Layered microporous membrane products and related methods

Abstract

DETAILED DESCRIPTION OF THE INVENTION Porous membrane products containing two or more membrane layers bonded together over a portion of the membrane area, methods and systems for preparing the porous membrane products, and methods of using the porous membrane products are described.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to porous membrane products containing two or more membrane layers bonded together over a portion of the membrane area, methods and systems for preparing the porous membrane products, and methods of using the porous membrane products. [Background technology]

[0002] Porous polymeric membranes, including those known as microporous membranes, are used to remove contaminants from various types of fluids. Some membranes are useful for removing general classes of contaminants from fluids. Others are designed to remove specific types of contaminants from fluids. Many types of microporous membranes are designed for general and specialized applications.

[0003] Fluids that may be treated to remove undesired materials include water, liquid industrial solvents and process fluids, industrial gases used in manufacturing or processing, liquids with medical or pharmaceutical uses, and liquids used in semiconductor and microelectronic device manufacturing. Undesired materials removed from fluids include impurities and contaminants such as particles, microorganisms, airborne molecular contaminants, and dissolved chemicals.

[0004] In some filtration applications, two different types of porous membranes may be used in series to remove multiple types of contaminants from a single fluid stream. Two or more different types of porous membranes may be assembled in different configurations to form a multi-membrane (multilayer) assembly designed to remove multiple target substances from a single fluid stream. For example, some types of porous membranes function to remove impurities from a fluid through a sieving mechanism, in which contaminants present in the fluid are physically trapped in the membrane pores based on their size. Other types of membranes function through a non-sieving mechanism, in which impurities smaller than the membrane pores are trapped within the porous membrane by being chemically or electrostatically attracted to the membrane material. Combining non-sieving and sieving membranes can remove both large and small particles.

[0005] Technical challenges exist when producing multi-membrane filter assemblies from two or more individual membranes: the processes used to bond separate porous membranes together into a multi-layer filter assembly can adversely affect the performance characteristics of the individual membranes, such as reducing fluid flow rates through the membranes.

[0006] In some methods, multi-membrane filter assemblies are prepared by bonding the surfaces of individual membranes together, for example, by placing an adhesive material on the membrane surfaces and compressing them to bond one membrane to another. However, adhesives can hinder membrane performance by clogging pores, which may collapse or deform upon compression. Furthermore, the presence of adhesives can add impurities to the fluid passing through the assembly.

[0007] Instead of bonding the membranes, different membranes can be arranged in a "stacked" configuration, generally without bonding at their surfaces, to maintain their individual filtering properties. However, handling such filters, where the individual layers are not bonded together, can be difficult, especially if one or both layers are very thin.

[0008] Yet another version of a multi-membrane filter assembly is a composite membrane formed by a lamination process that bonds two separate polymeric porous membranes together by placing the membranes in a "stack" assembly, bringing their surfaces into contact, and applying heat and pressure to bond the membranes into a composite. See, e.g., U.S. Patent Publication No. 2021 / 0365092.

[0009] These previous methods of preparing multi-membrane filter assemblies have various drawbacks or opportunities for improvement. Users of filtration technology maintain a continuing need to improve the performance of filter products, including multi-membrane filter assemblies. Summary of the Invention

[0010] The following description relates to multi-membrane filter assemblies prepared from two or more separate polymeric microporous membranes, as well as methods and systems for preparing and using these filter assemblies.

[0011] The methods herein include joining two or more different polymeric microporous membranes together to form a "multilayer membrane" with bonds formed between the two membranes over only a portion of the membrane's area, preferably over a relatively small portion of the membrane's area. According to an exemplary method, two or more membranes are secured together ("bonded" together) at their adjacent surfaces by forming bonds in a bonded area that encompasses a portion of the membrane, preferably a small or minor portion of the material, without affecting the unbonded areas of the membrane. In a specific example, two or more membranes are bonded together by forming a pattern of separate, individual bonds or "welds" between the two membranes. No adhesive is required.

[0012] Compared to known methods of bonding porous membranes together, the method of the present invention can reduce the impact on the performance of the resulting multi-membrane filter assembly. The process of forming bonds between membranes can have a detrimental effect on the filtration performance of the individual membranes, such as reducing the flow rate through the membranes at the bonded locations. The described method forms bonds between membranes only over a portion of the total membrane area, so the performance (e.g., flow rate) loss due to bonding is limited to the bonded areas. The unbonded areas, which represent the majority of the bonded membranes, retain the original performance of the individual membranes.

[0013] Additionally, the described methods can be useful for producing multi-membrane filter assemblies from the combination of two or more different types of microporous membranes with varying physical properties. The membranes bonded together may have different or complementary properties, such as filtration mechanism (sieving, non-sieving), chemical composition, pore size, thickness, melting point, bubble point, porosity, or ability to remove different contaminants from a particular type of fluid. By way of specific example, a multi-membrane filter assembly can be prepared from two or more membranes, including one membrane operating by a sieving filtration mechanism and a second membrane operating by a non-sieving mechanism.

