Wound-pleat filters and related methods

Abstract

Described are wind-pleat filters and methods for preparing and using these filters.

Description

[Technical Field]

[0001] The following description relates to wound-pleat filters and methods of preparing and using wound-pleat filters. [Background technology]

[0002] Filters are used in industry to remove undesirable substances from fluids. Examples of fluids that are treated using filters include air, drinking water, liquid industrial solvents and process fluids, industrial gases used for manufacturing or processing (e.g., in semiconductor fabrication), and liquids with medical or pharmaceutical uses.

[0003] Different types of filters are designed to process different fluids. Some filters remove significant amounts of large (in the opposite sense) substances from gas or liquid streams, such as dust particles from air or bacteria or cellular material from biological fluids. Other filters are used to remove barely detectable amounts of extremely small, non-solid substances, such as chemical molecules (e.g., hydrocarbons, metal atoms, or ions) suspended or dissolved in the gas or liquid. Impurities and contaminants removed from these types of fluids include micron- or nano-scale dissolved or suspended molecules present in the fluid in amounts in the parts per million (ppm) range or below. An example of this type of filtration application is the purification of liquid solvent solutions useful in microelectronic and semiconductor processing.

[0004] A typical filter design includes a porous filter element that allows the fluid stream to pass freely but retains impurities or particles contained in the fluid, removing them from the fluid. In this context, "removing" impurities or particles from a fluid stream refers to a process that reduces the overall amount of impurities or particles present in the fluid stream, but does not necessarily remove the overall amount of impurities or particles from the fluid stream.

[0005] The filter materials (sometimes referred to as "filter elements") used for different fluid applications can be selected from a variety of useful materials, including porous polymer membranes (films), thin fibrous woven and nonwoven sheets made from organic or synthetic fibers, open-cell foam sheets, adsorbent materials (particles), and liquids, among others.

[0006] As a fluid passes through a filter material, undesirable substances in the fluid (called "impurities") are retained by the filter material. In one filtration mechanism, called a "sieving" mechanism, as a liquid passes through the filter material, the liquid and impurities smaller than the pores of the filter material pass through the filter element, while impurities larger than the pores are retained by the filter and separated from the fluid. In a different filtration mechanism, called a "non-sieving" mechanism, impurities are not removed by physical separation (sieving), but are attracted to the surface of the filter material by electrostatic or chemical interactions. Impurities, such as dissolved (in liquids) or suspended (in gases) chemical molecules (e.g., hydrocarbons, metals, or metal ions), can be chemically or electrostatically attracted to the filter media material and retained by the filter material.

[0007] Filter products can be "dead-end" style filters, or "bypass" or "recirculation" style filters. Dead-end filters include a filter element contained in a housing, and fluid entering the housing must pass through the filter element to exit the housing as filtrate. Bypass filter designs also include a filter element contained in a housing, with the difference being that fluid flowing into the housing can either pass through a membrane and then exit the housing as filtrate, or pass through the housing as a bypass stream ("retentate" or "retentate") without passing through the membrane. The filter housing includes an inlet, an outlet for filtrate, and an outlet for bypass fluid stream. The bypass stream can be recirculated through the same filter housing and filter element, or it can pass through a separate filter element in a separate filter housing.

[0008] A standard filter for processing many fluids is the "pleated cylindrical filter" design. Pleated cylindrical filter products include a cylindrical housing adapted to contain a pleated filter element in the flow path between the housing inlet and the housing outlet. The filter is typically a dead-end filter, requiring fluid entering the housing at the inlet to pass through the pleated filter element before exiting the housing at the outlet. Pleated filter elements have a cylindrical configuration with fold pleats formed by longitudinal folds extending along the length and central axis of the cylindrical filter element. Cylindrical pleated filter elements can include a cylindrical outer support (e.g., a "cage"), a cylindrical inner support (a "core"), and an open interior space or channel along the center and central axis of the cylinder, i.e., an open cylindrical interior space. When flowing through the cartridge, liquid flows through the interior channel either before or after passing through the filter element.

[0009] When designing filters for industrial applications, particularly for use in cleanrooms for semiconductor or microelectronic device manufacturing, filter designs often emphasize a large filter element area per filter volume. The pleated cylindrical filter design, which has been the standard filter format for these filtration applications for decades, has been developed and refined to the point where it allows only small additional room for improvement. As filter membranes have become progressively thinner, the ability to increase membrane area per filter volume by reducing membrane thickness has approached or reached its limits. The ability to increase membrane area per filter volume by removing or reducing the thickness of the support layer has also approached or reached its limits. Summary of the Invention

[0010] The present description relates to new and inventive wind-pleat filters, methods of making the wind-pleat filters, and methods of using the wind-pleat filters for removing, for example, trace impurities from process fluids.

[0011] Wound-pleat filter products are not commonly used in industry and, to Applicant's understanding, remain unused in applications for removing trace impurities having particle sizes less than 100 nanometers from liquids and gases.

[0012] Applicant has identified a particular class of novel and inventive wind-pleat filter designs that are effective for use in filtering high purity liquid and gaseous fluids containing trace impurities, and in particular for processing liquids and gases used in processing high purity semiconductor and microelectronic devices (sometimes referred to as "process fluids").

[0013] A wind-pleat filter includes a cylindrical filter structure made of a multi-layer filter membrane assembly including two or more filter membrane layers, the multi-layer filter membrane assembly being wound along the length of the assembly around a central longitudinal axis. Each filter membrane layer of the assembly has a first end and a second end extending along the length of the membrane layer. As part of the wound assembly, the longitudinal ends of the membrane layers are part of a first wind pleat positioned at the first filter end of the wind-pleat filter and part of a second wind pleat positioned at the second filter end of the wind-pleat filter. Wind-pleat filters can be housed in a filter housing including a housing inlet and a housing outlet in a configuration that requires fluid flowing into the housing inlet to flow through the filter membrane layers before exiting the housing by passing through the housing outlet.

[0014] In the wind-pleat filter configuration, the multi-layer filter membrane assembly forms multiple windings, with one "winding" referring to the portion of the assembly's overall length that winds in one revolution around the central axis. Each layer of the wind-pleat filter is alternately connected to each of two adjacent layers, as part of an inlet pleat at the inlet end of one adjacent layer and as part of an outlet pleat at the outlet end of a second adjacent layer. Two "adjacent" layers may be part of one winding of the multi-layer filter assembly, or they may be part of different windings, with the membrane layer adjacent to another membrane layer either on the inside of the winding (closer to the center of the winding) or on the outside of the winding (farther from the center of the winding). A membrane layer edge that forms pleats in an "alternating" manner is a filter membrane layer of a wind-pleat filter having a first edge (e.g., "inlet" or "front" edge) that forms pleats with a first edge (e.g., "inlet" or "front" edge) of a first adjacent filter membrane layer and a second edge (e.g., "outlet" or "rear" edge) that forms pleats with a second edge (e.g., "outlet" or "rear" edge) of a second, or different, adjacent filter membrane layer.

[0015] Preferred wind-pleat filters can include a large filter membrane area per filter volume. The described wind-pleat filters can have multiple times the filter membrane area per filter volume of standard pleated cylindrical filter designs, such as two, four, or five or more times the filter membrane area per volume compared to commercially available pleated cylindrical filter designs (with filter membrane and spacer layers having the same thickness).

[0016] As an additional advantage, useful or preferred wind-pleat filters as described can include a significantly reduced amount of support layers in the filter product structure, which means a reduced amount of non-filtration layers, i.e., a reduced amount of layers that do not function to remove impurities. Typically, a standard pleated cylindrical filter design can include two support layers per filter membrane layer, with one non-filtration support layer positioned on the inlet side of the filter membrane layer and one non-filtration support layer positioned on the outlet side of the filter membrane layer. Wind-pleat filter designs as described can include and may require fewer support layers per filter layer, such as one support layer (spacer layer) per filter membrane layer. That is, one support layer can serve as support for two separate membrane layers on the upstream side, or one support layer can serve as support for two separate membrane layers on the downstream side. In conventional cylindrical pleated filters, due to the nature of the assembly process, at least two layers of support are positioned between adjacent membrane layers on the inlet or outlet side. According to the example wound-pleat filters as described herein, only one layer of support is present between adjacent membrane layers on either the inlet or outlet side of the filter.

[0017] Example wind-pleat filters may be useful for applications in which small amounts of impurities (e.g., "trace impurities") are removed from an already highly pure liquid. "Removing" an impurity from a fluid means removing at least a portion of the impurity from the fluid, i.e., reducing the amount of impurity present in the fluid, although it may not be possible to remove all of the impurity from the fluid.

[0018] Impurities, also referred to as "contaminants," can be chemicals present in a fluid (e.g., a process fluid) in very small amounts, such as concentrations in the parts per million or parts per billion range, or even smaller. An example process fluid that can be filtered or purified using a roll-pleat filter as described includes a process fluid that has already been treated and purified to remove some impurities but still contains very small amounts of residual impurities present in only "trace" amounts. The terms "parts per million" and "parts per billion" are used in a manner consistent with the use of these terms in chemical engineering, including the engineering of manufacturing microelectronic and semiconductor devices. In this regard, parts per million (PPM) is commonly used as a dimensionless measure of the small degree (concentration) of contaminants in a fluid (gas or liquid) and is expressed as milligrams of contaminant per liter of fluid (mg / L), measuring the mass of contaminant per volume of fluid. One part per million equals 0.000001 units.

[0019] Impurities in a process fluid are chemicals different from the process fluid, dissolved in a liquid process fluid, or suspended in a gaseous process fluid. Chemically described examples include hydrocarbon molecules, which can be uncharged or charged (ionic) molecules and oligomers, as well as inorganic compounds such as metal oxides (titanium dioxide), metal atoms, and metal ions.

[0020] Based on size, trace impurities in processing fluids may have sizes (largest dimension) of less than 100 nanometers, such as less than 90, 50, 25, 10, 5, or 1 nanometer. Particles of these sizes, when present in processing fluids used to process semiconductor or microelectronic devices, can create defects in the devices and reduce processing yields.

[0021] The trace impurities may be initially present in the process fluid in amounts less than 100, 10, or 1 ppm, or less than 100, 10, or 1 ppb. By passing the process fluid through a wind-pleat filter as described, the concentration of the trace impurities may be reduced by at least 20, 50, 70, or 80 percent, i.e., the filter will remove at least 20, 50, 70, or 80 percent of the trace impurities from the process fluid.

[0022] When used to remove these types of trace impurities from process fluids, roll-pleat filters as described can have long service lives measured in volumes of thousands of liters of fluid passing through the filter, such as 1,000, 5,000, or 10,000 liters. When removing trace impurities from a fluid over a service life in this range, the amount of trace impurities that accumulate within the filter can occupy less than 2 percent or less than 1 percent of the total available surface area of ​​the filter membrane.

[0023] Compared to traditional pleated cylindrical filter designs, roll-pleat filters have the relative advantage of being able to produce more efficient filters with a greater amount of filter membrane per filter volume. The roll-pleat filters described herein can be prepared with only one spacer layer required per filter membrane layer, whereas standard pleated cylindrical filter designs essentially include two spacer layers per filter membrane layer. The described roll-pleat design also allows for the elimination of the open channels typically required in the central axis and core of pleated cylindrical designs. Instead of open channels in the core, roll-pleat filter products can include additional roll filter membrane. Furthermore, roll-pleat filters have no limit on pleat height, do not pressurize a large outer diameter surface, do not require fluid to pass through the central opening of the cylinder, have a very uniform packing density, and, thanks to their assembly method and flow pattern, reduce pleat damage at the pleat edges of the filter membrane layer.

