Filter media layer containing mixed diameter fine fibers

Abstract

The present disclosure describes a high-performance filter medium (e.g., including high efficiency and low pressure drop). The filter medium includes a support layer and a layer of fine fibers, and some of the fine fibers in the fine fiber layer have an average diameter at least three times the average fiber diameter of the thin fine fibers in the fine fiber layer. The fine fiber layer can include multiple layers of fine fibers. In some embodiments, the thin fine fibers can be present in the same layer of fine fibers as the thick fine fibers. Additionally or alternatively, the thick fine fibers can be present in a first layer of fine fibers, and the thin fine fibers can be present in a second layer of fine fibers.

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 on October 8, 2019; U.S. Provisional Patent Application No. 62 / 947,998, filed on December 13, 2019; U.S. Provisional Patent Application No. 62 / 952,979, filed on December 23, 2019; U.S. Provisional Patent Application No. 62 / 992,003, filed on March 19, 2020; and U.S. Provisional Patent Application No. 63 / 004,602, filed on April 3, 2020, the entire disclosures of which are incorporated herein by reference.

Summary of the Invention

Means for Solving the Problems

[0002] This disclosure describes high - performance filter media (including, for example, high efficiency and low pressure drop). In some embodiments, this disclosure describes filter media that achieves the efficiency of filter media containing fine glass fibers without including fine glass fibers.

[0003] In one aspect, this disclosure describes a filter medium including a support layer and a fine fiber layer. The fine fiber layer is deposited on the support layer, and the fine fiber layer includes thick fine fibers and thin fine fibers. The thick fine fibers having an average diameter of at least 1 μm are at least 3 times the average diameter of the thin fine fibers.

[0004] In some embodiments, the thick fine fibers 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 fine fibers.

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

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

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

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

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

[0010] In some embodiments, the thin fine fibers of the second layer of fine fibers are mixed with the thick fine fibers of the second layer of fine 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 provide a fiber-forming polymer that includes a non-reactive polymer that is a polymer that cannot crosslink with a polymer non-reactive resinous aldehyde composition; provides a polymer non-reactive resinous aldehyde composition that includes one or more reactive groups capable of self-crosslinking; and is prepared by a method that includes 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 provide at least one fiber-forming polymer; provide at least two reactive additives that are reactive with each other and optionally reactive with the fiber-forming polymer; and are prepared by a method that includes 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 includes 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 thin fine fibers have an average diameter of at least 0.2 μm. In some embodiments, the thin 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.

[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 that includes the filter media described herein. The filter media forms, can form, or can form a 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 up to 100 micrometers. A fiber having an "average" diameter as used herein means that in a sample of a plurality of fibers, the average fiber diameter of the population of fibers in that sample has the average fiber diameter indicated. The population of fibers includes fibers having a diameter within 25% of the average fiber diameter. For example, a population of fibers having an average diameter of 1 μm includes fibers having a diameter of at least 750 nm and up to 1250 nm. In another example, a population of fibers having an average diameter of 250 nm includes fibers having a diameter of at least 188 nm and up to 313 nm. In a further example, a population of fibers having an average diameter of 500 nm includes fibers having a diameter of at least 375 nm and up to 625 nm. In yet another example, a population of fibers having an average diameter of 1400 nm includes fibers having a diameter of at least 1050 nm and up to 1750 nm. The fiber diameter can be measured using top-down SEM images. The sample can be sputter-coated. A useful sputter coater can be, for example, a mixture of gold and palladium, including a mixture with an Au:Pd ratio of 60:40. By measuring the fiber diameter at at least 30 locations within the sample, a more accurate measurement of the fiber diameter can be obtained. Software such as Trainable Weka Segmentation (ImageJ plugin) can be useful for the analysis of the fiber diameter.

[0021] As used herein, "microfiber" refers to a fiber having a diameter of up to 10 micrometers (μm). In some embodiments, the microfiber has 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 the circular cross-section of the fiber or the maximum cross-sectional dimension of the non-circular cross-section of the fiber.

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

[0024] As used herein, "mixed" fibers or "mixed fiber structures" refer to fibers having at least two different diameters, where fibers having a first average diameter and fibers having a second average diameter are mixed, i.e., 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, the fibers are mixed within the same layer of the media structure. When visualized using top-down SEM images, the fibers having a first average diameter can be observed to be disposed both below and above the fibers having a second average diameter.

[0025] As used herein, "laminated" fibers or "laminated fiber structures" refer to fibers having at least two different diameters, where the fibers having a first average diameter are not substantially intertwined with the fibers having a second average diameter as a result of the fibers of different diameters being applied to a substrate alternately.

[0026] As used herein, unless otherwise specified, the pore size (e.g., average intermediate flow pore size or average 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 from 0.0256 bar to 1.275 bar. For example, it can be useful to use a wetting liquid having 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 that changes from low pressure to high pressure, and then similarly tested in a dry state that changes from low pressure to high pressure. The tests are typically performed at ambient temperature conditions (e.g., 20 °C to 25 °C). 256 data points can be collected over the entire pressure scan range of both the wetting curve and the drying curve. Typically, the tortuosity factor and / or the shape factor are not used (i.e., a factor equal to 1 can be used for comparison with other test methods that use an adjustment factor). The average pore size (e.g., average intermediate flow pore size or average maximum pore size) can be calculated from the median of at least three measurements (obtained from at least three different sample locations). The individual measurements of the maximum pore size can be detected at the bubble point, which is confirmed after the fluid begins to pass through the sample, where three consecutive measurements increase by at least 1% and 256 data points are collected over the entire scan at a rate of about 17 data points / minute. The bubble point is the starting value of this three-point sequence. The individual measurements of the intermediate flow pore size can be calculated by determining the pressure at which the wetting curve and the "semi-dry" curve intersect. The semi-dry curve is obtained by mathematically dividing V’ dry by 2. V’ dry is the air flow through the dry sample as a function of the diameter.

[0027] As used herein, "beta ratio" or "β" is the ratio of upstream particles to downstream particles. The higher the efficiency of the filter, the higher the beta ratio. The beta ratio is defined as follows.

Number

[0028] As used herein, the "overall β ratio" or "overall β" is the ratio of the total number of all upstream particles in the assay process to the total number of all downstream particles in the assay process.

Number

[0029] As used herein, "filtration efficiency" or "efficiency" refers to the percentage of contaminants removed by the filter, calculated as follows.

Number

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

[0031] The terms "preferred" and "preferably" mean embodiments of the invention that can provide certain advantages under certain circumstances. However, in the same or other circumstances, other embodiments may also be preferred. Furthermore, the description 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 term "comprising" and its derivatives do not have a limiting meaning when these terms appear in the present specification and claims. Such terms are understood to mean including the recited steps or elements or groups of steps or elements, but not excluding other steps or elements or groups of steps or elements. "Consisting of" means including and being limited to all 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 can be present. "Consisting essentially of" means including the elements recited after this phrase and being limited to other elements that do not interfere with or contribute to the activity or action specified in the present 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 action of the recited elements.

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

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

[0035] In this specification, the description of a numerical range by endpoints includes all numerical values included within that range (for example, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0036] In this specification, the "maximum" number (for example, a maximum of 50) includes that number (for example, 50).

[0037] In any method disclosed in this specification that includes individual steps, the steps can be performed in any executable order. Also, if necessary, any combination of two or more steps can be performed simultaneously.

[0038] Unless otherwise specified, all headings are for the convenience of the reader and should not be used to limit the meaning of the text following the heading.

[0039] Throughout this specification, references to "one embodiment", "an embodiment", "a particular embodiment", or "some embodiments", etc., mean that the features, configurations, compositions, or characteristics described in connection with the embodiment are included in at least one embodiment of the present disclosure. Thus, the appearance of such phrases in various parts of this specification does not necessarily refer to the same embodiment of the present disclosure. Further, a particular feature, configuration, composition, or characteristic can be combined in any suitable manner in one or more embodiments.

[0040] References to standard methods (for example, ASTM, TAPPI, AATCC, etc.) refer to the latest methods available at the time of filing of the present disclosure, unless otherwise specified.

[0041] Unless otherwise specified, all numbers expressing quantities of ingredients, molecular weights, and the like used in this specification and the claims are to be understood as being modified in all instances by the term "about." The term "about" as used herein in connection with measured quantities refers to variations in the measured quantities that would be expected by a person of ordinary skill in the art making the measurement, taking into account the purpose of the measurement and the care appropriate for the precision of the measuring equipment used. Accordingly, unless otherwise indicated to the contrary, the numerical parameters set forth in this specification and the 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 application of the doctrine of equivalents to the claims, each numerical parameter should be construed in light of the reported significant digits and by applying ordinary rounding techniques.

[0042] Numerical ranges and parameters setting forth the broad scope of the invention are approximations, although the numerical values set forth in specific examples are reported as accurately as possible. However, each numerical value inherently contains a range necessarily resulting from the standard deviation found in the respective test measurements.

[0043] The above summary of the invention is not intended to describe every embodiment disclosed or all implementations of the invention. The following description more specifically illustrates exemplary embodiments. Throughout several parts of this specification, guidance is provided by lists of examples that can be used in various combinations. In each case, the listed lists serve only as representative groups and should not be construed as exclusive lists. BRIEF DESCRIPTION OF THE DRAWINGS

[0044]

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DETAILED DESCRIPTION OF THE INVENTION

[0045] The present disclosure describes high-performance filter media (including, for example, high efficiency and low pressure drop). In some embodiments, the present disclosure describes filter media that achieve the efficiency of filter media including fine glass fibers without including 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 a mixed diameter such that the fine fiber layer includes "thick" fine fibers having a fiber diameter that is 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 contain glass.

[0046] Typically, fine glass fibers are included in high-efficiency filter media. The glass fibers provide pore size control and, in cooperation with other fibers in the media, provide the media with substantial flow rate, high capacity, substantial efficiency, and high wet strength. However, when used in fuel or hydraulic filters, the glass fibers can break off from the media and cause wear in the engine.

[0047] However, it has been proven difficult to replace fine glass fibers with other fine fibers. In particular, including sufficient non-glass fine fibers to achieve the same efficiency as a media having fine glass fibers typically results in a thick or high-density 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 using a thinner or lower density fine fiber layer, desirable efficiency can be temporarily achieved, and permeability can be improved such that an acceptable pressure drop value can be achieved. However, the pressure drop increases during the life of the filter, and the efficiency of such a fine fiber layer typically collapses. Such a drop in efficiency is thought to be due to "rupture" of the fiber layer and is reflected by the loss of β. (See FIGS. 1A and 1F.) Additionally, upon analysis using scanning electron microscopy (SEM) after efficiency collapse, damage to the nanofiber fiber layer can be observed. (See FIG. 1B.)

[0049] Without wishing to be bound by theory, the efficiency collapse seen when using thinner or lower density fine fibers is thought to be the result of variations in the underlying support layer that result in variations in the pore sizes that the fine fibers must span. At positions where the pore sizes of the underlying support layer are larger and the bridging of the fine fibers is very large, breakage of the fine fibers occurs during use, resulting in loss of efficiency.

[0050] More uniform support layers exist, but the cost of such layers suppresses their use in filter media in terms of cost. Furthermore, more uniform layers do not necessarily exhibit the robustness required to manufacture filter media, including web processing performance. In contrast, spunbond support layers, for example, exhibit large variations in pore size, but are inexpensive and robust, and are therefore particularly suitable for use as support layers in filter media.

[0051] As described above, the fine fibers included in the filter medium of the present disclosure have a mixed diameter such that the fiber layer includes "thick" fine fibers having a fiber diameter that is at least three times the average fiber diameter of the "thin" fine fibers. In some embodiments, the "thick" fine fibers have a fiber diameter that is up to six times the average fiber diameter of the "thin" fine fibers. Without wishing to be bound by theory, it is believed that the larger diameter fine fibers provide support to the smaller diameter fine fibers, thereby enabling the smaller diameter fine fibers to span the pores of the underlying support layer and resist "rupture" of the fibers even when the medium is exposed to higher pressures. Further, the smaller diameter fine fibers allow for the formation of smaller pores, and the achievement of higher efficiency values is tolerated. See, for example, Wang et al., Physical Review Materials, 2020, 4:083803.

[0052] Unexpectedly, including thick fine fibers having an average fiber diameter that is at least three times the average fiber diameter of the thin fine fibers provided the best combination in terms of efficiency and pressure drop. Thick fine fibers having an average fiber diameter of about 2.8 times the average fiber diameter of the thin fine fibers provided better fiber survivability than a layer of fine fibers using only thin fine fibers, but the filter medium did not exhibit the same level of performance as that observed with mixed diameter fine fibers where the thick fine fibers had an average fiber diameter that was at least three times the average fiber diameter of the thin fine fibers. (See Examples 13 and 14.)

[0053] In some embodiments, the thick microfibers can have a diameter that is at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm greater than the diameter of the thin microfibers. As noted above, the thick microfibers have an average fiber diameter that is at least 3 times the average fiber diameter of the thin microfibers, but one or both of the thick and thin microfibers can include a distribution of fibers of various diameters that provide the average diameter. When the thick and thin microfibers include, for example, a diameter distribution, the diameter of the thickest thick microfiber can be at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm greater than the diameter of the thinnest thin microfiber. In such embodiments, the thick and thin microfibers can form a bimodal distribution. In some embodiments, the thick microfibers can have a diameter that is at most 1 μm, at most 2 μm, or at most 3 μm greater than the diameter of the thin microfibers. In an exemplary embodiment, the diameter of the thickest thick microfiber can be greater than the diameter of the thinnest thin microfiber in the range of 0.2 μm to 2 μm.

[0054] In some embodiments, as further described herein, the microfiber layer includes a single (or first) microfiber layer that includes both thick microfibers having a fiber diameter that is at least 3 times the average fiber diameter of the thin microfibers (see FIG. 1G). In some embodiments, the microfiber layer can include a plurality of layers (e.g., a first microfiber layer, a second microfiber layer, etc.).

[0055] In some embodiments, the overall thickness of the microfiber 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 microfiber layer thicknesses greater than 50 μm result in a medium having an undesirably high pressure drop. In some embodiments, when it is desirable to minimize the pressure drop, a thinner microfiber layer thickness (e.g., a thickness of at most 5 μm, a thickness of at most 10 μm, or a thickness of at most 30 μm) can be preferred.

[0056] In some embodiments, the overall thickness of the nanofiber layer can be measured using scanning electron microscopy (SEM). For example, a sample including at least the nanofiber 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 such that the support layer is cut before the nanofiber layer. It can 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 can be useful to use software to outline the nanofiber portion in the SEM image and to enable reshading to facilitate determination of the thickness of the sample. Next, the maximum thickness of the nanofiber portion in the image can be determined using the reshaded image. In some embodiments, the total thickness of the nanofiber 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 nanofibers can mainly include thick nanofibers, and the second layer of nanofibers can mainly include thin nanofibers. For example, the first layer of nanofibers can include up to 10% or up to 20% thick nanofibers (i.e., nanofibers having a fiber diameter that is at least three times the average fiber diameter of the smaller diameter fibers). In some embodiments, including where the first layer of nanofibers is composed of or mainly includes thick nanofibers, the second layer of nanofibers can include up to 10% or up to 20% of the larger diameter nanofibers (i.e., nanofibers having a fiber diameter that is 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 nanofibers of the nanofiber layer that make up most of the smaller diameter nanoparticles with larger diameter nanofibers, the nonwoven structure can be opened up and the permeability and depth loading of the second layer of nanofibers can be increased while retaining the efficiency due to the network structure of the smaller diameter nanofibers.

[0059] In some embodiments, as further discussed herein, the thick and thin fibrils can be mixed within a single fibril layer. Such mixing results in a decrease in the solidity of the fibril layer as compared to a fibril layer containing only thin fibrils. Without wishing to be bound by theory, it is believed that such a decrease in solidity is seen because the thick fibrils act as spacers, allowing for more air movement between the fibrils.

[0060] The filter media described herein provides a low initial dP value and does not exhibit efficiency or beta decay over the expected life of the filter. (See Example 1 and Figure 1C.) Additionally, when analyzed using SEM, damage to the fibril layer when the media layer is exposed to pressure (e.g., up to 20 psi) is minimized. (See Figure 1D.)

[0061] Support layer The filter media described herein includes 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, fibrous materials are used for the support layer. The fibers of the support layer can be formed from natural fibers 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 includes fibers having an average diameter of at least 5 microns or at least 10 microns. In some embodiments, the support layer can include fibers having an average diameter of up to 250 microns.

[0064] In some embodiments, the support layer has a thickness of at least 0.005 inches (125 microns), often at least 0.01 inches (250 microns). In some embodiments, the support layer has a thickness of up to 0.03 inches (750 microns).

[0065] In some embodiments, the support layer is at least 8 g / m 2 , at least 10 g / m 2 , at least 15 g / m 2 or at least 20 g / m 2 in basis weight. In some embodiments, the support layer is at most 70 g / m 2 , at most 100 g / m 2 or at most 150 g / m 2 in basis weight. In an exemplary embodiment, the support layer has a basis weight in the range of 8 g / m 2 to 150 g / m 2 . In another exemplary embodiment, the support layer has a basis weight in the range of 15 g / m 2 to 100 g / m 2 . The basis weight of the support layer can be measured using TAPPI T410 om-08.

[0066] In some embodiments, the support layer has a solids content 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 solids content 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 solids content in the range of 10% to 40%. In another exemplary embodiment, the support layer has a solids content in the range of 20% to 30%. The solids content 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 density of the fiber, and Z is the thickness of the medium measured by TAPPI T411 om-15). When measuring the thickness of the medium, a foot pressure of 1.5 psi can be used.

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

[0068] In some embodiments, the support layer has an average maximum pore diameter of at most 10 μm, at most 15 μm, at most 20 μm, at most 25 μm, at most 30 μm, at most 35 μm, at most 40 μm, at most 50 μm, at most 60 μm, at most 70 μm, at most 80 μm, at most 90 μm, at most 100 μm or at most 150 μm. In an exemplary embodiment, the support layer has an average maximum pore diameter of at most 90 μm. In some embodiments, the average maximum pore diameter is preferably determined using capillary flow porometry.

[0069] In some embodiments, the support layer has an average minimum pore diameter 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 an exemplary embodiment, the support layer has an average minimum pore diameter of at least 20 μm. In some embodiments, the average minimum pore diameter 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., pore size, solidity, basis weight or thickness or combinations of these characteristics or each of these characteristics of the media) are consistent across the length and width of the media. For example, in an exemplary embodiment, the average mid-flow pore size varies by no more than 30%, more preferably no more than 25%, and even more preferably no more than 15% across the length and width of the media.

[0071] However, in some embodiments, further, as described 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, a spunbond support layer exhibits large variations in pore size but is an inexpensive and robust layer and is thus particularly suitable for use as a support layer in filter media.

[0072] Without wishing to be bound by theory, it is believed that the interaction 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 for achieving a structurally stable and efficient media. For example, a higher basis weight (e.g., 60 g / m 2Merely using a support layer with a maximum pore size exceeding a certain size (e.g., 90 μm) will not result in a structurally stable medium. This is because when the maximum pore size of the support layer exceeds a specific size, when the diameter of the fine fibers is below a specific size and / or when the thickness of the fine fibers is thin, the fine fiber layer will have its structure damaged during filtration with a sufficiently high pressure drop. For example, when thin fine fibers (e.g., having an average diameter of at most 0.5 μm) are used in a first fine fiber layer on a support layer having an average maximum pore size of 88 μm, it is found that an increase in the basis weight of the fine fiber layer requires an unsustainable high pressure to move fluid through the medium; in contrast, reducing the basis weight of the thin fine fiber layer results in damage to the layer structure during filtration. An increase in 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., up to an average diameter of at least 0.6 μm, more preferably at least 0.9 μm, even more preferably 1 μm) reduces the efficiency of the medium, but increasing the fiber diameter also reduces the pressure drop, resulting in a structurally stable medium that will not be structurally damaged during use.

