News Column

"Filtration Article with Fluoropolymer Knit" in Patent Application Approval Process

February 12, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent application by the inventors Propst, Eric Keith (Avondale, PA); Speck, Steven H. (Elkton, MD), filed on July 22, 2013, was made available online on January 30, 2014, according to news reporting originating from Washington, D.C., by VerticalNews correspondents.

This patent application is assigned to W. L. Gore & Associates, Inc.

The following quote was obtained by the news editors from the background information supplied by the inventors: "Porous membranes are widely used in the filtration of particulate, ionic, microbial and other contaminants from fluids in pharmaceutical, microelectronics, chemical and food industries. In use, the membranes are formed into a device (e.g., pleated cartridges which may be housed within a capsule, hollow tubes, stack of flat disks, etc.) which is placed in the fluid stream to be filtered.

"To meet chemical and temperature resistance requirements, most filtration devices used in semiconductor fabrication are constructed entirely of fluoropolymer materials. The trend towards narrower line widths in semiconductor manufacturing has placed an ever increasing burden on particulate contamination control in semiconductor fabrication. Such a trend has led to the introduction of fluoropolymer filtration membranes having rated pore sizes as low as 10 nm.

"While such membranes provide superior particle filtration, there is a desire to extend the life cycle, or time-in-use, of the membranes, while maintaining the filtration efficiency thereof. In this regard, in typical filtration implementations, a support layer may be positioned downstream of a fluoropolymer filtration membrane to support the membrane against the pressure of fluid flow. In addition, the support layer or another downstream layer may provide drainage functionality (e.g., by acting as a spacing layer with downstream passageways therethrough to thereby facilitate fluid flow through the membrane). In that regard, an upstream drainage layer may also be utilized.

"In such arrangements, known upstream and downstream layers are constructed of fluoropolymeric fiber materials (e.g., PTFE, PFA or PVDF) in the form of wovens, non-wovens or nets. Over extended periods, such woven, non-woven or net layers may exhibit movement of fibers in the layer structure to a degree that renders such layers unable to provide the desired support to the filtration membrane against applied fluid pressure. This may result in damage to the membrane microstructure, and degradation of filtration efficiency and drainage functionality, to the point that filter replacement is required. As may be appreciated, filter replacement entails not only system downtime, but also results in added filter costs and utilization of maintenance personnel resources.

"Therefore, a need exists for a fluid filtration article having extended time-in-use advantages, while providing satisfactory filtration efficiency over the extended life of the device. Fluid filtration articles constructed with the knit materials of the present invention fulfill such a need."

In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "In one aspect, an improved filtration article is provided for filtering particles from a fluid stream that includes first and second layers positionable across a fluid stream, wherein the first layer comprises a porous PTFE for filtering particles from the fluid stream and the second layer comprises strands of fluoropolymer fibers arranged to form a stable knit. The second layer may provide for at least one of support and drainage of the first layer.

"More particularly, the knit fluoropolymer fiber layer may include a plurality of interlocking regions that are each defined by corresponding different sets of at least two interlocking loop portions of the plurality of strands of fluoropolymer fibers. The interlocking regions of the knit may define a plurality of wales and a plurality of courses, wherein for at least a first portion of the strands each strand comprises different loop portions that partially define different, alternating ones of the interlocking regions located along at least two different wales.

"In relation to such aspect, the present inventors have recognized that the combinative use of a porous PTFE filtration layer and a knit fluoropolymer fiber layer yields a filtration article having an improved life cycle, while providing efficient particle filtration. More particularly, the inventors have recognized that the utilization of a knit fluoropolymer fiber layer having fiber strands with interlocking loop portions provides enhanced dimensional stability over extended time periods, thereby facilitating realization of the noted advantages.

"In contemplated implementations, the porous PTFE filtration has a bubble point, measured as described hereinbelow, greater than about 30 psi. For example, in fine particulate filtration applications, the porous PTFE filtration layer may have a bubble point greater than about 50 psi, and preferably greater than about 80 psi (e.g., for use in semiconductor fabrication applications).

"In certain implementations, the improved filtration article may be provided so that, within a cross section of each of the plurality of interlocking regions, different lengths of the corresponding interlocking loop portions are located within at least three different stratums. As may be appreciated, such an arrangement enhances stability across the knit while accommodating tortuous fluid flow about the fiber strands in the interlocking regions.

"For each of the interlocking regions the fiber strands of the knit layer may be provided so that the corresponding interlocking loop portions extend about an arc of at least 90.degree. along different corresponding arcuate paths. In some implementations, at least a portion of the interlocking loop portions corresponding with each of interlocking regions may be provided to extend about an arc of at least 180.degree. along different corresponding arcuate paths. In certain embodiments, at least a portion of the interlocking loop portions corresponding with at least a portion of the interlocking regions may be provided as closed loops.

"In a further aspect, the improved filtration article may be provided so that each of the plurality of interlocking regions is defined by corresponding different sets of at least three interlocking loop portions of the strands of fluoropolymer fibers. Such approach may be utilized to yield further enhanced dimensional stability.

"In various embodiments, the strands of fluoropolymer fibers utilized in the knit layer may be provided to have various features. For example, all or at least a portion of the fluoropolymer fibers may be of a rounded outer configuration and/or may be twisted. In some implementations, the strands of fluoropolymer fibers may comprise monofilaments or multifilaments. Further, in some applications, the strands of fluoropolymer fibers may comprise hollow filaments.

