Method of forming laminated single layer composite membrane

Abstract

To provide a composite membrane formed by lamination of two or more separate porous polymeric layers.SOLUTION: A composite membrane comprises a first porous polymeric layer, and a second porous polymeric layer laminated with the first porous polymeric layer, and is free of an adhesive.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to composite membranes prepared by laminating separate porous polymer layers without adhesives to form a monolayer composite. [Background technology]

[0002] Various types of porous polymeric membranes are used to remove undesirable materials from fluid streams to be purified and find utility in a variety of industrial applications. Fluids that are treated to remove undesirable materials include water, liquid industrial solvents and process fluids, industrial gases used in manufacturing or processing, and liquids with medical or pharmaceutical applications. Undesirable substances removed from fluids include impurities and contaminants such as particles, microorganisms, and dissolved chemical species such as ionic species. Examples of filter applications include the purification of various liquid materials used in the manufacture of semiconductors and microelectronic devices.

[0003] Polymer layers of porous materials can be combined in different configurations to form porous polymeric membranes configured to achieve removal of targeted materials. For example, some porous layers can remove impurities via a sieving mechanism, where particles present in the liquid that are larger than the pores of the member pass through and are prevented from being trapped on or within the membrane due to their relative size. Other membranes work via a non-sieving mechanism, where impurities smaller than the membrane pores are trapped within the pores by interaction with the membrane material. By combining a non-sieving membrane with a sieving membrane, both large and small particles can be removed.

[0004] As known in the art, it is difficult to combine different types of membranes to form a monolayer composite membrane material with good flow characteristics. Typically, one porous layer is placed in contact with another porous layer using an adhesive interlayer and / or with strong compression. However, the presence of adhesives can interfere with membrane performance. Filter flow is often significantly reduced as the pores become clogged or collapsed due to the adhesive. Furthermore, the presence of adhesives can add impurities to the liquid passing through the composite. Co-extrusion can also be used, but this is not practical for combining polymer layers with different membrane morphologies, and the heating required to extrude the polymeric materials often deteriorates their pore structure. Similarly, using excessive compression to bring two individual porous layers into intimate contact to form a monolayer can collapse the pore structure both throughout the porous layers and at the contact surface. For this reason, porous polymer layers of different morphologies are generally placed in a separate retentive layer stacking arrangement to maintain their individual filtration capabilities. However, handling such filters where the individual layers are not adhered to each other can be very difficult, especially if one or both of the layers are very thin.

[0005] Thus, there is a need for a method for combining porous polymer layers to form a composite membrane that functions as a single layer but maintains the characteristics of the individual layers from which it is prepared. Summary of the Invention

[0006] The present disclosure generally relates to composite membranes formed by the lamination of two or more separate porous layers, and methods and systems for lamination. Advantageously, the resulting composite is monolayered and can be handled without the composite easily separating into its component layers, yet effectively retains the filtration capabilities of the component layers prior to lamination.

[0007] In one embodiment, the present disclosure relates to a composite membrane comprising a first porous polymer layer laminated with a second porous polymer layer. The composite membrane does not have an adhesive added. Preferably, the first porous polymer layer has a different morphology than the second porous polymer layer, and more preferably, the layers differ in thickness. The composite membrane is a single layer and has substantially the same flow rate and / or flow time as a non-laminated composite of these same layers.

[0008] In another embodiment, the present disclosure relates to a composite membrane comprising a first region and a second region, the composite comprising both a first porous polymer and a second porous polymer without an interlaminar region between the first and second regions. The first region comprises a first porous polymer and has a thickness of less than about 20 μm. The second region comprises a second porous polymer and has a thickness of about 50 μm to about 200 μm. Preferably, the second porous polymer is different from the first porous polymer. The first region, the second region, or both, may further comprise a compressed region.

