Layered microporous membrane and filter cartridge

Abstract

The utility model relates to a layered microporous membrane and a filter cartridge. The layered microporous membrane is characterized in that the layered microporous membrane comprises: a first microporous membrane, a second microporous membrane bonded to the first microporous membrane at a bonding region covering less than 20% of the area of the layered microporous membrane.

Description

Technical Field

[0001] The utility model relates to a porous membrane product containing two or more membrane layers which are combined together at a part of the membrane area, a method and a system for preparing the porous membrane product, and a method for using the porous membrane product. Background Art

[0002] Porous polymeric membranes, including microporous membranes, are used to remove contaminants from various types of fluids. Some membranes can be used to remove common classes of contaminants from fluids. Other membranes can be designed to remove specific types of contaminants from fluids. Many types of microporous membranes are designed for both general and specialized applications.

[0003] Fluids that are treated to remove undesirable 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. Undesirable materials removed from fluids include impurities and contaminants, such as particles, microorganisms, airborne molecular contaminants, and dissolved chemical materials.

[0004] For some filtration applications, two different types of porous membranes can be used together in series to remove various types of pollutants from a single fluid stream. Two or more different types of porous membranes can be assembled in different arrangements to form a multi-membrane (multi-layer) assembly designed to remove multiple target materials from a single fluid stream. For example, some types of porous membranes are used to remove impurities from fluid via a screening mechanism, wherein the pollutants present in the fluid are physically trapped based on the pores of the size tunicate. Other types of membranes work via non-screening mechanisms, and impurities smaller than the membrane pores are trapped in the porous membrane by means of chemical or electrostatic attraction of impurities to the membrane material. By combining non-screening membranes with screening membranes, both large particles and smaller particles can be removed.

[0005] Technical challenges exist when creating a multi-membrane filter assembly from two or more individual membranes. The processes used to bond the individual porous membranes together into a multi-layer filter assembly can have adverse effects on the performance properties of the individual membranes, such as reduced fluid flow through the membranes.

[0006] By some methods, multiple membrane filter assemblies are prepared by bonding the surfaces of individual membranes together, such as by placing an adhesive material at the membrane surfaces using compression to bond one membrane to another. However, the adhesive may interfere with membrane performance by plugging pores, and the pores may collapse or deform due to compression. In addition, the presence of the adhesive may add impurities to the fluid passing through the assembly.

[0007] As an alternative to bonding membranes, different membranes may be positioned in a "stacked" arrangement of separate membranes, often 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 when one or both of the layers are very thin.

[0008] Yet another type of 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 "stacked" assembly with contacting surfaces and applying heat and pressure to bond the membranes into the composite. See U.S. Patent 2021 / 0365092.

[0009] These previous modes of making multi-membrane filter assemblies have various disadvantages or room for improvement.Users of filtration technology are continually demanding increased capabilities for filter products that include multi-membrane filter assemblies. Utility Model Content

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

[0011] The methods of the present specification involve bonding two or more different polymeric microporous membranes together to form a "multilayer membrane" comprising a bond formed between the two membranes at only a portion of the area of ​​the membrane (preferably, over a relatively small portion of the area of ​​the membrane). By way of example, two or more membranes are fixed together ("bonded" together) at their adjacent surfaces by forming a bond at a bonded area that covers a portion of the membrane (preferably, a tiny or small portion of the material) without affecting the non-bonded areas of the membrane. By way of specific example, two or more membranes are bonded together by forming a pattern of separate discrete bonds or "welds" between the two membranes. No adhesive is required.

[0012] Compared to the known methods of combining porous membranes together, the utility model method can reduce the impact on the performance of the multi-membrane filter assembly produced. The process of forming a joint between the membranes may have an adverse effect on the filtration performance of the individual membranes, such as a reduction in the flow through the membrane at the location of the joint. The method as described forms a joint between the membranes at only a portion of the total area of ​​the membrane, and the performance (e.g., flow) reduction caused by the joint is limited to the area of ​​the joint. The non-joined area, which is a large part of the area of ​​the combined membrane, maintains the original performance of the individual membranes.

[0013] In addition, the described methods can be effective in producing a multi-membrane filter assembly by combining two or more different types of microporous membranes having various physical properties. The membranes combined together can have different or complementary properties, including: filtration mechanism (sieving, non-sieving), chemical composition, pore size, thickness, melting temperature, bubble point, porosity, or the ability to remove different contaminants from a particular type of fluid. According to a specific example, a multi-membrane filter assembly can be prepared from two or more membranes, including one membrane that operates by a sieving filtration mechanism and a second membrane that operates by a non-sieving mechanism.

