Patent Grant
7628941
The present invention generally relates to a method and apparatus for making uniform nanofiber webs, and more specifically relates to a method of making uniform nanofiber webs, wherein a source of process air is utilized to affect the spray pattern and quality of fibrillated material as it is expressed from a die assembly including a multi-fluid opening.
Meltspun technologies, which are known in the art to include the spunbond and meltblown processes, manage the flow of process gases, such as air, and polymeric material simultaneously through a die body to effect the formation of the polymeric material into continuous or discontinuous fiber. In most known configurations of meltblowing nozzles, hot air is provided through a passageway formed on each side of a die tip. The hot air heats the die and thus prevents the die from freezing as the molten polymer exits and cools. In this way the die is prevented from becoming clogged with solidifying polymer. In addition to heating the die body, the hot air, which is sometimes referred to as primary air, acts to draw, or attenuate the melt into elongated micro-sized filaments. In some cases, a secondary air source is further employed that impinges upon the drawn filaments so as to fragment and cool the filaments prior to being deposited on a collection surface. Typical meltblown fibers are known to consist of fiber diameters less than 10 microns.
More recently, methods of forming fibers with fiber diameters less than 1.0 micron, or 1000 nanometers, have been developed. These fibers are often referred to as ultra-fine fibers, sub-micron fibers, or nanofibers. Methods of producing nanofibers are known in the art and often make use of a plurality of multi-fluid nozzles, whereby an air source is supplied to an inner fluid passageway and a molten polymeric material is supplied to an outer annular passageway concentrically positioned about the inner passageway. While the physical properties of nanofiber webs are advantageous to a variety of nonwoven markets, commercial products have only reached limited markets due to associated cost.
U.S. Pat. No. 5,260,003 and No. 5,114,631 to Nyssen, et al., both hereby incorporated by reference, describe a meltblowing process and device for manufacturing ultra-fine fibers and ultra-fine fiber mats from thermoplastic polymers with mean fiber diameters of 0.2-15 microns. Laval nozzles are utilized to accelerate the process gas to supersonic speed; however, the process as disclosed has been realized to be prohibitively expensive both in operating and equipment costs.
U.S. Pat. No. 6,382,526 and No. 6,520,425 to Reneker, et al., also both hereby incorporated by reference, disclose a method of making nanofiber by forcing fiber forming material concentrically around an inner annular passageway of pressurized gas. The gas impinges upon the fiber forming material in a gas jet space to shear the material into ultra-fine fibers. U.S. Pat. No. 4,536,361 to Torobin, incorporated herein by reference, teaches a similar nanofiber formation method wherein a coaxial blowing nozzle has an inner passageway to convey a blowing gas at a positive pressure to the inner surface of a liquid film material, and an outer passageway to convey the film material. An additional method for the formation of nanofibers is taught in U.S. Pat. No. 6,183,670 to Torobin, et al., which is hereby incorporated by reference.
Spacing of nozzles within the die body may be arranged such that material exiting the nozzle arrangement can be collected in a more uniform manner upon a forming surface. It has been recognized that a linear formation of equally spaced nozzles may result in a striping pattern that is visibly noticeable within the collected web. The stripes are found to reflect the spacing between adjacent nozzles. The striping effect seen in the web can further be described as “hills and valleys” whereby the “hills” exhibit a noticeably higher basis weight than that of the “valleys”. The industry may also refer to such basis weight inconsistencies as gauge bands.
U.S. Pat. Nos. 5,582,907 and 6,074,869, both incorporated herein by reference, address striping observed in meltblown webs by organizing nozzles into two linearly arranged parallel rows each having substantially equally spaced. Additionally, the two rows of nozzles are offset such that the nozzles are staggered in relationship to each other. Further, the staggered nozzles of the two rows are angled inward toward each other. In this fashion, each nozzle is utilizing a respective supply of primary process air, but lacks an ancillary air source to assist with web formation. These patents further assert external disruption of the polymeric material by an alternate gas source detracts from achievement of sufficient web uniformity.
A need remains for a process that can utilize multi-fluid openings for facilitating the distribution of molten polymer and a gas in the formation of nanofibers and further incorporates an ancillary gas source that assists with a uniform fiber collection across the width of the web.