[0014] Previous methods, such as thermal surface lamination, can form effective multi-layer filter assemblies from different materials, but material selection can be limited by film properties such as melting or softening temperatures. These processes work well with films that have similar properties, but may be successful when combining films with different melting or softening temperatures.

[0015] This method does not require that the individual membranes to be bonded together have similar melting points, and the method is useful for bonding two or more membranes with dissimilar melting points together. Furthermore, this method can be adapted to form multi-membrane filter assemblies from three or more different individual membranes.

[0016] The method of the present invention is a useful alternative to previous techniques for forming multi-membrane filter assemblies and can be useful for producing multi-layer filter assemblies having new and useful combinations of membrane materials and having useful or improved filtration performance.

[0017] In one aspect, the description relates to a method for forming a layered polymeric microporous membrane having a first microporous membrane bonded to a second microporous membrane at a plurality of bond regions, the method comprising contacting a surface of the first microporous membrane with a surface of the second microporous membrane and applying energy to the bond regions to form bonds between the surface of the first microporous membrane and the surface of the second microporous membrane at the plurality of bond regions.

[0018] In another aspect, the present specification relates to a layered polymeric microporous membrane comprising a first polymeric microporous membrane and a second polymeric microporous membrane bonded to the first polymeric microporous membrane at a bond area encompassing less than 20 percent of the area of ​​the layered polymeric microporous membrane. [Brief explanation of the drawings]

[0019] [Figure 1A] 1 illustrates exemplary systems and methods described. [Figure 1B] 1 illustrates exemplary systems and methods described. [Figure 1C] 1 illustrates exemplary systems and methods described. [Figure 2A] 1 illustrates exemplary systems and methods described. [Figure 2B] 1 illustrates exemplary systems and methods described. [Figure 2C] 1 illustrates exemplary systems and methods described. [Figure 3] 1 shows an example of the described filter product.

[0020] The figures are schematic and not necessarily to scale. DETAILED DESCRIPTION OF THE INVENTION

[0021] The following description relates to multi-membrane filter assemblies, sometimes referred to herein as "multilayer membranes" or "layered membranes," that are prepared from two or more individual polymeric microporous membranes, as well as methods and systems for preparing and using these filter assemblies.

[0022] A multi-membrane filter assembly is a combination of two or more individual polymeric microporous membranes bonded together with bonded regions (also known as "welded regions") that occupy only a portion of the area of ​​the membranes and are formed from the polymeric material of the polymeric microporous membranes.

[0023] The described layered membranes differ from previous multi-membrane filter assemblies, including previous multi-layer composite membranes made by bonding two individual membranes together through a lamination process that applies heat and compression over the entire area of ​​the individual membranes. Specifically, compared to laminated composite membranes, the layered membranes herein include a bonded area that encompasses only a portion of the area of ​​the membranes.

[0024] The bond (also known as a "weld") that attaches the two membrane surfaces together is formed from the polymeric material of the membrane, eliminating the need for added adhesive materials. For purposes of this membrane feature, an adhesive is not a component of the microporous membrane, but rather a material added to the surface of the microporous membrane for the purpose of adhering the membrane to a second membrane. Examples include adhesives known as pressure-sensitive adhesives, structural adhesives, thermoplastic adhesives, curable adhesives (e.g., heat-curable or radiation-curable adhesives), etc., which are applied to a surface, flow on the surface, and solidify to adhere to the surface. Exemplary adhesives can contain reactive or non-reactive polymers selected from epoxy polymers, polyacrylates, silicones, etc., among others.

[0025] To form the bond as described, the surfaces of the films are brought into contact with each other and energy is applied to only a portion of the film, forming a bond in a limited area referred to as the "bond area" or "weld area." This energy raises the temperature of the film in the bond area to a temperature at which the polymers of the film soften or melt and fuse together sufficiently to adhere the two films together in the bond area when the temperature of the film is lowered, for example, to room temperature (e.g., 20-25 degrees Celsius).

[0026] In useful examples, the bonded area encompasses less than 20 percent of the area of ​​the lamellar film, e.g., less than 10 percent or less than 5 percent of the area of ​​the lamellar film, e.g., 0.5 to 10 percent of the area of ​​the lamellar film. The remaining area of ​​the film, i.e., the "unbonded" area, includes films that are in contact at adjacent surfaces but are not bonded together. The amount of unbonded area of ​​the lamellar film can be at least 80, 90, 95, 97, or 99.5 percent of the area of ​​the lamellar film.

[0027] The bonded regions can have any size and shape. Exemplary bonded regions can include regular patterns of connecting or disconnected lines, or patterns of discrete geometric shapes such as dots, squares, triangles, etc. The bonded regions can have any useful dimensions, including at least one dimension on the millimeter scale, e.g., dimensions less than 5, 3, or 1 mm.