[0014] By previous methods such as hot surface lamination, effective multilayer filter assemblies can be formed from different materials, but the choice of materials can be limited by the properties of the membranes, such as melting or softening temperatures. These processes work well for membranes with similar properties, but may also be successful for combining membranes with different melting or softening temperatures.

[0015] The method does not require that the individual membranes being bonded together have similar melting points, and the method can be used to bond two or more membranes having different melting points together. In addition, the method can be adapted to form a multi-membrane filter assembly from three or more different individual membranes.

[0016] The present method is an effective alternative to prior art techniques for forming multi-membrane filter assemblies and can be used to produce multi-layer filter assemblies having novel and effective combinations of membrane materials with effective or improved filtration performance.

[0017] In one aspect, the specification relates to a method of forming a stratified polymeric microporous membrane having a first microporous membrane bonded to a second microporous membrane at a plurality of bonded regions. The method comprises: contacting a surface of the first microporous membrane with a surface of the second microporous membrane, and forming a bond between the surface of the first microporous membrane and the surface of the second microporous membrane at the plurality of bonded regions by applying energy to the bonded regions.

[0018] In another aspect, the description is directed to a stratified polymeric microporous membrane. The stratified membrane includes: a first polymeric microporous membrane, and a second polymeric microporous membrane bonded to the first polymeric microporous membrane at a bond area covering less than 20% of the area of ​​the stratified polymeric microporous membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1A , 1B and 1C show example systems and methods as described.

[0020] Figure 2A , 2B and 2C show example systems and methods as described.

[0021] Figure 3 An example of a filter product as described is shown.

[0022] The drawings are schematic and not necessarily drawn to scale. DETAILED DESCRIPTION

[0023] The following description relates to multi-membrane filter assemblies (sometimes also referred to herein as "multilayer membranes" or "layered membranes") prepared from two or more individual polymeric microporous membranes, and methods and systems for making and using these filter assemblies.

[0024] A multi-membrane filter assembly is a combination of two or more individual polymeric microporous membranes bonded together at a bonding area (ie, a "weld area") that constitutes only a portion of the area of ​​the membranes and is formed from the polymeric material of the polymeric microporous membranes.

[0025] The described layered membranes are different from previous multi-membrane filter assemblies, which included previous multi-layer composite membranes formed by bonding two individual membranes together by means of a lamination step that included heat and compression applied over the entire area of ​​the individual membranes. Specifically, compared to laminated composite membranes, the layered membranes of the present specification include a bonding area that covers only a portion of the area of ​​the membrane.

[0026] The joint (i.e., "weld") that holds the surfaces of the two membranes together is formed by the polymeric material of the membranes without the need for the addition of adhesive material. For the purposes of this feature of the membrane, an adhesive is a material that is not a component of the microporous membrane that is added to the surface of the microporous membrane for the purpose of bonding the membrane to a second membrane. Examples include adhesives known as pressure sensitive adhesives, structural adhesives, thermoplastic adhesives, curable adhesives (e.g., thermosetting or radiation curable adhesives), etc., which are applied to a surface and flow onto the surface and solidify to bond to the surface. Example adhesives may contain reactive or non-reactive polymers selected from epoxy polymers, polyacrylates, and silicones, among others.

[0027] To form a bond as described, the surfaces of the films are brought into contact with each other and energy is applied at only a portion of the area of ​​the films to form a bond at a limited area referred to as a "bonding area" or "welding area." The energy raises the temperature of the films at the bonding area to a temperature that causes the polymers of the films to soften or melt and become fused together to an extent sufficient to bond the two films together at the bonding area when the temperature of the films is allowed to decrease, for example to room temperature (e.g., 20 to 25 degrees Celsius).

[0028] According to effective examples, the bonded area covers less than 20% of the area of ​​the layered film, such as less than 10% or 5% of the area of ​​the layered film, such as 0.5 to 10% of the area of ​​the layered film. The remaining area of ​​the film (the "non-bonded" area) contains the film that is in contact at the adjacent surfaces but not bonded together. The amount of the non-bonded area of ​​the layered film can be at least 80, 90, 95, 97 or 99.5% of the area of ​​the layered film.

[0029] The bonding area can be of any size and shape. Example bonding areas can include a regular pattern of connected or unconnected lines, or a pattern of individual geometric shapes such as dots, squares, triangles, etc. The bonding area can be of any effective size, such as at least one dimension on the millimeter scale, such as less than 5, 3 or 1 mm.

