NANOFIBER BEARING PERMEABLE FILTER LAMINAE

Abstract

A filter media construct includes a plurality of flexible laminas joined in a stack, each lamina including an array of nanofibers extending from a surface thereof. Each lamina is configured to be permeable to a fluid such that the fluid can flow through each lamina normal to the surface thereof and in any direction along at least a portion of said surface when the fluid is flowed through the construct. The laminas can include a plurality of perforations extending therethrough such that the fluid flows through at least some of the perforations of the laminas when the fluid is flowed through the construct. A contaminant contained in the fluid is at least partially filtered from the fluid by the nanofibers when the fluid is flowed along the surface of any lamina or into or through the perforations.

Claims

1. A flexible filter media construct, comprising: a plurality of flexible laminas joined in a stack, each lamina including an array of nanofibers extending from a surface thereof and a plurality of perforations extending therethrough; wherein said laminas are arranged in the stack such that a fluid flowed into the construct can flow through the perforations of each successive lamina in the stack and in any direction across the surface of each successive lamina in the stack as the fluid flows through the construct.

2-4. (canceled)

5. The flexible filter media construct of claim 1, wherein: the perforations are funnel-shaped; each perforation includes a concave upstream approach adjacent thereto; and the surface of each lamina from which extends the array of nanofibers forms at least a portion of the upstream approach of each perforation.

6. The flexible filter media construct of claim 1, wherein the perforations are uniformly distributed across the surface of each lamina.

7. The flexible filter media construct of claim 1, wherein the perforations are formed by a method which removes a segment of material from the laminas.

8. The flexible filter media construct of claim 1, wherein the perforations are formed by a method which does not remove a segment of material from the laminas.

9. The flexible filter media construct of claim 8, further comprising a concavity formed in the surface of each lamina around each respective perforation.

10. The flexible filter media construct of claim 1, wherein each lamina of the plurality of laminas supports or is supported by another lamina of the plurality.

11. The flexible filter media construct of claim 1, further comprising a flexible turbulence-inducing layer arranged between two adjacent laminas of the plurality of laminas.

12. The flexible filter media construct of claim 11, wherein each lamina of the plurality of laminas supports or is supported by either another lamina or the flexible turbulence-inducing layer.

13-17. (canceled)

18. A flexible filter media construct, consisting of: a plurality of laminas joined in a stack, each lamina including a flexible film portion having a surface and an array of nanofibers extending from the surface; and a plurality of uniformly distributed openings defined through the film portion of each lamina such that a fluid flowed through the construct can flow through the openings normal to the surface of the film portion and in any direction along the surface of the film portion of each lamina; wherein a contaminant contained in the fluid is at least partially filtered from the fluid by the nanofibers when the fluid is flowed along the surface or into or through the perforations.

19-20. (canceled)

21. A flexible filter media construct, comprising: a plurality of flexible laminas joined in a stack, each lamina including: a first surface, a second surface, an array of nanofibers extending from the first surface, and a plurality of perforations extending from the first surface to the second surface; wherein the lamina stack defines a fluid flow path extending in every direction across the surface of each successive lamina in the stack and through the perforations of each successive lamina in the stack.

22. The flexible filter media construct of claim 21, wherein the perforations extending through each lamina are uniformly distributed across the first surface of each lamina.

23. The flexible filter media construct of claim 22, wherein the laminas are arranged in the stack such that the perforations of any two adjacent laminas in the stack do not align.

24. The flexible filter media construct of claim 21, wherein: the perforations are funnel-shaped; and the first surface of each lamina from which extends the array of nanofibers defines a concave deformation surrounding each respective perforation.

25. The flexible filter media construct of claim 21, wherein each lamina of the plurality of laminas supports or is supported by another lamina of the plurality.

26. The flexible filter media construct of claim 21, further comprising a flexible turbulence-inducing layer arranged between two adjacent laminas of the plurality of laminas.

27. The flexible filter media construct of claim 26, wherein each lamina of the plurality of laminas supports or is supported by either another lamina or the flexible turbulence-inducing layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Non-limiting and non-exhaustive embodiments are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various drawings unless otherwise specified. In the drawings, not all reference numbers are included in each drawing, for the sake of clarity.

[0049] FIG. 1A is a first perspective view of a system for making continuous strips of polymer film with nanofiber arrays formed on a surface thereof for permeable laminae of the present invention.

[0050] FIG. 1B is a second perspective view of the objects of FIG. 1A.