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

[0074] The support layer can be formed of any suitable material. Examples of materials suitable for the support layer include spunbond, wet-laid, carded or meltblown nonwoven materials or combinations thereof including, for example, spunbond-meltblown-spunbond. The fibers can be in the form of a woven or nonwoven fabric. Examples of synthetic nonwoven fabrics include polyester nonwoven, nylon nonwoven, polyolefin (e.g., polypropylene) nonwoven, polycarbonate nonwoven or blends or multi-component nonwovens thereof. Sheet-like support layers (e.g., cellulose, synthetic and / or glass or combined webs) are typical examples of filter support layers. Other examples of suitable support layers include polyester or bicomponent polyester fibers or polypropylene / polyethylene terephthalate or polyethylene / polyethylene terephthalate bicomponent fibers of spunbond.

[0075] In some embodiments, the support layer may preferably include polymer fibers. In some embodiments, the polymer fibers may include nylon fibers or polyester fibers.

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

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

[0078] In an exemplary embodiment, the support layer includes CEREX 23200 (Cerex Advanced Fabrics, Inc., Cantoment, FL). CEREX 23200 contains nylon 6,6, has a thickness of 8.4 mils (0.21 mm), a basis weight of 67.8 g / m 2 ², a solidity of 28% and a permeability per solidity of 615.1. The pore size of CEREX 23200 is shown in Table 2C.

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

[0080] In some embodiments, the fine fiber layer may 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 may have a thickness of up to 5 μm, up to 10 μm, up to 30 μm or up to 50 μm.

[0082] In some embodiments, the overall 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 freezing (e.g., in liquid nitrogen). It can be useful to cross-section the sample while orienting the sample such that the support layer is cut before the fine fiber layer. It may be further useful to cross-section the sample while immersing the sample 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 enabling outlining and re-shadowing of the fine fiber portion in the SEM image. The maximum thickness of the fine fiber portion in the image can then be determined using the re-shadowed image. In some embodiments, the overall 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] The first layer of fine fibers In some embodiments, the first layer of fine fibers includes "thick" fine fibers having an average fiber diameter that is at least 3 times the average fiber diameter of the "thin" fine fibers. That is, the first layer of fine fibers may include fibers of mixed diameters.

[0084] Additionally or alternatively, the thin fibrils may be present in a second layer of fibrils. When the thin fibrils are present in the second layer of fibrils rather than the first layer of fibrils, the first layer of fibrils may comprise only "thick" fibrils having an average diameter that is at least 3 times the average fiber diameter of the minimum average fiber diameter of the second fibril layer. In such embodiments, the thick fibrils of the first fibril layer may have a diameter that is at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm greater than the diameter of the fibrils of the second fibril layer. As noted above, the thick fibrils have an average fiber diameter that is at least 3 times the average fiber diameter of the thin fibrils, and 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 of the first fibril layer and the thin fibrils of the second fibril layer comprise, for example, a distribution of diameters, the diameter of the thickest thin fibril may be at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm greater than the diameter of the thinnest thick fibril. In some embodiments, the thick fibrils of the first fibril layer may have a diameter that is up to 1 μm, up to 2 μm, or up to 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 up to 1.1 μm, up to 1.2 μm, up to 1.3 μm, up to 1.4 μm, up to 1.5 μm, up to 2 μm, up to 3 μm, up to 4 μm, up to 5 μm, or up to 10 μm. An exemplary image of the first fibril layer includes thick fibrils deposited on a support layer, as shown in FIG. 1E.

[0086] In embodiments where the first fine fiber layer includes "thick" fine fibers and "thin" fine fibers, and the thick fine fibers have an average diameter that is at least 3 times the average fiber diameter of the thin fine fibers, the thin fine fibers can have an average diameter of up to 0.3 μm, up to 0.4 μm, up to 0.5 μm, or up to 0.6 μm. In some embodiments, the average fiber diameter of the thin fine fibers in the first fine fiber layer can be at least 0.2 μm. For example, the average fiber diameter of the thin fine fibers 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.

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

[0088] Exemplary combinations of "thick" and "thin" fine fiber diameters include, for example, fibers with diameters of 1 μm and 0.25 μm (see Examples 1 - 11); or fibers with diameters of 1.4 μm and 0.25 μm (see Example 12). Example 13 further discloses fibers with diameters of 1.4 μm and 0.5 μm, but the thick fine fibers (1.4 μm) do not have an average diameter that is at least 3 times the average diameter of the thin fine fibers (0.5 μm).

[0089] While not wishing to be bound by theory, the inclusion of a layer of fine fibers including thick fibers is thought to enable the use of a more "open" support layer than a filter medium that does not include a layer including thick fibers. By using a more "open" support layer, the material passing through the filter encounters less of the material that impedes flow, providing a lower pressure drop than a support layer having smaller pores or a higher basis weight.

[0090] First layer of fine fibers - thick fibers In some embodiments, the first layer of fine fibers comprises mainly (e.g., more than 95%) thick fibers or does not include thin fibers. In such embodiments, a second layer of fine fibers including thin fibers is deposited on top of the first layer of fibers as described below.

[0091] In such embodiments, the thick fibers of the first fine fiber layer can have a diameter that is at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm greater than the diameter of the thin fibers of the second fine fiber layer. As noted above, the thick fibers have an average fiber diameter that is at least 3 times the average fiber diameter of the thin fibers, and one or both of the thick fibers and the thin fibers can include a distribution of fibers of various diameters that provide the average diameter. When the thick fibers of the first fine fiber layer and the thin fibers of the second fine fiber layer include, for example, a distribution of diameters, the diameter of the thickest thick fiber can be at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm greater than the diameter of the thinnest thin fiber. In some such embodiments, the thick fibers and the thin fibers can form a bimodal distribution. In some embodiments, the thick fibers of the first fine fiber layer can have an average diameter that is at most 1 μm, at most 2 μm, or at most 3 μm greater than the average diameter of the thin fibers of the second fine fiber layer.

[0092] In some embodiments, including where the filter medium includes a second layer of fine fibers, the first layer of fine fibers is 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 and has a basis weight of at least 0.5 g / m 2 and has a basis weight of at least 1 g / m 2 and has a basis weight of at least 1.5 g / m 2 and has a basis weight of at least 2 g / m 2 or has a basis weight of at least 2.5 g / m 2 In some embodiments, the first layer of fine fibers has a basis weight of up to 1.5 g / m 2 and has a basis weight of up to 2 g / m 2 and has a basis weight of up to 2.5 g / m 2 and has a basis weight of up to 3 g / m 2 and has a basis weight of up to 3.5 g / m 2 and has a basis weight of up to 4 g / m 2 and has a basis weight of up to 4.5 g / m 2 and has a basis weight of up to 5 g / m 2 and has a basis weight of up to 10 g / m 2 and has a basis weight of up to 15 g / m 2 and has a basis weight of up to 20 g / m 2 and has a basis weight of up to 25 g / m 2 and has a basis weight of up to 50 g / m 2 In some embodiments, the first layer of fine fibers has a basis weight of at least 0.1 g / m 2 and up to 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 up to 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 the fine fibers) / (area of the scrim). The mass of the fine fibers can be calculated from the polymer used to produce the fibers and the spinning conditions according to the following equation: Mass of the fine fibers = (% w / v of polymer in solution) × (pump rate) × (spinning time).

[0093] In some embodiments, including those where the filter medium includes a second layer of fine fibers, the first layer of fine fibers has an average middle flow pore diameter 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 middle flow pore diameter of up to 10 μm, up to 15 μm, up to 20 μm, up to 25 μm, up to 30 μm, or up to 35 μm. In an exemplary embodiment, the first layer of fine fibers has an average middle flow pore diameter in the range of 10 μm to 25 μm. In some embodiments, the average middle flow pore diameter is preferably determined using capillary flow porometry.

[0094] In some embodiments, including those where the filter medium includes a second layer of fine fibers, the first layer of fine fibers has an average maximum pore diameter of up to 10 μm, up to 15 μm, up to 20 μm, up to 25 μm, up to 30 μm, or up to 35 μm. In some embodiments, the average maximum pore diameter of the first layer of fine fibers is preferably determined using capillary flow porometry.

[0095] In some embodiments, including those where the filter medium includes a second layer of fine fibers, the first layer of fine fibers has a thickness of at least the average diameter of the thick fine fibers of 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 an average diameter of the thick fine fibers 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. In some embodiments, the first layer of fine fibers has a thickness greater than 1 μm.

[0097] In some embodiments, the first layer of fine fibers has a thickness of up to 5 μm, up to 10 μm, up to 30 μm, or up to 50 μm.

[0098] In some embodiments, the overall 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 freezing (e.g., in liquid nitrogen). It can be useful to cross-section the sample while orienting the sample such that the support layer is cut in front of the fine fiber layer. It may be even more useful to cross-section the sample while immersing the sample in liquid nitrogen. An exemplary magnification that can be used is 1000 times. It can be useful to use software that aids in determining the thickness of the sample by enabling outlining and re-shadowing of the fine fiber portion in the SEM image. Then, using the re-shadowed image, the maximum thickness of the fine fiber portion in the image can be determined. In some embodiments, the overall 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 where the filter medium includes a second layer of fine fibers, the first layer of fine fibers can have a lower solidity than the second layer of fine fibers. That is, the first layer of fine fibers can 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 up to 10%, up to 20%, up to 25%, up to 30%, up to 40% or up to 50%. In an exemplary embodiment, 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 (c) of the fine fiber layer can be calculated from the dimensionless fiber drag parameter, F * 1.0 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 microfibers - Mixed diameter microfibers In some embodiments, the first layer of microfibers includes thick microfibers and thin microfibers, and the thick microfibers have an average diameter that is at least 3 times the average fiber diameter of the thin microfibers. In such embodiments, the second layer of microfibers may or may not be deposited on top of the first layer of fibers, as described below.

[0101] In some embodiments, the thick microfibers of the first microfiber layer may have a diameter that is at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm greater than the diameter of the thin microfibers of the first microfiber layer. As noted above, the thick microfibers have an average fiber diameter that is at least 3 times the average fiber diameter of the thin microfibers, and one or both of the thick and thin microfibers may include a distribution of fibers of various diameters that provide the average diameter. When the thick or thin microfibers include a distribution of diameters, the diameter of the thickest thin microfiber may be at least 0.2 μm, at least 0.3 μm, or at least 0.4 μm greater than the diameter of the thinnest thick microfiber. In some embodiments, the thick microfibers may have a diameter that is at most 1 μm, at most 2 μm, or at most 3 μm greater than the diameter of the thin microfibers.

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

[0103] When the first layer of fine fibers includes both thin and thick fine fibers, the fibers of mixed diameter can be mixed (as a result of being formed simultaneously; see FIG. 1I), or can be layered (as a result of being applied alternately to the substrate; see FIGS. 1J and 1L), or both (see FIG. 1M). When the fibers of mixed diameter are layered (as a result of being applied alternately to the substrate), a single layer of fine fibers can include sub-layers of thick and thin fine fibers.

[0104] In some embodiments, the first layer of fine fibers can include at least 0.5%, at least 1%, at least 2%, at least 5%, at least 7%, at least 10%, at least 12%, at least 14%, at least 16%, at least 20%, at least 50%, at least 60%, at least 70%, or at least 80% thick fine fibers. In some embodiments, the first layer of fine fibers can include up to 1%, up to 2%, up to 5%, up to 7%, up to 10%, up to 12%, up to 14%, up to 16%, up to 20%, up to 50%, up to 60%, up to 70%, up to 80%, 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 the proportion of one or more 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 in Tables 1A - 1C. Additional exemplary ranges of thick fine fibers in the first layer of fine fibers include 10% - 90% thick fine fibers, 20% - 80% thick fine fibers, or 30% - 70% thick fine fibers.

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

[0106] In some embodiments, the proportion of thick microfibers can be determined based on the spinning time using the equations provided in the section on calculating the proportion of fibers in the examples.

[0107] In some embodiments, the proportion of thick microfibers can be determined by nano-computed tomography (nano-CT). For example, a sample of the filter media can be embedded in resin that is scanned as if it were cut along the Z-axis. Useful images can be obtained by using synchrotron-quality Nanoscale 3D X-ray imaging equipment such as, for example, an Xradia 810 Ultra (Zeiss, Oberkochen, Germany). It may be useful to then stitch the images together to form a 3D digital structure to determine the proportion of fibers having a particular diameter. The proportion of thin / thick microfibers can be calculated by the ratio of the number of thin / thick microfibers to the number of all fibers (both thin and thick fibers) in the digital structure.

[0108] In some embodiments, the proportion of thick microfibers can be determined using microscopic observation. For example, sample images can be obtained through 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 the fibers within the image range and subsequently classifying them as thin and thick microfibers based on group diameter within a 25% variation. The fiber diameter can be measured and / or classified using image processing software such as ImageJ. The proportion of thin / thick microfibers can be calculated by the ratio of the number of thin / thick microfibers to the number of all fibers (both thin and thick fibers) within the image range.

[0109] In some embodiments, the first layer of fine fibers has an average mid-flow pore diameter 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 mid-flow pore diameter of up to 0.5 μm, up to 1 μm, up to 5 μm, up to 10 μm, up to 15 μm, up to 20 μm, up to 25 μm, up to 30 μm, or up to 35 μm. In an exemplary embodiment, the first layer of fine fibers has an average mid-flow pore diameter in the range of 10 μm to 25 μm. In some embodiments, the average mid-flow pore diameter is preferably determined using capillary flow porometry.

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

[0111] In some embodiments, the first layer of fine fibers has a basis weight 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 0.5 g / m 2 , at least 1 g / m 2 , at least 1.5 g / 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 up to 1.5 g / m 2 , up to 2 g / m 2 , up to 2.5 g / m 2 , up to 3 g / m 2 , up to 3.5 g / m 2 , up to 4 g / m 2 , up to 4.5 g / m 2 , up to 5 g / m 2 , up to 10 g / m 2 , up to 15 g / m 2 , up to 20 g / m 2 , up to 25 g / m 2, having a basis weight of up to 50 g / m 2 In some embodiments, the first layer of microfibers has a basis weight of at least 0.1 g / m 2 and up to 20 g / m 2 In another exemplary embodiment, the first layer of microfibers has a basis weight of at least 0.1 g / m 2 and up to 1 g / m 2 In a further exemplary embodiment, the first layer of microfibers has a basis weight of 0.43 g / m 2 When fibers of different diameters are layered, the basis weight of the first layer of microfibers is additive. The basis weight of the first layer of microfibers can be from the mass of the first layer of microfibers and the area of the scrim according to the following equation: Basis weight of the first layer of microfibers = (Mass of the first layer of microfibers) / (Area of the scrim). The mass of the microfibers can be calculated from the polymer used to produce the fibers and the spinning conditions according to the following equation: Mass of the microfibers = (%w / v of polymer in solution) × (Pump rate) × (Spinning time).

[0112] In some embodiments, the first layer of microfibers has a solids content 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 microfibers has a solids content of up to 10%, up to 20%, up to 25%, up to 30%, up to 40% or up to 50%. In an exemplary embodiment, the first layer of microfibers has a solids content in the range of 0.5% to 30%. The solids content (c) of the first layer of microfibers can be calculated from the dimensionless fiber drag parameter, F * 1.0 from the following: 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 microfibers has a thickness of at least the average diameter of the average microfibers of the first layer of microfibers. In some embodiments, the first layer of microfibers 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 microfibers has a thickness that is the thickness of several fibers having the average diameter of the first layer of microfibers. For example, the first layer of microfibers 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 microfibers has a thickness of up to 1 μm, up to 5 μm, up to 10 μm, up to 30 μm, or up to 50 μm.

[0116] In some embodiments, the overall thickness of the microfiber layer can be measured using scanning electron microscopy (SEM). For example, a sample including at least the microfiber layer and the support layer can be prepared for SEM by cross-sectioning the sample while freezing (e.g., in liquid nitrogen). It can be useful to cross-section the sample while orienting the sample such that the support layer is cut in front of the microfiber layer. It can be even more useful to cross-section the sample while immersing the sample in liquid nitrogen. An exemplary magnification that can be used is 1000×. It can be useful to use software that aids in determining the thickness of the sample by enabling outlining and re-shadowing of the microfiber portion in the SEM image. Then, using the re-shadowed image, the maximum thickness of the microfiber portion in the image can be determined. In some embodiments, the overall thickness of the microfiber layer can be determined by averaging at least five maximum thicknesses from five separate images of the same sample.

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

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

[0119] In some embodiments, the smallest 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. In some embodiments, the average fiber diameter of the smallest fibers of the second fine fiber layer has an average diameter of at least 0.2 μm. For example, the average fiber diameter of the smallest 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.

[0120] In some embodiments, the second layer of fine fibers may include a single layer that includes fibers having an average diameter that is at most one-third of the average fiber diameter of the fibers of the first layer of fine fibers (see, for example, FIG. 1H).

[0121] In some embodiments, the second layer of fine fibers may include fine fibers of mixed diameters. For example, the second layer of fine fibers may include two different diameters of fine fibers (i.e., thin fine fibers and thick fine fibers) (see FIGS. 1I and 1J), and the thick fine fibers have an average diameter that is at least three times the diameter of the thin fine fibers.

[0122] In some embodiments, the thin fibers of the second fibrous layer have an average diameter of up to 0.3 μm, up to 0.4 μm, up to 0.5 μm, or up to 0.6 μm. In some embodiments, the thin fibers of the second fibrous layer have an average fiber diameter of at least 0.2 μm. For example, the average fiber diameter of the thin fibers of the second fibrous 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 fibers of the second layer of fibers have an average fiber diameter of at least 1 μm or greater than 1 μm. In some embodiments, the thick fibers of the second layer of fibers have an average fiber diameter of up to 1 μm, up to 1.1 μm, up to 1.2 μm, up to 1.3 μm, up to 1.4 μm, up to 1.5 μm, up to 2 μm, up to 3 μm, up to 4 μm, up to 5 μm, or up to 10 μm.

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

[0125] When the second layer of fibers includes thin and thick fibers, the fibers of mixed diameters can be mixed (as a result of being formed simultaneously) (see Figure 1I), or can be layered (as a result of being applied alternately to the substrate) (see Figures 1J and 1L), or both (see Figure 1M). When the fibers of mixed diameters are layered (as a result of being applied alternately to the substrate), a single layer of thin fibers can include sub-layers of thick and thin fibers.

[0126] The second layer of the fine fibers can comprise any suitable mixture of fibers of mixed diameter. 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 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 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 second layer of fine fibers can comprise the proportion of one or more 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.

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

[0128] In some embodiments, the proportion of thick fine fibers can be determined based on the spinning time using the equations provided in the fiber proportion calculation section of the examples.

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

[0130] In some embodiments, the proportion of thick microfibers can be determined using microscopy. For example, sample images can be obtained through 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 the fibers within the image range, which are subsequently classified as thin and thick microfibers based on group diameter within a 25% variation. The fiber diameter can be measured and / or classified using image processing software such as ImageJ. The proportion of thin / thick microfibers can be calculated by the ratio of the number of thin / thick microfibers to the number of all fibers (both thin and thick fibers) within the image range.

[0131] For example, in an exemplary embodiment, the second layer of fine fibers can include at least 0.5% and up to 20% thick fibers, more preferably at least 1% and up to 10% thick fibers or even more preferably at least 5% and up to 7% thick fibers. Additional ranges can also be useful, including, for example, at least 3% and up to 9% thick fibers or at least 4% and up to 8% thick fibers. Without wishing to be bound by theory, it is believed that by optimizing the proportion of thick fibers in the second layer of fine fibers, the fine fiber structure is collapsed and support is provided to the fine fibers without resulting in a corresponding loss of efficiency.

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

[0133] Any suitable combination of layers of fine and thick fibers 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 of 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 of 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 fine fibers, then a sublayer of mixed fine and thick fibers, and the sublayer of thick fibers can be the uppermost layer.

[0135] In some embodiments, the second layer of fine fibers has an average mid-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 mid-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 an exemplary embodiment, the first layer of fine fibers has an average mid-flow pore size in the range of 10 μm to 25 μm. In some embodiments, the average mid-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 fibers.

