Wind-pleated filters and related methods

Abstract

This invention provides a method for removing impurities from a fluid. [Solution] A multilayer filter membrane assembly comprising a first porous filter membrane layer and a second porous filter membrane layer, wherein each of the first and second porous filter membrane layers comprises a multilayer filter membrane assembly comprising an inlet surface, an outlet surface, a length, an inlet end, an outlet end, and a width between the inlet end and the outlet end, wherein the multilayer filter membrane assembly is wound along its length and around a central axis to form a wound-pleated filter, the inlet surface of the first porous filter membrane layer facing the inlet surface of the second porous filter membrane layer, the wound inlet pleats comprising the inlet ends of adjacent filter membrane layers at the inlet end of the wound-pleated filter, and the wound outlet pleats comprising the outlet ends of adjacent filter membrane layers at the outlet end of the wound-pleated filter.

Description

Technical Field

[0001] The following description relates to a wound-pleat filter and a method of preparing and using a wound-pleat filter.

Background Art

[0002] Filters are used in the industry to remove undesirable substances from fluids. Examples of fluids processed 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 having medical or pharmaceutical applications.

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

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

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

[0006] A fluid passes through a filter material, and undesirable substances in the fluid (referred to as "impurities") are retained by the filter material. In some filtration mechanisms, called "sieving" mechanisms, as the 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 other filtration mechanisms, called "non-sieving" mechanisms, 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 chemical molecules (e.g., hydrocarbons, metals, or metal ions) dissolved (in a liquid) or suspended (in a gas) can be chemically or electrostatically attracted to the material of the filter medium and retained by the filter material.

[0007] Filter products can be "dead-end" filters, or "bypass" or "recirculating" filters. A dead-end filter includes filter elements contained within a housing, and the fluid entering the housing must pass through the filter elements to flow out of the housing as a filtrate. A bypass filter design also includes filter elements contained within a housing, but the difference is that the fluid flowing into the housing may either pass through a membrane before exiting the housing as a filtrate, or pass through the housing as a bypass flow ("concentrated liquid" or "retained liquid") without passing through a membrane. The filter housing includes an inlet, an outlet for the filtrate, and an outlet for the bypass fluid flow. The bypass flow can be recirculated through the same filter housing and filter elements, or it can pass through a separate filter element in a separate filter housing.

[0008] A standard filter for handling many fluids is of the “pleated cylindrical filter” design. A pleated cylindrical filter product includes a cylindrical housing adapted to contain a pleated filter element in the flow path between the housing's inlet and outlet. The filter is typically a dead-end filter, requiring that the fluid entering the housing at the inlet pass through the pleated filter element before exiting the housing at the outlet. The pleated filter element has a cylindrical configuration with pleated folds formed by longitudinal folds extending along the length and central axis of the cylindrical filter element. A cylindrical pleated filter element may include a cylindrical outer support (e.g., a “cage”), a cylindrical inner support (a “core”), and an open internal space or channel along the center and central axis of the cylinder, i.e., an open cylindrical internal space. When flowing through the cartridge, the liquid flows through the internal channel either before or after passing through the filter element.

[0009] When designing filters for industrial applications, specifically for use in cleanrooms for the manufacture of semiconductors or microelectronic devices, filter design often emphasizes a large filter element area per unit 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 there is little room for further improvement. Filter films have been progressively thinner, and the ability to increase film area per unit volume by reducing film thickness is approaching or reaching its limits. The ability to increase film area per unit volume by removing or reducing the thickness of the support layer is also approaching or reaching its limits. [Overview of the project]

[0010] This description relates to a novel and inventive wound-pleated filter for removing, for example, trace impurities from a processing fluid, a method for manufacturing the wound-pleated filter, and a method for using the wound-pleated filter.

[0011] Wind-pleated filter products are not generally used in industry, and to the applicant's understanding, they have not been used in applications for removing trace impurities with particle sizes of less than 100 nanometers from liquids and gases.

[0012] The applicant has identified a particular type of novel and inventive wound-pleated filter design that is effective for use in filtering high-purity liquid and gaseous fluids containing trace amounts of impurities, and specifically for processing liquids and gases (sometimes referred to as “processing fluids”) used in processing high-purity semiconductors and microelectronic devices.

[0013] A wound-pleated filter includes a cylindrical filter structure made of a multilayer filter membrane assembly comprising two or more filter membrane layers, which is 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 wound pleat located at the first filter end of the wound-pleated filter and part of a second wound pleat located at the second filter end of the wound-pleated filter. The wound-pleated filter may be housed in a filter housing that includes a housing inlet and a housing outlet in a configuration that requires a 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 form of a wound-pleated filter, the multilayer filter film assembly forms multiple windings, with one “winding” referring to a portion of the total length of the assembly that winds in one rotation around a central axis. Each layer of the wound-pleated 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. The two “adjacent” layers may be part of one winding of the multilayer filter assembly, or the adjacent film layer may be part of a different winding that is either inside the winding (closer to the center of the winding) or outside the winding (further from the center of the winding). A filter layer edge that forms pleats in an "alternating" manner is a filter layer of a wound-pleated filter having a first edge (e.g., "inlet" or "front" edge) that forms pleats at the first edge (e.g., "inlet" or "front" edge) of a first adjacent filter layer, and a second edge (e.g., "outlet" or "rear" edge) that forms pleats at the second edge (e.g., "outlet" or "rear" edge) of a second, i.e., different adjacent filter layer.

[0015] A preferred wound-pleated filter may include a large filter film area per unit volume of the filter. A wound-pleated filter as described may have a filter film area per unit volume that is several times greater than that of a standard pleated cylindrical filter design, such as two, four, or five times or more the filter film area per unit volume compared to a commercially available pleated cylindrical filter design (with a filter film and spacer layer of the same thickness).

[0016] As an additional advantage, useful or preferred wound-pleated filters, as described, can include a considerably reduced amount of support layers in the filter product structure, which means a reduction in the amount of non-filtration layer, i.e., a reduction in the amount of layer that does 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 located on the inlet side of the filter membrane layer and one non-filtration support layer located on the outlet side of the filter membrane layer. A wound-pleated filter design, as described, can 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 upstream, or one support layer can serve as support for two separate membrane layers downstream. In conventional cylindrical pleated filters, due to the nature of the assembly process, at least two layers of support will be located between adjacent membrane layers on either the inlet or outlet side. According to the example of a wound-pleated filter described herein, only one support layer is present between adjacent membrane layers at either the inlet or outlet side of the filter.

[0017] The wind-pleated filter in question may be useful for applications that remove small amounts of impurities (e.g., "trace impurities") from already highly pure liquids. "Removing" impurities from a fluid means removing at least a portion of the impurities from the fluid; that is, it may not be possible to remove all impurities from the fluid, but it does mean reducing the amount of impurities present in the fluid.

[0018] Impurities, also referred to as "contaminants," can be chemical substances present in a fluid (e.g., a processing fluid) at extremely small concentrations, such as parts per million or parts per billion, or even smaller. An example of a processing fluid that may be filtered or purified using a roll-pleated filter, as described, might contain a processing fluid that has already been processed and purified to remove a certain amount of impurities, but still contains very small amounts of remaining impurities present only in "trace" quantities. The terms "parts per million" and "parts per billion" are used in a manner consistent with their use in chemical technology, including in the manufacturing of microelectronic and semiconductor devices. In this regard, parts per million (PPM) is commonly used as a dimensionless measurement of small degrees (concentrations) of contaminants in a fluid (gas or liquid), expressed as milligrams of contaminants per liter of fluid (mg / L), measuring the mass of contaminants per unit volume of fluid. Parts per million is equal to 0.000001 units.

[0019] Impurities in a processing fluid are chemical substances different from the processing fluid that are dissolved in the liquid processing fluid or suspended in the gaseous processing fluid. Examples of chemically described impurities include uncharged or charged (ionic) molecules and hydrocarbon molecules that may be 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 can have dimensions of less than 100 nanometers (maximum dimension), such as 90, 50, 25, 10, 5, or less than 1 nanometer. Particles of these sizes, when present in processing fluids used to process semiconductors or microelectronic devices, can create defects in the devices and reduce processing yield.

[0021] Trace impurities may initially be present in the processing fluid in amounts less than 100, 10, or 1 ppm, or less than 100, 10, or 1 ppb. By passing the processing fluid through a wound-pleated filter as described, the concentration of trace impurities can be reduced by at least 20, 50, 70, or 80 percent, meaning the filter removes at least 20, 50, 70, or 80 percent of the trace impurities from the processing fluid.

[0022] When used to remove these types of trace impurities from a processing fluid, roll-pleated filters, as described, can have long service lives, measured by the volume of fluid passing through the filter, such as 1,000, 5,000, or 10,000 liters, or several thousand liters. When removing trace impurities from a fluid over this service life, the amount of trace impurities deposited in the filter may occupy less than 2 percent or less than 1 percent of the total available surface area of ​​the filter membrane.

