Filter medium layers including mixed diameter fine fibers

Abstract

To provide a high performance (including high filter efficiency and low pressure drop) filter medium.SOLUTION: A filter medium includes: a support layer which has an average minimum fine pore diameter of at least 35 μm, an average maximum fine pore diameter up to 150 μm and a thickness up to 750 μm; a first fine fiber layer which includes mixedly first fine fibers having an average diameter less than 1 μm, and second fine fibers having an average diameter of at least 1 μm, and of at least 3 times the average diameter of the average diameter of the first fine fibers; and a second fine fiber layer which includes mixedly the first fine fibers having the average diameter less than 1 μm, and the second fine fibers having the average diameter of at least 1 μm, and of at least 3 times the average diameter of the average diameter of the first fine fibers.SELECTED DRAWING: Figure 1F

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. Summary of the Invention [Means for solving the problem]

[0002] The present disclosure describes high performance filter media (e.g., including high efficiency and low pressure drop). In some embodiments, the present disclosure describes filter media that achieve the efficiency of filter media that include fine glass fibers without the inclusion of fine glass fibers.

[0003] In one aspect, the present disclosure describes a filter medium comprising a support layer and a fine fiber layer. The fine fiber layer is disposed on the support layer, and the fine fiber layer comprises thick fine fibers and thin fine fibers. The thick fine fibers have an average diameter of at least 1 μm and are at least three times the average diameter of the thin fine fibers.

[0004] In some embodiments, the thick fibrils have a diameter that is at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the diameter of the thin fibrils.

[0005] In some embodiments, the fine fiber layer comprises a first layer of fine fibers, the first layer of fine fibers comprising thick fine fibers and thin fine fibers.

[0006] In some embodiments, the fine fiber layer comprises a first layer of fine fibers and a second layer of fine fibers, the first layer of fine fibers being deposited on the support layer, and the second layer of fine fibers being deposited on the first layer of fine fibers.

[0007] When the fine fiber layer comprises a first layer of fine fibers and a second layer of fine fibers, in some embodiments, the first layer of fine fibers comprises fibers having an average diameter at least three times the average fiber diameter of the fine fibers in the second layer of fine fibers.

[0008] In some embodiments, the second layer of fine fibers comprises fibers of two different diameters. When the second layer of fine fibers comprises fibers of two different diameters, the fibers of two different diameters can comprise thin fine fibers and thick fine fibers, where the thick fine fibers have an average diameter at least three times the average diameter of the thin fine fibers.

[0009] In some embodiments, the thin fibrils of the second layer of fibrils are deposited on the first layer of fibrils, and the thick fibrils of the second layer of fibrils are deposited on the thin fibrils of the second layer of fibrils.

[0010] In some embodiments, the fine fibers of the second layer of fibers are mixed with the thick fibers of the second layer of fibers.

[0011] In some embodiments, at least some of the fine fibers are prepared by a method including providing a fiber-forming polymer; providing a polymer-reactive resinous aldehyde composition that is reactive with the fiber-forming polymer; and combining the fiber-forming polymer and the reactive resinous aldehyde composition to form a plurality of fine fibers.

[0012] In some embodiments, at least some of the fine fibers are prepared by a method including: providing a fiber-forming polymer comprising a non-reactive polymer, where the non-reactive polymer is a polymer that cannot crosslink with the polymer non-reactive resinous aldehyde composition; providing a polymer non-reactive resinous aldehyde composition comprising one or more reactive groups that are capable of self-crosslinking; and combining the fiber-forming polymer and the reactive resinous aldehyde composition to form a plurality of fine fibers.

[0013] In some embodiments, at least some of the fine fibers are prepared by a process comprising: providing at least one fiber-forming polymer; providing at least two reactive additives that are reactive with each other and, optionally, with the fiber-forming polymer; and combining the at least one fiber-forming polymer and the at least two reactive additives under conditions effective to form a plurality of fine fibers.

[0014] In some embodiments, the support layer comprises a spunbond layer.

[0015] In some embodiments, the support layer and the fine fiber layer form a composite having a composite intermediate flow pore size that is at most 6 μm, at most 9 μm, or at most 11 μm.

[0016] In some embodiments, the fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm.

[0017] In some embodiments, the fine fibrils have an average diameter of at least 0.2 μm, hi some embodiments, the fine fibrils 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.

[0018] In some embodiments, the fine fibers are compatible with at least one of a hydraulic fluid, a fuel, or a lubricant.

[0019] In another aspect, the present disclosure describes a filter element including the filter media described herein. The filter media can form, form, or form part of the efficiency layer of the filter element. In some embodiments, the filter element further includes a loading layer.

[0020] As used herein, "fiber" has an average fiber diameter of at most 100 micrometers. 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 is the indicated 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 1 μm 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. Fiber diameters can be measured using top-down SEM imaging. Samples 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.

[0021] 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 0.1 μm.

[0022] The term "diameter" with respect to a fiber refers to either the diameter of a circular cross-section of the fiber or the largest cross-sectional dimension of a non-circular cross-section of the fiber.

[0023] As used herein, the term "particle size" refers to the diameter of a particle as determined as described in ISO 11171:2016.

[0024] As used herein, "mixed" fibers or "mixed fiber structure" refers to fibers having at least two different diameters, where the fibers having a first average diameter are mixed with the fibers having a second average diameter, i.e., the fibers are intermingled within the same layer of the 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.

[0025] 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.

[0026] As used herein, unless otherwise specified, pore size (e.g., mean mean flow pore size or mean maximum pore size) is determined using capillary flow porometry. Capillary flow porometry can be performed using a continuous pressure scan mode. An exemplary range of applied pressures that can be used is 0.0256 bar to 1.275 bar. For example, it can be useful to use a wetting liquid with a surface tension of 16 dynes / cm and a contact angle of 0, including Porofil Wetting Solution (Quantachrome Instruments, Anton Paar, Boynton Beach, FL). The sample is first tested in a wet state, varying from low to high pressure, and then in a dry 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 wet and dry curves. Typically, the tortuosity factor and / or shape factor are not used (i.e., a factor equal to 1 can be used for comparison with other test methods that use adjustment factors). The mean pore size (e.g., mean intermediate flow pore size or mean 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 can be found at the bubble point, which is identified after fluid begins to pass through the sample, three consecutive measurements increase by at least 1%, and 256 data points are collected across the scan at a rate of approximately 17 data points / minute. The bubble point is the value at the start of this three-point series. Individual measurements of intermediate flow pore size can be calculated by determining the pressure at which the wet curve and the "semi-dry" curve intersect. The semi-dry curve is expressed as V' dry It is obtained by mathematically dividing V' by 2. dry is the air flow through the dry sample as a function of diameter.

[0027] As used herein, "β ratio" or "β" 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

[0028] As used herein, "overall β ratio" or "overall β" is the ratio of the sum of all upstream particles in the course of an assay to the sum of all downstream particles in the course of an assay.

number

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

[0032] 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.

[0033] As used herein, the phrase "substantially free" means that the element listed after the phrase is not present in an amount that interferes with or contributes to the activity or effect specified in this disclosure for the listed element. For example, a media that is "substantially free" of glass does not contain glass in an amount sufficient to contribute to the efficiency of the filter media.

[0034] Unless otherwise specified, "a," "an," "the," and "at least one" are used interchangeably and mean one or more than one.

[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.).

[0036] As used herein, a "up to" number (eg, up to 50) is inclusive of that number (eg, 50).

[0037] 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.

[0038] Unless so specified, 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.

[0039] Throughout this specification, references to "one embodiment," "embodiment," "particular embodiments," or "some embodiments" mean that the features, configurations, compositions, or characteristics described in connection with an embodiment are 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, the particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more embodiments.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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]

[0044] [Figure 1A] Figure 1A shows β values ​​versus elapsed time (minutes) for samples (thin fibrils placed directly on a scrim) made and tested as described in Example 1. In Figure 1A, the "thick" fibrils have a fiber diameter at least three times the average fiber diameter of the "thin" fibrils. [Figure 1B]Figure 1B shows an exemplary SEM image (1000x magnification) of a sample (thin fibrils mounted directly on the scrim) made as described in Example 1 and tested on the FHAST bench. In Figure 1B, the "thick" fibrils have a fiber diameter at least three times the average fiber diameter of the "thin" fibrils. [Figure 1C] Figure 1C shows β values ​​versus elapsed time (minutes) for samples made as described in Example 1 (thin fibrils layered on thick fibrils placed directly on the scrim). In Figure 1C, the "thick" fibrils have a fiber diameter at least three times the average fiber diameter of the "thin" fibrils. [Figure 1D] Figure ID shows an exemplary SEM image (1000x magnification) of a sample (thin fibrils stacked on thick fibrils) made as described in Example 1 and tested on the FHAST bench. In Figure ID, the "thick" fibrils have a fiber diameter at least three times the average fiber diameter of the "thin" fibrils. [Figure 1E] Figure 1E shows exemplary SEM images of a thick fine fiber layer deposited on a nylon scrim (prior to depositing the thin fine fibers on the thick fine fiber layer) at 500x magnification (top panel) and 2000x magnification (bottom panel). In Figure 1E, the "thick" fine fibers have a fiber diameter at least three times the average fiber diameter of the "thin" fine fibers. [Figure 1F] FIG. 1F shows a schematic diagram of a sample prepared as described in Example 1 (thin fine fibers placed directly on a scrim). [Figure 1G] FIG. 1G shows a schematic diagram of a sample made as described in Example 1 (thin fibrils layered on thick fibrils placed directly on the scrim). [Figure 1H] Figure 1H shows a schematic diagram of an exemplary media configuration. In each configuration, a support media is not shown but is typically located downstream of the media. [Figure 1I] Figure 1I shows a schematic diagram of an exemplary media configuration. In each configuration, a support media is not shown but is typically located downstream of the media. [Figure 1J]1J shows schematic diagrams of exemplary media configurations. In each configuration, a support media is not shown but is typically located downstream of the media. [Figure 1K] 1K shows a schematic diagram of an exemplary media configuration. In each configuration, a support media is not shown but is typically located downstream of the media. [Figure 1L] FIG. 1L shows a schematic diagram of a sample made as described in Example 1 (thin fibrils layered on thick fibrils placed directly on the scrim). [Figure 1M] Figure 1M shows a schematic diagram of an exemplary media configuration. In each configuration, a support media is not shown but is typically located downstream of the media. [Figure 2A] FIG. 2A shows exemplary SEM images (1000x magnification) of samples made as described in Example 2 using Solution 1 to achieve thin fibrils (left panel), Solution 1 and Solution 2 to achieve mixed diameter (small and large) mixed fibrils (middle panel), and Solution 2 to achieve thick fibrils (right panel). [Figure 2B] FIG. 2B shows the dP increase over the course of the study for vehicles prepared and tested as described in Example 2. [Figure 2C] FIG. 2C shows the overall β values ​​for various dust particle sizes for bare scrim or media prepared and tested as described in Example 2. [Figure 3A] FIG. 3A shows exemplary SEM images (1000x magnification) of samples prepared as described in Example 3 according to pendant drop sample preparation method 2 for 2 minutes using Solution 1 to achieve thin fibrils (left panel), Solution 1 and Solution 2 to achieve mixed diameter (small and large) fibrils (middle panel), or Solution 2 to achieve thick fibrils (right panel). [Figure 3B]Figure 3B shows exemplary SEM images of samples made using Method 2 for 5 minutes (Figure 3B) or 1 minute (Figure 3C) using cospinning solution 1 and solution 2 to achieve mixed diameter (small and large) mixed fibrils. The intermixing of fibers in the network is indicated by the presence of single thin fibrils above and below the thick fibrils. [Figure 3C] Figure 3C shows exemplary SEM images of samples made using Method 2 for 5 minutes (Figure 3B) or 1 minute (Figure 3C) using cospinning solution 1 and solution 2 to achieve mixed diameter (small and large) mixed fibrils. The intermixing of fibers in the network is indicated by the presence of single thin fibrils above and below the thick fibrils. [Figure 3D] Figure 3D shows a comparison of media dP increase over the course of the test for media containing thin fine fibers, mixed diameter mixed fibers, or thick fine fiber media (Figure 3D) and media containing mixed diameter mixed fibers with various basis weights (Figure 3E). [Figure 3E] Figure 3E shows a comparison of media dP increase over the course of the test for media containing thin fine fibers, mixed diameter mixed fibers, or thick fine fiber media (Figure 3D) and media containing mixed diameter mixed fibers with various basis weights (Figure 3E). [Figure 3F] Figure 3F shows a comparison of overall β values ​​across a range of dust particle sizes for media containing solely thin fine fibers, media containing mixed diameter mixed fibers, or media containing solely thick fine fibers (Figure 3F), and media containing mixed diameter mixed fibers with various basis weights (Figure 3G). [Figure 3G] Figure 3G shows a comparison of overall β values ​​across a range of dust particle sizes for media containing solely thin fine fibers, media containing mixed diameter mixed fibers, or media containing solely thick fine fibers (Figure 3F), and media containing mixed diameter mixed fibers with various basis weights (Figure 3G). [Figure 3H] Figure 3H shows the dependence of the mean maximum pore size (top panel) and mean mean flow pore size (bottom panel) during electrospinning for media containing solely thin fibers, mixed diameter fibers, or solely thick fibers. The dotted lines indicate the best polynomial fit to the data, and the corresponding equations are provided on the plot. [Figure 4]Figure 4 shows the increase in basis weight observed with increasing fraction of thick fine fibers contained within a medium containing mixed diameter fibers. Inset: Linear increase in basis weight up to 10% thick fine fiber content. [Figure 5A] Figure 5A shows SEM images at 1,000x magnification for a series of fiber media samples of various compositions (media containing only small diameter fibers, media containing mixed diameter layered fibers with 2-20% thick fine fibers, or media containing only thick fine fibers) as described in Example 5. The letters in each panel indicate the electrospinning sequence described in Table 1A. The letters in the panels of Figure 5A indicate the electrospinning sequence described in Table 1A. [Figure 5B] Figure 5B shows SEM images at 1,000x magnification for a series of fiber-media samples of various compositions (media containing only small diameter fibers, media containing mixed diameter fibers with 2-20% thick fine fibers, or media containing only thick fine fibers) as described in Example 5. The letters in the panels of Figure 5B indicate the electrospinning sequence described in Table 1A. [Figure 5C] FIG. 5C shows a comparison of pore sizes (in micrometers (μm)) measured by capillary flow porometry for mixed diameter fiber media of various compositions and structures (bottom panel, mixed diameter fibers in separate layers vs. top panel, mixed diameter fibers in a single layer). [Figure 5D] FIG. 5D shows the effect of intermediate flow pore size (top panel) and the incorporation of mixed fiber diameter media into thick fine fibers (bottom panel) on the figure of merit (FOM). [Figure 5E] FIG. 5E shows β values ​​versus elapsed time (minutes) for a sample (mixed fiber diameter blended layer (containing 5% thick fine fibers)) prepared and tested as described in Example 5. [Figure 5F] FIG. 5F shows β values ​​versus elapsed time (min) for a sample prepared and tested as described in Example 5 (a mixed fiber diameter mixed layer (containing 5% thick fine fibers) deposited on a support layer of thick fine fibers). [Figure 5G]Figure 5G shows a comparison of the media pressure drop increase over the course of the test with media containing mixed diameter blended fibers as described in Example 5. The bottom panel shows an enlarged view of a portion of the top panel. [Figure 5H] Figure 5H shows a comparison of overall β values ​​for various dust particle sizes with media containing mixed diameter fibers as described in Example 5. The bottom panel shows an enlarged view of a portion of the top panel. [Figure 5I] Figure 5I shows a comparison of the media pressure drop increase over the course of the test with media containing layers of mixed diameter fibers as described in Example 5. The bottom panel shows an enlarged view of a portion of the top panel. [Figure 5J] Figure 5J shows a comparison of overall β values ​​for various dust particle sizes with media containing layers of mixed diameter fibers as described in Example 5. The bottom panel shows an enlarged view of a portion of the top panel. [Figure 5K] FIG. 5K shows the pressure drop of the clean media when the media composition is changed to include mixed fiber diameters, where the fibers are mixed or layered. [Figure 6A] Figure 6A shows an exemplary image of a media sample containing 0.22 g / m2 of thin fibrils supported by 0.43 g / m2 of thick fibrils (0.65 g / m2 total), made as described in Example 6. The top layer of thin fibrils covers an underlying network of thick fibrils. [Figure 6B] FIG. 6B shows the pressure drop during a liquid filtration test for media samples containing various basis weights (0.09 g / m, 0.10 g / m, 0.22 g / m, 0.31 g / m, 0.45 g / m, or 0.56 g / m) of thin fine fibers supported by a fixed amount of thick fine fibers, prepared as described in Example 6. [Figure 6C] FIG. 6C shows the efficiency for particulate contaminants of various diameters for media samples containing various basis weights (0.09 g / m, 0.10 g / m, 0.22 g / m, 0.31 g / m, 0.45 g / m, or 0.56 g / m) of thin fine fibers supported by a fixed amount of thick fine fibers, prepared as described in Example 6. [Figure 7A]7A shows an exemplary image of a layered media sample prepared as described in Example 7 (a base layer of thick fibers, followed by a layer of thin fibers and a layer of mixed thin and thick fibers, with a layer of thick fibers on top (thick / thin / mixed / thick or L / S / mixed / L); the mixed layer was prepared as described in Table 1A, setting I). The top layer of thick fibers covers the layer containing the mix of thin and thick fibers. [Figure 7B] FIG. 7B shows an exemplary image of a cross-section of a layered media sample (L / S / L) prepared as described in Method 6 and Example 6. [Figure 7C] FIG. 7C shows the pressure drop over the liquid filtration test period for a media sample comprising a layer of mixed diameter fibers supported by thick fine fibers prepared and tested as described in Example 7. [Figure 7D] FIG. 7D shows the overall β values ​​for particulate contamination for media samples containing a layer of mixed diameter fibers supported by thick fine fibers as described in Example 7. [Figure 8A] FIG. 8A shows a representative SEM image of a network of mixed thin and thick fibrils deposited on a layer of thick fibrils prepared as described in Example 8. [Figure 8B] FIG. 8B shows the pressure drop over the liquid filtration test period for a media sample comprising a layer of mixed diameter blended fibers supported by thick nanofibers prepared and tested as described in Example 8. [Figure 8C] FIG. 7C shows the overall β values ​​for particulate contamination for media samples containing a layer of mixed diameter fibers supported by thick fine fibers prepared and tested as described in Example 8. [Figure 9A] FIG. 9A shows cross-sectional views of exemplary fine fibers comprising a polymer and a polymer-reactive resinous aldehyde composition, illustrating three-phase and two-phase structures, respectively. [Figure 9B] FIG. 9B shows cross-sectional views of exemplary fine fibers comprising a polymer and a polymer-reactive resinous aldehyde composition, illustrating three-phase and two-phase structures, respectively. [Figure 10A]FIG. 10A shows diagrams of exemplary fine fibers comprising a polymer and a polymer-reactive resinous aldehyde composition, showing three-phase and two-phase structures, respectively. [Figure 10B] FIG. 10B shows diagrams of exemplary fine fibers comprising a polymer and a polymer-reactive resinous aldehyde composition, showing three-phase and two-phase structures, respectively. [Figure 11A] 11A and 11B show the ratio of total fine fiber basis weight to the average maximum pore size of the composite (including the first layer of fine fibers, the second layer of fine fibers, etc.) plotted against the basis weight of the second layer of fine fibers, as further described in Example 10. FIG. 11B shows a subset of the samples in FIG. 11A , allowing for more detailed examination of samples that did not survive the liquid filtration performance test without fine fiber damage, indicated by an "x." The dashed line indicates the slope of the line expected to delineate composites that can withstand the liquid filtration performance test and will not suffer fiber damage during use of the filtration layer from composites that will suffer fiber damage during use of the filtration layer. The circular data points represent samples that survived the liquid filtration performance test without damage. The circular data points located below the dashed line correspond to media samples in which a first layer of thick fine fibers was deposited as described in Methods 4, 5, 6, and 7. [Figure 11B] 11A and 11B show the ratio of total fine fiber basis weight to the average maximum pore size of the composite (including the first layer of fine fibers, the second layer of fine fibers, etc.) plotted against the basis weight of the second layer of fine fibers, as further described in Example 10. FIG. 11B shows a subset of the samples in FIG. 11A , allowing for more detailed examination of samples that did not survive the liquid filtration performance test without fine fiber damage, indicated by an "x." The dashed line indicates the slope of the line expected to delineate composites that can withstand the liquid filtration performance test and will not suffer fiber damage during use of the filtration layer from composites that will suffer fiber damage during use of the filtration layer. The circular data points represent samples that survived the liquid filtration performance test without damage. The circular data points located below the dashed line correspond to media samples in which a first layer of thick fine fibers was deposited as described in Methods 4, 5, 6, and 7. [Figure 12A]12A-12B show initial pressure drop plotted against composite mean maximum pore size (FIG. 12A) or composite intermediate flow pore size (FIG. 12B) for composites including one or more layers of fine fibers and support layers as further described in Example 11. Triangles represent samples that maintained fine fiber structural integrity during testing, while squares represent samples that experienced fine fiber rupture during testing. [Figure 12B] 12A-12B show initial pressure drop plotted against composite mean maximum pore size (FIG. 12A) or composite intermediate flow pore size (FIG. 12B) for composites including one or more layers of fine fibers and support layers as further described in Example 11. Triangles represent samples that maintained fine fiber structural integrity during testing, while squares represent samples that experienced fine fiber rupture during testing. [Figure 13A] Figure 13A shows a representative SEM image of a network of layered 0.25 μm and 1.4 μm fibers deposited on a layer of thick fine fibers, prepared as described in Example 12A (i.e., the "thick" fine fibers have a fiber diameter 5.6 times the average fiber diameter of the "thin" fine fibers). [Figure 13B] FIG. 13B shows a representative SEM image of a mixed 0.25 μm and 1.4 μm fiber network deposited on a thick fine fiber layer, prepared as described in Example 12A. [Figure 13C] FIG. 13C shows a plot comparing pore sizes for mixed diameter fine fiber media containing mixed (circles) and layered (squares) 0.25 μm and 1.4 μm fibers, made by pulse spinning as further described in Example 12A. [Figure 13D] Figure 13D shows the pressure drop in a mixed diameter fine fiber media containing layered 0.25 μm and 1.4 μm fibers, prepared by pulse spinning as further described in Example 12 A. In Figures 13D-13G, the bottom panels show enlarged views of the lower left portion of the plots in the top panels. [Figure 13E]Figure 13E shows the pressure drop in a mixed diameter fine fiber media containing mixed 0.25 μm and 1.4 μm fibers, produced by pulse spinning as further described in Example 12 A. In Figures 13D-13G, the bottom panels show enlarged views of the lower left portion of the plots in the top panels. [Figure 13F] Figure 13F shows the efficiency (overall β) for mixed diameter fine fiber media containing layered 0.25 μm and 1.4 μm fibers, produced by pulse spinning as further described in Example 12 A. In Figures 13D-13G, the bottom panels show enlarged views of the lower left portions of the plots in the top panels. [Figure 13G] Figure 13G shows the efficiency (overall β) for mixed diameter fine fiber media containing mixed 0.25 μm and 1.4 μm fibers, produced by pulse spinning as further described in Example 12 A. In Figures 13D-G, the bottom panels show enlarged views of the lower left portions of the plots in the top panels. [Figure 13H] FIG. 13H shows a plot comparing pore sizes for mixed diameter fine fiber media containing mixed (circles) and layered (squares) 0.25 μm and 1.4 μm fibers, made by cospinning as further described in Example 12B. [Figure 13I] Figure 13I shows the pressure drop in a mixed diameter fine fiber media containing mixed 0.25 μm and 1.4 μm fibers, made by cospinning as further described in Example 12B. In Figures 13I-13J, the bottom panels show enlarged views of the lower left portions of the plots in the top panels. [Figure 13J] Figure 13J shows the efficiency (overall β) for mixed diameter fine fiber media containing layered 0.25 μm and 1.4 μm fibers, made by cospinning as further described in Example 12B. In Figures 13I-13J, the bottom panels show enlarged views of the lower left portions of the plots in the top panels. [Figure 13K] FIG. 13K shows a plot comparing pore sizes for mixed diameter fine fiber media containing 0.25 μm and 1.4 μm fibers in an L / S / mixed / L configuration, as further described in Example 12C. [Figure 13L]Figure 13L shows the pressure drop in a mixed diameter fine fiber media containing mixed 0.25 μm and 1.4 μm fibers, made by cospinning as further described in Example 12C. In Figures 13L-13M, the bottom panels show enlarged views of the lower left portion of the plots in the top panels. [Figure 13M] Figure 13M shows the efficiency (overall β) for mixed diameter fine fiber media containing layered 0.25 μm and 1.4 μm fibers, made by cospinning as further described in Example 12C. In Figures 13L-13M, the bottom panels show enlarged views of the lower left portions of the plots in the top panels. [Figure 14A] Figure 14A shows a representative SEM image of a network of layered 0.5 μm and 1.4 μm fibers deposited on a layer of thick fine fibers, prepared as described in Example 13A (i.e., the "thick" fine fibers have a fiber diameter 2.8 times the average fiber diameter of the "thin" fine fibers). [Figure 14B] FIG. 14B shows a representative SEM image of a mixed 0.5 μm and 1.4 μm fiber network deposited on a thick fine fiber layer, prepared as described in Example 13A. [Figure 14C] FIG. 14C shows a plot comparing pore sizes for mixed diameter fine fiber media containing mixed (circles) and layered (squares) 0.5 μm and 1.4 μm fibers, made by pulse spinning as further described in Example 13A. [Figure 14D] FIG. 14D shows a plot comparing the figure of merit (FOM) for mixed diameter fine fiber media containing mixed (circles) and layered (squares) 0.5 μm and 1.4 μm fibers, produced by pulse spinning as further described in Example 13A. [Figure 14E] Figure 14E shows the pressure drop in a mixed diameter fine fiber media containing layered 0.5 μm and 1.4 μm fibers, prepared by pulse spinning as further described in Example 13 A. In Figures 14E-14H, the bottom panels show enlarged views of the lower left portions of the plots in the top panels. [Figure 14F]Figure 14F shows the pressure drop in a mixed diameter fine fiber media containing mixed 0.5 μm and 1.4 μm fibers, made by pulse spinning as further described in Example 13 A. In Figures 14E-14H, the bottom panels show enlarged views of the lower left portions of the plots in the top panels. [Figure 14G] Figure 14G shows the efficiency (overall β) for mixed diameter fine fiber media containing layered 0.5 μm and 1.4 μm fibers, produced by pulse spinning as further described in Example 13 A. In Figures 14E-H, the bottom panels show enlarged views of the lower left portions of the plots in the top panels. [Figure 14H] Figure 14H shows the efficiency (overall β) for mixed diameter fine fiber media containing mixed 0.25 μm and 1.4 μm fibers, produced by pulse spinning as further described in Example 13 A. In Figures 14E-H, the bottom panels show enlarged views of the lower left portions of the plots in the top panels. [Figure 14I] FIG. 14I shows a comparison of efficiency (% Penetration, left axis) and figure of merit (FOM, right axis) for filter media containing mixed 0.5 μm and 1.4 μm fibers made by co-spinning as further described in Example 13B. [Figure 15A] FIG. 15A shows a cross plot of the % improvement in initial dP and β values ​​for 3 um particles for all mixed diameter fiber media structures (squares) described in Example 14 compared to glass fiber-containing media with β=1000 for <4 um particles (circles at origin). [Figure 15B] FIG. 15B shows a plot comparing the initial dP in various mixed fiber media and glass fiber-containing media (circles) across contaminant diameters with a β rating of 1000, as further described in Example 14. [Figure 16A] FIG. 16A shows an exemplary cross-sectional view of a fine fiber layer on a support layer. [Figure 16B] 16B-16D show exemplary diagrams of how the thickness of the fine fiber layer is measured, as further described in the Examples. [Figure 16C]16B-16D show exemplary diagrams of how the thickness of the fine fiber layer is measured, as further described in the Examples. [Figure 16D] 16B-16D show exemplary diagrams of how the thickness of the fine fiber layer is measured, as further described in the Examples. DETAILED DESCRIPTION OF THE INVENTION

[0045] The present disclosure describes high-performance filter media (e.g., including high efficiency and low pressure drop). In some embodiments, the present disclosure describes filter media that achieve the efficiency of filter media containing fine glass fibers without the inclusion of fine glass fibers. The filter media includes a support layer and a fine fiber layer. The fine fiber layer includes at least one layer of fine fibers, but may optionally include multiple layers of fine fibers. The fine fibers included in the filter media have mixed diameters such that the fine fiber layer includes "thick" fine fibers having a fiber diameter at least three times the average fiber diameter of the "thin" fine fibers. The "thick" fine fibers have an average diameter of at least 1 μm or greater than 1 μm. In some embodiments, the filter media is substantially free of glass or does not include glass.