[0137] In some embodiments, the second layer of fine fibers is 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 0.5 g / m 2 , at least 1 g / m 2 , at least 1.5 g / m 2 , at least 2 g / m 2 or at least 2.5 g / m 2 and has a basis weight. In some embodiments, the second layer of fine fibers is at most 1.5 g / m 2 , at most 2 g / m 2 , at most 2.5 g / m 2 , at most 3 g / m 2 , at most 3.5 g / m 2 , at most 4 g / m 2 , at most 4.5 g / m 2 , at most 5 g / m 2 , at most 10 g / m 2 , at most 15 g / m 2 , at most 20 g / m 2 , at most 25 g / m 2, having a basis weight of up to 50 g / m 2 In some embodiments, the second layer of fine fibers has a basis weight of at least 0.1 g / m 2 and up to 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 up to 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 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 from the mass of the second layer of fine fibers and the area of the scrim according to the following equation: Basis weight of the second layer of fine fibers = (Mass of the second layer of fine fibers) / (Area of the scrim). The mass of the second layer of fine fibers can be calculated from the polymer used to produce the fibers and the spinning conditions according to the following equation: Mass of the fine fibers = (% w / v of polymer in solution) × (Pump rate) × (Spinning time).

[0138] In some embodiments, the second layer of fine fibers has a higher solids content 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 solids content 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 solids content of up to 10%, up to 20%, up to 25%, up to 30%, up to 40% or up to 50%. In an exemplary embodiment, the second layer of fine fibers has a solids content in the range of 0.5% to 30%. The solids content (c) of the second layer of fine fibers can be calculated from the dimensionless fiber drag parameter, F * 1.0 as follows: 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 microfibers has a thickness of at least the average diameter of the average microfibers of the second layer of microfibers. In some embodiments, the second layer of microfibers has a thickness of at least 0.5 μm or at least 1 μm.

[0140] In some embodiments, the second layer of microfibers has a thickness that is the thickness of several fibers having the average diameter of the second layer of microfibers. For example, the second layer of microfibers 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 microfibers has a thickness of up to 5 μm, up to 10 μm, up to 30 μm, up to 40 μm, or up to 45 μm.

[0142] In some embodiments, the overall thickness of the microfiber layer can be measured using scanning electron microscopy (SEM). For example, a sample including at least the microfiber layer and the support layer can be prepared for SEM by cross-sectioning the sample while freezing (e.g., in liquid nitrogen). It can be useful to cross-section the sample while orienting the sample such that the support layer is cut in front of the microfiber layer. It can be even more useful to cross-section the sample while immersing the sample 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 enabling outlining and re-shadowing of the microfiber portion in the SEM image. Then, using the re-shadowed image, the maximum thickness of the microfiber portion in the image can be determined. In some embodiments, the overall thickness of the microfiber 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 medium can be directly related to the thickness of the second layer of microfibers.

[0144] Characteristics of the filter medium As described above, the filter medium includes a support layer and a layer of fine fibers. These layers can form a composite material.

[0145] In some embodiments, the filter medium has a composite material average maximum pore diameter of at most 20 μm, preferably at most 15 μm, more preferably at most 14 μm. In some embodiments, the composite material average maximum pore diameter of the filter medium is at least 0.1 μm. As used herein, "composite material average maximum pore diameter" refers to the average maximum pore diameter of the composite material including the support layer and the fine fiber layer.

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

[0147] When the fine fiber layer includes a plurality of fine fiber layers, the composite material includes each fine fiber layer.

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

[0149] Without wishing to be bound by theory, the composite material average maximum pores and the composite material average intermediate flow pore diameter depend, inter alia, on the fine fiber diameter, the relative amounts of thin and thick fine fibers, and the composite material morphology (e.g., layered or mixed).

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

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

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

[0153] Fine fibers produced from a polymer and a reactive additive In some embodiments, the fine fibers of the present disclosure can be produced by combining a fiber-forming polymer material with at least two reactive additives that are capable of reacting with each other, for example, in a fiber-forming process or a post-treatment process, as further described in International Publication No. WO 2014 / 164130. The at least two reactive additives are optionally reactive with the fiber-forming polymer.

[0154] In some embodiments, the microfibers of the present disclosure can include at least one fiber-forming polymer and at least two reactive additives that are covalently bonded to each other and optionally covalently bonded to the fiber-forming polymer. In some embodiments, at least one of the reactive additives is self-condensable. In some embodiments, at least one of the reactive additives enhances at least one property of the microfibers as compared to microfibers in the absence of such reactive additives. In this context, "enhance" means to improve or cause one or more properties.

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

[0156] In certain embodiments, the reactive additives are monomers, oligomers or low molecular weight polymers. For example, in certain embodiments, the reactive additives have a weight average molecular weight of less than 3000 Daltons. In certain embodiments, all of the reactive additives used to produce the microfibers have a weight average molecular weight of less than 3000 Daltons. In some embodiments, the weight average molecular weight of the reactive additives can be determined using time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0157] The reactive additive can have various reactive functional groups. For example, these can include an alkoxy group, a hydroxyl group, an acid group (e.g., a carboxylic acid group), an isocyanate group, a diglycidyl ether group, and a dichloro group. Any one molecule of a compound functioning as a reactive additive can contain one or more of one type of functional group or two or more different functional groups. The reactive additive can include a mixture of compounds having various numbers or types of functional groups. The hydroxyl group-functional component can include a diol, a triol, a polyol, or a mixture thereof. Examples of the carboxylic acid-functional component include compounds having a plurality of carboxylic acid groups (e.g., a diacid, a triacid, or a mixture thereof). Examples of the glycidyl ether-functional component include compounds having a plurality of glycidyl ether groups (e.g., diglycidyl ether, triglycidyl ether, or a mixture thereof). Examples of the amine-functional component include a primary amine compound, a secondary amine compound, a tertiary amine compound, or a mixture thereof. Examples of the amine-functional component include compounds having a plurality of primary, secondary, or tertiary amine groups (e.g., diamine, triamine, or a mixture thereof). Examples of the isocyanate-functional component include compounds having a plurality of isocyanate groups (e.g., diisocyanate, triisocyanate, or a mixture thereof). In addition, the reactive additive 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, sorbitol are polyfunctional hydroxyl group-containing reactive additives, citric acid and dimethylolpropionic acid are polyfunctional 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 polyfunctional amine-containing reactive additives.

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

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

[0161] In some embodiments, as further described below, the resinous aldehyde composition includes a "polymer-reactive resinous aldehyde composition". The "polymer-reactive resinous aldehyde composition" includes alkoxy groups, as further described in U.S. Patent No. 9,587,328. In the final fiber, at least a portion of the polymer-reactive resinous aldehyde composition can participate in cross-linking of the polymer and optionally in self-cross-linking. The fiber-forming polymer material also includes reactive groups. In this regard, "reactive" means that the polymer includes one or more functional groups (e.g., active hydrogen groups) that can be cross-linked by the alkoxy groups of the polymer-reactive resinous aldehyde composition used in producing the fine fibers.

[0162] In some embodiments, as further described below, the resinous aldehyde composition includes a "polymer-nonreactive resinous aldehyde composition". The polymer-nonreactive resinous aldehyde composition includes reactive groups for self-cross-linking, as further described in U.S. Patent No. 9,435,056. In the final fiber, at least a portion of the polymer-nonreactive resinous aldehyde composition participates in self-cross-linking.

[0163] As used herein, "resin" or "resinous" means monomers, oligomers, and / or polymers that are particularly capable of moving to the surface of the fine fibers during fiber formation. In this specification, the term "resinous aldehyde composition" means the starting materials as well as the materials in the final fibers.

[0164] These components can be combined in solution or in a molten form. In certain embodiments, the microfibers are electrospun from a solution or dispersion. Accordingly, the polymer 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] Microfibers made from a polymer crosslinked by a polymer reactive resinous aldehyde composition As further described in U.S. Patent No. 9,587,328, in some embodiments, the microfibers of the present disclosure can be produced by combining a fiber-forming polymer material with a polymer reactive resinous aldehyde composition containing an alkoxy group (e.g., a reactive melamine-formaldehyde resin).

[0166] Referring to FIGS. 9A and 9B, when the fibers 100 / 102 are formed, the polymer reactive resinous aldehyde composition preferably forms at least one outer concentric (coaxial) layer or phase such as a second coating phase 22 (fiber 102, FIG. 9B) mainly containing the polymer reactive resinous aldehyde composition (e.g., a melamine aldehyde composition), or a second coating phase 20 (fiber 100, FIG. 9A) containing a mixture of the polymer material and the polymer reactive resinous aldehyde composition and a third outer phase (outermost phase) 30 (FIG. 9A) mainly containing the polymer reactive resinous aldehyde composition, i.e., two outer concentric layers or phases. That is, the polymer reactive resinous aldehyde composition can migrate to the surface to form a two-phase fiber (FIG. 9B) or a three-phase fiber (FIG. 9A), where the core 10 (FIG. 9A) or 12 (FIG. 9B) mainly contains a polymer material (e.g., nylon). Generally, the higher the content of the polymer reactive resinous aldehyde compared to the polymer, the greater the tendency to form a three-phase fiber.

[0167] In some embodiments, the fine fibers of the present disclosure can preferably be prepared from a polymer-reactive resinous aldehyde composition containing an alkoxy group and a polymer containing an active hydrogen group, and the molar ratio of the polymer-reactive resinous aldehyde composition to the polymer is such that the molar ratio of the alkoxy group of the polymer-reactive resinous aldehyde composition to the active hydrogen group 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 can be such that the molar ratio of the alkoxy group of the polymer-reactive resinous aldehyde composition to the active hydrogen group of the polymer is 300:100 or less, 250:100 or less, or 210:100 or less.

[0168] In certain embodiments, a weight ratio of the polymer-reactive resinous aldehyde composition to the polymer that 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 may be used. In some embodiments, the weight ratio can be used to control the formation of a useful outer phase that includes the polymer-reactive resinous aldehyde composition surrounding the core polymer. The outer coating layer, which consists mainly of the polymer-reactive resinous aldehyde composition (e.g., melamine-formaldehyde), provides improved properties such as moisture resistance to the fine fibers and fine fiber layers of the present disclosure compared to commercially available fibers and fiber layers. In this regard, "consists mainly of" means that the referenced material is present in a major amount (i.e., more than 50% by weight) of the materials in that particular region (e.g., coating, layer, or phase).

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

[0170] A suitable polymeric reactive resinous aldehyde composition contains two or more alkoxy groups per molecule capable of crosslinking the polymers used in manufacturing the fine fibers described herein. Exemplary polymeric 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 reactive resinous aldehyde compositions include aldehyde-based agents that can be used in crosslinking reactions. The polymeric reactive resinous aldehyde composition is typically non-volatile. Also, (when combined with polymers such as nylon, as described in detail below) the polymeric reactive resinous aldehyde composition must be soluble in a solvent selected for the polymeric material for processes such as electrospinning. Useful polymeric reactive resinous aldehyde compositions as crosslinking agents include condensation products of urea and aldehydes, condensation products of phenol and aldehydes, or condensation products of melamine and aldehydes. One useful classification of crosslinked resins includes nitrogen compound-based resins such as melamine, urea, benzoguanamine, glycoluril, and other similar resins produced by reacting nitrogen compounds with aldehydes. Such amine-based crosslinked resins are soluble in process solvents and have reactivity with various polymer species.

[0171] Useful polymeric reactive resinous aldehyde compositions (e.g., melamine aldehyde compositions) can contain crosslinking agents and optionally other non-reactive room-stable resin components that can be combined in solution or in a molten form with various polymeric materials. Melamine forms resinous compositions together with various other co-reactants.

[0172] Useful melamine aldehyde compositions include melamine-aldehyde products generally formed by the reaction between melamine and aldehyde compounds. Useful aldehyde compounds include C 1~6 alkanals such as formaldehyde, acetaldehyde, butyraldehyde, isobutyraldehyde, etc. Such mixtures of aldehydes can be used as needed. 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 polymeric reactive resinous aldehyde composition includes a condensation product of urea and an aldehyde, a condensation product of phenol and an aldehyde, a condensation product of melamine and an aldehyde, or a mixture thereof. In certain embodiments, the polymeric reactive resinous aldehyde composition includes 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 resin; hexabutoxymethyl melamine; butoxymethyl melamine; highly alkylated mixed ether melamine; methoxymethyl methylol melamine, highly methylated melamine resin; melamine - formaldehyde resin co - etherified by methanol and n - butoxyethanol / n - butanol blend; melamine - formaldehyde resin co - etherified by methanol and n - butanol in n - butanol; butyl melamine - formaldehyde resin dissolved in n - butanol and butyl glycol blend; hexabutoxymethyl melamine; partially n - butylated melamine; high solids, highly methylated melamine resin;Various polymer-reactive resinous aldehyde compositions sold under the trade name CYMEL available from Cytec Industries of West Paterson, NJ, including, 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 UI-20-E, CYMEL UI-38-I, CYMEL 1123, CYMEL 659, CYMEL 1172, CYMEL 1170;Compounds and mixtures thereof are included, including various polymer-reactive resinous aldehyde compositions sold under the trade name LUWIPAL available from BASF AG, Ludwigshafen, Germany, including LUWIPAL LR 8955, LUWIPAL LR 8968 and LUWIPAL LR 8984. Such resins are also available from INEOS Melamines Inc. and are sold under the trade names RESIMENE (e.g., RESIMENE HM 2608), MAPRENAL and MADURIT. Optionally, various combinations of polymer-reactive resinous aldehyde compositions may be used.;

[0175] In an exemplary embodiment, a melamine-formaldehyde resin (sometimes referred to herein simply as "melamine composition" or "melamine resin") is used. The term melamine-formaldehyde resin means a melamine-based resin having two or more (at least two) alkoxy functional groups (methoxy, ethoxy, propoxy, butoxy, etc.) per molecule of melamine. In addition to the alkoxy functional groups, the melamine-formaldehyde resin may have NH, hydroxyl or carboxylic acid functional groups. Uncrosslinked melamine-formaldehyde is a thermosetting plastic (thermosetting material) additive used for polymer crosslinking that strengthens the crosslinked polymer upon heating. Once cured, it is not possible to reform or cure to form different shapes. Crosslinked melamine-formaldehyde plastics differ from other types of thermoplastics (e.g., acetate, acrylic and nylon) that soften upon heating and harden upon cooling in that they retain their strength and shape. Crosslinked melamine-formaldehyde is resistant to coloring 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 others or mixtures of these solvents.

[0176] Melamine-formaldehyde resin is produced from the reaction of formaldehyde and melamine. Melamine (chemical formula C3H6N6) and formaldehyde (chemical formula CH2O) have the following structures: [Chemical formula] and melamine is 1,3,5-triazine-2,4,6-triamine; or 2,4,6-triamino-s-triazine; or cyanuramide. A typical structure of melamine-formaldehyde resin is Structure I or II: [Chemical formula] (In Compound I, X is H or alkoxy or hydroxyl, and at least two X groups are alkoxy). Preferably, when the compound has two or three alkoxy groups, the alkoxy groups do not exist on the same nitrogen substituent. Melamine resin Compound I requires at least two reactive or crosslinkable alkoxy groups. A typical 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.) and (OR is an alkoxy group (such as methoxy, ethoxy, butoxy, etc.)).

[0177] Melamine resins are part of a larger classification of amino resins. They are used as binders in plywood and particleboard and as anti-wrinkle agents in fabrics. They are also molded for electrical devices and various commercial and household items. They are also used as crosslinking agents in paper towels to increase water resistance. When referring to melamine-formaldehyde resin, it means an 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 produce the film, a polymer having an active hydrogen group (mainly amide, hydroxyl, carboxyl or anhydride functional group) was used as a reaction partner for HMMM.

[0179] Optionally and 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, e.g., para-toluenesulfonic acid. In certain embodiments, a catalyst such as an acid catalyst is used in an amount of preferably at least 4 wt% based on the polymer solids to enhance the crosslinking rate. Typically, in the crosslinking reaction of the present disclosure, a catalyst such as an acid catalyst is used in an amount of 10 wt% or less.

[0180] Optionally, as described herein, the fine fibers formed from the crosslinking reaction between the polymer-reactive resinous aldehyde composition and the polymer material can be enhanced with respect to rate and crosslinking extent, for example, by exposing the fine fibers to a heat treatment. Such heat treatment typically includes a temperature of at least 80°C, at least 100°C or at least 120°C and typically 150°C or less, and typically at least 5 seconds and typically within 10 minutes.

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

[0182] The polymer or polymer mixture or blend must contain at least one fiber-forming polymer containing one or more active hydrogen groups that can be crosslinked by a polymer-reactive resinous aldehyde composition. Preferred such polymer materials are capable of reacting with the polymer-reactive resinous aldehyde composition and contain one or more active hydrogen groups that can be crosslinked thereto. Active hydrogen groups include, but are not limited to, thiol (-SH), hydroxyl (-OH), carboxylate (-CO2H), amide (-C(O)-NH- or -C(O)-NH2), amino (-NH2) or imino (-NH-) and anhydride (-COO)2R groups (upon hydrolysis). These groups can be found in pendant polymer groups or in the polymer backbone.

[0183] Polymer materials suitable for use in the polymer compositions of the present disclosure include addition polymers and condensation polymer materials having active hydrogen. Suitable examples include poly(maleic anhydride), poly(meth)acrylic acid, polyamides, cellulose ethers and esters, polyamines such as chitosan and mixtures, blends, alloys and blocks, graft or random copolymers thereof. Such copolymers can include one or more other moieties in addition to those listed in the foregoing text. Preferred materials included in these general classifications include poly(vinyl alcohol) of various degrees of hydrolysis (e.g., 87% to 99.5%), either crosslinked or non-crosslinked. Preferred addition polymers tend to be glassy, i.e., have a T g (glass transition temperature) higher than room temperature. Additionally, polymer materials having low crystallinity, such as poly(vinyl alcohol) materials, are also useful as the polymer materials of the present disclosure.

[0184] Other preferred examples of useful polymer 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 vinyl alcohol copolymers; poly(maleic anhydride) homopolymers or copolymers, including, for example, styrene-maleic anhydride copolymers; and polyurethanes. As used herein, poly(meth)acrylic acid means poly(acrylic acid) and poly(methacrylic acid) polymers.

[0185] As the polymer material in the fibers of the present disclosure, a number of types of polyamides are also useful. One useful classification of polyamide condensation polymers is nylon materials. The term "nylon" is a general name for all long-chain synthetic polyamides. Typically, nylon nomenclature includes a series of numbers; for example, nylon-6,6 indicates that the starting materials are C6 diamine and 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 polycondensation of ε-caprolactam in the presence of a smaller amount of water. This reaction forms nylon-6, a linear polyamide (produced from a cyclic lactam also known as ε-aminocaproic acid). Additionally, nylon copolymers are also contemplated. Exemplary nylon materials include nylon-6, nylon 6,6, nylon 6,10, mixtures or copolymers thereof.

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

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

[0188] Additive polymers such as polyvinyl alcohol and amorphous additive polymers such as poly(acrylonitrile) copolymers with acrylic acid are also useful. Since they are soluble or dispersible in various solvents and solvent blends at low pressures and low temperatures, they can be solution-spun relatively easily. For example, poly(vinyl alcohol) having a degree of hydrolysis from 87% to 99.9+% can be used as the polymer 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, and poly(maleic anhydride), polyvinyl pyrrolidone, and copolymers thereof. Preferred active hydrogen groups include hydroxyl, amino, and amide groups. Various combinations of polymer materials can be used as needed.

[0190] Optionally, in addition to the polymer having a reactive hydrogen group, the polymer material used in the fibers of the present disclosure may include one or more non-reactive polymers. In this regard, "non-reactive" is defined as being unable to crosslink with the melamine-formaldehyde resin or other polymer-reactive resinous aldehyde composition used. For example, polymer materials such as many polyolefins, polyvinyl chloride, chlorinated polyethylene, and other such materials that do not have groups capable of crosslinking with the polymer-reactive resinous aldehyde composition can be used. Other non-reactive polymers include polyacetal, polyester (e.g., aromatic-based and aliphatic, including 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 sulfide, polyarylene oxide (e.g., including polyphenylene oxide), polysulfone, modified polysulfone (e.g., including polyethersulfone), poly(vinyl pyridine) (e.g., poly(4-vinyl pyridine), poly(2-vinyl pyridine), and their random and block copolymers (e.g., including styrene vinyl pyridine, vinyl pyridine-co-butyl methacrylate, vinyl pyridine-co-methyl methacrylate, etc.)), polyvinyl acetate and its copolymers (e.g., including ethylene-co-vinyl acetate), etc.Preferred materials falling into these general classifications include acrylic resins (e.g., styrene acrylonitrile (SAN), styrene maleic anhydride (SMA), styrene-co-vinylpyridine, styrene-co-butadiene, styrene-co-ethylene propylene, 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.) including polyethylene, polypropylene, poly(vinyl chloride), poly(methyl methacrylate), polystyrene and its copolymers (including both block copolymers such as random and ABA type block copolymers), poly(vinylidene fluoride) and its copolymers (e.g., including PVDF-co-HFP), poly(vinylidene chloride), mixtures, blends or alloys. Examples of useful block copolymers include ABA type copolymers (e.g., styrene-EP-styrene) (where "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 U.S. LLC, Houston, TX; and SYMPATEX polyester-b-ethylene oxide available from SympaTex Technologies Inc., Hampton, NH. Optionally, various combinations of non-reactive polymers can be used.