[0028] Layered membranes, as described, comprise two or more individual layers (membranes) bonded together at bond regions. Useful polymeric microporous membranes (also referred to simply as "microporous membranes" or "membranes") include those that can be bonded together by applying energy to the bond regions according to the methods herein to provide a useful multi-membrane filter assembly.

[0029] Individual membranes that can be used to form layered membranes can be characterized as open-pore, polymeric, microporous membranes (e.g., in the form of a thin sheet or film) containing interconnected pores that form passageways extending from one surface of the membrane to the opposite surface of the membrane. The passageways provide tortuous tunnels or paths through which the fluid to be filtered must pass. Contaminants in the fluid are removed from the fluid by being captured by the membrane either mechanically or electrostatically, for example, by a "sieving" mechanism or a "non-sieving" mechanism, or both. A sieving mechanism is a filtration method in which contaminants are removed from a liquid flow by being retained in the membrane pores due to mechanical interference of the pores with the movement of the contaminants. For example, the size dimension of the contaminants may be larger than the size of the membrane pores. A "non-sieving" filtration mechanism is a filtration method in which the filtration membrane retains contaminants contained in the fluid flowing through the membrane in a manner that is not solely mechanical, but also includes, for example, an electrostatic mechanism that electrostatically attracts and retains the contaminants to the surface of the filtration membrane.

[0030] Useful membranes include open-pore membranes having pore sizes in the micron range, and are referred to herein as "microporous" membranes. Typical average pore sizes are in the micron or submicron range, e.g., from about 0.001 micron to about 10 microns. Membranes with average pore sizes of about 0.001 to about 0.05 microns are sometimes classified as ultrafiltration membranes. Membranes with average pore sizes between about 0.05 and 10 microns are sometimes classified as microporous membranes. Membranes may also be characterized by pores with average pore sizes in the nanometer and subnanometer range, e.g., 0.5 to 100 nanometers, and may be characterized as nanoporous membranes.

[0031] Porous membranes can also be characterized based on their "porosity." As used herein, the "porosity" (also referred to as "porosity") of a porous membrane is a measure of the membrane's void (i.e., "empty") space as a percentage of the membrane's volume, calculated as the ratio of the membrane's void volume to the membrane's total volume. A membrane with zero percent porosity is completely solid. Examples of useful membranes can have a porosity that allows the membrane to function effectively as described herein, allowing a suitable flow rate of fluid to pass through the membrane while also removing a high percentage of contaminants or impurities from the fluid. Examples of useful membranes can have a porosity of up to 80 percent, e.g., a porosity in the range of 30-70 percent, or 40-60 percent.

[0032] Various types of polymers are known and useful for forming microporous membranes. Examples include thermoplastic polymers, polyolefins such as polypropylene and polyethylene, polysulfones, polyimides, polyamides, and fluoropolymers (e.g., polytetrafluoroethylene, or "PTFE"). More specific examples include ultra-high molecular weight polyethylene ("UHMWPE"), expanded polyethylene, expanded polypropylene, and polytetrafluoroethylene.

[0033] According to an exemplary multi-membrane filter assembly, the assembly can be prepared by bonding together two or more individual membranes having different but complementary physical characteristics (e.g., thickness), filtration characteristics, or processing properties. The membranes may have different or complementary properties, including filtration mechanism (sieving, non-sieving), chemical composition, pore size, thickness, melting point, bubble point, porosity, or ability to remove different contaminants from a particular type of fluid.

[0034] A multi-membrane filter assembly ("layered membrane") can be formed, for example, from two or more individual microporous membranes having different filtration mechanisms. A layered membrane can be formed to include a combination of one microporous membrane ("sieving membrane") that removes contaminants from a fluid by a sieving mechanism and a second microporous membrane ("non-sieving membrane") that removes contaminants from a fluid by a non-sieving mechanism. Additionally or alternatively, the sieving and non-sieving membranes can have different chemical compositions, thicknesses, porosities, pore sizes (bubble points), etc.

[0035] More specifically, the first membrane may be a sieving membrane that exhibits a relatively high bubble point, e.g., a bubble point of at least 150 pounds per square inch (psi), at least 180 psi, or at least 200 psi, measured either as the initial bubble point or the average bubble point. Examples of sieving membranes that exhibit high bubble points include membranes fabricated with a porosity of less than 50 or 60 percent (e.g., 40-55 percent) and a thickness of less than 20 μm (microns), including less than 15 μm and less than 10 μm. Examples of such membranes can be fabricated from oriented (e.g., biaxially oriented) polyolefins (polypropylene or polyethylene) or fluoropolymers.