[0024] In one aspect, the following description relates to a wind-pleat filter useful for reducing the amount of trace impurities in a fluid. The wind-pleat filter includes a multilayer filter membrane assembly including a first porous filter membrane layer and a second porous filter membrane layer, each of which includes an inlet surface, an outlet surface, a length, an inlet end extending along the length, an outlet end extending along the length, and a width between the inlet and outlet ends. The porous filter membrane layer assembly is wound around a central axis along its length to form the wind-pleat filter. The inlet surface of the first porous filter membrane layer faces the inlet surface of the second porous filter membrane layer. The filter also includes a wind inlet pleat including the inlet ends of adjacent filter membrane layers at the inlet end of the wind-pleat filter, and a wind outlet pleat including the outlet ends of adjacent filter membrane layers at the outlet end of the wind-pleat filter.

[0025] In another aspect, the description relates to a wind-pleat filter. The filter includes a multi-layer filter membrane assembly including a first porous filter membrane layer and a second porous filter membrane layer, each of which has an inlet surface, an outlet surface, a length, an inlet end extending along the length, an outlet end extending along the length, and a width between the inlet and outlet ends. The porous filter membrane layer assembly is wound around a central axis along its length to form a wind-pleat filter including multiple porous filter membrane layer assembly windings. The inlet surface of the first porous filter membrane layer faces the inlet surface of the second porous filter membrane layer. The filter also includes pleats including an outlet end of the first porous filter membrane layer and an outlet end of an adjacent porous filter membrane layer, the pleats including folds, welds, or a thermoplastic binder; a wound inlet end of the membrane layer at the inlet end of the wind-pleat filter; and a wound outlet end of the membrane layer at the outlet end of the wind-pleat filter.

[0026] Another aspect relates to a method of removing impurities from a fluid by passing the fluid containing trace impurities through a filter as described, such that the filter membrane retains a portion of the trace impurities.

[0027] In another aspect, the description relates to a method of preparing a wind-pleat filter, wherein the multi-layer filter membrane assembly includes a first porous filter membrane layer and a second porous filter membrane layer, each of the first porous filter membrane layer and the second porous filter membrane layer having an inlet surface, an outlet surface, a length, an inlet end extending along the length, an outlet end extending along the length, and a width between the inlet and outlet ends, wherein the inlet surface of the first porous filter membrane layer faces the inlet surface of the second porous filter membrane layer, the method including: winding the multi-layer filter membrane assembly to form a wind-pleat filter comprising a plurality of multi-layer filter membrane layer windings; forming a pleat including the outlet end of the first porous filter membrane layer and the outlet end of an adjacent porous filter membrane layer, the pleat including a fold, a weld, or a thermoplastic binder; and forming a pleat including the inlet end of the first porous filter membrane layer and the inlet end of the adjacent porous filter membrane layer, the pleat including the fold, a weld, or a thermoplastic binder.

[0028] In yet another aspect, the description relates to a method for preparing a roll-pleated filter from a plurality of membrane layers, the method including aligning leading and trailing edges of the membrane layers, rolling the layers along their length to form a wind-roll filter having a plurality of wraps, and connecting adjacent leading and trailing edges of alternating membrane layers of the wraps. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a cross-sectional view of an example roll-pleat filter as described in a filter housing. [Figure 2A-2B] FIG. 1 is a side perspective view of an example multi-layer filter membrane assembly as described. [Figure 3] FIG. 1 is an end view of an example roll-pleat filter as described. [Figure 4A] FIG. 1 is an end perspective view of an example roll-pleat filter as described. [Figure 4B]4 is a cross-sectional view of an example portion of the example roll-pleat filter of FIG. 3 as described. [Figures 5A-5F] 1 illustrates steps of an example method for preparing a roll-pleated filter as described. [Figures 6A-6D] 1 shows an example of the automated steps of a method for preparing a roll-pleated filter. [Figure 7] 1 illustrates the alignment of layers in a roll pleated filter. [Figures 8A-8C] 1 shows an example filter product as described, including a roll-pleat filter and housing. DETAILED DESCRIPTION OF THE INVENTION

[0030] All figures are schematic and not to scale.

[0031] The present invention provides a wind-pleat filter, sometimes referred to herein as a "roll-pleat filter," which includes a cylindrical filter structure including a multi-layer filter membrane assembly that is wound (or "rolled") along the length of the assembly around a central longitudinal axis of the wind-pleat filter. The multi-layer filter assembly includes multiple (at least two) filter membrane layers. In the wind-pleat filter configuration, first and second (front and back, or inlet and outlet) longitudinal ends of the filter layers are formed into first and second wind pleats that are located at opposite ends of the roll-pleat filter structure. Alternate ends of the filter membrane layers are formed (e.g., folded or connected) into pleats, and the membrane assembly is wound into a wound-pleat filter including wind inlet pleats and wind outlet pleats, with the inlet sides (inlet surfaces) of the filter membrane layers connected by the pleats on one side of the filter membrane layers and the outlet sides (outlet surfaces) of the filter membrane layers connected by the pleats on a second side (opposite side) of the filter membrane layers.

[0032] A multi-layer filter membrane assembly includes at least two filter membrane layers. Each of the two filter membrane layers has a length, a width, a thickness, a front end along the length (alternatively referred to as the "first" or "inlet" end), and a rear end along the length (alternatively referred to as the "second" or "outlet" end). Each membrane layer also has two opposite surfaces separated by the thickness of the membrane layer, one surface referred to herein as the front surface (alternatively referred to as the "first" or "inlet" surface) and one surface referred to as the rear surface (alternatively referred to as the "second" or "rear" surface).

[0033] When the filter layer is part of a multi-layer filter membrane assembly, the width, front ends, and rear ends of the two membranes are all substantially aligned along their length. The two (or more) membrane layers of the assembly are also flat along their width and face each other with the first (front) surface of a membrane layer facing the first (front) surface of an adjacent membrane layer.

[0034] A surface "facing" an adjacent surface means that the two surfaces are generally opposed and positioned parallel or substantially parallel. The two surfaces may be in direct opposing contact, or may face each other through an intermediate layer, such as a spacer layer, present between the two surfaces of adjacent filter membranes.

[0035] Thus, in addition to at least two filter membrane layers, one or more additional filtration or non-filtration layers, such as a spacer layer or one or more additional filter membrane layers, may be present in the assembly. A spacer layer may be present between a first membrane layer and an adjacent membrane layer (between the front surface of the first membrane layer and the front surface of the adjacent (second) membrane layer). Alternatively or additionally, a second spacer layer may be positioned on the rear surface (outlet surface) of a membrane layer such that when the layers are rolled, the second spacer layer will be positioned between the rear surface of the first membrane layer and the rear surface of the adjacent (second) membrane layer.

[0036] As desired, a wind-pleat filter may be designed for use to process fluid flow in only one direction ("unidirectional" use), or may be designed to be used to process fluid flow in either of two directions between an inlet and an outlet, i.e., a selected direction through the filter at the start of use that does not change during use.

[0037] In the form of a wound-pleat filter, the multi-layer filter layer assembly can form multiple wraps, where one "wrap" refers to a portion of the overall length of the multi-layer assembly that is wound around the central axis in one full rotation. A wound-pleat filter including multiple wraps is formed from two or more filter membrane layers of a wound multi-layer assembly that are positioned adjacent to one another. That is, generally, except for the innermost and outermost membrane layers, each filter membrane layer forms pleats at each of its two ends with the ends of its two adjacent filter membrane layers, one end of the filter membrane layer forms pleats with the end of one adjacent filter membrane layer, and a second end of the filter membrane layer forms pleats with the end of a different adjacent filter membrane layer.

[0038] Each filter layer has an inlet surface facing the inlet surface of an adjacent layer (opposite) and an outlet surface facing the outlet surface of a different adjacent layer (except for the innermost and outermost filter membrane layers). Two "adjacent" layers may be part of a single turn of the multi-layer filter assembly, or adjacent layers may be part of different turns, with the inner layer (closer to the center of the turn) or the outer layer (farther from the center of the turn). The innermost layer of the first inner turn will not have an adjacent layer on the inside, and the outermost layer of the last outer turn will not have an adjacent layer on the outside.

[0039] In an example wind-pleat filter, a filter membrane layer having a front surface facing the front surface of an adjacent membrane layer can form a pleat with the adjacent membrane layer at a second (rear) end of the two layers, and a filter membrane layer having a rear surface facing the rear surface of a second (different) adjacent membrane layer can form a pleat with the second (different) adjacent membrane layer at a first (front) end. In this arrangement, each filter membrane layer of the wind-pleat filter has a front surface facing the front surface of the first adjacent filter membrane layer, a rear surface facing the rear surface of the second adjacent filter membrane layer, a front end that forms a pleat with the front end of the second adjacent filter membrane layer, and a rear end that forms a pleat with the rear end of the first adjacent filter membrane layer.

[0040] The first (front) surface of each filter membrane layer opens to the first (front, inlet) filter end of the wind-roll filter and to an inlet space adjacent to and between the two opposing front (inlet) surfaces of a pair of adjacent filter membrane layers that are connected at their respective rear ends to form pleats. The inlet space and the first surface of each adjacent membrane open to, or are in fluid communication with, the first (front, inlet) filter end of the roll-pleated filter, and optionally, a spacer is positioned in the inlet space between the two opposing front surfaces of the pair of adjacent filter membrane layers. The inlet space may have a volume that can include a spacer layer between the two opposing first (front) surfaces, or it may have a volume of only the space between the two opposing first (front) surfaces without a spacer between the two opposing first (front) surfaces.

[0041] The second (rear) surface of each filter membrane layer is open to the second (rear, outlet) filter end of the wind-roll filter and to an outlet space adjacent to and located between the two opposing rear surfaces of a pair of adjacent filter membrane layers that are connected at their first (front, inlet) ends to form pleats. The outlet space and the second (rear, outlet) surface of each of the two adjacent filter membrane layers are in fluid communication with the second filter end of the wind-roll filter, optionally through a spacer. The outlet space may have a volume that may include a spacer layer between the two opposing second (rear) surfaces, or it may have a volume of only the space between the two opposing second (rear) surfaces without a spacer between the two opposing second (rear) surfaces.

[0042] In use, a fluid (liquid or gas) is introduced into the first filter end of the roll-pleat filter and is exposed to the inlet space and the inlet surface of the membrane. The fluid can flow into the inlet space and contact the front (inlet) side of the filter membrane layer. The fluid can flow through the filter membrane layer, traversing the thickness of the layer and the second (outlet) surface of the filter membrane layer, to flow into the outlet space and to the second (outlet) filter end of the roll-pleat filter. The roll-pleat filter can be constructed as a dead-end filter with a filter housing that requires all fluid passing into the housing inlet to pass through the filter membrane layer of the roll-pleat filter before leaving the filter housing through the housing outlet.

