers having different characteristics than the first bicomponent fibers may improve the ease with which the fibers can be formed into sheets, layers, and / or filter media.

[0188] For example, the first bicomponent fiber can include a low melting point polymer having a melting point of at least 100°C, at least 120°C, or at least 140°C. In some embodiments, the low melting point polymer has a melting point in the range of 140°C to 160°C. The first bicomponent fiber can further include a high melting point polymer having a melting point of at least 235°C or at least 240°C. In some embodiments, the low melting point polymer has a melting point in the range of 240°C to 260°C. The second bicomponent fiber can include a low melting point polymer having a melting point of at least 50°C, at least 60°C, or at least 70°C. In some embodiments, the low melting point polymer has a melting point in the range of 70°C to 115°C. The second bicomponent fiber can further include a high melting point polymer having a melting point of at least 200°C, at least 220°C, or at least 240°C. In some embodiments, the high melting point polymer has a melting point in the range of 240°C to 260°C.

[0189] Bicomponent fibers typically have fiber diameters in the range of 5 μm to 50 μm, often in the range of 10 μm to 20 μm. Bicomponent fibers typically have lengths in the range of 0.1 millimeters (mm) to 20 mm, often about 0.2 mm to about 15 mm.

[0190] Bicomponent fibers can be formed from any suitable material, including various thermoplastic materials, including, for example, polyolefins (polyethylene, polypropylene, etc.); polyesters (polyethylene terephthalate, PET, polybutylene terephthalate, PBT, etc.); and nylons (nylon 6, nylon 6.6, nylon 6.12, etc.). Any thermoplastic material that can have a suitable melting point can be used in the bicomponent fibers, while higher melting point polymers can be used for the higher melting point portion of the fiber. Bicomponent fibers can have, for example, a PET / PET or nylon 6 / nylon 6.6 structure, with the PET / nylon components having different melting points.

[0191] Exemplary bicomponent fibers may include polyolefin / polyester (sheath / core) bicomponent fibers, whereby the polyolefin, such as a polyethylene sheath, melts at a lower temperature than the core, such as a polyester, polyester / polyester, or nylon / nylon material. Typical thermoplastic polymers include polyolefins such as polyethylene, polypropylene, polybutylene, and copolymers thereof; polytetrafluoroethylene; polyesters such as polyethylene terephthalate; vinyl acetates such as polyvinyl acetate and polyvinyl chloride acetate; polyvinyl butyral; acrylics such as polyacrylate and polymethyl acrylate, polymethyl methacrylate; polyamides such as nylon; polyvinyl chloride, polyvinylidene chloride; polystyrene; polyvinyl alcohol; polyurethanes; cellulosic resins such as cellulose nitrate, cellulose acetate, cellulose acetate butyrate, ethyl cellulose, and the like; copolymers of any of the above materials, such as ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, styrene-butadiene block copolymer, Kraton rubber, and the like.

[0192] Efficiency Fiber Efficiency fibers can be formed from any suitable material. For example, efficiency fibers can include glass, metal, silica, polymer fibers, or other related fibers, or mixtures thereof. Efficiency fibers are typically monocomponent fibers (i.e., individual fibers typically consist of a single composition). Efficiency fibers can have diameters ranging from 0.1 μm to 50 μm, or more preferably, from 0.1 μm to 10 μm.

[0193] In some embodiments, the efficiency fibers include glass fibers.

[0194] In some embodiments, the efficiency fibers include short cut thin fibers of a material other than glass. In some embodiments, the efficiency fibers preferably do not include glass fibers.

[0195] Short cut fine fibers may include, for example, hydrophilic, hydrophobic, oleophilic, or oleophobic fibers.

[0196] Short cut fine fibers may comprise one or more of a variety of materials, including naturally occurring cotton, linen, wool, various cellulosic and proteinaceous natural fibers, or synthetic fibers, including, for example, rayon, acrylic, aramid, nylon, polyolefin, and polyester fibers.

[0197] Microfibrillated cellulose In some embodiments, the efficiency layer may comprise microfibrillated cellulose. For example, when the efficiency fibers are short-cut thin fibers, the efficiency layer may comprise microfibrillated cellulose. In some embodiments, including when the short-cut thin fibers comprise synthetic sample fibers, the efficiency layer may comprise microfibrillated cellulose.

[0198] Microfibrillated cellulose (MFC) in this specification refers to the material defined by G. Chinga-Carrasco in Nanoscale Research Letters, 2011, 6:417: "MFC materials can consist of (1) nanofibrils, (2) fine fibers, (3) fibrous fragments, and (4) fibers. This means that MFC is not necessarily synonymous with microfibrils, nanofibrils, or any other cellulose nanostructure. However, properly formed MFC materials contain nanostructures, i.e., nanofibrils, as the primary component." The diameters (or "transverse dimensions" in the case of microfibrillated cellulose fibers) of these components are reproduced in Table 1 of the same reference and are as follows: (1) nanofibrils (less than 0.1 μm); (2) fine fibers (less than 1 μm); and (3) fibers or fibrous fragments (10 μm to 50 μm).

[0199] Furthermore, the term "microfibrillated cellulose" as used herein does not include dry-ground cellulose (also called micronized or ultrafine cellulose) or microcrystalline cellulose obtained by removing the amorphous portion by acid hydrolysis as described in U.S. Pat. No. 5,554,287.

[0200] In certain embodiments, the microfibrillated cellulose fibers used do not contain a "tree structure" (described in U.S. Patent Application Publication No. 2012 / 0043038), and the described fibrillation process results in exterior and interior segments of the fiber surface partially separating from the main fiber structure, resulting in fibrils attached by one segment to the main fiber structure. Such fibrils provide the fiber with more structure to attach to other fibers, for example in a paper structure. In certain embodiments, this is undesirable.

[0201] Typically, microfibrillated cellulose fibers useful in the filter media of the present disclosure have a lateral dimension (e.g., width in two dimensions) of at most 4 μm. Typically, useful microfibrillated cellulose fibers have a lateral dimension of at least 700 nanometers (nm).

[0202] In certain embodiments, the majority (i.e., greater than 50%) of the microfibrillated cellulose fibers have transverse dimensions of up to 4 microns. In certain embodiments, the majority (i.e., greater than 50 percent) of the microfibrillated cellulose fibers have transverse dimensions of between 700 nm and 4 microns.

[0203] support layer The support layer (also referred to herein as the substrate) of the filter media may comprise any material suitable for providing support for the continuous fine fiber layer during its manufacture, during its use, or both. The support layer may comprise or be formed from any suitable porous material.

[0204] Typically, a fibrous material is used for the support layer. The fibers of the support layer can be formed from natural and / or synthetic fibers. Suitable fibers can include cellulose fibers, glass fibers, metal fibers, or synthetic polymer fibers, or combinations or mixtures thereof.

[0205] In certain embodiments, the support layer comprises fibers having an average diameter of at least 5 microns or at least 10 microns, hi some embodiments, the support layer may comprise fibers having an average diameter of up to 250 microns.

[0206] In some embodiments, the support layer is at least 0.005 inches (125 microns) thick, often at least 0.01 inches (250 microns) thick. In some embodiments, the support layer is at most 0.03 inches (750 microns) thick.

[0207] In some embodiments, the support layer has a thickness of at least 8 g / m 2 , at least 10 g / m 2 , at least 15g / m 2 or at least 20 g / m 2 In some embodiments, the support layer has a basis weight of at most 70 g / m 2 , up to 100g / m 2 or a maximum of 150 g / m 2 In an exemplary embodiment, the support layer has a basis weight of 8 g / m 2 ~150g / m 2 In another exemplary embodiment, the support layer has a basis weight in the range of 15 g / m 2 ~100g / m 2 Basis weight can be measured in accordance with TAPPI T410 om-08.