[0036] The second microporous membrane may be a non-sieving membrane and may be relatively thick and have a lower bubble point compared to the sieving membrane. Examples of non-sieving membranes may have a bubble point of less than 150 psi, e.g., a bubble point in the range of 50-150 or 100-150 psi, measured either as the initial bubble point or the average bubble point, a porosity of greater than 40 or 50 percent (e.g., 45-70 percent), and a thickness in the range of 5, 10, 20, or 50 microns up to 200 microns, e.g., a thickness in the range of 100-200 microns. Non-sieving membranes may optionally be surface-treated to enhance non-sieving retention of contaminants. Examples of non-sieving membranes may be melt-cast, non-stretched microporous membranes prepared from nylon, polyolefins (e.g., polyethylene, ultra-high molecular weight polyethylene), or fluoropolymers, any of which may be surface-modified to exhibit an electrostatic charge.

[0037] The bubble point is a characteristic of a membrane that correlates with the size of its pores (i.e., average pore diameter). Smaller pore sizes in membranes can have higher bubble points, which often translates to better filtration performance, such as higher retention of smaller-sized particles. However, a higher bubble point typically also translates to a relatively higher resistance to flow through the porous membrane, resulting in a lower fluid flow rate for a given pressure drop.

[0038] One method for determining the bubble point of a porous membrane involves placing a membrane sample in a holder. Air is pressurized through the holder and the flow rate is measured as a function of pressure. This is known as dry air flow. A low-surface tension fluid, HFE-7200 (3M), is introduced to the membrane, wetting it. The gas pressure is gradually increased. The pressure at which gas first flows as bubbles through the sample is called the initial bubble point. The average bubble point is the pressure at which the ratio of the air flow rate through the wet membrane to the air flow rate through the dry membrane is 0.5. Tests are performed at temperatures ranging between 20 and 22 degrees Celsius.

[0039] The individual films used to form the layered film can also be characterized based on their melting temperatures. Different layers of the layered film may have the same or similar melting temperatures, but do not necessarily have the same or similar melting properties. Two individual films made to prepare the layered film may have different melting points, for example, differing by at least 10, 20, or 30 degrees Celsius. As a specific example, one film may be polypropylene and the second film may be polyethylene, with the two films having melting points differing by at least 10, 20, or 30 degrees Celsius.

[0040] Furthermore, the described thermal lamination and ultrasonic methods can generally be used to form multi-membrane assemblies containing two or more membranes with different thickness ranges. This method can be used to bond two or more membranes, each with a small thickness, for example, two or more membranes with thicknesses in the range of 5-100 microns or 10-50 microns. This method can also be used to bond two or more membranes with a larger thickness, for example, two or more membranes with thicknesses greater than 100 microns or greater than 200 microns. This method can also be used to bond two or more membranes with a combination of small and large thicknesses, for example, to bond a first membrane with a thickness in the range of 5-100 microns to a second membrane with a thickness greater than 100 microns or greater than 200 microns.

[0041] The methods herein involve attaching (bonding) two or more different polymeric microporous membranes together with a bond that is formed over only a portion of the membrane's area, preferably over a relatively small portion of the membrane's area. According to an exemplary method, two or more membranes are adhered together ("bonded together") at their adjacent surfaces by a bond that encompasses only a portion of the membrane's total area, preferably a bond that encompasses a small or minor portion of the membrane's area, without the need for added adhesive material in the bonded area and without significantly affecting the membrane's filtration properties (e.g., flowability, retention) or morphology (e.g., pore size, porosity, bubble point) in the unbonded areas.

[0042] Compared to other methods of bonding membranes together, the methods of the present invention can reduce detrimental effects on the performance of the resulting multi-membrane filter assembly. Generally, the process of forming a bond between two individual membranes by applying heat, compression, or adding an adhesive can reduce the filtration performance of the individual membranes, such as by causing a reduction in flow rate through the membranes. The methods described form bonds between membranes over only a portion of the total membrane area, so that any detrimental effects on performance (e.g., reduced flow rate) caused by forming the bond are limited to the bonded area. The unbonded areas of the membranes may be a large or small portion of the area of ​​the bonded membranes, yet retain the original performance of the individual membranes.

[0043] According to the described method, bonds are formed between two or more polymeric microporous membranes in a bond region by applying a sufficient amount of energy to the bond region while avoiding applying the same amount of energy to unbonded regions of the membranes. To form the bond, two or more membranes are contacted and energy is applied to raise the temperature of the two membranes in the bond region. The temperature of the bond region is raised to a temperature at which the polymers of the membranes in the bond region soften or melt and fuse together sufficiently to adhere the two membranes together in the bond region when the temperature of the two membranes is lowered, for example, to room temperature (e.g., 20-25 degrees Celsius).

[0044] To form a bond in the bonding region, the temperature of the individual membranes in the bonding region may be raised to a temperature such that the membranes soften or melt, and the polymer of the membrane combines with the polymer of the adjacent contacting membrane to form a bond when the membranes cool. Energy is applied to soften or melt one or both membranes. When the membranes are kept in contact with at least a slight amount of pressure, the polymer of the softened or melted membrane in the bonding region can flow or otherwise combine to form a bond between the two membrane surfaces. In a specific exemplary method, at least one of the membranes can be heated to a temperature above the melting temperature of the membrane. In another exemplary method, two or more membranes in contact with each other are both heated to a temperature above the melting temperature of both membranes.