[0043] The roll-pleated filter as described differs from the typical "pleated cylindrical filter" design found in common commercial use. A "pleated cylindrical filter" refers to a filter that includes a cylindrical pleated filter element that includes a plurality of longitudinal (unwound) parallel pleats extending along the filter element in the direction of the central axis of the pleated cylindrical filter, and also includes a central channel that is open in the direction along the central axis of the pleated cylindrical filter. Although pleated cylindrical filters can be used as "dead-end" filters, the pleats in this design are not located at the wound end of the pleated cylindrical filter, but extend in alignment with the central axis of the cylinder. In use, fluid flows through the central channel ("central opening") of the pleated cylindrical filter either before or after passing through the pleated filter element.

[0044] In contrast, with the wind-pleat filter designs described herein in this application, fluid does not need to flow through or reside within the central opening of the filter. A central opening is not required, and the space along the central axis of the roll-pleat filter may be used for other purposes, such as to contain an additional length of wound filter membrane layer or to contain one or more devices that enhance or monitor the performance of the roll-pleat filter.

[0045] As non-limiting examples, a roll-pleat filter may include any of the following in space along the central axis of the filter: a sensor for monitoring the filter life of the roll-pleat filter during use; a monitor for sensing trapped gas in the filter housing; a vent mechanism for removing trapped gas; a drainage mechanism for removing trapped liquid for repair or the like; an optical particle counter for measuring particles in a sample of fluid passing through the filter; a sensor for measuring fluid capacitance, pressure, or temperature; or a sensor for measuring any other condition or parameter that would be useful to measure during use of the filter.

[0046] The described wound-pleat filter also differs from typical "spiral-wound filter" designs commonly found in commercial use for specific applications. "Spiral-wound filter" refers to a common commercial filter product that includes a spirally wound filter membrane with fluid presence and flow through a central channel (opening) of the filter, without alternating pleated (folded, bonded, welded, or otherwise connected) wind ends at opposite filter ends of the wind cylinder. Examples of these types of spiral-wound filter products are commonly used in reverse osmosis filtration systems with bypass or recirculation modes of operation. Typical systems containing these types of spiral-wound filter membranes include multiple flow paths within the filter housing, including not only a flow path through the filter membrane within the housing (for "permeate"), but also an alternative flow path that bypasses the filter membrane (for unfiltered "retentate" or "retentate"). Fluid entering a housing containing this type of spiral-wound filter can exit the filter housing without passing through the filter membrane.

[0047] Roll-pleat filters can be made from any multilayer membrane assembly assembled to include any useful number of membrane layers (e.g., two, four, six, etc.), have any useful length or width, and include any useful number of wraps. Example filters can be prepared from multilayer membrane assemblies having lengths of 1 to 100 meters, e.g., from 2 meters to 20 or 50 meters. Example roll-pleat filters can include 1 to 500 wraps, e.g., 2 to 300 wraps. Roll-pleat filters can be wound around a central axis with essentially no open space along the central axis, or with spaces having any useful diameter or relatively small diameters, such as openings with diameters in the range of 0.125 to 1 inch. The membrane assemblies and layers of the membrane assemblies can have widths (which result in the "length" of the wound filter) in the range of 10 to 100 centimeters, e.g., 20 to 50 centimeters. Example membranes can have a total surface area at the inlet surface ranging from 0.1 or 0.5 square meters to 100 square meters, for example 10 to 80 square meters, and can be selected by the number of wraps.

[0048] An example of a roll-pleat filter as described in a filter housing is shown in FIG. 1. As shown, filter assembly 30 includes filter (e.g., filter cartridge) 10 and housing 32. Housing 32 includes an inlet 34 at one end (bottom) of housing 32 and an outlet 36 at a second end (top) of housing 32. Housing 32 defines an interior space 38 that is adapted to accommodate filter 10 in a manner that requires fluid entering housing inlet 34 to pass through the filter membrane layer of filter 10 before passing through housing outlet 36; i.e., filter assembly 30 is configured as a "dead-end" filter assembly. Filter 30 may optionally include additional inlets and outlets (e.g., vents) that are typically present as part of a dead-end filter and that are used intermittently to vent or drain the housing.

[0049] Filter 10 is a roll-pleat filter as described herein. Filter 10 includes multiple rolled filter membrane layers 40 with alternating pleated (folded, bonded, or otherwise connected) edges. The filter membrane layers 40 are rolled around a central axis to form filter 10. An optional axial space 58 is present along the central axis and may or may not be connected to interior space 38. During use, fluid is not forced to flow through axial space 58 in a manner that prevents fluid from passing through filter membrane layers 40.

[0050] Each membrane layer 40 has a length (in the winding direction, not shown), a width (w), a thickness, a first (leading) end 42 along the winding length (alternatively referred to as the "first" or "entrance" end), and a second (trailing) end 44 also along the winding length (alternatively referred to as the "second" or "exit" end). Each membrane layer 40 also has two opposite surfaces (46, 48) separated by the thickness of the filter membrane layer, one surface referred to herein as the leading surface 46 (alternatively referred to as the "first" or "entrance" surface) and a second surface referred to as the trailing surface 48 (alternatively referred to as the "second" or "trailing" surface).

[0051] The inlet space 60 is the space adjacent to and between the two opposing front surfaces 46 of alternating pairs of adjacent filter membrane layers 40 that are part of the wind pleats (e.g., "wind outlet pleats") 54 at their respective second (rear) ends 44. The inlet space 60 also includes a portion of the interior space 38 within the housing 32 between the inlet 34 and the inlet surfaces 46 of the membrane layers 40. Optionally, although not shown, a spacer layer may be included in the inlet space 60 between the opposing inlet surfaces 46 of the alternating pairs of adjacent membrane layers 40.

[0052] The outlet space 62 is the space adjacent to and between the two opposing rear surfaces 48 of adjacent filter membrane layers 40 that are part of the wind pleats (e.g., "wind inlet pleats") 52 at their respective first (front, inlet) ends 42. The outlet space 62 also includes a portion of the interior space 38 within the housing 32 that is between the outlet 36 and the outlet surfaces 48 of the membrane layers 40. Optionally, although not shown, a spacer layer may be included in the outlet space 62 between the opposing outlet surfaces 48 of alternating adjacent membrane layers 40.

[0053] Each membrane layer 40 (except for the innermost and outermost turns) forms a wound inlet pleat 52 with an adjacent membrane layer 40 at the end of the filter membrane layer and at one end (the inlet end) of the roll-pleated filter. The inlet end 42 forms a rolled inlet pleat 52, which may be a fold between the inlet ends 42 of alternating adjacent membrane layers 40, a binder applied to the inlet ends 42 of alternating adjacent membrane layers 40, or a molten polymer at the inlet ends 42 of alternating adjacent membrane layers 40.

[0054] Each membrane layer 40 (except for the innermost and outermost wraps) forms a wound outlet pleat 54 with an adjacent membrane layer 40 at the opposite end (outlet end) of the roll-pleated filter. The outlet ends 44 form a rolled outlet pleat 54, which may be a fold between the outlet ends 44 of alternating adjacent membrane layers 40, a binder applied to the outlet ends 44 of alternating adjacent membrane layers 40, or a molten polymer at the inlet ends 44 of alternating adjacent membrane layers 40.

[0055] Each membrane layer 40 (except for the innermost and outermost turns) is connected to two adjacent membrane layers 40 at edges 42 and 44 in an alternating manner. As shown, adjacent membranes 40 with their first surfaces 46 facing each other form a wind outlet pleat 54 at their second (rear, outlet) end 44. Adjacent membranes 40 with their second surfaces 48 facing each other form a wind inlet pleat 52 at their first (front, inlet) end 42. This arrangement of the pleated first (front, inlet) and second (rear, outlet) ends of adjacent filter membrane layers is referred to as the alternating pleat edge arrangement of adjacent filter layer membranes in a wind-pleat filter.

[0056] Connected pairs of adjacent filter membrane layer edges can be included as part of a wound pleat formed by any technique or structure. The pleats are generally in the form of connected or folded edges of adjacent membrane layers that are folded to form pleats at the connected edges, forming closed ends of the inlet or outlet spaces of the wound-pleat filter, allowing fluid to flow through the inlet and filter membrane layers to the outlet spaces and preventing fluid from bypassing the filter membrane layers.

[0057] The pleats between the edges of adjacent membrane layers may be formed by or include a binder, such as a solvent-free thermoplastic binder, disposed between or in contact with the front or rear ends of two adjacent filter membrane layers. The binder is a thermoplastic material that can be reversibly liquefied and solidified by the application and removal of thermal energy. The binder is preferably a 100 percent solids thermoplastic polymer without volatile organic solvents or other chemical components that may be released in gas form from the binder during use of the filter. Exemplary binders include thermoplastic polyolefins, which may be fluorinated or perfluorinated. Specific examples include polypropylene, polyethylene, polytetrafluoroethylene (PTFE), and polyfluoroalkylene (PFA). Binders of any polymer composition may contain a large amount of thermoplastic polymer and a small amount of organic solvent, such as at least 95, 99, or 99.9 weight percent thermoplastic solids and less than 5, 1, or 0.1 weight percent organic solvent based on the total weight of the binder.

[0058] Preferred polymer thermoplastics may also have advantages during automated assembly of roll-pleated filters, allowing for a small amount of flow of the heated thermoplastic binder after the thermoplastic is applied to the membrane layers. When winding pairs of membrane layers with a binder used to attach the adjacent ends of the membrane layers, the membrane layers can be wound at slightly different lengths or can have the same length. Each membrane layer can be sealed or otherwise adhered to the core on opposite sides of the roll, and resealed on the opposite side of the roll, so that the membrane layers are equal in length when the layers are properly sealed and there is no fluid path other than through either membrane layer to proceed from the inlet to the outlet of the roll-pleated filter. Preferred thermoplastic binders can be heated and capable of maintaining their ability to flow for a short period of time after being applied to the ends of the attached membrane layers, since the continued flowability of the binder facilitates the winding process that occurs after application of the binder to the layers by allowing the binder to flow to accommodate a slightly longer length for the outer layers of the membrane assembly. The membrane layers can be the same width. Each film layer can be sealed across its width on opposite sides of the core at the beginning of the roll and on opposite sides towards the end of the roll.

[0059] In other examples, the pleats may be in the form of folds between two adjacent membrane layers. A piece of porous filter membrane material may be folded along its length to form two adjacent filter membrane layers from the piece, with a folded pleat connecting the two layers at the edges. The folded piece of membrane material becomes two adjacent layers of a multi-layer porous filter membrane assembly. Each layer has an inlet surface and an outlet surface, and each layer has an inlet end along its length and an outlet end along its length that are aligned. The adjacent inlet ends (or outlet ends) of adjacent filter membrane layers remain connected, forming a fold pleat along the length of the adjacent filter membrane layers.

[0060] In yet another example, the front (inlet) or back (outlet) edges of adjacent filter membrane layers may be connected to form pleats by molten polymer of the adjacent (polymeric) membrane layers, which may be formed by any melting technique, such as laser welding or sonic welding.