[0208] In some embodiments, the support layer has a solidity of at least 5%, at least 10%, at least 20%, at least 25%, at least 30%, or at least 40%. In some embodiments, the support layer has a solidity of at most 10%, at most 20%, at most 25%, at most 30%, at most 40%, or at most 50%. In an exemplary embodiment, the support layer has a solidity in the range of 10% to 40%. In another exemplary embodiment, the support layer has a solidity in the range of 20% to 30%. In some embodiments, the solidity of the support layer is calculated using the following formula: c = BW / ρZ, where BW is the basis weight, ρ is the fiber density, and Z is the thickness of the media. If the efficiency layer includes different fibers, the mass ratio of the fibers can be used to determine the density (ρ). Basis weight can be measured according to TAPPI T410 om-08. Thickness can be measured according to TAPPI T411 om-15.

[0209] In some embodiments, the support layer has an intermediate flow pore size of at least 5 μm, at least 10 μm, at least 15 μm, at least 20 μm, or at least 25 μm. In some embodiments, the support layer has an intermediate flow pore size of at most 10 μm, at most 15 μm, at most 20 μm, at most 25 μm, at most 30 μm, at most 35 μm, at most 40 μm, at most 50 μm, at most 60 μm, at most 70 μm, at most 80 μm, or at most 90 μm. In exemplary embodiments, the support layer has an intermediate flow pore size in the range of 10 μm to 25 μm. In some embodiments, the intermediate flow pore size is preferably the average intermediate flow pore size determined using capillary flow porometry.

[0210] In some embodiments, the support layer has a maximum pore size of at most 10 μm, at most 15 μm, at most 20 μm, at most 25 μm, at most 30 μm, at most 35 μm, at most 40 μm, at most 50 μm, at most 60 μm, at most 70 μm, at most 80 μm, at most 90 μm, at most 100 μm, or at most 150 μm. In an exemplary embodiment, the support layer has a maximum pore size of at most 90 μm.

[0211] In some embodiments, the maximum pore size of the support layer (eg, nylon scrim) can be determined according to capillary flow porometry.

[0212] In some embodiments, the support layer preferably comprises a consistent media structure, i.e., the characteristics of the media (e.g., including pore size, solidity, basis weight, or thickness, or a combination of those characteristics or each of those characteristics of the media) are consistent across the length and width of the media. For example, in exemplary embodiments, the media flow pore size does not vary by more than 30%, more preferably by more than 25%, and even more preferably by more than 15% across the length and width of the media.

[0213] Without wishing to be bound by theory, it is believed that the interplay between the fiber diameter of the continuous fine fiber layer, the thickness of the continuous fine fiber layer(s), and the maximum pore size of the support layer is important in achieving a structurally stable and efficient media. For example, at higher basis weights (e.g., 60 g / m 2 Simply using a support layer with a maximum pore size (greater than 88 μm) does not result in a structurally stable medium because if the maximum pore size of the support layer exceeds a certain size (e.g., 90 μm), if the fiber diameter is below a certain size, and / or if the fiber thickness is too small, the continuous fine fiber layer will lose its structure during filtration at sufficiently high pressure drops. For example, when thin fine fibers (e.g., having an average diameter of up to 500 nm) were used in a continuous fine fiber layer on a support layer with a maximum pore size of 88 μm, it was found that increasing the basis weight of the continuous fine fiber layer required unsustainable high pressures to move fluid through the medium; in contrast, decreasing the basis weight of the continuous fine fiber layer caused the layer to lose its structure during filtration. Increasing the fiber diameter of at least one of the fibers in a continuous fine fiber layer deposited on a support layer having a maximum pore size of 88 μm (e.g., to an average diameter of at least 600 nm, more preferably at least 900 nm) reduced the efficiency of the media, but increasing the fiber diameter also reduced the pressure drop and resulted in a structurally stable media that did not structurally fail during use.

[0214] The support layer can be formed of any suitable material. Examples of suitable materials for the support layer include spunbond, wetlaid, carded, or meltblown nonwoven materials, or combinations thereof, including, for example, spunbond-meltblown-spunbond. The fibers can be in the form of woven or nonwoven fabrics. Examples of synthetic nonwoven fabrics include polyester nonwoven fabrics, nylon nonwoven fabrics, polyolefin (e.g., polypropylene) nonwoven fabrics, polycarbonate nonwoven fabrics, or blends or multicomponent nonwoven fabrics thereof. Sheet-like support layers (e.g., cellulosic, synthetic, and / or glass or combination webs) are typical examples of filter support layers. Other examples of suitable support layers include polyester or bicomponent polyester fibers, polypropylene / polyethylene terephthalate, or spunbonded polyethylene / polyethylene terephthalate bicomponent fibers.

[0215] In some embodiments, the support layer may preferably comprise polymer fibers. The polymer or polymers of the polymer fibers may be selected for their adhesion to the polymer of the continuous fine fiber layer. In some embodiments, the polymer fibers may comprise nylon fibers or polyester fibers. For example, if the continuous fine fiber layer comprises nylon fine fibers, the support layer may preferably comprise nylon.

[0216] In some embodiments, the support layer may preferably comprise spunbond fibers, which may be particularly suitable for use as a support layer for filter media because they exhibit a large variation in pore size but are otherwise inexpensive and strong layers.

[0217] In some embodiments, the support layer is a thin medium (eg, less than 0.5 mm) that exhibits high permeability; high tensile strength; and small, uniform pore sizes.

[0218] In an exemplary embodiment, the support layer comprises CEREX 23200 (Cerex Advanced Fabrics, Inc., Cantonment, FL), which comprises nylon 6,6, has a thickness of 8.4 mil (0.21 mm), and a weight of 67.8 g / m 2 basis weight, 28% solids and a permeability per solids of 615.1.

[0219] As described in the Examples, using capillary flow porometry, CEREX 23200 was found to have an average maximum pore diameter of 66.4 μm±21.9 μm, a median flow pore diameter of 51.4 μm±12.1 μm, and an average minimum pore diameter of 29.1 μm±9.7 μm.

[0220] The present invention is defined in the claims. However, below is provided a non-exhaustive list of non-limiting exemplary aspects. Any one or more features of these aspects may be combined with any one or more features of any other example, embodiment, or aspect described herein.