[0030] The layered membrane comprises two or more individual layers (membranes) bonded together at a bonding area as described. An effective polymeric microporous membrane (also referred to as a "microporous membrane" or simply a "membrane") comprises a polymeric microporous membrane that can be bonded together by applying energy at the bonding area by the method of the present specification to provide an effective multi-membrane filter assembly.

[0031] 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 sheets or films) containing interconnected pores that form a passage extending from one surface of the membrane to the opposite surface of the membrane. The passage provides a tortuous tunnel or path through which the filtered fluid must pass. Contaminants in the fluid are captured by the membrane in a mechanical or electrostatic manner, such as by a "sieving" or "non-sieving" mechanism or both, and removed from the fluid. The sieving mechanism is a filtering mode by which contaminants are removed from a liquid stream, which is retained at the membrane pores by mechanical interference with the membrane pores due to the movement of the contaminants. For example, the size of the contaminant may be greater than the size of the pores of the membrane. The "non-sieving" filtration mechanism is a filtering mode by which the filter membrane retains the contaminants contained in the fluid flowing through the membrane in a non-special mechanical manner, such as by including an electrostatic mechanism, whereby the contaminants are electrostatically attracted to the surface of the filter membrane and retained at the surface of the filter membrane.

[0032] Effective membranes include perforated membranes with pore sizes in the micron range, which are referred to herein as "microporous" membranes. Typical average pore sizes are in the micron or submicron range, such as about 0.001 micron to about 10 microns. Membranes with an average pore size of about 0.001 to about 0.05 microns are sometimes classified as ultrafiltration membranes. Membranes with an average pore size between about 0.05 and 10 microns are sometimes classified as microporous membranes. Membranes can also be characterized as nanoporous membranes, which are characterized by holes with an average pore size in the range of nanometers and sub-nanometers (e.g., 0.5 to 100 nanometers).

[0033] Porous membranes can also be characterized based on "porosity". As used herein, the "porosity" (sometimes also referred to as the "void fraction") of a porous membrane is a measure of the void (i.e., "empty") space in the membrane as a percentage of the volume of the membrane, and is calculated as the fraction of the volume of the voids of the membrane relative to the total volume of the membrane. A membrane with 0 percent porosity is completely solid. Examples of effective membranes can have a porosity that allows the membrane to be effective as described herein, thereby allowing a suitable flow rate of fluid to pass through the membrane while also removing most of the contaminants or impurities from the fluid. Examples of effective membranes can have a porosity of up to 80%, for example a porosity in the range of 30 to 70% or 40 to 60%.

[0034] Various types of polymers are known 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"), extended polyethylene, extended polypropylene, and polytetrafluoroethylene.

[0035] According to an example multi-membrane filter assembly, the assembly can be prepared by combining two or more individual membranes having different and complementary physical characteristics (e.g., thickness), filtration properties, or processing properties together. The membranes can have different or complementary properties, including: filtration mechanism (sieving, non-sieving), chemical composition, pore size, thickness, melting temperature, bubble point, porosity, or the ability to remove different contaminants from a particular type of fluid.

[0036] A multi-membrane filter assembly ("layered membrane") may be formed, for example, from two or more individual microporous membranes having different filtration mechanisms. The layered membrane may be formed as a combination of one microporous membrane that removes contaminants from a fluid by a sieving mechanism ("sieving membrane") combined with a second microporous membrane that removes contaminants from a fluid by a non-sieving mechanism ("non-sieving membrane"). Additionally or alternatively, the sieving and non-sieving membranes may have different chemical compositions, thicknesses, porosities, pore sizes (bubble points), etc.

[0037] More specifically, the first membrane can be a sieving membrane that exhibits a relatively high bubble point measured as an initial bubble point or a mean bubble point, such as a bubble point of at least 150 pounds per square inch (psi), or at least 180 psi, or at least 200 psi. Example sieving membranes that exhibit a high bubble point include formed membranes that may also have a porosity of less than 50 or 60% (e.g., 40 to 55%), and a thickness of less than 20 μm (micrometers), including less than 15 μm and less than 10 μm. Examples of such membranes may be made of stretched (e.g., biaxially stretched) polyolefins (polypropylene or polyethylene) or fluoropolymers.

[0038] The second microporous membrane can be a non-sieving membrane, which can be relatively thick and can have a lower bubble point than the sieving membrane. Examples of non-sieving membranes can have a bubble point of less than 150psi (e.g., within the range of 50 to 150 or 100 to 150psi) measured as an initial bubble point or a mean bubble point, a porosity greater than 40 or 50% (e.g., 45 to 70%), and can have 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 to 200 microns). The non-sieving membrane can be optionally surface treated to achieve enhanced non-sieving retention of pollutants. Examples of non-sieving membranes can be non-extended microporous membranes made of nylon, polyolefins (e.g., polyethylene, ultra-high molecular weight polyethylene) or fluoropolymers, any of which can be surface modified to exhibit electrostatic charges.