[0023] Compared to conventional pleated cylindrical filter designs, roll-pleated filters can have a relative advantage in that they allow for the production of more efficient filters with a larger amount of filter film per unit volume of filter. The roll-pleated filters described herein may be prepared requiring only one spacer layer per filter film layer, whereas standard pleated cylindrical filter designs inherently include two spacer layers per filter film layer. The roll-pleated designs described also allow for the elimination of the type of open channels that are required to be present in the central axis and core of pleated cylindrical designs. Instead of open channels in the core, roll-pleated filter products may contain an additional amount of roll filter film. Furthermore, roll-pleated filters have no limit on pleat height, large outer diameter surfaces are not pressurized, fluid does not need to pass through the central opening of the cylinder, have a very uniform packing density, and pleat damage at the edges of the pleats in the filter film layers is reduced thanks to the assembly method and flow pattern.

[0024] In one embodiment, the following description relates to a wound-pleated filter useful for reducing the amount of trace impurities in a fluid. The wound-pleated filter includes a multilayer filter membrane assembly comprising a first porous filter membrane layer and a second porous filter membrane layer, each of which comprises 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 assembly is wound along its length and around a central axis to form a wound-pleated 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 wound inlet pleat that includes the inlet end of an adjacent filter membrane layer at the inlet end of the wound-pleated filter, and a wound outlet pleat that includes the outlet end of an adjacent filter membrane layer at the outlet end of the wound-pleated filter.

[0025] In another embodiment, the description relates to a wound-pleated filter. The filter comprises a multilayer filter membrane assembly comprising a first porous filter membrane layer and a second porous filter membrane layer, each of the first and second porous filter membrane layers comprising 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 assembly is wound along the length and around a central axis to form a wound-pleated filter comprising a plurality of porous filter membrane 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 comprises pleats comprising the outlet end of the first porous filter membrane layer and the outlet end of an adjacent porous filter membrane layer, the pleats comprising a fold, a weld, or a thermoplastic binder, the wound inlet end of the membrane layer at the inlet end of the wound-pleated filter, and the wound outlet end of the membrane layer at the outlet end of the wound-pleated filter.

[0026] In another embodiment, the present invention relates to a method for removing impurities from a fluid by passing a fluid containing trace impurities through the filter described above, 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. The method involves a multilayer filter membrane assembly that 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 end and the outlet end, with the inlet surface of the first porous filter membrane layer facing the inlet surface of the second porous filter membrane layer. The method includes winding the multilayer filter membrane assembly to form a wind-pleat filter that includes a plurality of windings of the multilayer filter membrane assembly, and forming pleats that include the outlet end of the first porous filter membrane layer and the outlet end of an adjacent porous filter membrane layer, the pleats including a fold, a weld, or a thermoplastic binder, and forming pleats that include the inlet end of the first porous filter membrane layer and the inlet end of an adjacent porous filter membrane layer, the pleats including a fold, a weld, or a thermoplastic binder.

[0028] In yet another aspect, the description relates to a method of preparing a roll-pleat filter from a plurality of membrane layers. The method includes aligning the leading and trailing edges of the layers, rolling the layers along the length of the layers to form a wind-roll filter having a plurality of windings, and connecting the adjacent leading and trailing edges of the alternating membrane layers of the windings.

Brief Description of the Drawings

[0029] [Figure 1] A cross-sectional view of an example roll-pleat filter as described in the filter housing. [Figure 2A-2B] A perspective view from the side of an example multilayer filter membrane assembly as described. [Figure 3] An end view of an example roll-pleat filter as described. [Figure 4A] An end perspective view of an example roll-pleat filter as described. [Figure 4B]Figure 3 shows a cross-sectional view of a portion of a roll-pleated filter, as described in the example. [Figures 5A-5F] The steps of an example method for preparing a roll-pleated filter as described are shown below. [Figures 6A-6D] An example of automated steps in a method for preparing roll-pleated filters is shown. [Figure 7] This shows the alignment of layers in a roll pleated filter. [Figures 8A-8C] The following shows an example of a filter product, including a roll-pleated filter and housing, as described. [Modes for carrying out the invention]

[0030] All diagrams are schematic and not to a specific scale.

[0031] The present invention provides a wind-pleated filter, sometimes referred to herein as a “roll-pleated filter,” which includes a cylindrical filter structure comprising a multilayer filter film assembly wound (or “rolled up”) along the length of the assembly around the central longitudinal axis of the wind-pleated filter. The multilayer filter assembly comprises a plurality (at least two) of filter film layers. In the wind-pleated filter configuration, the first and second (front and rear, or inlet and outlet) ends of the filter layers in the longitudinal direction are formed into first and second wind pleats located at the opposite ends of the roll-pleated filter structure. The alternating ends of the filter film layers are formed into pleats (e.g., folded or joined), and the film assembly is wound into a wind-pleated filter including a wind inlet pleat and a wind outlet pleat, where the inlet side (inlet surface) of the filter film layers joined by the pleats is on one side of the filter film layer, and the outlet side (outlet surface) of the filter film layers joined by the pleats is on a second side (opposite side) of the filter film layer.

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

[0033] When a filter layer is part of a multilayer filter film assembly, the width, front end, and rear end of the two films are all substantially aligned along their length. The two (or more) film layers of the assembly are also flat along the width of the film layer and face each other such that the first (front) surface of one film layer faces the first (front) surface of the adjacent film layer.

[0034] Surfaces "facing" adjacent surfaces mean that the two surfaces are generally facing each other and positioned parallel or substantially parallel. The two surfaces may be in direct contact or facing each other through an intermediate layer, such as a spacer layer, present between the two surfaces of adjacent filter films.

[0035] Therefore, in addition to at least two filter film layers, one or more additional filtration or non-filtration layers, such as a spacer layer or one or more additional filter film layers, may be present in the assembly. The spacer layer may be located between the first film layer and the adjacent film layer (between the front surface of the first film layer and the front surface of the adjacent (second) film layer). Alternatively or additionally, the second spacer layer may be located on the rear surface (outlet surface) of the film layer such that, when the layers are wound, the second spacer layer is located between the rear surface of the first film layer and the rear surface of the adjacent (second) film layer.

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

[0037] In the form of a wound-pleated filter, a multilayer filter layer assembly can form multiple windings, with one "winding" referring to a portion of the total length of the multilayer assembly wound around a central axis in one turn (one rotation). A wound-pleated filter containing multiple windings is formed from two or more filter layers of a wound multilayer assembly that will be positioned adjacent to one another. In other words, generally speaking, with the exception of the innermost and outermost layers, each filter layer will form pleats at each of its two ends with the ends of the two adjacent filter layers, one end of a filter layer will form a pleat with the end of one adjacent filter layer, and the second end of a filter layer will form a pleat with the end of a different adjacent filter layer.

[0038] Each filter layer has an inlet surface facing (opposing) the inlet surface of an adjacent layer, and an outlet surface facing the outlet surface of a different adjacent layer (except for the innermost and outermost filter layers). Two "adjacent" layers may be part of one winding of a multilayer filter assembly, or adjacent layers may be part of different windings, either inside the layer (closer to the winding center) or outside the layer (further from the winding center). The innermost layer of the first inner winding will have no innerly adjacent layers, and the outermost layer of the last outer winding will have no outerly adjacent layers.

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

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

[0041] The second (rear) surface of each filter film layer is adjacent to the second (rear, outlet) filter end of the wind-roll filter and to the outlet space between the two opposing rear surfaces of adjacent filter film layers that are connected at the first (front, inlet) ends of each of the two adjacent filter film layers to form pleats. The outlet space and the second (rear, outlet) surfaces of each of the two adjacent filter film 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 includes a spacer layer between the two opposing second (rear) surfaces, or it may have a volume that consists only of space between the two opposing second (rear) surfaces without a spacer.

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

[0043] The roll-pleated filters described differ from the typical "pleated cylindrical filter" design found in common commercial use. A "pleated cylindrical filter" refers to a filter containing a cylindrical pleated filter element that includes multiple 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 of the central axis of the pleated cylindrical filter. While a pleated cylindrical filter can be used as a "dead-end" type filter, 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, the 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-pleated filter designs described herein, the fluid does not need to flow through or be located within the central opening of the filter. The central opening is not required, and the space along the central axis of the roll-pleated filter may be used for other purposes, such as to include an additional length of the wound filter film layer or to include one or more devices for improving or monitoring the performance of the roll-pleated filter.

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

[0046] The wind-pleated filters described differ from typical "spiral-winded filter" designs found in common commercial use for specific applications. "Spiral-winded filters" refer to common commercial filter products that include a spirally wound filter membrane with the presence and flow of fluid in a central channel (opening) of the filter, without alternating pleated (folded, joined, welded, or otherwise connected) winding ends at opposite ends of the winding cylinder. Examples of these types of spiral-winded filter products are commonly used in reverse osmosis filtration systems with bypass or recirculation modes of operation. Typical systems containing these types of spiral-winded filter membranes have multiple channels within the filter housing, including not only a channel through the filter membrane (for "permeation") but also alternative channels that bypass the filter membrane (for unfiltered "concentrated" or "retaining" fluid). Fluid entering a housing containing this type of spiral-winded filter can exit the filter housing without passing through the filter membrane.