[0221] Exemplary Embodiments Embodiment 1 is a filter medium comprising a support layer, a continuous fine fiber layer having a thickness of at most 50 μm; and an efficiency layer; wherein the composite comprising the support layer and the continuous fine fiber layer has a P95 / P50 ratio of at most 1.8, at most 1.9, or at most 2; and the efficiency layer has a P95 / P50 ratio of at least 1.8, at least 1.9, or at least 2; and the P95 value of the composite is within the range provided by the P5 and P50 values ​​of the efficiency layer. Example 2 is the filter medium of Example 1, wherein the composite has a P95 / P50 ratio greater than 1. Example 3 is the filter medium of Example 1 or 2, wherein the efficiency layer has a P95 / P50 ratio of at most 10, at most 15, or at most 20. Example 4 is the filter medium of any one of the preceding examples, wherein the continuous fine fiber layer has a thickness of at least 2 μm. Example 5 is the filter medium of any one of the preceding examples, wherein the thickness of the continuous fine fiber layer is measured by scanning electron microscopy (SEM). Example 6 is the filter medium of any one of the preceding examples, wherein the continuous fine fiber layer is disposed between the efficiency layer and the support layer. Example 7 is the filter medium of any one of the preceding examples, wherein the efficiency layer is disposed upstream of the filter medium. Example 8 is the filter medium of any one of the preceding examples, wherein the filter medium further comprises a second efficiency layer. Example 9 is the filter media of Example 8, wherein the second efficiency layer is positioned adjacent to and upstream of the efficiency layer. Example 10 is the filter medium of any one of the preceding examples, wherein the efficiency layer comprises wet-laid resin-free media, wet-laid resin-bonded glass media, melt-blown media, wet-laid cellulose media, or air-laid glass media. Example 11 is the filter medium of any one of the preceding examples, wherein the efficiency layer comprises wet-laid media. Example 12 is the filter medium of any one of the preceding examples, wherein the efficiency layer comprises bicomponent fibers and efficiency fibers, the efficiency fibers having a smaller diameter than the bicomponent fibers. Example 13 is the filter medium of Example 12, wherein the efficiency fibers comprise glass fibers. Example 14 is the filter medium of Example 12 or 13, wherein the efficiency fibers comprise short-cut fine fibers. Example 15 is the filter medium of any one of the preceding examples, wherein the efficiency layer comprises microfibrillated cellulose fibers. Example 16 is the filter medium of any one of the preceding examples, wherein the continuous fine fiber layer comprises fibers having a diameter of at most 10 micrometers (μm). Example 17 is the filter medium of any one of the preceding examples, wherein the continuous fine fiber layer comprises fibers having a diameter of at least 1 micrometer (μm). Example 18 is the filter medium of any one of the preceding examples, wherein the continuous fine fiber layer comprises fibers having an elliptical shape. Example 19 is the filter medium of any one of the preceding examples, wherein the continuous fine fiber layer comprises a mixture of fibers of different diameters. Example 20 is the filter medium of Example 19, wherein the fibers of different diameters are mixed within a single level of continuous fine fiber layers. Example 21 is the filter medium of example 19 or 20, wherein the fibers of different diameters form different strata in the continuous fine fiber layer. Aspect 22 is the filter medium of any one of aspects 19 to 21, wherein the fibers of different diameters include thick fine fibers and thin fine fibers, and the thick fine fibers have an average diameter at least three times the average fiber diameter of the thin fine fibers. Example 23 is the filter medium of Example 22, wherein the continuous fine fiber layer comprises a first layer of fine fibers comprising thick fine fibers and a second layer of fine fibers comprising thin fine fibers. Example 24 is the filter medium of example 22 or 23, wherein the thick fine fibers have an average diameter of at least 1 μm. Example 25 is the filter medium of any one of Examples 22-24, wherein the thick fibrils have a diameter at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm greater than the diameter of the thin fibrils. Example 26 is the filter medium of any one of the preceding examples, wherein the continuous fine fibers comprise polyamide. Example 27 is the filter medium of any one of the preceding examples, wherein the support layer comprises a spunbond layer.

[0033] Example 28 is the filter medium of any one of the preceding embodiments, further comprising an overall β 10μm is at least 5, at least 7, or at least 10 under circulating flow conditions. Example 29 is the filter medium of Example 28, wherein the circulating flow conditions are evaluated using ISO / CD 23369 Edition 1, except when testing flat sheet performance, the test is conducted in single-pass mode, and the test is conducted at 25°C; the flow rate through the medium is circulated at 5 mm / s to 1.25 mm / s for a 10-second cycle; ISO 12103-1, Medium Test Dust, provides an upstream particle concentration of 10 mg / L; continuous particle concentration measurements are collected every 6 seconds; and the fluid conductivity is controlled in the range of 1000 picosiemens / meter (pS / m) to 1500 pS / m. Embodiment 30 is a filter element comprising the filter medium of any one of the preceding embodiments. Example 31 is the filter element of Example 30, wherein the wire support is positioned downstream of the support layer. A thirty-second embodiment is a method for filtering a fluid using the filter element according to any one of the first to twenty-ninth embodiments or the filter element according to the thirty-first embodiment. Example 33 is the method of Example 32, wherein the fluid comprises air, gas, and liquid. Aspect 34 is the method of aspect 32 or 33, wherein the fluid comprises a hydraulic fluid, oil, fuel, or lubricant.

[0222] The present invention is illustrated by the following examples, it being understood that the particular examples, materials, amounts and procedures are to be interpreted broadly in accordance with the scope and spirit of the invention described herein. [Example]

[0223] Preparation of polymer solutions To prepare Solution 1, nylon copolymer resin (SVP 651 (Shakespeare Co., Columbia, SC), a terpolymer containing 45% nylon-6, 20% nylon-6,6, and 25% nylon-6,10 with a number-average molecular weight of 21,500 to 24,800 (see also Table 3)) was dissolved in alcohol (ethanol, 190 proof) and heated to 60°C to prepare a 9% nylon solids solution. After cooling, melamine-formaldehyde resin (CYMEL 1133, Cytec Industries of West Paterson, NJ) was added to the solution to achieve a 20:100 weight ratio of melamine-formaldehyde resin to nylon. The melamine-formaldehyde resin served as a crosslinker. Additionally, para-toluenesulfonic acid (7% based on polymer solids) was added to the solution. The solution was stirred until homogeneous. Solution 1 was used to make 0.25 μm fibers.

[0224] Solution 2 was prepared as described for Solution 1, except that a 17% nylon solids solution was used (similarly, the weight ratio of melamine-formaldehyde resin to nylon was 20:100 parts by weight). Solution 2 was used to fabricate 1 μm fibers.

[0225] Viscosity values ​​of 30±5 cP and 300±5 cP for Solutions 1 and 2, respectively, were measured at 25° C. using a Brookfield LV DV-I Prime Viscometer in combination with a Fisher Scientific Model 8005 temperature-controlled water bath.

[0226] To prepare Solution 3, copolyamide (Griltex D 1523A, EMS-Griltech, Switzerland) was dissolved in a solvent mixture of ethanol, benzyl alcohol, and water (16:1:1 weight ratio of ethanol:benzyl alcohol:water) and heated to 60°C to prepare a 21% (w / w) solution. Solution 3 had a viscosity of 473±10 cP, measured at 25°C using a Brookfield LV DV-I Prime Viscometer and a Fisher Scientific Model 8005 temperature-controlled water bath. Solution 3 was used to fabricate 1.4 μm fibers.

[0227] Pendant drop sample preparation The samples were prepared using a pendant drop apparatus, i.e., a syringe filled with polymer solution. A high voltage was applied to a needle attached to the syringe, and the polymer solution was pumped through at a specified pumping rate. As a droplet of polymer solution exited the needle, it formed a Taylor cone under the influence of an electrostatic field. A sufficiently high voltage caused a jet to be ejected from the Taylor cone, which stretched to form a thin fiber and deposited it on a medium attached to a rotating mandrel, which acted as a collector.

[0228] Fibers were formed on a support layer wound around a cylinder (4 inches in diameter, rotating at 300 rpm) by electrospinning at a distance of 4 inches from one or more syringes delivering one or more polymer solutions at a voltage of 24 kV and a pump rate of 0.075 mL / min. After electrospinning, the formed fine fibers were heat-treated at 140°C for 10 minutes.