[0051] FIG. 1C is an expanded view of the objects of FIG. 1B at location A.

[0052] FIG. 1D is an expanded view of the objects of FIG. 1B at location B.

[0053] FIG. 2 is a perspective view of a portion of a film with nanofiber arrays formed on a surface thereof for permeable laminae of the present invention.

[0054] FIG. 3 is a plan view of the objects of FIG. 2.

[0055] FIG. 4 is a side elevational view of the objects of FIG. 2.

[0056] FIG. 5 is an expanded view of the objects of FIG. 4 at location A depicting a first nanofiber configuration for a filter lamina of the present invention.

[0057] FIG. 6 is a side elevational view of a second nanofiber configuration for a filter lamina of the present invention.

[0058] FIG. 7 depicts the electrostatic field surrounding a nanofiber of FIG. 5.

[0059] FIG. 8 depicts the electrostatic field surrounding the nanofiber of FIG. 6.

[0060] FIG. 9 is a perspective view of a permeable filter lamina of the present invention.

[0061] FIG. 10 is a plan view of the objects of FIG. 9.

[0062] FIG. 11 is a side elevational view of the objects of FIG. 9.

[0063] FIG. 12 is an expanded view of the objects of FIG. 9 at location A.

[0064] FIG. 13 is an expanded view of the objects of FIG. 10 at location B.

[0065] FIG. 14 is an expanded sectional view of the objects of FIG. 13 along line A-A.

[0066] FIG. 15 is a sectional view of a filter construct incorporating permeable filter laminae of FIG. 9.

[0067] FIG. 16 is a perspective view of a system for forming nanofiber bearing film for perforated filter laminae of the present invention.

[0068] FIG. 17 is an expanded view of the objects of FIG. 16 at location C.

[0069] FIG. 18 is a perspective view of a portion of a permeable filter media construct formed of perforated filter laminae.

[0070] FIG. 19 is a plan view of the objects of FIG. 18.

[0071] FIG. 20 is a sectional view of the objects of FIG. 19 along line A-A showing the flow of a fluid through the filter media construct.

[0072] FIG. 21 is a perspective view of an alternate embodiment perforated filter lamina of the present invention.

[0073] FIG. 22 is a plan view of the objects of FIG. 21.

[0074] FIG. 23 is an expanded view of the objects of FIG. 21 at location A.

[0075] FIG. 24 is an expanded view of the objects of FIG. 22 at location B.

[0076] FIG. 25 is a plan view of a portion of an alternate embodiment perforated lamina of the present invention.

[0077] FIG. 26 is a perspective view of the objects of FIG. 25.

[0078] FIG. 27 is a side elevational view of a portion of an alternate embodiment perforated filter lamina of the present invention.

[0079] FIG. 28 is a perspective view of the objects of FIG. 27.

[0080] FIG. 29 is a plan view of the objects of FIG. 27.

[0081] FIG. 30 is a sectional view of the objects of FIG. 29 along line A-A.

[0082] FIG. 31 is a perspective view of nanofiber bearing film with intermittent slits formed therein for forming another alternate embodiment of a permeable filter lamina of the present invention.

[0083] FIG. 32 is a perspective view of an alternate embodiment filter lamina of the present invention formed from the film material of FIG. 31 by lateral stretching of the film so as to expand the intermittent slits.

[0084] FIG. 33 is a plan view of the objects of FIG. 32.

[0085] FIG. 34 is an expanded view of the objects of FIG. 32 at location A.

[0086] FIG. 35 is an expanded view of the objects of FIG. 33 at location B.

[0087] FIG. 36 is a perspective view of a portion of an alternate embodiment permeable filter lamina of the present invention.

DETAILED DESCRIPTION

[0088] The details of one or more embodiments of the presently disclosed subject matter are set forth in this document. Modifications to embodiments described in this document, and other embodiments, will be evident to those of ordinary skill in the art after a study of the information provided herein. The information provided in this document, and particularly the specific details of the described exemplary embodiments, is provided primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom. In case of conflict, the specification of this document, including definitions, will control.

[0089] The present disclosure relates to filter media and devices for removing a contaminant from a fluid stream. In a general embodiment, the nanofiber filters disclosed herein are designed to filter a substance or contaminant from a fluid stream using one or more user-defined arrays of nanofibers, such as those described in U.S. Patent Application Publication No. 2013/0216779 which is incorporated herein by reference in its entirety.