[0039] The bubble point is a characteristic of a membrane that is related to the pore size (i.e., average pore size) of the membrane. Smaller pore sizes of a membrane can be associated with higher bubble points and often with higher filtration performance (e.g., higher retention of smaller sized particles). However, typically higher bubble points are also associated with relatively higher resistance to flow through a porous membrane and a lower flow rate of the fluid for a given pressure drop.

[0040] By a method of determining the bubble point of a porous membrane, a sample of the membrane is placed in a holder. Air is compressed through the holder and the flow rate versus pressure is measured. This is called dry air flow. A low surface tension fluid HFE-7200 (3M) is introduced to the membrane to wet the membrane. The gas pressure is increased stepwise. The pressure at which the gas first flows through the sample as bubbles is called the initial bubble point. The mean bubble point is the pressure at which the ratio of the air flow of the wet membrane to the air flow of the dry membrane is 0.5. The test is performed at a temperature in the range between 20 and 22 degrees Celsius.

[0041] Individual films used to form a layered film may also be characterized based on melting temperature. Different layers of a layered film may have the same or similar melting temperatures, but need not have the same or similar melting properties. Two individual films formed to prepare a layered film may have different melting points, the melting points 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, the two films having melting points differing by at least 10, 20, or 30 degrees Celsius.

[0042] In addition, described hot lamination method and ultrasonic method can be generally used to form multi-film assembly, and described multi-film assembly comprises two or more films with combination of different thickness ranges.Described method can be used for combining two or more films with small thickness separately, for example, two or more films with thickness in the range of 5 to 100 microns or 10 to 50 microns.Described method can also be used for combining two or more films with larger thickness, for example, two or more films with thickness greater than 100 microns or greater than 200 microns.And, described method can be used for combining two or more films with combination of small thickness and large thickness, for example, first film with thickness in the range of 5 to 100 microns is bonded to second film with thickness greater than 100 microns or greater than 200 microns.

[0043] The method of the present specification involves attaching (bonding) two or more different polymeric microporous membranes together at a bond formed at only a portion of the area of ​​the membrane (preferably, over a relatively small portion of the area of ​​the membrane). By way of example, two or more membranes are bonded together ("bonded" together) at their adjacent surfaces by a bond covering only a portion of the total area of ​​the membrane (preferably, a tiny or small portion of the area of ​​the membrane), without the need to add adhesive material at the bonding area, and without significantly affecting the filtration properties (e.g., flow, retention) or morphology (e.g., pore size, porosity, bubble point) of the membrane at the non-bonding area.

[0044] Compared to other methods of bonding membranes together, the adverse effects of the present invention method on the performance of the resulting multi-membrane filter assembly can be reduced. Typically, the process of forming a bond between two individual membranes by applying heat, compression or adding an adhesive may reduce the filtration performance of individual membranes, for example, by causing a decrease in the flow through the membrane. The method as described forms a bond between the membranes at only a portion of the total area of ​​the membrane, and any adverse effects on performance (e.g., flow reduction) caused by forming the bond are limited to the area of ​​the bond. The non-bonded area of ​​the membrane, which may be a major portion or a majority of the area of ​​the bonded membrane, maintains the original performance of the individual membrane.

[0045] According to the described method, a bond is formed between two or more polymeric microporous membranes at a bond area by applying energy to the bond area in an amount sufficient to form the bond while avoiding applying the same amount of energy to non-bonded areas of the membranes. To form the bond, two or more membranes are brought into contact and energy is applied to raise the temperature of the two membranes at the bond area. The temperature of the bond area is raised to a temperature that causes the polymers of the membranes to soften or melt and become fused together at the bond area to a degree sufficient to bond the two membranes together at the bond area when the temperature of the two membranes is allowed to decrease, for example, to room temperature (e.g., 20 to 25 degrees Celsius).

[0046] In order to form a bond at the bonding area, the temperature of the individual film at the bonding area can be raised to a certain temperature, at which temperature, the film softens or melts so that when the film cools, the polymer of the film combines with the polymer of the adjacent contacted film to form a bond. Energy is applied to cause one or both of the films to soften or melt. When the film is kept in contact with at least a slight degree of pressure, the softening or molten polymer of the film at the bonding area can flow or otherwise combine to form a bond between the two film surfaces. In a specific example method, at least one of the films can be heated to a temperature above the melting temperature of the film. In other example methods, two or more films in contact with each other are heated to a temperature above the melting temperature of the two films.