[0229] Method 1: A mixed fiber layer was fabricated by co-spinning two different electrospinning precursor solutions (solution 1 and solution 2) from two different syringes, delivered at the same pump rate (0.075 mL / min) and for the same duration (5 min). 2The solution was deposited onto a 0.2 mm thick spunbond nylon scrim with a basis weight of 1000 kJ / g and 28% solids (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL). Two control samples were separately prepared using the same pump speed and duration by spun Solution 1 or Solution 2 from a single syringe to form layers containing only thin or thick fine fibers, respectively.

[0230] To improve the structural stability through cross-linking, all samples were subjected to post-synthesis treatment: after electrospinning, the formed fibers were heat-treated at 140 °C for 10 min.

[0231] Method 2: A series of mixed fiber layers were fabricated by co-spinning solution 1 and solution 2 from two different syringes, delivered at the same pump rate (0.075 mL / min) and for the same duration. 2 The mixture was deposited onto a 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) with a basis weight of 1000 spunbond nylon and a solids content of 28%. Two control samples were separately prepared using the same pump speed and duration by co-spinning either Solution 1 or Solution 2 from two syringes to produce layers containing only thin fine fibers or thick fine fibers, respectively. In contrast to Method 1, co-spinning either Solution 1 or Solution 2 from two syringes (rather than one syringe) resulted in a closer match between the basis weight of the control sample and the sample containing the mixed fiber layer.

[0232] All samples were subjected to post-synthesis treatment to improve structural stability through cross-linking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 min.

[0233] Method 3: A series of fiber layers with fibers of different diameters were fabricated at 70 g / m² by alternately (“pulsing”) spinning from one of two syringes containing Solution 1 or Solution 2, alternately delivered at the same pump speed (0.075 mL / min) according to the timing sequence in Table 1. 2 The mixture was deposited onto a 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) having a basis weight of 1000 spunbond nylon and a solids content of 28%.

[0234] All samples were subjected to post-synthesis treatment to improve structural stability through cross-linking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 min.

[0235] Method 4: Using a two-step procedure, a series of mixed fiber structures were fabricated at 70 g / m 2 The mixture was deposited onto a 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) having a basis weight of 1000 spunbond nylon and a solids content of 28%.

[0236] In the first step, thick fine fibers (0.43 g / m) were obtained by pumping Solution 2 at a pump speed of 0.075 mL / min for 2 min. 2 (corresponding to a coverage of 100%) was deposited onto the scrim to act as a support layer underneath the subsequent fibers.

[0237] In the second step, layers of mixed diameter fibers were deposited by alternating (“pulse”) spinning from either of two syringes containing Solution 1 or Solution 2 (for thin and thick fibers, respectively), alternately delivered at the same pump speed (0.075 mL / min) according to the timing sequence in Table 1.

[0238] Approximately 0.65 to 0.86 g / m 2All samples with total basis weights in the range of 1000 to 14000 were subjected to post-synthesis treatment to improve structural stability through cross-linking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 min.

[0239] Method 5 Using a two-step procedure, a series of structures with different basis weights due to the contribution of the fine fiber component were fabricated, with a maximum of 70 g / m 2 The mixture was deposited onto a 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) having a basis weight of 1000 spunbond nylon and a solids content of 28%.

[0240] In the first step, thick fine fibers (0.43 g / m) were obtained by pumping Solution 2 at a pump speed of 0.075 mL / min for 2 min. 2 (corresponding to a coverage of 100%) was deposited onto the scrim to act as a support layer underneath the subsequent fibers.

[0241] In the second step, a layer of fine fine fibers was deposited by feeding Solution 1 at a pump rate of 0.075 mL / min. The basis weight of the layer of fine fine fibers was 0.09 g / m 2 , 0.10g / m 2 , 0.22 g / m 2 , 0.31g / m 2 , 0.45g / m 2 or 0.56 g / m 2 These were achieved using electrospinning times of 48, 60, 120, 168, 240, or 300 seconds, respectively. After electrospinning, the formed fibers were heat-treated at 140°C for 10 minutes.

[0242] [Table 1]

[0243] Method 6 A series of media samples were prepared containing multiple layers with various sizes of fine fibers. The samples included a base layer of thick fine fibers, followed by a layer of thin fine fibers and a layer of thick fine fibers on top (thick / thin / thick or L / S / L). Alternatively, the samples included a base layer of thick fine fibers, followed by a layer of thin fine fibers, then a layer of a mixture of thin and thick fine fibers and a layer of thick fine fibers on top (thick / thin / mixed / thick or L / S / mixed / L).

[0244] Solution 2 was spun for 2 minutes to obtain thick fine fibers (0.43 g / m 2 A second layer of thin fine fibers (0.22 g / m²) was then deposited onto the scrim. Without wishing to be bound by theory, it is believed that the thick fine fibers act as a support layer underneath the next fiber layer. Next, a second layer of thin fine fibers (0.22 g / m²) was deposited by spinning Solution 1 for 2 minutes. 2 A layer of thick fibrils (0.43 g / m²) was deposited on the spun ... 2 All solutions were delivered at a pump rate of 0.075 mL / min.

[0245] Approximately 1.31 to 1.52 g / m 2 All samples with total basis weights in the range of 1000 to 14000 were subjected to post-synthesis treatment to improve structural stability through cross-linking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 min.

[0246] Method 7 A series of media samples were also prepared that included a base layer of thick fibrils and a mixed layer of thin and thick fibrils.

[0247] First, a first fine fiber layer containing thick fine fibers (0.43 g / m) was prepared by spinning solution 2 for 2 min at a pump rate of 0.075 mL / min. 2(corresponding to a coverage rate of 70g / m 2 The thin and thick fibers were deposited onto a 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) with a basis weight of 1000 spunbond nylon and a solids content of 28%. A second thin fiber layer containing mixed thin and thick fibers was then deposited by co-spinning two different electrospinning precursor solutions (Solution 1 and Solution 2) from two different syringes delivered at the same pump speed (0.075 mL / min) and for the same duration (2.5 or 4.5 min).

[0248] All samples were subjected to post-synthesis treatment to improve structural stability through cross-linking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 min.

[0249] Method 8A A single-size fiber structure (nominal fiber diameter 1.4 μm, basis weight 0.67 g / m) was obtained by spinning for 2.5 minutes at a needle-to-collector distance of 4 inches and a bias of 24 kV. 2 A coating of 70 g / m2 was applied to a substrate with a basis weight of 70 g / m2 from a polymer solution (21% w / w Griltex D 1523A (EMS-Griltech AG, Switzerland) in a solvent mixture of ethanol:benzyl alcohol:water in a weight ratio of 16:1:1) (solution 3) delivered at a pump rate of 0.075 mL / min. 2 and deposited onto a 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) with a solids content of 28%.

[0250] Method 8B A single-size fiber structure (nominal fiber diameter 1 μm, basis weight 2.59 g / m) was obtained by spinning for 12 minutes at a needle-to-collector distance of 4 inches and a bias of 24 kV. 2 A coating weight of 70 g / m2 was obtained from a polymer solution (17% w / w SVP 651 in ethanol (see Table 3)) (Solution 2) delivered at a pump rate of 0.075 mL / min.2 and deposited onto a 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) with a solids content of 28%.

[0251] Method 8C A single-size fiber structure (nominal fiber diameter 1.4 μm, basis weight 4.02 g / m) was obtained by spinning for 15 minutes at a needle-to-collector distance of 4 inches and a bias of 24 kV. 2 A coating of 1000 μm (coverage of 1000 μm) was applied to a nylon scrim (Cerex, 70 g / m) from a polymer solution (21% w / w Griltex D 1523A (EMS-Griltech, Switzerland) in a solvent mixture of ethanol:benzyl alcohol:water in a weight ratio of 16:1:1) (solution 3) delivered at a pump rate of 0.075 mL / min. 2 ) was deposited on the

[0252] Method 9: Thick fine fibers (0.54 g / m) were obtained by spinning solution 3 for 2 minutes at a needle-to-collector distance of 4 inches and a bias of 24 kV. 2 (corresponding to a coverage of 1000 ppm) was deposited onto the scrim.