[0045] The energy may be in the form of thermal energy transferred to the membrane from a heated surface, or ultrasonic energy, or another useful form of energy. The energy can be applied to the bonded regions using any useful energy source and with sufficient precision to raise the temperature of the bonded regions without similarly raising the temperature of the unbonded regions of the membrane. The unbonded regions may experience a temperature increase, but not to a temperature that would soften or melt the polymers of the membrane in the unbonded regions and cause them to adhere together. Preferably, the unbonded regions of the membrane do not experience a significant change in morphology or flow properties, and the unbonded regions of the membrane retain their through-membrane flow levels, average pore size, bubble point, and porosity substantially unchanged by the process of forming bonds in the bonded regions.

[0046] According to an exemplary method, ultrasonic energy is used to form the bond. While two microporous membranes are held in contact at their surfaces, pressure is applied to the bonding area, keeping the surfaces of the membranes in contact. While the surfaces of the bonding area are held in contact, ultrasonic energy is applied to the membranes, raising the temperature of the membranes in the bonding area. The ultrasonic energy raises the temperature of the polymers in the two membranes, causing the polymers in the bonding area to flow or mix together. The heated polymers are then allowed to cool, creating a bond (or "weld") between the mixed polymers in the bonding area. Using these processes, heat is applied precisely to the bonding area, and the polymers in areas of the membranes outside the bonding area (i.e., the unbonded areas of the membranes) do not experience a temperature increase that significantly affects the properties of the membrane.

[0047] Ultrasonic welding techniques are effective in forming layered membrane products as described by applying ultrasonic energy to the bonding area of ​​two contacting membranes to raise the temperature of the membrane's polymer in the bonded area, causing the heated polymer to form a bond in the bonded area without significantly affecting the membrane's properties in the unbonded areas. An exemplary ultrasonic welding technique uses high-frequency (e.g., 20-40 kHz) ultrasonic energy to generate low-amplitude (e.g., 1-25 μm) mechanical vibrations, generating heat in the bonded area. The heat softens or melts the polymer in the bonded area, allowing it to fuse together to form a bond or "weld" between the two membranes as the polymer cools.

[0048] An alternative form of energy applied to the bond area can be thermal energy applied to the membrane with an amount of pressure sufficient to hold the surfaces together for bonding while the membrane remains in contact at the bond area. Thermal energy can be applied to the bond area through a heated surface that contacts only the bond area without substantially increasing the temperature of the unbonded areas of the membrane.

[0049] Systems and methods useful for forming layered films as described are shown in Figures 1A, 1B, and 1C. In Figure 1A, an ultrasonic welding apparatus 100 includes a rolling anvil 110 and a "sonotrode" (also known as a "horn") 120. The rolling anvil 110 has a rotating cylindrical surface 112 that includes a pattern of multiple elevated extensions 114, which are protrusions that extend radially upward a fixed distance from the surface 112. Each extension 114 includes a welding surface 118 located at the end of the extension. The horn 120 is positioned along the length of the rolling anvil 110 at a distance from the rolling anvil 110, forming a gap 116 between the welding surface 118 of the anvil 110 and the horn 120. The gap 116 can be defined as the distance between the welding surface 118 at the end of the extension 114 and the surface of the horn 120 facing the extension 114. The size of the gap can be approximately equal to the combined thickness of the membranes (130, 140) that move through the gap 116 during use. The size of the gap can be such that the membranes can pass through the gap while applying a slight amount of pressure to the membranes to maintain contact between them during bonding.

[0050] In use, the microporous membranes 130 and 140 are held together on their surfaces and pass through the gap 116 while the anvil roller 110 rotates and the membranes move with the rotating surface of the rolling anvil 110 (see arrows). The anvil roller 110 is rotatably supported at its opposite end as part of the apparatus 100 so that the anvil roller can contact the underside of the assembly of membranes 130 and 140 and move the assembled and contacted membranes through the gap 116 and under the horn 120.

[0051] As the membranes 130 and 140 pass under the horn 120 while supported by the welding surface 118, the horn 120 generates ultrasonic energy to which the membrane polymers adhere. The ultrasonic energy increases the temperature of the membrane, causing the membrane polymers to soften or melt in the bonded area where they contact the surface 118 and fuse together as they cool. The bonded membranes form a layered membrane 124 that passes through the assembly 100, the layered membrane 124 including the bonded area 122.

[0052] 1B, welding apparatus 100 is a variation of welding apparatus 100 of FIG. 1A. Apparatus 100 of FIG. 1B includes nip roller 126 located upstream relative to anvil roller 110 and horn 120. Nip roller 126 receives webs 130 and 140, brings the web surfaces into contact with each other before the webs contact anvil roller 110, and is effective to remove air from between the webs before they are bonded by anvil roller 110 and horn 120.

