Patent Application
20090127747
The present invention generally relates to electrostatic spinning of fine fibers from a polymeric solution in an electrostatic field created by a voltage differential between a spinning electrode and a collecting electrode and more particularly relates to a new spinning electrode equipment arrangement and/or electro-spinning methods for reducing solvent loss.
The production of fine fibers from polymeric solution through electrostatic spinning (a.k.a. “electro-spinning”) via an electric field created by a voltage differential between a collecting electrode and a spinning electrode is known. For example, as shown in U.S. Pat. No. 6,743,273, polymeric solution is pumped to a spinning electrode in the form of a rotating emitter in which the pump solution is pumped from a reservoir and forced through holes in the emitter. Upon exiting, the electrostatic potential between a grid and the emitter imparts a charge which causes the liquid to be “spun” as thin fine fibers where they are collected on a substrate as an efficiency layer. During this process, the solvent is evaporated off the fine fibers which draws down the fiber diameter during their flight.
Another example of an electrostatic spinning device is shown in Patent Publication Nos. US2006/0290031 and WO2006/131081. The spinning electrode designs disclosed in these applications are in the form of a rotating drum-like body that may take several different forms. The drum is situated and bathed within a polymeric solution reservoir and is rotated about an axis perpendicular relative to the path of a collection media. By rotating the drum through the polymer solution, the spinning surface of the charged electrode is coated with the polymeric solution. Various drum like body variations are shown throughout these two patent publications to include providing a multiple pointed tips to create discrete spinning locations where fine fibers are generated.
The present invention provides for improvements over the existing state of the art as it relates to electrostatic fine fiber production and spinning electrode design and/or in relation to the production of fine fiber filtration media.
A first aspect of the present invention is directed toward an apparatus for generation of fine fibers in which a polymer solution dipping basin is substantially covered for reducing solvent loss. The apparatus includes a spray electrode for generating fine fibers, and a dipping basin containing polymer solution in which the dipping basin has an open end. A cover is arranged to substantially cover the opening end of the dipping basin. A drive unit moves the spray electrode around the cover to include a first portion in the dipping basin and a second portion exposed for generation of fine fibers.
Another aspect of the present invention is directed toward a method of producing fine fibers. The method includes electro-spinning fine fibers from a polymer solution coating on an electrode under an electrostatic field at a first location; dipping the electrode in a polymer solution at a second location; and maintaining an evaporation area between the first and second locations to reduce evaporation of solvent.
Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:
While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.
For purposes of illustration, an embodiment according to the invention is illustrated in partial schematic form as a fine fiber production machine 10 as part of a filter media production system 12 in
As shown, the sheet 18 of media runs along a first direction 30 through the fine fiber production machine 10 generally from an entrance region 32 to an exit region 34. The sides 36 of the filter media sheet generally run parallel with this first direction 30 naturally.
The fine fiber production machine includes an electrostatic field that is generated between first and second electrodes to include one or more spinning electrodes 40 whereat fine fibers are generated on the one hand and a collection electrode 42 to which the fine fibers are drawn under the force provided by the electrostatic field. As shown, the media sheet 18 is typically run between the spinning electrode 40 and the collection electrode 42 such that the fine fibers are usually not deposited upon the collection electrode 42 but instead deposited on the filter media sheet 18. The collection electrode 42 is preferably a conductive perforated plate of substantial surface area for maximizing locations to where threads are collected. Many small holes 46 are formed in the perforated plate to facilitate vacuum suction of evaporated solvent through a blower driven ventilation hood system 48 that evacuates evaporated solvent to an external location such as outside a facility. As schematically shown, the collection electrode 42 spans at least the width of media and width a length of spinning electrodes 40, collectively, as does the ventilation hood system 48. The filter media substrate layer runs in contact and is supported against the collection electrode 42 under suction pressure against gravity. Preferably, this support arrangement is flat and planar as illustrated.
To generate the electrostatic field, a high voltage supply is provided and that is connected to at least one of the electrodes 40, 42 for generating a high voltage differential between the electrodes 40, 42 on the order of between 10,000 and 150,000 volts or more (and more preferably for the production of fine fibers for filter media between 75,000 and 120,000 volts), although other voltage ranges may be possible. Typically, the collection electrode 42 will simply be grounded however, the voltage generation source may provide a potential to the collection electrode other then ground such that the spinning electrode may not necessarily be at such a high voltage potential relative to ground. In either event, a voltage source is arranged to generate a voltage differential between the first and second electrodes sufficient for generating the spinning of fine fibers from polymeric solution through an electrostatic field.