[0253] A second layer of fine fine fibers (0.22 g / m) was then deposited by spinning Solution 1 for 2 minutes at a needle-to-collector distance of 4 inches and a bias of 24 kV. 2 (corresponding to a coverage of 1000mV) was deposited.

[0254] A third layer of thick fine fibers (0.54 g / m) was fabricated by spinning solution 3 for 2 minutes at a needle-to-collector distance of 4 inches and a bias of 24 kV. 2 (corresponding to a coverage of 1000mV) was deposited.

[0255] Finally, a top layer of thick fine fibers (0.54 g / m) was obtained by spinning solution 3 for 2 minutes at a needle-to-collector distance of 4 inches and a bias of 24 kV. 2 (corresponding to a coverage of 1000mV) was deposited.

[0256] Preparation of media handsheets Handsheets were prepared by weighing the component fibers to achieve the required basis weight when formed into a 30 cm x 30 cm sheet. A FORMAX 12" x 12" stainless steel sheet mold (catalog number G-100, Adirondack Machine Corporation, Hudson Falls, NY) was used as the handsheet former, and a uniform nonwoven scrim layer with pores less than 100 μm was placed at the bottom of the former (a removable forming wire was not used). The former was then nearly filled with cold tap water, leaving room for adding 1.5 L of additional water. 1 mL of Tide HE laundry soap (Procter & Gamble, Cincinnati, OH) was added to the water in the handsheet former. To prepare the fibers, 1 L of cold tap water was added to a Vitamix blender along with 200 mL of 5% acetic acid in water. The weighed fibers were added to the blender and mixed at medium-low speed for 180 seconds. The contents of the blender were then added to a handsheet former, and the contents of the handsheet former were mixed to ensure uniform fiber distribution. Water was drained from the bottom of the handsheet former, allowing the fibers to form a sheet as they were collected on the nonwoven scrim. Water was removed from the sheet using vacuum suction on the wire side, and the handsheet (still on the scrim) was dried at 120°C for 10 minutes in a single-sided hotplate speed dryer (Model 135 Speed ​​Dryer, Emerson Apparatus, Gorham, ME). The sheet was removed (from the scrim) and allowed to cool to ambient conditions before use.

[0257] Media characterization Steady flow condition test The β ratio was evaluated under steady-state flow conditions using ISO 16889:2008 (Hydraulic fluid power - Filters - Multi-pass method for evaluating the filtration performance of filter elements). However, when testing flat-sheet performance, the test was performed in single-pass mode rather than the multi-pass mode required by the test standard. The test was performed at 25°C rather than 40°C as required by the test standard. The flow rate through the media was 5 mm / s. ISO 12103-1, Medium Test Dust (Powder Technology, Inc., Arden Hills, MN) was used to achieve an upstream particle concentration of 10 mg / L. Continuous particle concentration measurements were collected every 6 seconds.

[0258] Circulating flow condition test The β ratio was evaluated under circulating flow conditions using ISO / CD 23369 Edition 1 (Hydraulic Fluid Power - Multi-pass Method for Evaluating the Filtration Performance of Filter Elements Under Circulating Flow Conditions). However, when testing flat-sheet performance, the test was performed in single-pass mode instead of the multi-pass mode required by the test standard. Tests were performed at 25°C instead of 40°C as required by the test standard. The flow rate through the media was circulated from 5 mm / s to 1.25 mm / s in a 10-second cycle (approximately 5 seconds at each speed). ISO 12103-1 Medium Test Dust (Powder Technology, Inc., Arden Hills, MN) was used to achieve an upstream particle concentration of 10 mg / L. Continuous particle concentration measurements were collected every 6 seconds. The fluid conductivity was controlled in the range of 1000 to 1500 picosiemens per meter (pS / m).

[0259] Particle Counter Calibration The particle counter was calibrated for use with ISO test procedures according to ISO 11171:2016 (Hydraulic fluid power - Calibration of automatic particle counters for liquids).

[0260] Pressure drop Pressure drop was measured as described in ISO 3968:2017 using the test conditions shown in Table 2.

[0261] [Table 2]

[0262] Scanning Electron Microscopy (SEM) Samples were prepared for top-down SEM imaging by sputter-coating the surface with a mixture of gold and palladium, including a 60:40 Au:Pd mixture. Typically, accelerating voltages of 5 kV or 10 kV were used, and images were collected at 500x, 1000x, and 2500x magnifications using a secondary electron detector or a backscattered electron detector.

[0263] A 3 mm x 20 mm sample containing the fine fibers on the support layer was prepared for cross-sectional SEM imaging by placing the sample, fiber-side down, in a weighing tin on a hard surface, filling the tin with liquid nitrogen, and submerging the sample. After at least 30 seconds, a razor blade was used to cut the sample (while still submerged in liquid nitrogen) to expose the cross section. After an additional 10-20 seconds of cutting, the sample was removed from the liquid nitrogen and placed in the SEM for imaging. The sample was then sputter-coated with 60:40 Au:Pd. Images were typically collected at 1000x magnification using a secondary electron detector, using an accelerating voltage of 5 kV.

[0264] Fiber diameter Fiber diameter screening by scanning electron microscopy (SEM) was performed by imaging fibers with a top-down SEM and measuring the fiber diameter (or other dimension of interest) in the resulting micrographs. Image processing software such as ImageJ (FIJI Is Just ImageJ (FIJI), the latest version of ImageJ) and / or Trainable Weka Segmentation (an ImageJ plug-in) was used for fiber screening. Fiber diameter was measured at at least 30 locations on the sample.

[0265] Thin fiber layer thickness The thickness of the fine fiber samples prepared as described above was measured by scanning electron microscopy (SEM) through cross-sectional analysis of the SEM. The thickness of the fine fiber layer in at least five images from different parts of the sample was determined using FIJI. Specifically, the top and bottom of the fine fiber layer were drawn using the polygon tool, the area outside the selected fine fiber cross section was erased, the selected area of ​​the fine fiber cross section was recolored white using the threshold tool to correct for fibers at the boundary of the selected section, and the maximum thickness of the image was measured and recorded. Five of these maximum values ​​were rounded to the nearest tenth of a micron and averaged to obtain the thickness of the fine fiber sample.

[0266] Calculation of fiber ratio based on spinning time The relative amounts of thin and thick fine fibers (based on total fiber count) are determined using the following formula:

number

number

[0267] Calculation of fiber ratio based on microscopy Images of the samples were obtained by SEM at appropriate magnification (e.g., 500x, 1000x, or 2500x). The presence of one or more fiber populations was determined by counting all fibers in the image and classifying them into thin and thick fine fibers based on diameter groupings that varied within 25%. Fiber diameter was measured using image processing software such as ImageJ. The proportion of thin fine fibers was calculated by taking the ratio of the number of thin fine fibers to the number of total fibers (both thin and thick fibers) in the image.

[0268] solidity The solidity (c) of a nonwoven layer (including, for example, a non-fine fiber layer or a composite including a fine fiber layer and a non-fine fiber layer) is calculated using the following formula: c=BW / ρZ where BW is the basis weight, ρ is the density of the fiber, and Z is the thickness of the medium. If the nonwoven layer contains different fibers, the mass ratio of the fibers can be used to determine the density (ρ).