[0053] Referring to Figure 1C, welding apparatus 100 is a variation of welding apparatus 100 of Figure 1A. Apparatus 100 of Figure 1C includes a third film 150 that is part of an assembly of films (130, 140, and 150) that is processed by passing through gap 116 to form bonded region 122 of layered film 124. According to the method of Figure 1C, more than two films can be used to form layered film 124 bonded together at bonded region 122.

[0054] Compared to other methods for forming multi-membrane filter assemblies from multiple individual polymeric microporous membranes, such as lamination methods that affect the entire membrane surface, the described method is more capable of forming layered membranes from three or more separate membranes because the layered membranes form bonds between three or more layers in limited areas of the membrane, i.e., bonded areas, rather than across the entire membrane surface. Although bonding can have a detrimental effect on the filtration performance of the layered membrane in the bonded areas, the amount of bonded area is limited, and the performance of the unbonded areas is not affected by the bonding process.

[0055] According to an alternative method shown in Figures 2A, 2B, and 2C, the bonded area can be formed not by ultrasonic energy applied to the bonded area, but by thermal energy applied to the bonded area by a heated surface. As shown in Figures 2A, 2B, and 2C, an ultrasonic welding apparatus 200 includes a rolling anvil 210 and a roller 220. The rolling anvil 210 has a rotating cylindrical surface 212 that includes a pattern of multiple raised heated extensions 214, which are protrusions that extend radially upward a fixed distance from the surface 212. Each heated extension 214 includes a heated welding surface ("heated surface") 218 ​​located at the end of the extension. In an alternative example, the surface of the roller 220 may be heated, and the extensions 214 and surface 218 may be heated or unheated.

[0056] The roller 220 is positioned along the length of the rolling anvil 210 at a distance from the rolling anvil 210 to form a gap 216 between the heated surface 218 of the anvil 210 and the horn 120. The gap 216 can be defined as the distance between the heated surface 218 at the end of the extension 214 and the surface of the roller 220 facing the extension 114. The size of the gap 216 can be approximately equal to the combined thickness of the membranes (130, 140) that move through the gap 216 during use. The size of the gap can be such that the membranes can pass through the gap while applying a slight amount of pressure to the membranes to maintain contact between them during bonding.

[0057] In use, microporous membranes 130 and 140 are held together at their surfaces and pass through gap 216 while anvil roller 210 and roller 220 rotate (see arrows). As the membranes pass through gap 216, heated surface 218 contacts the welded areas of the membranes and applies heat to the welded areas, increasing the temperature of the welded areas. As the temperature increases, the polymers of the membranes in the bonded areas soften or melt and, upon cooling, fuse together. The bonded membranes form layered membrane 124, which passes through assembly 100, and layered membrane 124 includes bonded areas 122.

[0058] Referring to Figure 2B, welding apparatus 200 is a variation of welding apparatus 200 of Figure 2A. Apparatus 200 of Figure 2B includes nip roller 226 located upstream relative to anvil roller 210 and roller 220. Nip roller 226 receives web 130 and web 140, brings the surfaces of the webs into contact with each other before they pass through gap 216, and is effective to remove air from between the webs before they are bonded by contact with heated surface 218 as they pass between anvil roller 210 and roller 220 at gap 216.

[0059] Referring to Figure 1C, welding apparatus 200 is a variation of welding apparatus 200 of Figure 2A. Apparatus 200 of Figure 2C includes a third film 150 that is part of an assembly of films (130, 140, and 150) that is processed by passing through gap 216 to form bonded region 122 of layered film 124. According to the method of Figure 2C, more than two films can be used to form layered film 124 bonded together at bonded region 122.

[0060] The multi-membrane filter assemblies ("filter membranes") described herein, or filters or filter components containing filter membranes, are useful in methods for filtering liquid chemicals to purify or otherwise remove unwanted materials from the liquid chemicals, and are particularly useful for producing high-purity liquid chemicals useful in industrial processes requiring chemical inputs with very high levels of purity. Generally, the liquid chemicals can be any of a variety of useful commercially available materials, and can be liquid chemicals useful in any of a variety of different industrial or commercial applications. Specific examples of the filter membranes described can be used to filter or purify liquid chemicals used in semiconductor or microelectronic fabrication applications, such as for filtering liquid solvents or other process solutions used in semiconductor photolithography, wet etching or cleaning processes, ultrapure water, or plating chemistry processes.