[0046] High-efficiency filter media typically contain fine glass fibers. The glass fibers provide pore size control and, in combination with other fibers in the media, provide the media with substantial flow rates, high capacity, substantial efficiency, and high wet strength. However, when used in fuel or hydraulic filters, the glass fibers can shed from the media, causing wear in the engine.

[0047] However, replacing fine glass fibers with other fine fibers has proven difficult, particularly since including enough non-glass fine fibers to achieve the same efficiency as media with fine glass fibers typically results in a thick or dense fine fiber layer such that the media has low permeability, resulting in increased pressure drop to levels associated with shorter filter life and higher energy use.

[0048] Furthermore, when thinner or less dense fine fiber layers are used, desirable efficiency may be temporarily achieved, and permeability may be improved to achieve acceptable pressure drop values; however, over the life of the filter, the pressure drop increases and the efficiency of such fine fiber layers typically collapses. This decline in efficiency is attributed to "rupture" of the fiber layer and is reflected by a loss of β. (See Figures 1A and 1F.) Additionally, damage to the nanofiber fiber layer can be observed when analyzed using scanning electron microscopy (SEM) after the efficiency collapse. (See Figure 1B.)

[0049] Without wishing to be bound by theory, it is believed that the efficiency collapse seen when thinner or less dense fine fibers are used is the result of variations in the underlying support layer which result in variations in the pore size that must be spanned by the fine fibers. In locations where the pore size of the underlying support layer is larger and the fine fiber bridging is too great, fine fiber breakage occurs during use, resulting in a loss of efficiency.

[0050] Although more uniform support layers exist, the cost of such layers prohibits their use in filter media. Furthermore, more uniform layers do not necessarily exhibit the robustness required to manufacture filter media with web handling capabilities. In contrast, spunbond support layers, for example, exhibit large variations in pore size, but are inexpensive and robust layers, making them particularly suitable for use as support layers in filter media.

[0051] As noted above, the fine fibers included in the filter media of the present disclosure have mixed diameters, such that the fine fiber layer includes "thick" fine fibers having a fiber diameter at least three times the average fiber diameter of the "thin" fine fibers. In some embodiments, the "thick" fine fibers have a fiber diameter up to six times the average fiber diameter of the "thin" fine fibers. While not wishing to be bound by theory, it is believed that the larger diameter fine fibers provide support to the smaller diameter fine fibers, allowing them to span the pores of the underlying support layer and resist fiber "burst," even when the media is exposed to higher pressures. Furthermore, the smaller diameter fine fibers allow for smaller pore morphologies, allowing for the achievement of higher efficiency values. See, for example, Wang et al., Physical Review Materials, 2020, 4:083803.

[0052] Unexpectedly, containing thick fine fibers with an average fiber diameter at least three times the average fiber diameter of the thin fine fibers provides the best combination of efficiency and pressure drop.Though thick fine fibers with an average fiber diameter of about 2.8 times the average fiber diameter of the thin fine fibers provide better fiber viability than a layer of fine fibers that uses thin fine fibers alone, the filter medium does not exhibit the same level of performance as observed with mixed diameter fine fibers, where the thick fine fibers have an average fiber diameter at least three times the average fiber diameter of the thin fine fibers.(See Examples 13 and 14.)

[0053] 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, the thick fibrils have an average fiber diameter at least three times the average fiber diameter of the thin fibrils, but one or both of the thick fibrils and the thin fibrils may comprise a distribution of fibers of various diameters that provide the average diameter. When the thick fibrils and the thin fibrils comprise, for example, a distribution of diameters, the diameter of the thick fibrils with the smallest diameter may be at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the diameter of the thin fibrils with the largest diameter. In 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. In an exemplary embodiment, the diameter of the smallest diameter thick fibrils may be in the range of 0.2 μm to 2 μm greater than the diameter of the largest diameter thin fibrils.

[0054] In some embodiments, as further described herein, the fine fiber layer comprises a single (or first) fine fiber layer that includes both thick fine fibers having a fiber diameter at least three times the average fiber diameter of the thin fine fibers (see FIG. 1G). In some embodiments, the fine fiber layer can include multiple layers (e.g., a first fine fiber layer, a second fine fiber layer, etc.).

[0055] In some embodiments, the overall thickness of the fine fiber layer is at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm. Without wishing to be bound by theory, it is believed that a fine fiber layer thickness greater than 50 μm results in a medium with an undesirably high pressure drop. In some embodiments, where it is desired to minimize pressure drop, a thinner fine fiber layer thickness (e.g., at most 5 μm thick, at most 10 μm thick, or at most 30 μm thick) may be preferred.

[0056] In some embodiments, the total thickness of the fine fiber layer can be measured using scanning electron microscopy (SEM). For example, a sample including at least the 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 portion in the SEM image and enable 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 portion 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.

[0057] In one exemplary embodiment, the first layer of fine fibers may comprise primarily thick fine fibers, and the second layer of fine fibers may comprise primarily thin fine fibers. For example, the first layer of fine fibers may comprise at most 10% or at most 20% thick fine fibers (i.e., fine fibers having a fiber diameter at least three times the average fiber diameter of the smaller diameter fibers). In some embodiments, including when the first layer of fine fibers is composed of or comprises primarily thick fine fibers, the second layer of fine fibers may comprise at most 10% or at most 20% larger diameter fine fibers (i.e., fine fibers having a fiber diameter at least three times the average fiber diameter of the thinner fibers).

[0058] Without wishing to be bound by theory, by replacing a small portion of the small diameter fibrils in the fibril layer, which constitutes a majority of smaller diameter nanoparticles, with larger diameter nanofibers, the nonwoven structure can be opened up and the permeability and depth loading potential of the second layer of fibrils increased while retaining the efficiency due to the network structure of the smaller diameter nanofibers.

[0059] In some embodiments, as discussed further herein, thick and thin fine fibers may be mixed within a single fine fiber layer. Such mixing reduces the solidity of the fine fiber layer compared to a fine fiber layer containing only thin fine fibers. Without wishing to be bound by theory, it is believed that this reduction in solidity occurs because the thick fine fibers act as spacers, allowing more air movement between the fibers.

[0060] The filter media described herein provide low initial dP values ​​and do not exhibit efficiency or beta decay throughout the expected life of the filter. (See Example 1 and Figure 1C.) Additionally, when analyzed using SEM, damage to the fine fiber layer is minimized when the media layer is exposed to pressure (including, for example, up to 20 psi). (See Figure 1D.)

[0061] support layer The filter media described herein include a support layer (also referred to herein as a substrate). The support layer can include or be formed from any suitable porous material.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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 The basis weight of the support layer can be measured using a TAPPI T410 om-08.

[0066] 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%. The solidity of the support layer can be calculated using the equation c=BW / ρZ, where BW is the basis weight measured using TAPPI T410 om-08, ρ is the fiber density, and Z is the caliper of the media measured by TAPPI T411 om-15. When measuring the caliper of the media, a foot pressure of 1.5 psi can be used.

[0067] In some embodiments, the support layer has an average 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 average 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 average intermediate flow pore size in the range of 10 μm to 25 μm. In some embodiments, the average intermediate flow pore size is preferably determined using capillary flow porometry.

[0068] In some embodiments, the support layer has an average 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 exemplary embodiments, the support layer has an average maximum pore size of at most 90 μm. In some embodiments, the average maximum pore size is preferably determined using capillary flow porometry.

[0069] In some embodiments, the support layer has an average minimum pore size of at least 5 μm, at least 10 μm, at least 15 μm, at least 20 μm, at least 25 μm, at least 30 μm, at least 35 μm, at least 40 μm, or at least 50 μm. In exemplary embodiments, the support layer has an average minimum pore size of at least 20 μm. In some embodiments, the average minimum pore size is preferably determined using capillary flow porometry.

[0070] 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 average mean 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.

[0071] However, in some embodiments, as further noted above, at least one aspect of consistency or uniformity (e.g., pore size consistency) may be sacrificed for the robustness required for the manufacture of the filter media (including web processing performance). For example, spunbond support layers exhibit large pore size variations, but are inexpensive and robust layers, making them particularly suitable for use as support layers in filter media.

[0072] Without wishing to be bound by theory, it is believed that the interplay between the fiber diameter of the fine fiber layer (especially the first layer of fine fibers), the thickness of the fine fiber layer, 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 2Simply using a support layer with a maximum pore size greater than 90 μm will 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 fine fiber diameter is below a certain size, and / or if the fine fibers are thin, the 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 0.5 μm) were used in a first fine fiber layer on a support layer with an average maximum pore size of 88 μm, it was found that increasing the basis weight of the fine fiber layer required unsustainable high pressures to move fluid through the medium; in contrast, decreasing the basis weight of the thin fine fiber layer caused the layer to lose its structure during filtration. Increasing the fiber diameter of at least one of the fibers in the first fine fiber layer deposited on a support layer having an average maximum pore size of 88 μm (e.g., to an average diameter of at least 0.6 μm, more preferably at least 0.9 μm, and even more preferably 1 μm) reduced the efficiency of the media, but the increased fiber diameter also reduced the pressure drop and resulted in a structurally stable media that did not structurally fail during use.

[0073] As further described in Example 10, a plot of the ratio of overall fine fiber basis weight to overall composite average maximum pore size is plotted against the basis weight of the second layer of fine fibers, allowing for the identification of characteristics (fine fiber basis weight and overall composite average maximum pore size) that correlate with fine fiber layers that will experience damage during FHAST bench testing. As shown in Figure 11, composites that can withstand liquid filtration performance testing and will not suffer fiber damage during use of the filtration layer can be delineated from composites that will suffer fiber damage during use of the filtration layer.

[0074] 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.

[0075] In some embodiments, the support layer may preferably comprise polymeric fibers, hi some embodiments, the polymeric fibers may comprise nylon fibers or polyester fibers.

[0076] In some embodiments, the support layer may preferably comprise spunbond fibers.

[0077] In one exemplary embodiment, the support layer can be a nylon scrim.

[0078] In an exemplary embodiment, the support layer comprises CEREX 23200 (Cerex Advanced Fabrics, Inc., Cantonment, FL). CEREX 23200 comprises nylon 6,6, has a thickness of 8.4 mil (0.21 mm), and a weight of 67.8 g / m 2 The pore size of CEREX 23200 is shown in Table 2C.

[0079] Fine fiber layer The filter medium described herein comprises a fine fiber layer. The fine fiber layer always comprises a first layer of fine fibers (also referred to as a first fine fiber layer) deposited on a support layer. As further discussed herein, the fine fiber layer may optionally comprise one or more additional layers of fine fibers. For example, the fine fiber layer may comprise a second layer of fine fibers (also referred to as a second fine fiber layer) deposited on the first layer of fine fibers.

[0080] In some embodiments, the 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.

[0081] In some embodiments, the fine fiber layer can have a thickness of at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm.

[0082] In some embodiments, the total thickness of the fine fiber layer can be measured using scanning electron microscopy (SEM). For example, a sample including at least the 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 can be useful to cross-section the sample while orienting the sample so that the support layer is cut before the fine fiber layer. It can be even more useful to cross-section the sample while immersed in liquid nitrogen. An exemplary magnification that can be used is 1000x. It can be useful to use software that aids in determining the thickness of the sample by allowing for outlining and re-shading of fine fiber portions in the SEM image. The re-shaded 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 from five separate images of the same sample.

[0083] First layer of fine fibers In some embodiments, the first layer of fine fibers comprises "thick" fine fibers having an average diameter at least three times the average fiber diameter of the "thin" fine fibers, i.e., the first layer of fine fibers may comprise fibers of mixed diameters.

[0084] Additionally or alternatively, the thin fine fibers may be present in a second layer of fine fibers. When the thin fine fibers are present in the second layer of fine fibers but not in the first layer of fine fibers, the first layer of fine fibers may contain only "thick" fine fibers having an average diameter at least three times the average fiber diameter of the smallest average fiber diameter of the second layer of fine fibers. In such embodiments, the thick fine fibers of the first layer of fine fibers 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 fibers of the second layer of fine fibers. As noted above, the thick fine fibers have an average fiber diameter at least three times the average fiber diameter of the thin fine fibers, and one or both of the thick and thin fine fibers may contain a distribution of fibers of various diameters that provide the average diameter. If the thick fibrils of the first fine fiber layer and the thin fibrils of the second fine fiber layer comprise, for example, a distribution of diameters, the diameter of the smallest diameter thick fibrils may be at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm greater than the diameter of the largest diameter thin fibrils. In some embodiments, the thick fibrils of the first fine fiber layer may have diameters at most 1 μm, at most 2 μm, or at most 3 μm greater than the diameter of the thin fibrils.

[0085] In some embodiments, the "thick" fibrils of the first layer of fibrils preferably have an average diameter of at least 1 μm or greater than 1 μm. The "thick" fibrils of the first layer of fibrils 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 first layer of fibrils includes thick fibrils deposited on a support layer, as shown in FIG. 1E.

[0086] In embodiments in which the first fine fiber layer comprises "thick" 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, 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 average fiber diameter of the thin fine fibers of the first fine fiber layer may be at least 0.2 μm. For example, the average fiber diameter of the thin fine fibers may be in the range of 0.2 μm to 0.6 μm, in the range of 0.3 μm to 0.5 μm, or in the range of 0.2 μm to 0.3 μm.

[0087] In such embodiments, the thick fine fibers of the first fine fiber layer 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 fine fibers of the first fine fiber layer. As noted above, the thick fine fibers have an average fiber diameter at least three times the average fiber diameter of the thin fine fibers, and one or both of the thick fine fibers and the thin fine fibers may comprise a distribution of fibers of various diameters that provide the average diameter. If the thick fine fibers of the first fine fiber layer and the thin fine fibers of the first fine fiber layer comprise, for example, a distribution of diameters, the diameter of the thick fine fibers with the smallest diameter may be at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the diameter of the thin fine fibers with the largest diameter. In some such embodiments, the thick fine fibers and the thin fine fibers may form a bimodal distribution. In some embodiments, the thick fine fibers of the first fine fiber layer may have a diameter at most 1 μm, at most 2 μm, or at most 3 μm larger than the diameter of the thin fine fibers of the first fine fiber layer.

[0088] Exemplary combinations of "thick" and "thin" fibril diameters include, for example, 1 μm and 0.25 μm diameter fibers (see Examples 1-11); or 1.4 μm and 0.25 μm diameter fibers (see Example 12). Example 13 further discloses 1.4 μm and 0.5 μm diameter fibers, although the thick fibrils (1.4 μm) do not have an average diameter at least three times the average fiber diameter of the thin fibrils (0.5 μm).

[0089] Without wishing to be bound by theory, it is believed that the inclusion of a layer of fine fibers containing thick fine fibers allows for the use of a more "open" support layer than filter media that do not include a layer containing thick fine fibers. The use of a more "open" support layer provides a lower pressure drop than support layers with smaller pores or higher basis weights because materials passing through the filter encounter fewer materials to obstruct flow.

[0090] First layer of thin fibers - thick thin fibers In some embodiments, the first layer of fine fibers comprises predominantly (e.g., greater than 95%) thick fine fibers or no thin fine fibers. In such embodiments, a second layer of fine fibers comprising thin fine fibers is deposited on the first layer of fibers, as described below.

[0091] In such embodiments, the thick fine fibers of the first fine fiber layer 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 fine fibers of the second fine fiber layer. As noted above, the thick fine fibers have an average fiber diameter at least three times the average fiber diameter of the thin fine fibers, and one or both of the thick fine fibers and the thin fine fibers may comprise a distribution of fibers of various diameters that provide the average diameter. If the thick fine fibers of the first fine fiber layer and the thin fine fibers of the second fine fiber layer comprise, for example, a distribution of diameters, the diameter of the thick fine fibers with the smallest diameter may be at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the diameter of the thin fine fibers with the largest diameter. In some such embodiments, the thick fine fibers and the thin fine fibers may form a bimodal distribution. In some embodiments, the thick fine fibers of the first fine fiber layer may have an average diameter at most 1 μm, at most 2 μm, or at most 3 μm larger than the average diameter of the thin fine fibers of the second fine fiber layer.

[0092] In some embodiments, including when the filter media includes a second layer of fine fibers, the first layer of fine fibers has a 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 / m2 , 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 first layer of fine fibers 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 some embodiments, the first layer of fine fibers has a basis weight of at least 0.1 g / m 2 and a maximum of 20 g / m 2 In another exemplary embodiment, the first layer of fine fibers has a basis weight of at least 0.1 g / m 2 and a maximum of 1 g / m 2 In a further exemplary embodiment, the first layer of fine fibers has a basis weight of 0.25 g / m 2 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 equation: 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 fibers according to the following equation: Mass of fine fibers = (% w / v of polymer in solution) x (pump speed) x (spinning time).

[0093] In some embodiments, including when the filter media includes a second layer of fine fibers, the first layer of fine fibers has an average intermediate flow pore size of at least 5 μm, at least 10 μm, at least 15 μm, or at least 20 μm. In some embodiments, the first layer of fine fibers has an average 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, or at most 35 μm. In exemplary embodiments, the first layer of fine fibers has an average intermediate flow pore size in the range of 10 μm to 25 μm. In some embodiments, the average intermediate flow pore size is preferably determined using capillary flow porometry.

[0094] In some embodiments, including when the filter media includes a second layer of fine fibers, the first layer of fine fibers has an average maximum pore size of 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 some embodiments, the average maximum pore size of the first layer of fine fibers is preferably determined using capillary flow porometry.

[0095] In some embodiments, including when the filter media includes a second layer of fine fibers, the first layer of fine fibers has a thickness of at least the average diameter of the large fibers in the first layer of fine fibers. In some embodiments, the first layer of fine fibers has a thickness of at least 0.7 μm, at least 1 μm, at least 2 μm, or at least 5 μm.

[0096] In some embodiments, the first layer of fine fibers has a thickness that is the thickness of several fibers having the average diameter of the large fibers in the first layer of fine fibers. For example, the first layer of fine fibers can have a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm. In some embodiments, the first layer of fine fibers has a thickness greater than 1 μm.

[0097] In some embodiments, the first layer of fibrils has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm.

[0098] In some embodiments, the total thickness of the fine fiber layer can be measured using scanning electron microscopy (SEM). For example, a sample including at least the 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 can be useful to cross-section the sample while orienting the sample so that the support layer is cut before the fine fiber layer. It can be even more useful to cross-section the sample while immersed in liquid nitrogen. An exemplary magnification that can be used is 1000x. It can be useful to use software that aids in determining the thickness of the sample by allowing for outlining and re-shading of fine fiber portions in the SEM image. The re-shaded 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 from five separate images of the same sample.

[0099] In some embodiments, including when the filter media includes a second layer of fine fibers, the first layer of fine fibers may have a lower solidity than the second layer of fine fibers. That is, the first layer of fine fibers may preferably be more open than the second layer of fine fibers. In some embodiments, the first layer of fine fibers has a solidity of at least 0.1%, at least 0.5%, at least 1%, at least 5%, at least 10%, at least 20%, at least 25%, at least 30%, or at least 40%. In some embodiments, the first layer of fine fibers has a solidity of at most 10%, at most 20%, at most 25%, at most 30%, at most 40%, or at most 50%. In exemplary embodiments, the first layer of fine fibers has a solidity in the range of 0.1% to 40%. In another exemplary embodiment, the first layer of fine fibers has a solidity in the range of 0.1% to 20%. The solidity of the fine fiber layer (c) is calculated using the dimensionless fiber drag parameter, F, using the following equation: * 1.0 It can be calculated from: F * 1.0 =4.3548e8.8822c As further described in the Examples, F * 1.0 can be calculated from the modified Kirsch-Fuchs equation:

[0100] First Layer of Fine Fibers—Mixed Diameter Fine Fibers In some embodiments, the first layer of fine fibers comprises thick fine fibers and thin fine fibers, the thick fine fibers having an average diameter at least three times the average fiber diameter of the thin fine fibers. In such embodiments, a second layer of fine fibers may or may not be deposited on the first layer of fibers, as described below.

[0101] In some embodiments, the thicker fine fibers of the first fine fiber layer can 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 thinner fine fibers of the first fine fiber layer. As noted above, the thicker fine fibers have an average fiber diameter at least three times the average fiber diameter of the thinner fine fibers, and one or both of the thicker fine fibers and the thinner fine fibers can comprise a distribution of fibers of various diameters that provide the average diameter. When the thicker or thinner fine fibers comprise a distribution of diameters, the diameter of the smallest diameter thicker fine fiber can 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 fine fiber. In some embodiments, the thicker fine fibers can have a diameter at most 1 μm, at most 2 μm, or at most 3 μm larger than the diameter of the thinner fine fibers.

[0102] When the first layer of fine fibers comprises thin and thick fine fibers, the layer can comprise any suitable mixture of fibers of mixed diameters. Exemplary layered fiber structures that can be used for the first layer of fine fibers include one or more of Set A5, Set B, Set D5, Set E, Set I5, or Set J in Tables 1A-1C. Exemplary mixed fiber structures that can be used for the second layer of fine fibers include one or more of Set A6, Set D, Set D6, Set I, or Set L in Tables 1A-1C.

[0103] When the first layer of fibrils comprises thin fibrils and thick fibrils, the mixed diameter fibers may be mixed (as a result of being formed simultaneously) (see FIG. 1I), or may be layered (as a result of being applied alternately to the substrate) (see FIGS. 1J and 1L), or may be both (see FIG. 1M). When the mixed diameter fibers are layered (as a result of being applied alternately to the substrate), a single layer of fibrils may comprise sublayers of thick and thin fibrils.

[0104] In some embodiments, the first layer of fine fibers can include at least 0.5% thick fine fibers, at least 1% thick fine fibers, at least 2% thick fine fibers, at least 5% thick fine fibers, at least 7% thick fine fibers, at least 10% thick fine fibers, at least 12% thick fine fibers, at least 14% thick fine fibers, at least 16% thick fine fibers, at least 20% thick fine fibers, at least 50% thick fine fibers, at least 60% thick fine fibers, at least 70% thick fine fibers, or at least 80% thick fine fibers. In some embodiments, the first layer of fine fibers can include up to 1% thick fine fibers, up to 2% thick fine fibers, up to 5% thick fine fibers, up to 7% thick fine fibers, up to 10% thick fine fibers, up to 12% thick fine fibers, up to 14% thick fine fibers, up to 16% thick fine fibers, up to 20% thick fine fibers, up to 50% thick fine fibers, up to 60% thick fine fibers, up to 70% thick fine fibers, up to 80% thick fine fibers, or up to 90% thick fine fibers. Some exemplary mixtures are shown in Tables 1A-1C. For example, the first layer of fine fibers can include a percentage of thick fine fibers from one or more of Sets A5, A6, B, D, D5, D6, E, I, I5, I6, J, or L in Tables 1A-1C. Additional exemplary ranges for the coarse fine fibers in the first layer of fine fibers include 10% to 90% coarse fine fibers, 20% to 80% coarse fine fibers, or 30% to 70% coarse fine fibers.

[0105] In some embodiments, the percentage of thick fibrils can be estimated from the diameters of the thin and thick fibrils, the % solids in the precursor spinning solution, the syringe pump feed rate, and the electrospinning time.

[0106] In some embodiments, the percentage of thick fine fibers can be determined based on spinning time using the equation provided in the Calculating Fiber Percentage section of the Examples.

[0107] In some embodiments, the proportion of thick fine fibers can be determined by nano-computed tomography (nano-CT). For example, a filter medium sample can be embedded in resin and scanned as if cut along the Z-axis. Useful images can be obtained by using a synchrotron-quality nanoscale 3D X-ray imaging device, such as Xradia 810 Ultra (Zeiss, Oberkochen, Germany). To use the digital structure to determine the proportion of fibers with a specific diameter, it can be useful to then stitch the images together to form a 3D digital structure. The proportion of thin / thick fine fibers can be calculated by the ratio of the number of thin / thick fine fibers to the number of all fibers (both thin and thick fibers) in the digital structure.