[0047] The energy may be in the form of heat energy, ultrasonic energy, or another effective form of energy transferred from a heated surface to the film. The energy may be applied to the bonding region using any effective energy source, and with a high degree of accuracy to cause the temperature of the bonding region to rise without causing the temperature of the non-bonding region of the film to rise similarly. The non-bonding region may experience a temperature rise, but does not reach a temperature that causes the polymer of the film at the non-bonding region to soften or melt and bond together. Preferably, the non-bonding region of the film does not experience significant morphology or flow property changes, and the non-bonding region of the film maintains the level of the flow through the film, the average pore size, the bubble point, and the porosity that are substantially not changed by the process of forming a bond at the bonding region.

[0048] According to the example method, ultrasonic energy is used to form a joint. Two microporous membranes are kept in contact at their surfaces, and pressure is applied at the bonding area to keep the surface contact of the membrane. While the surface at the bonding area is kept in contact, ultrasonic energy is applied to the membrane to increase the temperature of the membrane at the bonding area. Ultrasonic energy raises the temperature of the polymers of the two membranes so that the polymers at the bonding area flow together or blend. Subsequently, by allowing the heated polymer to cool, a joint (or "weld") is formed at the bonding area by the blended polymer. Using these processes, heat is applied at the bonding area with a higher degree of accuracy, and the polymer at the region other than the bonding area (that is, the non-bonding area of ​​the membrane) of the membrane does not experience a temperature rise that significantly affects the properties of the membrane.

[0049] Ultrasonic welding techniques are effectively used to form layered film products as described by applying ultrasonic energy to the bonding area of ​​two contacting films to raise the temperature of the polymer of the film at the bonding area, so that the heated polymer forms a bond at the bonding area without significantly affecting the properties of the film at the non-bonding area. Example ultrasonic welding techniques can use ultrasonic energy at a high frequency (e.g., 20 to 40 kHz) to generate low amplitude (e.g., 1 to 25 μm) mechanical vibrations to generate heat at the bonding area. The heat can cause the polymer at the bonding area to soften or melt and become fused together, so that when the polymer cools, the polymer at the bonding area has formed a bond or "weld" between the two films.

[0050] An alternative form of energy applied to the bonding area may be thermal energy applied to the membranes while the membranes are held in contact at the bonding area, with an amount of pressure sufficient to hold the surfaces together to achieve bonding. Thermal energy may be applied to the bonding area via heated surfaces that contact only the bonding area, without significantly raising the temperature of non-bonding areas of the membrane.

[0051] Systems and methods that can be used to form layered films as described herein Figure 1A , 1B and 1C. Figure 1A , the ultrasonic welding apparatus 100 comprises a rolling anvil 110 and a "sonic generator" (i.e., "horn") 120. The rolling anvil 110 has a rolling cylindrical surface 112 including a pattern of a plurality of elevated extensions 114, which are protrusions that extend radially a certain distance above the surface 112. Each extension 114 includes a welding surface 118 located at the end of the extension. The horn 120 is located at a distance away from the rolling anvil 110 along the length of the rolling anvil 110 to form 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 films (130, 140) that travel through the gap 116 during use. The size of the gap can allow the film to pass through the gap while applying a slight degree of pressure to the film to maintain contact between the films during bonding.

[0052] In use, microporous membranes 130 and 140 are held together at the surfaces of the membranes and pass through gap 116 (see arrows) while anvil roller 110 rotates and while the membranes travel along the rolling surface of rolling anvil 110. Anvil roller 110 is rotatably supported at its opposite ends as part of apparatus 100 so that the anvil roller is allowed to contact the lower surface of the assembly of membranes 130 and 140 and move the assembled and contacted membranes through gap 116 under horn 120.

[0053] As the films 130 and 140 pass under the horn 120 while being supported at the welding surface 118, the horn 120 generates ultrasonic energy that is absorbed by the polymer of the film. The ultrasonic energy raises the temperature of the film to cause the polymer of the film to soften or melt at the bonding area, which contacts the surface 118 and fuses together after cooling. The bonded films form a layered film 124 that passes through the assembly 100, which includes the bonding area 122.

[0054] refer to Figure 1B , the welding device 100 is Figure 1A A variation of the welding apparatus 100 . Figure 1B The apparatus 100 includes a nip roller 126 located at an upstream position relative to the anvil roller 110 and the horn 120. The nip roller 126 receives the film 130 and the film 140 and places the surfaces of the films in contact with each other at a certain position before the films contact the anvil roller 110 and effectively removes air from between the films before the films are bonded at the anvil roller 110 and the horn 120.