The present invention is directed to a method and apparatus for making nanofiber webs, wherein a source of process air is utilized to affect the spray pattern and quality of fibrillated material expressed from a die assembly including a multi-fluid opening. Appropriately, the aforementioned process air is defined herein as an alternate or ancillary air source apart from primary process air, which primary air is simultaneously supplied with the molten polymeric material to the fiber forming multi-fluid opening. The ancillary air source of the invention is further distinct from secondary air, which is also known in the art as quenching air. The ancillary air can be described as a continuous fluid curtain of shielding or shaping air. While the use of air is preferred, the invention contemplates the use of alternate suitable gases, such as nitrogen. For the purpose of this disclosure, the ancillary air is referred to herein as a “fluid curtain nozzle” or “continuous air curtain”.
According to the present invention, disclosed herein is a method of forming uniform nanofiber webs, The method includes a multi-fluid opening, wherein the opening includes a passage for directing a gas and a separate passage for directing a polymeric material through the opening. The method further includes at least one fluid curtain nozzle positioned in operative association with the multi-fluid opening. According to the method of the present invention, a molten polymeric material and a gas fluid is simultaneously supplied to separate respective passages of the multi-fluid opening. The gas is directed through the multi-fluid opening to impinge upon the polymeric material to thereby form a spray pattern. A fluid is also directed through the fluid curtain nozzle for controlling the spray pattern of nanofiber expressed from the multi-fluid opening and subsequently, the nanofiber is collected on a surface to form a uniform nanofiber web.
In addition to controlling the spray pattern of the nanofiber expressed from the multi-fluid opening, the fluid curtain is believed to further control the temperature of the multi-fluid opening, wherein the temperature of the multi-fluid opening may be elevated by fluid curtain.
In one embodiment, continuous air curtains are employed to affect the spray pattern and quality of fibrillated material as the material is expressed from a multi-fluid opening including an array of two or more multi-fluid nozzles. The multi-fluid nozzles have an inner passageway for directing a first fluid, such as gas, and an outer annular passageway surrounding the inner passageway for directing a second fluid or molten polymeric fiber forming material. In addition, at least one continuous air curtain is positioned in operative association with the complete plural nozzle array to affect the polymeric spray formation pattern, which can be generally described as conical. The one or more air curtains are observed to “compress” and shape the spray pattern of fibrillated material that is emitted from the nozzles thereby decreasing the distance from which the fibers are spaced across the conic spray formation. Further, as the air curtains impinge upon the polymeric spray to affect the spray pattern, the air curtains can also function to shield the spray formations between adjacent plural nozzle arrays to diminish interaction or comingling of the fibrous material between adjacent nozzle arrays. Reduced comingling of the fibrillated polymeric spray of nanofiber between adjacent nozzle arrays is believed to significantly improve the uniformity of the web as the nanofibers are gathered onto a collection surface.
In one contemplated embodiment, a method for forming the uniform nanofiber web comprises an array of two or more multi-fluid nozzles preferably aligned in a generally linear arrangement, wherein a plurality of the multi-fluid nozzle arrays are positioned parallel to one another across the width of the fiber forming apparatus. In addition, at least one air curtain nozzle is positioned in operative association with each of the plural multi-fluid nozzle arrays, wherein the air curtain nozzle defines a generally elongated slot through which fluid is directed for formation of the fluid (air) curtain.
The present invention also contemplates the use of one or more air curtains with various other multi-fluid opening configurations, such as slot dies. Examples of slot die configurations include a double slot die and a single slot die. It is believed that the use of one or more air curtains in operative association with the double slot multi-fluid opening or single slot multi-fluid opening affects fiber formation and enhances the uniformity of the resultant web.
Other features and advantages of the present invention will become readily apparent from the following detailed description, the accompanying drawings, and the appended claims.
While the present invention is susceptible of embodiment in various forms, there is shown in the drawings, and will hereinafter be described, a presently preferred embodiment of the invention, with the understanding that the present disclosure is to be considered as an exemplification of the invention, and is not intended to limit the invention to the specific embodiment illustrated.
The method of making nanofiber webs in accordance with the present invention can be practiced in keeping with the teachings of U.S. Pat. Nos. 4,536,361 and 6,183,670, both previously incorporated herein by reference. The present invention further contemplates a method of forming fibrillated nanofibers and nanofiber webs, wherein one embodiment, shown in
It is also in the purview of the present invention to provide a die assembly including a slot configuration for delivery of a gas and a polymeric material. In such a configuration, it is contemplated to provide a polymeric material as a continuous film on a film forming surface, wherein non-limiting examples of film forming surfaces may include linear, wave-like, grooved, and the like.