[0108] In some embodiments, the percentage of thick fine fibers can be determined using microscopic observation. For example, a sample image can be obtained through a SEM at an appropriate magnification (e.g., 500x, 1000x, or 2500x). The presence of one or more fiber populations can be determined by counting all fibers within the image, followed by classification into thin and thick fine fibers based on group diameters within a 25% variation. Fiber diameters can be measured and / or classified using image processing software such as ImageJ. The percentage of thin / thick fine fibers can be calculated by the ratio of the number of thin / thick fine fibers to the number of total fibers (both thin and thick fibers) within the image.

[0109] In some embodiments, the first layer of fine fibers has an average intermediate flow pore size of at least 0.1 μm, at least 0.5 μm, at least 1 μm, at least 5 μm, at least 10 μm, at least 15 μm, or at least 20 μm. In some embodiments, the first layer of fine fibers has an average intermediate flow pore size of at most 0.5 μm, at most 1 μm, 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 exemplary embodiments, the first layer of fine fibers has an average intermediate flow pore size in the range of 10 μm to 25 μm. In some embodiments, the average intermediate flow pore size is preferably determined using capillary flow porometry.

[0110] When fibers of different diameters are layered, the effective pore size of the first layer of fine fibers is defined by the layer containing the smallest fine fibers.

[0111] In some embodiments, the first layer of fine fibers has a 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 first layer of fine fibers 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 some embodiments, the first layer of fine fibers has a basis weight of at least 0.1 g / m 2 and a maximum of 20 g / m 2 In another exemplary embodiment, the first layer of fine fibers has a basis weight of at least 0.1 g / m 2 and a maximum of 1 g / m 2 In a further exemplary embodiment, the first layer of fine fibers has a basis weight of 0.43 g / m 2 The basis weight of the first layer of fine fibers is 1 / (1 / 2). When fibers of different diameters are layered, the basis weight of the first layer of fine fibers is additive. The basis weight of the first layer of fine fibers can be determined from the mass of the first layer of fine fibers and the area of ​​the scrim according to the following equation: Basis Weight of First Layer of Fine Fibers = (Mass of First Layer of Fine Fibers) / (Area of ​​Scrim). The mass of the fine fibers can be calculated from the polymer and spinning conditions used to produce the fibers according to the following equation: Mass of Fine Fibers = (% w / v of polymer in solution) x (Pump Speed) x (Spinning Time).

[0112] In some embodiments, the first layer of fine fibers has a solidity of at least 0.5%, at least 1%, at least 5%, at least 10%, at least 20%, at least 25%, at least 30%, or at least 40%. In some embodiments, the first layer of fine fibers has a solidity of at most 10%, at most 20%, at most 25%, at most 30%, at most 40%, or at most 50%. In exemplary embodiments, the first layer of fine fibers has a solidity in the range of 0.5% to 30%. The solidity (c) of the first layer of fine fibers is calculated using the dimensionless fiber drag parameter, F, using the following equation: * 1.0 It can be calculated from: F * 1.0 =4.3548e 8.8822c As further described in the Examples, F * 1.0 can be calculated from the modified Kirsch-Fuchs equation:

[0113] In some embodiments, the first layer of fine fibers has a thickness of at least the average diameter of the average fine fibers of the first layer of fine fibers, hi some embodiments, the first layer of fine fibers has a thickness of 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.

[0114] In some embodiments, the first layer of fine fibers has a thickness that is the thickness of several fibers having the average diameter of the first layer of fine fibers. For example, the first layer of fine fibers can have a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm.

[0115] In some embodiments, the first layer of fibrils has a thickness of at most 1 μm, at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm.

[0116] In some embodiments, the total thickness of the fine fiber layer can be measured using scanning electron microscopy (SEM). For example, a sample including at least the 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 can be useful to cross-section the sample while orienting the sample so that the support layer is cut before the fine fiber layer. It can be even more useful to cross-section the sample while immersed in liquid nitrogen. An exemplary magnification that can be used is 1000x. It can be useful to use software that aids in determining the thickness of the sample by allowing for outlining and re-shading of fine fiber portions in the SEM image. The re-shaded 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 from five separate images of the same sample.

[0117] Second layer of fine fibers The filter media described herein may include a second layer of fine fibers deposited on the first layer of fine fibers. In some embodiments, the filter media may additionally include a third layer of fine fibers, a fourth layer of fine fibers, or the like, as further described herein.

[0118] As noted above, in some embodiments, the first layer of fine fibers comprises fine fibers having an average diameter at least three times the average fiber diameter of the fibers in the second layer of fine fibers. In some embodiments, the first layer of fibers comprises fine fibers having an average diameter at least three times the average fiber diameter of the smallest fibers in the second layer of fine fibers.

[0119] In some embodiments, the smallest fibers in the second layer of fine fibers 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 average fiber diameter of the smallest fibers in the second layer of fine fibers has an average diameter of at least 0.2 μm. For example, the average fiber diameter of the smallest fibers in the second layer of fine fibers can be in the range of 0.2 μm to 0.6 μm, the range of 0.3 μm to 0.5 μm, or the range of 0.2 μm to 0.3 μm.

[0120] In some embodiments, the second layer of fine fibers may comprise a single layer comprising fibers having an average diameter that is at most one-third the average fiber diameter of the fibers in the first layer of fine fibers (see, e.g., Figure 1H).

[0121] In some embodiments, the second layer of fibrils may comprise fibrils of mixed diameters, for example, the second layer of fibrils may comprise fibrils of two different diameters (i.e., thin fibrils and thick fibrils) (see Figures 1I and 1J), where the thick fibrils have an average diameter at least three times that of the thin fibrils.

[0122] In some embodiments, the fine fibers of the second fine fiber layer 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 average fiber diameter of the fine fibers of the second fine fiber layer is at least 0.2 μm. For example, the average fiber diameter of the fine fibers of the second fine fiber layer can be in the range of 0.2 μm to 0.6 μm, in the range of 0.3 μm to 0.5 μm, or in the range of 0.2 μm to 0.3 μm.

[0123] In some embodiments, the thick fibrils of the second layer of fibrils have an average fiber diameter of at least 1 μm or greater than 1 μm, hi some embodiments, the thick fibrils of the second layer of fibrils have an average fiber diameter of at most 1 μm, 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.

[0124] Exemplary combinations of "thick" and "thin" fibril diameters include, for example, 1 μm and 0.25 μm diameter fibers (see Examples 1-11); and 1.4 μm and 0.25 μm diameter fibers (see Example 12).

[0125] If the second layer of fibrils comprises thin fibrils and thick fibrils, the mixed diameter fibers may be mixed (as a result of being formed simultaneously) (see FIG. 1I), or may be layered (as a result of being applied alternately to the substrate) (see FIGS. 1J and 1L), or may be both (see FIG. 1M). If the mixed diameter fibers are layered (as a result of being applied alternately to the substrate), a single layer of fibrils may comprise sublayers of thick and thin fibrils.

[0126] The second layer of fine fibers can comprise any suitable mixture of fibers of mixed diameters. For example, if the second layer of fine fibers comprises thin and thick fine fibers, the second layer of fine fibers can comprise at least 0.5% thick fine fibers, at least 1% thick fine fibers, at least 2% thick fine fibers, at least 5% thick fine fibers, at least 7% thick fine fibers, at least 10% thick fine fibers, at least 12% thick fine fibers, at least 14% thick fine fibers, at least 16% thick fine fibers, at least 20% thick fine fibers, at least 50% thick fine fibers, at least 60% thick fine fibers, at least 70% thick fine fibers, or at least 80% thick fine fibers. For example, if the second layer of fine fibers comprises thin fine fibers and thick fine fibers, the second layer of fine fibers can comprise at most 1% thick fine fibers, at most 2% thick fine fibers, at most 5% thick fine fibers, at most 7% thick fine fibers, at most 10% thick fine fibers, at most 12% thick fine fibers, at most 14% thick fine fibers, at most 16% thick fine fibers, at most 20% thick fine fibers, at most 50% thick fine fibers, at most 60% thick fine fibers, at most 70% thick fine fibers, at most 80% thick fine fibers, or at most 90% thick fine fibers. Some exemplary mixtures are shown in Tables 1A-1C. For example, the second layer of fine fibers can include a proportion of thick fine fibers from one or more of Set A5, Set A6, Set B, Set D, Set D5, Set D6, Set E, Set I, Set I5, Set I6, Set J, or Set L of Tables 1A-1C.

[0127] In some embodiments, the percentage of thick fibrils is estimated from the diameters of the thin and thick fibrils, the % solids in the precursor spinning solution, the syringe pump feed rate, and the electrospinning time.

[0128] In some embodiments, the percentage of thick fine fibers can be determined based on spinning time using the equation provided in the Calculating Fiber Percentage section of the Examples.

[0129] In some embodiments, the proportion of thick fine fibers can be determined by nano-computed tomography (nano-CT). For example, a filter medium sample can be embedded in resin and scanned as if cut along the Z-axis. Useful images can be obtained by using a synchrotron-quality nanoscale 3D X-ray imaging device, such as Xradia 810 Ultra (Zeiss, Oberkochen, Germany). To use the digital structure to determine the proportion of fibers with a specific diameter, it can be useful to then stitch the images together to form a 3D digital structure. The proportion of thin / thick fine fibers can be calculated by the ratio of the number of thin / thick fine fibers to the number of all fibers (both thin and thick fibers) in the digital structure.

[0130] In some embodiments, the percentage of thick fine fibers can be determined using microscopic observation. For example, a sample image can be obtained through a SEM at an appropriate magnification (e.g., 500x, 1000x, or 2500x). The presence of one or more fiber populations can be determined by counting all fibers within the image, followed by classification into thin and thick fine fibers based on group diameters within a 25% variation. Fiber diameters can be measured and / or classified using image processing software such as ImageJ. The percentage of thin / thick fine fibers can be calculated by the ratio of the number of thin / thick fine fibers to the number of total fibers (both thin and thick fibers) within the image.

[0131] For example, in exemplary embodiments, the second layer of fine fibers may include at least 0.5% and at most 20% thick fine fibers, more preferably at least 1% and at most 10% thick fine fibers, or even more preferably at least 5% and at most 7% thick fine fibers. Additional ranges may also be useful, including, for example, at least 3% and at most 9% thick fine fibers or at least 4% and at most 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 to the thin fine fibers without disrupting the thin fine fiber structure and resulting in a corresponding loss in efficiency.

[0132] In some embodiments, when fibers of different diameters are layered, the second layer of fine fibers may include a sublayer including thin fine fibers and / or a sublayer including thick fine fibers deposited on a top sublayer of thick fine fibers (see FIGS. 1J-1M). Without wishing to be bound by theory, it is believed that including a top layer or sublayer of thick fine fibers may protect the previously deposited layer from being blown away and / or damaged when back-pulse cleaning (from downstream) is performed during intended use of the filter media.

[0133] Any suitable combination of thin and thick fine fiber layers can be used. Exemplary layered fiber structures that can be used for the second layer of fine fibers include one or more of Set A5, Set B, Set D5, Set E, Set I5, or Set J in Tables 1A-1C. Exemplary mixed fiber structures that can be used for the second layer of fine fibers include one or more of Set A6, Set D, Set D6, Set I, or Set L in Tables 1A-1C.

[0134] In some embodiments, both layered and mixed structures can be included in the second fine fiber layer. For example, as further described in Example 7, the second fine fiber layer can include a sublayer of thin fine fibers, followed by a sublayer of mixed thin and thick fine fibers, with the thick fiber sublayer being the top layer.

[0135] In some embodiments, the second layer of fine fibers has an average intermediate flow pore size of at least 0.1 μm, at least 0.5 μm, at least 1 μm, at least 5 μm, at least 10 μm, at least 15 μm, or at least 20 μm. In some embodiments, the first layer of fine fibers has an average intermediate flow pore size of at most 0.5 μm, at most 1 μm, 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 exemplary embodiments, the first layer of fine fibers has an average intermediate flow pore size in the range of 10 μm to 25 μm. In some embodiments, the average intermediate flow pore size is preferably determined using capillary flow porometry.

[0136] When fibers of different diameters are layered, the effective pore size of the second layer of fine fibers is defined by the layer containing the smallest fine fibers.

[0137] In some embodiments, the second layer of fine fibers has a 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 second layer of fine fibers 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 some embodiments, the second layer of fine fibers has a basis weight of at least 0.1 g / m 2 and a maximum of 20 g / m 2 In another exemplary embodiment, the second layer of fine fibers has a basis weight of at least 0.1 g / m 2 and a maximum of 1 g / m 2 In a further exemplary embodiment, the second layer of fine fibers has a basis weight of 0.43 g / m 2 The basis weight of the second layer of fine fibers is 1 / (2.5). When fibers of different diameters are layered, the basis weight of the second layer of fine fibers is additive. The basis weight of the second layer of fine fibers can be determined from the mass of the second layer of fine fibers and the area of ​​the scrim according to the following equation: Basis Weight of Second Layer of Fine Fibers = (Mass of Second Layer of Fine Fibers) / (Area of ​​Scrim). The mass of the second layer of fine fibers can be calculated from the polymer and spinning conditions used to produce the fibers according to the following equation: Mass of Fine Fibers = (% w / v of Polymer in Solution) x (Pump Speed) x (Spinning Time).

[0138] In some embodiments, the second layer of fine fibers has a higher solidity than the first layer of fine fibers. That is, the first layer of fine fibers is preferably more open than the second layer of fine fibers. In some embodiments, the second layer of fine fibers has a solidity of at least 0.5%, at least 1%, at least 5%, at least 10%, at least 20%, at least 25%, at least 30%, or at least 40%. In some embodiments, the second layer of fine fibers has a solidity of at most 10%, at most 20%, at most 25%, at most 30%, at most 40%, or at most 50%. In exemplary embodiments, the second layer of fine fibers has a solidity in the range of 0.5% to 30%. The solidity (c) of the second layer of fine fibers is calculated using the dimensionless fiber drag parameter, F, using the following equation: * 1.0 It can be calculated from: F * 1.0 =4.3548e 8.8822c As further described in the Examples, F * 1.0can be calculated from the modified Kirsch-Fuchs equation:

[0139] In some embodiments, the second layer of fine fibers has a thickness of at least the average diameter of the average fine fibers of the second layer of fine fibers, hi some embodiments, the second layer of fine fibers has a thickness of at least 0.5 μm or at least 1 μm.

[0140] In some embodiments, the second layer of fine fibers has a thickness that is the thickness of several fibers having the average diameter of the second layer of fine fibers. For example, the second layer of fine fibers can have a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm.

[0141] In some embodiments, the second layer of fibrils has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, at most 40 μm, or at most 45 μm.

[0142] In some embodiments, the total thickness of the fine fiber layer can be measured using scanning electron microscopy (SEM). For example, a sample including at least the 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 can be useful to cross-section the sample while orienting the sample so that the support layer is cut before the fine fiber layer. It can be even more useful to cross-section the sample while immersed in liquid nitrogen. An exemplary magnification that can be used is 1000x. It can be useful to use software that aids in determining the thickness of the sample by allowing for outlining and re-shading of fine fiber portions in the SEM image. The re-shaded 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 from five separate images of the same sample.

[0143] In some embodiments, the overall efficiency of the media may be directly related to the thickness of the second layer of fine fibers.

[0144] Filter media characteristics As noted above, the filter media includes a support layer and a layer of fine fibers, which may form a composite.

[0145] In some embodiments, the filter medium has a composite average maximum 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 average maximum pore size of at least 0.1 μm. As used herein, "composite average maximum pore size" refers to the average maximum pore size of a composite including a support layer and a fine fiber layer.

[0146] In some embodiments, the filter medium has a composite mean intermediate flow pore size of at most 11 μm, preferably at most 9 μm, and more preferably at most 6 μm. In some embodiments, the filter medium has a composite mean intermediate flow pore size of at least 0.1 μm. As used herein, "composite mean intermediate flow pore size" refers to the mean intermediate flow pore size of a composite including a support layer and a fine fiber layer.

[0147] When the fine fiber layer includes multiple fine fiber layers, the composite includes each of the fine fiber layers.

[0148] In some embodiments, the composite mean maximum pore size and / or the composite mean intermediate flow pore size are preferably determined using capillary flow porometry.

[0149] Without wishing to be bound by theory, the composite average maximum pore size and composite average mean flow pore size depend, among other things, on the fiber diameter, the relative amounts of thin and thick fibers, and the composite morphology (e.g., layered or mixed).

[0150] As described in Example 11, the composite average maximum pore size and / or composite average intermediate flow pore size of a filter medium can be related to the filter medium's ability to withstand a pressure drop of at least 20 psi during liquid filtration, and will exhibit better filter performance than filter media that cannot withstand the same conditions.

[0151] Fine fiber The fine fibers of the present disclosure comprise a fiber-forming polymeric material. In some embodiments, the fine fibers of the present disclosure may be produced by spinning the fiber-forming polymeric material alone. In some embodiments, the fine fibers of the present disclosure may be produced by spinning the fiber-forming polymeric material in combination with another substance.

[0152] Fine fiber technology contemplated for polymeric materials mixed or blended with various other substances is disclosed in Chung et al., U.S. Pat. No. 6,743,273; Chung et al., U.S. Pat. No. 6,924,028; Chung et al., U.S. Pat. No. 6,955,775; Chung et al., U.S. Pat. No. 7,070,640; Chung et al., U.S. Pat. No. 7,090,715; Chung et al., U.S. Patent Application Publication No. 2003 / 0106294; Barris et al., U.S. Pat. No. 6,800,117; and Gillingham et al., U.S. Pat. No. 6,673,136. Additionally, Ferrer et al., U.S. Pat. No. 7,641,055, mixed or blended polysulfone polymers with polyvinylpyrrolidone polymers to obtain a single-phase polymer alloy used in the electrospinning of fine fiber materials, thereby producing a water-insoluble, high-strength polymeric material.

[0153] Fine fibers made from polymers and reactive additives In some embodiments, fine fibers of the present disclosure can be produced by combining a fiber-forming polymeric material with at least two reactive additives that are capable of reacting with each other, for example, during the fiber-forming process or a post-treatment process, as further described in WO 2014 / 164130. The at least two reactive additives are optionally reactive with the fiber-forming polymer.

[0154] In some embodiments, fine fibers of the present disclosure may comprise at least one fiber-forming polymer; and at least two reactive additives covalently bonded to each other and, optionally, to the fiber-forming polymer. In some embodiments, at least one of the reactive additives is self-condensing. In some embodiments, at least one of the reactive additives enhances at least one property of the fine fiber compared to a fine fiber without such reactive additive. In this context, "enhancing" means improving or generating one or more properties.

[0155] The reactive additives are selected so that they are preferably soluble in the solvent selected for the polymeric material for a process such as electrospinning.

[0156] In certain embodiments, the reactive additive is a monomer, oligomer, or small molecular weight polymer. For example, in certain embodiments, the reactive additive has a weight average molecular weight of less than 3000 Daltons. In certain embodiments, all of the reactive additives used to produce the fine fibers have a weight average molecular weight of less than 3000 Daltons. In some embodiments, the weight average molecular weight of the reactive additive can be determined using time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0157] Reactive additives can have a variety of reactive functional groups. For example, they can include alkoxy groups, hydroxyl groups, acid groups (e.g., carboxylic acid groups), isocyanate groups, diglycidyl ether groups, and dichloro groups. Any single molecule of a compound that functions as a reactive additive can contain one or more of the same type of functional group or two or more different functional groups. Reactive additives can include mixtures of compounds with various numbers or types of functional groups. Hydroxyl group-functional components can include diols, triols, polyols, or mixtures thereof. Carboxylic acid-functional components can include compounds with multiple carboxylic acid groups (e.g., diacids, triacids, or mixtures thereof). Glycidyl ether-functional components can include compounds with multiple glycidyl ether groups (e.g., diglycidyl ethers, triglycidyl ethers, or mixtures thereof). Amine-functional components can include primary amine compounds, secondary amine compounds, tertiary amine compounds, or mixtures thereof. Amine-functional components can include compounds with multiple primary, secondary, or tertiary amine groups (e.g., diamines, triamines, or mixtures thereof). The isocyanate-functional component can include compounds having multiple isocyanate groups (e.g., diisocyanates, triisocyanates, or mixtures thereof). In addition, reactive additives can have two or more reactive functional groups. For example, citric acid and dimethylolpropionic acid have hydroxyl and carboxylic acid groups.

[0158] In certain embodiments, at least one of the reactive additives is trifunctional or higher. This means that the reactive additive has three or more reactive functional groups per molecule. For example, 1,1,1-trimethylolpropane is a trifunctional alkoxy-containing compound; glycerol, pentaerythritol, erythritol, threitol, dipentaerythritol, and sorbitol are multifunctional hydroxyl-containing reactive additives; citric acid and dimethylolpropionic acid are multifunctional carboxylic acid-containing reactive additives; trimethylolpropane triglycidyl ether is a trifunctional glycidyl ether-containing reactive additive; triphenylmethane triisocyanate is a trifunctional isocyanate-containing reactive additive; and triethylenetetramine, trimethylolpropane, and tri(poly(propylene glycol)amine-terminated) ether are multifunctional amine-containing reactive additives.

[0159] The following are examples of various reactive additives categorized by functional group: (I) alkoxy-functional; (II) hydroxyl-functional; (III) acid-functional; (IV) glycidyl ether-functional; (V) isocyanate-functional; (VI) amine-functional; and (VII) dichloro-functional. Various reactivity combinations (i.e., combinations of materials that are reactive with each other) can be used in producing the fine fibers of the present disclosure. For example, one or more reactive additives from group (I) can be reacted with one or more reactive additives from groups (II) and / or (III) and / or (IV) and / or (V) and / or (VI). One or more reactive additives from group (II) can be reacted with one or more reactive additives from groups (III) and / or (IV) and / or (V) and / or (VI) and / or (VII). One or more reactive additives from group (III) can be reacted with one or more reactive additives from groups (IV) and / or (V) and / or (VI) and / or (VII).

[0160] Fine fibers made from polymers and resinous aldehyde compositions In some embodiments, fine fibers of the present disclosure may be produced by combining a fiber-forming polymeric material with a resinous aldehyde composition, such as a melamine-formaldehyde resin.

[0161] In some embodiments, as described further below, the resinous aldehyde composition comprises a "polymer reactive resinous aldehyde composition." The "polymer reactive resinous 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 resinous aldehyde composition can participate in crosslinking of the polymer, and optionally self-crosslinking. The fiber-forming polymeric 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 resinous aldehyde composition used in producing the fine fibers.

[0162] In some embodiments, the resinous aldehyde composition comprises a "polymeric non-reactive resinous aldehyde composition," as further described below. The polymeric non-reactive resinous 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 polymeric non-reactive resinous aldehyde composition participates in self-crosslinking.

[0163] 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 "resinous aldehyde composition" refers to the starting materials as well as the materials in the final fiber.

[0164] These components can be combined in solution or in molten form. In certain embodiments, the fine fibers are electrospun from a solution or dispersion. Thus, the polymeric material and the resinous aldehyde (e.g., melamine aldehyde) composition are dispersible or soluble in at least one common solvent or solvent blend suitable for electrospinning.

[0165] Fine fibers made from polymers crosslinked with polymer-reactive resinous aldehyde compositions As further described in U.S. Pat. No. 9,587,328, in some embodiments, fine fibers of the present disclosure may be produced by combining a fiber-forming polymeric material with a polymeric reactive resinous aldehyde composition containing alkoxy groups (e.g., reactive melamine-formaldehyde resin).

[0166] 9A and 9B, as fiber 100 / 102 forms, the polymer reactive resinous aldehyde composition preferably forms at least one outer concentric (i.e., phase) such as second coating phase 22 (fiber 102, FIG. 9B) comprising primarily the polymer reactive resinous aldehyde composition (e.g., a melamine aldehyde composition) or two outer concentric (i.e., phases) such as second coating phase 20 (fiber 100, FIG. 9A) comprising a blend of polymeric material and polymer reactive resinous aldehyde composition and third outer (outermost) phase 30 (FIG. 9A) comprising primarily the polymer reactive resinous aldehyde composition. That is, the polymer reactive resinous aldehyde composition may migrate to the surface to form a two-phase fiber (FIG. 9B) or a three-phase fiber (FIG. 9A) in which core 10 (FIG. 9A) or 12 (FIG. 9B) comprises primarily a polymeric material (e.g., nylon). Generally, the higher the reactive resinous aldehyde content of the polymer relative to the polymer, the greater the tendency to form three-phase fibers.

[0167] In some embodiments, fine fibers of the present disclosure may preferably be prepared from a polymer reactive resinous aldehyde composition comprising alkoxy groups and a polymer comprising active hydrogen groups, wherein the molar ratio of the polymer reactive resinous aldehyde composition to the polymer is such that the molar ratio of the alkoxy groups of the polymer reactive resinous aldehyde composition to the active hydrogen groups of the polymer is greater than 5:100, or greater than 10:100, or greater than 20:100, or greater than 40:100, or greater than 60:100. In some embodiments, the molar ratio of the polymer reactive resinous aldehyde composition to the polymer may be such that the molar ratio of the alkoxy groups of the polymer reactive resinous aldehyde composition to the active hydrogen groups of the polymer is 300:100 or less, 250:100 or less, or 210:100 or less.

[0168] In certain embodiments, weight ratios of polymer reactive resinous aldehyde composition to polymer greater than 5:100, or greater than 10:100, or greater than 20:100, or greater than 40:100, or greater than 60:100 may be used. In some embodiments, the weight ratio may be used to control the formation of a useful outer phase comprising the polymer reactive resinous aldehyde composition surrounding the core polymer. An outer coating layer of predominantly polymer reactive resinous aldehyde composition (e.g., melamine-formaldehyde) provides the fine fibers and fine fiber layers of the present disclosure with improved properties, such as moisture resistance, compared to commercially available fibers and fiber layers. In this context, "predominantly" means that the referenced material is present in a particular region (e.g., coating, layer, or phase) in a major amount (i.e., greater than 50% by weight) of the material in that region.

[0169] For example, in an exemplary embodiment, the weight ratio of the polymer reactive resinous aldehyde composition to the polymer can range from 5:100 to 300:100, and in another exemplary embodiment, the weight ratio of the polymer reactive resinous aldehyde composition to the polymer can range from 20:100 to 100:100.