In one embodiment, an apparatus includes a single spinning electrode 40. For example, the single electrode of
Turning in greater detail to an individual production cell 50, with reference to
Mounted into one of the plastic walls 56 is the metal electrical terminal 60 that extends through one of the walls 56 and that is connected by an electrical wire 52 to the high voltage supply 44. The terminal 60 is in communication with the polymeric solution 58 and thereby charges the solution for communication of the voltage potential therethrough along to the spinning electrode 40.
Additionally, to provide for periodic replenishment of the polymeric solution, a fluid coupling such as quick connect coupling 62 that conventionally includes a one-way check valve is mounted into and through one of the walls 56 to allow for periodic replenishment of the polymeric solution through the addition of more such solution. This may be hooked up to a fluid replenishment system that periodically replenishes the basin with more polymeric solution to include a fluid metering unit 64 and a reservoir 66. Control valves or individual metering units (one dedicated to each cell) may be provided to individually control the solution in each cell.
As shown, the spinning electrode 40 may take the form of a strand and as shown in the embodiment, an endless strand in the form of an endless chain 70. The endless chain 70 is preferably made of metal or other conductive material such that it is readily conductive and is in electrical circuit with the high voltage supply 44 by virtue of electrical communication provided by and through the polymeric solution 58. The endless chain 70 preferably includes a plurality of individual discrete segments 72 as shown best in
The endless chain 70 is mounted along an endless path 80 around two guides which may take the form of movable guide wheels 82 that are spaced at opposite ends of the dipping basin 54. The guide wheels 82 may be sheave like structures as shown and can be metal, plastic or other suitable material. The guide wheels 82 are mounted for rotation on insulating axels 84 such as plastic material axels so as to insulate the voltage potential within the dipping basin 54. The axels 84 are rotatable relative to the walls 56 of the dipping basin 54. The endless chain 70 is entrained about the guide wheels 82 to include a linear spinning path 86 that is exposed outside of the polymeric solution 58. The spinning path 86 faces and is closest to the collection electrode 42. The endless chain 70 also has a linear return path 88 which runs through the dipping basin 54 and the polymeric solution 58 for the purpose of periodically regenerating the segments of the endless chain, that is by dipping the chain and running it through the polymeric solution. At any one time a portion of the chain is being regenerated with solution and a portion is exposed for electro-spinning.
To drive the endless chain 70 along the endless path 80 about the guide wheels 82, a suitable drive unit is provided, which includes a rotary motor 90 having a rotary output upon an output shaft 92. The output is then transferred through gearing to a transmission shaft 94 that transmits through the chain and sprocket mechanism 96 to electrical isolation drives 98. These drives 98 include separated but closely arranged housings 100 (See
As can be seen from
Additionally, as shown best in
As evident from the foregoing, the linear spinning path 86 and movement direction of the endless chain 70 is transverse relative to the movement direction 30 of the collection media sheet 18. Preferably and as shown this transverse arrangement is preferably perpendicular although it is appreciated that other transverse arrangements including angles other than 90° may be used. Thus, in the context herein, transverse includes but does not mean perpendicular but is broader in the sense and is meant to also include a strand for electro-spinning generation that moves generally crosswise in a direction generally between the opposed sides 36 of the collection media sheet 18.
According to an operational mode embodiment, during operation the filter media collection sheet 18 runs along the first direction continuously as well as the endless chain 70 moving about the endless path 80 continuously. However, it will be appreciated that intermittent operation of either can be accomplished if desired for various purposes.