[0090] While the terms used herein are believed to be well understood by one of ordinary skill in the art, definitions are set forth herein to facilitate explanation of the subject matter disclosed herein.

[0091] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter disclosed herein belongs. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the presently disclosed subject matter, representative methods, devices, and materials are now described.

[0092] To facilitate the understanding of the embodiments described herein, a number of terms are defined below. The terms defined herein have meanings as commonly understood by a person of ordinary skill in the portions relevant to the present invention. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as set forth in the claims.

[0093] The terms “a”, “an”, and “the” refer to “one or more” when used in this application, including the claims. Thus, for example, reference to “a contaminant” includes a plurality of particles of the contaminant, and so forth. The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

[0094] All references to singular characteristics or limitations of the present disclosure shall include the corresponding plural characteristic(s) or limitation(s) and vice versa, unless otherwise specified or clearly implied to the contrary by the context in which the reference is made.

[0095] All combinations of method or process steps as used herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made.

[0096] The methods and devices of the present disclosure, including components thereof, can comprise, consist of, or consist essentially of the essential elements and limitations of the embodiments described herein, as well as any additional or optional components or limitations described herein or otherwise useful.

[0097] This description and appended claims may include the words “below”, “above”, “side”, “top”, “bottom”, “upper”, “lower”, “when”, “upright”, etc. to provide an orientation of embodiments of the invention to allow for proper description of example embodiments. The foregoing positional terms refer to the apparatus when in an upright orientation. A person of skill in the art will recognize that the apparatus can assume different orientations when in use. It is also contemplated that embodiments of the invention may be in orientations other than upright without departing from the spirit and scope of the invention as set forth in the appended claims. Further, it is contemplated that “above” means having an elevation greater than, and “below” means having an elevation less than such that one part need not be directly over or directly under another part to be within the scope of “above” or “below” as used herein.

[0098] The phrase “in one embodiment,” as used herein does not necessarily refer to the same embodiment, although it may. Conditional language used herein, such as, among others, “can”, “might”, “may”, “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states.

[0099] Unless otherwise indicated, all numbers expressing physical dimensions, quantities of ingredients, properties such as reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.

[0100] As used herein, the term “about,” when referring to a value or to an amount of mass, weight, time, volume, concentration, percentage or a physical dimension such as length, width, or diameter, is meant to encompass variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified value or amount, as such variations are appropriate to perform the disclosed methods.

[0101] As used herein, ranges can be expressed as from “about” one particular value, and/or to “about” another particular value. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[0102] As used herein, the term “fluid” is defined as any liquid or gas which can be passed through the filter media and filter devices disclosed herein. Multiple fluids having different specific gravities and viscosities can be used as well as gas and vapor streams, depending on the application.

[0103] As used herein, the term “nanofiber” refers to a fiber structure having a diameter of less than 1000 nanometers for more than half the length of the structure. In some embodiments, the nanofibers disclosed herein can comprise a tapered base portion and a relatively longer fiber portion which extends from the base portion. In such embodiments, the fiber portion has a diameter of less than 1000 nm and a length greater than that of the base portion, and the base portion can have a diameter of from about 10 micron to less than 1.0 micron. Additionally, in some embodiments, the base portion can also have a length of from about 1.0 micron to about 10 microns, and the fiber portion can have a length of from about 10 to 100 times greater than the length of the base portion. Nanofibers having larger diameter base portions in the range of from about 2.0 microns to about 10 microns are best suited for applications wherein the bases must provide stiffness to the nanofiber in the fluid stream.

[0104] In some preferred embodiments, nanofibers suitable for use in the nanofiber filter media and filter devices disclosed herein can have an overall length of from about 10 to about 100 microns. Accordingly, suitable nanofibers can also have a length to diameter ratio of from 10:1 to about 1000:1. In one embodiment, the length to diameter ratio is from about 10:1 to about 100:1. By contrast, nanofibers known in the art, including electrospun nanofibers, melt-blown nanofibers and microfiber-derived nanofibers (i.e., microfibers split during processing to obtain sub-micron diameter structures), typically have much greater length to diameter ratios in the range of 1,000,000:1 to 100,000,000:1. As a result, the nanofibers used in nanofiber filter media and filter devices disclosed herein can have from about 10 to about 1000 times more tips per unit length than electrospun nanofibers, melt blown nanofibers and microfiber derived nanofibers.