[0047] A roll-pleated filter can be made from any multilayer film assembly assembled to contain any useful number of film layers (e.g., 2, 4, 6, etc.), have any useful length or width, and contain any useful number of turns. An example filter may be prepared from a multilayer film assembly having a length of 1 to 100 meters, for example from 2 meters to 20 or 50 meters. An example roll-pleated filter may contain 1 to 500 turns, for example from 2 to 300 turns. A roll-pleated filter may 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 diameter, such as an opening with a diameter in the range of 0.125 to 1 inch. The film assemblies and the layers of the film assemblies may have widths (which become the "length" of the wound filter) in the range of 10 to 100 centimeters, for example from 20 to 50 centimeters. The example membrane can have a total surface area at the entrance surface ranging from 0.1 or 0.5 square meters to 100 square meters, such as 10 to 80 square meters, and can be selected by the number of turns.

[0048] An example of a roll-pleated filter as described in a filter housing is shown in Figure 1. As shown, the filter assembly 30 includes a filter (e.g., a filter cartridge) 10 and a housing 32. The housing 32 includes an inlet 34 at one end (bottom) and an outlet 36 at a second end (top). The housing 32 defines an internal space 38, which is adapted to house the filter 10 in such a manner that fluid entering the housing inlet 34 must pass through the filter membrane layer of the filter 10 before passing through the housing outlet 36; in other words, the filter assembly 30 is configured as a “dead-end” filter assembly. The filter 30 may optionally include additional inlets and outlets (e.g., vents) that are commonly present as part of a dead-end filter and are used intermittently to ventilate the housing or drain fluid from the housing.

[0049] The filter 10 is a roll-pleated filter as described herein. The filter 10 comprises a plurality of wound filter film layers 40 with alternating pleated (folded, joined, or otherwise connected) edges. The filter film layers 40 are wound around a central axis to form the filter 10. An optional axial space 58 exists along the central axis and may or may not be connected to the internal space 38. During use, the fluid is not directed to flow through the axial space 58 in such a manner that the fluid is prevented from passing through the filter film layers 40.

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

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

[0052] The outlet space 62 is the space adjacent to and between two opposing rear surfaces 48 of adjacent filter film layers 40, which are part of the wind pleats (e.g., "wind inlet pleats") 52 at each first (front, inlet) end 42. The outlet space 62 also includes a portion of the internal space 38 within the housing 32 between the outlet 36 and the outlet surface 48 of the film layer 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 film layers 40.

[0053] Each film layer 40 (excluding the innermost and outermost windings) forms a wind inlet pleat 52 with the adjacent film layer 40 at the edge of the filter film layer and at one end (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 film layers 40, a binder applied to the inlet ends 42 of alternating adjacent film layers 40, or a molten polymer of the inlet ends 42 of alternating adjacent film layers 40.

[0054] Each film layer 40 (except for the innermost and outermost windings) forms a wound outlet pleat 54 with the adjacent film 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 the alternating adjacent film layers 40, a binder applied to the outlet ends 44 of the alternating adjacent film layers 40, or molten polymer at the inlet ends 44 of the alternating adjacent film layers 40.

[0055] Each film layer 40 (excluding the innermost and outermost windings) is connected to two adjacent film layers 40 in an alternating manner at edges 42 and 44. As shown, adjacent films 40 having a first surface 46 facing each other form a wind outlet pleat 54 at a second (rear, outlet) end 44. Adjacent films 40 having a second surface 48 facing each other form a wind inlet pleat 52 at a first (front, inlet) end 42. This arrangement of pleated first (front, inlet) and second (rear, outlet) ends of adjacent filter film layers is referred to as the arrangement of alternating pleated ends of adjacent filter layer films in a wind-pleated filter.

[0056] A connected pair of ends of adjacent filter film layers may be included as part of a wound pleat formed by any technique or structure. The pleat is generally a form of connected or folded ends of adjacent film layers that form a pleat at the wound and connected ends, forming a closed end of the inlet or outlet space of a wound-pleated filter, allowing fluid to flow through the inlet space and filter film layers to the outlet space and preventing fluid from bypassing the filter film layers.

[0057] Pleats between the edges of adjacent film layers may be formed by, or may include, a solvent-free thermoplastic binder positioned between the front or rear ends of two adjacent filter film layers, or in contact with those front or rear ends. 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 solid thermoplastic polymer without volatile organic solvents or other chemical components that may be released from the binder in gaseous form during use of the filter. Examples of binders include thermoplastic polyolefins that can be fluorinated or totally fluorine-substituted. Specific examples include polypropylene, polyethylene, polytetrafluoroethylene (PTFE), and polyfluoroalkylene (PFA). Binders of any polymer composition may include a large amount of thermoplastic polymer and a small amount of organic solvent, for example, at least 95, 99, or 99.9 weight percent thermoplastic solid and less than 5, 1, or 0.1 weight percent of organic solvent based on the total weight of the binder.

[0058] Preferred polymer thermoplastics may also have advantages during the automated assembly of roll-pleated filters, allowing for a small flow of heated thermoplastic binder after the thermoplastic material has been applied to the film layers. When winding pairs of film layers with a binder used to bond adjacent ends of the film layers together, the film layers may be wound to slightly different lengths or to have the same length. Each film layer may be sealed across the core on the opposite side of the core, or otherwise bonded and then sealed again on the opposite side of the roll, so that the layers are properly sealed together and there is no other fluid passage to proceed from the inlet to the outlet of the roll-pleated filter except through either film layer. Preferred thermoplastic binders may be heatable and able to maintain their ability to flow for short periods of time after being applied to the ends of the bonded film layers, so as the subsequent flowability of the binder allows the binder to flow to accommodate slightly longer lengths for the outer layers of the film assembly, thus facilitating the winding process that occurs after the application of the binder to the layers. The film layers may be of the same width. Each film layer can be sealed transversely along the width on the opposite side of the core at the beginning of the roll and on the opposite side at the end of the roll.

[0059] In other examples, the pleats may be in the form of a fold 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 a single piece of porous filter membrane material, such that the folded pleats connect the two layers at their ends. The folded piece of membrane material becomes two adjacent layers of a multilayer porous filter membrane assembly. Each layer has an inlet surface and an outlet surface, and each layer has an inlet end along the aligned length and an outlet end along the length. The adjacent inlet ends (or outlet ends) of the adjacent filter membrane layers remain connected, forming a fold pleat along the length of the adjacent filter membrane layers.

[0060] In another example, the front (inlet) ends or rear (outlet) ends of adjacent filter film layers may be connected to form pleats with the molten polymer of the adjacent (polymer) film layers. The molten polymer can be formed by any melting technique, such as laser welding or ultrasonic welding.

[0061] Referring again to Figure 1, in use, the fluid can flow from the inlet 34 into the filter assembly 30 and into the inlet-side space 60. The fluid passes from the inlet to the inlet-side space 60, through the inlet-side space 60, and must pass through one of the membrane layers 40 to enter the outlet-side space 62 (see arrow). From the outlet-side space 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 may be prepared by preparing a multilayer assembly having at least two film layers with substantially aligned front and rear ends along a substantially aligned length and substantially aligned width and length, rolling the assembly along the length of the assembly, and forming pleats at the front and rear ends of the alternating film layers. The step of forming pleats at the front and rear ends of adjacent alternating film layers may be performed before, during, or after rolling the assembly. A useful multilayer assembly may include at least two filter film layers (see Figure 2A), such as a single pair of two filter film layers, and may include three or more filter film layers (see Figure 2B).

[0063] Figure 2A shows an example of a multilayer assembly as described. The multilayer assembly 120 includes two filter film layers having aligned lengths and aligned ends extending along the length. Filter film layer 102 and filter film layer 104 each have a length L and a width w. Film layer 102 includes a front end 106 extending along length L and a rear end 118 also extending along length L. Film 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 film 102 and the rear end 122 of film 104 are connected at a rear pleat 108 (for example, by folding as shown) along the entire length L of film layers 102 and 104.

[0064] The rear end 118 of film layer 102 and the rear end 122 of film layer 104 can form pleats 108 by any useful method or material. For example, the rear end 122 can be connected to the rear end 118 to form pleats 108 by any one or more of the following: a binder such as a thermoplastic polymer binder placed in contact with the two layers and at their respective rear ends; molten polymer derived from two opposing film layers at the film ends (e.g., formed by laser welding two polymer films at their edges); or a fold formed along the length of a piece of twice-width film (having a width of 2w) that forms an assembly 120 with two opposing film layers 102 and 104, each having a width w, with folded pleats 108 at ends 118 and 122 when folded along the center of the width and along the length L.