[0061] Some specific, non-limiting examples of liquid solvents that can be filtered using the filter membranes as described include n-butyl acetate (nBA), isopropyl alcohol (IPA), 2-ethoxyethyl acetate (2EEA), cyclohexanone, ethyl lactate, gamma-butyrolactone, hexamethyldisilazane, methyl-2-hydroxyisobutyrate, methyl isobutylcarbinol (MIBC), n-butyl acetate, methyl isobutyl ketone (MIBK), isoamyl acetate, propylene glycol monoethyl ether, propylene glycol methyl ether (PGME), 2-heptanone, and propylene glycol monomethyl ether acetate (PGMEA).

[0062] The filter membrane can be included within a larger filter structure, such as a filter or filter cartridge used in a filtration system. The filtration system places the filter membrane in a liquid chemical flow path, for example, as part of a filter or filter cartridge, and causes the liquid chemical to flow through the filter membrane, allowing the filter membrane to remove impurities and contaminants from the liquid chemical. The filter or filter cartridge structure can include one or more of a variety of additional materials and structures that support the filter membrane within the filter and allow fluid to flow from the filter inlet, through the filter membrane, and through the filter outlet, thereby passing through the filter membrane as it passes through the filter. The filter membrane supported by the filter structure can be any useful shape, such as a pleated cylinder, a cylindrical pad, one or more non-pleated (flat) cylindrical sheets, a pleated sheet, etc.

[0063] One example of a filter structure comprising a filter membrane in the form of a pleated cylinder can be prepared to include the following component parts: a rigid or semi-rigid core that supports the pleated cylindrical filter membrane at its internal inlet; a rigid or semi-rigid cage that supports or surrounds the outside of the pleated cylindrical filter membrane on the outside of the filter membrane; optional end pieces or "pucks" located at each of the two opposite ends of the pleated cylindrical filter membrane; and a filter housing that includes an inlet and an outlet, any of which may be included in the filter construction but may not be required. The filter housing can be of any useful desired size, shape, and material, and preferably can be made of a suitable polymeric material.

[0064] As an example, FIG. 3 shows a filter component 330, which is a product having a pleated cylindrical component 310 and an end piece 322, along with other optional components. The cylindrical component 310 includes a filter membrane 312 as described herein and is pleated. The end piece 322 is attached (e.g., "potted") to one end of the cylindrical filter component 310. The end piece 322 can preferably be made of a melt-processable polymeric material. A core (not shown) can be disposed in the interior opening 324 of the pleated cylindrical component 310, and a cage (not shown) can be disposed around the outside of the pleated cylindrical component 310. A second end piece (not shown) can be attached ("potted") to a second end of the pleated cylindrical component 330. The resulting pleated cylindrical component 330, having two opposite panned ends and an optional core and cage, can then be placed into a filter housing that includes an inlet and an outlet configured such that the amount of fluid entering the inlet must pass through the filtration membrane 312 before exiting the filter at the outlet.

[0065] The filter housing can be of any useful desired size, shape and material, preferably a fluorinated or non-fluorinated polymer, such as nylon, polyethylene, or a fluorinated polymer, such as poly(tetrafluoroethylene-co-perfluoro(alkyl vinyl ether)), TEFLON® perfluoroalkoxyalkane (PFA), perfluoromethylalkoxy (MFA), or another suitable fluoropolymer (e.g., perfluoropolymer).

Claims

1. 1. A method of forming a layered microporous membrane comprising a first microporous membrane bonded to a second microporous membrane at a plurality of bond regions, the method comprising: contacting a surface of the first microporous membrane with a surface of a second microporous membrane; and applying energy to the bond regions to form bonds between the surface of the first microporous membrane and the surface of the second microporous membrane at the plurality of bond regions; A method comprising:

2. 10. The method of claim 1, wherein the bonded area comprises less than 20 percent of the area of ​​the layered microporous membrane.

3. 10. The method of claim 1, wherein forming the bond comprises applying energy to the first and second microporous membranes in the bond region to increase the temperature of the bond region and fuse the polymer of the first microporous membrane with the polymer of the second microporous membrane in the bond region.

4. below: raising the temperature of the bond region to a temperature above the melting temperature of the first microporous membrane, above the melting temperature of the second microporous membrane, or above the melting temperature of the first microporous membrane and above the melting temperature of the second microporous membrane; and reducing the temperature of the bonding region while maintaining the first microporous membrane bonded to the second microporous membrane at the bonding region; The method of claim 3, comprising:

5. 10. The method of claim 1, wherein the first microporous membrane has a first microporous membrane melting point and the second microporous membrane has a second microporous membrane melting point, the difference between the first microporous membrane melting point and the second microporous membrane melting point being at least 20 degrees Celsius.

6. 6. The method of any one of claims 1 to 5, wherein one of the first microporous membrane or the second microporous membrane comprises a polymer selected from ultra-high molecular weight polyethylene, polysulfone, oriented polyethylene, oriented polypropylene, polyimide, polyamide, and polytetrafluoroethylene.

7. 6. The method of any one of claims 1 to 5, wherein one of the first and second microporous membranes comprises polyethylene and one of the first and second microporous membranes comprises polypropylene.