[0105] The related terms “nanofiber array” and “array of nanofibers,” which are used interchangeably herein, collectively refer to a plurality of freestanding nanofibers of user-defined physical dimensions and composition integrally formed on and extending from a backing member, such as a film, according to user-defined spatial parameters. In some embodiments, the nanofiber arrays disclosed herein include nanofibers which extend from a surface of the backing member at an angle substantially normal to a plane containing the surface of the backing member from which the nanofibers extend. By contrast, electrospun nanofibers, melt-blown nanofibers, and microfiber-derived nanofibers are neither integrally formed on nor do they extend from a backing member.

[0106] User-tunable physical characteristics of the nanofiber arrays disclosed herein include fiber spacing, diameter (also sometimes referred to herein as “width”), height (also sometimes referred to herein as “length”), number of fibers per unit of backing member surface area (also referred to herein as “fiber surface area density”), fiber composition, fiber surface texture, and fiber denier. For example, nanofiber arrays used in the filter media and filter devices disclosed herein can comprise millions of nanofibers per square centimeter of backing member, with fiber diameter, length, spacing, material composition, and texture configured to perform a filtration function. In some embodiments, one or more of fiber surface area density, diameter, length, spacing, composition, and texture are controlled and optimized to perform a filtration function. In certain embodiments, the nanofiber arrays can be optimized or “tuned” to perform a specific filtration function or target a preselected substance or specific retentate. In further embodiments, an array of nanofibers disposed on a portion of a filter lamina forming a flow passage of a filter device disclosed herein is configured to filter a substance from a fluid containing the substance when the fluid is flowed through the flow passage.

[0107] The nanofiber arrays disclosed herein, when formed on a substantially planar surface of a backing member, can include nanofibers spaced along an X-axis and a Y-axis at the same or different intervals along either axis. In some embodiments, the nanofibers can be spaced from about 100 nm to 200 micron or more apart on the X-axis and, or alternatively, the Y-axis. In certain embodiments, the nanofibers can be spaced from about 1 micron to about 50 micron apart on one or both of the X-axis and the Y-axis. In a preferred embodiment, the nanofibers can be spaced from about 2 micron to about 7 micron apart on one or both of the X-axis and the Y-axis.

[0108] In some embodiments, an array of nanofibers can include nanofibers having an average length of at least 25 micron. In certain embodiments, the nanofibers can have a length of from about 10 micron to about 100 micron. In certain embodiments, the nanofibers can have a length of from about 15 micron to about 60 micron. In an exemplar embodiment, the nanofibers can have an average length of from about 20 micron to about 30 micron. In specific embodiments, the nanofibers can have a length of about 15.00 micron, 16.00 micron, 17.00 micron, 18.00 micron, 19.00 micron, 20.00 micron, 21.00 micron, 22.00 micron, 23.00 micron, 24.00 micron, 25.00 micron, 26.00 micron, 27.00 micron, 28.00 micron, 29.00 micron, 30.00 micron, 31.00 micron, 32.00 micron, 33.00 micron, 34.00 micron, 35.00 micron, 36.00 micron, 37.00 micron, 38.00 micron, 39.00 micron, 40.00 micron, 41.00 micron, 42.00 micron, 43.00 micron, 44.00 micron, 45.00 micron, 46.00 micron, 47.00 micron, 48.00 micron, 49.00 micron, 50.00 micron, 51.00 micron, 52.00 micron, 53.00 micron, 54.00 micron, 55.00 micron, 56.00 micron, 57.00 micron, 58.00 micron, 59.00 micron, or 60.00 micron.

[0109] The nanofiber backing member surface area density can range from about 25,000,000 to about 100,000 nanofibers per square centimeter. In some embodiments, the nanofiber surface area density can range from about 25,000,000 to about 2,000,000 nanofibers per square centimeter. In specific embodiments, the nanofiber surface density is about 6,000,000 nanofibers per square centimeter. In an exemplar embodiment, the nanofiber surface area density is about 2,000,000 nanofibers per square centimeter.

[0110] In some embodiments, an array of nanofibers can include nanofibers having an average denier of from about 0.001 denier to less than 1.0 denier. In an exemplar embodiment, the nanofibers forming a nanofiber array disclosed herein can be less than one denier and have a diameter ranging from about 50 nm to about 1000 nm.

[0111] Nanofiber arrays and methods for producing nanofiber arrays suitable for use in the filter media and filter devices disclosed herein are described by the present inventors in US Patent Application Publication No. 2013/0216779, US Patent Application Publication No. 2016/0222345, and White et al., Single-pulse ultrafast-laser machining of high aspect nanoholes at the surface of SiO2, Opt. Express. 16:14411-20 (2008), each of which is incorporated herein by reference in its entirety.