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

[0066] Figure 2B shows an example of a multilayer assembly 150 including four filter film layers having aligned lengths and aligned edges. The filter film layers 102, 104, 103, and 105 each have a length L and a width w. Each film layer includes a front edge 111 that forms a fold pleat between the front edges of adjacent filter films and a rear edge 113 that forms a fold pleat between the rear edges of different adjacent film layers. Each film has an inlet surface (the lower side of the film layer, as shown) 121 facing the inlet surface 121 of the adjacent film layer. Each film has an outlet surface (the upper side of the film layer, as shown) 123 on the opposite side of the inlet surface. Films 103 and 104 have outlet surfaces (the upper side of the film layer, as shown) 123 facing each other.

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

[0068] Referring to Figure 3, the diagram shows an end view of a roll-pleated filter 160 formed from a multilayer assembly 120 (alternatively, assembly 150). The roll-pleated filter 160 is formed by rolling assembly 120 along a length L starting at the inner winding end 114 and continuing along the entire length L to the outer winding end 116, and joining the widthwise edges 140 and 142 and 144 and 146 together along the overall width (w). Film layers 102 and 104 are aligned with the front surface 130 of film layer 104, which is oriented toward the (opposite) front surface 132 of film layer 102 (see dashed line in Figure 3). When rolled along length L, assembly 120 forms the roll-pleated 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 film layers, but are not shown in Figure 3.

[0069] Figures 4A and 4B show an end-face perspective view and a side section view, respectively, of an example roll-pleated filter made from a multilayer assembly including two filter film layers 240 and two spacer layers 250, 252, with the front and rear ends of the film layers alternately formed into pleats using a thermoplastic binder.

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

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

[0072] Roll-pleated filters as described may be prepared by any method useful for combining filter film layers and optional spacer layers in a manner for forming roll-pleated filters as described. Generally useful methods may be used to prepare roll-pleated filters from multiple film layers and optional spacer layers, including at least two film layers, by steps including, in any useful order, aligning the front and rear longitudinal ends of the film 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 ends of alternating film layers of windings. The step of forming pleats between adjacent alternating film layers may be performed before, during, or after rolling the layers to form the roll-pleated filter. The widthwise ends at the beginning and end of the length must also be sealed over the entire width by, for example, a binder or welding (laser welding, sonic welding). These steps can be carried out in a batch manner, or using an automated system that performs the steps of forming pleats (for example, by connecting ends together or folding a larger film into two film layers of a multilayer assembly), aligning the layers, and winding the layers in a continuous or semi-continuous manner.

[0073] As a more definitive option, a liquefied (heated, melted) polymer binder may be applied to the ends of two adjacent filter film layers to form pleats, just before the two bonded and pleated layers are wound to form a wind-roll filter, i.e., they may be positioned in contact with each other and with the binder. Initially, a heated, flowable amount of polymer binder is applied to the space between the two film layers at adjacent ends, and the two ends are brought into contact with the binder to connect the ends and form pleats. Immediately after the binder is applied, the layers are rolled into a wind. The winding is done immediately after the application of the liquefied polymer binder, while the binder remains heated, soft, and flowable, so that the layers and binder are wound before the binder cools and solidifies, allowing for some movement between the layers in the longitudinal direction between the winds due to the difference in the wind lengths of the two film layers. The binder has a melting temperature lower than the melting temperature of the film layers and any optional spacing layers.

[0074] Alternatively, a liquefied (heated, melted) polymer binder may be added in a single step to one end of a pair of adjacent film layers, allowing the binder to cool and solidify. The two layers can then be wound onto a roll while the binder remains cooled and non-flowable. After winding, heat can be applied to the polymer binder at the winding 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 inlet ends, outlet ends, or both.

[0075] As an alternative, the edges of adjacent film layers in a wound multilayer assembly may be joined using welding or a binder at the outer layers of the winding to form pleats when the assembly is wound, where multiple film layers and an optional spacer layer are formed into the winding. See, for example, Figures 6A and 6B below. For example, generally, film layer 1, film layer 2, support (spacer layer) layer 1, and support (spacer layer) layer 2 may be fed into the winding by aligning the outer layers of the winding at different locations on the outer surface of the winding. At one location in the winding, film layer 1, film 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 connect and seal the aligned longitudinal ends of the three layers (forming pleats) by melting the two film layers and the support between the two film layers at the first end of the winding. At the opposite end of the winding, film layer 1, film layer 2, and support 2 are accessible as three exposed layers so that a heat source or laser can be applied to connect and seal the aligned longitudinal ends of the three layers (forming pleats) by melting the two film layers and the support between the two film layers.

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

[0077] In the first step, a filter film 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 film layer 240 has a length (not shown), a width (w), and a thickness.

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

[0079] In general, in this example or other examples, the binder can be applied to the layers of the assembly in any manner that provides effective formation of pleats. The binder may be applied to the surface of the support (spacer) layer, to the film layer parallel to the edge of the support layer (as depicted in Figures 4A and 4B), or to one or both of the adjacent film surfaces, to the support surface or all or both of the surfaces, or in any combination thereof as herein. Alternatively, the film layers may be melted together to form a weld at the location of the pleats.

[0080] In some specific examples, the support layers are located between the edges to be joined, and the binder is applied between the joining edges and the support layers, either through the support layers or in conjunction with the support layers, to provide adhesion. In other examples, the binder is positioned along or close to the edges of adjacent support layers so that the support layers are brought into contact with the binder to hold the support layers in place and bond them to their corresponding film layers. In other embodiments, the binder may not be in contact with the support material until after the next film layer is applied with pressure and optional heat to extrude the binder so that it contacts the support material and potentially captures it, and expands over a small portion of the length of the device. The process of compressing the binder under the next film layer may also require applying the binder away from the actual film edges to ensure that the binder does not overflow from the end of the roll, or overflow from the end of the roll by an amount that reduces flow performance or adversely affects the assembly process.

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

[0082] A second filter film layer 240, having a front end 242, a rear end 244, a front surface 246, and a rear surface 248, is positioned across the front spacer layer 250 such that the front surface 246 of the second filter film layer 240 is in contact with the surface of the front spacer layer 250. See Figure 5D.

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

[0084] A second (exit) spacer layer 252 is positioned across the rear (exit) surface 248 of the second film 240. See Figure 5F.

[0085] All of the film layer 240 and spacer layers 250, 252 are sealed along the width at one end of the length (inner end) with a binder or the like. The assembled layers, as shown in Figure 5F, are rolled along the length from the end sealed with the binder (inner end) into a cylindrical roll-pleated filter, such as the cylindrical roll-pleated filter in Figure 4A. All of the film layer and spacer layer at the exposed end of the length (outer end) are sealed along the exposed end of the length with a binder or the like. The cylindrical roll-pleated filter is inserted into a cylindrical housing with the front end of the wind pleats at the inlet end of the housing and the rear end of the wind pleats at the outlet end of the housing, and the housing is adapted to the fluid flow so that the filter film layer 240 passes through as it passes from the housing inlet to the housing outlet.

[0086] As an alternative, Figures 6A and 6B illustrate the steps of forming a roll-pleated filter using continuous or semi-continuous processing. As illustrated, the system 300 includes a source 310 for film 1, a source 312 for film 2, a source 314 for spacer 1, and a source 316 for spacer 2. These sources supply film layers 311, 313, spacer layer 315, and spacer layer 317 to the roll 320.

[0087] During the formation of the roll 320 from the film layer 311, film layer 313, spacer layer 315, and spacer layer 317, laser welding to form pleats is performed on the alternating ends of each of the two film layers using laser welders 340 and 342, one at the inlet end 350 of the roll 320 and the other at the exit end 352 of the roll 320.

[0088] More specifically, referring to Figure 6B, the film layer 311, film layer 313, support (spacer) layer 315, and support (spacer) layer 317 are fed from their respective source rolls 310, 312, 314, and 316 to roll 320. The inlet ends of each of the film layer 311, film layer 313, and support layer 317 are accessible as three exposed layers outside the winding inlet end 350 at the bottom of roll 320 (as shown). The laser 340 applies a laser beam 341 to the three layers to melt, connect, and seal the inlet ends of these three layers (see Figure 6B) and to form pleats at the inlet ends of the three layers. In Figure 6B, the shading across the inlet ends of layers 311, 317, and 313 represents the laser welds formed between the alternating inlet ends of the winding roll 320.

[0089] At the exit end 352 on the opposite end of the roll 320, an equivalent arrangement is used, and a laser 342 can be used to form a seal and pleat at the connected end of the exit end of layers 311 and 315, with the spacer 315 between layers 311 and 315.

[0090] Lasers 340 and 342 may be selected to produce laser beams in a frequency range that is effective for targeting the appropriate layer in the roll 320, for melting the edges of the target layer, and for generating the necessary seal and forming pleats.