[0055] refer to Figure 1C , the welding device 100 is Figure 1A A variation of the welding apparatus 100 . Figure 1C The device 100 includes a third film 150 that is part of the assembly of films (130, 140, and 150) that pass through the gap 116 and is processed through the bonding area 122 that forms the layered film 124. Figure 1C In the method of FIG. 1 , three or more films may be used to form a layered film 124 bonded together at a bonding area 122 .

[0056] Compared to other methods of forming a multi-membrane filter assembly from a plurality of individual polymeric microporous membranes (e.g., lamination methods that affect the entire area of ​​the membrane), the method as described is more capable of forming a layered membrane from three or more individual membranes because the layered membrane forms a bond between the three or more layers at a limited area of ​​the membrane (i.e., at the bonding area, rather than over the entire surface of the membrane). Although the bond may cause an adverse effect on the filtration performance of the layered membrane at the bonding area, the amount of the area of ​​the bond is limited, and the performance of the non-bonded area is not affected by the bonding process.

[0057] according to Figure 2A , 2B As an alternative to the method shown in 2C, the bond area can be formed not by ultrasonic energy applied to the bond area but by thermal energy applied to the bond area by a heated surface. Figure 2A , 2B2C, the ultrasonic welding apparatus 200 includes a rolling anvil 210 and a roller 220. The rolling anvil 210 has a rolling cylindrical surface 212 including a pattern of a plurality of elevated heated extensions 214, which are protrusions that extend radially a distance above the surface 212. Each heated extension 214 includes a heated welding surface ("heated surface") 218 ​​at the end of the extension. In an alternative example, the surface of the roller 220 may be heated, and the extensions 214 and the surface 218 may be heated or unheated.

[0058] The roller 220 is located at a distance along the length of the rolling anvil 210 facing away 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 films (130, 140) that travel through the gap 216 during use. The size of the gap can allow the film to pass through the gap while applying a slight degree of pressure to the film to maintain contact between the films during bonding.

[0059] In use, the microporous membranes 130 and 140 are held together at the surface of the membranes and pass through the gap 216 (see arrow) while the anvil roller 210 and the roller 220 rotate. As the membrane passes through the gap 216, the heated surface 218 contacts the weld area of ​​the membrane and applies heat to the weld area to increase the temperature of the weld area. The increase in temperature causes the polymer of the membrane at the bond area to soften or melt and fuse together after cooling. The bonded membranes form a layered membrane 124 that passes through the assembly 100, which includes the bond area 122.

[0060] refer to Figure 2B , the welding device 200 is Figure 2A A variation of the welding device 200 . Figure 2B The apparatus 200 includes a nip roller 226 located at an upstream position relative to the anvil roller 210 and the roller 220. The nip roller 226 receives the film 130 and the film 140 and places the surfaces of the films in contact with each other at a certain position before the films pass through the gap 216, and effectively removes air from between the films before the films are bonded by contacting the heated surface 218 when passing between the anvil roller 210 and the roller 220 at the gap 216.

[0061] refer to Figure 1C , the welding device 200 is Figure 2A A variation of the welding device 200 . Figure 2C The apparatus 200 includes a third film 150 that is part of the assembly of films (130, 140, and 150) that passes through the gap 216 and is processed by forming the bonding area 122 of the layered film 124. Figure 2CIn the method of FIG. 1 , three or more films may be used to form a layered film 124 bonded together at a bonding area 122 .

[0062] The multi-membrane filter assembly ("filter membrane") as described herein, or a filter or filter assembly containing the filter membrane, can be suitable for use in a method of filtering a liquid chemical material to purify the liquid chemical material or otherwise remove undesirable materials therefrom, particularly to produce a high purity liquid chemical material suitable for use in industrial processes that require a chemical material input having a very high purity level. In general, the liquid chemical material can be any of a variety of suitable commercially available materials, and can be a liquid chemical material suitable for use in any of a variety of different industrial or commercial applications. Specific examples of filter membranes as described can be used to filter or purify liquid chemicals used in semiconductor or microelectronic manufacturing applications, such as for filtering liquid solvents or other process solutions used in semiconductor photolithography processes, wet etching or cleaning steps, ultrapure water, or plating chemistry processes.

[0063] Some specific, non-limiting examples of liquid solvents that can be filtered using the filtration membrane as described include: n-butyl acetate (nBA), isopropyl alcohol (IPA), 2-ethoxyethyl acetate (2EEA), cyclohexanone, ethyl lactate, γ-butyrolactone, hexamethyldisilazane, methyl 2-hydroxyisobutyrate, methyl isobutyl carbinol (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).