[0061] 1 , in use, fluid can flow into the filter assembly 30 through the inlet 34 and into the inlet volume 60. The fluid must pass from the inlet to the inlet volume 60, through the inlet volume 60, and through one of the membrane layers 40 to enter the outlet volume 62 (see arrows). From the outlet volume 62, the fluid is allowed to exit the filter assembly 30 by passing through the outlet 36 of the housing 32.

[0062] A roll-pleated filter as described can be prepared by preparing a multilayer membrane assembly having at least two membrane layers with substantially aligned front and rear ends along its length and substantially aligned widths and lengths, rolling the assembly along its length, and forming pleats at the front and rear ends of alternating membrane layers. The step of forming pleats at the front and rear ends of adjacent alternating membrane layers can be performed before, during, or after rolling the assembly. Useful multilayer membrane assemblies include at least two filter membrane layers, such as a single pair of two filter membrane layers (see FIG. 2A), and may include three or more filter membrane layers (see FIG. 2B).

[0063] 2A shows an example of a multi-layer assembly as described. Multi-layer assembly 120 includes two filter membrane layers having aligned lengths and aligned edges extending along the lengths. Filter membrane layer 102 and filter membrane layer 104 each have a length L and a width w. Membrane layer 102 includes a front end 106 extending along length L and a rear end 118 also extending along length L. Membrane layer 104 includes a front end 110 extending along length L and a rear end 122 also extending along length L. The rear end 118 of membrane 102 and the rear end 122 of membrane 104 are connected (e.g., by folding as shown) at rear pleat 108 along the entire length L of membrane layer 102 and membrane layer 104.

[0064] The trailing edge 118 of the membrane layer 102 and the trailing edge 122 of the membrane layer 104 can form the pleat 108 by any useful method or material. By way of example, the trailing edge 122 can be connected to the trailing edge 118 to form the pleat 108 by any one or more of: a binder, such as a thermoplastic polymer binder, placed in contact with the two layers at their respective trailing edges; a molten polymer from two opposing membrane layers at the membrane edge (e.g., formed by laser welding two polymer membranes at their edges); or a fold formed along the length of a double-wide piece of membrane (having a width of 2w) that, when folded along the center of its width and along the length L, forms an assembly 120 with two opposing membrane layers 102 and 104, each having a width w, with the folded pleat 108 at the edges 118 and 122.

[0065] A roll-pleated filter as described can be prepared by rolling the assembly 120 along the length of the assembly and forming pleats at the front (inlet) and back (outlet) ends of the alternating membrane layers.

[0066] 2B shows an example of a multi-layer assembly 150 including four filter membrane layers with aligned lengths and aligned edges. Filter membrane layers 102, 104, 103, and 105 each have a length L and a width w. The membrane layers include a leading edge 111 where leading edges of adjacent filter membranes fold together to form a pleat, and a trailing edge 113 where trailing edges of different adjacent membrane layers fold together to form a pleat. Each membrane has an inlet surface 121 (the lower side of the membrane layer as shown) that faces the inlet surface 121 of the adjacent membrane layer. Each membrane has an outlet surface 123 (the upper side of the membrane layer as shown) opposite the inlet surface. Membranes 103 and 104 have outlet surfaces (the upper side of the membrane layer as shown) 123 that face each other.

[0067] A roll-pleated filter as described can be prepared by rolling the assembly 150 along the length of the assembly and forming pleats at the leading and trailing edges of the alternating membrane layers.

[0068] Referring to FIG. 3 , shown is an end view of a roll-pleat filter 160 formed from the multilayer membrane assembly 120 (alternatively, assembly 150). The roll-pleat filter 160 is formed by rolling the assembly 120 along a length L starting at the inner winding end 114, rolling along the entire length L to the outer winding end 116, and bonding together widthwise edges 140 and 142 and 144 and 146 along the entire width (w). The membrane layers 102 and 104 are aligned with the front surface 130 of membrane layer 104 oriented toward the (opposing) front surface 132 of membrane layer 102 (see dashed line in FIG. 3 ). When rolled along the length L, the assembly 120 forms the roll-pleat assembly 160 with the rear surface 134 of layer 104 facing the rear surface 136 of layer 102. Optional spacer layers may be included between the surfaces of adjacent membrane layers, but are not shown in FIG. 3 .

[0069] 4A and 4B show an end perspective view and a side cross-sectional view, respectively, of an example roll-pleat filter made from a multi-layer assembly including two filter membrane layers 240 and two spacer layers 250, 252, with the leading edges of the membrane layers and the trailing edges of the membrane layers alternately formed into pleats using a thermoplastic binder.

[0070] 4A and 4B, a roll-pleat filter 210 includes a plurality of wind-pleat filter membrane layers 240. Each filter membrane layer 240 is separated by an inlet spacer layer 250 at adjacent inlet surfaces of the membrane layer, which forms an inlet space between the two adjacent inlet surfaces. Each filter membrane layer 240 is separated by an outlet spacer layer 252 at adjacent outlet surfaces of the membrane layer, which forms an outlet space between the two adjacent outlet surfaces of the membrane layer. Each membrane layer 240 has a length, a width (w), a thickness, a first (front) end 242 along its length (alternatively referred to as the "first" end or "inlet" end), and a second (rear) end 244 along its length (alternatively referred to as the "second" end or "outlet" end). Each membrane layer 240 also has two opposite surfaces (246, 248 as shown in FIG. 4B) separated by the thickness of the filter membrane layer, one surface referred to herein as the front surface 246 (alternatively referred to as the "first" or "inlet" surface) and the second surface referred to as the back surface 248 (alternatively referred to as the "second" or "back" surface).

[0071] Each membrane layer 240 (other than the innermost and outermost turns) is connected to an adjacent membrane layer 240 at one end (the inlet end) of the roll-pleat filter by a thermoplastic binder 220 to form a pleat. Each membrane layer 240 is connected in an alternating manner to a second adjacent membrane layer 240 at a second end (the outlet end) of the roll-pleat filter to form a second pleat. For example, as shown, first (front, inlet) ends 242 of adjacent membranes 240 separated by spacers 252 and having second surfaces 248 facing each other are connected at the inlet end 262 by a thermoplastic binder 220 extending along the wind length L of the wind-pleat filter 210 to form a wound inlet pleat. The second (rear, outlet) ends 244 of adjacent membrane layers 240 having first surfaces 246 facing each other (separated by spacers 250) are connected by thermoplastic material 220 at the opposite end (outlet end 264) of the wind-pleat filter 210 to form a wound outlet pleat. This arrangement of the first (front, inlet) and second (rear, outlet) edges of adjacent filter membrane layers to form a pleat is an arrangement of alternating connected ends or alternating pleat ends of adjacent filter layer membranes of the wind-pleat filter 210. The beginning and end of the roll must also be properly sealed to eliminate bypass.

[0072] The roll-pleat filter as described can be prepared by any method useful for combining filter membrane layers and optional spacer layers in a manner to form the roll-pleat filter as described. Generally, by a useful method, a roll-pleat filter can be prepared from multiple membrane layers, including at least two membrane layers, and optional spacer layers, by steps that include, in any useful order, aligning the front and rear longitudinal edges of the membrane layers, rolling the layers along the length of the layers to form a wind-roll filter having multiple windings, and forming pleats between adjacent front and rear edges of alternating membrane layers of the windings. The step of forming pleats between the edges of adjacent alternating membrane layers can be performed before, during, or after rolling the layers to form the roll-pleat filter. The widthwise edges at the beginning and end of the length must also be sealed across the entire width, for example, by a bonding agent or welding (laser welds, sonic welding), etc. These steps can be performed in a batchwise manner or using an automated system that performs the steps of forming pleats (e.g., by joining ends together or folding a larger membrane into two membrane layers in a multi-layer assembly), aligning the layers, and winding the layers in a continuous or semi-continuous manner.

[0073] As a more specific option, a liquefied (heated, melted) polymer binder may be applied to the edges of two adjacent filter membrane layers to form pleats, i.e., placed in contact with each other and the binder, just before the two bonded and pleated layers are wound to form a wind-roll filter. First, a quantity of heated, flowable polymer binder is applied to the location between the two membrane layers at the adjacent edges, and the two edges are brought into contact with the binder to connect the edges and form pleats. Immediately after applying the binder, the layers are rolled into a roll. The rolling is performed immediately after applying the liquefied polymer binder while the binder remains heated and soft and flowable, so that the layers and binder are rolled before the binder cools and solidifies to allow for some longitudinal movement between the layers during the roll due to differences in the winding lengths of the two membrane layers. The binder has a melting temperature less than (lower than) the melting temperature of the membrane layers and optional spacing layer.

[0074] As a different option, a liquefied (heated, melted) polymer binder can be added to one end of a pair of adjacent membrane layers in one step, and the binder can be allowed to cool and solidify. The two layers can then be wound into a roll while the binder remains cool and non-flowable. After winding, heat can be applied to the polymer binder at the wound end to liquefy (melt) the binder at the end, forming pleats and sealing the adjacent layers together at the end. This method can be used to seal the inlet end, the outlet end, or both.

[0075] As yet another option, the ends of adjacent membrane layers of a wound multilayer membrane assembly may be connected using welding or bonding agents at the outer layers of the winding where multiple membrane layers and optional spacer layers are formed into a winding to form pleats as the assembly is wound. See, for example, FIGS. 6A and 6B below. For example, generally, membrane layer 1, membrane layer 2, support (spacer layer) layer 1, and support (spacer layer) layer 2 may be fed into the winding by joining the outer layers of the winding at different locations on the outer surface of the winding. At one location on the winding, membrane layer 1, membrane layer 2, and support 1 are accessible as three exposed layers at one winding end of the winding so that a heat source or laser can be applied to melt the two membrane layers and the support between the two membrane layers at the first end of the winding, thereby connecting and sealing the aligned longitudinal ends of the three layers together (forming pleats). At opposite ends of the winding, membrane layer 1, membrane layer 2, and support 2 are accessible as three exposed layers so that a heat source or laser can be applied to melt the two membrane layers and the support between the two membrane layers, thereby connecting and sealing the aligned longitudinal ends of the three layers together (forming pleats).

[0076] One non-limiting example of a useful sequence of steps for preparing a roll-pleated filter is shown in Figures 5A-5F.

[0077] In a first step, a filter membrane layer 240 is provided having a front (inlet) longitudinal end 242, a rear (outlet) longitudinal end 244, a front (inlet) surface 246, and a rear (outlet) surface 248. The filter membrane layer 240 has a length (not shown), a width (w), and a thickness.

[0078] A thermoplastic binder 220 is applied to the trailing ends 244 along the length (not shown) of the filter membrane layers 240. See Figure 5B. In an alternative embodiment, the trailing ends 244 of adjacent membrane layers 240 may be connected by molten polymer of the layers, which may be formed, for example, by laser welding.

[0079] Generally, in this or other examples, the bonding agent can be applied to the layers of the assembly in any manner that provides for effective formation of the pleats. The bonding agent may be applied to the surface of the support (spacer) layer, to the membrane layer parallel to the edge of the support layer (as depicted in FIGS. 4A and 4B), or to one or both of the adjacent membrane surfaces, to one or both of the support surfaces or all of the surfaces, or any combination thereof or herein. Alternatively, the membrane layers may be fused together to form welds at the pleat locations.