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

[0092] During the formation of the roll 320 from film layer 311, film layer 313, spacer layer 315, and spacer layer 317, a binder 348 is applied at alternating ends along the respective edge surfaces of the two film layers 311 and 313 using extruders 344 and 346. The binder 348 (e.g., heated thermoplastic) is applied along the edges of the film layers by extrusion onto the surfaces of the film layers 311 and 313. At their edges, the spacer layers 315 and 317 are not present between the film layers; that is, the edge of spacer layer 315 is offset from the edge of film layer 311 at the exit end 352 to allow the binder 348 to be placed between the film layers 311 and 313, and the edge of spacer layer 317 is offset from the edge of film layer 313 at the inlet end 350 to allow the binder 348 to be placed between the film layers 311 and 313.

[0093] The arrangement uses a binder 348 to bond the alternating surfaces of the film 311 and film 313 together at their edges, forming alternating pleated ends between the film 311 and 313, with one pleated end at the inlet end 350 of the roll 320 and the other pleated end at the outlet end 352 of the roll 320. Roller assemblies 360a and 360b contact the outer film layers 311, 313 and spacer layers 315, 317 on the opposite side of the roll 320 and rotate in the opposite direction of the 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 the smoothing roller are identical, i.e., continuous along the width.

[0094] More specifically, referring to Figure 6D, the film layer 311 and the support (spacer) layer 315 are fed into the roll 320 before moving between the roll 320 and the roller assembly 360a on one side of the roll 320. The film layer 313 and the support (spacer) layer 317 are fed into the roll 320 before moving between the roll 320 and the roller assembly 360b.

[0095] To position the binder 348 in contact with the two surfaces of the film 311 and 313, the edge of the support layer 315 is spaced laterally from the edge of the film layer 311 at the exit end 352, forming a bonding surface 321 for applying the binder 348 to the upper surface of the film layer 311 (as shown). Similarly, the edge of the support layer 317 is spaced laterally from the edge of the film layer 313 at the inlet end 350, forming a bonding surface 323 for applying the binder 348 to bring the binder into contact with the opposite surfaces of both films 311 and 313.

[0096] As the film layer 313 (located above the support layer 317 as shown) is wound around the roll 320, the film layer 313 passes through the extruder 344, and a certain amount of binder 348b is applied to the bonded surface 323 at the edge of the film layer 313 at the inlet end 350. The support layer 317 and the film layer 313, with the binder 348b applied along the bonded surface 323, curl up on the roll 320 and, on the opposite side of the roll 320, come into contact with the bottom surface of the film 311 (as shown), which comes into contact with the support layer 317 and the binder 348b, forming pleats between the two films 311 and 313 at the inlet end 350. When the bottom surface of the film layer 311 comes into contact with the binder 348 applied to the bonding surface 323 of the film 313, the roller 362a applies pressure to the film and binder 348b, along with optional heat, to form a smooth and uniform layer of binder material 348b between the two opposing film surfaces at the inlet end 350. Simultaneously, the smoothing roller 364a comes into contact with the upper (outer) surface of the support layer 315, mechanically adjusting the position of the roller 362a and the extruder 344 relative to the roll 320 as the roll 320 increases in diameter.

[0097] A similar process is carried out at the exit end 352 (not fully visible in Figure 6D). As the film layer 311 (located below the support layer 315 as shown) is wound around the roll 320, the film layer 311 passes through the extruder 346 and a certain amount of binder 348a is applied to the bonded surface 321 at the edge of the film layer 311 at the exit end. The support layer 315 and the film layer 311, with the binder 348a applied along the bonded surface 321, curl up on the roll 320 and, on the opposite side of the roll 320 (not visible), come into contact with the surface of the film 313, which comes into contact with the support layer 315 and the binder 348a, forming a pleat between the two films at the exit end 352. When the surface of the film layer 313 comes into contact with the binder 348 applied to the bonding surface 321 of the film 311, the roller 362 applies pressure, along with optional heat, to the film and binder to form a smooth and uniform layer of the binder material 348 between the two opposing film surfaces at the inlet end 350. Simultaneously, the smoothing roller 364 comes into contact with the upper (outer) surface of the support layer 315, mechanically adjusting the position of the roller 362 and the extruder 344 relative to the roll 320 as the diameter of the roll 320 increases.

[0098] System 350 additionally controls the alignment of the edges of the membranes 311 and 313 and the support layers 315 and 317 as the membranes and support layers are wound onto the roll 320. The degree of alignment of the different layers may specifically affect the performance of the wound filter with respect to the fluid flow through the wound filter. See Figure 7. The alignment of the support layers may not be very important to the flow properties of the filter. The support layers may be slightly protruding (extending beyond the membrane layers) to slightly recessed at either the inlet or outlet end without affecting the fluid flow to or from the wound filter. Preferably, the edge of the winding end of the support layer may extend beyond the edge of the adjacent wound membrane layer ("protrude" from the edge) by 1 mm or 3 mm or less at either the inlet or outlet end. At the outlet end, the membrane layer may be allowed to protrude or recess slightly, so as not to cause the fluid flow from the outlet end to overlap or interfere with the protruding portion of the membrane at the outlet end. Preferably, the edge of the wound end of the membrane layer at the outlet end may extend beyond the edge of the adjacent wound support layer ("protrude" relative to the edge) by 1 millimeter or 3 millimeters or less at the outlet end.

[0099] If the film protrudes excessively from the adjacent support material layer at the inlet end, the film may overlap and interfere with the fluid flowing into the support layer. See Figure 7. In a preferred roll, the alignment of film 311 and 313 is controlled to create a high degree of alignment of the edges of film 311 and 313 at the inlet end 350. Preferably, the winding edge of the film layer at the inlet end may extend beyond the inlet end edge of the adjacent support layer ("protrudes" from the edge) by 1 mm or less, such as 0.5 mm or less. Alternatively or additionally, the winding edge of the film layer at the inlet end may extend beyond the winding edge of the next adjacent film layer ("protrudes" from the edge) by 1 mm or less, such as 0.5 mm or less, and be separated from the next adjacent film layer by the inlet end of the support layer or by the binder; see Figure 7. It should be noted that all descriptions of edge sealing throughout this document mean that sealing may occur in close proximity to or within the edge of the film material layer. To maximize the functional film area, it is desirable to bond the film layers as close to the edges as possible. To limit the risk of binders protruding from the film layers and potentially inhibiting fluid flow to the support layers, it may be desirable to seal them away from the edges to accommodate some variation in the process. It is desirable to have binders at the edges, or even slight protrusions of adjacent film layers, provided that they do not protrude enough to cause inhibition of flow to adjacent supports.

[0100] Figures 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 internal space containing a roll-pleated filter 210. As shown, the filter assembly 280 contains the filter 210 within the housing 270. The housing 270 includes an inlet 272 at one end of the housing 270 (the bottom end or inlet end, as shown) and an outlet 274 at a second end of the housing 270 (the top end or outlet end, as shown). The housing 270 defines an internal space 282 which houses the filter 210 in such a manner that any fluid entering the inlet 272 must pass through the filter film layer 240 of the filter 210 before it can pass through the outlet 274; in other words, the filter assembly 280 is configured as a dead-end filter assembly.

[0101] The filter 210 is a roll-pleated filter as described herein. The filter 210 comprises multiple wound filter film layers 240 formed by rolling multiple filter film layers and an optional spacer layer around a central axis including an axial space 290, the axial space 290 forming an open space along the central axis of the filter 210 as shown, and separated from the internal space 282 of the filter assembly 280 that houses the filter 210. Fluid flowing to the inlet 272 does not enter the axial space 290.

[0102] The axial space 290 does not contain the fluid that has passed through the filter 210 and is advantageously available for use to allow for additional functionality of the filter assembly 280. For example, the axial space 290 can house an electronic sensor to monitor the state or performance of the filter 210, and for example, an electronic temperature sensor or an electronic pressure sensor may be inserted through or pass through the axial space 290 into the internal space 282 to enable direct or indirect monitoring of the state of the filter 210 or the fluid passing through the internal space 282. Optionally, the axial space 290 may include 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. Still, as an alternative, 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 roll membrane layer that begins approximately at the location of the central axis.

[0103] Roll-pleated filters as described herein include two or more filter membrane layers, each of which may be individually referred to as “filter membrane” or simply “membrane” in this specification. An example of a useful filter membrane is a membrane made from a porous polymer, i.e., a porous polymer filter membrane. A useful porous polymer membrane has two opposing surfaces (or opposing “sides”) that function as an inlet surface and an outlet surface, with the membrane thickness being between the two opposing surfaces. The membrane includes a porous structure across the membrane thickness that allows fluid to flow from one side of the membrane (inlet side) through the membrane thickness to the opposite side of the membrane (outlet side) and through that opposite side of the membrane (outlet side). When a 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 a gas, as the fluid passes through the membrane, but retains impurities present in the fluid.