[0269] Caliper was measured according to TAPPI T411 om-15 entitled "Thickness (caliper) of paper, paperboard, and combined board" using a foot pressure of 1.5 psi. Basis weight was measured using TAPPI T410 om-08.

[0270] Because measuring the thickness of the fine fiber layer is difficult, the solidity of the fine fiber layer is calculated using an adapted version of the Kirsch-Fuchs equation (see Kirsch et al., "Studies on Fibrous Aerosol Filters—III Diffusional Deposition of Aerosol in Fibrous Filter," Ann. Occup. Hyg. 1968;11:299-304) using experimentally measured pressure drop values. Pressure drop (ΔP or dP) is determined using the FHAST bench, as described in the Liquid Filtration Performance Testing section below.

[0271] First, the dimensionless fiber drag parameter F * 1.0 is calculated from the modified Kirsch-Fuchs formula:

number

[0272] Next, the solidity (c) is calculated using the following formula: * 1.0 Calculate from: F * 1.0 =4.3548e 8.8822c .

[0273] For mixed fiber media, the effective fiber diameter is calculated from the following formula, taking into account the relative amounts of fine and coarse fibers:

number

[0274] The basis weight of the fine fiber layer or layers is calculated as follows: Total basis weight of the fine fiber layer = (mass of fine fiber) / (area of ​​scrim).

[0275] The mass of fine fibre is calculated as follows: Mass of fine fibers = (polymer in solution (% w / v)) x (pump speed) x (spinning time).

[0276] If the method of formation of the fine fibers is unknown, the mass of the fine fibers can be calculated after separation of the fine fibers from the scrim or substrate (e.g., by peeling or delaminating) as follows: Mass of fine fibers = (total mass of media sample) - (mass of bare scrim or substrate).

[0277] Capillary flow porometry (pore size measurement) Pore ​​size measurements were performed by capillary flow porometry using continuous pressure scans on a Porometer 3G (Quanachrome Instruments, Boynton Beach, CA).

[0278] Flow Porometry Method A In this method, Porofil Wetting Solution (Quantachrome Instruments, Anton Paar, Boynton Beach, FL) was used as the wetting fluid, and samples were tested in both wet and dry states (first wet, then dry). 25 mm diameter samples were subjected to continuous pressure scans from 0.0256 bar to 1.275 bar to determine pore sizes with diameters ranging from 1 μm to 100 μm.

[0279] Flow porometry method B The method used silicone oil with a surface tension of 20.1 dynes / cm and a wetting contact angle of 0, and samples were tested in both wet and dry states (first dry, then wet). Samples with a 6 mm diameter were subjected to successive pressure scans selected to measure the majority of the cumulative pore size distribution, ranging from 2% to 98%.

[0280] For both methods, samples were tested under wet and dry conditions from low to high pressures. The airflow and sample pressure during the saturated portion of the test are commonly referred to as the wetting curve. 256 data points were collected across the pressure scan range for both the dry and wetting curves. Data points were collected at a rate of approximately 17 data points per minute across the entire scan. Tests were conducted at ambient conditions (e.g., 20°C to 25°C). No adjustments were made to the pore size refinement by applying empirical tortuosity and / or shape factors.

[0281] In a flow porometry test procedure, a series of pressure (typically plotted on the x-axis) and airflow (typically plotted on the y-axis) data for a dry sample and a set of pressure and airflow data for a saturated (wet) sample are collected. These two data sets are commonly referred to as the dry curve and the wet curve. That is, Drying curve=V dry = airflow through the dry sample as a function of pressure, Wetting curve = V wet = airflow through a saturated sample as a function of pressure.

[0282] Based on capillary theory, the pressure difference (ΔP) across the sample can be converted to pore diameter (d) using the Young-Laplace equation.

number

[0283] This transformation allows the definition of the drying and wetting curves as a function of pore size: Drying curve=V' dry = airflow through the dry sample as a function of diameter, Wetting curve = V' wet = airflow through a saturated sample as a function of diameter.

[0284] The cumulative flow pore size distribution (Q) is defined as the ratio of the wet curve to the dry curve as a function of pore size, where:

number

[0285] The cumulative distribution can be expressed as the increase in cumulative distribution from 0% to 100% or as the decrease in cumulative distribution from 100% to 0%. Pore size herein is defined from the increase in cumulative flow pore size distribution, where: Cumulative flow pore distribution increase = 1-Q(d) is.

[0286] To better define the points along this curve, we define various P(x%) values ​​that are equivalent to the corresponding pore diameter (d). P(x%)=d, where x%=1-Q(d).

[0287] Examples include, but are not limited to: P5 is the pore size with an increase in cumulative flow pore distribution of 5%. P10 is the pore size with an increase in cumulative flow pore distribution of 10%. P50 is the pore size with an increase in cumulative flow pore distribution of 50%. P90 is the pore size with an increase in cumulative flow pore distribution of 90%. P95 is the pore size with an increase of 95% of the cumulative flow pore distribution.

[0288] Where maximum pore size is reported, it was determined by detecting the bubble point using the automated bubble point (BP Auto Tolerance) method with a Porometer 3G (Quanachrome Instruments, Boynton Beach, CA). According to this method, the bubble point is detected after fluid begins to pass through the sample and three consecutive measurements show an increase of at least 1%. The bubble point is the value at the start of these three consecutive points.

[0289] Air filtration performance Air filtration performance was evaluated using a High Efficiency Flat Sheet (HEFS) TSI Automated Filter Tester, Model 8127, test bench (TSI Incorporated, Shoreview, MN), which measures particle capture efficiency using 0.3 μm oil (bis(2-ethylhexyl) sebacate, Sigma-Aldrich) droplets (aerosol) applied to a 4-inch diameter media sample at a flow rate of 14.7 liters per minute (L / min). TSI's CertiTest Model 8127 Automated Filter Tester is designed to test filters, respirator cartridges, and filter media according to the latest U.S. government and industry-wide specifications and meets the standards of 42 CFR §84 (June 8, 1995).

[0290] Liquid filtration performance test Liquid filtration performance was evaluated on a flat-sheet, high-precision, single-pass, two-fluid (FHAST) bench with the following characteristics: flow rate control: 57 mL / min to 580 mL / min with a ±2% error; temperature control: 25 °C to 40 °C with a ±0.25 °C error; dP measurements: 0 psi to 25 psi with a ±0.065% error; particle size: 1.7 μm to 20 μm; maximum particle concentration: 1,000,000 / mL; dilution performance: 5:1 to 100:1. The FHAST bench was used in static mode using ISO Medium Test Dust according to ISO 11171:2016 at a concentration of 10 milligrams per liter (mg / L) in hydraulic fluid and a flow rate of 0.347 L / min, added to a 2-inch diameter media sample. Media dP values ​​and efficiency at specific contaminant particle sizes (measured using a commercially available particle counter, specifically the PAMAS 4132 Particle Counting System for Liquids calibrated with ISO Medium Test Dust per ISO 11171:2016 (Hydraulic Fluid Power - Calibration of Automatic Particle Counters for Liquids)) were collected at regular time intervals (approximately every 7 seconds) over the test period, ending when a preset media maximum dP of 20 psi (measured with two test media dP sensors: (A) 0 psi to 5 psi, ±0.025% accuracy differential pressure transducer; high-precision, low-range dP sensor, and (B) 0 psi to 25 psi, ±0.065% accuracy differential pressure transducer; low-precision, high-range dP sensor) was reached.