[0191] Optionally, non-reactive polymers can be used in an amount that does not adversely affect the positive effect of crosslinking that occurs when using polymers having active hydrogen.

[0192] Additive non-reactive polymers such as poly(vinylidene fluoride), syndiotactic polystyrene, copolymers of vinylidene fluoride and hexafluoropropylene, polyvinyl acetate, amorphous additive 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 pressures and low temperatures, and can therefore be solution-spun relatively easily. However, when they are solution-spun, highly crystalline polymers such as polyethylene and polypropylene typically require high temperatures, high-pressure solvents or solvent blends. Therefore, solution-spinning of polyethylene and polypropylene is very difficult.

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

[0194] Referring to FIGS. 10A and 10B, when the fibers 200 / 202 are formed, the polymeric non-reactive resinous aldehyde composition preferably forms at least one outer concentric layer (i.e., phase) such as a second coating phase 222 (fiber 202, FIG. 10B) mainly containing the polymeric non-reactive resinous aldehyde composition (e.g., a melamine aldehyde composition) or a second coating phase 220 (fiber 200, FIG. 10A) containing a mixture of the polymeric material and the polymeric non-reactive resinous aldehyde composition and a third outer phase (outermost phase) 230 (FIG. 10A) mainly containing the polymeric non-reactive resinous aldehyde composition. That is, the polymeric 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), where the core 210 (fiber 200) or 212 (FIG. 10B) mainly contains a polymeric material (e.g., poly(4-vinylpyridine), also described as P4VP).

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

[0196] Preferably, the fine fibers of the present disclosure are prepared from a self-crosslinkable polymer non-reactive resinous aldehyde composition containing a reactive group (preferably an alkoxy group) and a polymer that does not contain or contains a low amount of a reactive group (i.e., a group capable of reacting with the reactive group of the polymer non-reactive resinous aldehyde composition), wherein the weight ratio of the self-crosslinkable polymer non-reactive resinous aldehyde to the 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-crosslinkable polymer 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-crosslinkable polymer non-reactive resinous aldehyde composition to the non-reactive polymer can be in the range of 5:100 to 300:100. In another exemplary embodiment, the weight ratio of the self-crosslinkable polymer non-reactive resinous aldehyde composition to the non-reactive polymer can be in the range of 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 structure. The interpenetrating network structure 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] A suitable polymer non-reactive resinous aldehyde composition can self-crosslink in the fiber manufacturing process described herein and contains one or more reactive groups. Such reactive groups include alkoxy groups as well as hydroxyl, carboxylic acid and / or -NH groups. Exemplary polymer 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 polymer non-reactive resinous aldehyde compositions include aldehyde-based agents that can be used in self-crosslinking reactions. The resinous aldehyde composition is typically non-volatile. Also, the polymer non-reactive resinous aldehyde composition must be soluble in a solvent selected for the polymer material for processes such as electrospinning. Resinous aldehyde compositions useful as crosslinking agents include condensation products of urea and aldehydes, condensation products of phenol and aldehydes or condensation products of melamine and aldehydes. One useful classification of crosslinked resins includes nitrogen compound-based resins such as melamine, urea, benzoguanamine, glycoluril and other similar resins produced by reacting nitrogen compounds with aldehydes. Such self-crosslinking resins are soluble in process solvents and have reactivity with various polymer species.

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

[0202] Useful melamine aldehyde compositions include melamine - aldehyde products generally formed by the reaction between melamine and aldehyde compounds. Useful aldehyde compounds include C 1~6 alkanals such as formaldehyde, acetaldehyde, butyraldehyde, isobutyraldehyde, etc. Such mixtures of aldehydes can be used as required. 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 - 6 or 4 - 6 alkoxy groups per molecule.

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

[0204] Useful polymer - non - reactive resinous aldehyde compositions (e.g., melamine aldehyde compositions), among those that self - crosslink, 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; methoxymethylmethylol melamine resin.

[0205] The various melamine compositions that self-crosslink are sold under the trade name CYMEL available from Cytec Industries, West Paterson, NJ, including, 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 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., and the various melamine compositions are sold under the trade name LUWIPAL available from BASF AG, Ludwigshafen, Germany, including, for example, LUWIPAL LR 8955, LUWIPAL LR 8968 and LUWIPAL LR 8984. Such resins are available from INEOS Melamines Inc. and are sold under the trade names RESIMENE (e.g., RESIMENE HM2608), MAPRENAL and MADURIT. The primary condition of 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 required, provided that such combinations contain at least one self-crosslinkable polymer non-reactive aldehyde component.

[0206] In many preferred embodiments, a melamine-formaldehyde resin (sometimes referred to herein simply as a "melamine" composition or "melamine" resin) is used. The term melamine-formaldehyde resin means a melamine-based resin having two or more (at least two) alkoxy functional groups (such as methoxy, ethoxy, propoxy, butoxy, etc.) per molecule of melamine. 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 combinations thereof to impart the ability to self-crosslink. Depending on the functional groups in the melamine-formaldehyde resin, the uncrosslinked resin is soluble in both water-soluble and water-insoluble or organic solvents such as alcohols, hydrocarbons (such as toluene, xylene, etc.) or others or mixtures of these solvents.

[0207] The melamine-formaldehyde resin is produced from the reaction of formaldehyde and melamine. Melamine (chemical formula C3H6N6) and formaldehyde (chemical formula CH2O) have the following structures:

Chem.

Chem.

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

[0209] The polymer or polymer mixture or blend must contain at least one fiber-forming polymer and should contain no or very few reactive groups that can be crosslinked by the polymer-non-reactive resinous aldehyde composition. Exemplary polymer reactive groups that should not be present include active hydrogen groups. Active hydrogen groups include, but are not limited to, thiol (-SH), hydroxyl (-OH), carboxylate (-CO2H), amide (-C(O)-NH- or -C(O)-NH2), amino (-NH2) or imino (-NH-) and anhydride (-COO)2R groups (upon hydrolysis).

[0210] Suitable polymer materials for use in the polymer compositions of the present disclosure include addition polymers and condensation polymer materials that are non-reactive polymers. In this regard, "non-reactive" is defined as being unable to be cross-linked using a polymer non-reactive resinous aldehyde composition, as described above and in U.S. Patent No. 9,587,328 (compared to reactive polymers such as nylon). For example, polymer materials such as many polyolefins, polyvinyl chloride, chlorinated polyethylene, and other such materials that do not have groups capable of cross-linking with a polymer reactive resinous aldehyde composition can be used. Other non-reactive polymers include polyacetals, polyesters (including both aromatic-based and aliphatic, such as 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 polyphenylene oxide), polysulfones, modified polysulfones (including polyethersulfone), poly(vinyl pyridine) (including poly(4-vinyl pyridine), poly(2-vinyl pyridine), and their random and block copolymers (including styrene vinyl pyridine, vinyl pyridine-co-butyl methacrylate, vinyl pyridine-co-methyl methacrylate, etc.)), polyvinyl acetate and its copolymers (including ethylene-co-vinyl acetate), etc.Preferred materials falling into these general classifications include acrylic resins such as polyethylene, polypropylene, poly(vinyl chloride), poly(methyl methacrylate), polystyrene and its copolymers (including both block copolymers such as random and ABA type block copolymers), for example, styrene acrylonitrile (SAN), styrene maleic anhydride (SMA), styrene-co-vinyl pyridine, styrene-co-butadiene, styrene-co-ethylene propylene, 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 its copolymers (for example, including PVDF-co-HFP), poly(vinylidene chloride), mixtures, blends or alloys. Examples of useful block copolymers include ABA type copolymers (for example, styrene-EP-styrene) (where "EP" means ethylene propylene) or AB (for example, styrene-EP) polymers, KRATON styrene-b-butadiene and styrene-b-hydrogenated butadiene (ethylene propylene) available from Kraton Polymers U.S. LLC, Houston, TX; and SYMPATEX polyester-b-ethylene oxide available from SympaTex Technologies Inc., Hampton, NH. Optionally, various combinations of non-reactive polymers can be used.

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

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

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

[0214] The fine fiber layer can be formed by any suitable method. For example, the fine fibers of the present disclosure can be manufactured using various 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 the support layer.

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

[0217] Fiber manufacturing method In the fiber spinning process for manufacturing 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 the polymer is cooled to a rubbery state and then to a solid state. The aldehyde composition can migrate to the surface during the transition of the fluid polymer to the 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 precipitation of the fibers and coagulation when it exits. The name of this process is derived from this "wet" bath. Acrylic, rayon, aramid, modacrylic fibers, and spandex are manufactured 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. This evaporation is usually achieved by an air or inert gas stream. Since there is no associated precipitation liquid, there is no need to dry the fibers and the solvent is more easily recovered. Melt spinning is used for polymers that can be melted. The polymer is coagulated by cooling after being extruded from the spinneret.

[0218] In a typical process, pellets or granules of a solid polymer are fed to an extruder. The pellets are compressed, heated, and melted by an extrusion screw and then fed to a spinning pump and into a spinneret. The direct spinning process avoids the stage of solid polymer pellets. The polymer melt is produced from a polymer finisher that pumps the polymer directly from the raw materials to the spinning mill. Direct spinning is mainly applied during the production of polyester fibers and filaments and contributes to high production capacities (more than 100 tons per day). Gel spinning, also known as dry-wet spinning, is used to obtain high strength or other special properties in the fiber. The polymer is in a "gel" state and is only partially liquid, whereby the polymer chains are somewhat bonded together. These bonds result in strong intermolecular forces in the fiber, thereby increasing its tensile strength. Also, the polymer chains within the fiber have a high degree of orientation, thereby increasing the 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 manufacturing the fine fibers of the present disclosure is the meltblowing process. Meltblowing (also described as "MB" in this document) is a process for manufacturing fibrous webs or articles directly from polymers or resins using high-speed air or another suitable force to thin filaments. This process is unique because it is used almost exclusively for manufacturing microfibers rather than fibers of the diameter of normal fabric fibers. MB microfibers generally have diameters in the range of 2 to 4 μm (micrometers or microns or μ), although they may be as small as about 0.1 μm or as large as about 10 to 15 μm. Differences between MB nonwovens and other nonwovens, such as softness, coating or opacity, and porosity, may generally result from differences in filament diameter. As soon as the molten polymer is extruded from the die hole, a high-speed hot air stream (exiting from the upper and bottom sides of the die nose piece) thins the polymer stream and microfibers are formed. As the hot air stream containing the microfibers travels towards the collector screen, a large amount of surrounding air (also called secondary air) is entrained, whereby the fibers are cooled and solidified. The solidified fibers are then randomly deposited on the collection screen, forming a self-bonded nonwoven web. The fibers are generally randomly deposited (and highly entangled thereon) due to turbulence in the air stream, although there is a slight bias in the machine direction due to some directionality imparted by the movement of the collector. The collector speed and the collector distance from the die nose piece can be varied to produce various meltblown webs. Usually, a vacuum is applied inside the collector screen to draw out the hot air and enhance the fiber placement process.

[0220] To manufacture a permeable, coarse fiber-like material for the support layer, any of the methods listed above for manufacturing the fine fibers of the present disclosure can be used. To manufacture a permeable, coarse fiber-like material for the support layer, spunbond technology can be used. Spunbond fabrics are manufactured by extruding, depositing the spun filaments in a uniform and random pattern onto a collection belt, and subsequently bonding the fibers together. The fibers are separated during the web placement process by an air jet or an electrostatic charge. The collection surface is typically perforated to prevent the airflow from biasing and transporting the fibers in an uncontrolled manner. The 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 the melting point is increased by molecular orientation, fibers that are not highly drawn can be used as thermally bonded fibers. Polyethylene or random ethylene-propylene copolymers are used as the low melting point bonding sites. Spunbond products are utilized in carpet backing, geotextiles, and disposable medical / sanitary products. Because the fabric manufacturing is combined with the fiber manufacturing, this process is generally more economical than when using staple fibers to manufacture nonwoven fabrics. The spinning process is similar to the production of continuous filament yarns 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 purpose of this process is to produce a wide web, and thus, a number of spinnerets are arranged in parallel to yield sufficient fibers across the width. A group of spinnerets is often described as a block or a bank. In commercial production, two or more blocks are used side by side vertically to increase the fiber coverage rate.

[0221] In the spunbond process, prior to deposition on a moving belt or screen, the output of the spinneret typically consists of one hundred or more individual filaments that are drawn down to orient the molecular chains within the fiber in order to increase fiber strength and decrease extensibility. This is accomplished by rapidly stretching the plastic fiber immediately after it exits the spinneret. In practice, the fiber is accelerated either mechanically or pneumatically. In most processes, the fiber is accelerated pneumatically in multiple filament bundles, although other arrangements are described where linearly aligned arrays of individual filaments are accelerated pneumatically.

[0222] In conventional fabric spunbond processes, some orientation of the fibers is achieved by applying air to the filaments at a speed of about 3,200 m / min to produce partially oriented yarn (POY). The POY can be mechanically drawn in a separate step to enhance strength. In spunbond, the production filament bundles are partially oriented by pneumatic acceleration at speeds of 6,000 m / min or more. Particularly for lightweight structures (e.g., 17 g / m 2 ) such high speeds result in partial orientation and high speeds in web formation. The formation of wide webs at high speeds is a highly productive operation.

[0223] For many applications, the partial orientation of the coarser fibers in the support layer increases strength and decreases 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 drawn on a heated roll at a typical draw ratio of 3.5:1. The filaments are then accelerated pneumatically onto a moving belt or screen. This process is slower but gives a stronger web.

[0224] The spunbond web is formed by pneumatic deposition of filament bundles onto a moving belt. The air gun uses high-pressure air to move the filaments through a lower-pressure compression region, using a higher velocity as in the case of a Venturi tube. To achieve maximum uniformity, with respect to the web to be coated, the individual filaments can be separated before reaching the belt. This separation is achieved by inducing an electrostatic charge on the bundle, under tension and prior to deposition. 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 can be at least 30,000 electrostatic units per square meter (esu / m 2 2).

[0225] The microfibers of the present disclosure can preferably be manufactured using an electrospinning process. A suitable electrospinning apparatus for forming microfibers generally includes a reservoir containing a microfiber-forming solution and a dispensing device comprising a rotating part with a plurality of offset holes. When it rotates in an electrostatic field, the droplets of the solution on the dispensing device are accelerated by the electrostatic field towards a collecting medium. A grid on which the collecting medium (i.e., the substrate or combined substrates) is placed faces a dispenser arranged away from it. Air can be drawn through the grid. A high-voltage electrostatic potential is maintained between the dispenser and the grid by a suitable electrostatic voltage source. A substrate is placed between the dispenser and the grid to collect the fibers.

[0226] In particular, the electrostatic potential between the grid and the emitter charges the material, after which the liquid is emitted as thin fibers, which extend towards the grid and, when they arrive, are collected on the substrate. In the case of polymers in solution, a portion of the solvent evaporates from the fibers during their flight towards the substrate. As the solvent continues to evaporate, the fine fibers adhere to the substrate fibers. The electrostatic field strength is selected such that the polymer material is accelerated from the emitter to the collection medium and the acceleration is sufficient to make the polymer material into a very thin microfiber or nanofiber structure. The deposition time can be used to control the number of emitted fibers deposited on the forming medium, thereby enabling control of the thickness of each layer deposited thereon. The electrospinning process typically uses a polymer solution having a solids concentration of 5% to 20% (on the polymer). Solvents that are safe and easy to use are desirable for industrial applications. On the other hand, in many cases, the fibers formed by such solvents need to survive and function in a wide range of environments.

[0227] Method for manufacturing a layer of fine fibers comprising single diameter fibers In another aspect, the present disclosure describes the manufacture 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 that includes both thick fine fibers having an average fiber diameter that is at least 3 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 where the first layer of fine fibers includes fine fibers having an average fiber diameter that is at least 3 times the average fiber diameter of the thinnest fibers of the second layer of fine fibers. This chapter describes a method for manufacturing a layer of fine fibers that includes a first layer of fine fibers comprising single diameter fibers. The following sections describe the manufacture of a layer of fine fibers that includes both thick fine fibers having an average fiber diameter that is at least 3 times the average fiber diameter of the thinner fine fibers of the same layer (e.g., the first layer of fine fibers or the second layer of fine fibers).

[0228] Suitable polymers and polymer concentrations can be selected by one of ordinary skill in the art that provides the desired diameter and other properties for the first layer of microfibers. For example, in some embodiments, the fibers are preferably compatible with the fluid (e.g., hydraulic fluid, fuel, lubricant) in which they are used for filtration. (So that the microfiber structure does not deteriorate chemically or physically upon mere contact with the fluid) If it does not react with the fluid or any other components and additives therein and is insoluble in the fluid, the fibers are considered to be compatible with the fluid. In an exemplary embodiment, the polymer solution comprises Solution 2 or Solution 4 as described in the examples.

[0229] Method for manufacturing a layer of microfibers comprising mixed diameter microfibers In a further aspect, the present disclosure describes the manufacture of a layer of microfibers comprising a layer of microfibers containing both thicker microfibers having an average fiber diameter at least three times that of the average fiber diameter of the thinner microfibers in the same layer. Such a layer can be deposited directly on a support layer (i.e., the first microfiber layer), or it can be deposited on a first microfiber layer (i.e., the second microfiber layer), or both. In addition, a layer of microfibers containing both thicker microfibers having an average fiber diameter at least three times that of the average fiber diameter of the thinner microfibers in the same layer can form a third microfiber layer, a fourth microfiber layer, and the like.

[0230] Suitable polymers and polymer concentrations can be selected by one of ordinary skill in the art that provides the desired diameter and other properties for the second layer of microfibers. For example, in some embodiments, the fibers are preferably compatible with the fluid (e.g., hydraulic fluid, fuel, lubricant) in which they are used for filtration. (So that the microfiber structure does not deteriorate chemically or physically upon mere contact with the fluid) If it does not react with the fluid or any other components and additives therein and is insoluble in the fluid, the fibers are considered to be compatible with the fluid. In an exemplary embodiment, the polymer solution comprises Solution 1, Solution 2, Solution 3, and / or Solution 4 as 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 co - spinning, including, for example, using two (or more) syringes where each syringe contains 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 formation of the fibers 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 an alternating pattern of the fibers. For example, when two (or more) fibers are formed by electrospinning, the fibers can be formed by alternating spinning, including, for example, using two (or more) syringes where each syringe contains 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 formation of the fibers using pulses of each polymer solution of at least 30 seconds.

[0233] Any suitable method that can be used to form a combination of layers of thin and thick fine fibers can be used. Exemplary methods that can be used to form a layered fiber structure include one or more of the methods of 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 a mixed fiber structure include one or more of the methods of 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 a layered fiber structure and a mixed fiber structure. An exemplary method of forming such a structure is described in Example 7.

[0234] Usage Method and Filter Element In some embodiments, the filter media disclosed herein may be included in a filter element that includes a wire support. The wire support may be located downstream of the support layer.

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

[0236] Filter elements including flat panel filters, cartridge filters, or other filtration components may be manufactured from the filter media of the present disclosure. 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 the filter media disclosed herein. That is, the filter media described herein may form an efficiency layer or a portion of the efficiency layer. In some embodiments, the filter element may further include a loading layer. Any suitable media may be used as the loading layer, including, for example, a layer of meltblown nonwoven fabric or another media designed to act as a depth loading layer.