8. 6. The method of any one of claims 1 to 5, wherein forming bonds between a surface of the first microporous membrane and a surface of the second microporous membrane in a plurality of bond regions comprises applying ultrasonic energy to the bond regions to heat the bond regions.

9. 6. The method of any one of claims 1 to 5, wherein forming bonds between a surface of the first microporous membrane and a surface of the second microporous membrane in a plurality of bond regions comprises applying heat to the bond regions using a heated surface having areas of bond regions and positioning the bond regions between the heated surface and a roller.

10. The first microporous membrane comprises: an initial bubble point of at least 150 pounds per square meter; a porosity of less than 55 percent, and A thickness of less than 20 microns The method according to any one of claims 1 to 5, wherein the sieving membrane has the formula:

11. The method of any one of claims 1 to 5, wherein the second microporous membrane has a thickness in the range of 20 to 200 microns.

12. The second microporous membrane comprises: an initial bubble point of less than 150 pounds per square meter; a porosity of greater than 40 percent, and More than 50 microns thick 12. The method of claim 11, wherein the membrane is a non-sieving membrane having:

13. 6. The method of any one of claims 1 to 5, wherein one of the first and second microporous membranes comprises polyethylene and one of the first and second microporous membranes comprises polypropylene.

14. below: contacting a surface of the first microporous membrane with a surface of a third microporous membrane; and bonding the first microporous membrane to the second microporous membrane and the third microporous membrane at a plurality of bond regions by applying energy to the bond regions to melt the polymer at the bond regions; and Solidifying the molten polymer to form a bonded area 6. The method of claim 1, comprising:

15. 6. The method of any one of claims 1 to 5, wherein the first microporous membrane has a thickness in the range of 5 to 100 microns and the second microporous membrane has a thickness in the range of 5 to 100 microns.

16. 6. The method of any one of claims 1 to 5, wherein the first microporous membrane has a thickness in the range of 5 to 100 microns and the second microporous membrane has a thickness greater than 100 microns.

17. 6. The method of any one of claims 1 to 5, wherein the first microporous membrane has a thickness greater than 100 microns and the second microporous membrane has a thickness greater than 100 microns.

18. A layered polymeric microporous membrane prepared according to the method of any one of claims 1 to 5.

19. below: a first microporous membrane; a second microporous membrane bonded to the first microporous membrane at a bond area encompassing less than 20 percent of the area of ​​the layered microporous membrane; A layered microporous membrane comprising:

20. 20. The membrane of claim 19, wherein the bonded area comprises less than 10 percent of the area of ​​the layered microporous membrane.

21. 20. The membrane of claim 19, wherein the first microporous membrane has a first microporous membrane melting point and the second microporous membrane has a second microporous membrane melting point, the difference between the first microporous membrane melting point and the second microporous membrane melting point being at least 20 degrees Celsius.

22. 20. The membrane of claim 19, wherein at least one of the first microporous membrane and the second microporous membrane comprises a polymer.

23. 23. The membrane of any one of claims 19-22, wherein one of the first and second microporous membranes comprises polyethylene and one of the first and second microporous membranes comprises polypropylene.

24. The first microporous membrane comprises: an initial bubble point of at least 150 pounds per square meter; a porosity of less than 55 percent, and A thickness of less than 20 microns 23. The membrane of any one of claims 19 to 22, which is a sieving membrane having

25. 22. The membrane of any one of claims 19 to 21, wherein the second microporous membrane has a thickness in the range of 20 to 200 microns.

26. The second microporous membrane comprises: an initial bubble point of less than 150 pounds per square meter; a porosity of greater than 40 percent, and More than 50 microns thick 26. The membrane of claim 25, which is a non-sieving membrane having

27. 23. The membrane of any one of claims 19 to 22, comprising a third microporous membrane bonded to the first microporous membrane and bonded to a second microporous membrane at a bonding region.

28. 23. The membrane of any one of claims 19 to 22, wherein the first microporous membrane has a thickness in the range of 5 to 100 microns and the second microporous membrane has a thickness in the range of 5 to 100 microns.

29. 23. The membrane of any one of claims 19 to 22, wherein the first microporous membrane has a thickness in the range of 5 to 100 microns and the second microporous membrane has a thickness greater than 100 microns.

30. 23. The membrane of any one of claims 19 to 22, wherein the first microporous membrane has a thickness greater than 100 microns and the second microporous membrane has a thickness greater than 100 microns.

31. 23. A filter cartridge comprising the membrane of any one of claims 19 to 22, the filter cartridge comprising a filter housing including an inlet and an outlet, and the membrane supported within the housing between the inlet and the outlet such that liquid entering the inlet passes through the membrane before passing through the outlet.

32. 32. A method of using the filter cartridge of claim 31, comprising passing a fluid through the inlet, passing the fluid through the membrane, and passing the fluid through the outlet, wherein the fluid is useful in a semiconductor manufacturing process.

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