[0112] A preferred method for manufacturing laminae of the present invention has the ability to produce continuous elongate strips of film with arrays of nanofibers formed on at least one surface thereof. In method 100, a variation of a film producing technique referred to as “chill roll casting” and depicted in FIGS. 1A through 1D, polymer 120 is supplied via tubular member 122 to extrusion head 108. Polymer 120 is heated above its melt point by heater 124 and the melted polymer 110 is then applied to rotating cylindrical roll 102 (referred to as a “chill roll”) formed of silica or another suitable material. An array of nanoholes 106 is formed in the circumferential surface 104 of roll 102 so as to form a mold, the nanohole array being complementary to the array of nanofibers to be formed. The nanoholes are formed using methods previously described herein. Molten polymer 110 flows into nanoholes 106 as it is applied to circumferential surface 104 of rotating chill roll 102. Chill roll 102 is maintained at a temperature such that during a predetermined portion of the roll rotation of chill roll 102, polymer 110 in nanoholes 106 is cooled along with the portion of polymeric material 110 coating circumferential surface 104 of roll 102. A cylindrical metallic roll 112, commonly referred to as a “anvil roll” or “quench roll” functions as the compressing element and is positioned adjacent to chill roll 102 such that after a predetermined angular rotation of chill roll 102 polymeric material 110 coating the surface of chill roll 102 is compressed between surface 104 of chill roll 102 and surface 114 of the quench roll 112. As implied by the name “quench roll” polymeric material 110 undergoes rapid cooling during contact with quench/anvil roll 112 so that it may be subsequently stripped from the surface of chill roll 102 as a continuous elongate strip of film 118. When the polymer strip 118 is removed from chill roll 102, material 110 that had previously flowed into nanoholes 106 forms molded nanofibers 116 on the surface of film strip 118. Polymer 120 is not contained in a solution so the use of environmentally undesirable solvents is not required.

[0113] Under certain conditions, with suitable polymers, quench roll 112 is eliminated. The thickness of film strip 118 is determined by process parameters. These may include properties of polymer 120, the temperature of polymer 110 as it is deposited on surface 104 of chill roll 102, the temperature and rotational speed of chill roll 102, and other factors that affect the cooling of film strip 118. Under these conditions, material is drawn into nanoholes 106 of surface 104 of chill roll 102 by surface tension as a compressing element is not used.

[0114] FIGS. 2 through 5 diagrammatically depict a segment of a filter media lamina 200 of the present invention. Lamina 200 has a flexibly planar film portion 202 having a thickness 203, with a first surface 205 on which are formed nanofibers 204. Nanofibers 204 have a first diameter 210 near the base of each fiber 204 and generally decrease in diameter toward the distal end of the fiber. Nanofibers 204 have a length 212 and are spaced a first distance 206 apart in a first direction and a second distance 208 apart in a second direction perpendicular to the first direction. Lamina 200 is depicted with first distance 206 and second distance 208 between adjacent nanofibers 204 constant over surface 205. In other embodiments, either distance 206 or distance 208 or both may vary along surface 205 of lamina 200. Nanofibers 204 are shown in ordered parallel rows. In other embodiments other arrangements are used depending on the particular filtering process requirements. Similarly, height 212 and diameter 210 of nanofibers 204 are constant across the surface of lamina 200. In other embodiments height 212 and diameter 210 of nanofibers on a first portion of surface 205 of lamina 200 may have first values, while on a second portion of surface 205, height 212 and diameter 210 may have second values.

[0115] As defined herein the term “nanofiber” refers to a fiber structure having a diameter of less than 1000 nanometers for more than half the length of the structure. In some embodiments, the nanofibers of filter media of the present invention may have a tapered base portion and a relatively longer fiber portion which extends from the base portion. For example, as shown in FIG. 6, nanofiber 304 extends from planar film portion 302 and has a tapered proximal base portion 303 of diameter 310 with elongate distal portion 305 of diameter 307 formed thereon, and a length 312.