[0009] In another embodiment, the present disclosure relates to a method of forming a composite membrane, the method including feeding a first porous polymer layer and a second porous polymer layer into a laminator and heating the first porous polymer layer and the second porous polymer layer to a lamination temperature of the laminator. The heated first porous polymer layer and the heated second polymer layer may be laminated together without an adhesive to form a composite membrane and then cooled. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of one embodiment of a single layer composite membrane of the present disclosure comprising two porous polymer layers. [Diagram 2] 1 is a micrograph of one embodiment of a single layer composite membrane of the present disclosure comprising two different porous polymer layers. [Diagram 3] FIG. 1 is a schematic diagram of one embodiment of a lamination system for making a composite member of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] It should be understood that the above figures are not necessarily to scale and may in some cases present somewhat simplified representations of various preferred features illustrating the underlying principles of the present disclosure. Specific design features of the present disclosure, including, for example, specific dimensions, orientations, locations, and shapes, are determined in part by the intended application and environment of use.

[0012] The present disclosure relates to composite membranes formed by the lamination of two or more distinct porous polymer layers, as well as methods and systems for the lamination of two or more distinct porous polymer layers.

[0013] The resulting composite membranes disclosed herein, although essentially monolayer, have substantially the same filtration properties as the stacked combination of porous polymer layers from which they are prepared, e.g., a composite membrane includes two or more separate porous polymer layers laminated together to form a single layer.

[0014] As used herein, a "porous polymeric layer" is a polymeric material that includes porous (e.g., microporous) interconnected passages that extend from one surface of the layer to the opposing surface of the layer. The passages generally provide tortuous tunnels or paths through which the liquid to be filtered must pass. Contaminants, such as particles or dissolved species, that pass through the porous polymeric layer become trapped by or within the pores, either on the basis of size (i.e., sieving mechanisms) or on the basis of chemistry (i.e., non-sieving mechanisms).

[0015] A variety of different types of polymer layers can be used to form the composite membranes of the present disclosure. Each of the polymer layers can be the same or different, depending on the target application of the composite membrane, cost, availability of materials, etc. For example, in one embodiment, the composite membrane includes a first porous polymer layer laminated with a second porous polymer layer, each layer having the same or different material type and / or filtration mechanism (sieving or non-sieving). Suitable polymer layers include, for example, polyamide, polysulfone, polyether-sulfone, and polyolefin layers.

[0016] Surprisingly, it has been found that a single layer composite can be formed from two different types of porous polymer layers laminated using the techniques described herein without significant loss of flow performance. For example, it has been found that a porous polymer layer capable of removing impurities by a sieving mechanism can be laminated without adhesive with a porous polymer layer capable of removing impurities by a non-sieving mechanism to obtain a single layer composite membrane with excellent filtration and flow performance properties. A single layer composite membrane may include the porous polymer layers in any order, for example, a non-sieving layer laminated on top of a sieving layer or vice versa. The positioning of the layers (i.e., top, first, second, etc.) described herein is relative to the intended flow direction of the fluid through the composite membrane, with the top layer being the first porous polymer layer in contact with the fluid.

[0017] The thickness of a layer of a composite membrane may vary depending, for example, on the cost, availability, and handling (i.e., physical and / or mechanical properties) of the polymer layer from which it is formed. For example, in the case of a composite membrane comprising a first porous polymer layer laminated with a second porous polymer layer, the first porous polymer layer may have the same or different thickness as the second porous polymer layer. In some embodiments, the porous polymer layers may have different thicknesses. For example, the first porous polymer layer intended to be in initial contact with the target fluid may have a thickness less than that of the second porous polymer layer. In particular, the first porous polymer layer may be an ultra-thin porous layer having a thickness of less than 20 μm, including less than 10 μm and less than 5 μm. The second porous polymer layer may be relatively thick, having a thickness of more than 20 μm, such as about 20 μm to about 200 μm, about 50 μm to about 200 μm, about 50 μm to about 150 μm, and about 50 μm to about 100 μm. It has surprisingly been found that the techniques described herein can be used to laminate thicker layers to ultra-thin porous layers while substantially maintaining flow through the resulting monolayer composite.