[0238] In some embodiments, the filter media of the present disclosure may be used, for example, to filter a fluid including a fluid flow. Fluids include air, gas, and liquid. In some embodiments, the filter media of the present disclosure may be used to remove particulates from a fluid flow.

[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 disposed 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 that transports 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 disposed upstream of other layers in the filter element. Exemplary liquids can include, for example, aqueous liquids, hydraulic fluids, oils, fuels, lubricants, and the like. Aqueous liquids can include natural and artificial streams such as effluents, cooling water, process water, and the like.

[0242] In some exemplary embodiments, the filter media disclosed herein can replace the efficiency layer in the filter element of International Publication No. WO 2015 / 157638; International Publication No. WO 2016 / 210153; International Publication No. 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 the flow rate varies, including, for example, hydraulic applications. Variations in the flow rate result in multiple opportunities for particles to pass through the media openings, and thus variations in the flow rate, including, for example, periodic flow conditions, have an adverse effect on filter media performance, particularly filter media efficiency.

[0244] At the time of the present invention, the impact on filter media performance of varying the flow rate 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 results in more opportunities for bypasses to be formed in the filter (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 periodic flow conditions without worsening the pressure drop.

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

[0246] The invention is defined in the claims. However, below is a non-exhaustive list of non-limiting exemplary aspects. Any one or more features of these aspects can be combined with any one or more features of another example, embodiment, or aspect described herein.

[0247] Aspects of an exemplary filter media comprising at least one fine fiber layer Aspect A1 is a filter media 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 the first layer of fine fibers comprises thick fine fibers and thin fine fibers, and the thick fine fibers have an average diameter that is at least three times the average diameter of the thin fine fibers.

[0248] Aspect A2 is the filter medium of Aspect A1, where the thick 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 thick 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] Aspect A3 is the filter medium of Aspect A1 or A2, where the first layer of fine fibers contains thin fine fibers, 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 0.3 μm, at most 0.4 μm, at most 0.5 μm, or at most 0.6 μm, or both.

[0250] Aspect A4 is the filter medium of any one of the above aspects, where the first layer of fine fibers contains at most 10% thick fine fibers or at most 20% thick fine fibers.

[0251] Aspect A5 is the filter medium of any one of the above aspects, where the first layer of fine fibers contains 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] Aspect A6 is the filter medium of any one of the above aspects, where the first layer of fine fibers contains the proportion of one or more thick fine fibers in 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 in Tables 1A - 1C.

[0253] Aspect A7 is the filter medium of any one of Aspects A1 - A6, where the proportion of thick fine fibers is determined based on the spinning time.

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

[0255] Aspect A9 is a filter medium according to any one of the above aspects, wherein the first layer of fine fibers includes a layered fiber structure.

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

[0257] Aspect A11 is a filter medium of Aspect A9, wherein the first layer of fine fibers includes thin fine fibers and thick fine fibers, within the first layer of fine fibers, the thin fine fibers are deposited on the first sub-layer of the thick fine fibers, and the second sub-layer of the thick fine fibers is deposited on the thin fine fibers.

[0258] Aspect A12 is a filter medium according to any one of Aspects A1 to A8, wherein the first layer of fine fibers includes a mixed fiber structure.

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

[0260] Aspect A14 is a filter medium according to any one of the above aspects, further including a second layer of fine fibers.

[0261] Aspect A15 is a filter medium according to any one of the above aspects, wherein the fine fibers are compatible with at least one of a hydraulic fluid, a fuel or a lubricant.

[0262] Aspect A16 is a filter medium according to any one of the above aspects, wherein the support layer includes nylon.

[0263] Aspect A17 is a filter medium according to any one of the above aspects, wherein the support layer has an average intermediate flow pore diameter of at least 5μm, at least 10μm, at least 15μm, at least 20μm or at least 25μm and at most 10μm, at most 15μm, at most 20μm, at most 25μm, at most 30μm, at most 35μm, at most 40μm, at most 50μm, at most 60μm, at most 70μm, at most 80μm or at most 90μm.

[0264] Aspect A18 is the filter medium of Aspect A17, where the average middle flow pore diameter is determined using capillary flow porometry.

[0265] Aspect A19 is the filter medium of any one of the above aspects, where the support layer has an average maximum pore diameter 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] Aspect A20 is the filter medium of Aspect A19, where the average maximum pore diameter is determined using capillary flow porometry.

[0267] Aspect A21 is the filter medium of any one of the above aspects, where the support layer has an average minimum pore diameter 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] Aspect A22 is the filter medium of Aspect A21, where the average minimum pore diameter is determined using capillary flow porometry.

[0269] Aspect A23 is the filter medium of any one of the above aspects, where the support layer has an average middle flow pore diameter, and the average middle flow pore diameter 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% over the entire length and width of the medium.

[0270] Aspect A24 is the filter medium of any one of the above aspects, where the filter medium includes a composite material containing a support layer and a fine fiber layer, and the filter medium has a composite material average maximum pore diameter of at most 14 μm, at most 15 μm, or at most 20 μm, or the filter medium has a composite material average maximum pore diameter of at least 0.1 μm, or both.

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

[0272] Aspect A26 is the filter medium of Aspect A24 or A25, wherein the composite material pore diameter is determined using capillary flow porometry.

[0273] Aspect A27 is the filter medium of any one of the above aspects, wherein the thick fine fibers have a diameter that is at least 0.2 μm, at least 0.3 μm or at least 0.4 μm larger than the thin fine fibers.

[0274] Aspect A28 is the filter medium of any one of the above aspects, 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.

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

[0276] Aspect A30 is the filter medium of any one of the above aspects, wherein the support layer includes a spunbond layer.

[0277] Aspect A31 is a filter element including the filter medium of any one of the above aspects.

[0278] Aspect A32 is the filter element of Aspect A31, wherein the filter element includes an efficiency layer, and the efficiency layer includes the filter medium.

[0279] Aspect A33 is the filter element of Aspect A32, wherein the filter element further includes 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 the second layer of fine fibers comprises fibers having an average diameter that is at least three times the average fiber diameter of the fibers in the first 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 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 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, and the thick fine fibers have an average diameter that is 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, 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] Aspect B6 is the filter medium of Aspect B4 or B5, where the thick fine fibers have an average diameter greater than 1 μm.

[0286] Aspect B7 is the filter medium of any one of Aspects B4 to B6, where the second layer of fine fibers contains at most 10% thick fine fibers or at most 20% thick fine fibers.

[0287] Aspect B8 is the filter medium of any one of Aspects B4 to B7, where the second layer of fine fibers contains 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.

[0288] Aspect B9 is the filter medium of any one of Aspects B4 to B6, where the second layer of fine fibers contains the proportion of one or more thick fine fibers in 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 in Tables 1A to 1C.

[0289] Aspect B10 is the filter medium of any one of Aspects B7 to B9, where the proportion of thick fine fibers is determined based on the spinning time.

[0290] Aspect B11 is the filter medium of any one of Aspects B7 to B9, where the proportion of thick fine fibers is determined using microscopic observation or nano-CT.

[0291] Aspect B12 is the filter medium of any one of Aspects B3 to B11, where the second layer of fine fibers contains a layered fiber structure.

[0292] Aspect B13 is the filter medium of Aspect B12, where the second layer of fine fibers contains one or more layered fiber structures in Set A5, Set B, Set D5, Set E, Set I5, or Set J in Tables 1A to 1C.

[0293] Aspect B14 is the filter medium of Aspect B12, wherein the second layer of fine fibers includes fine and thick fine fibers, within the second layer of fine fibers, the fine fine fibers are deposited on the first sub-layer of the thick fine fibers, and the second sub-layer of the thick fine fibers is deposited on the fine fine fibers.

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

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

[0296] Aspect B17 is the filter medium of any one of Aspects B3 - B11, wherein the second layer of fine fibers includes a layer of fine fine fibers, then a layer of mixed fine and thick fine fibers, and a layer of thick fine fibers.

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

[0298] Aspect B19 is the filter medium of any one of Aspects B1 - B18, wherein the support layer includes nylon.

[0299] Aspect B20 is the filter medium of any one of Aspects B1 - B19, wherein the support layer has an average intermediate flow pore size of at least 5μm, at least 10μm, at least 15μm, at least 20μm or at least 25μm and up to 10μm, up to 15μm, up to 20μm, up to 25μm, up to 30μm, up to 35μm, up to 40μm, up to 50μm, up to 60μm, up to 70μm, up to 80μm or up to 90μm.

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

[0301] Aspect B22 is a filter medium of any one of Aspects B1 to B21, wherein the support layer has an average maximum pore diameter 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] Aspect B23 is a filter medium of Aspect B22, wherein the average maximum pore diameter is determined by capillary flow porometry.

[0303] Aspect B24 is a filter medium of any one of Aspects B1 to B23, wherein the support layer has an average minimum pore diameter 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] Aspect B25 is a filter medium of Aspect B24, wherein the average minimum pore diameter is determined using capillary flow porometry.

[0305] Aspect B26 is a filter medium of any one of Aspects B1 to B25, wherein the support layer has an average intermediate flow pore diameter, and the average intermediate flow pore diameter 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% over the entire length and width of the medium.

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

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

[0308] Aspect B29 is the filter medium of aspect B27 or B28, wherein the composite material pore diameter is determined using capillary flow porometry.

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

[0310] Aspect B31 is the filter medium of any one of aspects 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] Aspect B32 is the filter medium of any one of aspects 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] Aspect B33 is the filter medium of aspects 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] Aspect B34 is the filter medium of any one of aspects B1 - B33, wherein the support layer comprises a spunbond layer.

[0314] Aspect B35 is a filter element including any one of the filter media of Aspects B1 to B34.

[0315] Aspect B36 is the filter element of Aspect B35, wherein the filter element includes an efficiency layer, and the efficiency layer includes a filter medium.

[0316] Aspect B37 is the filter element of Aspect B36, wherein the filter element further includes a loading layer.

[0317] Exemplary aspects of layered filter media Aspect C1 is a filter medium including 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 includes thin fine fibers and thick fine fibers, the thick fine fibers having an average diameter of at least 3 times the average diameter of the thin 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, and the first layer of fine fibers includes fine fibers having an average fiber diameter of at least 3 times the average fiber diameter of the thin fine fibers in the second layer of fine fibers.

[0318] Aspect C2 is the filter medium of Aspect C1, wherein the thick fine fibers in the second layer of fine fibers include at most 10% of the fine fibers in the second layer of fine fibers.

[0319] Aspect C3 is the filter medium of Aspect C1 or C2, wherein the thick fine fibers in the second layer of fine fibers include at least 5% and at most 7% of the fine fibers in the second layer of fine fibers.

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

[0321] Aspect C5 is the filter medium of any one of Aspects C2 to C4, wherein the ratio of the thick fine fibers is determined based on the spinning time.

[0322] Aspect C6 is a filter medium of any one of Aspects C2 to C4, wherein the proportion of thick fine fibers is determined using microscopic observation or nano-CT.

[0323] Aspect C7 is a filter medium of any one of Aspects C1 to C6, wherein the thick fine fibers in the second layer of fine fibers have an average diameter of at least 1 μm or greater than 1 μm, or the thick fine fibers in 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] Aspect C8 is a filter medium of any one of Aspects C1 to C7, wherein the first layer of fine fibers contains 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 contains 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] Aspect C9 is a filter medium of any one of Aspects C1 to C8, wherein the thin fine fibers in the second layer of fine fibers have an average diameter of at least 0.2 μm, or the thin fine fibers in the second layer of fine fibers have an average diameter of at most 0.6 μm, or both.

[0326] Aspect C10 is a filter medium of any one of Aspects C1 to C9, wherein the support layer contains nylon.

[0327] Aspect C11 is a filter medium of any one of Aspects C1 - C10, wherein the support layer has an average intermediate flow pore diameter of at least 5μm, at least 10μm, at least 15μm, at least 20μm or at least 25μm and at most 10μm, at most 15μm, at most 20μm, at most 25μm, at most 30μm, at most 35μm, at most 40μm, at most 50μm, at most 60μm, at most 70μm, at most 80μm or at most 90μm.

[0328] Aspect C12 is a filter medium of Aspect C11, wherein the average minimum pore diameter is determined using capillary flow porometry.

[0329] Aspect C13 is a filter medium of any one of Aspects C1 - C12, wherein the support layer has an average maximum pore diameter of at most 10μm, at most 15μm, at most 20μm, at most 25μm, at most 30μm, at most 35μm, at most 40μm, at most 50μm, at most 60μm, at most 70μm, at most 80μm, at most 90μm, at most 100μm or at most 150μm.

[0330] Aspect C14 is a filter medium of Aspect C13, wherein the average maximum pore diameter is determined using capillary flow porometry.

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

[0332] Aspect C16 is a filter medium of Aspect C15, wherein the average minimum pore diameter is determined using capillary flow porometry.

[0333] Aspect C17 is a filter medium of any one of Aspects C1 - C16, wherein the support layer has an average intermediate flow pore diameter, and the average intermediate flow pore diameter 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% over the entire length and width of the medium.

[0334] Aspect C18 is a filter medium of any one of aspects C1 to C17, wherein the filter medium includes a composite material including a support layer and a fine fiber layer, and the filter medium has a maximum composite material average maximum pore diameter of 14 μm, 15 μm or 20 μm at most, or the filter medium has a composite material average maximum pore diameter of at least 0.1 μm, or both.

[0335] Aspect C19 is a filter medium of any one of aspects C1 to C18, wherein the filter medium includes a composite material including a support layer and a fine fiber layer, and the filter medium has a maximum composite material average middle flow pore diameter of 11 μm, 9 μm or 6 μm at most, or the filter medium has a composite material average middle flow pore diameter of at least 0.1 μm, or both.

[0336] Aspect C20 is a filter medium of aspect C18 or C19, wherein the composite material pore diameter is determined using capillary flow porometry.

[0337] Aspect C21 is a filter medium of any one of aspects C1 to C20, wherein the thick fine fibers have a diameter that is at least 0.2 μm, at least 0.3 μm or at least 0.4 μm larger than that of the thin fine fibers.

[0338] Aspect C22 is a filter medium of any one of aspects C1 to 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 5 μm, 10 μm, 30 μm or 50 μm at most, or both.

[0339] Aspect C23 is a filter medium of any one of aspects C1 to 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 the second fine fiber layer has a thickness of 5 μm, 10 μm, 30 μm, 40 μm or 45 μm at most, or both.

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

[0341] Aspect C25 is the filter medium of any one of Aspects C1 - C24, where the support layer includes a spunbond layer.

[0342] Aspect C26 is a filter element including the filter medium of any one of Aspects C1 - C25.

[0343] Aspect C27 is the filter element of Aspect C26, where the filter element includes an efficiency layer, and the efficiency layer includes a filter medium.

[0344] Aspect C28 is the filter element of Aspect C27, where the filter element further includes a loading layer.

[0345] Aspects of exemplary hybrid filter media Aspect D1 is a filter medium including a support layer, a first layer of fine fibers, and a second layer of fine fibers, where 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 includes thin fine fibers and thick fine fibers, the thick fine fibers have an average diameter of at least 3 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 includes fine fibers having an average fiber diameter of at least 3 times the average fiber diameter of the thin fine fibers in the second layer of fine fibers.

[0346] Aspect D2 is the filter medium of Aspect D1, where the thick fine fibers in the second layer of fine fibers include at most 10% of the fine fibers in the second layer of fine fibers.

[0347] Aspect D3 is the filter medium of Aspect D1 or D2, where the thick fine fibers in the second layer of fine fibers include at least 3% and at most 9%, at least 5% and at most 7%, or at least 4% and at most 8% of the fine fibers in the second layer of fine fibers.

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

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

[0350] Aspect D6 is the filter medium of any one of Aspects D2 - D4, wherein the proportion of thick fine fibers is determined using microscopic observation or nano - CT.

[0351] Aspect D7 is the filter medium of any one of Aspects D1 - D6, wherein the thick fine fibers in the second layer of fine fibers have an average diameter of at least 1 μm or greater than 1 μm, or the thick fine fibers in 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.

[0352] Aspect D8 is the filter medium of any one of Aspects 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] Aspect D9 is the filter medium of any one of Aspects D1 - D8, wherein the thin fine fibers in the second layer of fine fibers have an average diameter of at least 0.2 μm, or the thin fine 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, or both.

[0354] Aspect D10 is a filter medium of any one of aspects D1 - D9, wherein the support layer contains nylon.

[0355] Aspect D11 is a filter medium of any one of aspects D1 - D10, wherein the support layer has an average middle flow pore diameter of at least 5μm, at least 10μm, at least 15μm, at least 20μm or at least 25μm and at most 10μm, at most 15μm, at most 20μm, at most 25μm, at most 30μm, at most 35μm, at most 40μm, at most 50μm, at most 60μm, at most 70μm, at most 80μm or at most 90μm.

[0356] Aspect D12 is a filter medium of aspect D11, wherein the average middle flow pore diameter is determined using capillary flow porometry.

[0357] Aspect D13 is a filter medium of any one of aspects D1 - D12, wherein the support layer has an average maximum pore diameter of at most 10μm, at most 15μm, at most 20μm, at most 25μm, at most 30μm, at most 35μm, at most 40μm, at most 50μm, at most 60μm, at most 70μm, at most 80μm, at most 90μm, at most 100μm or at most 150μm.

[0358] Aspect D14 is a filter medium of aspect D13, wherein the average maximum pore diameter is determined using capillary flow porometry.

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

[0360] Aspect D16 is a filter medium of aspect D15, wherein the average minimum pore diameter is determined using capillary flow porometry.

[0361] Aspect D17 is a filter medium according to any one of Aspects D1 to D16, wherein the support layer has an average intermediate flow pore diameter, and the average intermediate flow pore diameter of the support layer varies by no more than 30%, no more than 25%, or no more than 15% over the entire length and width of the medium.

[0362] Aspect D18 is a filter medium according to any one of Aspects D1 to D17, wherein the filter medium includes a composite material including a support layer and a fine fiber layer, and the filter medium has a composite material average maximum pore diameter of at most 14 μm, at most 15 μm, or at most 20 μm, or the filter medium has a composite material average maximum pore diameter of at least 0.1 μm, or both.

[0363] Aspect D19 is a filter medium according to any one of Aspects D1 to D18, wherein the filter medium includes a composite material including a support layer and a fine fiber layer, and the filter medium has a composite material average intermediate flow pore diameter of at most 11 μm, at most 9 μm, or at most 6 μm, or the filter medium has a composite material average intermediate flow pore diameter of at least 0.1 μm, or both.

[0364] Aspect D20 is a filter medium according to Aspect D18 or D19, wherein the composite material pore diameter is determined using capillary flow porometry.

[0365] Aspect D21 is a filter medium according to any one of Aspects D1 to D20, wherein the second layer of fine fibers includes thin fine fibers and thick fine fibers, and the thick fine fibers 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 fine fibers.

[0366] Aspect D22 is a filter medium according to any one of Aspects D1 to D21, wherein the first layer of fine fibers includes fine fibers having a diameter that is 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 in the second layer of fine fibers.

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

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

[0369] Aspect D25 is a filter medium of Aspect 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] Aspect D26 is a filter medium of any one of Aspects D1 - D25, wherein the support layer includes a spunbond layer.

[0371] Aspect D27 is a filter element including a filter medium of any one of Aspects D1 - D26.

[0372] Aspect D28 is a filter element of Aspect D27, wherein the filter element includes an efficiency layer, and the efficiency layer includes a filter medium.

[0373] Aspect D29 is a filter element of Aspect D28, wherein the filter element further includes a loading layer.

[0374] Exemplary products according to a process aspect including at least one fine fiber layer Aspect 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 fine and thick fine fibers, the thick fine fibers having an average diameter that is at least 3 times the average diameter of the fine fine fibers, and at least some of the fine fibers 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. The filter medium is prepared by a method comprising.

[0375] Aspect 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 fine and thick fine fibers, the thick fine fibers having an average diameter that is at least 3 times the average diameter of the fine fine fibers, and at least some of the fine fibers comprising a fiber-forming polymer that is a non-reactive polymer that cannot crosslink with a polymer-nonreactive resinous aldehyde composition; providing a polymer-nonreactive resinous aldehyde composition comprising one or more reactive groups capable of self-crosslinking; and combining the fiber-forming polymer and the reactive resinous aldehyde composition to form a plurality of fine fibers. The filter medium is prepared by a method comprising.