[0170] Suitable polymer reactive resinous aldehyde compositions contain two or more alkoxy groups per molecule that are capable of crosslinking the polymers used in producing the fine fibers described herein. Exemplary polymer reactive resinous aldehyde compositions are synthetic resins produced by treating various aldehydes with reactants under condensation reaction conditions. Useful such reactants include phenol, urea, aniline, benzoguanamine, glycoluril, and melamine. Useful polymer reactive resinous aldehyde compositions include aldehyde-based agents that can be used in crosslinking reactions. Polymer reactive resinous aldehyde compositions are typically nonvolatile. Also, (when combined with a polymer such as nylon, as described in more detail below) the polymer reactive resinous aldehyde composition must be soluble in the solvent selected for the polymeric material for processes such as electrospinning. Polymer reactive resinous aldehyde compositions useful as crosslinkers include the condensation products of urea and an aldehyde, phenol and an aldehyde, or melamine and an aldehyde. One useful class of crosslinked resins includes nitrogen-based resins such as melamine, urea, benzoguanamine, glycoluril, and other similar resins made by reacting aldehydes with nitrogen compounds. Such amine-based crosslinked resins are soluble in process solvents and reactive with a variety of polymeric species.

[0171] Useful polymer-reactive resinous aldehyde compositions (e.g., melamine aldehyde compositions) include a crosslinker and optionally other non-reactive, room-temperature stable resin components that can be combined in solution or in molten form with various polymeric materials. Melamine, along with various other co-reactants, forms the resinous composition.

[0172] Useful melamine aldehyde compositions include melamine-aldehyde products typically formed by the reaction between melamine and aldehyde compounds. Useful aldehyde compounds include C aldehydes, including formaldehyde, acetaldehyde, butyraldehyde, isobutyraldehyde, and the like. 1~6 Alkanals are included. Mixtures of such aldehydes may be used if desired. Melamine aldehyde resins and other suitable polymeric reactive resinous aldehyde compositions contain components having at least two alkoxy groups per molecule. Typical partially and fully reacted melamine aldehydes have 3 to 6 or 4 to 6 alkoxy groups per molecule.

[0173] In certain embodiments, the polymer reactive resinous aldehyde composition comprises a condensation product of urea and an aldehyde, a condensation product of a phenol and an aldehyde, a condensation product of melamine and an aldehyde, or a mixture thereof. In certain embodiments, the polymer reactive resinous aldehyde composition comprises a condensation product of benzoguanamine and an aldehyde, a condensation product of glycoluril and an aldehyde, or a mixture thereof.

[0174] Useful polymeric reactive resinous aldehyde compositions (e.g., melamine aldehyde compositions) include highly methylated melamine; partially methylated melamine; methylated high imino melamine; highly alkylated mixed ether melamine; highly alkylated, carboxylated high imino mixed ether melamine; highly n-butylated melamine; n-butylated high imino and partially n-butylated melamine; partially iso-butylated melamine; partially n-butylated urea; partially iso-butylated urea; glycoluril; highly alkylated mixed ether melamine-formaldehyde; highly alkylated mixed ether carboxylated melamine-formaldehyde; Carboxylated melamine resins; hexabutoxymethyl melamine; butoxymethyl melamine; highly alkylated mixed ether melamines; methoxymethyl methylol melamine, highly methylated melamine resins; melamine-formaldehyde resins co-etherified with methanol and n-butoxyethanol / n-butanol blends; melamine-formaldehyde resins co-etherified with methanol and n-butanol in n-butanol; butyl melamine-formaldehyde resins dissolved in n-butanol and butyl glycol blends; hexabutoxymethyl melamine; partially n-butylated melamine; high solids, highly methylated melamine resins;For example, CYMEL 301, CYMEL 303 LF, CYMEL 350, CYMEL 3745, CYMEL MM-100, CYMEL 370, CYMEL 373, CYMEL 3749, CYMEL 323, CYMEL 325, CYMEL 327, CYMEL 328, CYMEL 385, CYMEL 481, CYMEL 1116, CYMEL 1130, CYMEL 1133, CYMEL 1135, CYMEL 1161, CYMEL 1168, CYMEL 1125, CYMEL 1141, CYMEL 202, CYMEL 203, CYMEL 254, CYMEL 1156, CYMEL 1158, CYMEL 9370, CYMEL MB-98, CYMEL MB-11-B, CYMEL MB-14-B, CYMEL 615, CYMEL 651, CYMEL 683, CYMEL 688, CYMEL MI-12-I, CYMEL MI-97-IX, CYMEL UM-15, CYMEL U-80, CYMEL UB-24-BX, CYMEL UB-25-BE, CYMEL UB-26-BX, CYMEL UB-30-B, CYMEL UB-90-BX, CYMEL U-227-8, CYMEL U-610, CYMEL U-640, CYMEL U-646, CYMEL U-662, CYMEL U-663, CYMEL U-665, CYMEL UI-19-I, CYMEL UI-19-IE, CYMEL various polymeric reactive resinous aldehyde compositions sold under the trade name CYMEL available from Cytec Industries of West Paterson, NJ, including UI-20-E, CYMEL UI-38-I, CYMEL 1123, CYMEL 659, CYMEL 1172, CYMEL 1170, and the like;and compounds and mixtures thereof, including various polymer-reactive resinous aldehyde compositions sold under the LUWIPAL trade name available from BASF AG of Ludwigshafen, Germany, including LUWIPAL LR 8955, LUWIPAL LR 8968, and LUWIPAL LR 8984. Such resins are also available from INEOS Melamines Inc. and sold under the trade names RESIMENE (e.g., RESIMENE HM 2608), MAPRENAL, and MADURIT. Various combinations of polymer-reactive resinous aldehyde compositions can be used, if desired;

[0175] In an exemplary embodiment, a melamine-formaldehyde resin (sometimes referred to herein simply as a "melamine composition" or "melamine resin") is used. The term "melamine-formaldehyde resin" refers to a melamine-based resin having two or more (at least two) alkoxy functional groups (e.g., methoxy, ethoxy, propoxy, butoxy) per melamine molecule. In addition to the alkoxy functional groups, the melamine-formaldehyde resin may also have NH, hydroxyl, or carboxylic acid functional groups. Non-crosslinked melamine-formaldehyde is a thermosetting plastic additive used for polymer crosslinking, which strengthens the crosslinked polymer upon heating. Once cured, it cannot be remolded or cured to form a different shape. Crosslinked melamine-formaldehyde plastics retain their strength and shape, unlike other types of thermoplastics (e.g., acetate, acrylic, and nylon), which soften upon heating and harden upon cooling. Crosslinked melamine-formaldehyde is color-resistant and resistant to strong solvents and water. Depending on the functional groups in the melamine-formaldehyde resin, the uncrosslinked resin can be both water-soluble and water-insoluble or soluble in organic solvents such as alcohols, hydrocarbons (toluene, xylene, etc.), or other or mixtures of these solvents.

[0176] Melamine-formaldehyde resins are produced from the reaction of formaldehyde with melamine. Melamine (chemical formula C3H6N6) and formaldehyde (chemical formula CHO) have the following structure: [ka] wherein the melamine is 1,3,5-triazine-2,4,6-triamine; or 2,4,6-triamino-s-triazine; or cyanuric triamide. Representative structures of melamine-formaldehyde resins are shown in Structure I or II: [ka] (In compound I, X is H or alkoxy or hydroxyl, and at least two X groups are alkoxy). Preferably, when a compound has two or three alkoxy groups, the alkoxy groups are not on the same nitrogen substituent. Melamine resin compound I requires a minimum of two reactive or crosslinkable alkoxy groups. Representative compound II is a fully reacted compound described as a hexa(alkoxymethyl)melamine type resin, where R is H or alkyl (methyl, ethyl, butyl, etc.) (such that OR is an alkoxy group (methoxy, ethoxy, butoxy, etc.)).

[0177] Melamine resins are part of the larger class of amino resins. They are used as binders in plywood and particle board and as wrinkle inhibitors in fabrics. They are also molded for electrical devices and various commercial and household products. They are also used as crosslinkers in paper towels to increase water resistance. When describing melamine-formaldehyde resin, we mean uncrosslinked melamine resin. It is sold under various trade names, including CYMEL, LUWIPAL, RESIMENE, MAPRENAL, etc.

[0178] An exemplary such melamine resin is hexa(methoxymethyl)melamine (HMMM) (e.g., Structure II above, where R is methyl). To prepare the films, polymers with active hydrogen groups (mainly amide, hydroxyl, carboxyl, or anhydride functionalities) were used as reaction partners for HMMM.

[0179] Depending on the polymer reactive resinous aldehyde composition, for example, the crosslinking reaction described herein may require a strong acid catalyst, such as a sulfonic acid, for example, para-toluenesulfonic acid. In certain embodiments, the catalyst, such as an acid catalyst, is preferably used in an amount of at least 4 wt.% based on the polymer solids to enhance the crosslinking rate. Typically, in the crosslinking reaction of the present disclosure, 10 wt.% or less of the catalyst, such as an acid catalyst, is used.

[0180] If desired, the fine fibers formed from the crosslinking reaction between the polymer reactive resinous aldehyde composition and the polymeric material as described herein can be enhanced in terms of rate and extent of crosslinking, for example, by exposing the fine fibers to a heat treatment, such as a heat treatment typically involving a temperature of at least 80°C, at least 100°C, or at least 120°C, and typically up to 150°C, typically for at least 5 seconds and typically no more than 10 minutes.

[0181] In the fibers of the present disclosure, the polymer reactive resinous aldehyde composition of the present disclosure is combined with a polymeric material, including a polymer or a mixture or blend of polymers. The polymer or mixture or blend of polymers is selected so that it can be combined with the polymer reactive resinous aldehyde composition in a solution, dispersion, or melt. The combination of the polymeric material and the polymer reactive resinous aldehyde composition must, in certain embodiments, be substantially stable in the melt or in solution or dispersion for a sufficient time so that fibers can be formed.

[0182] The polymer or polymer mixture or blend must contain at least one fiber-forming polymer containing one or more active hydrogen groups crosslinkable by the polymer reactive resinous aldehyde composition. Preferred such polymeric materials contain one or more active hydrogen groups capable of reacting with and crosslinking to the polymer reactive resinous aldehyde composition. Active hydrogen groups include, but are not limited to, thiol (-SH), hydroxyl (-OH), carboxylate (-COH), amide (-C(O)-NH- or -C(O)-NH), amino (-NH) or imino (-NH-), and anhydride (-COO)R groups (upon hydrolysis). These groups may be found in pendant polymer groups or in the polymer backbone.

[0183] Suitable polymeric materials for use in the polymer compositions of the present disclosure include addition polymers and condensation polymeric materials having active hydrogens. Suitable examples include poly(maleic anhydride), poly(meth)acrylic acid, polyamides, cellulose ethers and esters, polyamines such as chitosan, and mixtures, blends, alloys, and block, graft, or random copolymers thereof. Such copolymers may contain one or more other moieties in addition to those listed in the text above. Preferred materials within these general categories include poly(vinyl alcohol), crosslinked or uncrosslinked, with various degrees of hydrolysis (e.g., 87% to 99.5%). Preferred addition polymers tend to be glassy, ​​i.e., have a T above room temperature. g (glass transition temperature). Additionally, polymeric materials with low crystallinity, such as poly(vinyl alcohol) materials, are also useful as polymeric materials of the present disclosure.

[0184] Other preferred examples of useful polymeric materials include cellulose derivatives selected from the group consisting of ethyl cellulose, hydroxyethyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate phthalate, and mixtures thereof; poly(meth)acrylic acid homopolymers and copolymers, including, for example, styrene-(meth)acrylic acid copolymers and ethylene-(meth)acrylic acid copolymers; polyvinyl alcohol homopolymers or copolymers, including, for example, polyvinyl butyral and ethylene-covinyl alcohol copolymers; poly(maleic anhydride) homopolymers or copolymers, including, for example, styrene-maleic anhydride copolymers; and polyurethanes. Poly(meth)acrylic acid, as used herein, refers to poly(acrylic acid) and poly(methacrylic acid) polymers.

[0185] Numerous types of polyamides are also useful as polymeric materials in the fibers of the present disclosure. One useful class of polyamide condensation polymers is nylon materials. The term "nylon" is a generic name 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 digit indicates the C6 diamine, and the second digit indicates the C6 dicarboxylic acid compound). Another nylon can be produced by the polycondensation of ε-caprolactam in the presence of a smaller amount of water. This reaction forms nylon-6 (made 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.

[0186] Copolymers can be made by combining various diamine compounds, various diacid compounds, and various cyclic lactam structures in a reaction mixture, and then forming nylon with the monomer materials randomly arranged in a polyamide structure. For example, nylon-6,6-6,10 materials are made by combining hexamethylenediamine and the C6 and C6 diacids. 10Nylon-6-6,6-6,10 is a nylon made from a blend of epsilon aminocaproic acid, hexamethylenediamine, and C6 and C 10 It is a nylon made by copolymerization of a blend of diacid materials. As used herein, the term "copolymer" includes polymers made from two or more different monomers, including terpolymers and the like.

[0187] Block copolymers are also useful as the polymeric material in the fibers of the present disclosure. For such copolymers, the choice of solvent or solvent blend is important. The solvent or solvent blend selected is chosen so that both blocks are soluble in the solvent. Examples of useful block copolymers include PEBAX ε-caprolactam-b-ethylene oxide, available from Arkema Inc. of Philadelphia, PA; and polyurethanes of ethylene oxide and isocyanate.

[0188] Addition polymers such as polyvinyl alcohol and amorphous addition polymers such as poly(acrylonitrile) copolymers with acrylic acid are also useful. Because they are soluble or dispersible in a variety of solvents and solvent blends at low pressure and temperature, they can be solution-spun relatively easily. For example, poly(vinyl alcohol) having a degree of hydrolysis ranging from 87% to 99.9+% can be used as the polymeric material in the fibers of the present disclosure.

[0189] Preferred polymers in this embodiment include polyamides (especially nylon), polyesteramides, polyvinyl alcohol, ethylene-co-vinyl alcohol polymers, polyvinyl butyral, poly(maleic anhydride), polyvinylpyrrolidone, and copolymers thereof. Preferred active hydrogen groups include hydroxyl, amino, and amide groups. Various combinations of polymeric materials can be used as desired.

[0190] Optionally, in addition to the polymer having reactive hydrogen groups, the polymeric material used in the fibers of the present disclosure may include one or more non-reactive polymers. In this context, "non-reactive" is defined as being unable to crosslink with the melamine-formaldehyde resin or other polymer reactive resinous aldehyde composition used. For example, polymeric materials such as many polyolefins, polyvinyl chloride, chlorinated polyethylene, and other such materials that do not have groups that can crosslink with the polymer reactive resinous aldehyde composition may be used. Other non-reactive polymers include polyacetals, polyesters (both aromatic and aliphatic, including, for example, poly(ethylene terephthalate) (PET), polybutylene terephthalate (PBT), polycaprolactone (PCL), poly-L-lactic acid (PLLA), poly-D-lactic acid (PLDA), etc.), polyester-co-polyethylene oxide, polyalkylene sulfides, polyarylene oxides (including, for example, polyphenylene oxide), polysulfones, modified polysulfones (including, for example, polyethersulfone), poly(vinylpyridine) (including, for example, poly(4-vinylpyridine), poly(2-vinylpyridine) and their random and block copolymers (including, for example, styrene vinylpyridine, vinylpyridine-co-butyl methacrylate, vinylpyridine-co-methyl methacrylate, etc.)), polyvinyl acetate and its copolymers (including, for example, ethylene-co-vinyl acetate), etc.Preferred materials within these general categories include polyethylene, polypropylene, poly(vinyl chloride), poly(methyl methacrylate), acrylic resins including polystyrene and copolymers thereof (including both random and block copolymers such as ABA block copolymers) (including, for example, styrene acrylonitrile (SAN), styrene maleic anhydride (SMA), styrene-co-vinylpyridine, styrene-co-butadiene, styrene-co-ethylenepropylene, styrene-co-methyl methacrylate, styrene-co-ethyl methacrylate, styrene-co-butyl methacrylate, styrene-co-methyl acrylate, styrene-co-ethyl acrylate, styrene-co-butyl acrylate, etc.), poly(vinylidene fluoride) and copolymers thereof (including, for example, PVDF-co-HFP), poly(vinylidene chloride), mixtures, blends, or alloys. Examples of useful block copolymers include ABA type copolymers (e.g., styrene-EP-styrene) ("EP" means ethylene propylene) or AB (e.g., styrene-EP) polymers, KRATON styrene-b-butadiene and styrene-b hydrogenated butadiene (ethylene propylene) available from Kraton Polymers US LLC of Houston, TX; and SYMPATEX polyester-b-ethylene oxide available from SympaTex Technologies Inc. of Hampton, NH. Various combinations of non-reactive polymers can be used if desired.

[0191] If desired, a non-reactive polymer may be used in an amount that does not adversely affect the positive effects of crosslinking that occurs when using a polymer having active hydrogens.

[0192] Addition non-reactive polymers such as poly(vinylidene fluoride), syndiotactic polystyrene, copolymers of vinylidene fluoride and hexafluoropropylene, polyvinyl acetate, amorphous addition polymers such as polystyrene, poly(vinyl chloride) and its various copolymers, and poly(methyl methacrylate) and its various copolymers are soluble or dispersible in various solvents and solvent blends at low pressure and temperature, and therefore can be solution-spun relatively easily. However, highly crystalline polymers such as polyethylene and polypropylene typically require high temperature and high pressure solvents or solvent blends when they are solution-spun. Therefore, solution spinning of polyethylene and polypropylene is very difficult.

[0193] Fine fibers made from polymers crosslinked with polymer-non-reactive resinous aldehyde compositions As further described in U.S. Pat. No. 9,435,056, in some embodiments, fine fibers of the present disclosure may be produced by combining a fiber-forming polymeric material with a polymeric non-reactive resinous aldehyde composition that contains reactive groups for self-crosslinking.

[0194] 10A and 10B, as fiber 200 / 202 forms, the polymer non-reactive resinous aldehyde composition preferably forms at least one outer concentric layer (i.e., phase), such as second coating phase 222 (fiber 202, FIG. 10B) comprising primarily the polymer non-reactive resinous aldehyde composition (e.g., a melamine aldehyde composition), or two outer concentric layers (i.e., phases), such as second coating phase 220 (fiber 200, FIG. 10A) comprising a mixture of polymeric material and the polymer non-reactive resinous aldehyde composition, and third outer (outermost) phase 230 (FIG. 10A) comprising primarily the polymer non-reactive resinous aldehyde composition. That is, the polymer non-reactive resinous aldehyde composition can migrate to the surface to form a two-phase fiber (FIG. 10B) or a three-phase fiber (FIG. 10A) in which the core 210 (fiber 200) or 212 (FIG. 10B) comprises primarily a polymeric material (e.g., poly(4-vinylpyridine), also written as P4VP).

[0195] In this context, "predominantly" means that the referenced material is present in a particular region (e.g., coating, layer, or phase) in a major amount (i.e., greater than 50% by weight) of the material in that region.

[0196] Preferably, the fine fibers of the present disclosure are prepared from a self-crosslinking polymeric non-reactive resinous aldehyde composition that contains reactive groups (preferably alkoxy groups) and a polymer that contains no or low amounts of reactive groups (i.e., groups that can react with the reactive groups of the polymeric non-reactive resinous aldehyde composition), wherein the weight ratio of self-crosslinking polymeric non-reactive resinous aldehyde to non-reactive polymer is greater than 5:100, or greater than 10:100, or greater than 20:100, or greater than 40:100, or greater than 60:100.

[0197] In some embodiments, the weight ratio of the self-crosslinking polymeric non-reactive resinous aldehyde composition to the non-reactive polymer is 300:100 or less, 250:100 or less, 210:100 or less, or 100:100 or less.

[0198] For example, in an exemplary embodiment, the weight ratio of the self-crosslinking polymeric non-reactive resinous aldehyde composition to the non-reactive polymer can range from 5:100 to 300:100, and in another exemplary embodiment, the weight ratio of the self-crosslinking polymeric non-reactive resinous aldehyde composition to the non-reactive polymer can range from 20:100 to 100:100.

[0199] In some embodiments, the weight ratio can be used to control the formation of a polymer / semi-interpenetrating network type structure. The interpenetrating network is a self-crosslinked polymer non-reactive resinous aldehyde. This structure can provide improved properties, such as moisture resistance, to the fine fibers and fine fiber layers of the present invention.

[0200] Suitable polymeric non-reactive resinous aldehyde compositions contain one or more reactive groups capable of self-crosslinking in the fiber manufacturing process described herein. Such reactive groups include alkoxy groups as well as hydroxyl, carboxylic acid, and / or -NH groups. Exemplary polymeric non-reactive resinous aldehyde compositions are synthetic resins produced by treating various aldehydes with reactants under condensation reaction conditions. Useful such reactants include phenol, urea, aniline, benzoguanamine, glycoluril, and melamine. Useful polymeric non-reactive resinous aldehyde compositions include aldehyde-based agents that can be used in the self-crosslinking reaction. Resinous aldehyde compositions are typically nonvolatile. They must also be soluble in the solvent selected for the polymeric material for processes such as electrospinning. Resinous aldehyde compositions useful as crosslinkers include the condensation products of urea and aldehyde, phenol and aldehyde, or melamine and aldehyde. One useful class of crosslinked resins includes nitrogen-based resins such as melamine, urea, benzoguanamine, glycoluril, and other similar resins made by reacting aldehydes with nitrogen compounds. Such self-crosslinked resins are soluble in process solvents and reactive with a variety of polymeric species.

[0201] Useful polymer-non-reactive resinous aldehyde compositions (e.g., melamine aldehyde compositions) include a crosslinker and optionally other non-reactive, room-temperature stable resin components that can be combined in solution or in molten form with various polymeric materials. Melamine, along with various other co-reactants, forms the resinous composition.

[0202] Useful melamine aldehyde compositions include melamine-aldehyde products typically formed by the reaction between melamine and aldehyde compounds. Useful aldehyde compounds include C aldehydes, including formaldehyde, acetaldehyde, butyraldehyde, isobutyraldehyde, and the like. 1~6 Alkanals are included. Mixtures of such aldehydes can be used if desired. Melamine aldehyde resins and other suitable resinous aldehyde compositions contain components having at least two alkoxy groups per molecule. Typical partially and fully reacted melamine aldehydes have 3 to 6 or 4 to 6 alkoxy groups per molecule.

[0203] In certain embodiments, the polymer non-reactive resinous aldehyde composition comprises a condensation product of urea and an aldehyde, a condensation product of a phenol and an aldehyde, a condensation product of melamine and an aldehyde, or a mixture thereof. In certain embodiments, the polymer non-reactive resinous aldehyde composition comprises a condensation product of benzoguanamine and an aldehyde, a condensation product of glycoluril and an aldehyde, or a mixture thereof.

[0204] Useful polymeric non-reactive resinous aldehyde compositions (e.g., melamine aldehyde compositions) include partially methylated melamine; methylated high imino melamine; high imino mixed ether melamine; n-butylated high imino and partially n-butylated melamine; partially iso-butylated melamine; partially n-butylated urea; partially iso-butylated urea; glycoluril; and methoxymethyl methylol melamine resins, among those that are self-crosslinking.

[0205] Various self-crosslinking melamine compositions are available, for example, CYMEL 3745, CYMEL MM-100, CYMEL 3749, CYMEL 323, CYMEL 325, CYMEL 327, CYMEL 328, CYMEL 370, CYMEL 373, CYMEL 385, CYMEL 1158, CYMEL 1172, CYMEL UM-15, CYMEL U-64, CYMEL U-65, CYMEL U-21-571, CYMEL U-93-210, CYMEL U-216-10-LF, CYMEL U-227-8, CYMEL U-1050-10, CYMEL U-1052-8, CYMEL U-1054, CYMEL UB-25-BE, CYMEL Melamine resins sold under the CYMEL trade name, including UB-30-B, CYMEL U-662, CYMEL U-663, CYMEL U-1051, CYMEL UI-19-1, CYMEL UI-21E, CYMEL UI-27-EI, CYMEL UI-38-I, etc., are available from Cytec Industries of West Paterson, NJ, and various melamine compositions are sold under the LUWIPAL trade name, including, for example, LUWIPAL LR 8955, LUWIPAL LR 8968, and LUWIPAL LR 8984, are available from BASF AG of Ludwigshafen, Germany. Such resins are available from INEOS Melamines Inc. and are sold under the trade names RESIMENE (e.g., RESIMENE HM2608), MAPRENAL, and MADURIT. A primary requirement for such materials is their ability to self-condense (i.e., self-crosslink). Various combinations of polymer-non-reactive resinous aldehyde compositions can be used as desired, provided that such combinations include at least one self-crosslinking polymer-non-reactive aldehyde component.

[0206] In many preferred embodiments, melamine-formaldehyde resins (sometimes referred to herein simply as "melamine" compositions or "melamine" resins) are used. The term "melamine-formaldehyde resin" refers to a melamine-based resin having two or more (at least two) alkoxy functional groups (e.g., methoxy, ethoxy, propoxy, butoxy) per melamine molecule. In addition to the alkoxy functional groups, the melamine-formaldehyde resin contains imine (-NH-), carboxylic acid (-C(O)OH), or hydroxyl (-OH) functional groups, or a combination thereof, to impart the ability to self-crosslink. Depending on the functional groups in the melamine-formaldehyde resin, the uncrosslinked resin can be both water-soluble and water-insoluble, or soluble in organic solvents such as alcohols, hydrocarbons (e.g., toluene, xylene), or other solvents, or mixtures of these solvents.

[0207] Melamine-formaldehyde resins are produced from the reaction of formaldehyde with melamine. Melamine (chemical formula C3H6N6) and formaldehyde (chemical formula CHO) have the following structure: [ka] wherein the melamine is 1,3,5-triazine-2,4,6-triamine; or 2,4,6-triamino-s-triazine; or cyanuric triamide. A representative structure of a melamine-formaldehyde resin is Structure I: [ka] (In Compound I, each X and each Y are independently H, —(CH) x -OR (R=H or (C1-C4) alkyl and x=1-4) or -(CH2) y -C(O)OH (y=1-4), and further, at least two of the X and Y groups are -(CH2) x -OR (R=(C1-C4) alkyl and x=1-4), and at least one of the X and Y groups is H, -(CH2) x -OH (x = 1 to 4) and / or -(CH2) yPreferably, the compound has two or three -(CH2) x When there are -OR (R=(C1-C4) alkyl and x=1-4) groups, they are not on the same nitrogen substituent.