[0104] A porous membrane contains interconnected passages (pores, channels, or cavities) in the form of multiple randomly oriented, winding paths extending from one surface of the membrane to the opposite surface. These passages generally provide winding channels or paths through which the fluid to be filtered must pass, and through which impurities can be removed from the fluid by a sieving or non-sieving mechanism.

[0105] The "sieving" filtration mechanism allows a porous membrane to physically prevent impurities present in the fluid from passing through the membrane—that is, from entering, passing through, and exiting the membrane. Impurities larger than the pores (e.g., particles) are prevented from entering the membrane, or their passage may be physically prevented by the membrane's structure. Impurities smaller than the membrane's pores may be able to enter the membrane, but the "sieving" mechanism still prevents them from completely passing through the membrane by trapping them on the surface or in the winding pathways within the membrane. The filtered fluid then passes through the membrane, resulting in the flow of fluid containing a reduced amount of impurities removed by the filter through the sieving mechanism.

[0106] Another filtration mechanism, sometimes called a "non-sieving" mechanism, removes impurities not by physical separation (sieving), but by electrostatic or chemical interactions that attract them to the surface of the filter membrane. 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 filter membrane material, especially if the molecules are charged (i.e., anions, cations, etc.), and can be retained by the filter material.

[0107] Useful membranes are sometimes referred to as "open-pore" membranes in contrast to "closed-pore" membranes. Open-pore membranes can take the form of thin films or sheets of extruded porous polymer material having an open-pore porous structure with a relatively uniform thickness, comprising a polymer matrix that defines a number of open "bubbles" which are three-dimensional cavities or pores. The open bubbles can be described as openings, pores, channels, or passages that are broadly interconnected between adjacent bubbles to allow fluid to flow from one side of the membrane (inlet surface) to the other side (outlet surface) across the thickness of the membrane.

[0108] Porous polymer filter membranes can be constructed from porous polymer films having an open-pore structure with pores, where the average pore size can be selected based on the expected use of the membrane, i.e., based on 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 for processing fluids used in semiconductor materials or microcomputer-aided computing devices range from about 0.001 microns to about 10 microns, in the range of microns or less. An example porous polymer filter membrane may have pores of a size (average pore size) that can be considered either a microporous filter membrane or an ultrafiltration membrane. Microporous membranes may have average pore sizes ranging from about 0.05 microns to about 10 microns, and the pore size is selected based on one or more factors including the size or type of particles of impurities to be removed, pressure and pressure drop requirements, flow requirements, and viscosity requirements of the fluid processed by the filter. Ultrafiltration membranes may have average pore sizes ranging from 0.001 microns to about 0.05 microns. Pore ​​size is often reported as the average pore size of porous materials, which can be measured by known techniques such as mercury intrusion (MP), scanning electron microscopy (SEM), liquid displacement spectroscopy (LLDP), or atomic force microscopy (AFM).

[0109] The filter membranes described herein can be made from any of a variety of polymers, including many polymers that are clearly known to be useful for preparing porous polymer filter membranes. Examples of polymers currently known or preferred 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 nylon (e.g., nylon 6, nylon 66). The filter membranes can be made from a single type of polymer, or from two or more different polymers, either as a compound or mixture, or as different layers of a 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 with other fluorinated or non-fluorinated monomers. Examples of polyesters include polyethylene terephthalate and polybutylene terephthalate, as well as related copolymers.

[0111] Porous polymer filter films may contain a completely fluorinated polymer essentially made from a fluorinated monomer, such as a fluorinated polymer material that can be fluorinated or totally fluorinated, or a fluorinated polymer material that can be made from a fluorinated polymer material, or essentially made from a fluorinated polymer material. An example filter layer may contain a polyolefin such as polyethylene (e.g., UPE), may consist of a polyolefin, or essentially consist of a polyolefin. A porous polymer filter layer essentially made from a fluorinated material may contain less than 0.5, 0.1, or 0.01 weight percent of fluorine. A porous polymer filter layer essentially made from a polyolefin such as polyethylene may be derived from a monomer containing at least 99, 99.5, 99.0, or 99.9 weight percent of a polyolefin (e.g., polyethylene) monomer.

[0112] A porous polymer filter film of any composition may be optionally treated, such as by plasma treatment, to enhance its adhesion or filtration properties.

[0113] Various techniques are known for forming porous filter membranes. Examples of these techniques include, among many others (including thermally induced phase inversion (TIPS) and induced phase inversion (NIPS) techniques), molten extrusion (e.g., molten casting) techniques and immersion casting (phase inversion) techniques. Different techniques for forming porous membrane materials can be used to form different porous membrane structures with respect to the size and distribution of pores formed in the membrane; that is, different techniques may be used to produce different pore dimensions and membrane structures, sometimes referred to as "morphology," meaning the uniformity, shape, and distribution of pores within the membrane.

[0114] Useful membrane morphologies include homogeneous (isotropic) and asymmetrical (anisotropic). Porous membranes with substantially uniformly sized pores evenly distributed throughout the membrane are often referred to as isotropic or “homogeneous.” Anisotropic (also known as “asymmetrical”) membranes can be considered to have a morphology in which a gradient of pore size exists across the membrane; for example, a membrane may have a porous structure in which the pore structure changes along the thickness of the membrane, with relatively larger pores on one surface and relatively smaller pores on the other. The term “asymmetrical” is often used interchangeably with the term “anisotropic.” Often, a portion of a membrane with relatively smaller pores (compared to other areas 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 roll-pleated filters as described, anisotropic membranes can be used in a dense region toward the inlet space and an open region toward the outlet space, or in an open region toward the inlet space and a dense region toward the outlet space.

[0115] Filter membranes can also be characterized by their foaming point, which can be measured by various techniques. According to the example foaming point test method, a porous polymer filter membrane of the sample is immersed and wetted in 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 foaming point. Measuring using an HFE 7200 at a temperature of 20–25°C, the foaming points of the useful or preferred porous polymer filter membrane examples described herein may range from 1 to 400 pounds (psi) per square inch, for example, from 2 psi to 300 psi, in the range of 10–200 psi.

[0116] Porous filter membranes can also be characterized by their porosity. A porous polymer filter layer, as described herein, may have any degree of porosity that will make the porous polymer filter layer effective, as described herein, in filtering a flow of liquid to produce a highly pure filtered liquid material. An example porous polymer filter layer may have relatively high porosity, such as at least 30 percent or at least 50 percent porosity, for example, in the range of 30 to 85 percent porosity. In the art of porous bodies, as used herein, the porosity (sometimes referred to as void fraction) of a porous body is the degree of empty (i.e., "empty") space in the body as a percentage of the total volume of the body, and is calculated as the ratio of the volume of voids in the body to the total volume of the body. A body with zero percent porosity is completely solid.

[0117] The porous polymer filter film described may be in the form of a sheet (thin film) with any useful thickness, such as 10 to 100 microns or in the range of 2 to 200 microns. Optionally, the thickness of the filter film layer may vary along the width of the film between the inlet and outlet ends, or gradually decrease. For example, the filter film may have a greater thickness at the inlet end and a smaller thickness at the outlet end.

[0118] The filter described may optionally include two spacer layers. One spacer layer may be located in the input space between the opposing input surfaces of adjacent film layers, and the other spacer layer may be located in the output space between the opposing exit surfaces of adjacent film layers.

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

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

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

[0122] The roll-pleated filters described herein may be useful for processing fluids from a wide range of commercially important liquids or gases. These fluids include liquids in any industry, but specifically, fluids used as processing solvents, cleaning agents, and other processing solutions for semiconductor and microelectronic device processing, used at very high levels of purity. Examples of these types of fluids include liquid materials (e.g., solvents) used in photolithography, cleaning, or various other processes in the preparation of microelectronic devices. Specific examples include processing solutions for spin-on glass (SOG) technology, back-surface anti-reflective coating (BARC) methods, photolithography, cleaning, purging steps, and deposition steps (e.g., chemical vapor deposition (including plasma chemical vapor deposition and other variations)), and atomic layer deposition.

[0123] Impurities are chemical substances different from the processing fluid that are dissolved in the liquid processing fluid or suspended in the gaseous processing fluid. Examples of chemically described impurities include hydrocarbon molecules, including charged (ionic) molecules and oligomers, and inorganic compounds such as metal oxides (titanium dioxide), metal atoms, and metal ions. In fluids that are in gaseous form, contaminants can be any substance known as “airborne molecular contaminants” (AMCs), which are chemical substances in the form of vapors or aerosols that, if present, have a harmful effect on the product or processing. These chemicals can be organic or inorganic and include acids, bases, polymer additives, organometallic compounds, and dopants. Sources of airborne molecular contaminants include building materials in buildings and cleanrooms, the general environment, processing chemicals, and personnel.