In another illustrative embodiment, as shown in
In yet another illustrative embodiment, as shown in
In yet another embodiment, the slot configuration includes a film forming surface, a gas exit passage, and an impingement surface, wherein the gas exiting the die is directed against the formed film on an impingement surface. In such an embodiment, the film forming surface may be a horizontal surface, otherwise referred to as 0°, or positioned at an angle up to about 80°. Preferably, the film forming surface is positioned at about 0° to about 60°. The film forming surface can be described to also have a length. The film forming surface preferably has a length of about 0 to about 0.120 inches. In addition, the impingement surface also has a preferred surface position, wherein the impingement surface may be perpendicular to the film forming surface or otherwise described as having a 90° angle relative to the film forming surface or the impingement surface may be at an angle than 90° relative to the film forming surface. Further, the impingement surface has a preferred length of between about 0-0.150 inches, more preferably between about 0-0.060 inches, and most preferably between about 0-0.001 inches.
According to the invention molten polymeric material suitable for formation of the nanofibers and nanofiber webs of the present invention are those polymers capable of being meltspun including, but are not limited to polyolefin, polyamide, polyester, poly(vinylchloride), polymethylmethacrylate (and other acrylic resins), polystyrene, polyurethane, and copolymers thereof (including ABA type block copolymers), polyvinylalcohol in various degrees of hydrolysis in cross-linked and non-cross-linked forms, as well as elastomeric polymers, plus the derivatives and mixtures thereof. Modacrylics, polyacrylonitriles, aramids, melamines, and other flame-retardant polymers have been contemplated as well. The polymers may be further selected from homopolymers; copolymers, and conjugates and may include those polymers having incorporated melt additives or surface-active agents.
As illustrated in
In such an embodiment, the slot may demonstrate a linear configuration, which is positioned in operative association with the entire array of nozzles to control and shape the spray patterns of the array. Preferably, the slot has a length of about at least the length of the plural multi-fluid nozzle array, and most preferably has a length which is approximately equal to the length of the array plus two times the center-to-center spacing of the individual nozzles. Thus, in a current embodiment, wherein a nozzle array includes three individual nozzles spaced approximately 0.42 in, center-to-center an associated air curtain nozzle has a slot length of approx. 1.7 in. Further, the slot preferably is provided with a width of about 0.003 in. to about 0.050 in. Air temperatures suitable for use with the process of the present invention preferably exhibit a range between 10° C. and 400° C., and more preferably exhibit a range between 25° C. and 360° C.
The air curtain has been observed to further shield the spray patterns of adjacent multi-fluid nozzle arrays, thereby reducing the degree of comingling between the multi-fluid nozzle arrays, as well as minimizing excess comingling of fibers of adjacent multi-fluid nozzles within an array. In addition, with respect to the slot configuration embodiments, the air curtain is further believed to affect the shape of the spray pattern of the fibrillated film. Without intending to be bound by theory, it is believed that a controlled spray pattern of fibrillated material results in a more uniform collection of nanofibers on a surface to produce a more uniform web.
Web uniformity usually refers to the degree of consistency across the width of the web and can be determined by several systems of measurement, including, but not limited to, coefficient of variation of pore diameter, air permeability, and opacity. Web uniformity metrics tend to be basis weight dependent. The nonwoven nanofiber fabric of the present invention may exhibit basis weights ranging from very light to very heavy, wherein the range captures fabric less than 5 gsm through fabrics greater than 200 gsm.
One acceptable uniformity metric is disclosed in U.S. Pat. No. 5,173,356, which is hereby incorporated by reference and includes collecting small swatches taken from various locations across the width of the web (sufficiently far enough away from the edges to avoid edge effects) to determine a basis weight uniformity. Additional acceptable methods for evaluating uniformity may be practiced in accordance with original paper, “Nonwoven Uniformity—Measurements Using Image Analysis”, disclosed in the Spring 2003 International Nonwovens Journal Vol. 12, No. 1, also incorporated by reference.
Despite the aforementioned methods of evaluating uniformity, lighter weight webs may nonetheless exhibit non-uniform performance characteristics due to differences in the intrinsic properties of the individual web fibers. As taught in U.S. Pat. No. 6,846,450, incorporated herein by reference, light weight webs may be evaluated for uniformity by measuring properties of the fibers rather than the web. It's been further contemplated to measure web uniformity in an inline process by way of various commercially available scanning devices that monitor web inconsistencies. In addition to improved web uniformity, it's believed the nanofiber web formed on the collection surface exhibits a loftier caliper as the nanofibers are deposited in a more controlled manner through the use of air curtains.