[0080] According to some specific examples, a support layer is present between the joining edges, and a binder is applied between the joining edges and the support layer in a manner to provide adhesion through or in conjunction with the support layer. In other examples, the binder is placed along the edge of an adjacent support layer or adjacent to the support layer so that the support layer is contacted by the binder to hold the support layer in place and adhere it to its corresponding membrane layer. In other embodiments, the binder may not contact the support material until after the next membrane layer is applied with pressure and optional heat to extrude the binder and expand over a small portion of the length of the device so that it contacts and potentially captures the support material. The process of compressing the binder under the next membrane layer may also require the binder to be applied away from the actual membrane edge to ensure that the binder does not overflow the end of the roll or that it does not overflow the end of the roll in an amount that reduces flow performance or adversely affects the assembly process.

[0081] Referring again to the figure, a first front spacer layer 250 is disposed across the front surface 246 of the layer 240 between the front end 242 and the rear end 244. See Figure 5C.

[0082] A second filter membrane layer 240 having a front end 242, a rear end 244, a front surface 246, and a rear surface 248 is positioned over the front spacer layer 250 with the front surface 246 of the second filter membrane layer 240 contacting the surface of the front spacer layer 250. See Figure 5D.

[0083] A thermoplastic binder 220 is applied to the front end 242 of the second membrane 240 along the length of the front end 242. See Figure 5E.

[0084] A second (outlet) spacer layer 252 is disposed over the rear (outlet) surface 248 of the second membrane 240. See Figure 5F.

[0085] All of the membrane layer 240 and spacer layers 250, 252 are sealed, such as with a binder, at one end of their length (the inner end) and along their width. The assembled layers, such as those shown in FIG. 5F, are rolled along their length from the end sealed with the binder (the inner end) into a cylindrical roll-pleat filter, such as the cylindrical roll-pleat filter of FIG. 4A. All of the membrane layers and spacer layers at the exposed end of their length (the outer end) are sealed, such as with a binder, at the exposed end of their length. The cylindrical roll-pleat filter is inserted into a cylindrical housing with the leading wind pleat end at the inlet end of the housing and the trailing wind pleat end at the outlet end of the housing, the housing adapted to allow fluid flow through the filter membrane layer 240 as it passes from the housing inlet to the housing outlet.

[0086] 6A and 6B illustrate steps for forming a roll-pleated filter using a continuous or semi-continuous process. As shown, system 300 includes a membrane 1 source 310, a membrane 2 source 312, a spacer 1 source 314, and a spacer 2 source 316. These sources provide membrane layer 311, membrane layer 313, spacer layer 315, and spacer layer 317 to roll 320.

[0087] During the formation of roll 320 from membrane layer 311, membrane layer 313, spacer layer 315, and spacer layer 317, laser welds to form pleats are formed at alternate ends of each of the two membrane layers using laser welders 340 and 342, one at the entrance end 350 of roll 320 and the other at the exit end 352 of roll 320.

[0088] More specifically, with reference to FIG. 6B, membrane layer 311, membrane layer 313, support (spacer layer) layer 315, and support (spacer layer) layer 317 are each fed from respective source rolls 310, 312, 314, and 316 onto roll 320. The entrance edges of each of membrane layer 311, membrane layer 313, and support layer 317 are accessible at the bottom (as shown) of roll 320 as three exposed layers outside winding entrance edge 350. Laser 340 applies laser beam 341 to these three layers (see FIG. 6B) to melt, connect, and seal the entrance edges of the three layers and form pleats at the entrance edges of the three layers. In FIG. 6B, the shading across the entrance edges of layers 311, 317, and 313 represents the laser welds formed between alternating entrance edges of wind roll 320.

[0089] At the opposite end of roll 320, at exit end 352, a similar arrangement is used, and laser 342 can be used to form seals and pleats at the connected edges of the exit ends of layers 311 and 315, with spacer 315 between layers 311 and 315.

[0090] Lasers 340 and 342 can be selected to produce laser beams in a frequency range that is effective to target the appropriate layers in roll 320, melt the edges of the targeted layers, and create the necessary seals and form the pleats.

[0091] Another example method is shown in Figures 6C and 6D. This example uses a bonding agent to bond alternating edges of each of two membranes together to form pleats at the membrane edges, and additionally includes steps and equipment for applying the bonding agent to the bonded area between the membranes uniformly and with consistent placement and dimensions at the membrane edges. As shown, system 350 includes a membrane 1 supply 310, a membrane 2 supply 312, a spacer 1 supply 314, and a spacer 2 supply 316. These sources provide membrane layer 311, membrane layer 313, spacer layer 315, and spacer layer 317 to roll 320.

[0092] During the formation of roll 320 from membrane layer 311, membrane layer 313, spacer layer 315, and spacer layer 317, bonding material 348 is applied along the edge surfaces of each of the two membrane layers 311, 313 at alternating edges using extruders 344 and 346. A bonding agent 348 (e.g., a heated thermoplastic) is applied by extrusion along the edges of the membrane layers to the surfaces of membrane layers 311, 313. At those edges, spacer layers 315, 317 are not present between the membrane layers; that is, the edge of spacer layer 315 is offset from the edge of membrane layer 311 at exit end 352 to allow bonding agent 348 to be disposed between membrane layers 311 and 313, and the edge of spacer layer 317 is offset from the edge of membrane layer 313 at entrance end 350 to allow bonding agent 348 to be disposed between membrane layers 311 and 313.

[0093] The arrangement uses a bonding agent 348 to bond alternating surfaces together at the edges of membranes 311 and 313, forming alternating pleated edges between membranes 311 and 313, one pleated edge at the entrance end 350 of roll 320 and one pleated edge at the exit end 352 of roll 320. Roller assemblies 360a and 360b contact the outer membrane layers 311, 313 and spacer layers 315, 317 on opposite sides of roll 320 and rotate in opposite directions to roll 320 during assembly. Each roller assembly 360a, 360b includes a heating roller 362 and a smoothing roller 364. In other embodiments, the heating roller and smoothing roller are identical, i.e., continuous along the width.

[0094] 6D, membrane layer 311 and support (spacer layer) layer 315 are fed onto roll 320 before being transferred between roll 320 and roller assembly 360a on one side of roll 320. Membrane layer 313 and support (spacer layer) layer 317 are fed onto roll 320 before being transferred between roll 320 and roller assembly 360b.

[0095] The edge of support layer 315 is spaced laterally from the edge of membrane layer 311 at outlet end 352 to form a bonding surface 321 on the upper surface (as shown) of membrane layer 311 for applying bonding agent 348 so as to place bonding agent 348 in contact with the two surfaces of membranes 311 and 313. Similarly, the edge of support layer 317 is spaced laterally from the edge of membrane layer 313 at inlet end 350 to form a bonding surface 323 for applying bonding agent 348 so as to place bonding agent 348 in contact with the opposing surfaces of both membranes 311 and 313.

[0096] As membrane layer 313 (positioned above support layer 317 as shown) wraps around roll 320, it passes through extruder 344 and a quantity of binder 348b is applied to bonding surface 323 at the edge of membrane layer 313 at entrance end 350. Support layer 317 and membrane layer 313, with binder 348b applied along bonding surface 323, are curled up on roll 320 and brought into contact with the bottom surface (as shown) of membrane 311 on the opposite side of roll 320, which bottom surface contacts support layer 317 and binder 348b, forming pleats between the two membranes 311 and 313 at entrance end 350. As the bottom surface of membrane layer 311 contacts binder 348 applied to bonding surface 323 of membrane 313, roller 362a applies pressure, along with optional heat, to the membrane and binder 348b to form a smooth, uniform layer of binder material 348b between the two opposing membrane surfaces at inlet end 350. Simultaneously, smoothing roller 364a contacts the top (outer) surface of support layer 315, mechanically adjusting the position of roller 362a and extruder 344 relative to roll 320 as roll 320 increases in diameter.

[0097] A similar process takes place at the exit end 352 (not fully visible in FIG. 6D ). As the membrane layer 311 (positioned below the support layer 315 as shown) wraps around the roll 320, it passes through the extruder 346, and an amount of binder 348 a is applied to the bonding surface 321 at the edge of the membrane layer 311 at the exit end. The support layer 315 and the membrane layer 311, with binder 348 a applied along the bonding surface 321, are curled up on the roll 320 and, on the opposite side of the roll 320 (not visible), brought into contact with the surface of the membrane 313, which contacts the support layer 315 and binder 348 a, forming pleats between the two membranes at the exit end 352. As the surface of membrane layer 313 contacts binder 348 applied to bonding surface 321 of membrane 311, roller 362 applies pressure, along with optional heat, to the membrane and binder to form a smooth, uniform layer of binder material 348 between the two opposing membrane surfaces at inlet end 350. Simultaneously, smoothing roller 364 contacts the upper (outer) surface of support layer 315, mechanically adjusting the position of roller 362 and extruder 344 relative to roll 320 as the diameter of roll 320 increases.

[0098] System 350 additionally controls the alignment of the edges of membranes 311 and 313 and support layers 315 and 317 as the membranes and support layers are wound onto roll 320. The degree of alignment of different layers can differentially affect the performance of the wound filter, particularly with respect to fluid flow through the wound filter. See FIG. 7. The alignment of the support layers may be less critical to the flow properties of the filter. The support layers can range from slightly protruding (extending beyond the membrane layers) to slightly recessed at either the inlet or outlet end without affecting fluid flow to or from the wound filter. Desirably, the edges of the wound ends of the support layers may extend beyond ("overhang" relative to) the edges of the adjacent wound membrane layers at the inlet or outlet ends by 1 or 3 millimeters or less. At the outlet end, the membrane layer may be allowed to protrude or recess slightly so that fluid flow from the outlet end does not cause the protruding portion of the membrane at the outlet end to fold over and interfere with fluid flow from the outlet end. Desirably, the edge of the wound edge of the membrane layer at the outlet end may extend beyond ("protrude" relative to) the edge of the adjacent wound support layer at the outlet end by no more than 1 or 3 millimeters.

[0099] If the membrane overhangs the adjacent support material layer at the inlet end too much, it may fold over and interfere with fluid flow into the support layer. See FIG. 7. In a preferred roll, the alignment of membranes 311 and 313 is controlled to create a high degree of edge alignment of membranes 311 and 313 at the inlet end 350. Desirably, the edge of the winding edge of the membrane layer at the inlet end may extend beyond ("overhang" relative to) the edge of the inlet end of the adjacent support layer by 1 millimeter or less, such as 0.5 millimeter or less. Alternatively or additionally, the edge of the winding edge of the membrane layer at the inlet end may extend beyond ("overhang" relative to) the edge of the winding edge of the next adjacent membrane layer by 1 millimeter or less, such as 0.5 millimeter or less, and be separated from the next adjacent membrane layer by the inlet end of the support layer or by a bonding agent; see FIG. 7. It should be noted that any mention of edge sealing throughout this document means that sealing may occur in proximity to or within the proximity of the edge of the membrane material layer. To maximize the amount of functional membrane area, it is desirable to adhere the membrane layers as close to the edges as possible. To limit the risk of binder protruding from the membrane layer and potentially inhibiting fluid flow to the support layer, it may be desirable to seal away from the edges to accommodate some variations in the process. It is desirable to have binder at the edges, or even to have it slightly protrude from the adjacent membrane layer, provided that it does not protrude enough to cause inhibition of flow to the adjacent support.