[0064] The filter membrane can be contained within a larger filter structure, such as a filter or filter cartridge, used in a filtration system. The filtration system places a filter membrane, such as part of a filter or filter cartridge, in a flow path of a liquid chemical material so that the liquid chemical material flows through the filter membrane, so that the filter membrane can remove impurities and contaminants from the liquid chemical material. The structure of the filter or filter cartridge may include one or more of a variety of additional materials and structures that support the filter membrane within the filter so that the fluid flows from the filter inlet through the filter membrane and flows through the filter outlet, thereby passing through the filter membrane when passing through the filter. The filter membrane supported by the filtration structure can be in any suitable shape, such as a pleated cylinder, a cylindrical pad, one or more non-pleated (flat) cylindrical sheets, a pleated sheet, etc.

[0065] One example of a filtration structure comprising a filter membrane in the form of a pleated cylinder may be prepared to include the following components, any of which may be included in the filter construction but may not be required: a rigid or semi-rigid core that supports the pleated cylindrical filter membrane at its interior opening; a rigid or semi-rigid cage that supports or surrounds the exterior of the pleated cylindrical filter membrane at the exterior of the filter membrane; optional end pieces or "disks" located at each of the two opposing ends of the pleated cylindrical filter membrane; and a filter housing that includes an inlet and an outlet. The filter housing may be of any suitable and desired size, shape, and material, and preferably may be made of a suitable polymeric material.

[0066] As an example, Figure 3 A filter assembly 330 is shown, which is a product having a pleated cylindrical assembly 310 and an end piece 322 and other optional components. The cylindrical assembly 310 includes a filter membrane 312 as described herein and is pleated. The end piece 322 is attached (e.g., "canned") to one end of the cylindrical filter assembly 310. The end piece 322 may preferably be made of a melt-processable polymeric material. A core (not shown) may be placed at the interior opening 324 of the pleated cylindrical assembly 310, and a cage (not shown) may be placed around the exterior of the pleated cylindrical assembly 310. A second end piece (not shown) may be attached ("canned") to the second end of the pleated cylindrical assembly 330. The resulting pleated cylindrical assembly 330 having two opposing canned ends and an optional core and cage may then be placed into a filter housing, the filter housing including an inlet and an outlet, and configured such that the amount of fluid entering the inlet must pass through the filter membrane 312 before exiting the filter at the outlet.

[0067] The filter housing may be of any suitable and desired size, shape and material, and may preferably be a fluorinated or non-fluorinated polymer, such as nylon, polyethylene or a fluorinated polymer such as poly(tetrafluoroethylene-co-perfluoro(alkyl vinyl ether)), Perfluoroalkoxyalkane (PFA), perfluoromethylalkoxy (MFA), or another suitable fluoropolymer (eg, perfluoropolymer).

[0068] A number of aspects are described below. It should be understood that any one or more features described in the following aspects can be combined with any one or more other aspects.

[0069] Aspect 1. A method of forming a stratified microporous membrane comprising a first microporous membrane bonded to a second microporous membrane at a plurality of bonding regions, the method comprising:

[0070] bringing the surface of the first microporous membrane into contact with the surface of the second microporous membrane, and

[0071] Bonds are formed between the surface of the first microporous membrane and the surface of the second microporous membrane at a plurality of bonding areas by applying energy to the bonding areas.

[0072] Aspect 2. The method according to aspect 1, wherein the bonding region covers less than 20% of the area of ​​the stratified microporous membrane.

[0073] Aspect 3. A method according to aspect 1, wherein forming a bond includes applying energy to the first microporous membrane and the second microporous membrane at the bonding area to increase the temperature of the bonding area and cause the polymer of the first microporous membrane to fuse with the polymer of the second microporous membrane at the bonding area.

[0074] Aspect 4. The method according to aspect 3, comprising:

[0075] raising the temperature at the bonding area to a temperature that is: 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

[0076] The temperature of the bonding area is allowed to decrease, wherein the first microporous membrane is bonded to the second microporous membrane at the bonding area.

[0077] Aspect 5. The method according to aspect 1, wherein the first microporous membrane has a first microporous membrane melting point, the second microporous membrane has a second microporous membrane melting point, and the difference between the first microporous membrane melting point and the second microporous membrane melting point is at least 20 degrees Celsius.