The present invention further contemplates the use of air curtains to improve the quality of the fibrillated material by forming more uniform nanofibers and creating a controlled environment from the time the polymer is first sprayed from the die assembly until the time the formed nanofibers are gathered on a collection surface. Fiber uniformity may be measured by those methods known in the art, such as by a scanning electron microscopic once the fabric is offline or inline by way of ensemble laser diffraction, as disclosed in original paper, “Ensemble Laser Diffraction for Online Measurement of Fiber Diameter Distribution During the Melt Blown Process, of the Summer 2004 International Nonwovens Journal, which is hereby incorporated by reference. Without intending to be bound by theory, when air curtains are used in conjunction with an array or two or more multi-fluid nozzles, it is believed that the air curtains form a controlled gradient-like effect of ancillary air as it diverges from the multi-fluid nozzle tip toward the fiber collection surface. In the region of the nozzle tip, the air currents influence the fiber formation process by acting to control the temperature at the nozzle tip. This control can include elevating the temperature of the fluid nozzles with the fluid (air) current. As the air from the curtains diverges from the nozzle tip, the air curtains of the invention are believed to entrain surrounding environmental air, which acts to isolate the newly formed nanofibers, while minimizing the deleterious effects of “shot” on web formation. Shot is known in the art as a collection of polymer that fails to form fiber during the fiber formation process and deposits onto the fiber collection surface as a polymeric globule deleteriously affecting the web formation.
In accordance with the present invention, the formed nanofibers are generally self bonding when deposited on a collection surface; however, it is in the purview of the present invention that the nanofiber web may be further consolidated by thermal calendaring or other bonding techniques known to those skilled in the art. It is further in the purview of the invention to combine the nonwoven nanofiber web of the present invention with additional fibrous and non-fibrous substrates to form a multilayer construct. Substrates which can be combined with the nanofiber web (N) may be selected from the group consisting of carded webs (C), spunbond webs (S), meltblown webs (M), and films (F) of similar or dissimilar basis weights, fiber composition, fiber diameters, and physical properties. Non-limiting examples of such constructs include S-N, S-N-S, S-M-N-M-S, S-N-N-S, S-N-S/S-N-S, S-M-S/S-N-S, C-N-C, F-N-F, etc., wherein the multilayer constructs may be bonded or consolidated by way of hydraulic needling, through air bonding, adhesive bonding, ultrasonic bonding, thermal point bonding, smooth calendaring, or by any other bonding technique known in the art.
The nonwoven construct comprised of the uniform nanofiber web may be utilized in the manufacture of numerous home cleaning, personal hygiene, medical, and other end use products where a nonwoven fabric can be employed. Disposable nonwoven undergarments and disposable absorbent hygiene articles, such as a sanitary napkins, incontinence pads, diapers, and the like, wherein the term “diaper” refers to an absorbent article generally worn by infants and incontinent persons that is worn about the lower torso of the wearer can benefit from the improved uniformity of a nanofiber nonwoven in the absorbent layer construction.
In addition, the material may be utilized as medical gauze, or similar absorbent surgical materials, for absorbing wound exudates and assisting in the removal of seepage from surgical sites. Other end uses include wet or dry hygienic, anti-microbial, or hard surface wipes for medical, industrial, automotive, home care, food service, and graphic arts markets, which can be readily hand-held for cleaning and the like.
The nanofiber webs of the present invention may be included in constructs suitable for medical and industrial protective apparel, such as gowns, drapes, shirts, bottom weights, lab coats, face masks, and the like, and protective covers, including covers for vehicles such as cars, trucks, boats, airplanes, motorcycles, bicycles, golf carts, as well as covers for equipment often left outdoors like grills, yard and garden equipment, such as mowers and roto-tillers, lawn furniture, floor coverings, table cloths, and picnic area covers.
The nanofiber material may also be used in top of bed applications, including mattress protectors, comforters, quilts, duvet covers, and bedspreads. Additionally, acoustical applications, such as interior and exterior automotive components, carpet backing, insulative and sound dampening appliance and machinery wraps, and wall coverings may also benefit from the nanofiber web of the present invention. The uniform nanofiber web is further advantageous for various filtration applications, including bag house, plus pool and spa filters.