[0124] Some specific non-limiting examples of liquid organic solvents that can be filtered using a wound-pleated 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 isobutyl carbinol (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, polar organic solvents such as isopropyl alcohol may contain trace amounts of hydrocarbons, metal oxides, or metal ions. The example methods described may involve removing one or more of these impurities from the 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., methane, propane, butane, or different nonpolar alkanes such as C5-C10 alkanes), alkane impurities, hydrocarbon oligomeric derivatives of the nonpolar organic solvent, or metals. The example methods described may involve removing one or more of these impurities from the nonpolar organic solvent such as hexane. [Examples]

[0127] Example 1 A wound-pleated filter useful for reducing the amount of trace impurities in a fluid, A multilayer filter membrane assembly comprising a first porous filter membrane layer and a second porous filter membrane layer, wherein each of the first porous filter membrane layer and the second porous filter membrane layer 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 end and the outlet end. The porous filter membrane assembly is wound along its length and around its central axis to form a wound-pleated filter. The inlet surface of the first porous filter film layer faces the inlet surface of the second porous filter film layer. A wound-pleated filter has a wound inlet pleat at the inlet end of the wound-pleated filter that includes the inlet end of the adjacent filter film layer. A wound-pleated filter has a wound outlet pleat at the outlet end of the wound-pleated filter that includes the outlet end of the adjacent filter film layer. A wound-pleated filter including a multilayer filter membrane assembly.

[0128] Example 2 The filter of Example 1, comprising windings of multiple porous filter film layers.

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

[0130] Example 4 A filter in any one of Examples 1 to 3, wherein the wound inlet pleats include a fold between the inlet ends of adjacent porous filter membrane layers, or the inlet ends of two adjacent porous filter membrane layers joined together by a binder, or the inlet ends of two adjacent porous filter membrane layers joined together by welding.

[0131] Example 5 A single filter of Examples 1 to 4, wherein the wound outlet pleats include a fold between the outlet ends of adjacent porous filter film layers, the outlet ends of two adjacent porous filter film layers joined together by a binder, or the outlet ends of two adjacent porous filter film layers joined together by welding.

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

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

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

[0135] Example 9 A filter according to any one of Examples 1 to 8, wherein each of the first and second film layers comprises a polymer film capable of reducing the amount of trace impurities from the fluid as the fluid passes through it.

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

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

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

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

[0140] Example 14 A filter from any one of Examples 1 to 13, having a total inlet surface area ranging from 0.1 to 100 square meters.

[0141] Example 15 A multilayer filter membrane assembly comprising a first porous filter membrane layer and a second porous filter membrane layer, but without any additional porous filter membrane layers, is one of the filters from Examples 1 to 14.

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

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

[0144] Example 18 A multilayer filter membrane assembly comprising a first porous filter membrane layer, a second porous filter membrane layer, and a third porous filter membrane layer, one of the filters from Examples 1 to 14.

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

[0146] Example 20 A wind-pleated filter comprising a multilayer filter membrane assembly including a first porous filter membrane layer and a second porous filter membrane layer, each of the first and second porous filter membrane layers comprising 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, wherein the porous filter membrane assembly is wound along the length and around a central axis to form a wind-pleated filter comprising a plurality of porous filter membrane assembly windings, the first porous filter membrane layer A wind-pleated filter comprising a multilayer filter membrane assembly, wherein the inlet surface of the first porous filter membrane layer faces the inlet surface of the second porous filter membrane layer, the wind-pleated filter 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 wind-pleated filter includes pleats including a fold, a weld, or a thermoplastic binder, the wind-pleated filter has a wind inlet end of the membrane layer at the inlet end of the wind-pleated filter, and the wind-pleated filter has a wind outlet end of the membrane layer at the outlet end of the wind-pleated filter.

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

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

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

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

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

[0152] Example 26 The thermoplastic binder is one of the filters from Examples 20 to 25, comprising a thermoplastic polymer selected from polyolefins, fluoropolymers, and perfluoropolymers.

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

[0154] Example 28 The thermoplastic binder is one of the filters from Examples 20 to 27, containing less than 1 weight percent of an organic solvent.

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

[0156] Example 30 The impurities are present in the liquid in amounts less than 100 parts per million, according to the method of Example 29.

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

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

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

[0160] Example 34 The fluid is selected from 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), one of the methods from Examples 29 to 32.

[0161] Example 35 The fluid is a polar organic solvent, and the impurities are hydrocarbons, metal oxides, or metal ions, according to any one of the methods in Examples 29 to 34.

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

[0163] Example 37 The fluid is a nonpolar organic solvent, and the impurities are nonpolar hydrocarbons or metals, according to any one of the methods in Examples 29 to 36.

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

[0165] Example 40 A method for preparing a wound-pleated filter, A multilayer filter film assembly comprises a first porous filter film layer and a second porous filter film 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 end and the outlet end. The inlet surface of the first porous filter film layer faces the inlet surface of the second porous filter film layer. To form a wound-pleated filter that includes winding multiple multilayer filter film assemblies, A pleat comprising the outlet end of a first porous filter film layer and the outlet end of an adjacent porous filter film layer, forming a pleat that includes a fold, a weld, or a thermoplastic binder. A pleat comprising the inlet end of a first porous filter film layer and the inlet end of an adjacent porous filter film layer, forming a pleat that includes a fold, a weld, or a thermoplastic binder. Methods that include...

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

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

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

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

[0170] Example 45 Any one of Examples 40 to 44, comprising applying a binder to connect the inlet end of a first porous filter layer of a porous filter layer assembly to the inlet end of a second porous filter layer of a porous filter layer assembly.

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

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

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

[0174] Example 49 The method of Example 48, which involves connecting the edges of adjacent film layers before rolling the layers to form a roll-pleated filter.

[0175] Example 50 The method of Example 49, which involves joining the edges of adjacent film layers after rolling up the layers, in order to form a roll-pleated filter.

[0176] Example 51 Any one of the methods described in Examples 48 to 50, which involves connecting the edges of adjacent film layers by forming a weld or by applying a binder.

[0177] Example 52 Any one of the methods from Examples 48 to 51, which includes connecting the edges of adjacent film layers by applying a thermoplastic binder.

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

[0179] Example 54 The method of Example 53, which includes controlling the alignment of the edge of the first film layer at the inlet end and the edge of the second film layer at the inlet end.

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

Claims

1. A wound-pleated filter useful for reducing the amount of trace impurities in a fluid, A multilayer filter membrane assembly comprising a first porous filter membrane layer and a second porous filter membrane layer, wherein each of the first porous filter membrane layer and the second porous filter membrane layer comprises 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 assembly is wound along its length and around its central axis to form a wound-pleated filter. The inlet surface of the first porous filter film layer faces the inlet surface of the second porous filter film layer. The wind inlet pleat includes the inlet end of the adjacent filter film layer at the inlet end of the wind-pleated filter. The wind outlet pleat includes the outlet end of the adjacent filter film layer at the outlet end of the wind-pleated filter. A wound-pleated filter including a multilayer filter membrane assembly.

2. The filter according to claim 1, comprising windings of multiple porous filter film layers.

3. The filter according to claim 1 or 2, comprising an outlet surface of a first porous filter film layer facing the outlet surface of an adjacent porous filter film layer.

4. The winding entrance pleats, The fold between the inlet edges of adjacent porous filter film layers, The inlet ends of two adjacent porous filter film layers bonded together by a binder, or The entrance ends of two adjacent porous filter film layers joined together by welding. A filter according to any one of claims 1 to 3, including the filter described in any one of claims 1 to 3.

5. The wind exit pleats, Folding between the outlet ends of adjacent porous filter film layers, The outlet end of two adjacent porous filter film layers bonded together by a binder, or The outlet end of two adjacent porous filter film layers joined together by welding A filter according to any one of claims 1 to 4, including the filter described in any one of claims 1 to 4.

6. The filter according to claim 4 or 5, wherein the binder comprises a thermoplastic polymer selected from polyolefins, fluoropolymers, and perfluoropolymers.

7. The filter according to claim 4 or 5, wherein the binder is selected from polypropylene, polyethylene, polytetrafluoroethylene (PTFE), and polyfluoroalkylene (PFA).

8. The filter according to any one of claims 4 to 7, wherein the binder is a thermoplastic polymer containing less than 1 weight percent of an organic solvent.

9. The filter according to any one of claims 1 to 8, wherein each of the first and second film layers includes a polymer film capable of reducing the amount of trace impurities from a fluid as the fluid passes through it.

10. The filter according to any one of claims 1 to 9, wherein each of the first porous filter film layer and the second porous filter film layer comprises a polymer selected from polyamide, polyimide, polyamide-polyimide, polysulfone, fluoropolymer, and nylon.

11. The filter according to any one of claims 1 to 10, wherein each of the first porous filter membrane layer and the second porous filter membrane has a thickness in the range of 2 to 200 microns.

12. The filter according to any one of claims 1 to 11, wherein each of the first porous filter membrane layer and the second porous filter membrane includes a polymer membrane having a symmetrical morphology.