[0291] Beta ratios were evaluated under steady-state flow conditions (347 mL / min through a 2-inch diameter media sample) using ISO 16889:2008 (Hydraulic Fluid Power—Filters—Multi-Pass Method for Evaluating the Filtration Performance of Filter Elements). However, when testing flat-sheet performance, the test was conducted in single-pass mode rather than the multi-pass mode required by the test standard. A 10 mg / L concentration of ISO 12103-1 A3 Medium Test Dust (Powder Technology, Inc., Arden Hills, MN) was added to hydraulic fluid (Mobil Aero HF, MIL-PRF-5606). Instantaneous beta values ​​were recorded every 7 seconds over the test period. The test was terminated when a final dP of 20 psi was reached.

[0292] figure of merit The figure of merit is a measure of the performance of a filter medium and its ability to provide a particular level of stream cleanliness with minimal energy use. Generally, a higher figure of merit value is better than a lower value.

[0293] Figure of merit (FOM) values ​​were calculated from permeability (P, ratio of upstream to downstream counts), pressure drop (dP, inches of water column) and face velocity (u, fpm). FOM=(-log 10 P) / (dP / u).

[0294] Permeability (P), pressure drop (dP) and face velocity (u) were measured using a HEFS TSI automatic filter tester, model 8127, test bench as described above.

[0295] Scanning Electron Microscopy (SEM) Samples were prepared for SEM imaging by sputter coating with gold. Typically, an accelerating voltage of 5 kV or 10 kV was used, and images were collected at 500x, 1000x, and 2500x magnification using a secondary electron detector or a backscattered electron detector.

[0296] Example 1 An XP / fine fiber / scrim medium was formed by combining Synteq XP™ synthetic liquid medium ("10XP", Donaldson Company, Inc., Minneapolis, MN) with a 10 micron efficiency rating as the efficiency layer, a support layer (CEREX 23200, Cerex Advanced Fabrics, Inc., Cantonment, FL), and a continuous fine fiber layer deposited on the support layer using electrospinning. The continuous fine fiber layer (having a diameter of 0.9 μm) was formed from SVP 651 (see Table 3). The efficiency layer was the most upstream layer; the continuous fine fiber layer was positioned downstream of the efficiency layer; and the support layer (scrim) was positioned downstream of the continuous fine fiber layer.

[0297] The layers were placed on top of each other and placed into a filter housing.

[0298] Beta ratios versus particle size were measured for Synteq XP™ synthetic liquid media with a 10 micron efficiency rating ("10XP," Duramax P164378, Donaldson Company, Inc., Minneapolis, MN), Synteq XP™ synthetic liquid media with a 5 micron efficiency rating ("5XP," Duramax P165332, Donaldson Company, Inc., Minneapolis, MN), and XP / fine fiber / scrim media under steady flow conditions (as described in the Steady Flow Conditions Test) or circulating flow conditions (as described in the Circulating Flow Conditions Test). The results are shown in Figure 3.

[0299] As shown in Figure 3B, comparable efficiencies were observed for Synteq XP™ synthetic liquid media and XP / fine fiber / scrim media with a 5 micron efficiency rating, but the XP / fine fiber / scrim media and XP / fine fiber / scrim media showed improved pressure drop.

[0300] [Table 3]

[0301] Example 2 XP / fine fiber / scrim media was formed as described in Example 1. The XP / fine fiber / scrim media and Synteq XP™ synthetic liquid media (Donaldson Company, Inc., Minneapolis, MN) with a 10 micron efficiency rating were placed on a wire support and pleated to form a filter element. The filter elements were then tested under steady flow conditions (as described in Steady Flow Condition Test) or circulating flow conditions (as described in Circulating Flow Condition Test). The results are shown in Figure 4 (Steady Flow Condition) and Figure 5 (Circulating Flow Condition).

[0302] Under steady-state flow conditions, Synteq XP™ synthetic liquid media without a fine fiber layer achieved a reduction in the International Organization for Standardization (ISO) cleanliness code (measured and defined as described in ISO 4406:2017) (from 22 / 21 / 17 to 18 / 14 / 4), and the addition of a fine fiber layer achieved a further reduction in the cleanliness code (to 14 / 8 / 3) with comparable pressure drops, i.e., within 20% of the pressure drop of filter elements containing XP / fine fiber / scrim media, typically within 10% of the pressure drop of filter elements containing Synteq XP™ synthetic liquid media without fine fibers.

[0303] Under dynamic flow conditions, Synteq XP™ synthetic liquid media without a fine fiber layer achieved a smaller reduction in cleanliness code (from 22 / 21 / 17 to 22 / 18 / 8), while the addition of the fine fiber layer achieved a much larger reduction in cleanliness code (from 22 / 21 / 17 to 18 / 14 / 4), also at the same pressure drop as achieved without the fine fiber layer under steady flow conditions.

[0304] Example 3 Media were prepared according to Pendant Drop Sample Preparation Method 3, Set A in Table 1 (thin fine fibers deposited directly on the scrim) and Pendant Drop Sample Preparation Method 4, Set A in Table 1 (thin fine fibers deposited on a thick fine fiber layer deposited on the scrim).

[0305] An exemplary image of a thick fine fiber layer deposited on a scrim is shown in Figure 2B.

[0306] An exemplary image of thin fine fibers deposited directly onto a scrim is shown in FIG. 2C, and an exemplary image of thin fine fibers deposited onto a thick fine fiber layer deposited onto a scrim is shown in FIG. 2D (thin fine fibers deposited onto a thick fine fiber layer deposited onto a scrim).

[0307] Example 4 The medium was prepared according to the pendant drop sample preparation method 1. The resulting nonwoven fabric had a weight of 1.64 g / m 2 The paper had a theoretical basis weight of 1.01 g.

[0308] Control nonwoven media fabricated by co-spinning each single electrospinning precursor solution from two different syringes contained 0.56 g / m of Solution 1 and Solution 2, respectively. 2 or 1.08 g / m 2 The paper had a theoretical basis weight of 1.01 g.

[0309] An SEM image of the resulting medium is shown in Figure 2E.

[0310] Example 5 The sample integrity of the composite samples was evaluated during FHAST bench testing up to 20 psi (at a face velocity of 0.56 ft / min, as further described in the Liquid Filtration Performance Test Methods), and the initial pressure drop for each composite was plotted against the maximum pore size of the composite. As used in this example, "composite" refers to any layer of fine fibers (e.g., including first, second, etc. layers of fine fibers) and a support layer. A composite includes at least one layer of fine fibers.

[0311] The average maximum composite pore size (P100) and the average intermediate composite flow pore size (P50) of each sample were measured by flow porometry according to Flow Porometry Method A.

[0312] Each sample contained fine fibers of mixed diameters and a substrate. Some samples contained a layer of fine fibers including "thick" and "thin" fine fibers, prepared as described in Methods 1, 2, or 3. Some samples contained a first layer of continuous fine fibers and a second layer of continuous fine fibers, prepared as described in Methods 4, 5, 6, or 7, where the first layer of continuous fine fibers contained fine fibers having an average diameter at least three times the average fiber diameter of the smallest fibers in the second layer of continuous fine fibers.

[0313] The results are shown in Figure 6. Triangles represent samples that maintained fine fiber structural integrity throughout the FHAST bench test; squares represent samples that experienced fine fiber blowout during the FHAST bench test (as indicated by beta decay). Samples containing two fine fiber layers, with the first layer containing fine fibers having an average diameter at least three times the average fiber diameter of the smallest fiber in the second fine fiber layer, are shown as filled shapes. Samples containing one fine fiber layer containing mixed diameter fibers are shown as unfilled shapes.