[0116] The process used to produce nanoholes 106 in chill roll 102 uses the energy of a single laser pulse to vaporize material so as to form the nanohole. The vaporized material of chill roll 102 is expelled to form a nanohole 106. The process is well controlled within limits, however the precise geometry of a nanohole 106 is determined by the flow of superheated vaporized material at the site. Accordingly, there may be minor variations in the form of nanoholes 106, and in the nanofibers 116 that are molded therein. Also, nanofibers 116, particularly those with long tendrilous forms, may stretch somewhat during extraction from nanoholes 106. Therefore, it will be understood that when it is stated that nanofibers in an array have a height, height is a nominal height, and individual fibers may have a height that is somewhat greater or less than nominal height. Similarly, when considering diameters of nanofibers, diameter is a nominal value and there may be natural variations in the diameters in nanofibers within an array.

[0117] Nanofibers of the present invention may be broadly characterized by the ratio of their length (212 in FIGS. 5 and 312 in FIG. 6) to their average diameter. Typically nanofibers of filter media of the present invention have length to diameter ratios between 10:1 and 1,000:1. Nanofibers with length to diameter ratios at the lower end of the range may be used in applications in which the fibers require a degree of stiffness to optimally affect a fluid stream flowing thereby.

[0118] The nanofiber arrays formed on filter laminae of the present invention may form a tuned topography. That is laminae may be optimally configured to remove specific contaminants such as pathogens, chemical contaminates, biological agents, and toxic or reactive compounds from a fluid to be filtered. By selecting specific values for longitudinal distance 206 and transverse distance 208 between adjacent nanofibers (FIGS. 2 through 5), and diameters 210 and 310, and lengths 212 and 312 of nanofibers 204 and 304 (FIGS. 5 and 6) laminae may be formed that preferentially remove a specific contaminant. Indeed, filtering devices may be formed in which laminae of a first configuration optimally designed for removal of a first contaminant are combined with laminae designed to remove a second contaminant. Additional laminae with tuned topographies for removing specific contaminants may be added to remove these substances from the flow stream. The laminae may be intermingled in a filter device, or formed in discrete layers each containing a single lamina configuration or a combination of two or more configurations.

[0119] Filter media laminae with nanofibers of the present invention may be formed from virtually any polymeric material. These polymeric materials have inherent electrostatic properties and exert an electrostatic force at a point on the surface of an object formed therefrom that is inversely related to the radius of curvature of the surface at that point. As the radius of the surface at a given point is reduced, the electrostatic attractive force at that point increases. Accordingly, the electrostatic force exerted by a nanofiber is much greater than that exerted by a microfiber. This is of particular importance in filter applications in which contaminants smaller than the pore size of the filter must be removed from a fluid stream. Electrostatic forces draw contaminants to fibers for removal from the fluid stream. As the diameter of the fibers is decreased, the electrostatic force exerted by the fibers increases. The attractive force of a nanofiber is generally orders of magnitude greater than that of a microfiber, and therein lies the incentive for creating nanofiber filters. The high level of electrostatic force exerted by nanofibers allows them to efficiently remove contaminants from a fluid stream.

[0120] FIGS. 7 and 8 depict field lines 230 and 330 depicting the intensity of an electrostatic force field line surrounding nanofibers 204 and 304 respectively. As described previously, the field intensity at a point on the surface of a fiber is inversely proportional to the radius of curvature of the fiber at that point. This is reflected in the field line depicted. It should be noted that the field intensity is maximal at the distal end of the fibers. In prior art nanofiber filter medial formed by electrospinning or other conventional methods the nanofibers are virtually continuous with length to diameter ratios ranging from 1,000,000:1 to 100,000,000. Accordingly, for a given cumulative nanofiber length, fibers of the present invention will have from about ten to about one thousand times as many fiber ends. The associated higher electrostatic potential of nanofiber media formed in accordance with the present invention allows the construction of filters with efficiencies not attainable using nanofibers formed by electrospinning or other conventional methods.

[0121] The arrangement of nanofibers in an array can impact filtration specificity and efficiency by modulating the strong gradients in the electrical and chemical potential fields of normally highly reactive sub-micron length scale structures. Control of these gradients at process length scales can enhance efficiency of transport or flow. However, if two nanofibers are in close proximity and the potential fields overlap, then the gradient of the potential field is reduced and the advantages of the nanoscale topography are reduced. The arrangement of nanofibers in a nanofiber array of the proper scale and spacing will preserve the separation of nanofibers thus optimizing the potential field gradient.