[0018] The porous polymer layers of the composite membranes may comprise a variety of materials having thicknesses in these ranges, however, in some embodiments, the monolayer composite membrane comprises a porous polyethylene (PE) layer laminated with a porous polyolefin layer, such as an ultra-high molecular weight polyethylene (UHMWPE) layer. The porous PE layer may comprise, for example, expanded polyethylene prepared by extrusion of a polyethylene resin containing a diluent, followed by stretching, extraction, and finally annealing. A variety of expanded porous PE layers are known to those skilled in the art and may be used in the embodiments of the present disclosure. The UHMWPE layer may be any known in the art, typically having a thickness of about 1×10 6 Daltons (Da) or more, e.g., about 1 × 10 6 ~9×10 6 Da, or 1.5 × 10 6 ~9×10 6 These porous polymers are formed from resins having molecular weights in the Da range. These porous polymers can also be formed to have a symmetric pore size distribution or an asymmetric pore size distribution (e.g., decreasing pore size from one side of the porous polymer layer to the other).

[0019] Specific embodiments of the present disclosure are shown in Figures 1 and 2. In particular, Figure 1 shows a composite membrane including two different porous polymer layers laminated together. As shown, the composite membrane 100 includes a first porous polymer layer 110 and a second porous polymer layer 120, the order of which is relative to the intended flow of the target liquid through the composite membrane, as indicated by the arrows. In this embodiment, the first porous polymer layer has a thickness that is less than the thickness of the second porous polymer layer. Also, the layers are of different materials. However, as mentioned above, it is within the scope of the present disclosure that the two layers may be the same and / or the thickness of the second layer may be the same or less than the first layer.

[0020] Importantly, as shown in Figures 1 and 2, the composite membrane does not include an adhesive or adhesive layer between the first porous polymer layer 110 and the second porous polymer layer 120. Also, preferably, as discussed in more detail below, an intermediate layer is not formed that includes both porous polymer layers. Rather, as shown, the two porous polymer layers are in direct contact with one another.

[0021] Moreover, the contact layers remain in contact after lamination, particularly during handling, thereby forming a monolayer composite. As used herein, the term "monolayer composite" refers to a composite material formed from two or more separate porous layers that does not readily separate into its constituent porous polymer layers, thereby allowing the composite to be handled as a single unit or layer. Rather, an applied force is required to separate the layers of the monolayer composite. For example, in one embodiment of the present disclosure, a peel force of about 0.5 lbf to about 5 lbf, such as about 0.8 lbf to about 3 lbf or about 1.0 lbf to about 2.0 lbf, about 1.5 lbf, etc., can be used to separate the layers of the composite membrane into the original starting porous polymer layers. These force values ​​are generally higher than those experienced during normal membrane processing, such as during pleating, allowing for the formation of a filter device from this monolayer composite.

[0022] A more detailed view is shown in Figure 2, which is a micrograph of a particular embodiment of a composite membrane of the present disclosure. The composite membrane includes a first porous polymer layer laminated with a second porous polymer layer, the positioning of which is relative to the intended flow direction in use as indicated by the arrow. In this particular embodiment, the first porous polymer layer is an expanded porous PE layer and the second porous polymer layer is a solution-cast porous UHMWPE layer. These layers are laminated by the method of the present disclosure and do not include an adhesive layer between them, which is clearly shown in the micrograph of Figure 2.

[0023] Although it does not include an adhesive layer, it has also been found that the two layers surprisingly adhere well to each other and are not easily separated from each other, and the composite membrane is a single-layer composite. As shown in FIG. 2, the composite membrane 200 includes a first region 210 formed by a first porous polymer layer and a second region 220 formed from a second porous polymer layer. The first region has a thickness of less than 20 μm, and the second region has a thickness of about 50 μm to about 200 μm. However, the composite member 200 does not further include any interlayer region that includes either an adhesive or a combination of both the first and second porous polymer layers. Instead, as shown, the two layers are in direct contact with each other, with no air pockets formed between them. As will be discussed in more detail below, compression can be used to bring the bonded layers into contact without significantly affecting the porosity of the layers. This is also shown in FIG. 2, where the second region 220 includes a compressed region 230, which is still highly porous. Close inspection of the first region 210 also shows the presence of a compression region. Without wishing to be bound by any particular theory, it is believed that the combination of lamination temperature and gentle compression allows the individual porous polymer layers to come into intimate contact without significantly reducing the relative pore structure. This allows the combined layers to function as a monolayer membrane with minimal overall flow reduction. Thus, the composite membrane 200 can be handled and further processed as a monolayer membrane, such as by pleating or otherwise folding it into a desired filter housing, without concern for the layers separating.