[0100] 7A, 7B, and 7C show an example of a filter assembly including a filter housing 270 having an inlet 272 and an outlet 274 leading to an interior space that houses a roll-pleat filter 210. As shown, filter assembly 280 contains filter 210 within housing 270. Housing 270 includes inlet 272 at one end of housing 270 (the bottom or inlet end (as shown)) and outlet 274 at a second end of housing 270 (the top or outlet end (as shown)). Housing 270 defines interior space 282, which houses filter 210 in a manner that requires fluid entering inlet 272 to pass through filter membrane layer 240 of filter 210 before it can pass through outlet 274; i.e., filter assembly 280 is configured as a dead-end filter assembly.

[0101] Filter 210 is a roll-pleat filter as described herein. Filter 210 includes multiple rolled filter membrane layers 240 formed by rolling multiple filter membrane layers and optional spacer layers around a central axis that includes an axial space 290, which, as shown, forms an open space along the central axis of filter 210 and is separated from an interior space 282 of filter assembly 280 that houses filter 210. Fluid flowing into inlet 272 does not enter axial space 290.

[0102] The axial space 290 does not contain fluid that has passed through the filter 210 and is advantageously available for use to allow additional functionality of the filter assembly 280. For example, the axial space 290 can house electronic sensors to monitor the condition or performance of the filter 210; for example, an electronic temperature sensor or electronic pressure sensor may be inserted through the axial space 290 and into the interior space 282 to enable direct or indirect monitoring of the condition of the filter 210 or the fluid passing through the interior space 282. Optionally, the axial space 290 may contain a solid structure, such as a cylindrical (e.g., tubular or solid) roll or rod, for additional structure or support of the filter along the central axis. As yet another option, the axial space 290 may be small (having a small diameter) or substantially absent, and the central (axial) portion of the roll-pleated membrane may include a rolled membrane layer beginning at approximately the location of the central axis.

[0103] The roll-pleat filter as described includes two or more filter membrane layers, each of which may be individually referred to herein as a "filter membrane" or simply a "membrane." Examples of useful filter membranes include membranes made from porous polymers, i.e., porous polymer filter membranes. Useful porous polymer membranes have two opposing surfaces (or opposing "sides") that function as an inlet surface and an outlet surface, with the thickness of the membrane lying between the two opposing surfaces. The membrane includes a porous structure across its thickness that allows fluid to flow from one side of the membrane (the inlet side) through the thickness of the membrane to the other side of the membrane (the outlet side). As fluid passes through the filter membrane, contaminants are removed from the fluid by the membrane. Thus, the membrane is permeable to the fluid, which may be a liquid or gas, as it passes through the membrane, but retains impurities present in the fluid.

[0104] Porous membranes contain interconnecting passageways (pores, channels, voids) in the form of a plurality of randomly oriented, tortuous pathways extending from one surface of the membrane to the opposite surface of the membrane. The passageways generally provide a tortuous channel or path through which the fluid to be filtered must pass and through which impurities can be removed from the fluid by sieving or non-sieving mechanisms.

[0105] Through a "sieving" filtration mechanism, a porous membrane can physically prevent impurities present in a fluid from passing through the membrane, i.e., entering and passing through the membrane and exiting the outlet side of the membrane. Impurities (e.g., particles) larger than the pores will be prevented from entering the membrane or may be physically prevented from passing through the membrane by the structure of the membrane. Impurities smaller than the membrane's pores may be able to enter the membrane, but the "sieving" mechanism may still prevent the impurities from passing through the membrane entirely by trapping them at the surface or within the tortuous path spaces within the membrane. The fluid being filtered will pass through the membrane, resulting in a flow of fluid containing a reduced amount of impurities removed by the filter through the sieving mechanism.

[0106] Another filtration mechanism, referred to as the "non-sieving" mechanism, involves impurities that are not removed by physical separation (sieving), but are instead attracted to the surface of the filter membrane by electrostatic or chemical interactions. Impurities such as dissolved or suspended chemical molecules (e.g., hydrocarbons, metals, or metal ions) can be chemically (by chelation mechanisms) or electrostatically attracted to the material of the filter membrane and retained by the filter material, especially if the molecules contain a charge (i.e., are anions, cations, etc.).

[0107] Useful membranes are sometimes referred to as "open-pore" membranes, in contrast to "closed-pore" membranes. Open-pore membranes can be in the form of thin films or sheets of extruded porous polymeric material having an open-pore porous structure of relatively uniform thickness, including a polymer matrix that defines numerous open "cells," which are three-dimensional void structures or pores. The open cells can be loosely referred to as interconnected openings, pores, channels, or passageways between adjacent cells for allowing fluid flow through the thickness of the membrane from one side (the inlet surface) to the other side (the outlet surface) of the membrane.

[0108] Porous polymer filter membranes can be constructed from porous polymer films having an open pore structure with pores having an average pore size that can be selected based on the anticipated use of the membrane, i.e., the type of fluid to be filtered or purified using the membrane. Typical pore sizes and average pore sizes for filters used to process high-purity liquids, such as for semiconductor materials or process fluids used in microprocessing devices, are in the micron or submicron range, such as from about 0.001 micron to about 10 microns. Example porous polymer filter membranes can have pores of a size (average pore size) that qualifies them as either microporous filter membranes or ultrafiltration membranes. Microporous membranes can have an average pore size ranging from about 0.05 micron to about 10 microns, with the pore size selected based on one or more factors, including the size or type of impurity particles to be removed, pressure and pressure drop requirements, flow requirements, and the viscosity requirements of the fluid to be processed by the filter. Ultrafiltration membranes can have an average pore size ranging from 0.001 micron to about 0.05 micron. Pore ​​size is often reported as the average pore size of the porous material, which can be measured by known techniques, such as by mercury intrusion porosimetry (MP), scanning electron microscopy (SEM), liquid displacement porosimetry (LLDP), or atomic force microscopy (AFM).

[0109] Filter membranes useful according to the present description can be made from any of a variety of polymers, including many polymers specifically known to be useful for preparing porous polymer filter membranes. Examples of currently known or preferred polymers include polyamides, polyimides, polyamide-polyimides, polysulfones such as polyethersulfone or polyphenylsulfone, fluoropolymers such as polyvinylidene fluoride, polyolefins such as polyethylene and polypropylene, fluorinated polymers such as perfluoroalkoxy (PFA), and nylons (e.g., nylon 6, nylon 66). Filter membranes can be made from a single type of polymer, or from two or more different polymers, either in a composite or blend, or as different layers of the membrane.

[0110] Suitable polyolefins include, for example, polyethylene (e.g., ultra-high molecular weight polyethylene (UPE)), polypropylene, α-polyolefins, poly-3-methyl-1-butene, poly-4-methyl-1-butene, and copolymers of ethylene, propylene, 3-methyl-1-butene, or 4-methyl-1-butene with each other or with small amounts of other olefins; examples of polyhaloolefins include polytetrafluoroethylene, polyvinylidene fluoride, and copolymers of these and other fluorinated or non-fluorinated monomers. Example polyesters include polyethylene terephthalate and polybutylene terephthalate, as well as related copolymers.

[0111] The porous polymer filter membrane may be fluorinated or perfluorinated, or may comprise a completely non-fluorinated polymer made essentially from non-fluorinated monomers, such as a non-fluorinated polymer material, consisting of, or consisting essentially of a non-fluorinated polymer material. Example filter layers may include, consist of, or consist essentially of a polyolefin, such as polyethylene (e.g., UPE). A porous polymer filter layer consisting essentially of a non-fluorinated material may contain less than 0.5, 0.1, or 0.01 weight percent fluorine. A porous polymer filter layer consisting essentially of a polyolefin, such as polyethylene, may be derived from monomers containing at least 99, 99.5, 99.0, or 99.9 weight percent polyolefin (e.g., polyethylene) monomer.

[0112] Porous polymer filter membranes of any composition may optionally be treated, such as plasma treated, to enhance adhesion or filtration properties.

[0113] Various techniques are known for forming porous filter membranes. Exemplary techniques include, among others, melt extrusion (e.g., melt casting) and dip casting (phase inversion) techniques (including, for example, thermally induced phase inversion (TIPS) and induced phase inversion (NIPS) techniques). Different techniques for forming porous membrane materials can be used to form different porous membrane structures in terms of the size and distribution of the pores formed in the membrane; that is, different techniques can be used to create different pore sizes and membrane structures, sometimes referred to as "morphology," which refers to the uniformity, shape, and distribution of the pores within the membrane.

[0114] Examples of useful membrane morphologies include homogeneous (isotropic) and asymmetric (anisotropic). Porous membranes with pores of substantially uniform size distributed uniformly throughout the membrane are often referred to as isotropic or "homogeneous." Anisotropic (also known as "asymmetric") membranes can be considered to have a morphology in which a gradient of pore size exists across the membrane; for example, a membrane can have a porous structure with relatively larger pores at one membrane surface and relatively smaller pores at the other membrane surface, with the pore structure varying along the membrane thickness. The term "asymmetric" is often used interchangeably with the term "anisotropic." Often, a portion of a membrane with relatively smaller pores (compared to other regions of the membrane) is referred to as a "dense" region, and a portion of a membrane with larger pores is often referred to as an "open" region. In the roll-pleated filters as described, anisotropic membranes can be used with dense regions towards the inlet space and open regions towards the outlet space, or with open regions towards the inlet space and dense regions towards the outlet space.

[0115] Filter membranes can also be characterized by their bubble points, which can be measured by various techniques. According to an example bubble point test method, a sample porous polymer filter membrane is immersed and wetted with a liquid having a known surface tension, and a gas is applied to one side of the sample at a known pressure. The gas pressure is gradually increased. The lowest pressure at which the gas flows through the sample is called the bubble point. The bubble points of example porous polymer filter membranes useful or preferred according to the present description, measured using an HFE 7200 at a temperature of 20-25°C, can range from 1 to 400 pounds per square inch (psi), such as from 2 psi to 300 psi, for example, in the range of 10 to 200 psi.

[0116] Porous filter membranes can also be characterized by their porosity. The porous polymer filter layers described herein can have any porosity that will make them effective as described herein for filtering a liquid stream to produce a filtered liquid material of high purity. Example porous polymer filter layers can have relatively high porosity, such as at least 30 percent or at least 50 percent porosity, such as a porosity in the range of 30 to 85 percent. As used herein, in the art of porous bodies, the porosity (sometimes referred to as the void fraction) of a porous body is the degree of void (i.e., "empty") space in the body as a percentage of the body's total volume, calculated as the ratio of the body's void volume to the body's total volume. A body with zero percent porosity is completely solid.

[0117] The porous polymer filter membranes as described can be in the form of sheets (thin films) having any useful thickness, e.g., thicknesses in the range of 2 to 200 microns, such as 10 to 100 microns. Optionally, the thickness of the filter membrane layer can vary or taper along the width of the membrane between the inlet and outlet ends of the membrane. For example, the filter membrane can have a greater thickness at the inlet end and a lesser thickness at the outlet end.

[0118] The filter as described may optionally but preferably include two spacer layers: one spacer layer may be present in the input space between the opposing input surfaces of adjacent membrane layers, and one spacer layer may be present in the output space between the opposing exit surfaces of adjacent membrane layers.