[0208] In the fibers of the present disclosure, the polymer non-reactive resinous aldehyde composition of the present disclosure is combined with a polymeric material comprising a polymer or a polymer mixture or blend. The polymer or polymer mixture or blend is selected so that it can be combined with the polymer non-reactive resinous aldehyde composition in solution, dispersion, or the melt. The combination of the polymeric material and the polymer non-reactive resinous aldehyde composition must, in certain embodiments, be substantially stable in the melt or in solution or dispersion for a sufficient time so that a fiber can be formed.

[0209] The polymer or polymer mixture or blend must contain at least one fiber-forming polymer and should contain very few or no reactive groups crosslinkable by the polymer non-reactive resinous aldehyde composition. Exemplary polymer reactive groups that should be absent include active hydrogen groups. Active hydrogen groups include, but are not limited to, thiol (-SH), hydroxyl (-OH), carboxylate (-COH), amide (-C(O)-NH- or -C(O)-NH), amino (-NH) or imino (-NH-), and anhydride (-COO)R groups (upon hydrolysis).

[0210] Suitable polymeric materials for use in the polymer compositions of the present disclosure include addition polymers and condensation polymeric materials that are non-reactive polymers. In this regard, "non-reactive" is defined as the inability to crosslink using the polymer non-reactive resinous aldehyde composition (as compared to reactive polymers (e.g., nylon)), as described above and in U.S. Pat. No. 9,587,328. For example, polymeric materials such as many polyolefins, polyvinyl chloride, chlorinated polyethylene, and other such materials that do not have groups that can crosslink with the polymer reactive resinous aldehyde composition can be used. Other non-reactive polymers include polyacetals, polyesters (both aromatic and aliphatic, including, for example, poly(ethylene terephthalate) (PET), polybutylene terephthalate (PBT), polycaprolactone (PCL), poly-L-lactic acid (PLLA), poly-D-lactic acid (PLDA), etc.), polyester-co-polyethylene oxide, polyalkylene sulfides, polyarylene oxides (including, for example, polyphenylene oxide), polysulfones, modified polysulfones (including, for example, polyethersulfone), poly(vinylpyridine) (including, for example, poly(4-vinylpyridine), poly(2-vinylpyridine) and their random and block copolymers (including, for example, styrene vinylpyridine, vinylpyridine-co-butyl methacrylate, vinylpyridine-co-methyl methacrylate, etc.)), polyvinyl acetate and its copolymers (including, for example, ethylene-co-vinyl acetate), etc.Preferred materials within these general categories include polyethylene, polypropylene, poly(vinyl chloride), poly(methyl methacrylate), acrylic resins including polystyrene and copolymers thereof (including both random and block copolymers such as ABA block copolymers) (including, for example, styrene acrylonitrile (SAN), styrene maleic anhydride (SMA), styrene-co-vinylpyridine, styrene-co-butadiene, styrene-co-ethylenepropylene, styrene-co-methyl methacrylate, styrene-co-ethyl methacrylate, styrene-co-butyl methacrylate, styrene-co-methyl acrylate, styrene-co-ethyl acrylate, styrene-co-butyl acrylate, etc.), poly(vinylidene fluoride) and copolymers thereof (including, for example, PVDF-co-HFP), poly(vinylidene chloride), mixtures, blends, or alloys. Examples of useful block copolymers include ABA type copolymers (e.g., styrene-EP-styrene) ("EP" means ethylene propylene) or AB (e.g., styrene-EP) polymers, KRATON styrene-b-butadiene and styrene-b hydrogenated butadiene (ethylene propylene) available from Kraton Polymers US LLC of Houston, TX; and SYMPATEX polyester-b-ethylene oxide available from SympaTex Technologies Inc. of Hampton, NH. Various combinations of non-reactive polymers can be used if desired.

[0211] Addition non-reactive polymers such as poly(vinylidene fluoride), syndiotactic polystyrene, copolymers of vinylidene fluoride and hexafluoropropylene, polyvinyl acetate, amorphous addition polymers such as polystyrene, poly(vinyl chloride) and its various copolymers, and poly(methyl methacrylate) and its various copolymers are soluble or dispersible in various solvents and solvent blends at low pressure and temperature, and therefore can be solution-spun relatively easily. However, highly crystalline polymers such as polyethylene and polypropylene typically require high temperature and high pressure solvents or solvent blends when they are solution-spun. Therefore, solution spinning of polyethylene and polypropylene is very difficult.

[0212] Depending on the need and depending on the polymer non-reactive resinous aldehyde composition, for example, the self-crosslinking reaction described herein may require a strong acid catalyst such as sulfonic acid, for example, para-toluenesulfonic acid.In certain embodiments, the catalyst such as acid catalyst is preferably used in an amount of at least 4 wt% based on polymer solids to enhance the self-crosslinking rate.Typically, in the self-crosslinking reaction of the present disclosure, the catalyst such as acid catalyst is used in an amount of 10 wt% or less.

[0213] Manufacturing method In another aspect, the present disclosure describes a method for making a fine fiber layer and a support layer.

[0214] The fine fiber layer may be formed by any suitable method. For example, the fine fibers of the present disclosure may be produced using a variety of techniques, including electrospinning, force spinning, wet spinning, dry spinning, melt spinning, extrusion spinning, direct spinning, gel spinning, and the like.

[0215] In some embodiments, the first fine fiber layer is preferably formed on a support layer.

[0216] The fine fibers are collected on a support layer, for example, during electrostatic or melt spinning, and are often heat treated after fiber production. Preferably, a first layer of fine fibers is disposed as a layer of fibers on a first surface of a layer of permeable coarse fiber media (i.e., a support layer).

[0217] Fiber manufacturing method In the fiber spinning process that produces the fine fibers of the present disclosure, the polymer to be spun is typically converted to a fluid state (e.g., by dissolving or melting in a solvent). The fluid polymer is then forced through a spinneret, where it cools to a rubbery state and then to a solid state. The aldehyde composition may migrate to the surface during the fluid polymer's transition to a solid state. Wet spinning is typically used for polymers that need to be dissolved in the solvent being spun. The spinneret is immersed in a chemical bath that causes the fiber to precipitate and coagulate as it exits. The name of the process comes from this "wet" bath. Acrylic, rayon, aramid, modacrylic fibers, and spandex are produced by this process. Dry spinning is also used for polymers dissolved in a solvent. This differs in that coagulation is achieved by evaporation of the solvent, which is usually achieved by air or an inert gas stream. Because there is no precipitating liquid involved, there is no need to dry the fiber, and the solvent is more easily recovered. Melt spinning is used for polymers that can be melted. After the polymer is extruded from the spinneret, it is solidified by cooling.

[0218] In a typical process, solid polymer pellets or granules are fed into an extruder. The pellets are compressed, heated, and melted by the extrusion screw, then fed into a spinning pump and into a spinneret. The direct spinning process avoids the solid polymer pellet stage. The polymer melt is produced from the raw material and a polymer finisher that is pumped directly to the spinning mill. Direct spinning is primarily applied in the production of polyester fibers and filaments, contributing to high production capacities (greater than 100 tons / day). Gel spinning, also known as dry-wet spinning, is used to achieve high strength or other special properties in the fiber. The polymer is in a "gel" state, only partially liquid, which causes some of the polymer chains to bond together. These bonds create strong interchain forces in the fiber, thereby increasing its tensile strength. The polymer chains within the fiber also have a high degree of orientation, thereby increasing its strength. The fiber is first air-dried and then further cooled in a liquid bath. This process produces some high-strength polyethylene and aramid fibers.

[0219] Another method for producing fine fibers of the present disclosure is the meltblowing process. Meltblowing (also referred to herein as "MB") is a process for producing fibrous webs or articles directly from polymers or resins using high-velocity air or another suitable force to attenuate the filaments. This process is unique because it is used almost exclusively to produce microfibers rather than fibers of the diameter of conventional textile fibers. MB microfibers generally have diameters in the range of 2-4 μm (micrometers, or microns, or μ), but they can be as small as 0.1 μm or as large as 10-15 μm. Differences between MB nonwovens and other nonwovens, such as softening, coverage or opacity, and porosity, can generally be attributed to differences in filament diameter. As soon as the molten polymer is extruded through the die holes, high-velocity hot air streams (exiting the top and bottom sides of the die nose piece) attenuate the polymer stream, forming microfibers. As the hot air stream containing microfibers advances toward the collector screen, it entrains a large amount of surrounding air (also called secondary air), which cools and solidifies the fibers. The solidified fibers then randomly deposit on the collection screen, forming a self-bonded nonwoven web. The fibers are generally randomly deposited (and highly entangled) due to turbulence in the airflow, but there is a slight bias in the machine direction due to some directionality imparted by the collector movement. The collector speed and collector distance from the die nose piece can be varied to produce various meltblown webs. A vacuum is usually applied inside the collector screen to draw out the hot air and enhance the fiber placement process.

[0220] Any of the methods listed above for producing fine fibers of the present disclosure can be used to produce the permeable coarse fibrous material for the support layer. Spunbond technology can be used to produce the permeable coarse fibrous material for the support layer. Spunbond fabrics are produced by depositing extruded, spun filaments in a uniform, random manner onto a collecting belt, followed by bonding the fibers. The fibers are separated during the web-laying process by air jets or electrostatic charges. The collecting surface is usually perforated to prevent airflow from deflecting and transporting the fibers in an uncontrolled manner. Bonding imparts strength and integrity to the web by applying heated rolls or heated needles to partially melt the polymer and fuse the fibers together. Because molecular orientation increases the melting point, fibers that are not highly oriented can be used as thermally bonded fibers. Polyethylene or random ethylene propylene copolymers are used as low-melting bonding sites. Spunbond products are used in carpet backing, geotextiles, and disposable medical / hygienic products. Because fabric production is combined with fiber production, this process is generally more economical than using staple fibers to produce nonwoven fabrics. The spinning process is similar to continuous filament yarn production and utilizes similar extruder conditions for a given polymer. Fibers are formed when the molten polymer exits the spinneret and is quenched by cold air. The goal of this process is to produce a wide web, so multiple spinnerets are arranged side by side to produce enough fiber across the width. A group of spinnerets is often described as a block or bank. In commercial production, two or more blocks are used in tandem to increase fiber coverage.

[0221] In the spunbond process, the output of the spinneret typically consists of hundreds or more individual filaments that must be attenuated to orient the molecular chains within the fiber before deposition on a moving belt or screen to increase fiber strength and reduce extensibility. This is accomplished by rapidly stretching the plastic fiber immediately after it leaves the spinneret. In practice, the fiber is accelerated mechanically or pneumatically. In most processes, the fiber is pneumatically accelerated in bundles of multiple filaments, although other arrangements have been described in which linearly aligned rows of individual filaments are pneumatically accelerated.

[0222] In conventional fabric spunbonding processes, some orientation of the fibers is achieved by blowing the filaments at a speed of about 3,200 m / min to produce a partially oriented yarn (POY). The POY may be mechanically stretched in a separate step to enhance strength. In spunbonding, the produced filament bundle is partially oriented by air pressure acceleration speeds of 6,000 m / min or more. 2 ), such high speeds result in partial orientation and high speed of web formation. Formation of wide webs at high speeds is a highly productive operation.

[0223] For many applications, partial orientation of the coarse fibers in the support layer increases strength and reduces extensibility sufficiently to produce a functional fabric (e.g., diaper coverstock). However, some applications, such as primary carpet backing, require filaments with very high tensile strength and low elongation. For such applications, the filaments are stretched over heated rolls at a typical stretch ratio of 3.5:1. The filaments are then accelerated by air pressure onto a moving belt or screen. This process is slower but produces a stronger web.

[0224] Spunbond webs are formed by pneumatic deposition of bundles of filaments onto a moving belt. Air guns use high pressure air to move the filaments through a lower pressure compression zone, but higher velocities, as in the case of a Venturi tube. For a web to achieve maximum uniformity and coverage, the individual filaments can be separated before reaching the belt. Under tension and prior to deposition, this separation is achieved by inducing an electrostatic charge on the bundle. The charge can be induced by triboelectricity or by applying a high voltage charge. The former is the result of rubbing the filaments against a grounded conductive surface. The electrostatic charge on the filaments should be at least 30,000 electrostatic units per square meter (esu / m 2 ) can be.

[0225] The fine fibers of the present disclosure can be preferably manufactured using an electrospinning process. An electrospinning apparatus suitable for forming fine fibers includes a reservoir containing a fine fiber-forming solution and a discharge device, generally consisting of a rotating portion including a plurality of offset holes. As it rotates in an electrostatic field, droplets of the solution on the discharge device are accelerated by the electrostatic field toward a collection medium. A grid, on which the collection medium (i.e., a substrate or a combination of substrates) is disposed, faces an emitter disposed away from it. Air can be drawn through the grid. A high-voltage electrostatic potential is maintained between the emitter and the grid by a suitable electrostatic voltage source. To collect the fibers, a substrate is disposed between the emitter and the grid.

[0226] Specifically, the electrostatic potential between the grid and the emitter imparts an electric charge to the material, which then expels the liquid as thin fibers, which are elongated toward the grid and collected on the substrate upon arrival. In the case of polymers in solution, a portion of the solvent evaporates from the fibers during their flight to the substrate. As the solvent continues to evaporate, the thin fibers adhere to the substrate fibers. The electrostatic field strength is selected to ensure that the polymer material is accelerated from the emitter to the collection medium, sufficient to form the polymer material into a very thin microfiber or nanofiber structure. The deposition time can be used to control the number of expelled fibers deposited on the formation medium, thereby allowing for control of the thickness of each layer deposited thereon. Electrospinning processes typically use polymer solutions with a solids concentration (on the polymer) of 5% to 20%. Safe and easily used solvents are desirable in industrial applications. On the other hand, fibers formed with such solvents often need to survive and function in a wide range of environments.

[0227] Method for producing a layer of fine fibers comprising single diameter fibers In another aspect, the present disclosure describes the production of a layer of fine fibers deposited on a support layer. As further described above, the layer of fine fibers can include a single (or first) layer of fine fibers containing both thick fine fibers having an average diameter at least three times the average fiber diameter of the thinner fine fibers, or the layer of fine fibers can include at least two layers of fine fibers, with the first layer of fine fibers containing fine fibers having an average diameter at least three times the average fiber diameter of the thinnest fibers of the second fine fiber layer. This section describes a method for producing a layer of fine fibers, including a first fine fiber layer containing single-diameter fine fibers. The following section describes the production of a layer of fine fibers containing both thick fine fibers having an average diameter at least three times the average fiber diameter of the thinner fine fibers of the same layer (e.g., the first fine fiber layer or the second fine fiber layer).

[0228] The appropriate polymer and polymer concentration can be selected by one of ordinary skill in the art to provide the desired diameter and other properties for the first layer of fine fibers. For example, in some embodiments, the fibers are preferably compatible with the fluids they are used to filter (e.g., hydraulic fluids, fuels, lubricants). A fiber is considered compatible with a fluid if it does not react with the fluid or any other components and additives therein and is insoluble in the fluid (so that the fine fiber structure does not chemically or physically deteriorate upon mere contact with the fluid). In an exemplary embodiment, the polymer solution comprises Solution 2 or Solution 4 described in the Examples.

[0229] Method for producing a layer of fine fibers containing mixed diameter fine fibers In a further aspect, the present disclosure describes the manufacture of a fine fiber layer comprising a layer of fine fibers that includes both thick fine fibers having an average diameter at least three times the average fiber diameter of the thinner fine fibers in the same layer. Such a layer can be deposited directly onto a support layer (i.e., a first fine fiber layer), or it can be deposited onto a first fine fiber layer (i.e., a second fine fiber layer), or both. In addition, a layer of fine fibers that includes both thick fine fibers having an average diameter at least three times the average fiber diameter of the thinner fine fibers in the same layer can form a third fine fiber layer, a fourth fine fiber layer, etc.

[0230] The appropriate polymer and polymer concentration can be selected by one of ordinary skill in the art to provide the desired diameter and other properties for the second layer of fine fibers. For example, in some embodiments, the fibers are preferably compatible with the fluids they are used to filter (e.g., hydraulic fluids, fuels, lubricants). A fiber is considered compatible with a fluid if it does not react with the fluid or any other components and additives therein and is insoluble in the fluid (so that the fine fiber structure does not chemically or physically deteriorate upon mere contact with the fluid). In an exemplary embodiment, the polymer solution includes Solution 1, Solution 2, Solution 3, and / or Solution 4 described in the Examples.

[0231] 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 simultaneously by cospinning, which involves 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 using very short (e.g., up to 10 seconds, up to 20 seconds, or up to 30 seconds) pulses of each polymer solution.

[0232] 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, for example, 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 fibers of different diameters are layered, the fibers can be formed by alternating fiber formation using pulses of each polymer solution for at least 30 seconds.

[0233] Any suitable method can be used to form a combination of layers of thin and thick fine fibers. 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 Tables 1A-1C. 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 Tables 1A-1C. In some embodiments, a combination of layers can be formed that includes both layered and mixed fiber structures. An exemplary method of forming such a structure is described in Example 7.

[0234] Usage and filter elements 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 located downstream of the support layer.

[0235] In some embodiments, the filter media, including, for example, the filter media contained in the filter element, may be pleated.

[0236] The filter media of the present disclosure can be manufactured into filter elements, including 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.

[0237] In some embodiments, the filter element may include an efficiency layer, and the efficiency layer may include a filter medium disclosed herein. That is, the filter medium described herein may form the efficiency layer or form a portion of the efficiency layer. In some embodiments, the filter element may further include a load layer. Any suitable medium may be used as the load layer, including, for example, a layer of meltblown nonwoven fabric or another medium designed to act as a depth load layer.

[0238] 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 particulates from a fluid stream.

[0239] In some embodiments, the filter media of the present disclosure may 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 may be positioned upstream of other layers in the filter element.

[0240] In some embodiments, the filter media of the present disclosure can be used to filter gases. The gas 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 substantial amount of entrained oil therein as an aerosol. In a further exemplary embodiment, the filter media of the present disclosure can be used in a gas turbine.

[0241] 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 is used to filter liquids, the filter media can be positioned upstream of other layers in 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 effluents, cooling water, process water, etc.

[0242] In some exemplary embodiments, the filter media disclosed herein may replace an efficiency layer in a filter element of WO 2015 / 157638; WO 2016 / 210153; WO 2018 / 208819; U.S. Patent No. 7,160,451; U.S. Patent No. 7,238,285; U.S. Patent No. 7,988,860; U.S. Patent No. 8,263,214; U.S. Patent No. 8,834,610; U.S. Patent No. 8,673,040; or U.S. Patent No. 8,721,756.

[0243] In some embodiments, the filter media of the present disclosure can be used in applications where flow rates fluctuate, including, for example, hydraulic applications. Fluctuations in flow rates, including, for example, cyclical flow conditions, can have a negative impact on filter media performance, particularly filter media efficiency, because the fluctuations in flow rates provide multiple opportunities for particles to pass through the media openings.

[0244] At the time of the present invention, the impact of varying flow rate on filter media performance was typically minimized by increasing the efficiency of the filter media, but increasing the efficiency of the filter media also results in a corresponding increase in pressure drop, i.e., an increase in the pressure required to force fluid through the filter media. Such an increase in pressure drop creates more opportunities for the filter to be bypassed (e.g., by a bypass valve), increasing energy consumption and shortening filter life. In contrast, the filter media of the present disclosure can achieve increased efficiency under cyclic flow conditions without worsening pressure drop.

[0245] Additional exemplary embodiments of filter elements comprising the filter media described herein and methods of making and using those filter elements, particularly under cyclic flow conditions, are provided in a co-pending application entitled FILTER MEDIUM COMPRISING A FINE FIBER LAYER (Attorney Docket No. 0444.000106WO01), filed on even date herewith.

[0246] 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.

[0247] Exemplary Filter Media Embodiments Comprising At Least One Fine Fiber Layer Embodiment A1 is a filter medium comprising a support layer and a first layer of fine fibers, wherein the first layer of fine fibers is deposited on the support layer, the first layer of fine fibers comprising thick fine fibers and thin fine fibers, the thick fine fibers having an average diameter at least three times the average diameter of the thin fine fibers.

[0248] Embodiment A2 is the filter medium of embodiment A1, wherein the large fine fibers in the first layer of fine fibers have an average diameter of at least 1 μm or greater than 1 μm, or the large fine fibers in the first layer of fine fibers 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, or both.

[0249] Embodiment A3 is the filter medium of embodiment A1 or A2, wherein the first layer of fine fibers comprises fine fine fibers, and the fine fine fibers have an average diameter of at least 0.2 μm, or the fine fine fibers 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, or both.

[0250] Embodiment A4 is the filter medium of any one of the above embodiments, wherein the first layer of fine fibers comprises at most 10% coarse fine fibers or at most 20% coarse fine fibers.

[0251] Embodiment A5 is the filter medium of any one of the above embodiments, wherein the first layer of fine fibers comprises at least 3% and at most 9% thick fine fibers, at least 5% and at most 7% thick fine fibers, or at least 4% and at most 8% thick fine fibers.

[0252] Embodiment A6 is the filter media of any one of the above embodiments, wherein the first layer of fine fibers comprises a proportion of one or more of the thick fine fibers of Set A5, Set A6, Set B, Set D, Set D5, Set D6, Set E, Set I, Set I5, Set I6, Set J, or Set L of Tables 1A-1C.

[0253] Embodiment A7 is the filter medium of any one of embodiments A1 to A6, in which the proportion of thick fine fibers is determined based on the spinning time.

[0254] Embodiment A8 is the filter medium of any one of Embodiments A1-A6, wherein the proportion of thick fine fibers is determined using microscopic observation or nano-CT.

[0255] Embodiment A9 is the filter medium of any one of the above embodiments, wherein the first layer of fine fibers comprises a layered fiber structure.

[0256] Embodiment A10 is the filter medium of Embodiment A9, wherein the first layer of fine fibers comprises one or more layered fiber structures of Set A5, Set B, Set D5, Set E, Set I5, or Set J of Tables 1A-1C.

[0257] Embodiment A11 is the filter medium of embodiment A9, wherein the first layer of fine fibers comprises thin fine fibers and thick fine fibers, and within the first layer of fine fibers, the thin fine fibers are deposited on a first sublayer of thick fine fibers, and a second sublayer of thick fine fibers is deposited on the thin fine fibers.

[0258] Embodiment A12 is the filter medium of any one of Embodiments A1-A8, wherein the first layer of fine fibers comprises a mixed fiber structure.

[0259] Embodiment A13 is the filter medium of Embodiment A12, wherein the first layer of fine fibers comprises one or more mixed fiber structures of Set A6, Set D, Set D6, Set I, or Set L of Tables 1A-1C.

[0260] Embodiment A14 is the filter medium of any one of the above embodiments, further comprising a second fine fiber layer.

[0261] Embodiment A15 is the filter medium of any one of the previous embodiments, wherein the fine fibers are compatible with at least one of hydraulic fluid, fuel, or lubricant.

[0262] Embodiment A16 is the filter medium of any one of the above embodiments, wherein the support layer comprises nylon.

[0263] Embodiment A17 is the filter medium of any one of the above embodiments, wherein the support layer has an average 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 and 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.

[0264] Embodiment A18 is the filter medium of Embodiment A17, wherein the mean intermediate flow pore size is determined using capillary flow porometry.

[0265] Embodiment A19 is the filter medium of any one of the above embodiments, wherein the support layer has an average 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.

[0266] Embodiment A20 is the filter medium of embodiment A19, wherein the average maximum pore size is determined using capillary flow porometry.

[0267] Embodiment A21 is the filter medium of any one of the above embodiments, wherein the support layer has an average minimum pore size of at least 5 μm, at least 10 μm, at least 15 μm, at least 20 μm, at least 25 μm, at least 30 μm, at least 35 μm, at least 40 μm, or at least 50 μm.

[0268] Embodiment A22 is the filter medium of embodiment A21, wherein the average minimum pore size is determined using capillary flow porometry.

[0269] Embodiment A23 is the filter medium of any one of the above embodiments, wherein the support layer has an average intermediate flow pore size, and the average intermediate flow pore size of the support layer does not vary by more than 30%, does not vary by more than 25%, or does not vary by more than 15% across the length and width of the medium.

[0270] Embodiment A24 is the filter medium of any one of the above embodiments, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average maximum pore size of at most 14 μm, at most 15 μm, or at most 20 μm, or the filter medium has a composite average maximum pore size of at least 0.1 μm, or both.

[0271] Embodiment A25 is the filter medium of any one of the above embodiments, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average mean flow pore size of at most 11 μm, at most 9 μm, or at most 6 μm, or the filter medium has a composite average mean flow pore size of at least 0.1 μm, or both.

[0272] Embodiment A26 is the filter medium of embodiment A24 or A25, wherein the composite pore size is determined using capillary flow porometry.

[0273] Embodiment A27 is the filter medium of any one of the above embodiments, wherein the thick fibrils have a diameter at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the thin fibrils.

[0274] Embodiment A28 is the filter medium of any one of the above embodiments, wherein the first fine fiber layer has a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm, or wherein the first fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm, or both.

[0275] Embodiment A29 is the filter medium of embodiment A28, wherein the thickness of the fine fiber layer is determined using scanning electron microscopy (SEM).

[0276] Embodiment A30 is the filter medium of any one of the above embodiments, wherein the support layer comprises a spunbond layer.

[0277] Embodiment A31 is a filter element comprising the filter medium of any one of the above embodiments.

[0278] Embodiment A32 is the filter element of embodiment A31, wherein the filter element includes an efficiency layer, and the efficiency layer includes a filter media.

[0279] Embodiment A33 is the filter element of embodiment A32, wherein the filter element further comprises a loading layer.

[0280] Exemplary Filter Media Embodiments Comprising At Least Two Fine Fiber Layers Embodiment B1 is a filter medium comprising a support layer, a first layer of fine fibers, and a second layer of fine fibers, wherein the first layer of fine fibers is deposited on the support layer and comprises fibers having an average diameter at least three times the average fiber diameter of the fine fibers of the second layer of fine fibers, and the second layer of fine fibers is deposited on the first layer of fibers.

[0281] Embodiment B2 is the filter medium of embodiment B1, wherein the fine fibers in the first layer of fine fibers have an average diameter greater than 0.6 μm, at least 0.7 μm, at least 0.8 μm, at least 0.8 μm, at least 1 μm, or greater than 1 μm; or the fine fibers in the first layer of fine fibers 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, or both.