[0122] An electrostatic charge may be imparted to the filter media of the present invention to increase the attractive force of the nanofiber arrays formed on laminae. Filter laminae of the present invention may be formed from a polymer or polymer blend with suitable electret properties. Among these materials are polypropylene, poly(phenylene ether) and polystyrene. In certain embodiments these laminae may have a lamellar construction that has a first layer formed of an electret material on which are formed nanofiber arrays of the present invention, and a second layer bonded thereto with desirable physical and/or electrical properties. The materials selected for each layer may be optimized for a specific filtering application. Charging of the media may be accomplished by corona discharge, triboelectrification, polarization, induction, or another suitable method. Over time the imparted electrostatic charge may be dissipated by particle loading, and/or by quiescent or thermal stimulation decay.

[0123] Filter laminae of the present invention have a controlled permeability so that fluid flow passes through the plane of the laminae (see, e.g., FIGS. 15 and 20 for an example of flow through the plane of the laminae). After the film material with nanofibers arrays is formed according to methods previously herein described, pores or perforations are formed in the laminae. In some embodiments, perforations are formed by mechanical punching; in others by slitting and lateral stretching of the material so that the slits form openings in the film; and in still others the film is formed of a polymeric material with properties that allow the pores to be formed by stretching or other mechanical or non-mechanical methods.

[0124] For instance, permeable lamina 400 depicted in FIGS. 9 through 14 is identical in all aspects of form and function to lamina 200 (FIGS. 2 through 5) except as subsequently herein described. Lamina 400 is formed of a polymeric material in which pores 431 are formed in film portion 402 by methods known in the art that do not included mechanical perforation. Pores 431 are distributed throughout film portion 402, and, as depicted in FIG. 14, provide a path for filtrate to permeate film portion 402 of lamina 400. In use, filter media including laminae 400 are positioned in a fluid stream wherein the fluid is exposed to nanofibers 404 before passing through pores 431 as filtrate. In preferred embodiments fluid upstream from lamina 400 is turbulent so as to maximize the portion of the flow that brings contaminant within capture distance of the electrostatic forces of nanofibers 404 before flowing through pores 431.

[0125] Referring now to FIG. 15, media construct 470 comprises laminae 400 separated by turbulence inducing layers 472, 474, and 476. In a preferred embodiment layers 472, 474 and 476 are formed of filter ribbons as taught by Hofmeister et al., in US Patent Application Publication Nos. 2020/0368655 and 2020/00368656. Lamina 400 may all have identical arrays of nanofibers 404, or each may have a unique configuration optimized for the removal of a specific contaminant.

[0126] In other embodiments of the present invention, perforations are formed in nanofiber bearing film mechanically by punching or piercing. FIGS. 16 and 17 depicts a system for producing nanofiber bearing film of the present invention wherein perforations are automatically formed. System 500 is identical to system 100 in all aspects of form and function except as subsequently described herein. System 500 has a perforating system that creates perforations 581 in film 518 with nanofibers 516. In a preferred embodiment, perforations 581 are formed by continuous cutting method in which film 518 passes between two rotating rolls. A first roll with a featureless circumferential surface supports film 518. A second roll has sharpened circular protrusions formed on its circumferential surface. As film 518 passes between these first and second rolls, the circular protrusions act as punches to remove a circular segment of film to form perforations 581. System 500 has a perforation forming mechanism integrated into system 500. In other embodiments, perforations are formed in a secondary punching operation performed after film 518 is removed from system 500. Any method for forming perforations 581 in film 518 falls within the scope of this invention.

[0127] Multiple laminae in which perforations have been formed may be assembled to form filter media of the present invention. For example, FIGS. 18 and 19 depict a segment 683 of a filter element comprised of four laminae 600 in which multiple perforations 681 are formed, and FIG. 20 depicts the flow of a fluid 685 depicted by arrows through filter segment 683. Laminae 600 depicted in FIGS. 18-20 are identical in all aspects of form and function to lamina 200 (FIGS. 2 through 5), except as herein described. Perforations 681 in laminae 600 and the interlaminar spaces between laminae 600 form a labyrinth through which fluid 685 must flow. This flow path exposes fluid 685 to nanofibers 604 formed on the surface of the film portion 602 of laminae 600. Preferably, flow through the interlaminar spaces is turbulent so as to maximize the portion of fluid 685 that passes in sufficiently close proximity to nanofibers 604 for the electrostatic force of nanofibers 604 to capture the contaminant and remove it from the fluid stream. The interlaminar space between laminae 600 may be maintained by protrusions (not shown) formed on laminae 600, or more preferably, by placing turbulence inducing media between laminae 600. Turbulence in the interlaminar spaces may be favorably affected by the size, placement and density of the perforations 681 formed on the laminae.