[0376] Aspect E3 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 fine and thick fine fibers, the thick fine fibers having an average diameter that is at least 3 times the average diameter of the fine fine fibers, and 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 reactive 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. The filter medium is prepared by a method comprising.

[0377] Aspect E4 is a filter medium of any one of aspects E1 to E3, wherein the thick 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 thick 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.

[0378] Aspect E5 is a filter medium of any one of aspects E1 to E4, wherein the first layer of fine fibers contains thin fine fibers, 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 0.3 μm, at most 0.4 μm, at most 0.5 μm or at most 0.6 μm, or both.

[0379] Aspect E6 is a filter medium of any one of aspects E1 to E5, wherein the first layer of fine fibers contains at most 10% thick fine fibers or at most 20% thick fine fibers.

[0380] Aspect E7 is a filter medium of any one of aspects E1 to E6, wherein the first layer of fine fibers contains 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.

[0381] Aspect E8 is a filter medium of any one of aspects E1 to E7, wherein the first layer of fine fibers contains the proportion of one or more thick fine fibers in 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 in Tables 1A to 1C.

[0382] Aspect E9 is a filter medium of any one of aspects E6 to E8, wherein the proportion of thick fine fibers is determined based on the spinning time.

[0383] Aspect 10 is a filter medium of any one of aspects E6 to E8, wherein the proportion of thick fine fibers is determined using microscopic observation or nano-CT.

[0384] Aspect E11 is a filter medium according to any one of Aspects 1 to 10, wherein the first layer of fine fibers includes a layered fiber structure.

[0385] Aspect E12 is a filter medium according to Aspect E11, wherein the first layer of fine fibers includes one or more layered fiber structures of Set A5, Set B, Set D5, Set E, Set I5, or Set J in Tables 1A to 1C.

[0386] Aspect E13 is a filter medium according to Aspect E11, wherein the first layer of fine fibers includes thin fine fibers and thick fine fibers, within the first layer of fine fibers, the thin fine fibers are deposited on the first sub-layer of fine fibers, and the second sub-layer of thick fine fibers is deposited on the thin fine fibers.

[0387] Aspect E14 is a filter medium according to any one of Aspects E1 to E10, wherein the first layer of fine fibers includes a mixed fiber structure.

[0388] Aspect E15 is a filter medium according to Aspect E14, wherein the first layer of fine fibers includes one or more mixed fiber structures of Set A6, Set D, Set D6, Set I, or Set L in Tables 1A to 1C.

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

[0390] Aspect E17 is a filter medium according to any one of Aspects E1 to E16, wherein the support layer includes nylon.

[0391] Aspect E18 is a filter medium according to any one of Aspects E1 to E17, wherein the support layer has an average intermediate flow pore size of at least 5μm, at least 10μm, at least 15μm, at least 20μm, or at least 25μm and a maximum of 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 50μm, 60μm, 70μm, 80μm, or 90μm.

[0392] Aspect E19 is the filter medium of Aspect E18, where the average intermediate flow pore diameter is determined using capillary flow porometry.

[0393] Aspect E20 is the filter medium of any one of Aspects E1 - E19, where the support layer has an average maximum pore diameter of at most 10μm, at most 15μm, at most 20μm, at most 25μm, at most 30μm, at most 35μm, at most 40μm, at most 50μm, at most 60μm, at most 70μm, at most 80μm, at most 90μm, at most 100μm, or at most 150μm.

[0394] Aspect E21 is the filter medium of Aspect E20, where the average maximum pore diameter is determined using capillary flow porometry.

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

[0396] Aspect E23 is the filter medium of Aspect E22, where the average minimum pore diameter is determined using capillary flow porometry.

[0397] Aspect E24 is the filter medium of any one of Aspects E1 - E23, where the support layer has an average intermediate flow pore diameter, and the average intermediate flow pore diameter 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 entire length and width of the medium.

[0398] Aspect E25 is the filter medium of any one of Aspects E1 - E24, where the filter medium includes a composite material containing a support layer and a fine fiber layer, and the filter medium has a composite material average maximum pore diameter of at most 14μm, at most 15μm, or at most 20μm, or the filter medium has a composite material average maximum pore diameter of at least 0.1μm, or both.

[0399] Aspect E26 is a filter medium of any one of Aspects E1 to E25, wherein the filter medium includes a composite material including a support layer and a fine fiber layer, and the filter medium has a composite material average intermediate flow pore diameter of at most 11 μm, at most 9 μm or at most 6 μm, or the filter medium has a composite material average intermediate flow pore diameter of at least 0.1 μm, or both.

[0400] Aspect E27 is a filter medium of Aspect E25 or E26, wherein the composite material pore diameter is determined using capillary flow porometry.

[0401] Aspect E28 is a filter medium of any one of Aspects E1 to E27, wherein the thick fine fibers have a diameter that is at least 0.2 μm, at least 0.3 μm or at least 0.4 μm larger than that of the thin fine fibers.

[0402] Aspect E29 is a filter medium of any one of Aspects E1 to 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 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] Aspect E30 is a filter medium of Aspect E29, wherein the thickness of the first fine fiber layer is determined using scanning electron microscopy (SEM).

[0404] Aspect E31 is a filter medium of any one of Aspects E1 to E30, wherein the support layer includes a spunbond layer.

[0405] Aspect E32 is a filter medium of any one of Aspects E1 to E31, further including a second fine fiber layer.

[0406] Aspect E33 is a filter element including a filter medium of any one of Aspects E1 to E32.

[0407] Aspect E34 is a filter element of Aspect E33, wherein the filter element includes an efficiency layer, and the efficiency layer includes a filter medium.

[0408] Aspect E35 is the filter element of Aspect E34, wherein the filter element further includes a loading layer.

[0409] Exemplary product according to a process aspect including at least two fine fiber layers Aspect F1 is a filter medium including 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 includes 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, the second layer of fine fibers is deposited on the first layer of fibers, and at least some of the fine fibers provide 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. A filter medium prepared by a method comprising:

[0410] Aspect F2 is a filter medium including 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 includes 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, the second layer of fine fibers is deposited on the first layer of fibers, and at least some of the fine fibers provide a fiber-forming polymer that is a non-reactive polymer that cannot crosslink with a polymer-nonreactive resinous aldehyde composition; providing a polymer-nonreactive resinous aldehyde composition including one or more reactive groups capable of self-crosslinking; and combining the fiber-forming polymer and the reactive resinous aldehyde composition to form a plurality of fine fibers. A filter medium prepared by a method comprising:

[0411] Aspect 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, the second layer of fine fibers 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, the second layer of fine fibers is deposited on the first layer of fibers, and at least some of the fine fibers provide at least one fiber-forming polymer; providing at least two reactive additives that are reactive with each other and optionally reactive with the fiber-forming polymer; and combining at least one fiber-forming polymer and at least two reactive additives under conditions effective to form a plurality of fine fibers. A filter medium prepared by a method comprising.

[0412] Aspect F4 is a filter medium of any one of Aspects F1 - F3, wherein the fine fibers of 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 of the first layer of fine fibers have an average diameter of up to 1.1 μm, up to 1.2 μm, up to 1.3 μm, up to 1.4 μm, up to 1.5 μm, up to 2 μm, up to 3 μm, up to 4 μm, up to 5 μm or up to 10 μm, or both.

[0413] Aspect F5 is a filter medium of any one of Aspects F1 - F4, wherein the second layer of fine fibers comprises fine fibers of mixed diameter.

[0414] Aspect F6 is a filter medium of Aspect F5, wherein the second layer of fine fibers comprises thick fine fibers having an average diameter at least three times the average diameter of the thin fine fibers.

[0415] Aspect F7 is a filter medium of Aspect F5 or F6, where the second layer of fine fibers contains thick fine fibers and thin fine fibers, 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] Aspect F8 is a filter medium of Aspect F5 or F6, where the thick fine fibers have an average diameter greater than 1 μm.

[0417] Aspect F9 is a filter medium of any one of Aspects F5 - F8, where the second layer of fine fibers contains at most 10% thick fine fibers or at most 20% thick fine fibers.

[0418] Aspect F10 is a filter medium of any one of Aspects F5 - F8, where the second layer of fine fibers contains 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.

[0419] Aspect F11 is a filter medium of any one of Aspects F5 - F8, where the second layer of fine fibers contains the proportion of one or more thick fine fibers in 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 in Tables 1A - 1C.

[0420] Aspect F12 is a filter medium of any one of Aspects F9 - F11, where the proportion of thick fine fibers is determined based on the spinning time.

[0421] Aspect F13 is a filter medium of any one of Aspects F9 - F11, where the proportion of thick fine fibers is determined using microscopic observation or nano - CT.

[0422] Aspect F14 is a filter medium of any one of aspects F5 to F13, wherein the second layer of fine fibers includes a layered fiber structure.

[0423] Aspect F15 is a filter medium of aspect F14, wherein the second layer of fine fibers includes one or more layered fiber structures of set A5, set B, set D5, set E, set I5 or set J in Tables 1A to 1C.

[0424] Aspect F16 is a filter medium of aspect F14, wherein the second layer of fine fibers includes thin fine fibers and thick 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.

[0425] Aspect F17 is a filter medium of any one of aspects F5 to F13, wherein the second layer of fine fibers includes a mixed fiber structure.

[0426] Aspect F18 is a filter medium of aspect F17, wherein the second layer of fine fibers includes one or more mixed fiber structures of set A6, set D, set D6, set I or set L in Tables 1A to 1C.

[0427] Aspect F19 is a filter medium of any one of aspects F5 to F13, wherein the second layer of fine fibers includes thin fine fibers and thick fine fibers, within the second layer of fine fibers, the thin fine fibers are deposited on the first sub-layer of thick fine fibers, and the second sub-layer of thick fine fibers is deposited on the thin fine fibers.

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

[0429] Aspect F21 is a filter medium of any one of aspects F1 to F20, wherein the support layer includes nylon.

[0430] Aspect F22 is a filter medium of any one of Aspects F1 to F21, having an average intermediate flow pore diameter 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] Aspect F23 is a filter medium of Aspect F22, where the average maximum pore diameter is determined using capillary flow porometry.

[0432] Aspect F24 is a filter medium of any one of Aspects F1 to F23, having an average maximum pore diameter 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] Aspect F25 is a filter medium of Aspect F24, where the average maximum pore diameter is determined using capillary flow porometry.

[0434] Aspect F26 is a filter medium of any one of Aspects F1 to F25, having an average minimum pore diameter 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] Aspect F27 is a filter medium of Aspect F25, where the average minimum pore diameter is determined using capillary flow porometry.

[0436] Aspect F28 is a filter medium of any one of Aspects F1 to F27, where the support layer has an average intermediate flow pore diameter, and the average intermediate flow pore diameter 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 entire length and width of the medium.

[0437] Aspect F29 is a filter medium of any one of aspects F1 to F28, wherein the filter medium includes a composite material including a support layer and a fine fiber layer, and the filter medium has a maximum composite material average maximum pore diameter of 14 μm, 15 μm or 20 μm at most, or the filter medium has a composite material average maximum pore diameter of at least 0.1 μm, or both.

[0438] Aspect F30 is a filter medium of any one of aspects F1 to F29, wherein the filter medium includes a composite material including a support layer and a fine fiber layer, and the filter medium has a maximum composite material average middle flow pore diameter of 11 μm, 9 μm or 6 μm at most, or the filter medium has a composite material average middle flow pore diameter of at least 0.1 μm, or both.

[0439] Aspect F31 is a filter medium of aspect F29 or F30, wherein the composite material pore diameter is determined using capillary flow porometry.

[0440] Aspect F32 is a filter medium of any one of aspects F1 to F31, wherein the first layer of fine fibers includes fine fibers having a diameter that is 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 fine fiber layer.

[0441] Aspect F33 is a filter medium of any one of aspects F1 to 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 the first fine fiber layer has a thickness of 5 μm at most, 10 μm at most, 30 μm at most or 50 μm at most, or both.

[0442] Aspect F34 is a filter medium of any one of aspects F1 to 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 the second fine fiber layer has a thickness of 5 μm at most, 10 μm at most, 30 μm at most, 40 μm at most or 45 μm at most, or both.

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

[0444] Aspect F36 is a filter medium of any one of aspects F1 - F35, where the support layer includes a spunbond layer.

[0445] Aspect F37 is a filter element including a filter medium of any one of aspects F1 - F36.

[0446] Aspect F38 is a filter element of aspect F37, where the filter element includes an efficiency layer, and the efficiency layer includes a filter medium.

[0447] Aspect F39 is a filter element of aspect F38, where the filter element further includes a loading layer.

[0448] The present invention is illustrated by the following examples. It should be understood that specific examples, materials, amounts, and procedures should be broadly interpreted in accordance with the scope and spirit of the present invention described herein.

Examples

[0449] Preparation of Polymer Solution To prepare Solution 1, a nylon copolymer resin (SVP 651 obtained from Shakespeare Co., Columbia, SC, a terpolymer having a number average molecular weight of 21,500 to 24,800 and containing 45% nylon-6, 20% nylon-6,6 and 25% nylon-6,10) was dissolved in alcohol (ethanol, 190 proof) and heated to 60 °C to prepare a 9% nylon solids solution. After cooling, a melamine-formaldehyde resin (CYMEL 1133, Cytec Industries of West Paterson, NJ) was added to the solution such that the weight ratio of melamine-formaldehyde resin to nylon was 20:100 parts by weight. The melamine-formaldehyde resin functions as a crosslinking agent. In addition, para-toluenesulfonic acid (7% based on polymer solids) was added to the solution. The solution was stirred until homogeneous. Solution 1 was used to produce 0.25 μm fibers.

[0450] Solution 2 was prepared as described for Solution 1, except that a 17% nylon solids solution was used (likewise, the weight ratio of melamine-formaldehyde resin to nylon was 20:100 parts by weight). Solution 2 was used to produce 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 combination of a Brookfield LV DV-I Prime Viscometer and 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 (likewise, the weight ratio of melamine-formaldehyde resin to nylon was 20:100 parts by weight). Solution 3 had a viscosity of 77 ± 5 cP when measured at 25 °C using a combination of a Brookfield LV DV-I Prime Viscometer and a Fisher Scientific Model 8005 temperature-controlled water bath. Fibers of 0.5 μm were made using Solution 3.

[0453] To prepare Solution 4, a copolyamide (Griltex D 1523A, EMS-Griltech, Switzerland) was dissolved in a solvent mixture of ethanol, benzyl alcohol and water (weight ratio of ethanol:benzyl alcohol:water being 16:1:1), and heated to 60 °C to prepare a 21% (w / w) solution. Solution 4 had a viscosity of 473 ± 10 cP when measured at 25 °C using a combination of a Brookfield LV DV-I Prime Viscometer and a Fisher Scientific Model 8005 temperature-controlled water bath. Fibers of 1.4 μm were made using Solution 4.

[0454] Preparation of samples by pendant drop Samples were prepared using a pendant drop apparatus, i.e., a syringe filled with the polymer solution. A high voltage was applied to the needle attached to the syringe, and the polymer solution was pumped at a specified pump rate. When the droplet of the polymer solution emerged from the needle, this droplet formed a Taylor cone under the influence of an electrostatic field. The jet was released from the Taylor cone at a sufficiently high voltage, and this jet was extended to form fine fibers, which were deposited onto a medium attached to a rotating mandrel that functioned 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 supplying one or more polymer solutions at a voltage of 24 kV and a pump speed of 0.075 mL / min. After electrospinning, the formed fine fibers were heat-treated at 140 °C for 10 minutes.

[0456] Method 1: By co - spinning two different electrospinning precursor solutions (Solution 1 and Solution 2) from two different syringes supplied at the same pump speed (0.075 mL / min) and the same duration (5 min), a mixed fiber layer was deposited on a 0.2 - mm - thick spunbond nylon scrim having a basis weight of 70 g / m 2 and a solidity of 28% (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL). By rotating Solution 1 or Solution 2 from a single syringe to form layers containing only thin or thick fine fibers respectively, two control samples were made separately using the same pump speed and duration.

[0457] To improve the structural stability by cross - linking, all samples were subjected to post - synthesis treatment. After electrospinning, the formed fibers were heat - treated at 140 °C for 10 minutes.

[0458] Method 2: By co - spinning Solution 1 and Solution 2 from two different syringes supplied at the same pump speed (0.075 mL / min) and the same duration, a series of mixed fiber layers were formed on a 70 g / m 2The areal weight was deposited on a spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) with a thickness of 0.2 mm and 28% solids content. 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 fine or thick microfibers respectively. In contrast to Method 1, by co - spinning either Solution 1 or Solution 2 from two syringes (instead of one syringe), the areal weight of the control samples and the areal weight of the samples containing the mixed fiber layer were closer.

[0459] For all samples, a post - synthesis treatment was performed to improve the structural stability by cross - linking. After electrospinning, the formed fibers were heat - treated at 140 °C for 10 minutes.

[0460] Method 3: A series of fiber layers with different diameters were deposited on a spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) with an areal weight of 70 g / m 2 and a thickness of 0.2 mm and 28% solids content by alternately (“pulsing”) spinning from one of two syringes containing Solution 1 or Solution 2 at the same pump speed (0.075 mL / min) according to a series of timings in Table 1A.

[0461] For all samples, a post - synthesis treatment was performed to improve the structural stability by cross - linking. After electrospinning, the formed fibers were heat - treated at 140 °C for 10 minutes.

[0462] Method 4: A series of mixed - fiber structures were deposited on a spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) with an areal weight of 70 g / m 2 and a thickness of 0.2 mm and 28% solids content using a two - step procedure.

[0463] In the first step, by supplying Solution 2 at a pump rate of (0.075 mL / min) for 2 minutes, thick fine fibers (corresponding to a coating rate of 0.43 g / m 2 ) were deposited on the scrim to function as the support layer under the next fibers.

[0464] In the second step, a layer of fine fibers with a mixed diameter was deposited by alternately ("pulsing") spinning from either of two syringes containing Solution 1 or Solution 2 (for thin and thick fine fibers respectively), which were alternately supplied at the same pump rate (0.075 mL / min) according to the series of timings in Table 1A.

[0465] For all samples having a total basis weight in the range of approximately 0.65 - 0.86 g / m 2 , post-synthesis treatment was carried out to improve the structural stability by crosslinking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 minutes.

[0466] Method 5 Using a 2-step procedure, a series of structures with different basis weights due to the contribution of the thin fine fiber component were deposited on a 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) having a basis weight of 70 g / m 2 and a solidity of 28%.

[0467] In the first step, by supplying Solution 2 at a pump rate of (0.075 mL / min) for 2 minutes, thick fine fibers (corresponding to a coating rate of 0.43 g / m 2 ) were deposited on the scrim to function as the support layer under the next fibers.

[0468] In the second step, a layer of thin fine fibers was deposited by supplying Solution 1 at a pump rate of 0.075 mL / min. The basis weight of the layer of thin fine fibers was 0.09 g / m 2 , 0.10 g / m 2 , 0.22 g / m2 , 0.31 g / m 2 , 0.45 g / m 2 or 0.56 g / m 2 and these were achieved using electrospinning times of 48 seconds, 60 seconds, 120 seconds, 168 seconds, 240 seconds or 300 seconds respectively. After electrospinning, the fibers formed were heat treated at 140 °C for 10 minutes.

[0469]

Table 1

[0470] Method 6 A series of media samples were made that included multiple layers with fine fibers of various sizes. The samples included a base layer of thick fine fibers, followed by a layer of thin fine fibers and then 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 in which thin and thick fine fibers were mixed and then a layer of thick fine fibers on top (thick / thin / mixed / thick or L / S / mixed / L).