[0282] Embodiment B3 is the filter medium of embodiment 1 or 2, wherein the second layer of fine fibers comprises fine fibers of mixed diameters.

[0283] Embodiment B4 is the filter medium of embodiment B3, wherein the second layer of fine fibers comprises thick fine fibers and thin fine fibers, the thick fine fibers having an average diameter at least three times the average diameter of the thin fine fibers in the second layer of fine fibers.

[0284] Embodiment B5 is the filter medium of embodiment B3 or B4, wherein the second layer of fine fibers comprises thick fine fibers and thin fine fibers, and the thick fine fibers have an average diameter of at least 1 μm or greater than 1 μm, or the thick fine fibers 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, or both, and the thin fine fibers have an average diameter of at least 0.2 μm, or the thin fine fibers have an average diameter of at most 0.6 μm, or both.

[0285] Embodiment B6 is the filter medium of embodiment B4 or B5, wherein the thick microfibers have an average diameter greater than 1 μm.

[0286] Embodiment B7 is the filter medium of any one of Embodiments B4-B6, wherein the second layer of fine fibers includes at most 10% coarse fine fibers or at most 20% coarse fine fibers.

[0287] Embodiment B8 is the filter medium of any one of embodiments B4-B7, wherein the second layer of fine fibers comprises at least 3% and at most 9% coarse fine fibers, at least 5% and at most 7% coarse fine fibers, or at least 4% and at most 8% coarse fine fibers.

[0288] Embodiment B9 is the filter media of any one of Embodiments B4-B6, wherein the second layer of fine fibers comprises a proportion of one or more of the thick fine fibers of Set A5, Set A6, Set B, Set D, Set D5, Set D6, Set E, Set I, Set I5, Set I6, Set J, or Set L of Tables 1A-1C.

[0289] Embodiment B10 is the filter medium of any one of embodiments B7 to B9, in which the proportion of thick fine fibers is determined based on spinning time.

[0290] Embodiment B11 is the filter medium of any one of Embodiments B7-B9, wherein the proportion of thick fine fibers is determined using microscopic observation or nano-CT.

[0291] Embodiment B12 is the filter medium of any one of Embodiments B3-B11, wherein the second layer of fine fibers comprises a layered fiber structure.

[0292] Embodiment B13 is the filter medium of Embodiment B12, wherein the second layer of fine fibers comprises one or more layered fiber structures of Set A5, Set B, Set D5, Set E, Set I5, or Set J of Tables 1A-1C.

[0293] Embodiment B14 is the filter medium of embodiment B12, wherein the second layer of fine fibers comprises thin fine fibers and thick fine fibers, and within the second layer of fine fibers, the thin fine fibers are deposited on a first sublayer of thick fine fibers and a second sublayer of thick fine fibers are deposited on the thin fine fibers.

[0294] Embodiment B15 is the filter medium of any one of Embodiments B3-B11, wherein the second layer of fine fibers comprises a mixed fiber structure.

[0295] Embodiment B16 is the filter medium of Embodiment B15, wherein the second layer of fine fibers comprises one or more mixed fiber structures of Set A6, Set D, Set D6, Set I, or Set L of Tables 1A-1C.

[0296] Embodiment B17 is the filter medium of any one of Embodiments B3-B11, wherein the second layer of fine fibers includes a layer of thin fine fibers, followed by a layer of mixed thin and thick fine fibers, and a layer of thick fine fibers.

[0297] Embodiment B18 is the filter medium of any one of Embodiments B1-B17, wherein the fine fibers are compatible with at least one of a hydraulic fluid, a fuel, or a lubricant.

[0298] Embodiment B19 is the filter medium of any one of embodiments B1-B18, wherein the support layer comprises nylon.

[0299] Embodiment B20 is the filter medium of any one of Embodiments B1-B19, wherein the support layer has an average 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 and 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.

[0300] Embodiment B21 is the filter medium of embodiment B20, wherein the mean intermediate flow pore size is determined by capillary flow porometry.

[0301] Embodiment B22 is the filter medium of any one of Embodiments B1-B21, wherein the support layer has an average 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.

[0302] Embodiment B23 is the filter medium of embodiment B22, wherein the average maximum pore size is determined by capillary flow porometry.

[0303] Embodiment B24 is the filter medium of any one of Embodiments B1-B23, wherein the support layer has an average minimum pore size of at least 5 μm, at least 10 μm, at least 15 μm, at least 20 μm, at least 25 μm, at least 30 μm, at least 35 μm, at least 40 μm, or at least 50 μm.

[0304] Embodiment B25 is the filter medium of embodiment B24, wherein the average minimum pore size is determined using capillary flow porometry.

[0305] Embodiment B26 is the filter medium of any one of Embodiments B1-B25, wherein the support layer has an average intermediate flow pore size, and the average intermediate flow pore size of the support layer does not vary by more than 30%, does not vary by more than 25%, or does not vary by more than 15% across the length and width of the medium.

[0306] Embodiment B27 is the filter medium of any one of Embodiments B1-B26, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average maximum pore size of at most 14 μm, at most 15 μm, or at most 20 μm, or the filter medium has a composite average maximum pore size of at least 0.1 μm, or both.

[0307] Embodiment B28 is the filter medium of any one of Embodiments B1-B27, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average mean flow pore size of at most 11 μm, at most 9 μm, or at most 6 μm, or the filter medium has a composite average mean flow pore size of at least 0.1 μm, or both.

[0308] Embodiment B29 is the filter medium of embodiment B27 or B28, wherein the composite pore size is determined using capillary flow porometry.

[0309] Embodiment B30 is the filter medium of any one of Embodiments B1-B29, wherein the first layer of fine fibers comprises fine fibers having a diameter at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the fiber diameter of the fine fibers of the second layer of fine fibers.

[0310] Embodiment B31 is the filter medium of any one of Embodiments B1-B30, wherein the first fine fiber layer has a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm, or the first fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm, or both.

[0311] Embodiment B32 is the filter medium of any one of Embodiments B1-B31, wherein the second fine fiber layer has a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm, or the second fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, at most 40 μm, or at most 45 μm, or both.

[0312] Embodiment B33 is the filter medium of Embodiments B31-B32, wherein the thickness of the first fine fiber layer or the second fine fiber layer or both is determined using scanning electron microscopy (SEM).

[0313] Embodiment B34 is the filter medium of any one of Embodiments B1-B33, wherein the support layer comprises a spunbond layer.

[0314] Embodiment B35 is a filter element including the filter medium of any one of embodiments B1 to B34.

[0315] Embodiment B36 is the filter element of embodiment B35, wherein the filter element comprises an efficiency layer, and the efficiency layer comprises a filter media.

[0316] Embodiment B37 is the filter element of embodiment B36, wherein the filter element further comprises a loading layer.

[0317] Exemplary Layered Filter Media Embodiments Embodiment C1 is a filter medium comprising a support layer, a first layer of fine fibers, and a second layer of fine fibers, wherein the first layer of fine fibers is deposited on the support layer, the second layer of fine fibers is deposited on the first layer of fibers, and the second layer of fine fibers further comprises thin fine fibers and thick fine fibers, the thick fine fibers having an average diameter at least three times the average diameter of the thin fine fibers, the thin fine fibers are deposited on the first layer of fine fibers, and the thick fine fibers are deposited on the thin fine fibers, and the first layer of fine fibers comprises fine fibers having an average diameter at least three times the average fiber diameter of the thin fine fibers in the second layer of fine fibers.

[0318] Embodiment C2 is the filter medium of embodiment C1, wherein the coarse fibers of the second layer of fibers comprise at most 10% of the fibers of the second layer of fibers.

[0319] Embodiment C3 is the filter medium of embodiment C1 or C2, wherein the coarse fibers of the second layer of fibers comprise at least 5% and at most 7% of the fibers of the second layer of fibers.

[0320] Embodiment C4 is the filter medium of embodiment C1, wherein the second layer of fine fibers comprises one or more layered fiber structures of Set A5, Set B, Set D5, Set E, Set I5, or Set J of Tables 1A-1C.

[0321] Embodiment C5 is the filter medium of any one of embodiments C2-C4, wherein the proportion of thick fine fibers is determined based on spinning time.

[0322] Embodiment C6 is the filter media of any one of embodiments C2-C4, wherein the percentage of thick fine fibers is determined using microscopy or nano-CT.

[0323] Embodiment C7 is the filter medium of any one of embodiments C1-C6, wherein the thick fibrils of the second layer of fine fibers have an average diameter of at least 1 μm or greater than 1 μm, or the thick fibrils of the second layer of fine fibers 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, or both.

[0324] Embodiment C8 is the filter medium of any one of embodiments C1-C7, wherein the first layer of fine fibers comprises fine fibers having an average diameter of at least 0.6 μm, at least 0.7 μm, at least 0.8 μm, or at least 0.9 μm, at least 1 μm, or greater than 1 μm, or wherein the first layer of fine fibers comprises fine fibers having 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, or both.

[0325] Embodiment C9 is the filter medium of any one of embodiments C1-C8, wherein the fine fibers in the second layer of fine fibers have an average diameter of at least 0.2 μm, or the fine fibers in the second layer of fine fibers have an average diameter of at most 0.6 μm, or both.

[0326] Embodiment C10 is the filter media of any one of embodiments C1-C9, wherein the support layer comprises nylon.

[0327] Embodiment C11 is the filter medium of any one of embodiments C1-C10, wherein the support layer has an average medium 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 and 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.

[0328] Embodiment C12 is the filter medium of embodiment C11, wherein the average minimum pore size is determined using capillary flow porometry.

[0329] Embodiment C13 is the filter medium of any one of embodiments C1-C12, wherein the support layer has an average 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.

[0330] Embodiment C14 is the filter medium of embodiment C13, wherein the average maximum pore size is determined using capillary flow porometry.

[0331] Embodiment C15 is the filter medium of any one of embodiments C1-C14, wherein the support layer has an average minimum pore size of at least 5 μm, at least 10 μm, at least 15 μm, at least 20 μm, at least 25 μm, at least 30 μm, at least 35 μm, at least 40 μm, or at least 50 μm.

[0332] Embodiment C16 is the filter medium of embodiment C15, wherein the average minimum pore size is determined using capillary flow porometry.

[0333] Embodiment C17 is the filter medium of any one of embodiments C1-C16, wherein the support layer has an average intermediate flow pore size, and the average intermediate flow pore size of the support layer does not vary by more than 30%, does not vary by more than 25%, or does not vary by more than 15% across the length and width of the medium.

[0334] Embodiment C18 is the filter medium of any one of embodiments C1-C17, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average maximum pore size of at most 14 μm, at most 15 μm, or at most 20 μm, or the filter medium has a composite average maximum pore size of at least 0.1 μm, or both.

[0335] Embodiment C19 is the filter medium of any one of embodiments C1-C18, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average mean flow pore size of at most 11 μm, at most 9 μm, or at most 6 μm, or the filter medium has a composite average mean flow pore size of at least 0.1 μm, or both.

[0336] Embodiment C20 is the filter medium of embodiment C18 or C19, wherein the composite pore size is determined using capillary flow porometry.

[0337] Embodiment C21 is the filter medium of any one of embodiments C1-C20, wherein the thicker fibrils have a diameter at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the thinner fibrils.

[0338] Embodiment C22 is the filter medium of any one of embodiments C1-C21, wherein the first fine fiber layer has a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm, or the first fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm, or both.

[0339] Embodiment C23 is the filter medium of any one of embodiments C1-C22, wherein the second fine fiber layer has a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm, or wherein the second fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, at most 40 μm, or at most 45 μm, or both.

[0340] Embodiment C24 is the filter medium of embodiment C22 or C23, wherein the thickness of the first fine fiber layer or the second fine fiber layer or both is determined using scanning electron microscopy (SEM).

[0341] Embodiment C25 is the filter medium of any one of embodiments C1-C24, wherein the support layer comprises a spunbond layer.

[0342] Embodiment C26 is a filter element including the filter medium of any one of embodiments C1 to C25.

[0343] Embodiment C27 is the filter element of embodiment C26, wherein the filter element includes an efficiency layer, and the efficiency layer includes a filter media.

[0344] Embodiment C28 is the filter element of embodiment C27, wherein the filter element further comprises a loading layer.

[0345] Exemplary Mixed Filter Media Embodiments Embodiment D1 is a filter medium comprising a support layer, a first layer of fine fibers, and a second layer of fine fibers, wherein the first layer of fine fibers is deposited on the support layer, the second layer of fine fibers is deposited on the first layer of fibers, and further wherein the second layer of fine fibers comprises thin fine fibers and thick fine fibers, wherein the thick fine fibers have an average diameter at least three times the average diameter of the thin fine fibers and the thin fine fibers are mixed with the thick fine fibers, and the first layer of fine fibers comprises fine fibers having an average diameter at least three times the average fiber diameter of the thin fine fibers in the second layer of fine fibers.

[0346] Embodiment D2 is the filter medium of embodiment D1, wherein the coarse fibers of the second layer of fibers comprise at most 10% of the fibers of the second layer of fibers.

[0347] Embodiment D3 is the filter medium of embodiment D1 or D2, wherein the thick fibers of the second layer of fibers comprise at least 3% and at most 9%, at least 5% and at most 7%, or at least 4% and at most 8% of the fibers of the second layer of fibers.

[0348] Embodiment D4 is the filter media of embodiment D1, wherein the second layer of fine fibers comprises one or more mixed fiber structures of Set A6, Set D, Set D6, Set I, or Set L of Tables 1A-1C.

[0349] Embodiment D5 is the filter medium of any one of embodiments D2 to D4, wherein the proportion of thick fine fibers is determined based on spinning time.

[0350] Embodiment D6 is the filter medium of any one of embodiments D2-D4, wherein the percentage of thick fine fibers is determined using microscopy or nano-CT.

[0351] Embodiment D7 is the filter medium of any one of Embodiments D1-D6, wherein the thick fibrils of the second layer of fibrils have an average diameter of at least 1 μm or greater than 1 μm, or the thick fibrils of the second layer of fibrils 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, or both.

[0352] Embodiment D8 is the filter medium of any one of Embodiments D1-D7, wherein the first layer of fine fibers comprises thin fine fibers having an average diameter of at least 0.6 μm, at least 0.7 μm, at least 0.8 μm, or at least 0.9 μm, at least 1 μm, or greater than 1 μm; or the first layer of fine fibers comprises fine fibers having 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, or both.

[0353] Embodiment D9 is the filter medium of any one of embodiments D1-D8, wherein the fine fibers of the second layer of fine fibers have an average diameter of at least 0.2 μm, or the fine fibers of the second layer of fine fibers 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, or both.

[0354] Embodiment D10 is the filter media of any one of embodiments D1-D9, wherein the support layer comprises nylon.

[0355] Embodiment D11 is the filter medium of any one of Embodiments D1-D10, wherein the support layer has an average medium 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 and 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.

[0356] Embodiment D12 is the filter medium of embodiment D11, wherein the mean intermediate flow pore size is determined using capillary flow porometry.

[0357] Embodiment D13 is the filter medium of any one of Embodiments D1-D12, wherein the support layer has an average 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.

[0358] Embodiment D14 is the filter medium of embodiment D13, wherein the average maximum pore size is determined using capillary flow porometry.

[0359] Embodiment D15 is the filter medium of any one of embodiments D1-D14, wherein the support layer has an average minimum pore size of at least 5 μm, at least 10 μm, at least 15 μm, at least 20 μm, at least 25 μm, at least 30 μm, at least 35 μm, at least 40 μm, or at least 50 μm.

[0360] Embodiment D16 is the filter medium of embodiment D15, wherein the average minimum pore size is determined using capillary flow porometry.

[0361] Embodiment D17 is the filter medium of any one of Embodiments D1-D16, wherein the support layer has an average intermediate flow pore size, and the average intermediate flow pore size of the support layer does not vary by more than 30%, does not vary by more than 25%, or does not vary by more than 15% across the length and width of the medium.

[0362] Embodiment D18 is the filter medium of any one of Embodiments D1-D17, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average maximum pore size of at most 14 μm, at most 15 μm, or at most 20 μm, or the filter medium has a composite average maximum pore size of at least 0.1 μm, or both.

[0363] Embodiment D19 is the filter medium of any one of Embodiments D1-D18, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average mean flow pore size of at most 11 μm, at most 9 μm, or at most 6 μm, or the filter medium has a composite average mean flow pore size of at least 0.1 μm, or both.

[0364] Embodiment D20 is the filter medium of embodiment D18 or D19, wherein the composite pore size is determined using capillary flow porometry.

[0365] Embodiment D21 is the filter medium of any one of Embodiments D1-D20, wherein the second layer of fine fibers comprises thin fine fibers and thick fine fibers, and the thick fine fibers have a diameter at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the thin fine fibers.

[0366] Embodiment D22 is the filter medium of any one of Embodiments D1-D21, wherein the first layer of fine fibers comprises fine fibers having a diameter at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the fiber diameter of the fine fibers of the second layer of fine fibers.

[0367] Embodiment D23 is the filter medium of any one of Embodiments D1-D22, wherein the first fine fiber layer has a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm, or wherein the first fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm, or both.

[0368] Embodiment D24 is the filter medium of any one of Embodiments D1-D23, wherein the second fine fiber layer has a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm, or wherein the second fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, at most 40 μm, or at most 45 μm, or both.

[0369] Embodiment D25 is the filter medium of embodiment D23 or D24, wherein the thickness of the first fine fiber layer or the second fine fiber layer or both is determined using scanning electron microscopy (SEM).

[0370] Embodiment D26 is the filter medium of any one of embodiments D1-D25, wherein the support layer comprises a spunbond layer.

[0371] Embodiment D27 is a filter element including the filter medium of any one of embodiments D1 to D26.

[0372] Embodiment D28 is the filter element of embodiment D27, wherein the filter element includes an efficiency layer, and the efficiency layer includes a filter media.

[0373] Embodiment D29 is the filter element of embodiment D28, wherein the filter element further comprises a loading layer.

[0374] Exemplary Products of Process Embodiments Including At Least One Fine Fiber Layer Embodiment E1 is a filter medium comprising a support layer and a first layer of fine fibers, wherein the first layer of fine fibers is deposited on the support layer and comprises thin fine fibers and thick fine fibers, the thick fine fibers having an average diameter at least three times the average diameter of the thin fine fibers, and at least some of the fine fibers are prepared by a process comprising: providing a fiber-forming polymer; providing a polymer-reactive resinous aldehyde composition that is reactive with the fiber-forming polymer; and combining the fiber-forming polymer and the reactive resinous aldehyde composition to form a plurality of fine fibers.

[0375] Embodiment E2 is a filter medium comprising a support layer and a first layer of fine fibers, wherein the first layer of fine fibers is deposited on the support layer and comprises thin fine fibers and thick fine fibers, the thick fine fibers having an average diameter at least three times the average diameter of the thin fine fibers, and at least some of the fine fibers are prepared by a process comprising: providing a fiber-forming polymer comprising a non-reactive polymer, the non-reactive polymer being a polymer that cannot crosslink with the polymer non-reactive resinous aldehyde composition; providing a polymer non-reactive resinous aldehyde composition comprising one or more reactive groups that are capable of self-crosslinking; and combining the fiber-forming polymer and the reactive resinous aldehyde composition to form a plurality of fine fibers.

[0376] Embodiment E3 is a filter medium comprising a support layer and a first layer of fine fibers, the first layer of fine fibers deposited on the support layer and comprising thin fine fibers and thick fine fibers, the thick fine fibers having an average diameter at least three times the average diameter of the thin fine fibers, and at least some of the fine fibers prepared by a process comprising: providing at least one fiber-forming polymer; providing at least two reactive additives that are reactive with each other and, optionally, with the fiber-forming polymer; and combining the at least one fiber-forming polymer and the at least two reactive additives under conditions effective to form a plurality of fine fibers.

[0377] Embodiment E4 is the filter medium of any one of Embodiments E1-E3, wherein the large fibrils in the first layer of fibrils have an average diameter of at least 1 μm or greater than 1 μm, or the large fibrils in the first layer of fibrils 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, or both.

[0378] Embodiment E5 is the filter medium of any one of Embodiments E1-E4, wherein the first layer of fine fibers comprises fine fibers, and the fine fibers have an average diameter of at least 0.2 μm, or the fine fibers 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, or both.

[0379] Embodiment E6 is the filter medium of any one of Embodiments E1-E5, wherein the first layer of fine fibers includes at most 10% coarse fine fibers or at most 20% coarse fine fibers.

[0380] Embodiment E7 is the filter medium of any one of embodiments E1-E6, wherein the first layer of fine fibers comprises at least 3% and at most 9% coarse fine fibers, at least 5% and at most 7% coarse fine fibers, or at least 4% and at most 8% coarse fine fibers.

[0381] Embodiment E8 is the filter media of any one of Embodiments E1-E7, wherein the first layer of fine fibers comprises a proportion of one or more of the thick fine fibers of Set A5, Set A6, Set B, Set D, Set D5, Set D6, Set E, Set I, Set I5, Set I6, Set J, or Set L of Tables 1A-1C.

[0382] Embodiment E9 is the filter medium of any one of embodiments E6-E8, wherein the proportion of thick fine fibers is determined based on spinning time.

[0383] Example 10 is the filter medium of any one of Examples E6-E8, wherein the percentage of thick fine fibers is determined using microscopy or nano-CT.

[0384] Embodiment E11 is the filter medium of any one of Embodiments 1-10, wherein the first layer of fine fibers comprises a layered fiber structure.

[0385] Embodiment E12 is the filter medium of Embodiment E11, wherein the first layer of fine fibers comprises one or more layered fiber structures of Set A5, Set B, Set D5, Set E, Set I5, or Set J of Tables 1A-1C.

[0386] Embodiment E13 is the filter medium of embodiment E11, wherein the first layer of fibers comprises thin fibers and thick fibers, and within the first layer of fibers, the thin fibers are deposited on a first sublayer of fibers and a second sublayer of thick fibers is deposited on the thin fibers.

[0387] Embodiment E14 is the filter medium of any one of embodiments E1-E10, wherein the first layer of fine fibers comprises a mixed fiber structure.

[0388] Embodiment E15 is the filter medium of embodiment E14, wherein the first layer of fine fibers comprises one or more mixed fiber structures of Set A6, Set D, Set D6, Set I, or Set L of Tables 1A-1C.

[0389] Embodiment E16 is the filter medium of any one of embodiments E1-E15, wherein the fine fibers are compatible with at least one of a hydraulic fluid, a fuel, or a lubricant.

[0390] Embodiment E17 is the filter medium of any one of embodiments E1-E16, wherein the support layer comprises nylon.

[0391] Embodiment E18 is the filter medium of any one of embodiments E1-E17, wherein the support layer has an average medium 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 and 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.

[0392] Embodiment E19 is the filter medium of embodiment E18, wherein the mean intermediate flow pore size is determined using capillary flow porometry.

[0393] Embodiment E20 is the filter medium of any one of embodiments E1-E19, wherein the support layer has an average 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.

[0394] Embodiment E21 is the filter medium of embodiment E20, wherein the average maximum pore size is determined using capillary flow porometry.

[0395] Embodiment E22 is the filter medium of any one of Embodiments E1-E21, wherein the support layer has an average minimum pore size of at least 5 μm, at least 10 μm, at least 15 μm, at least 20 μm, at least 25 μm, at least 30 μm, at least 35 μm, at least 40 μm, or at least 50 μm.

[0396] Embodiment E23 is the filter medium of embodiment E22, wherein the average minimum pore size is determined using capillary flow porometry.

[0397] Embodiment E24 is the filter medium of any one of Embodiments E1-E23, wherein the support layer has an average intermediate flow pore size, and the average intermediate flow pore size of the support layer does not vary by more than 30%, does not vary by more than 25%, or does not vary by more than 15% across the length and width of the medium.

[0398] Embodiment E25 is the filter medium of any one of embodiments E1-E24, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average maximum pore size of at most 14 μm, at most 15 μm, or at most 20 μm, or the filter medium has a composite average maximum pore size of at least 0.1 μm, or both.

[0399] Embodiment E26 is the filter medium of any one of embodiments E1-E25, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average mean flow pore size of at most 11 μm, at most 9 μm, or at most 6 μm, or the filter medium has a composite average mean flow pore size of at least 0.1 μm, or both.

[0400] Embodiment E27 is the filter medium of embodiment E25 or E26, wherein the composite pore size is determined using capillary flow porometry.

[0401] Embodiment E28 is the filter medium of any one of embodiments E1-E27, wherein the thicker fibrils have a diameter at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the thinner fibrils.

[0402] Embodiment E29 is the filter medium of any one of embodiments E1-E28, wherein the first fine fiber layer has a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm, or wherein the first fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm, or both.

[0403] Embodiment E30 is the filter medium of embodiment E29, wherein the thickness of the first fine fiber layer is determined using scanning electron microscopy (SEM).

[0404] Embodiment E31 is the filter medium of any one of Embodiments E1-E30, wherein the support layer comprises a spunbond layer.

[0405] Embodiment E32 is the filter medium of any one of Embodiments E1-E31, further comprising a second fine fiber layer.

[0406] Embodiment E33 is a filter element including the filter medium of any one of embodiments E1-E32.

[0407] Embodiment E34 is the filter element of embodiment E33, wherein the filter element includes an efficiency layer, and the efficiency layer includes a filter media.

[0408] Embodiment E35 is the filter element of embodiment E34, wherein the filter element further comprises a loading layer.

[0409] Exemplary Products from Process Embodiments Including at Least Two Fine Fiber Layers Embodiment F1 is a filter media comprising a support layer, a first layer of fine fibers, and a second layer of fine fibers, wherein the first layer of fine fibers is deposited on the support layer and comprises thick fine fibers having an average diameter at least three times the average diameter of the thin fine fibers of the second layer of fine fibers, and the second layer of fine fibers is deposited on the first layer of fibers, and at least some of the fine fibers are prepared by a process comprising: providing a fiber-forming polymer; providing a polymer-reactive resinous aldehyde composition that is reactive with the fiber-forming polymer; and combining the fiber-forming polymer and the reactive resinous aldehyde composition to form a plurality of fine fibers.