[0078] Aspect 6. The method according to any one of aspects 1 to 5, wherein one of the first microporous membrane or the second microporous membrane comprises a polymer selected from the group consisting of ultra-high molecular weight polyethylene, polysulfone, extended polyethylene, extended polypropylene, polyimide, polyamide, and polytetrafluoroethylene.

[0079] Aspect 7. The method according to any one of aspects 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.

[0080] Aspect 8. A method according to any one of Aspects 1 to 5, wherein forming the bond between the surface of the first microporous membrane and the surface of the second microporous membrane at multiple bonding areas includes applying ultrasonic energy to the bonding areas to heat the bonding areas.

[0081] Aspect 9. A method according to any one of Aspects 1 to 5, wherein forming the bonding portion between the surface of the first microporous membrane and the surface of the second microporous membrane at multiple bonding areas includes: using a heated surface having the area of ​​the bonding area, and applying heat to the bonding area by placing the bonding area between the heated surface and a roller.

[0082] Aspect 10. The method according to any one of aspects 1 to 5, wherein the first microporous membrane is a sieving membrane having:

[0083] Initial bubble point of at least 150 psi,

[0084] Porosity less than 55%, and

[0085] Less than 20 microns thick.

[0086] Aspect 11. The method according to any one of aspects 1 to 5, wherein the second microporous membrane has a thickness in the range of 20 to 200 microns.

[0087] Aspect 12. The method according to aspect 11, wherein the second microporous membrane is a non-sieving membrane having:

[0088] Initial bubble point less than 150 psi,

[0089] Porosity greater than 40%, and

[0090] Thickness greater than 50 microns.

[0091] Aspect 13. The method according to any one of aspects 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.

[0092] Aspect 14. The method according to any one of aspects 1 to 5, comprising:

[0093] bringing the surface of the first microporous membrane into contact with the surface of the third microporous membrane, and

[0094] The first microporous membrane is bonded to the second microporous membrane and the

[0095] The third microporous membrane

[0096] applying energy to the bonded area to melt the polymer at the bonded area, and

[0097] The molten polymer is allowed to solidify to form the bonded area.

[0098] Aspect 15. The method according to any one of aspects 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.

[0099] Aspect 16. The method according to any one of aspects 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.

[0100] Aspect 17. The method according to any one of aspects 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.

[0101] Aspect 18. A stratified polymeric microporous membrane prepared according to the method of any one of aspects 1 to 5.

[0102] Aspect 19. A method of using a filter cartridge, the method comprising causing a fluid to flow into the inlet, through the membrane, and out of the outlet, wherein the fluid is suitable for use in a semiconductor manufacturing process.

Claims

1. A layered microporous membrane, characterized in that The layered microporous membrane comprises: The first microporous membrane, A second microporous membrane is bonded to the first microporous membrane at a bond area covering less than 20% of the area of ​​the stratified microporous membrane.

2. The film according to claim 1, characterized in that The bonded regions cover less than 10% of the area of ​​the stratified microporous membrane.

3. The film according to claim 1, characterized in that The first microporous membrane has a first microporous membrane melting point, the second microporous membrane has a second microporous membrane melting point, and the difference between the first microporous membrane melting point and the second microporous membrane melting point is at least 20 degrees Celsius.

4. The film according to claim 1, characterized in that At least one of the first microporous membrane and the second microporous membrane comprises a polymer.

5. The membrane according to any one of claims 1 to 4, characterized in that One of the first and second microporous membranes includes polyethylene, and one of the first and second microporous membranes includes polypropylene.

6. The membrane according to any one of claims 1 to 4, characterized in that The first microporous membrane is a sieving membrane having: Initial bubble point of at least 150 psi, A porosity of less than 55%, and Less than 20 microns thick.

7. The membrane according to any one of claims 1 to 3, characterized in that The second microporous membrane has a thickness in the range of 20 to 200 microns.

8. The film according to claim 7, characterized in that The second microporous membrane is a non-sieving membrane having: Initial bubble point less than 150 psi, Porosity greater than 40%, and Thickness greater than 50 microns.

9. The membrane according to any one of claims 1 to 4, characterized in that The membrane includes a third microporous membrane bonded to the first microporous membrane and to the second microporous membrane at a bonding region.

10. The membrane according to any one of claims 1 to 4, characterized in that 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.

11. The membrane according to any one of claims 1 to 4, characterized in that 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.

12. The membrane according to any one of claims 1 to 4, characterized in that The first microporous membrane has a thickness greater than 100 microns, and the second microporous membrane has a thickness greater than 100 microns.

13. A filter cartridge comprising a membrane according to any one of claims 1 to 4, characterized in that The filter cartridge includes a filter housing including an inlet, an outlet, and the membrane is 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.

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