During operation and as shown in
In the case of water soluble polymers in which water is used as the solvent, the apparatus may be used in an uncovered state. However, the disclosed embodiment has a significant optional and preferred feature that provides for significant advantages over traditional dipping systems by providing a central cover 116 that is arranged to substantially cover the otherwise open end 118 of the dipping basin. With this arrangement, it can be seen that the endless chain electrode is driven around the cover to include a first portion which is contained within the dipping basin and substantially encapsulated therein by the cover and a second portion that is exposed and capable of generating fine fibers. The cover 116 can be interposed between different parts of the spring electrode as shown and can substantially enclose dipping of the electrode. The cover 116 extends substantially between the spaced apart guide wheels 82 and in the present embodiment may include guide wheel slots 120 receiving the guide wheels therethrough and providing an opening through which the endless chain 70 can pass. In the case of the present embodiment, including two endless chains 70 per cell 50 with only two guide wheels 82 provided for each endless chain 70, a total of four slots 120 may be provided. Additional slots may be provided for additional guide wheels where other support apparatus as may be desired or needed. The cover 116 is particularly advantageous when the polymer solution involves a volatile solvent and/or a solvent other then water. For example, certain solvent materials can evaporate more quickly than water and therefore make it more difficult to maintain a desirable polymer to solution ratio. The cover 116 minimizes the amount of solvent that is exposed externally at any one moment and thereby minimizes solvent loss. This is also perhaps more advantageous from a materials savings and environmental standpoint.
For example, a comparison of a covered endless beaded chain embodiment according to the disclosure of
Nevertheless, considering evaporation relates in large part to available surface area (and such things as surface agitation and air flow—e.g. around the entry and exit regions of the dipping portion of the electrode), solvent savings is primarily due to the basin and electrode covering technique disclosed herein. For example, the embodiments of
In practicing one embodiment, the cover 116 can be fastened securely to the walls of the dipping basin 54 by virtue of screws or otherwise. The configuration and attachment of the cover may depend upon electrode configuration. Other arrangements or other types of electrode spinning systems are possible. Preferably, the cover reduces evaporation from solvent of the polymer solution by at least 25% as compared to an uncovered electrode spinning apparatus and even more preferably by at least 50%. For example, savings of approximately two-thirds of solvent is demonstrated by the above example.
Additionally, the illustrated embodiment includes end covers 122 at opposed ends of the cell 50 that are mounted to wall extensions 124 that extend above the cover 116 such that the end covers 122 are positioned over the opposed ends of the endless chain 70 and are disposed over the guide wheels 82. The end covers 122 also serve to reduce solvent evaporation but also serve as shrouds to limit the span of fine fiber production. As shown, the end cover span 126 between the inner edges of opposed end covers is about the same and preferably just slightly larger then the width of the corresponding media sheet 18 defined between opposed sides 36. The end cover 122 may be adjustable and/or interchangeable with other longer end covers such that the span 126 may be adjustable to accommodate different widths of collection media sheets 18 that may be run through the fine fiber production machine 10.
Turning to
In this embodiment, the fine fiber production machine includes an endless serpentine belt 142 that is driven in an endless path around multiple guide wheels 144. The serpentine belt 142 is preferably made of a conductive material and may take the form of a continuous endless metal band as shown to provide for a spinning electrode. The serpentine belt 142 includes several linear segments 146 between adjacent guide wheels 144 that each provide for multiple spinning locations. Generally, the edge 148 that would be disposed closest to the collection electrode provides for the spinning locations. This edge 148 can be serrated to provide multiple discrete and equally spaced sharp edges (not shown) and/or can be configured with pockets and the like to provide for local polymeric solution fluid reservoirs along the edge 148. Preferably, the guide wheels include teeth or other positioning structure which engage holes 152 and other similar positioning structure on the belt 142 such that the edge can be maintained at a constant spacing and thereby maintain a constant spacing distance 106 if such a constant spacing is desired.
The serpentine belt 142 is subject to a voltage source to generate the electrostatic field thereby serve as a spinning electrode. To provide for polymeric solution along the belt 142, this embodiment includes a wetting supply system that includes one or more needles 154 having control orifices 155 spaced adjacent to the edge 148 of the serpentine belt 142. Additionally, the needles are connected along fluid lines to a pressurized polymeric solution source afforded by a pump 156 that delivers polymeric solution from a reservoir 158. Thus, the strand generation need not necessarily be dipped but can be alternatively wetted in other means in accordance with this embodiment. Additionally, this embodiment also affords the ability for dipping the electrode in a dipping basin. For example, portions of the serpentine belt can be arranged to run vertically as opposed to horizontally due to the flexible nature of a serpentine belt. Alternatively, the right hand portion may be dipped in a dipping vessel containing polymeric solution with the collection media arranged to run vertical as opposed to horizontally.
Yet a third embodiment of the present invention is shown in
All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