[0410] Embodiment F2 is a filter media comprising a support layer, a first layer of fine fibers, and a second layer of fine fibers, wherein the first layer of fine fibers is deposited on the support layer and comprises thick fine fibers having an average diameter at least three times the average diameter of the thin fine fibers of the second layer of fine fibers, and the second layer of fine fibers is deposited on the first layer of fibers, and at least some of the fine fibers are prepared by a process comprising: providing a fiber-forming polymer comprising a non-reactive polymer, the non-reactive polymer being a polymer that cannot crosslink with a polymeric non-reactive resinous aldehyde composition; providing a polymeric non-reactive resinous aldehyde composition comprising one or more reactive groups that are capable of self-crosslinking; and combining the fiber-forming polymer and the reactive resinous aldehyde composition to form a plurality of fine fibers.

[0411] Embodiment F3 is a filter medium comprising a support layer, a first layer of fine fibers, and a second layer of fine fibers, wherein the first layer of fine fibers is deposited on the support layer and comprises thick fine fibers having an average diameter at least three times the average diameter of the thin fine fibers of the second layer of fine fibers, and the second layer of fine fibers is deposited on the first layer of fibers, and at least some of the fine fibers are prepared by a process comprising: providing at least one fiber-forming polymer; providing at least two reactive additives that are reactive with each other and, optionally, with the fiber-forming polymer; and combining the at least one fiber-forming polymer and the at least two reactive additives under conditions effective to form a plurality of fine fibers.

[0412] Embodiment F4 is the filter medium of any one of Embodiments F1-F3, wherein the fine fibers in the first layer of fine fibers have an average diameter greater than 0.6 μm, at least 0.7 μm, at least 0.8 μm, at least 0.8 μm, at least 1 μm, or greater than 1 μm; or the fine fibers in the first layer of fine fibers 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, or both.

[0413] Embodiment F5 is the filter medium of any one of embodiments F1-F4, wherein the second layer of fine fibers comprises fine fibers of mixed diameters.

[0414] Embodiment F6 is the filter medium of embodiment F5, wherein the second layer of fine fibers comprises coarse fine fibers having an average diameter at least three times the average diameter of the fine fine fibers.

[0415] Embodiment F7 is the filter medium of embodiment F5 or F6, wherein the second layer of fine fibers comprises thick fine fibers and thin fine fibers, and the thick fine fibers have an average diameter of at least 1 μm or greater than 1 μm, or the thick fine fibers 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, or both, and the thin fine fibers have an average diameter of at least 0.2 μm, or the thin fine fibers have an average diameter of at most 0.6 μm, or both.

[0416] Embodiment F8 is the filter medium of embodiment F5 or F6, wherein the thick microfibers have an average diameter greater than 1 μm.

[0417] Embodiment F9 is the filter medium of any one of embodiments F5-F8, wherein the second layer of fine fibers includes at most 10% coarse fine fibers or at most 20% coarse fine fibers.

[0418] Embodiment F10 is the filter medium of any one of embodiments F5-F8, wherein the second layer of fine fibers comprises at least 3% and at most 9% coarse fine fibers, at least 5% and at most 7% coarse fine fibers, or at least 4% and at most 8% coarse fine fibers.

[0419] Embodiment F11 is the filter media of any one of Embodiments F5-F8, wherein the second layer of fine fibers comprises a proportion of one or more of the thick fine fibers of Set A5, Set A6, Set B, Set D, Set D5, Set D6, Set E, Set I, Set I5, Set I6, Set J, or Set L of Tables 1A-1C.

[0420] Embodiment F12 is the filter medium of any one of embodiments F9-F11, wherein the proportion of thick fine fibers is determined based on spinning time.

[0421] Embodiment F13 is the filter medium of any one of embodiments F9-F11, wherein the proportion of thick fine fibers is determined using microscopy or nano-CT.

[0422] Embodiment F14 is the filter medium of any one of embodiments F5-F13, wherein the second layer of fine fibers comprises a layered fiber structure.

[0423] Embodiment F15 is the filter medium of embodiment F14, wherein the second layer of fine fibers comprises one or more layered fiber structures of Set A5, Set B, Set D5, Set E, Set I5, or Set J of Tables 1A-1C.

[0424] Embodiment F16 is the filter medium of embodiment F14, wherein the second layer of fine fibers comprises thin fine fibers and thick fine fibers, the thin fine fibers being deposited on the first layer of fine fibers, and the thick fine fibers being deposited on the thin fine fibers.

[0425] Embodiment F17 is the filter medium of any one of embodiments F5-F13, wherein the second layer of fine fibers comprises a mixed fiber structure.

[0426] Embodiment F18 is the filter medium of embodiment F17, wherein the second layer of fine fibers comprises one or more mixed fiber structures of Set A6, Set D, Set D6, Set I, or Set L of Tables 1A-1C.

[0427] Embodiment F19 is the filter medium of any one of Embodiments F5-F13, wherein the second layer of fine fibers comprises thin fine fibers and thick fine fibers, and within the second layer of fine fibers, the thin fine fibers are deposited on a first sublayer of thick fine fibers and a second sublayer of thick fine fibers are deposited on the thin fine fibers.

[0428] Embodiment F20 is the filter medium of any one of embodiments F1-F19, wherein the fine fibers are compatible with at least one of a hydraulic fluid, a fuel, or a lubricant.

[0429] Embodiment F21 is the filter medium of any one of embodiments F1-F20, wherein the support layer comprises nylon.

[0430] Embodiment F22 is the filter medium of any one of Embodiments F1-F21, wherein the support layer has an average 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 and 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.

[0431] Embodiment F23 is the filter medium of embodiment F22, wherein the average maximum pore size is determined using capillary flow porometry.

[0432] Embodiment F24 is the filter medium of any one of Embodiments F1-F23, wherein the support layer has an average 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.

[0433] Embodiment F25 is the filter medium of embodiment F24, wherein the average maximum pore size is determined using capillary flow porometry.

[0434] Embodiment F26 is the filter medium of any one of Embodiments F1-F25, wherein the support layer has an average minimum pore size of at least 5 μm, at least 10 μm, at least 15 μm, at least 20 μm, at least 25 μm, at least 30 μm, at least 35 μm, at least 40 μm, or at least 50 μm.

[0435] Embodiment F27 is the filter medium of embodiment F25, wherein the average minimum pore size is determined using capillary flow porometry.

[0436] Embodiment F28 is the filter medium of any one of Embodiments F1-F27, wherein the support layer has an average intermediate flow pore size, and the average intermediate flow pore size of the support layer does not vary by more than 30%, does not vary by more than 25%, or does not vary by more than 15% across the length and width of the medium.

[0437] Embodiment F29 is the filter medium of any one of embodiments F1-F28, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average maximum pore size of at most 14 μm, at most 15 μm, or at most 20 μm, or the filter medium has a composite average maximum pore size of at least 0.1 μm, or both.

[0438] Embodiment F30 is the filter medium of any one of Embodiments F1-F29, wherein the filter medium comprises a composite including a support layer and a fine fiber layer, and wherein the filter medium has a composite average mean flow pore size of at most 11 μm, at most 9 μm, or at most 6 μm, or the filter medium has a composite average mean flow pore size of at least 0.1 μm, or both.

[0439] Embodiment F31 is the filter medium of embodiment F29 or F30, wherein the composite pore size is determined using capillary flow porometry.

[0440] Embodiment F32 is the filter medium of any one of Embodiments F1-F31, wherein the first layer of fine fibers comprises fine fibers having a diameter at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm larger than the fiber diameter of the fine fibers of the second layer of fine fibers.

[0441] Embodiment F33 is the filter medium of any one of Embodiments F1-F32, wherein the first fine fiber layer has a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm, or wherein the first fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, or at most 50 μm, or both.

[0442] Embodiment F34 is the filter medium of any one of Embodiments F1-F33, wherein the second fine fiber layer has a thickness of at least 2 μm, at least 3 μm, at least 4 μm, or at least 5 μm, or wherein the second fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm, at most 40 μm, or at most 45 μm, or both.

[0443] Embodiment F35 is the filter medium of embodiment F33 or F34, wherein the thickness of the first fine fiber layer or the second fine fiber layer or both is determined using scanning electron microscopy (SEM).

[0444] Embodiment F36 is the filter medium of any one of embodiments F1-F35, wherein the support layer comprises a spunbond layer.

[0445] Embodiment F37 is a filter element including the filter medium of any one of embodiments F1 to F36.

[0446] Embodiment F38 is the filter element of embodiment F37, wherein the filter element comprises an efficiency layer, and the efficiency layer comprises a filter media.

[0447] Embodiment F39 is the filter element of embodiment F38, wherein the filter element further comprises a loading layer.

[0448] 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]

[0449] Preparation of polymer solutions To prepare Solution 1, nylon copolymer resin (SVP 651, a terpolymer containing 45% nylon-6, 20% nylon-6,6, and 25% nylon-6,10 with a number average molecular weight of 21,500–24,800, obtained from Shakespeare Co., Columbia, SC) 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 crosslinking agent. 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 fabricate 0.25 μm fibers.

[0450] 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.

[0451] 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.

[0452] Solution 3 was prepared as described for Solution 1, except that a 12% nylon solids solution was used and no melamine-formaldehyde resin was added (again, the weight ratio of melamine-formaldehyde resin to nylon was 20:100 parts by weight). Solution 3 had a viscosity of 77±5 cP, as measured at 25°C using a Brookfield LV DV-I Prime Viscometer combined with a Fisher Scientific Model 8005 temperature-controlled water bath. Solution 3 was used to make 0.5 μm fibers.

[0453] To prepare Solution 4, 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 4 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 4 was used to fabricate 1.4 μm fibers.

[0454] 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.

[0455] 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.

[0456] 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). 2 The 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.

[0457] 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.

[0458] 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. 2The 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.

[0459] 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.

[0460] Method 3: A series of fiber layers with fibers of different diameters were spinned at 70 g / m by alternating ("pulse") 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 1A. 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%.

[0461] 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.

[0462] 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%.

[0463] 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.

[0464] In the second step, layers of mixed diameter fibers were deposited by alternating ("pulsing") 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 1A.

[0465] Approximately 0.65 to 0.86 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.

[0466] 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%.

[0467] 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.

[0468] 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 / m2 , 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.

[0469] [Table 1]

[0470] 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).

[0471] 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.

[0472] 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.

[0473] 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.

[0474] 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).

[0475] 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.

[0476] Method 8 First, a first fine fiber layer (0.54 g / m) containing thick (1.4 μm diameter) fine fibers was prepared by spinning solution 4 for 2 minutes at a pump rate of 0.075 mL / min. 2 (corresponding to a coverage rate of 70g / m 2 The coating 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%.

[0477] Next, mixed layers of fibers of different diameters (0.25 μm and 1.4 μm) were produced as described in Method 4, following the timing sequence in Table 1B and using Solution 4 instead of Solution 2. (The timing sequence in Table 1B is the same as the timing sequence in Table 1A, but because Solution 4 is used instead of Solution 2, the resulting layers have different basis weights and fiber percentages.)

[0478] Method 9 First, a first fine fiber layer (0.54 g / m) containing thick (1.4 μm diameter) fine fibers was prepared by spinning solution 4 for 2 minutes at a pump rate of 0.075 mL / min. 2 (corresponding to a coverage rate of 70g / m 2 The coating 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%.

[0479] Next, mixed layers of fibers of different diameters (0.5 μm and 1.4 μm) were produced as described in Method 4, following the timing sequence in Table 1C, using Solution 3 instead of Solution 1 and Solution 4 instead of Solution 2. (The timing sequence in Table 1C is the same as the timing sequence in Table 1A, but because Solution 3 is used instead of Solution 1 and Solution 4 is used instead of Solution 2, the resulting layers have different basis weights and fiber percentages.)

[0480] [Table 2]

[0481] [Table 3]

[0482] Method 10 First, a first fine fiber layer (0.54 g / m) containing thick (1.4 μm diameter) fine fibers was prepared by spinning solution 4 for 2 minutes at a pump rate of 0.075 mL / min. 2(corresponding to a coverage rate of 70g / m 2 The coating 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%.

[0483] A second fibril layer containing mixed fibrils of different diameters (0.25 μm and 1.4 μm) was then deposited by cospinning two different electrospinning precursor solutions (Solution 1 and Solution 4) from two different syringes delivered at the same pump rate (0.075 mL / min) and for the same duration (1 min, 1.4 min, 2 min, 2.5 min, 3.6 min, or 4.5 min).

[0484] All samples underwent post-synthesis treatment to improve robustness through cross-linking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 min.

[0485] Method 11 First, a first fine fiber layer (0.54 g / m) containing thick (1.4 μm diameter) fine fibers was prepared by spinning solution 4 for 2 minutes at a pump rate of 0.075 mL / min. 2 (corresponding to a coverage rate of 70g / m 2 The coating 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%.

[0486] A second fibril layer containing mixed fibrils of different diameters (0.5 μm and 1.4 μm) was then deposited by cospinning two different electrospinning precursor solutions (Solution 3 and Solution 4) from two different syringes delivered at the same pump rate (0.075 mL / min) and for the same duration (2, 3, 4, or 5 min).

[0487] All samples underwent post-synthesis treatment to improve robustness through cross-linking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 min.

[0488] Method 12 A series of media samples containing multiple layers with various sizes of fine fibers were prepared. The samples included a base layer of thick (1.4 μm diameter) fine fibers, followed by a layer of thin (0.25 μm diameter) fine fibers and a layer of thick (1.4 μm diameter) fine fibers (thick / thin / thick or L / S / L). Alternatively, the samples included a base layer of thick (1.4 μm diameter) fine fibers, followed by a layer of thin (0.25 μm diameter) fine fibers, then a layer of a mixture of thin (0.25 μm diameter) and thick (1.4 μm diameter) fine fibers and a layer of thick (1.4 μm diameter) fine fibers (thick / thin / mixed / thick or L / S / mixed / L).

[0489] Solution 4 was spun for 2 minutes to obtain thick fine fibers (0.54 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 top layer of thick fibers (corresponding to a coverage of 0.54 g / m²) was deposited. When included, a middle (mixed) layer containing both thin and thick fibers was added by alternately ("pulsing") spinning from syringes containing Solution 1 or Solution 4 for thin and thick fibers, respectively, according to the timing sequence in Table 1B. Finally, a top layer of thick fibers (corresponding to a coverage of 0.54 g / m²) was deposited by spinning Solution 4 for 2 minutes. All solutions were delivered at a pump rate of 0.075 mL / min.

[0490] All samples underwent post-synthesis treatment to improve robustness through cross-linking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 min.

[0491] Method 13 First, a first fine fiber layer (0.54 g / m) containing thick (1.4 μm diameter) fine fibers was prepared by spinning solution 4 for 2 minutes at a pump rate of 0.075 mL / min. 2 (corresponding to a coverage rate of 70g / m 2The coating 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%.

[0492] Next, three additional layers of fine fine fibers (0.22 g / m each) were applied by rotating Solution 1 three times for 2 minutes. 2 (corresponding to a coverage of 1000mV) was deposited.

[0493] Finally, a top layer of thick fibrils (corresponding to a coverage of 0.54 g / m²) was deposited by spinning solution 4 for 2 minutes. All solutions were delivered at a pump rate of 0.075 mL / min.

[0494] All samples underwent post-synthesis treatment to improve robustness through cross-linking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 min.

[0495] Media characterization 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.

[0496] A 3 mm x 20 mm sample containing the fine fibers on the support layer was typically 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.

[0497] Calculation of fiber ratio based on spinning time The relative amounts of thin and thick fibrils (based on total fiber count) are determined using the following formula:

number

number

[0498] Fiber diameter The fine fiber samples produced in Examples 1-7 had an average fiber diameter of 10 microns or less. Typically, thin fine fibers had an average fiber diameter in the range of 200 nm to 600 nm as measured by scanning electron microscopy (SEM). Typically, thick fine fibers had an average fiber diameter of at least 700 nm as measured by scanning electron microscopy (SEM). Fiber diameter sorting was performed by imaging the fibers by 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 sorting. Fiber diameter was measured at at least 30 locations on the sample.

[0499] 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 delineated 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.

[0500] Capillary Flow Porometry (pore size) For each sample, capillary flow porometry (Porometer 3G micro, Through-Pore Size Analyzer, Quantachrome Instruments, Anton Paar, Boynton Beach, FL) measurements were performed to determine the average maximum pore size, average intermediate flow pore size, and average minimum pore size based on three replicates.

[0501] Porofil Wetting Solution was used as the wetting fluid (Quantachrome Instruments, Anton Paar, Boynton Beach, FL). Samples with a diameter of 25 mm were subjected to a pressure sweep (i.e., continuous pressure scan) from 0.0256 bar to 1.275 bar in both wet and dry states (first wet, then dry) to determine pore sizes within 1 micron to 100 microns.

[0502] 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. 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.

[0503] 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 = air flow through the dry sample as a function of pressure Wetting curve = V wet = Air flow through saturated sample as a function of pressure.

[0504] Based on capillary theory, the pressure across the sample (ΔP) can be converted to pore diameter (d) using the Young-Laplace equation.

number

[0505] This transformation allows the definition of the drying and wetting curves as a function of pore size: Drying curve=V' dry = air flow through the dry sample as a function of diameter Wetting curve = V' wet = Air flow through saturated sample as a function of diameter.

[0506] 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

[0507] The minimum pore size was calculated by determining the diameter where the dry and wet curves intersected.

[0508] The intermediate flow pore size was calculated at the pressure where the wet and "semi-dry" curves intersect. The semi-dry curve is V' dry is obtained by mathematically dividing by 2.

[0509] The maximum pore size was determined by detecting the bubble point. The bubble point was detected after the fluid started to pass through the sample and increased by at least 1% for three consecutive measurements. The bubble point was the value at the start of these three consecutive points.

[0510] 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).

[0511] 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.

[0512] 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)

[0513] 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.

[0514] Liquid filtration performance test Liquid filtration performance was evaluated using a flat-sheet, high-precision, single-pass, two-fluid (FHAST) bench. The FHAST bench contains a reservoir of hydraulic fluid loaded with particles of various sizes. The particle-loaded fluid is then passed through a media, and particle count and size measurements are performed upstream and downstream of the media. The FHAST bench has the following features: 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; and dilution performance: 5:1 to 100:1. The FHAST bench was used in steady flow mode using ISO Medium Test Dust, per 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, to add 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.

[0515] 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.

[0516] 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 fiber density, and Z is the thickness of the media.

[0517] 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.

[0518] Because it is difficult to measure the thickness of the fine fiber layer, 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.

[0519] First, the dimensionless fiber drag parameter F * 1.0 is calculated from the modified Kirsch-Fuchs formula:

number

[0520] Next, the solidity (c) is calculated using the following formula: * 1.0 Calculate from. F * 1.0 =4.3548e 8.8822c

[0521] For mixed fiber media, the effective fiber diameter is calculated by taking into account the relative amounts of fine and coarse fibers:

number

[0522] The basis weight of the fine fiber layer or layers is calculated as follows: Total basis weight of fine fiber layer = (mass of fine fiber) / (area of ​​scrim)

[0523] The mass of the fine fibers is calculated as follows: Mass of fine fibers = (polymer in solution (% w / v)) x (pump speed) x (spinning time)

[0524] 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 Fiber = (Total Mass of Media Sample) - (Mass of Bare Scrim or Substrate)

[0525] Example 1 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).

[0526] The media were tested as described in the Liquid Filtration Performance Testing section above. The results are shown in Figures 1A and 1C. The media with thin fine fibers deposited directly on the scrim (results shown in Figure 1A) had an initial pressure drop of 0.74 psi. The media with thin fine fibers deposited on a thick fine fiber layer deposited on the scrim (results shown in Figure 1C) had an initial pressure drop of 0.75 psi.

[0527] An exemplary image of a thick fine fiber layer deposited on a scrim before the thin fine fibers are deposited on the thick fine fiber layer is shown in FIG. 1E.

[0528] SEM images of the resulting media are shown in Figure 1B (thin fine fibers deposited directly on the scrim) and Figure 1D (thin fine fibers deposited on a thick fine fiber layer deposited on the scrim). Fiber "conditioning" and damage were observed in the thin fine fibers deposited directly on the scrim (Figure 1B). No fiber "conditioning" or damage was observed in the thin fine fibers deposited on a thick fine fiber layer deposited on the scrim (Figure 1D).

[0529] Example 2 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 theoretical basis weight was 1.01 g.

[0530] 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 theoretical basis weight was 1.01 g.

[0531] An SEM image of the resulting medium is shown in Figure 2A, and the characteristics of the resulting medium are shown in Table 2A.

[0532] The FOM values ​​of these media samples for air filtration are shown in Table 2B. Comparison of the FOM values ​​suggests that media containing mixed fibers of different diameters have improved performance (higher rejection of contaminants and lower pressure drop) compared to media containing only thin fine fibers (Table 2B).

[0533] Liquid filtration performance was evaluated on a flat-sheet, high-precision, single-pass, two-fluid (FHAST) bench, as described herein. Similar β values ​​were observed for the mixed fiber media and the thin fine fiber media (Figure 2B), but no benefit in terms of dP reduction was observed for the mixed fiber media compared to the thin fine fiber media (Figure 2C). The liquid filtration performance data (Figures 2B-2C) are consistent with porometry measurements (Table 2C), showing that the pore size of the mixed fiber media is smaller compared to the thin fine fiber media.

[0534] Without wishing to be bound by theory, it is believed that the media containing mixed fibers failed to show any reduction in pressure drop compared to media containing only thin fine fibers because the media containing mixed fibers exhibited a higher overall coverage of fibers compared to media containing only thin fine fibers or media containing only thick fine fibers. This difference in coverage is illustrated by the comparative basis weight: the media containing mixed fibers had a basis weight (0.56 g / m) of the media containing only thin fine fibers. 2 ) or basis weight of media containing only thick fine fibers (1.08 g / m 2 ) compared to a higher basis weight (1.64 g / m 2 )

[0535] [Table 4]

[0536] [Table 5]

[0537] [Table 6]

[0538] Example 3 The media were prepared according to pendant drop sample preparation method 2 with electrospinning times of 2, 3, or 5 minutes. The resulting nonwoven fabrics had weights of 0.65 g / m², 0.98 g / m², and 1.63 g / m², respectively. 2 The theoretical basis weight was 1.03 g.

[0539] The media for the control nonwoven fabrics made by co-spinning each electrospinning precursor solution from two different syringes for 2 minutes was 0.44 g / m for Solution 1 and 0.44 g / m for Solution 2, respectively. 2 and 0.86 g / m 2 The theoretical basis weight was 1.03 g.

[0540] An SEM image of the obtained medium is shown in FIG.

[0541] As described in Example 1, an increase in basis weight was observed as a result of co-spinning electrospinning precursor solutions to form thin and thick fibers. To accommodate this increase in basis weight, control media samples of only thin or only thick fibers produced by co-spinning from two syringes containing the same solution were also analyzed.

[0542] A comparison of the FOM values ​​for air filtration for media samples made using 2 min electrospinning suggests that the mixed fiber layer has improved performance (higher rejection of contaminants and lower pressure drop) compared to media containing only thin fine fibers (Table 3A).

[0543] Interestingly, increasing fiber coverage (due to prolonged electrospinning) also leads to an overall decrease in FOM values ​​for mixed fiber media due to a decrease in sweep pressure. Liquid filtration performance was evaluated using a flat-sheet, high-precision, single-pass, two-fluid (FHAST) bench, as described herein. Lower pressure drops were observed for mixed fiber media compared to thin, fine fibers alone (Figure 3D). However, comparison of β values ​​(Figure 3F) indicates that these samples operate in a trade-off regime, where improved media dP is obtained at the expense of efficiency. The performance of several mixed fiber media samples with different basis weights was also compared, and it was observed that higher fiber coverage leads to increased efficiency (Figure 3E) due to smaller pore size (Figure 3G—comparison of clean media dP), which causes a larger pressure drop. The FHAST bench results are consistent with porometry measurements (see Table 3B), indicating that pore size is highly related to the overall performance of the media samples. Furthermore, the maximum pore size and the intermediate flow pore size depended on the electrospinning time (Figure 3H).

[0544] [Table 7]

[0545] [Table 8]

[0546] Example 4 The media was prepared according to the pendant drop sample preparation method 3.

[0547] To provide a better degree of control over fiber media structure and composition, a "pulse" sequence (thin and thick fine fibers are alternately deposited onto a scrim support) was tested. In all cases, thin fine fibers are deposited first, followed by thick fine fibers, to produce a series of layered fiber media samples with thick fine fiber content, on a fiber percentage basis, varying from 2% to 20% (nominal value calculated using the equation described in the section Calculating Fiber Percentage Based on Spinning Time).

[0548] This method allows for the creation of different structures, including layered or mixed fibers (see Table 1A), resulting in gradient or non-uniform pore sizes. SEM images provided visual confirmation of the ability to control media morphology.

[0549] Figure 4 shows the increase in basis weight observed with increasing relative amount of thick fine fibers. A linear increase in basis weight is observed up to 10% thick fine fiber content.

[0550] Example 5 The media was prepared according to the pendant drop sample preparation method 4.

[0551] The resulting media contained a "support layer" of thick fine fibers (1 μm diameter) that was deposited prior to depositing the layer of mixed fiber diameter fibers.

[0552] As in Example 4, a "pulse" sequence was used to deposit alternating thin and thick fine fibers, but in contrast to Example 4, a scrim support modified with thick fine fibers was utilized.

[0553] In all cases, in the second step of the procedure (i.e., after the deposition of the first fine fiber layer containing thick fine fibers), the thin fine fibers are deposited first, followed by the thick fine fibers, to produce a series of mixed fiber diameter medium samples with thick fine fiber content, on a fiber percentage basis, varying from 2% to 20% (nominal value calculated using the equation described in the section Calculating Fiber Percentage Based on Spinning Time).

[0554] SEM images provided visual confirmation of the ability to control media morphology (Figures 5A and 5B). Figure 5A shows media containing only thin fibrils (Figure 5A, panel A), media containing layered fibers of mixed diameters (Figure 5A, panels A5, B, D5, E, I5, J), or media containing only thick fibrils (Figure 5A, panel M). Figure 5B shows media containing only thin fibrils (Figure 5B, panel A), media containing mixed fibers of mixed diameters (Figure 5B, panels A6, D, D6, I, I6, L), or media containing only thick fibrils (Figure 5B, panel M). The letters in each panel indicate the electrospinning sequence described in Table 1A.

[0555] Surprisingly, the pore sizes measured for media samples of different compositions showed only a weak correlation with the thick fiber fraction (see Table 4A and Figure 5C). These results suggest that for samples with modest fiber coverage (e.g., 5 g / m), porometry studies are unable to capture the presence of pore size gradients present in such media. Nevertheless, these data demonstrate that incorporating thick fibers into a network of thin fibers can be effective in broadening the pore size distribution.