[0471] By spinning Solution 2 for 2 minutes, thick fine fibers (corresponding to a coating rate of 0.43 g / m 2 ) were deposited on the scrim. Without wishing to be bound by theory, the thick fine fibers are thought to function as a support layer under the next fiber layer. Next, by rotating Solution 1 for 2 minutes, a second layer of thin fine fibers (corresponding to a coating rate of 0.22 g / m 2 ) was deposited. If included, an intermediate (mixed) layer containing both thin and thick fine fibers was added by alternately ("pulsing") spinning from a syringe containing Solution 1 or Solution 2 for thin and thick fine fibers respectively according to the series of timings in Table 1A. Finally, by spinning Solution 2 for 2 minutes, the top layer of thick fine fibers (corresponding to a coating rate of 0.43 g / m 2 ) was deposited. All solutions were supplied at a pump rate of 0.075 mL / min.

[0472] Approximately 1.31 to 1.52 g / m 2 For all samples having a total basis weight in the range of 2 , post-synthesis treatment was performed to improve the structural stability by crosslinking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 minutes.

[0473] Method 7: A series of media samples were also made that included a base layer of thick microfibers and a mixed layer of thin and thick microfibers.

[0474] First, a first microfiber layer containing thick microfibers (corresponding to a coverage of 0.43 g / m 2 ) was deposited onto a 70 g / m 2 basis weight, 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) having 28% solidity by spinning Solution 2 at a pump rate of 0.075 mL / min for 2 minutes. Next, a second microfiber layer containing a mixture of thin and thick microfibers was deposited by co-spinning two different electrospinning precursor solutions (Solution 1 and Solution 2) from two different syringes supplied at the same pump rate (0.075 mL / min) and the same duration (2.5 min or 4.5 min).

[0475] For all samples, post-synthesis treatment was performed to improve the structural stability by crosslinking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 minutes.

[0476] Method 8 First, a first microfiber layer containing thick (1.4 μm diameter) microfibers (corresponding to a coverage of 0.54 g / m 2 ) was deposited onto a 70 g / m 2 basis weight, 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) having 28% solidity by spinning Solution 4 at a pump rate of 0.075 mL / min for 2 minutes.

[0477] Next, according to the timing sequence of Table 1B, using Solution 4 instead of Solution 2, a mixed layer of fibers with different diameters (0.25 μm and 1.4 μm) was produced as described in Method 4. (The timing sequence of Table 1B is the same as that of Table 1A, but since Solution 4 is used instead of Solution 2, the resulting layer has a different basis weight and fiber ratio.)

[0478] Method 9 First, by spinning Solution 4 at a pump rate of 0.075 mL / min for 2 minutes, a first fine fiber layer (equivalent to a coating rate of 0.54 g / m 2 ) containing thick (1.4 μm diameter) fine fibers was deposited onto a 70 g / m 2 basis weight, 28% solids, 0.2 mm thick spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL).

[0479] Next, according to the timing sequence of Table 1C, using Solution 3 instead of Solution 1 and Solution 4 instead of Solution 2, a mixed layer of fibers with different diameters (0.5 μm and 1.4 μm) was produced as described in Method 4. (The timing sequence of Table 1C is the same as that of Table 1A, but since Solution 3 is used instead of Solution 1 and Solution 4 is used instead of Solution 2, the resulting layer has a different basis weight and fiber ratio.)

[0480]

Table 2

[0481]

Table 3

[0482] Method 10 First, by spinning Solution 4 at a pump rate of 0.075 mL / min for 2 minutes, a first fine fiber layer (equivalent to a coating rate of 0.54 g / m 2(equivalent to the coverage rate) was 70 g / m 2 was deposited onto a spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) with a basis weight of 70 g / m

[0483] Next, two different electrospinning precursor solutions (Solution 1 and Solution 4) from two different syringes, supplied at the same pump rate (0.075 mL / min) and the same duration (1 minute, 1.4 minutes, 2 minutes, 2.5 minutes, 3.6 minutes, or 4.5 minutes), were co-spun to deposit a second nanofiber layer containing mixed nanofibers of different diameters (0.25 μm and 1.4 μm).

[0484] All samples were subjected to a synthetic post-treatment to improve robustness by crosslinking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 minutes.

[0485] Method 11 First, a first nanofiber layer (0.54 g / m 2 equivalent to the coverage rate) containing thick (1.4 μm in diameter) nanofibers was deposited onto a spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) with a basis weight of 70 g / m 2 and a solidity of 28% and a thickness of 0.2 mm by spinning Solution 4 at a pump rate of 0.075 mL / min for 2 minutes.

[0486] Next, two different electrospinning precursor solutions (Solution 3 and Solution 4) from two different syringes, supplied at the same pump rate (0.075 mL / min) and the same duration (2 minutes, 3 minutes, 4 minutes, or 5 minutes), were co-spun to deposit a second nanofiber layer containing mixed nanofibers of different diameters (0.5 μm and 1.4 μm).

[0487] All samples were subjected to a synthetic post-treatment to improve robustness by crosslinking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 minutes.

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

[0489] By spinning Solution 4 for 2 minutes, thick fine fibers (equivalent to a coating rate of 0.54 g / m 2 were deposited on the scrim. Without wishing to be bound by theory, the thick fine fibers are thought to function as a support layer under the next fiber layer. Next, by rotating Solution 1 for 2 minutes, a second layer of thin fine fibers (equivalent to a coating rate of 0.22 g / m 2 was deposited. When included, an intermediate (mixed) layer containing both thin and thick fine fibers was added by alternately ("pulsing") spinning from syringes containing Solution 1 or Solution 4 for thin and thick fine fibers, respectively, according to the timing sequence in Table 1B. Finally, by spinning Solution 4 for 2 minutes, the top layer of thick fine fibers (equivalent to a coating rate of 0.54 g / m2) was deposited. All solutions were supplied at a pump rate of 0.075 mL / min.

[0490] All samples were post-treated synthetically to improve robustness by cross-linking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 minutes.

[0491] Method 13 First, by spinning Solution 4 for 2 minutes at a pump rate of 0.075 mL / min, a first fine fiber layer containing thick (1.4 μm in diameter) fine fibers (equivalent to a coating rate of 0.54 g / m 2 was deposited on a 70 g / m 2The basis weight was deposited onto a spunbond nylon scrim (Media Grade 23200, Cerex Advanced Fibers, Cantonment, FL) having a basis weight of 28% and a thickness of 0.2 mm.

[0492] Next, Solution 1 was rotated three times for 2 minutes each to deposit three additional layers of fine fibers (each corresponding to a coating rate of 0.22 g / m 2 ).

[0493] Finally, Solution 4 was spun for 2 minutes to deposit the top layer of thick fibers (corresponding to a coating rate of 0.54 g / m2). All solutions were supplied at a pump rate of 0.075 mL / min.

[0494] All samples were subjected to a post-synthesis treatment to improve robustness by crosslinking. After electrospinning, the formed fibers were heat-treated at 140 °C for 10 minutes.

[0495] Characterization of the Media Scanning Electron Microscopy (SEM) Samples were prepared for top-down SEM imaging by sputter coating the surface with a mixture of gold and palladium containing a 60:40 Au:Pd mixture. Typically, an acceleration voltage of 5 kV or 10 kV was used, and images were collected at magnifications of 500x, 1000x, and 2500x using a secondary electron detector or a backscattered electron detector.

[0496] A 3 mm x 20 mm sample containing fine fibers was fabricated on a support layer. Typically, with the fine fiber side of the sample facing down, it was placed on a weighing tin on a hard surface, and the tin was filled with liquid nitrogen to submerge the sample, thereby preparing the sample for cross-sectional SEM imaging. After at least 30 seconds, a razor blade was used to cut the sample (while still immersed in liquid nitrogen) to expose the cross-section. After cutting and another 10 - 20 seconds had elapsed, the sample was removed from the liquid nitrogen and set up for SEM imaging. Next, the sample was sputter-coated with 60:40 Au:Pd. Typically, an acceleration voltage of 5 kV was used, and an image was collected at a magnification of 1000 times using a secondary electron detector.

[0497] Calculation of fiber ratio based on spinning time The relative amounts of thick and thin fine fibers (based on the total number of fibers) were determined using the following equation: [Number] where D L and D S are the diameters of the thick and thin fine fibers, respectively; V L and V s are the volumes of the polymers containing the thick and thin fine fibers, respectively. The volume V is calculated for thin or thick fine fibers as follows: [Number] where ρ is the density of the polymer containing the thin or thick fine fibers, and %w / v refers to the solids based on the mass per volume of the polymer solution.

[0498] Fiber diameter The fine fiber samples produced in Examples 1 to 7 had an average fiber diameter of 10 microns or less. Typically, the thin fine fibers had an average fiber diameter in the range of 200 nm to 600 nm when measured by a scanning electron microscope (SEM). Typically, the thick fine fibers had an average fiber diameter of at least 700 nm when measured by a scanning electron microscope (SEM). The sorting of the fiber diameters was performed by imaging the fibers with a top-down SEM and measuring the fiber diameters (or other dimensions of interest) in the obtained 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 the sorting of the fibers. The diameter of the fibers was measured at at least 30 locations in the sample.

[0499] Thickness of the fine fiber layer The thickness of the fine fiber sample prepared as described above was measured by scanning electron microscopy (SEM) by cross-sectional analysis of the SEM. The thickness of the fine fiber layer of at least 5 images from different parts of the sample was determined using FIJI. Specifically, the upper and lower parts of the fine fiber layer were drawn using the polygon tool, the area outside the selected fine fiber cross-section was erased, the area of the selected fine fiber cross-section was recolored white using the threshold tool, the fibers at the boundary of the selected section were corrected, 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] As the wetting fluid, Porofil Wetting Solution (Quantachrome Instruments, Anton Paar, Boynton Beach, FL) was used. A sample with a diameter of 25 mm was subjected to a pressure sweep (i.e., a continuous pressure scan) from 0.0256 bar to 1.275 bar in both the wet and dry states (first wet and then dry) to determine the pore diameter within the range of 1 micron to 100 microns.

[0502] The samples were tested from low pressure to high pressure in both the wet and dry states. The air flow in the saturation part of the test and the pressure of the sample are generally called the wetting curve. A total of 256 data points were collected over the entire pressure scan range for both the dry curve and the wetting curve. The tests were conducted under ambient conditions (e.g., 20 °C to 25 °C). No adjustment of the pore diameter fineness was made by applying empirical bending coefficients and / or shape coefficients.

[0503] In the flow porometry test procedure, a set of data of a series of pressures (typically plotted on the x-axis) and air flows (typically plotted on the y-axis) of the dry sample and the pressures and air flows of the saturated (wet) sample are collected. These two data sets are generally called the dry curve and the wetting curve. That is, Dry curve = V dry = Air flow through the dry sample as a function of pressure Wetting curve = V wet = Air flow through the saturated sample as a function of pressure.

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

Equation

[0505] This conversion allows the drying curve and the wetting curve to be defined as functions of the pore diameter. That is, Drying curve = V’ dry = Air flow through the dry sample as a function of the diameter Wetting curve = V’ wet = Air flow through the saturated sample as a function of the diameter.

[0506] The cumulative flow pore size distribution (Q) is defined as the ratio of the wetting curve to the drying curve as a function of the pore diameter. Here,

Equation

[0507] The minimum pore diameter was calculated by determining the diameter at which the drying curve and the wetting curve intersect.

[0508] The intermediate flow pore diameter was calculated at the pressure where the wetting curve and the “semi-dry” curve intersect. The semi-dry curve is obtained by mathematically dividing V’ dry by 2.

[0509] The maximum pore diameter was determined by detecting the bubble point. The bubble point was detected after the fluid began to pass through the sample, and the three consecutive measured values increased by at least 1%. The bubble point is the starting value 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) that measures particle capture efficiency using 0.3 μm oil (bis(2-ethylhexyl) sebacate, Sigma-Aldrich) droplets (aerosol) added to a 4-inch diameter media sample at a flow rate of 14.7 liters per minute (L / min). The TSI 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 criteria of 42 CFR §84 (June 8, 1995).

[0511] Figure of Merit The figure of merit is a measure of the performance of the filter media and the ability of the filter media to provide a specific level of cleanliness of the stream with minimal energy use. Generally, a larger figure of merit value is better than a smaller value.

[0512] The figure of merit (FOM) value was calculated from the permeability (P, the 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] The permeability (P), pressure drop (dP), and face velocity (u) were measured using the HEFS TSI automated filter tester, Model 8127, test bench as described above.

[0514] Liquid Filtration Performance Test The liquid filtration performance was evaluated on a flat sheet, high-precision, single-pass 2-fluid (FHAST) bench. The FHAST bench includes a reservoir of hydraulic fluid loaded with particles of various diameters. Then, the particle-loaded hydraulic fluid passes through the media, and the particle number and diameter are measured upstream and downstream of the media. The FHAST bench has the following characteristics: Flow rate control: 57 mL / min to 580 mL / min with an error of ±2%; Temperature control: 25°C to 40°C with an error of ±0.25°C; dP measurement: 0 psi to 25 psi with an error of ±0.065%; Particle size: 1.7 μm to 20 μm; Maximum particle concentration: 1,000,000 / mL; Dilution performance: 5:1 to 100:1. The FHAST bench was used in a steady flow mode with a concentration of 10 milligrams per liter (mg / L) in hydraulic fluid and a flow rate of 0.347 L / min, using ISO Medium Test Dust compliant with ISO 11171:2016, and added to a 2-inch diameter media sample. The dP value and efficiency of the media at a specific contaminant particle size (measured using a commercially available particle counter, specifically the PAMAS 4132 Particle Counting System for Liquids calibrated with ISO Medium Test Dust compliant with ISO 11171:2016 (Hydraulic fluid power - Calibration of automatic particle counters for liquids)) were collected at regular time intervals (every approximately 7 seconds) over a test period that ended when the maximum dP of the pre-set media reached 20 psi (measured with two test media dP sensors: (A) a differential pressure transducer with an accuracy of ±0.025% for 0 psi to 5 psi; a high-precision, low-range dP sensor, and (B) a differential pressure transducer with an accuracy of ±0.065% for 0 psi to 25 psi; a low-precision, high-range dP sensor).

[0515] The beta ratio was evaluated under steady flow conditions (flowing a 2-inch diameter media sample at 347 mL / min) 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 instead of the multi-pass mode required by the test standard. ISO 12103-1 A3 Medium Test Dust (Powder Technology, Inc., Arden Hills, MN) at a concentration of 10 mg / L was added to the hydraulic fluid (Mobil Aero HF, MIL-PRF-5606). Instantaneous beta values were recorded every 7 seconds over the test period. The test ends when a final dP of 20 psi is reached.

[0516] Solidity The solidity (c) of a nonwoven layer (e.g., including a non-fibrillated layer or a composite material including a fibrillated layer and a non-fibrillated layer) is calculated using the following formula: c = BW / ρZ Where BW is the basis weight, ρ is the density of the fiber, and Z is the thickness of the media.

[0517] The thickness 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. The basis weight was measured using TAPPI T410 om-08.

[0518] Since it is difficult to measure the thickness of the fine fiber layer, the solidity of the fine fiber layer is calculated using a modified 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 the experimentally measured pressure drop value. The pressure drop (ΔP or dP) is determined using the FHAST bench as described in the section on liquid filtration performance testing below.

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

Equation

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

[0521] For a mixed fiber medium, the effective fiber diameter is calculated from the following equation considering the relative amounts of the fine and thick fibers:

Equation

[0522] The basis weight of one or more fine fiber layers is calculated as follows. Total basis weight of fine fiber layer = (mass of fine fibers) / (area of scrim)

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

[0524] When the method of forming the fine fibers is unknown, the mass of the fine fibers can be calculated as follows after separation of the fine fiber scrim or support (e.g., by peeling or delaminating). Mass of fine fibers = (total mass of media sample) - (mass of bare scrim or support)

[0525] Example 1 Media was made 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] As described in the section on the liquid filtration performance test above, the media was tested. The results are shown in Figures 1A and 1C. The media containing thin fine fibers deposited directly on the scrim (results shown in Figure 1A) had an initial pressure drop of 0.74 psi. The media containing 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 the thick fine fiber layer deposited on the scrim before the thin fine fibers are deposited on the thick fine fiber layer is shown in Figure 1E.

[0528] SEM images of the resulting media are shown in FIG. 1B (thin fibrils deposited directly on the scrim) and FIG. 1D (thin fibrils deposited on a layer of thick fibrils deposited on the scrim). In the thin fibrils deposited directly on the scrim (FIG. 1B), fiber “alignment” and damage were observed. In the thin fibrils deposited on a layer of thick fibrils deposited on the scrim (FIG. 1D), no fiber “alignment” or damage was observed.

[0529] Example 2 A media was made according to Pendant Drop Sample Preparation Method 1. The resulting nonwoven fabric had a theoretical basis weight of 1.64 g / m 2 .

[0530] Control nonwoven media made by co - spinning each single electrospinning precursor solution from two different syringes had a theoretical basis weight of 0.56 g / m 2 or 1.08 g / m 2 in Solutions 1 and 2, respectively.

[0531] SEM images of the resulting media are shown in FIG. 2A. Characteristics of the resulting media are shown in Table 2A.

[0532] FOM values for these media samples for air filtration are shown in Table 2B. From the comparison of FOM values, it is suggested 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 fibrils (Table 2B).

[0533] As described herein, liquid filtration performance was evaluated on a flat sheet, high - precision, single - pass 2 - fluid (FHAST) bench. Similar β - values were observed for media containing mixed fibers and media containing thin fibrils (FIG. 2B), but no benefit was observed for media containing mixed fibers in terms of the decrease in dP compared to media containing only thin fibrils (FIG. 2C). Liquid filtration performance data (FIGS. 2B - 2C) are consistent with porometry measurements (Table 2C), and the pore size of the media containing mixed fibers is smaller compared to the pore size of the media containing only thin fibrils.

[0534] Without being bound by theory, the media containing mixed fibers exhibits a higher total fiber coverage rate compared to media containing only thin fibrils or only thick fibrils. Therefore, it is believed that the media containing mixed fibers could not show any reduction in pressure drop compared to media containing only thin fibrils. This difference in coverage rate is illustrated by the comparison basis weight: the media containing mixed fibers had a higher basis weight (1.64 g / m 2 ) compared to the basis weight of the media containing only thin fibrils (0.56 g / m 2 ) or the basis weight of the media containing only thick fibrils (1.08 g / m 2 ).

[0535]

Table 4

[0536]

Table 5

[0537]

Table 6

[0538] Example 3 According to the pendant drop sample preparation method 2, media were prepared with electrospinning times of 2 minutes, 3 minutes, or 5 minutes. The obtained nonwovens had theoretical basis weights of 0.65 g / m2, 0.98 g / m2, and 1.63 g / m 2 , respectively.

[0539] Control nonwoven media prepared by co - electrospinning the respective electrospinning precursor solutions from two different syringes for 2 minutes had theoretical basis weights of 0.44 g / m 2 and 0.86 g / m 2 , respectively, for solution 1 and solution 2.

[0540] SEM images of the obtained media are shown in Figure 3.

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

[0542] From the comparison of the FOM values for air filtration for media samples made using 2 minutes of electrospinning, the mixed fiber layer is suggested to have improved performance (higher rejection of contaminants and lower pressure drop) compared to media containing only thin nanofibers (Table 3A).

[0543] Interestingly, an increase in fiber coverage (by prolonging electrospinning) leads to an overall decrease in the FOM value for the mixed fiber media as well, due to a decrease in the sweep pressure. As described herein, the liquid filtration performance was evaluated on a flat - sheet, high - precision, single - pass 2 - fluid (FHAST) bench. A lower pressure drop was observed for the mixed fiber media compared to the case of only thin nanofibers (Figure 3D). However, a comparison of the β values (Figure 3F) shows that these samples are operated in a trade - off regime where an improvement in 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 a higher fiber coverage leads to an increase in efficiency due to a smaller pore size that causes a larger pressure drop (comparison of clean media dP in Figure 3G). The FHAST bench results are consistent with the porometry measurements (see Table 3B), indicating that the pore size is highly related to the overall performance of the media samples. Furthermore, the maximum pore size and the median flow pore size were dependent on the electrospinning time (Figure 3H).

[0544]

Table 7

[0545]

Table 8

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

[0547] To provide a greater degree of control of the fibrous media structure and composition, a "pulse" sequence (where thin and thick fibrils are alternately deposited on a scrim support) was tested. In all cases, the thin fibrils were deposited first, followed by the thick fibrils, and a series of layered fibrous media samples were produced with a thick fibril content varying from 2% to 20% (nominal value calculated using the equation described in the section on calculating the proportion of fibrils based on spinning time) on a fibril ratio basis.