[0119] The spacer layer has two opposing surfaces (or opposing "sides") separated by a thickness, and also has a length and a width. The spacer layer functions to create a space (an inlet space or an outlet space) between adjacent inlet surfaces or adjacent outlet surfaces of the filter membrane layers of the roll-pleat filter. The spacer layer is designed to create the space while introducing a small amount of resistance to fluid flow through the space created by the spacer layer, thereby allowing fluid to flow through the space. The spacer layer does not need to act as a filter membrane to remove impurities or contaminants from the fluid passing through the spacer layer.

[0120] The spacer layer can be a filter membrane that can be constructed as an open structure, such as a polymer (e.g., an extruded porous polymer membrane), a woven or nonwoven fibrous material, a perforated membrane, a corrugated membrane, or the like, with a very open structure that allows good fluid flow through the spacer layer. The spacer layer as described can have any porosity that allows fluid flow through the volume of the spacer layer with low resistance to flow. Example spacer layers can have very high porosity while maintaining physical properties that maintain separation between adjacent surfaces of the filter membrane layer during use of the filter. Examples of useful porosities can be greater than 65, 70, or 80 percent, such as in the range of 65 to 98 percent.

[0121] The described spacer layer can be in the form of a sheet (thin film) having any useful thickness, for example, a thickness in the range of 10 to 2000 microns, such as 50 to 1000 microns. Optionally, the thickness of the spacer layer can vary or taper along the width of the membrane between the inlet and outlet ends of the membrane. For example, a filter membrane can have a greater thickness at the inlet end and a lesser thickness at the outlet end.

[0122] The roll-pleat filters described herein can be useful for processing a wide range of commercially important liquid or gaseous fluids. These fluids include liquids in any industry, but particularly fluids used as process solvents, cleaners, and other processing solutions for semiconductor and microelectronic device processing, where they are used at very high levels of purity. Examples of these types of fluids include liquid materials (e.g., solvents) used in photolithography, cleaning, and various other processes in microelectronic device preparation. Specific examples include processing solutions for spin-on-glass (SOG) techniques, back surface antireflective coating (BARC) methods, photolithography, cleaning, purging, and deposition steps (e.g., chemical vapor deposition (including plasma-enhanced chemical vapor deposition and other variations)), atomic layer deposition, and the like.

[0123] Impurities are chemicals distinct from the process fluid, dissolved in a liquid process fluid or suspended in a gaseous process fluid. Chemically described examples include inorganic compounds such as hydrocarbon molecules, metal oxides (titanium dioxide), metal atoms, and metal ions, including charged (ionic) molecules and oligomers. In gaseous fluids, contaminants can be any substance known as an "airborne molecular contaminant" (AMC), a chemical in vapor or aerosol form that, if present, has a detrimental effect on the product or process. These chemicals can be organic or inorganic in nature and include acids, bases, polymer additives, organometallic compounds, and dopants. Sources of airborne molecular contaminants include building and cleanroom construction materials, the general environment, process chemicals, and personnel.

[0124] Some specific, non-limiting examples of liquid organic solvents that can be filtered using a wound-pleat filter as described to remove trace impurities include alkanes (methane, butane, hexane, and other C3-C10 alkanes), n-butyl acetate (nBA), isopropyl alcohol (IPA), 2-ethoxyethyl acetate (2EEA), xylene, cyclohexanone, ethyl lactate, methyl isobutylcarbinol (MIBC), methyl isobutyl ketone (MIBK), isoamyl acetate, undecane, propylene glycol methyl ether (PGME), and propylene glycol monomethyl ether acetate (PGMEA).

[0125] Certain types of impurities may be present in certain types of liquid processing fluids. For example, a polar organic solvent such as isopropyl alcohol may contain trace amounts of hydrocarbons, metal oxides, or metal ions. The example method as described may include removing one or more of these impurities from a polar organic solvent such as isopropyl alcohol.

[0126] Nonpolar organic solvents such as alkanes (e.g., hexane) may typically contain impurities such as hydrocarbon analogs (e.g., different nonpolar alkanes such as methane, propane, butane, or C5-C10 alkanes), alkane impurities or hydrocarbon oligomeric derivatives of the nonpolar organic solvent, or metals. Example methods as described may include removing one or more of these impurities from a nonpolar organic solvent such as hexane. [Example]

[0127] Example 1 1. A wind-pleat filter useful for reducing the amount of trace impurities in a fluid, comprising: a multi-layer filter membrane assembly including a first porous filter membrane layer and a second porous filter membrane layer, each of the first porous filter membrane layer and the second porous filter membrane layer including an inlet surface, an outlet surface, a length, an inlet end extending along the length, an outlet end extending along the length, and a width between the inlet end and the outlet end; the porous filter membrane layer assembly is wound along its length about a central axis to form a wound-pleat filter; an inlet surface of the first porous filter membrane layer facing an inlet surface of the second porous filter membrane layer; The wind-pleat filter includes a wind inlet pleat that includes the inlet ends of adjacent filter membrane layers at the inlet end of the wind-pleat filter; The wind-pleat filter includes a wind outlet pleat that includes the outlet ends of the adjacent filter membrane layers at the outlet end of the wind-pleat filter. A wound-pleat filter comprising a multi-layer filter membrane assembly.

[0128] Example 2 The filter of Example 1, comprising a plurality of windings of the porous filter membrane layer.

[0129] Example 3 The filter of example 1 or 2, wherein the outlet surface of the first porous filter membrane layer faces the outlet surface of the adjacent porous filter membrane layer.

[0130] Example 4 The filter of any one of Examples 1 to 3, wherein the wound inlet pleat comprises a fold between the inlet ends of adjacent porous filter membrane layers, the inlet ends of two adjacent porous filter membrane layers bonded together by a bonding agent, or the inlet ends of two adjacent porous filter membrane layers bonded together by welding.

[0131] Example 5 The filter of any one of Examples 1 to 4, wherein the wound outlet pleat comprises a fold between the outlet ends of adjacent porous filter membrane layers, the outlet ends of two adjacent porous filter membrane layers bonded together by a bonding agent, or the outlet ends of two adjacent porous filter membrane layers bonded together by welding.

[0132] Example 6 The filter of example 4 or 5, wherein the binder comprises a thermoplastic polymer selected from polyolefins, fluoropolymers, and perfluoropolymers.

[0133] Example 7 The filter of example 4 or 5, wherein the binder is selected from polypropylene, polyethylene, polytetrafluoroethylene (PTFE), and polyfluoroalkylene (PFA).

[0134] Example 8 The filter of any one of Examples 4 to 7, wherein the binder is a thermoplastic polymer containing less than 1 weight percent of an organic solvent.

[0135] Example 9 The filter of any one of Examples 1 to 8, wherein the first membrane layer and the second membrane layer each comprise a polymer membrane capable of reducing the amount of trace impurities from a fluid as the fluid passes through.

[0136] Example 10 The filter of any one of Examples 1 to 9, wherein the first porous filter membrane layer and the second porous filter membrane layer each comprise a polymer selected from polyamide, polyimide, polyamide-polyimide, polysulfone, fluoropolymer, and nylon.

[0137] Example 11 The filter of any one of Examples 1 to 10, wherein the first porous filter membrane layer and the second porous filter membrane each have a thickness in the range of 2 to 200 microns.

[0138] Example 12 The filter of any one of Examples 1 to 11, wherein the first porous filter membrane layer and the second porous filter membrane each comprise a polymer membrane having a symmetrical morphology.

[0139] Example 13 The filter of any one of Examples 1 to 11, wherein the first porous filter membrane layer and the second porous filter membrane each comprise a polymer membrane having an asymmetric morphology.

[0140] Example 14 14. The filter of any one of Examples 1 to 13, having a total inlet surface area in the range of 0.1 to 100 square meters.

[0141] Example 15 The filter of any one of Examples 1 to 14, wherein the multi-layer filter membrane assembly includes a first porous filter membrane layer and a second porous filter membrane layer, and does not include an additional porous filter membrane layer.

[0142] Example 16 16. The filter of any one of Examples 1 to 15, comprising an inlet side spacer between the inlet surface of the first porous filter membrane layer and the inlet surface of the second porous filter membrane layer, and an outlet side spacer positioned between the outlet surface of the porous filter membrane layer and the outlet surface of the adjacent porous filter layer membrane.

[0143] Example 17 The filter of Example 16, wherein the inlet spacer and the outlet spacer each have a thickness in the range of 10 to 2000 microns.

[0144] Example 18 The filter of any one of Examples 1-14, wherein the multi-layer filter membrane assembly comprises a first porous filter membrane layer, a second porous filter membrane layer, and a third porous filter membrane layer.

[0145] Example 19 The filter of Example 18, wherein the outlet surface of the second porous filter membrane layer faces the outlet surface of the third porous filter membrane layer.

[0146] Example 20 a wind-pleat filter, the multi-layer filter membrane assembly including a first porous filter membrane layer and a second porous filter membrane layer, each of the first porous filter membrane layer and the second porous filter membrane layer including an inlet surface, an outlet surface, a length, an inlet end extending along the length, an outlet end extending along the length, and a width between the inlet and outlet ends, the porous filter membrane layer assembly being wound around a central axis along the length to form a wind-pleat filter including a plurality of porous filter membrane layer assembly windings, the first porous filter membrane layer a wind-pleat filter including a multi-layer filter membrane assembly, wherein an inlet surface of the first porous filter membrane layer faces an inlet surface of a second porous filter membrane layer, the wind-pleat filter including pleats including an outlet end of the first porous filter membrane layer and an outlet end of an adjacent porous filter membrane layer, the pleats including folds, welds, or a thermoplastic binder, the wind-pleat filter with the wind inlet ends of the membrane layers at the inlet end of the wind-pleat filter, and the wind-pleat filter with the wind outlet ends of the membrane layers at the outlet end of the wind-pleat filter.

[0147] Example 21 The filter of Example 20, comprising an outlet surface of a first porous filter membrane layer facing the outlet surface of a second porous filter membrane layer of an adjacent filter membrane layer, and a pleat including an inlet end of the first porous filter membrane layer and an inlet end of the adjacent filter membrane layer, the pleat including a fold, a weld, or a thermoplastic binder.

[0148] Example 22 The filter of example 20 or 21, wherein the first porous filter membrane layer and the second porous filter membrane layer each have a thickness in the range of 2 to 200 microns.

[0149] Example 23 The filter of any one of Examples 20-22, wherein the first porous filter membrane layer and the second porous filter membrane layer each comprise a polymer selected from polyamide, polyimide, polyamide-polyimide, polysulfone, fluoropolymer, and nylon.

[0150] Example 24 The filter of any one of Examples 20 to 23, comprising an inlet side spacer between the inlet surface of the first porous filter membrane layer and the inlet surface of the second porous filter membrane layer, and an outlet side spacer positioned between the outlet surface of the porous filter membrane layer and the outlet surface of the adjacent porous filter membrane.

[0151] Example 25 25. The filter of any one of Examples 20 to 24, wherein the inlet spacer and the outlet spacer each have a thickness in the range of 10 to 2000 microns.