[0128] FIGS. 21 through 24 depict a portion of laminae 700 in which the diameter of the perforations 781 has been increased so as to affect the flow velocity between laminae 700. In all other aspects, lamina 700 is identical to lamina 600. Interlaminar turbulence may also be affected by the shape of perforations 781 formed in the laminae. FIGS. 25 and 26 depict lamina 800 in which perforations 881 have the form of elongate slots. The shape and size of perforations in laminae of the present invention are features that may be optimized for specific filtering applications. Any perforation that provides flow from a first side of the lamina to the opposite side of the lamina falls within the scope of this invention.

[0129] Perforations in laminae 500 through 800 are formed by removing a discreet portion of the film of predetermined shape and size. In other embodiments the perforations are formed by piercing the film with a sharpened tool that does not remove a portion of the film. FIGS. 27 through 30 depict a perforation formed in a lamina 900 using a sharpened tool that does not remove a segment of lamina 900. Perforation 981 is formed by deformation of planar film portion 902. As best seen in FIG. 30, this deformation creates portions adjacent to perforation 981 in which nanofibers 904 are concentrated in the upstream approach 983 to perforation 981. This increases the likelihood that contaminant in the fluid stream will pass within capture distance of a nanofiber 904. Additionally, turbulence is created by the transition from perforation 981 to the interlaminar space between adjacent laminas when a plurality of laminas including a lamina 900 are formed into a filter media construct. Perforations 981 may be formed in a piercing operation by tooling designed specifically for this purpose. This deformation may also be created when a plurality of laminae 900 are assembled into a filter media construct using needling, a joining process for sheet materials of various types. As with previous embodiments, lamina 900 may be combined with other media in constructs previously herein described.

[0130] Openings in laminae of the present invention may also be formed by creating interrupted longitudinal slits in the film and then subjecting the film to a lateral spreading force. FIG. 31 depicts a portion of a film strip 1000 for forming a lamina of the present invention. Longitudinal slits 1042, 1043 are separated longitudinally by film portions 1044. Longitudinal slits 1042, 1043 are centered on laterally adjacent film portions 1044. Nanofibers 1016 can be centered between adjacent longitudinal slits 1042, 1043. Longitudinally extending film strip portions 1019 are bound on its sides by slits 1042, 1043 and film portion 1044. Applying a lateral stretching force to the edges of film 1000 as indicated by arrows in FIGS. 32 and 33 causes longitudinal slits 1042, 1043 to spread so as to create openings 1046 in film 1000, film 1000 now forming a mesh 1090. As best seen in FIGS. 34 and 35, openings 1046 are bound by longitudinally extending film strip portions 1019. Expanding film 1000 to form a mesh 1090 is accomplished by deformation of film strip portions 1019. This is not limited to deformation solely within the plane of film 1000, but also involves twisting of film strip portions 1019. In certain embodiments this deformation is controlled so as to create specific mesh geometries optimized for forming filter media for specific filtering applications. For instance, FIG. 36 depicts a mesh 1100 formed from a film portion with intermittent slits in the manner previously described. Deformation of portions 1119 is controlled so that portions 1119 are angularly offset from the basal plane of mesh 1100. In other words, portions 1119 of mesh 1100 are no coplanar with the overall basal plane of the 1100. In meshes 1100, the angular offset of portions 1119 increases as the width of openings 1146 is increased. These aspects of the configuration of mesh 1100 may be optimized for specific filter applications. Multiple meshes 1100 may be stacked one upon another so as to create filter media in which meshes 1100 create significant turbulence so as to increase filter efficiency.

[0131] Laminae of the present invention may be used in layered constructs with other media types. These constructs, may form composite sheets. These sheets may, in turn, be formed into configurations optimized for specific applications. For instance, these composite sheets may be formed into pleated filter elements.

[0132] Although embodiments of the present invention have been described in detail, it will be understood by those skilled in the art that various modifications can be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

[0133] This written description uses examples to disclose the invention and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

[0134] It will be understood that the particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention may be employed in various embodiments without departing from the scope of the invention. Those of ordinary skill in the art will recognize numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

[0135] All of the compositions and/or methods disclosed and claimed herein may be made and/or executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of the embodiments included herein, it will be apparent to those of ordinary skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.

[0136] Thus, although there have been described particular embodiments of the present invention, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.