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

[0549] Figure 4 shows the increase in basis weight observed with an increase in the relative amount of thick fibrils. A linear increase in basis weight is observed up to a thick fibril content of 10%.

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

[0551] The resulting medium included a "support layer" of thick fibrils (1 μm diameter) deposited prior to depositing a layer of mixed fiber diameter fibrils.

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

[0553] In all cases, in the second step of the procedure (i.e., after deposition of the first fibrous layer containing the thick microfibers), the thin microfibers are deposited first, followed by the thick microfibers, and a series of mixed fiber diameter media samples are produced having a thick microfiber content that varies between 2% and 20% (nominal value calculated using the equation described in the section on calculating the proportion of fibers based on spinning time) on a fiber proportion basis.

[0554] SEM images provided a visual confirmation of the ability to control the media morphology (Figs. 5A, 5B). Fig. 5A shows a media containing only thin microfibers (Fig. 5A, panel A), a media containing layered fibers of mixed diameters (Fig. 5A, panels A5, B, D5, E, I5, J) or a media containing only thick microfibers (Fig. 5A, panel M). Fig. 5B shows a media containing only thin microfibers (Fig. 5B, panel A), a media containing mixed fibers of mixed diameters (Fig. 5B, panels A6, D, D6, I, I6, L) or a media containing only thick microfibers (Fig. 5B, panel M). The letters for 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 fraction of thick microfibers (see Tables 4A and 5C). These results suggest that for samples with a moderate fiber coverage (e.g., 5 g / m2), the porometry test is unable to capture the presence of a pore size gradient present in such media. Nevertheless, these data demonstrate that the incorporation of thick microfibers into the network of thin microfibers can be effective in broadening the pore size distribution.

[0556] By comparing the air filtration performance measured by the FOM value (see Table 4B) of the mixed fiber diameter media structure or the mixed fiber structure having a layered fiber structure, it is suggested that the structures have similar effects (see Figure 5D, lower panel). Generally, both the layered fiber structure and the mixed fiber structure exhibit lower performance because more of the thinner fine fibers (which impart efficiency) are replaced by the thicker fine fibers. For the mixed fiber structure, there appears to be an optimal range of thicker fine fiber content (5% - 7%) such that the FOM remains comparable to that of a purely thin fine fiber network. In particular, the mixed fiber structure media samples retained a relatively high FOM (circles in the upper panel of Figure 5D) despite their large pore diameters. However, the FOM value and the pore diameter do not appear to correlate well.

[0557]

Table 9

[0558]

Table 10

[0559] Importantly, by providing a support layer of thicker fine fibers to the layer containing fibers of mixed fiber diameters, the beta collapse observed in media containing the same layer of mixed fiber diameters but without such a support layer of thicker fine fibers was eliminated. Exemplary comparisons are shown in Figures 5E and 5F. Figure 5E shows a mixed layer of mixed fiber diameters (containing 5% thicker fine fibers) fabricated as described in Method 3, Table 1A, Set B. The mixed layer has a basis weight of 0.71 g / m 2 and the support layer and the mixed layer have an initial pressure drop (dP) of 0.48 psi. Figure 5F shows a mixed layer of mixed fiber diameters (containing 5% thicker fine fibers) deposited on a support layer of thicker fine fibers (thicker fine fibers having a basis weight of 0.43 g / m 2 ) fabricated as described in Method 4, Table 1A, Set B. The mixed layer has a basis weight of 0.71 g / m 2 and the support layer and the two fine fiber layers have an initial pressure drop (dP) of 0.77 psi.

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

[0561] Example 6 (having a basis weight of 0.09 g / m 2 , 0.10 g / m 2 , 0.22 g / m 2 , 0.31 g / m 2 , 0.45 g / m 2 or 0.56 g / m 2 ), a media sample was made by Method 5 which included depositing a layer of thick fibers (having a basis weight of at least 0.43 g / m 2 ) as a support layer under a network of thin fibers. The pressure drop and overall β value were tested. The results are shown in FIGS. 6B-6C.

[0562] An exemplary SEM image showing the top layer of thin fibers covering the underlying network of supporting thick fibers is shown in FIG. 6A.

[0563] Media containing a layer of thin fibers in the basis weight range showed good efficiency with a low pressure drop.

[0564] Example 7 The media sample was made according to Method 6. The media included a first layer of thick fibrils, followed by a layer of thin fibrils, then a layer in which thin and thick fibrils were mixed, and finally a layer of thick fibrils (described as thick / thin / mixed / thick or L / S / mixed / L). Instead, the inner layer of mixed fibrils (between the two layers of thick fibrils) was deposited by electrospinning as described in Table 1A. As described herein, the pressure drop and overall β value were evaluated on a flat sheet, high-precision, single-pass 2-fluid (FHAST) bench. Exemplary images are shown in FIGS. 7A-7B. The results are shown in FIGS. 7C-7D.

[0565] Including a layer of thin and thick diameter fibrils mixed between the thick fibril layers is thought to be particularly useful for maintaining the structural integrity of the intermediate layer in applications that require back pulses for media cleaning / regeneration.

[0566] Example 8 The media sample was made according to Method 7 and included a layer of thick fibrils (having a basis weight of at least 0.43 g / m 2 ) under the layer of mixed thin and thick fibrils. The sample was compared to a media sample made according to Method 5 (a layer of thick fibrils under a network of thin fibrils).

[0567] The layer of mixed thin and thick fibrils included approximately 10% thick fibrils based on the total number of fibrils. This percentage was evaluated from the diameters of the thin and thick fibrils, the percentage of solids in the precursor spinning solution, the syringe pump feed rate, and the electrospinning time. The layer of mixed thin and thick fibrils was made by approximating the basis weight of the second (thin fibril) layer of the media made using Method 5 or by approximating the total number of fibrils in the second (thin fibril) layer of the media made using Method 5. As shown in Table 5A, the resulting media layer had a resulting basis weight of 0.82 g / m 2 - 1.47 g / m 2 , while the second (thin fibril) layer of the media made using Method 5 had a basis weight of 0.56 g / m 2 .

[0568] The pressure drop and overall β value of the resulting media were tested. The results are shown in FIGS. 8B-8C. An exemplary SEM image is shown in FIG. 8A.

[0569]

Table 11

[0570]

Table 12

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

[0572] The evaluation of air filtration performance by HEFS bench tests was consistent with the pore size results in that a lower pressure drop was achieved while maintaining the performance index (FOM) compared to that of samples with only thin fibers (see Table 5A, 0.82 g / m of mixed fibers with a comparable FOM of about 150 for thin fibers). 2 of the basis weight).

[0573] As described herein, liquid filtration performance was evaluated on a flat sheet, high-precision, single-pass 2-fluid (FHAST) bench. A significant improvement in media dP (FIG. 8A) was observed for the co-spun samples compared to the network of thin fibers supported by thick fibers. However, for these media with mixed thin and thick fibers, (compared to a β of 1000 for particles larger than 3 microns for only unmixed thin fibers,) an exchange of efficiency was made such that a β of 1000 was achieved for contaminant particles larger than 5 microns. Overall, media consisting of mixed thin and thick fibers with a thick fiber lower support layer showed good efficiency with a low pressure drop.

[0574] Example 9 - Comparison with Fine Glass Fibers Containing Media The filter medium of Example 5 was compared with two liquid media products containing fine glass fibers. The first glass medium had a β rating of 1,000 for particles less 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), including LyPore Grade 9428 and LyPore Grade 9221, respectively. The results are shown in FIGS. 5G - 5J and Table 6.

[0575] The two liquid media products containing the fine glass fibers tested had a higher pressure drop due to the thickness of these glass fiber-containing media and subsequently tolerated some range of depth loading. All samples containing up to 10% coarse fibril content had efficiency comparable to that of the glass media rated β5um = 1,000, especially for contaminants with a diameter of up to 5 μm (if slightly less good). Table 6A summarizes the improvement in media dP and efficiency benchmarked against the glass fiber media having a β rating of 1,000 for particles larger than 5 μm.

[0576] Table 6B summarizes the comparison of these two performance criteria for media containing only fine fibrils (but as indicated by the coarse fibrils).

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

[0578]

Table 13

[0579]

Table 14

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

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

[0582] For each sample being tested, the ratio of the total fine fiber basis weight to the average maximum pore diameter 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

Number

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

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

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

[0587] If the method of forming the fine fibers is unknown, the mass of the fine fibers can be calculated as follows after separation of the fine fiber scum or support (e.g., by peeling or delaminating). Mass of fine fibers = (total mass of the media sample) - (mass of the bare scum or support)

[0588] By plotting the ratio of the basis weight of the composite material to the maximum pore size of the composite material against the basis weight of the second layer of fine fibers, it becomes possible to identify the characteristics (the fine fiber basis weight and the maximum pore size of the composite material) that correlate with the fine fiber layer that will experience damage during the FHAST bench test. As shown in FIG. 11, samples that withstood the liquid filtration performance test were identified from samples that could not withstand the liquid filtration performance test and showed damage and / or beta decay to the fiber structure visualized using SEM images.

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

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

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

[0592] The results are shown in Figure 12. Triangles represent samples that maintained the structural integrity of the fibers through the FHAST bench test; squares represent samples in which fiber blowout occurred during the FHAST bench test (indicated by beta decay). Samples that included two layers of fibers, where the first layer included fibers having an average diameter at least three times the average fiber diameter of the smallest fibers of the second layer of fibers, are shown in filled shapes. Samples that included one layer of fibers with fibers of mixed diameter are shown in unfilled shapes.

[0593] Most of the media samples having only one layer of fibers (i.e., made using Methods 1, 2, or 3) showed damage to the fibers (indicated by open squares).

[0594] Some media samples with only one fine fiber layer withstood up to 20 psi during the FHAST bench test (shown by the white triangles). Without wishing to be bound by theory, these fine fiber layers are thought to have withstood the test because of their very high coverage (basis weight), although such a high basis weight comes at the expense of a high initial pressure drop.

[0595] In contrast, all media samples containing two fine fiber layers made using Method 4, 5, 6, or 7 maintained the structural integrity of the fine fibers (shown by the filled triangles).

[0596] The results show that both the average maximum pore size of the composite (Figure 12A) and the average intermediate flow pore size of the composite (Figure 12B) correlate with the ability of the composite to withstand the FHAST bench test. Clinical studies that highly correlate with the ability of a composite to withstand at least a 20 psi pressure drop during liquid filtration show superior filtration performance compared to filter media that cannot withstand the same conditions.

[0597] Some media samples with an average maximum pore size of the composite of 20 μm withstood the FHAST bench test, but a transition zone where some media samples began to fail the test was observed in media samples with an average maximum pore size of the composite of 14 μm - 20 μm.

[0598] Similarly, some media with an average intermediate flow pore size of the composite of 11 μm withstood the FHAST bench test, but a transition zone where some media samples began to fail the test was observed in media samples with an average maximum pore size of the composite of 6 μm - 11 μm.

[0599] For example, samples without a thick fiber support with an average maximum pore size of the composite of 11 μm cannot withstand the FHAST bench test, while samples with a thick fiber support with an average maximum pore size of the composite of 11 μm can withstand the FHAST bench test. Since finer fiber samples with larger pore sizes can be used, the efficiency can be finely tuned without a detrimental pressure drop of the resulting composite.

[0600] Example 12A The media sample was prepared according to Method 8 and included a layer of thick microfibers (having a basis weight of at least 0.54 g / m 2 2) under a layer of mixed diameter mixed fibers (0.25 μm fibers and 1.4 μm fibers).

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

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

[0603] The 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 1B) and Figure 13E (Set A, Set A6, Set D, Set D6, Set I, Set I6, Set L, and Set of Table 1B). This plot also shows the values of comparable liquid media products containing fine fibers having 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. The 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 1B) and Figure 13G (Set A, Set A6, Set D, Set D6, Set I, Set I6, Set L, and Set of Table 1B). This plot also shows the values of comparable liquid media products containing fine fibers having 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.

[0604] As shown in Figures 13D - 13J, media containing fibers of mixed fiber diameter with a 1% thick fiber content show similar efficiency to media layers containing only fine fibers, but show a significant improvement in pressure drop. In contrast, in media with a thick fiber media content greater than 5%, 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 thought that an increase in the amount of thick fibers in a media containing fibers of mixed fiber diameter "opens up" the fine fiber structure.

[0605] Example 12B Media samples were made according to Method 10 and included a layer of thick fibers (having a basis weight of at least 0.54 g / m 2 ) under a layer of mixed 0.25 μm fibers and 1.4 μm fine fibers.

[0606] The resulting media had (for precursor solutions supplied for 1 minute, 1.4 minutes, 2 minutes, 2.5 minutes, 3.6 minutes, or 4.5 minutes respectively) 0.38 g / m 2 , 0.53 g / m 2 , 0.76 g / m 2 , 0.95 g / m2 、1.37 g / m 2 or 1.71 g / m 2 The mixed fiber layer having a basis weight was included. The mixed fiber layer included a thick (1.4 μm diameter) fiber content of 6.5% based on the number of fibers. The basis weight and the calculated solidity are shown in Table 7C.

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

[0608] Figure 13C (see Example 12A) shows samples having the same basis weight and relative amounts of thin and thick fibers (e.g., for the first column of Table 7B, a set I of Table 1B of supported fibers with a thick fiber content of 6.5% and a basis weight of 0.38 g / m 2 ), for which the mixing of thin and thick fibers significantly "opens" the fine fiber structure, as indicated by the increase in pore diameter. Figure 13H shows the overall trend of the pore diameter decreasing with the increase in the mixed fiber coverage rate, and the pore diameter decrease is more significant when the basis weight increases from 0.38 to 0.53 g / m 2 .

[0609] The pressure drop (dP) values are shown in Figure 13I, and the efficiency values (overall β evaluation) are shown in Figure 13J.

[0610] Example 12C The media sample was prepared according to Method 12, which 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 in which thin (0.25 μm diameter) fine fibers and thick (1.4 μm diameter) fine fibers were mixed, and an upper layer of thick (1.4 μm diameter) fine fibers (thick / thin / mixed / thick or L / S / mixed / L). The basis weight and the calculated solidity are shown in Table 7D.

[0611] The pore diameter 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 FIG. 13L, and the efficiency values ​​(overall β rating) are shown in FIG. 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 underlayed (at least 0.54 g / m 2 The woven fabric contained a layer of thick fine fibers (having a basis weight of 1.0 g / m).

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

[0619] The maximum pore diameter, intermediate flow pore diameter, and minimum pore diameter of each sample were measured by capillary flow porometry. The results are shown in Table 8A. A comparison of the pore diameters of the mixed diameter fine fiber structure and the layered mixed diameter fine fiber structure is shown in FIG. 14C.

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

[0621] The results of the evaluation of air filtration performance by the HEFS bench test are shown in Table 8B. The performance index (FOM) values are shown in Table 8B and FIG. 14D. The pressure drop (dP) values are shown in Table 8B and FIGS. 14E (Set A, Set B, Set E, Set J, and Set M of Table 1C) and FIGS. 14F (Set A, Set D, Set I, Set L, and Set M of Table 1C), FIGS. 14E and 14F. This plot also shows the values of comparable liquid media products containing fine fibers having 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. The efficiency values (overall β rating) are shown in FIGS. 14G (Set A, Set B, Set E, Set J, and Set M of Table 1C) and FIGS. 14H (Set A, Set D, Set I, Set L, and Set M of Table 1C). This plot also shows the values of comparable liquid media products containing fine fibers having 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 H2O) across the various structures, the layered structure with 38% thick fiber content showed the highest efficiency and best FOM. Moreover, comparison of similar structures with other combinations of thin and thick fiber diameters as shown above (e.g., 0.25 μm / 1 μm and 0.25 μm / 1.4 μm) indicates that the 0.5 μm / 1.4 μm diameter fiber combination does not give optimal media filtration performance (lower efficiency and higher pressure drop).

[0623] Example 13B The media sample was prepared according to Method 11 and included a layer of thick microfibers (having a basis weight of at least 0.54 g / m2) under a layer of mixed 0.5 μm and 1.4 μm fibers.

[0624] The resulting mixed microfiber layer had a basis weight of 0.84 g / m 2 、1.25 g / m 2 、1.67 g / m 2 、 or 2.09 g / m 2 (for precursor solutions supplied for 2, 3, 4, or 5 minutes, respectively). The mixed microfiber layer included a 17% thick fiber (1.4 μm diameter) content on a fiber number basis.

[0625] The results of evaluating the air filtration performance by the HEFS bench test are shown in Table 8B and FIG. 14I. These results demonstrate that the mixed structure of 0.5 μm and 1.4 μm fibers can sacrifice the FOM due to a sharp increase in the pressure drop (dP) without a commensurate improvement in efficiency. For example, as the basis weight increases from 0.84 g / m 2 to 2.09 g / m 2 , the permeability decreases by about half (from 39.9 to 22.22), while the dP 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 the comparison of the best performing samples (with respect to pressure drop and efficiency for 3 μm particles) from three sets of media incorporating thin (0.25 μm or 0.5 μm in diameter) and thick (1 μm or 1.4 μm in diameter) fibers. The combinations of fiber diameters 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 percent improvement in the initial pressure drop (dP) and overall efficiency (β value) for 3 μm particles (benchmarked against a glass fiber-containing media having β = 1000 for particles less than 4 μm) is shown in FIG. 15A. As shown in FIG. 15A, the four structures showed significant improvement in both overall efficiency and dP compared to the glass fiber-containing media. In this plot, quadrant I is the target region (i.e., the benefit in both dP and β compared to the glass fiber-containing media). In particular, none of the mixed fiber diameter media structures dropped down to quadrant III (a decrease in both dP and β compared to the glass fiber-containing media). As shown in FIG. 15B, all of the mixed fiber diameter media structures show a pressure drop comparable to or better than the glass-containing media structures (having β = 1000) for various particle sizes.

[0632] Since the mixed fiber diameter media structures can be manufactured using a wide range of process windows, the desired efficiency can be targeted.

[0633] Example 15 Samples made according to Method 12 (L / S / Table 1B, Set M / L) were analyzed according to the method of "thickness of the fine fiber layer". An exemplary image is shown in FIG. 16A, where the full depth of the fine fiber layer can be confirmed in cross-section, and the fibers of the support layer can be partially confirmed at the bottom of the image.

[0634] FIG. 16B shows a depiction of a cross-section of a fine fiber using a polygonal tool. FIG. 16C shows an image after the outer region of the cross-section of the selected fine fiber has been removed. FIG. 16D shows the region of the cross-section of the selected fine fiber after being recolored white using a threshold tool (to compensate for fibers on the boundary of the selected section), and the dashed line indicates the maximum thickness (5.97 μm) of the image that is measured and recorded. 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 and electronically available materials cited herein are incorporated by reference. In the event of any conflict between the disclosure of this application and the disclosure of the documents incorporated herein by reference, the disclosure of this application shall control. The foregoing detailed description and examples are provided only to clarify understanding. No unnecessary limitations are to be construed therefrom. The present invention is not limited to the exact details shown and described, and variations obvious to those skilled in the art will be included within the invention as defined by the claims.

Claims

1. a filter medium comprising a support layer and a fine fiber layer wherein the fine fiber layer is disposed on the support layer, the fine fiber layer comprises thick fine fibers and thin fine fibers, the thick fine fibers having an average diameter of at least 1 μm and being at least three times the average diameter of the thin fine fibers, the fine fiber layer comprises a first layer of fine fibers and a second layer of fine fibers, the first layer of fine fibers comprising the thick fine fibers and the thin fine fibers, the first layer of fine fibers being disposed on the support layer, and the second layer of fine fibers being disposed on the first layer of fine fibers, the second layer of fine fibers comprises fibers of two different diameters, the fibers of two different diameters comprise thin fine fibers and thick fine fibers, the thick fine fibers having an average diameter of at least 1 μm and having an average diameter of at least three times the average diameter of the thin fine fibers, the thin fine fibers are disposed on the first layer of fine fibers, and the thick fine fibers are disposed on the thin fine fibers, a filter medium.

2. A filter element comprising the filter medium according to claim 1. ​

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