"As may be appreciated, the knit layer of the improved filtration article may be of a warp knit type. By way of primary example, a Raschel knit, a Tricot knit, or other similar knit may be employed.

"In this regard, and as noted above, for at least a first portion of the plurality of strands utilized in the knit layer each strand may include different loop portions that partially define different, alternating ones of the interlocking regions located along at least two different ones of the plurality of wales. Stated differently, for at least a first portion of the strands, each strand may zig-zag between and form loop portions at different, alternating ones of the interlocking regions located along at least two different wales of the knit layer. Such an arrangement advantageously distributes a fluid pressure load applied to the knit layer by distributing the load at and across interlocking regions located in different wales and courses. Further, in some embodiments, the knit layer may be provided so that, for at least a second portion of the plurality of strands of the knit layer, each strand comprises different loop portions that partially define different ones of all or substantially all of the interlocking regions located along a corresponding one of the plurality of wales, thereby yielding further load distribution.

"In an additional aspect, the knit layer of the improved filtration article may be provided with voids, or open spaces, which extend between the fiber strands and plurality of interlocking regions through the knit layer. In this regard, the knit layer may be provided so that, on each of the opposing sides of the knit layer, the voids define at least about 10% of the corresponding areas, thereby facilitating fluid flow therethrough. Further, the knit layer may be provided so that the strands of fluoropolymer fibers, including the interlocking regions defined thereby, define at least about 20% of the areas of the opposing sides of the knit layer, thereby facilitating effective use of the knit layer as a drainage layer in the filtration article. In some arrangements the interlocking regions may define at least about 40% of the areas.

"In contemplated embodiments of an improved filtration article, a knit fluoropolymer fiber layer may be positioned downstream of a porous PTFE layer (e.g., a PTFE membrane) to provide for at least support of the PTFE layer. More particularly, the knit layer may be provided to support the porous PTFE layer against the pressure of a fluid stream passing therethrough. Further, the knit layer may function as a drainage, or spacing, layer. In various arrangements a downstream knit layer may be disposed directly adjacent the PTFE layer or with one or more intermediate layers therebetween. The downstream knit layer may be interconnected to the PTFE layer.

"An additional knit fluoropolymer fiber layer may be disposed upstream of the porous PTFE layer to provide drainage functionality. The upstream knit layer may be disposed directly adjacent to the PTFE layer or with one or more intermediate layers therebetween. The upstream knit layer may be interconnected to the PTFE layer.

"In some implementations, a knit fluoropolymer fiber layer and a porous PTFE layer may each be of a pleated configuration. More particularly, such pleated layers may be disposed in at least partially nested co-relation. In one arrangement, the nested, pleated layers may be disposed about and along an axis to define a filtration article having a tubular configuration. In this regard, the pleats of each layer may be provided to extend substantially parallel to the axis. The filtration article may be disposed so that a fluid stream flows through the filtration article from the outside of the tubular configuration thereof to an internal space within the tubular configuration. Alternatively, an opposite fluid flow direction through the tubular configuration may be employed.

"In another characterization, a filtration article may be provided for positioning in a fluid stream applying a fluid pressure load upon such filtration article of between about 1 psid and 10 psid, wherein the plurality of interlocking regions of the knit layer define a plurality of voids therebetween across the knit layer. In this regard, each of the voids may have a first area prior to being positioned in the fluid stream and a corresponding second area while positioned in the fluid stream. The knit layer may be provided so that for each of the plurality of voids the corresponding second area is less than about two times the corresponding first area thereof.

"In a further aspect, a filtration article may be provided for positioning in a fluid stream applying a fluid pressure load upon the filtration article of between about 1 psid and 10 psid, wherein the knit layer is provided so that each of the interlocking regions thereof is located at corresponding distances from adjacent ones of the plurality of interlocking regions along the wales and courses thereof. In turn, for each of the plurality of interlocking regions the corresponding distances, while the knit layer is positioned in the fluid stream, may be within 200% of initial values thereof prior to being positioned in the fluid stream.

"In another aspect, a method for filtering particles from fluid in a fluid stream is provided. The method may include the step of filtering particles from a fluid stream utilizing a porous PTFE membrane positioned across the fluid stream. The method may further include supporting the porous PTFE membrane against the fluid pressure load applied by the fluid stream utilizing a stable knit layer positioned adjacent to and downstream of the porous PTFE membrane.

"The stable knit layer employed in the method may include a plurality of strands of fluoropolymer fibers arranged to form a knit having a plurality of interlocking regions that are each defined by corresponding different sets of at least two interlocking loop portions of the plurality of strands of fluoropolymer fibers. In this regard, the method may include distributing of the fluid pressure load across the knit layer at the interlocking regions.

"Numerous additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the embodiment descriptions provided hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 illustrates an embodiment of a filtration device comprising a filtration article embodiment of the present invention.

"FIGS. 2A and 2B illustrate embodiments of a knit layer of a filtration article embodiment of the present invention.

"FIGS. 3A and 3B are images of a knit layer embodiment of a filtration article embodiment of the present invention.

"FIG. 4A illustrates the knit construction of another knit layer embodiment shown in FIG. 4B."

URL and more information on this patent application, see: Propst, Eric Keith; Speck, Steven H. Filtration Article with Fluoropolymer Knit. Filed July 22, 2013 and posted January 30, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=5132&p=103&f=G&l=50&d=PG01&S1=20140123.PD.&OS=PD/20140123&RS=PD/20140123

Keywords for this news article include: Electronics, Semiconductor, W. L. Gore & Associates Inc.

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Source: Electronics Newsweekly


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