It has also been contemplated that a multilayer structure comprised of the nanofiber web of the present invention may be embossed or imparted with one or more raised portions by advancing the structure onto a forming surface comprised of a series of void spaces. Suitable forming surfaces include wire screens, three-dimensional belts, metal drums, and laser ablated shells, such as a three-dimensional image transfer device. Three-dimensional image transfer devices are disclosed in U.S. Pat. No. 5,098,764, which is hereby incorporated by reference; with the use of such image transfer devices being desirable for providing a fabric with enhanced physical properties as well as an aesthetically pleasing appearance.
Depending on the desired end use application of the uniform nonwoven nanofiber web, specific additives may be included directly into the polymeric melt or applied after formation of the web. Suitable non-limiting examples of such additives include absorbency enhancing or deterring additives, UV stabilizers, fire retardants, dyes and pigments, fragrances, skin protectant, surfactants, aqueous or non-aqueous functional industrial solvents such as, plant oils, animal oils, terpenoids, silicon oils, mineral oils, white mineral oils, paraffinic solvents, polybutylenes, polyisobutylenes, polyalphaolefins, and mixtures thereof, toluenes, sequestering agents, corrosion inhibitors, abrasives, petroleum distillates, degreasers and the combinations thereof. Additional additives include antimicrobial composition, including, but not limited to iodines, alcohols, such as such as ethanol or propanol, biocides, abrasives, metallic materials, such as metal oxide, metal salt, metal complex, metal alloy or mixtures thereof, bacteriostatic complexes, bactericidal complexes, and the combinations thereof.
From the foregoing, it will be observed that numerous modifications and variations can be affected without departing from the true spirit and scope of the novel concept of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated herein is intended or should be inferred. The disclosure is intended to cover, by the appended claims, all such modifications as fall within the scope of the claims.
This application claims the benefit of priority Provisional Application No. 60/672,676, filed Apr. 19, 2005. the disclosures of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2006/014719 | 4/19/2006 | WO | 00 | 5/29/2008 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2006/113791 | 10/26/2006 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2571457 | Ladisch | Oct 1951 | A |
| 3615995 | Buntin et al. | Oct 1971 | A |
| 4363646 | Torobin | Dec 1982 | A |
| 4536361 | Torobin | Aug 1985 | A |
| 5075068 | Milligan et al. | Dec 1991 | A |
| 5080569 | Gubernick et al. | Jan 1992 | A |
| 5141699 | Meyer et al. | Aug 1992 | A |
| 5160746 | Dodge, II et al. | Nov 1992 | A |
| 5173356 | Eaton et al. | Dec 1992 | A |
| 5236641 | Allen et al. | Aug 1993 | A |
| 5273565 | Milligan et al. | Dec 1993 | A |
| 5545371 | Lu | Aug 1996 | A |
| 5582907 | Pall | Dec 1996 | A |
| 5688468 | Lu | Nov 1997 | A |
| 5733635 | Terakawa et al. | Mar 1998 | A |
| 5824248 | Sweet et al. | Oct 1998 | A |
| 5993943 | Bodaghi et al. | Nov 1999 | A |
| 6001303 | Haynes et al. | Dec 1999 | A |
| 6048808 | Kurihara et al. | Apr 2000 | A |
| 6074869 | Pall et al. | Jun 2000 | A |
| 6136245 | Lu | Oct 2000 | A |
| 6183670 | Torobin et al. | Feb 2001 | B1 |
| 6183684 | Lu | Feb 2001 | B1 |
| 6296463 | Allen | Oct 2001 | B1 |
| 6315806 | Torobin et al. | Nov 2001 | B1 |
| 6382526 | Reneker et al. | May 2002 | B1 |
| 6520425 | Reneker | Feb 2003 | B1 |
| 6620503 | Qin et al. | Sep 2003 | B2 |
| 6692825 | Qin et al. | Feb 2004 | B2 |
| 6799957 | Allen | Oct 2004 | B2 |
| 6824729 | Oin et al. | Nov 2004 | B2 |
| 6846450 | Erickson et al. | Jan 2005 | B2 |
| 20030116874 | Haynes | Jun 2003 | A1 |
| 20040102122 | Boney et al. | May 2004 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20090039564 A1 | Feb 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60672676 | Apr 2005 | US |