[0556] Comparing the air filtration performance, as measured by FOM values ​​(see Table 4B), of mixed fiber diameter media structures with layered fiber structures or mixed fiber structures suggests that the structures have similar effects (see Figure 5D, bottom panel). In general, both layered and mixed fiber structures show lower performance because more of the thin fine fibers (which impart efficiency) have been replaced by thick fine fibers. For mixed fiber structures, there appears to be an optimal range of thick fine fiber content (5%-7%) where the FOM remains comparable to that of a purely thin fine fiber network. Notably, the mixed fiber structure media sample retained a relatively high FOM despite its large pore size (circles in Figure 5D, top panel). However, FOM values ​​and pore size do not appear to correlate well.

[0557] [Table 9]

[0558] [Table 10]

[0559] Importantly, providing a support layer of thick fine fibers in a layer containing fibers of mixed fiber diameters eliminated the beta decay observed in media that contained the same layer of mixed fiber diameters but did not contain such a support layer of thick fine fibers. An exemplary comparison is shown in Figures 5E and 5F. Figure 5E shows a mixed layer of mixed fiber diameters (containing 5% thick fine fibers) made as described in Method 3, Table 1A, Set B. The mixed layer had a mass of 0.71 g / m 2 The support layer and the mixed layer have an initial pressure drop (dP) of 0.48 psi. Figure 5F shows the results of the thick fine fibers (0.43 g / m) made as described in Method 4, Table 1A, Set B. 2 The mixed layer shows a mixed fiber diameter (containing 5% coarse fine fibers) deposited on a support layer of 0.71 g / m2 (coarse fine fibers having a basis weight of 0.71 g / m2). 2 and the support layer and two fine fiber layers have an initial pressure drop (dP) of 0.77 psi.

[0560] Moreover, as shown in Figures 5G-5J, media containing mixed fiber diameter fibers with 5%-7% thick fine fiber content exhibit similar efficiency to media layers containing only thin fine fibers, but show a slight improvement in pressure drop. Similar trends were observed in mixed fiber diameter media structures with layered structures and mixed fiber structures. In contrast, in media with greater than 10% thick fine fiber media content, the decrease in pressure drop was accompanied by a decrease in efficiency. (See Figures 5G-5J and 5K.) Without wishing to be bound by theory, it is believed that increasing the amount of thick fine fibers in media containing mixed fiber diameter fibers "opens up" the fine fiber structure.

[0561] Example 6 (0.09g / 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 as a support layer under a network of fine fine fibers (having a basis weight of at least 0.43 g / m 2 Media samples were prepared by Method 5, which involves depositing a layer of thick fine fibers (having a basis weight of 1000 sq ft). Pressure drop and overall β values ​​were tested. The results are shown in Figures 6B-6C.

[0562] An exemplary SEM image is shown in Figure 6A, where a top layer of thin fibrils coats an underlying network of supporting thick fibrils.

[0563] Media containing a thin layer of fine fibers across a range of basis weights showed good efficiency along with low pressure drop.

[0564] Example 7 Media samples were prepared according to Method 6. The media contained a first layer of thick fibers, followed by thin fibers, then a layer of mixed thin and thick fibers, and finally a layer of thick fibers (denoted as thick / thin / mixed / thick or L / S / mixed / L). Alternatively, an inner layer of mixed fibers (between two layers of thick fibers) was deposited by electrospinning, as described in Table 1A. Pressure drop and overall β values ​​were evaluated on a flat-sheet, high-precision, single-pass, two-fluid (FHAST) bench, as described herein. Exemplary images are shown in Figures 7A-7B. Results are shown in Figures 7C-7D.

[0565] It is believed that including layers of thin and thick diameter fibers intermixed between layers of thick fine fibers is particularly useful for maintaining the structural integrity of the intermediate layers in applications requiring backpulses for media cleaning / regeneration.

[0566] Example 8 Media samples were prepared according to Method 7, with a layer of mixed fine and coarse fine fibers (at least 0.43 g / m 2 The samples were compared to media samples made according to Method 5 (a layer of thick fine fibers under a network of thin fine fibers).

[0567] The mixed thin and thick fiber layer contained approximately 10% thick fibers based on the total number of fibers. This percentage was estimated from the diameter of the thin and thick fibers, the percentage of solids in the precursor spinning solution, the syringe pump feed rate, and the electrospinning time. The mixed thin and thick fiber layer was fabricated by approximating the basis weight of the second (thin fiber) layer of media fabricated using Method 5, or approximating the total number of fibers in the second (thin fiber) layer of media fabricated using Method 5. As shown in Table 5A, the resulting media layer had a basis weight of 0.82 g / m 2 ~1.47g / m 2 whereas the second (thinner fine fiber) layer of the media made using Method 5 had a resulting basis weight of 0.56 g / m 2 The sheet had a basis weight of 1.0001.

[0568] The resulting media was tested for pressure drop and overall β value. The results are shown in Figures 8B-8C. An exemplary SEM image is shown in Figure 8A.

[0569] [Table 11]

[0570] [Table 12]

[0571] The introduction of mixed thick fine fibers in a network of thin fine fibers increased the pore size compared to layers containing only thin fine fibers, despite the higher basis weight observed for those layers (see Table 5B).

[0572] Evaluation of air filtration performance by HEFS bench testing was consistent with the pore size results in that a lower pressure drop was achieved than with fine fine fibers alone while maintaining the figure of merit (FOM) (see Table 5A, 0.82 g / m for fine fine fibers with a comparable FOM of approximately 150). 2 of grammage of mixed fibers).

[0573] Liquid filtration performance was evaluated on a flat-sheet, high-precision, single-pass, two-fluid (FHAST) bench, as described herein. A significant improvement in media dP (Figure 8A) was observed for the co-spun samples compared to a network of thin fibrils supported by thick fibrils. However, for these media with mixed thin and thick fibrils, there was a tradeoff in efficiency, such that a β of 1000 was achieved for contaminant particles larger than 5 microns (compared to a β of 1000 for particles larger than 3 microns for unmixed thin fibrils alone). Overall, media consisting of mixed thin and thick fibrils with an underlying support layer of thick fibrils showed good efficiency with low pressure drop.

[0574] Example 9 - Comparison with Fine Glass Fiber Containing Media The filter media of Example 5 was compared to two liquid media products containing fine glass fibers. The first glass media had a β rating of 1,000 for particles smaller than 4 μm, and the second had a β rating of 1,000 for particles larger than 5 μm. Similar products are commercially available from Lydall, Inc. (Manchester, CT) and include LyPore Grade 9428 and LyPore Grade 9221, respectively. The results are shown in Figures 5G-5J and Table 6.

[0575] The two liquid media products tested containing fine glass fibers had higher pressure drops due to the thickness of these glass fiber-containing media, which subsequently allowed for some range of depth loading. All samples containing up to 10% thick fine fiber content had efficiencies comparable (if not slightly better) to glass media rated at β5um=1,000, especially for contaminants up to 5 μm in diameter. Table 6A summarizes the media dP and efficiency improvements, benchmarked against glass fiber media with a β rating of 1,000 for particles larger than 5 μm.

[0576] A comparison of these two performance metrics for media containing only thin fibrils (but indicated with thick fibrils) is summarized in Table 6B.

[0577] The media of Example 6 was also compared to a liquid media product containing fine glass fibers with a β rating of 1,000 for particles less than 4 μm. The media of Example 6 demonstrated significantly lower pressure drop, exceeding the efficiency of the glass fiber media with a β rating of 1,000 for particles less than 4 μm (see FIGS. 6A-6B).

[0578] [Table 13]

[0579] [Table 14]

[0580] The media of Example 7 was also compared to a liquid media product containing fine glass fibers with a β rating of 1,000 for particles less than 4 μm. Notably, samples with mixed layers containing up to 5% thick fine fiber content were also able to match the efficiency of glass fiber media with a β rating of 1,000 for particles less than 4 μm for contaminant particles up to 3 μm (FIGS. 7A-7B).

[0581] Example 10 To further examine the interplay between fiber diameter of the first fine fiber layer, fine fiber layer thickness, and average maximum pore size of the composite, the ability of the samples of Examples 1-8 to withstand liquid filtration performance tests was measured. As used in this example, "composite" refers to any layer of fine fibers (e.g., including the first, second, etc. layers of fine fibers) and a support layer. The composite includes at least one layer of fine fibers.

[0582] For each sample tested, the ratio of total fine fiber basis weight to the average maximum pore size of the composite was plotted against the basis weight of the second layer of fine fibers.

[0583] In FIG. 11, the x-axis represents the basis weight of the second layer of fine fibers, and the y-axis represents the

number

[0584] Because the pore size within the fine fiber layer depends on multiple factors such as fine fiber diameter, solidity, and uniformity, and because the basis weight of the fine fibers reflects the fiber diameter, solidity, and uniformity, the ratio of the total basis weight of the fine fibers to the average maximum pore size value of the composite was used to normalize the pore size values.

[0585] The total basis weight of the fine fiber layer is calculated as follows: Total basis weight of fine fiber layer = (mass of fine fiber) / (area of ​​scrim)

[0586] The mass of the fine fibers is calculated as follows: Mass of fine fibers = (polymer in solution (% w / v)) x (pump speed) x (spinning time)

[0587] If the method of formation of the fine fibers is unknown, the mass of the fine fibers, after separation of the fine fibers from the scrim or substrate (eg, by peeling or delaminating), can be calculated as follows: Mass of Fine Fiber = (Total Mass of Media Sample) - (Mass of Bare Scrim or Substrate)

[0588] Plotting the ratio of basis weight to maximum pore size of the composite against the basis weight of the fine fiber second layer allows for the identification of features (composite fine fiber basis weight and maximum pore size) that correlate with fine fiber layers that will experience damage during FHAST bench testing. As shown in Figure 11, samples that survived the liquid filtration performance test were distinguished from samples that did not survive the liquid filtration performance test and exhibited damage to the fiber structure and / or beta decay visualized using SEM images.

[0589] The dashed line indicates the slope of the line expected to delineate composites that can withstand the liquid filtration performance test and will not suffer fiber damage during use of the filtration layer from composites that will suffer fiber damage during use of the filtration layer. The dotted line in Figure 11B indicates the characteristics of a trend line with a similar slope. The circular data points located below the dashed line correspond to media samples in which a first layer of thick fine fibers was deposited as described in Methods 4, 5, 6, and 7.

[0590] Example 11 The sample integrity of the composite samples during FHAST bench testing up to 20 psi (at a superficial velocity of 0.56 ft / min, as further described in the Liquid Filtration Performance Test Method) was evaluated, and the initial pressure drop for each composite was plotted against the composite mean maximum pore size and the composite mean intermediate flow pore size. As used in this example, "composite" refers to any layer of fine fibers (including, for example, first, second, etc. layers of fine fibers) and a support layer. A composite includes at least one layer of fine fibers.

[0591] The composite maximum pore size and composite intermediate flow pore size for each sample were measured by flow porometry, and three measurements were averaged to obtain the composite average maximum pore size and composite average intermediate flow pore size. Each sample contained fine fibers and a substrate of mixed diameters. Some samples contained a layer of fine fibers containing "thick" and "thin" fine fibers, prepared as described in Methods 1, 2, or 3. Some samples contained a first layer of fine fibers and a second layer of fine fibers, prepared as described in Methods 4, 5, 6, or 7, where the first layer of fine fibers contained fine fibers with an average diameter at least three times the average fiber diameter of the smallest fibers in the second layer of fine fibers.

[0592] The results are shown in Figure 12. 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 open shapes.

[0593] 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).

[0594] 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.

[0595] 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).

[0596] The results show that both the composite's average maximum pore size (Figure 12A) and the composite's average intermediate flow pore size (Figure 12B) 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.

[0597] Some media samples with composite average maximum pore sizes 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 sizes between 14 μm and 20 μm.

[0598] Similarly, some media with composite mean intermediate flow pore sizes 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 sizes between 6 μm and 11 μm.

[0599] 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.

[0600] Example 12A Media samples were prepared according to Method 8, with a layer of mixed diameter fibers (0.25 μm fibers and 1.4 μm fibers) underneath (at least 0.54 g / m 2 The fabric contained a layer of thick fine fibers (having a basis weight of 1000 .mu.m).

[0601] SEM images provided visual confirmation of the ability to control media morphology (Figures 13A and 13B). Figure 13A shows media containing only thin fibrils (Figure 13A, panel A), media containing layered fibers of mixed diameters (Figure 13A, panels A5, B, D5, E, I5, J), or media containing only thick fibrils (Figure 13A, panel M). Figure 13B shows media containing only thin fibrils (Figure 13B, panel A), media containing mixed fibers of mixed diameters (Figure 13B, panels A6, D, D6, I, I6, L), or media containing only thick fibrils (Figure 13B, panel M). The letters in each panel indicate the electrospinning sequence described in Table 1B.

[0602] The composite maximum pore size, intermediate flow pore size, and minimum pore size for each sample were measured by capillary flow porometry. The results are shown in Table 7A. A comparison of the pore sizes of the blended mixed diameter fibril structure and the layered mixed diameter fibril structure is shown in Figure 13C.

[0603] Pressure drop (dP) values ​​are shown in Figure 13D (Set A, Set A5, Set B, Set D5, Set E, Set I5, Set J, and Set M of Table IB) and Figure 13E (Set A, Set A6, Set D, Set D6, Set I, Set I6, Set L, and Set M of Table IB). This plot also shows values ​​for comparable liquid medium products containing fine fibers with a β rating of 1,000 for particles less than 4 μm or a β rating of 1,000 for particles less than 5 μm. Efficiency values ​​(overall β rating) are shown in Figure 13F (Set A, Set A5, Set B, Set D5, Set E, Set I5, Set J, and Set M of Table IB) and Figure 13G (Set A, Set A6, Set D, Set D6, Set I, Set I6, Set L, and Set M of Table IB). The plot also shows values ​​for comparable liquid medium products containing fine fibers with a beta rating of 1,000 for particles less than 4 μm or a beta rating of 1,000 for particles less than 5 μm.

[0604] As shown in Figures 13D-13J, media containing mixed fiber diameter fibers with 1% thick fine fiber content exhibits similar efficiency to media layers containing only thin fine fibers, but exhibits significantly improved pressure drop. In contrast, in media with greater than 5% thick fine fiber media content, the decrease in pressure drop was accompanied by a decrease in efficiency. (See Figures 13E and 13G.) Without wishing to be bound by theory, it is believed that increasing the amount of thick fine fibers in media containing mixed fiber diameter fibers "opens up" the fine fiber structure.

[0605] Example 12B Media samples were prepared according to Method 10, with a layer of mixed 0.25 μm fibers and 1.4 μm fine fibers (at least 0.54 g / m 2 The fabric contained a layer of thick fine fibers (having a basis weight of 1000 .mu.m).

[0606] The resulting media was 0.38 g / m (for precursor solutions applied for 1, 1.4, 2, 2.5, 3.6 or 4.5 minutes, respectively). 2 , 0.53 g / m 2 , 0.76 g / m 2 , 0.95g / m2 , 1.37g / m 2 or 1.71 g / m 2 The mixed fine fiber layer contained a coarse (1.4 μm diameter) fiber content of 6.5% by fiber count. The basis weights and calculated solidities are shown in Table 7C.

[0607] The composite maximum pore size, intermediate flow pore size, and minimum pore size for each sample were measured by capillary flow porometry, and the results are shown in Table 7B and Figure 13H.

[0608] FIG. 13C (see Example 12A) shows the results for samples with the same basis weight and relative amounts of fine and coarse fibers (e.g., 0.38 g / m at 6.5% coarse fiber content for the first column of Table 7B). 2 For set I) of supported fibers in Table 1B, the blending of thin and thick fibers significantly "opens up" the fine fiber structure, as indicated by the increase in pore size. Figure 13H shows the overall trend of decreasing pore size with increasing blend fiber coverage, from 0.38 to 0.53 g / m2 basis weight. 2 As the temperature increases, the pore size reduction is more pronounced.

[0609] Pressure drop (dP) values ​​are shown in Figure 13I, and efficiency values ​​(overall β rating) are shown in Figure 13J.

[0610] Example 12C Media samples were prepared according to Method 12 and included a base layer of thick (1.4 μm diameter) fine fibers, followed by a layer of thin (0.25 μm diameter) fine fibers, then a layer of mixed thin (0.25 μm diameter) and thick (1.4 μm diameter) fine fibers, and then a layer of thick (1.4 μm diameter) fine fibers (thick / thin / mixed / thick or L / S / mixed / L). Basis weights and estimated solidities are shown in Table 7D.

[0611] The pore size of the L / S / mixed / L media was measured and the results are shown in Figure 13K.

[0612] The resulting pressure drop (dP) values ​​are shown in Figure 13L, and the efficiency values ​​(overall β rating) are shown in Figure 13M.

[0613] [Table 15]

[0614] [Table 16]

[0615] [Table 17]

[0616] [Table 18]

[0617] Example 13A Media samples were prepared according to Method 9, with a layer of mixed 0.5 μm and 1.4 μm fibers (at least 0.54 g / m 2 The fabric contained a layer of thick fine fibers (having a basis weight of 1000 .mu.m).

[0618] SEM images provided visual confirmation of the ability to control media morphology (Figures 14A and 14B). Figure 14A shows media containing only thin fibrils (Figure 14A, panel A), media containing layered fibers of mixed diameters (Figure 14A, panels B, E, and J), or media containing only thick fibrils (Figure 14A, panel M). Figure 14B shows media containing only thin fibrils (Figure 14B, panel A), media containing mixed fibers of mixed diameters (Figure 14B, panels D, I, and L), or media containing only thick fibrils (Figure 14B, panel M). The letters in each panel indicate the electrospinning sequence described in Table 1C.

[0619] The composite maximum pore size, intermediate flow pore size, and minimum pore size for each sample were measured by capillary flow porometry. The results are shown in Table 8A. A comparison of the pore sizes of the blended mixed diameter fibril structure and the layered mixed diameter fibril structure is shown in Figure 14C.

[0620] As seen in Example 8, the introduction of mixed thick fine fibers in a network of thin fine fibers increased the pore size compared to layers containing only thin fine fibers, despite the higher basis weight observed for those layers (see Table 8A and Figure 14C).

[0621] The results of the air filtration performance evaluation from the HEFS bench test are shown in Table 8B. Figure of Merit (FOM) values ​​are shown in Table 8B and Figure 14D. Pressure drop (dP) values ​​are shown in Table 8B and Figure 14E (Sets A, B, E, J, and M in Table 1C and Figure 14F (Sets A, D, I, L, and M in Table 1C), Figure 14E, and Figure 14F. The plot also shows values ​​for comparable liquid media products containing fine fibers with a β rating of 1,000 for particles less than 4 μm or a β rating of 1,000 for particles less than 5 μm. Efficiency values ​​(overall β rating) are shown in Figure 14G (Sets A, B, E, J, and M in Table 1C) and Figure 14H (Sets A, D, I, L, and M in Table 1C). The plot also shows values ​​for comparable liquid media products containing fine fibers with a β rating of 1,000 for particles less than 4 μm or a β rating of 1,000 for particles less than 5 μm.

[0622] These results indicate that at comparable pressure drop values ​​(e.g., 2-3 mm HO) across the various structures, the layered structure with a 38% thick fiber content exhibited the highest efficiency and best FOM. Moreover, as shown above, comparison of similar structures with other thin and thick fiber diameter combinations (e.g., 0.25 μm / 1 μm and 0.25 μm / 1.4 μm) indicates that the combination 0.5 μm / 1.4 μm diameter fibers does not provide optimal media filtration performance (lower efficiency and higher pressure drop).

[0623] Example 13B Media samples were prepared according to Method 11 and included a layer of thick fine fibers (having a basis weight of at least 0.54 g / m2) underneath a layer of mixed 0.5 μm and 1.4 μm fibers.

[0624] The resulting mixed fine fiber layer had a thickness of 0.84 g / m (for precursor solutions applied for 2, 3, 4, or 5 minutes, respectively). 2 , 1.25g / m 2 , 1.67g / m 2 or 2.09 g / m 2 The mixed fine fiber layer contained 17% coarse fiber (1.4 μm diameter) content by fiber count.

[0625] The results of the HEFS bench test air filtration performance evaluation are shown in Table 8B and Figure 14I. These results demonstrate that a mixed structure of 0.5 μm and 1.4 μm fibers can sacrifice FOM due to a sharp increase in pressure drop (dP) without a corresponding improvement in efficiency. For example, a 0.84 g / m 2 to 2.09 g / m 2 As the basis weight increases to , the permeability decreases by about half (from 39.9 to 22.22), but the dP approximately doubles (from 4.4 to 8 mm H2O).

[0626] [Table 19]

[0627] [Table 20]

[0628] [Table 21]

[0629] [Table 22]

[0630] Example 14 This example describes a comparison of the best-performing samples (in terms of pressure drop and efficiency relative to 3 μm particles) from three sets of media incorporating thin (0.25 μm or 0.5 μm diameter) and thick (1 μm or 1.4 μm diameter) fibers. The fiber diameter combinations included 0.25 μm and 1 μm; 0.5 μm and 1.4 μm; and 0.25 μm and 1.4 μm.

[0631] The results are summarized in Table 9. The percentage improvement in initial pressure drop (dP) and overall efficiency (β values) for 3 μm particles (benchmarked against glass fiber-containing media with β=1000 for particles less than 4 μm) is shown in FIG. 15A. As shown in FIG. 15A, the four structures showed significant improvements in both overall efficiency and dP compared to glass fiber-containing media. In this plot, Quadrant I is the target region (i.e., gains in both dP and β compared to glass fiber-containing media). Notably, none of the mixed fiber diameter media structures fell to Quadrant III (decreases in both dP and β compared to glass fiber-containing media). As shown in FIG. 15B, all of the mixed fiber diameter media structures showed comparable or better pressure drop than the glass-containing media structure (with β=1000) for various particle sizes.

[0632] Mixed fiber diameter media structures can be manufactured using a wide range of process windows so that desired efficiencies can be targeted.

[0633] Example 15 Samples prepared according to Method 12 (L / S / Table 1B, Set M / L) were analyzed according to the "Thickness of the Fine Fiber Layer" method. An exemplary image is shown in Figure 16A, 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.

[0634] Figure 16B shows the delineation of the cross-section of a fibril using the polygon tool. Figure 16C shows the image after the area outside the cross-section of the selected fibril has been removed. Figure 16D shows the area of ​​the cross-section of the selected fibril after it has been recolored white using the threshold tool (to compensate for fibers on the boundary of the selected section), with the dashed line indicating the maximum thickness of the image measured and recorded (5.97 μm). 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 5.

[0635] 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, and Fine fiber layer A filter medium comprising: the fine fiber layer is deposited on the support layer; The filter medium, wherein the fine fiber layer comprises large fine fibers and small fine fibers, the large fine fibers having an average diameter of at least 1 μm and at least three times the average diameter of the small fine fibers.

2. 2. The filter media of claim 1, wherein the fine fiber layer comprises a first layer of fine fibers, the first layer of fine fibers comprising the thick fine fibers and the thin fine fibers.

3. 3. The filter medium of claim 1, wherein the fine fiber layer comprises a first layer of fine fibers and a second layer of fine fibers, the first layer of fine fibers being deposited on the support layer, and the second layer of fine fibers being deposited on the first layer of fine fibers.

4. 4. The filter medium of claim 3, wherein the first layer of fine fibers comprises fibers having an average diameter at least three times the average fiber diameter of the fine fibers of the second layer of fine fibers.

5. the second layer of fine fibers comprises fibers of two different diameters; the fibrils of two different diameters include thin fibrils and thick fibrils, the thick fibrils having an average diameter at least three times the average diameter of the thin fibrils; 5. The filter medium of claim 3 or 4, wherein the thin fibrils are deposited on the first layer of fibrils and the thick fibrils are deposited on the thin fibrils.

6. the second layer of fine fibers comprises fibers of two different diameters; the fibrils of two different diameters include thin fibrils and thick fibrils, the thick fibrils having an average diameter at least three times the average diameter of the thin fibrils; 5. A filter medium according to claim 3 or 4, wherein the thin fine fibers are mixed with the thick fine fibers.

7. At least some of the fine fibers providing a fiber-forming polymer; providing a polymer-reactive resinous aldehyde composition that is reactive with said fiber-forming polymer; combining said fiber-forming polymer and reactive resinous aldehyde composition to form a plurality of fine fibers; 7. The filter medium of any one of claims 1 to 6, prepared by a method comprising:

8. At least some of the fine fibers providing a fiber-forming polymer comprising a non-reactive polymer, the polymer being a polymer that cannot be crosslinked with the polymer non-reactive resinous aldehyde composition; providing a polymeric non-reactive resinous aldehyde composition containing one or more reactive groups capable of self-crosslinking; combining said fiber-forming polymer and reactive resinous aldehyde composition to form a plurality of fine fibers; 7. The filter medium of any one of claims 1 to 6, prepared by a method comprising:

9. At least some of the fine fibers providing at least one fiber-forming polymer; providing at least two reactive additives that are reactive with each other and optionally with said fiber-forming polymer; combining said at least one fiber-forming polymer and said at least two reactive additives under conditions effective to form a plurality of fine fibers; 7. The filter medium of any one of claims 1 to 6, prepared by a method comprising:

10. The filter medium of any one of claims 1 to 9, wherein the support layer comprises a spunbond layer.

11. 11. A filter medium according to any preceding claim, 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.

12. 12. The filter medium of any one of claims 1 to 11, wherein the support layer and the fine fiber layer form a composite having a composite intermediate flow pore size that is at most 6 μm, at most 9 μm, or at most 11 μm.

13. 13. The filter medium of any one of claims 1 to 12, wherein the fine fiber layer has a thickness of at most 5 μm, at most 10 μm, at most 30 μm or at most 50 μm.

14. the fine fibrils have an average diameter of at least 0.2 μm; or the fine fibrils 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; or The filter medium of any one of claims 1 to 13, wherein the filter medium is both.

15. 15. The filter medium of any one of claims 1 to 14, wherein the fine fibers are compatible with at least one of hydraulic fluids, fuels, or lubricants.

16. A filter element comprising the filter medium according to any one of claims 1 to 15.

17. 17. The filter element of claim 16, comprising an efficiency layer, and said efficiency layer comprising said filter media.

18. The filter element of claim 17 further comprising a loading layer.

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