[0314] Most of the media samples with only one fine fiber layer (ie, made using methods 1, 2, or 3) showed fine fiber damage (indicated by open squares).

[0315] Some media samples with only one fine fiber layer withstood up to 20 psi during FHAST bench testing (indicated by open triangles). Without wishing to be bound by theory, it is believed that these fine fiber layers survived the test because the coverage (basis weight) was very high, but such high basis weight comes at the cost of a high initial pressure drop.

[0316] In contrast, all media samples containing two fine fiber layers made using methods 4, 5, 6, or 7 maintained the structural integrity of the fine fibers (indicated by filled triangles).

[0317] The results show that both the composite's average maximum pore size (Figure 6A) and the composite's average intermediate flow pore size (Figure 6B) correlate with the composite's ability to withstand the FHAST bench test. Clinical testing highly correlates with the composite's ability to withstand a pressure drop of at least 20 psi during liquid filtration, indicating superior filtration performance over media that cannot withstand the same conditions.

[0318] Some media samples with composite average maximum pore size (P100) as large as 20 μm survived the FHAST bench test, but a transition zone where some media samples began to fail the test was observed for media samples with composite average maximum pore size between 14 μm and 20 μm.

[0319] Similarly, some media with composite mean intermediate flow pore size (P50) as large as 11 μm survived the FHAST bench test, but a transition zone where some media samples began to fail the test was observed for media samples with composite mean maximum pore size between 6 μm and 11 μm.

[0320] For example, a sample without a thick fine fiber support and a composite average maximum pore size of 11 μm would not survive the FHAST bench test, but a sample with a thick fine fiber support and a composite average maximum pore size of 11 μm would survive the FHAST bench test. The ability to use fine fiber samples with larger pore sizes allows for fine tuning of the efficiency without detrimental pressure drop in the resulting composite.

[0321] Example 6 Composites including a fine fiber layer and a support layer were prepared according to Pendant Drop Sample Preparation Methods 8A-8C to form Fine Fiber Sample A, Fine Fiber Sample B, and Fine Fiber Sample C (each of which also included a support layer as described above).

[0322] An efficiency layer was prepared as described in the section on preparation of a media handsheet containing 40 wt-% glass fiber (Lauscha B-10-F, nominal fiber diameter 1 μm, Lauscha Fiber International, Lauscha, Germany) and 60 wt-% bicomponent fiber (Teijin TJ04CN, Teijin Limited, Tokyo, Japan) to form efficiency layer A.

[0323] Capillary flow porometry measurements were performed on Fine Fiber Sample A, Fine Fiber Sample B, Fine Fiber Sample C, and Efficiency Layer A according to Flow Porometry Method B. The results are shown in Table 4 and FIG.

[0324] [Table 4]

[0325] A medium was prepared as described in the section on preparation of medium handsheets containing 40 wt-% glass fiber (Lauscha B-26-R, nominal fiber diameter 2.4 μm, Lauscha Fiber International, Lauscha, Germany) and 60 wt-% bicomponent fiber (Teijin TJ04CN, Teijin Limited, Tokyo, Japan) to form Load Layer A.

[0326] The performance of the filter media containing both the load layer A and the efficiency layer A was evaluated under both steady-state and circulating-flow conditions. The results are shown in Table 5A. As can be seen from the results in Table 5A, the efficiency layer without the load layer and the fine fiber layer performed well under steady-state flow conditions, as indicated by low pressure drop (ΔP) and high efficiency, but under circulating-flow conditions, the efficiency dropped dramatically. Under steady-state flow conditions, the media was able to filter 10 μm diameter particles with high efficiency, but under steady-state flow conditions, the efficiency for particles of the same diameter was 50 times lower. Similarly, under steady-state flow conditions, the media was able to filter 99% of 9.3 μm diameter particles, but under circulating-flow conditions, the same 99% filtration could not be achieved unless the particles had a diameter of 27 μm.

[0327] As shown in Table 5B, the addition of certain fine fiber layers (Fine Fiber Sample A, Fine Fiber Sample B) can "restore" this efficiency loss while maintaining an acceptable pressure drop. In contrast, the addition of Fine Fiber Sample C results in an undesirably high pressure drop (more than three times the pressure drop exhibited by Load Layer A and Efficiency Layer A alone). Because Fine Fiber Sample C has smaller pores than Efficiency Layer A, the P95 of Fine Fiber Sample C (4.39 μm) does not fall within the P5-P50 range of Efficiency Layer A (4.70 μm-8.82 μm). In contrast, both Fiber Sample A and Fine Fiber Sample B have P95 values ​​that fall within the P5-P50 range of Efficiency Layer A (4.70 μm-8.82 μm).

[0328] If the pore size of the fine fiber layer is too small (e.g., as in Fine Fiber Sample C), the fine fibers block airflow through the filter media, resulting in an increased pressure drop. Furthermore, without wishing to be bound by theory, it is believed that a fine fiber layer with a pore size much smaller than that of the efficiency layer also results in lower efficiency because the fine fiber layer traps particles of a size that the efficiency layer cannot capture. In contrast, when the pore sizes of the fine fiber layer and the efficiency layer overlap, the fine fiber layer traps particles of a size that can also be captured by the efficiency layer.

[0329] [Table 5]

[0330] [Table 6]

[0331] Example 7 Samples prepared according to Method 9 were analyzed according to the "fine fiber layer thickness" method. An exemplary image is shown in Figure 8A, where the full depth of the fine fiber layer can be seen in cross section, and the fibers of the support layer can be partially seen at the bottom of the image.

[0332] Figure 8B shows the delineation of the cross-section of a fibril using the polygon tool. Figure 8C shows the image after the area outside the cross-section of the selected fibril has been removed. Figure 8D shows the area of ​​the cross-section of the selected fibril after it has been recolored to white using the threshold tool (to compensate for fibers on the boundary of the selected section), with the dashed line indicating the maximum thickness (5.97 μm) of the measured and recorded image. Five of these maximum values ​​were rounded to the nearest tenth of a micron, and then these rounded values ​​were averaged. The results are shown in Table 6.

[0333] [Table 7]

[0334] The complete disclosures of all patents, patent applications, and publications, as well as electronically available materials, cited herein are incorporated by reference. In the event of any inconsistency between the disclosure of this application and the disclosure of a document incorporated herein by reference, the disclosure of this application shall control. The foregoing detailed description and examples have been provided for clarity of understanding only. No unnecessary limitations should be construed therefrom. The invention is not limited to the exact details shown and described, for variations obvious to those skilled in the art will be encompassed within the invention defined by the claims.

Claims

1. Support layer; A continuous fine fiber layer having a thickness of up to 50 μm; and non-woven layer A filter medium comprising: the composite comprising the support layer and the continuous fine fiber layer has a P95 / P50 ratio of at most 2; the nonwoven layer has a P95 / P50 ratio of at least 1.8; A filter medium wherein the P95 value of the composite is within the range provided by the P5 and P50 values ​​of the nonwoven layers.

2. A filter material as described in claim 1, further comprising a further filtration layer, said further filtration layer being positioned adjacent to and upstream of said nonwoven fabric layer.

3. 3. The filter medium of claim 1, wherein the nonwoven layer comprises bicomponent fibers and second fibers, the second fibers having a smaller diameter than the bicomponent fibers.

4. 4. The filter medium of claim 1, wherein the nonwoven layer comprises microfibrillated cellulose fibers.

5. A filter element comprising the filter medium of any one of claims 1 to 4.

Images