[0152] Example 26 The filter of any one of Examples 20 to 25, wherein the thermoplastic binder comprises a thermoplastic polymer selected from a polyolefin, a fluoropolymer, and a perfluoropolymer.

[0153] Example 27 The filter of any one of Examples 20 to 26, wherein the binder is selected from polypropylene, polyethylene, polytetrafluoroethylene (PTFE), and polyfluoroalkylene (PFA).

[0154] Example 28 28. The filter of any one of Examples 20 to 27, wherein the thermoplastic binder comprises less than 1 weight percent organic solvent.

[0155] Example 29 A method of removing impurities from a fluid, comprising passing the fluid containing trace impurities through the filter of any one of Examples 1 to 28, such that the filter membrane retains a portion of the trace impurities.

[0156] Example 30 The method of Example 29, wherein the impurity is present in the liquid in an amount of less than 100 parts per million.

[0157] Example 31 The method of example 29 or 30, wherein the filter membrane retains at least 90 percent of the impurities present in the fluid.

[0158] Example 32 The method of any one of Examples 29 to 31, wherein the fluid is a process fluid used in semiconductor processing.

[0159] Example 33 The method of any one of Examples 29 to 32, wherein the fluid is a polar organic solvent or a non-polar organic solvent.

[0160] Example 34 33. The method of any one of Examples 29 to 32, wherein the fluid is selected from alkanes (methane, butane, hexane, and other C3 to C10 alkanes), n-butyl acetate (nBA), isopropyl alcohol (IPA), 2-ethoxyethyl acetate (2EEA), xylene, cyclohexanone, ethyl lactate, methyl isobutylcarbinol (MIBC), methyl isobutyl ketone (MIBK), isoamyl acetate, undecane, propylene glycol methyl ether (PGME), and propylene glycol monomethyl ether acetate (PGMEA).

[0161] Example 35 The method of any one of Examples 29 to 34, wherein the fluid is a polar organic solvent and the impurity is a hydrocarbon, a metal oxide, or a metal ion.

[0162] Example 36 The method of Example 35, wherein the fluid is isopropyl alcohol.

[0163] Example 37 The method of any one of examples 29 to 36, wherein the fluid is a non-polar organic solvent and the impurity is a non-polar hydrocarbon or a metal.

[0164] Example 38 The method of Example 37, wherein the fluid is hexane and the impurity is an alkane.

[0165] Example 40 1. A method for preparing a wound-pleat filter, comprising: the multi-layer filter membrane assembly includes a first porous filter membrane layer and a second porous filter membrane layer, each of the first porous filter membrane layer and the second porous filter membrane layer including an inlet surface, an outlet surface, a length, an inlet end extending along the length, an outlet end extending along the length, and a width between the inlet end and the outlet end; an inlet surface of the first porous filter membrane layer facing an inlet surface of the second porous filter membrane layer; winding the multi-layer filter membrane assembly to form a wind-pleat filter including a plurality of multi-layer filter membrane layer assembly windings; forming a pleat including an outlet end of a first porous filter membrane layer and an outlet end of an adjacent porous filter membrane layer, the pleat including a fold, a weld, or a thermoplastic binder; forming a pleat including an inlet end of a first porous filter membrane layer and an inlet end of an adjacent porous filter membrane layer, the pleat including a fold, a weld, or a thermoplastic binder; A method comprising:

[0166] Example 41 The method of example 40, comprising rolling the porous filter membrane layer assembly to position the outlet surface of the first porous filter membrane layer facing the outlet surface of the second porous filter membrane layer.

[0167] Example 42 42. The method of example 40 or 41, wherein the porous filter membrane layer assembly includes a fold line connecting the outlet end of the first porous filter membrane layer to the outlet end of the second porous filter membrane layer.

[0168] Example 43 The method of example 40, comprising applying a bonding agent to connect the outlet end of the first porous filter membrane layer of the porous filter membrane layer assembly to the outlet end of the second porous filter membrane layer of the porous filter membrane layer assembly.

[0169] Example 44 The method of Example 43, wherein the binder is a thermoplastic polymer, and the method includes heating the binder and applying the heated binder to the inlet end of the first porous filter membrane layer or to the inlet end of the second porous filter membrane by extrusion.

[0170] Example 45 The method of any one of Examples 40 to 44, comprising applying a bonding agent to connect the inlet end of the first porous filter membrane layer of the porous filter membrane layer assembly to the inlet end of the second porous filter membrane layer of the porous filter membrane layer assembly.

[0171] Example 46 The method of Example 45, wherein the binder is a thermoplastic polymer, and the method includes heating the binder and applying the heated binder to the inlet end of the first porous filter membrane layer or to the inlet end of the second porous filter membrane by extrusion.

[0172] Example 47 The method of Example 44 or 46, comprising, after applying the heated binder, applying pressure and optional heat to the applied binder.

[0173] Example 48 A method for preparing a roll-pleated filter from a plurality of membrane layers, the method comprising: aligning leading and trailing edges of the membrane layers; rolling the layers along their length to form a wind-roll filter having a plurality of wraps; and connecting adjacent leading and trailing edges of alternating membrane layers of the wraps.

[0174] Example 49 The method of example 48, including joining the edges of adjacent membrane layers prior to rolling the layers to form a roll-pleated filter.

[0175] Example 50 The method of example 49, including joining the edges of adjacent membrane layers after rolling the layers to form a roll-pleated filter.

[0176] Example 51 The method of any one of Examples 48 to 50, comprising connecting the edges of adjacent membrane layers by forming a weld or by applying a bonding agent.

[0177] Example 52 The method of any one of Examples 48 to 51, comprising applying a thermoplastic bonding agent to connect the edges of adjacent membrane layers.

[0178] Example 53 53. The method of any one of Examples 48 to 52, comprising: aligning a first membrane layer and a first support layer along a length; aligning a second membrane layer and a second support layer along a length; winding the aligned first membrane layer and first support layer along a length with the aligned second membrane layer and second support layer to form a roll; applying a first binder to a first surface of the first membrane layer at an inlet end of the first membrane layer; applying a second binder to a first surface of the second membrane layer at an outlet end of the second membrane layer; contacting a second surface of the second membrane layer at the inlet ends of the first membrane and the second membrane with the first binder; and contacting a second surface of the first membrane layer at the outlet ends of the first membrane and the second membrane with the second binder.

[0179] Example 54 54. The method of example 53, comprising controlling alignment of an edge of the first membrane layer at the inlet end with an edge of the second membrane layer at the inlet end.

[0180] Example 55 The method of any one of Examples 48 to 54, comprising winding an inlet side spacer between the inlet surface of the first porous filter membrane and the inlet surface of the second porous filter membrane, and winding an outlet side spacer between the outlet surface of the first porous filter membrane and the outlet surface of the second porous filter membrane.

Claims

1. 1. A filter useful for reducing the amount of trace impurities in a fluid, comprising: a multi-layer filter membrane assembly including a first porous filter membrane layer and a second porous filter membrane layer, each of the first porous filter membrane layer and the second porous filter membrane layer including an inlet surface, an outlet surface, a length, an inlet end extending along the length, an outlet end extending along the length, and a width between the inlet end and the outlet end; a plurality of porous filter membrane layer windings; the porous filter membrane layer assembly is wound along its length around a central axis to form a filter; an inlet surface of the first porous filter membrane layer facing an inlet surface of the second porous filter membrane layer; the inlet pleat includes the inlet end of the filter membrane layer adjacent the inlet end of the filter; the outlet pleat comprises an outlet end of the adjacent filter membrane layer at the outlet end of the filter; A filter comprising a multi-layer filter membrane assembly.

2. 10. The filter of claim 1, comprising an outlet surface of a first porous filter membrane layer facing an outlet surface of an adjacent porous filter membrane layer.

3. The entrance pleat is a fold between the inlet ends of adjacent porous filter membrane layers; the inlet ends of two adjacent porous filter membrane layers bonded together by a bonding agent; or the inlet ends of two adjacent porous filter membrane layers being joined together by welding contains, or The exit pleats are a fold between the outlet ends of adjacent porous filter membrane layers; the outlet ends of two adjacent porous filter membrane layers bonded together by a bonding agent; or The outlet ends of two adjacent porous filter membrane layers are joined together by welding. The filter of claim 1 , comprising:

4. 10. The filter of claim 1, wherein the first porous filter membrane layer and the second porous filter membrane each have a thickness in the range of 2 to 200 microns.

5. 10. The filter of claim 1, wherein the first porous filter membrane layer and the second porous filter membrane each comprise a polymeric membrane having a symmetrical morphology.

6. 10. The filter of claim 1, wherein the first porous filter membrane layer and the second porous filter membrane each comprise a polymeric membrane having an asymmetric morphology.

7. A filter useful for reducing the amount of trace impurities in a fluid, comprising: a multi-layer filter membrane assembly including a first porous filter membrane layer and a second porous filter membrane layer, each of the first porous filter membrane layer and the second porous filter membrane layer including an inlet surface, an outlet surface, a length, an inlet end extending along the length, an outlet end extending along the length, and a width between the inlet end and the outlet end; a plurality of porous filter membrane layer windings; the porous filter membrane layer assembly is wound along its length around a central axis to form a filter; an inlet surface of the first porous filter membrane layer facing an inlet surface of the second porous filter membrane layer; the inlet pleat includes the inlet end of the filter membrane layer adjacent the inlet end of the filter; the outlet pleat includes an outlet end of the filter membrane layer adjacent the outlet end of the filter; an inlet side spacer between the inlet surface of the first porous filter membrane layer and the inlet surface of the second porous filter membrane layer; an outlet side spacer positioned between the outlet surface of the porous filter membrane layer and the outlet surface of the adjacent porous filter layer membrane; The filter of claim 1 further comprising:

8. 8. The filter of claim 7, wherein the inlet spacer and the outlet spacer each have a thickness in the range of 10 to 2000 microns.

9. A filter, a multi-layer filter membrane assembly including a first porous filter membrane layer and a second porous filter membrane layer, each of the first porous filter membrane layer and the second porous filter membrane layer including an inlet surface, an outlet surface, a length, an inlet end extending along the length, an outlet end extending along the length, and a width between the inlet end and the outlet end; the porous filter membrane layer assembly is wound along its length about a central axis to form a filter comprising a plurality of windings of the porous filter membrane layer assembly; an inlet surface of the first porous filter membrane layer facing an inlet surface of the second porous filter membrane layer; the pleat includes an outlet end of the first porous filter membrane layer and an outlet end of an adjacent porous filter membrane layer, the pleat including a fold, a weld, or a thermoplastic binder; an inlet end of the membrane layer at the inlet end of the filter; an outlet end of the membrane layer at the outlet end of the filter; having filter.

10. an outlet surface of a first porous filter membrane layer facing an outlet surface of a second porous filter membrane layer of an adjacent filter membrane layer; a pleat including an inlet end of a first porous filter membrane layer and an inlet end of an adjacent filter membrane layer, the pleat including a fold, a weld, or a thermoplastic binder; 10. The filter of claim 9, comprising:

11. 11. A method of removing impurities from a fluid, comprising passing the fluid containing trace impurities through a filter according to any one of claims 1 to 10, such that the filter membrane retains a portion of the trace impurities.

12. 12. The method of claim 11, wherein the impurities are present in an amount less than 100 ppm.

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