13. The filter according to any one of claims 1 to 11, wherein each of the first porous filter membrane layer and the second porous filter membrane includes a polymer membrane having an asymmetrical morphology.

14. A filter according to any one of claims 1 to 13, having a total inlet surface area in the range of 0.1 to 100 square meters.

15. The filter according to any one of claims 1 to 14, wherein the multilayer filter membrane assembly comprises a first porous filter membrane layer and a second porous filter membrane layer, and does not include an additional porous filter membrane layer.

16. An inlet-side spacer between the inlet surface of the first porous filter film layer and the inlet surface of the second porous filter film layer, An outlet-side spacer is positioned between the outlet surface of the porous filter film layer and the outlet surface of the adjacent porous filter film layer. A filter according to any one of claims 1 to 15, including the filter described in any one of claims 1 to 15.

17. The filter according to claim 16, wherein each of the inlet spacer and the outlet spacer has a thickness in the range of 10 to 2000 microns.

18. The filter according to any one of claims 1 to 14, wherein the multilayer filter film assembly includes a first porous filter film layer, a second porous filter film layer, and a third porous filter film layer.

19. The filter according to claim 18, wherein the outlet surface of the second porous filter film layer faces the outlet surface of the third porous filter film layer.

20. It is a wound-pleated filter, A multilayer filter membrane assembly comprising a first porous filter membrane layer and a second porous filter membrane layer, wherein each of the first porous filter membrane layer and the second porous filter membrane layer comprises 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 film layer assembly is wound along its length and around a central axis to form a wound-pleated filter, which includes windings of multiple porous filter film layer assemblies. The inlet surface of the first porous filter film layer faces the inlet surface of the second porous filter film layer. The pleats include the outlet end of the first porous filter film layer and the outlet end of the adjacent porous filter film layer, and the pleats include a fold, a weld, or a thermoplastic binder. The winding inlet end of the film layer at the inlet end of the wind-pleated filter, The winding outlet end of the film layer at the outlet end of the wind-pleated filter, Having, Wind-pleated filter.

21. The outlet surface of the first porous filter layer facing the outlet surface of the second porous filter layer of the adjacent filter layer, A pleat including the inlet end of a first porous filter film layer and the inlet end of an adjacent filter film layer, the pleat including a fold, weld, or thermoplastic binder The filter according to claim 20, including the filter described in claim 20.

22. The filter according to claim 20 or 21, wherein each of the first porous filter film layer and the second porous filter film layer has a thickness in the range of 2 to 200 microns.

23. The filter according to any one of claims 20 to 22, wherein each of the first porous filter film layer and the second porous filter film layer comprises a polymer selected from polyamide, polyimide, polyamide-polyimide, polysulfone, fluoropolymer, and nylon.

24. An inlet-side spacer between the inlet surface of the first porous filter film layer and the inlet surface of the second porous filter film layer, An outlet-side spacer is positioned between the outlet surface of the porous filter film layer and the outlet surface of the adjacent porous filter film layer. A filter according to any one of claims 20 to 23, including the filter described in any one of claims 20 to 23.

25. The filter according to any one of claims 20 to 24, wherein each of the inlet spacer and the outlet spacer has a thickness in the range of 10 to 2000 microns.

26. The filter according to any one of claims 20 to 25, wherein the thermoplastic binder comprises a thermoplastic polymer selected from polyolefins, fluoropolymers, and perfluoropolymers.

27. The filter according to any one of claims 20 to 26, wherein the binder is selected from polypropylene, polyethylene, polytetrafluoroethylene (PTFE), and polyfluoroalkylene (PFA).

28. The filter according to any one of claims 20 to 27, wherein the thermoplastic binder comprises less than 1 weight percent of an organic solvent.

29. A method for removing impurities from a fluid, comprising passing the fluid containing trace impurities through a filter according to any one of claims 1 to 28 such that the filter membrane retains some of the trace impurities.

30. The method according to claim 29, wherein impurities are present in the liquid in an amount less than 100 ppm.

31. The method according to claim 29 or 30, wherein the filter film retains at least 90 percent of the impurities present in the fluid.

32. The method according to any one of claims 29 to 31, wherein the fluid is a processing fluid used in semiconductor processing.

33. The method according to any one of claims 29 to 32, wherein the fluid is a polar organic solvent or a non-polar organic solvent.

34. The method according to any one of claims 29 to 32, wherein the fluid is selected from 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).

35. The method according to any one of claims 29 to 34, wherein the fluid is a polar organic solvent and the impurities are hydrocarbons, metal oxides, or metal ions.

36. The method according to claim 35, wherein the fluid is isopropyl alcohol.

37. The method according to any one of claims 29 to 36, wherein the fluid is a nonpolar organic solvent and the impurities are nonpolar hydrocarbons or metals.

38. The method according to claim 37, wherein the fluid is hexane and the impurity is an alkane.

40. A method for preparing a wound-pleated filter, A multilayer filter film assembly comprising a first porous filter film layer and a second porous filter film layer, wherein each of the first porous filter film layer and the second porous filter film layer comprises 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 inlet surface of the first porous filter layer facing the inlet surface of the second porous filter layer is Using, Winding a multilayer filter film assembly to form a wound-pleated filter that includes winding multiple multilayer filter film layer assemblies, The method involves forming a pleat that includes the outlet end of a first porous filter film layer and the outlet end of an adjacent porous filter film layer, wherein the pleat includes a fold, a weld, or a thermoplastic binder, and the method involves forming a pleat that includes the outlet end of a first porous filter film layer and the outlet end of an adjacent porous filter film layer. The method involves forming a pleat that includes the inlet end of a first porous filter film layer and the inlet end of an adjacent porous filter film layer, wherein the pleat includes a fold, a weld, or a thermoplastic binder, and the method involves forming a pleat that includes the inlet end of a first porous filter film layer and the inlet end of an adjacent porous filter film layer. A method that includes this.

41. The method according to claim 40, comprising winding a porous filter layer assembly to position the outlet surface of the first porous filter layer facing the outlet surface of the second porous filter layer.

42. The method according to claim 40 or 41, wherein the porous filter film layer assembly includes a fold that connects the outlet end of a first porous filter film layer to the outlet end of a second porous filter film layer.

43. The method according to claim 40, comprising applying a binder to connect the outlet end of a first porous filter layer of a porous filter layer assembly to the outlet end of a second porous filter layer of a porous filter layer assembly.

44. The method according to claim 43, wherein the binder is a thermoplastic polymer, and the method comprises heating the binder and applying the heated binder to the inlet end of a first porous filter membrane layer or to the inlet end of a second porous filter membrane by extrusion.

45. The method according to any one of claims 40 to 44, comprising applying a binder to connect the inlet end of a first porous filter layer of a porous filter layer assembly to the inlet end of a second porous filter layer of a porous filter layer assembly.

46. The method according to claim 45, wherein the binder is a thermoplastic polymer, and the method comprises heating the binder and applying the heated binder to the inlet end of a first porous filter membrane layer or to the inlet end of a second porous filter membrane by extrusion.

47. The method according to claim 44 or 46, comprising applying pressure and optional heat to the applied binder after applying a heated binder.

48. A method for preparing a roll-pleated filter from multiple film layers, Aligning the leading and trailing edges of the film layer, To form a wind-roll filter with multiple windings, the layers are rolled along the length of the layers, Connecting adjacent leading and trailing edges of alternating winding film layers A method that includes this.

49. The method according to claim 48, comprising connecting the edges of adjacent film layers before rolling the layers to form a roll-pleated filter.

50. The method according to claim 49, comprising connecting the edges of adjacent film layers after rolling up the layers in order to form a roll-pleated filter.

51. The method according to any one of claims 48 to 50, comprising connecting the edges of adjacent film layers by forming a weld or by applying a binder.

52. The method according to any one of claims 48 to 51, comprising connecting the edges of adjacent film layers by applying a thermoplastic binder.

53. Aligning the first film layer and the first support layer along their length, Aligning the second membrane layer and the second support layer along the length, To form a roll, the aligned first film layer and first support layer are wound along the length together with the aligned second film layer and second support layer. At the entrance end of the first film layer, the first binder is applied to the first surface of the first film layer, At the exit end of the second film layer, the second binder is applied to the first surface of the second film layer, At the entrance ends of the first and second films, the first binder is brought into contact with the second surface of the second film layer, At the exit ends of the first and second films, the second binder is brought into contact with the second surface of the first film layer. The method according to any one of claims 48 to 52, including the method described in any one of claims 48 to 52.

54. The method according to claim 53, comprising controlling the alignment of the edge of the first film layer at the inlet end and the edge of the second film layer at the inlet end.

55. The method involves 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, The method involves winding an outlet-side spacer between the outlet surface of the first porous filter film and the outlet surface of the second porous filter film. The method according to any one of claims 48 to 54, including the method described in any one of claims 48 to 54.

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