[0024] Because the porosity of each of the polymer layers is substantially maintained, the monolayer composite can be used as a membrane for removing impurities and contaminants from a liquid stream of interest with minimal reduction in flow or throughput. For example, it has been surprisingly found that the monolayer composite membrane of the present disclosure has a flow rate of a test fluid, such as isopropyl alcohol (IPA), that is 90% or more of the flow rate of this fluid through a non-laminated combination of two porous polymer layers (i.e., a laminated composite in which the two porous polymer layers are in contact but do not adhere to each other and can be easily separated). Thus, the reduction in flow rate is 10% or less. Additionally or alternatively, it has been found that the monolayer composite membrane has a flow time of a test fluid, such as IPA, that is 120% or more of the flow time of the corresponding non-laminated combination of these layers (i.e., the flow time does not increase by more than 20%). Thus, the monolayer composite membrane has flow characteristics that are substantially the same as the flow characteristics of the laminated arrangement of porous polymer layers used to form it. The flow time is measured by measuring the flow rate of 500 mL of isopropyl alcohol (IPA) fluid at 14.2 psi and a temperature of 21° C., with a flow rate of 13.8 cm 2 The flow rate is measured as the time it takes for a fluid to pass through a membrane with a surface area of ​​13.8 cm at 14.2 psi and a temperature of 21° C. 2 The ion exchange rate is measured by measuring the total volume of isopropyl alcohol (IPA) fluid passing through a membrane having a surface area of ​​100 nm over a period of 1 minute.

[0025] In some embodiments, the bubble point value also remains substantially unchanged. For example, it has been unexpectedly found that when the bubble point of a first porous polymer layer is higher than that of a second porous polymer layer, the bubble point of the single layer composite membrane can be 90% or more of the first (i.e., higher) bubble point. As known in the art, the bubble point method is based on the premise that for a particular fluid and pore size with constant wetting, the pressure required to force a bubble through the pore is inversely proportional to the size of the pore. Higher bubble point values ​​are associated with smaller pore sizes. To determine the bubble point of a porous material, a sample of the porous material is immersed and wetted with ethoxy-nonafluorobutane HFE7200 (available from 3M) at a temperature of 20-25°C (e.g., 22°C). Gas pressure is applied to one side of the sample using compressed air, and the gas pressure is gradually increased. The minimum pressure at which gas will flow through the sample is called the bubble point. When measuring the bubble point of the monolayer composite membrane disclosed herein, compressed air is directed through a polymeric porous layer having a greater thickness. It has been found that the monolayer composite membrane of the present disclosure laminated using the method described herein does not significantly reduce the pore size, but substantially maintains the bubble point of the porous polymer layer having the highest bubble point. Therefore, the pore size is not significantly reduced.

[0026] Thus, the present disclosure further relates to a method for preparing a monolayer composite membrane laminate. In an embodiment of the method, two or more porous polymer layers (such as the first and second porous polymer layers described above) are provided and fed into a laminator to be combined. Preferably, the laminator is a single laminator unit, although multiple lamination zones may be used. The two or more layers are heated in the laminator to a temperature sufficient to laminate the layers without the use of adhesive, and are laminated at this temperature to form a monolayer composite. The heating and lamination may be performed simultaneously or in separate steps. The formed composite membrane may then be cooled. For example, a cooling zone may be used to harden the composite. By "laminated" it is meant that after cooling, the layers remain adhered to each other and are not easily separated, e.g., requiring a force to peel the layers off. For example, the peel force to separate the layers may be about 0.5 lbf to about 5 lbf, e.g., about 0.8 lbf to about 3 lbf, or about 1.0 lbf to about 2.0 lbf, about 1.5 lbf, etc. Since a force is required to separate the laminated porous polymer layers from which the composite membrane is prepared, the composite can function as a single layer composite.

[0027] In the lamination method, any of the porous polymer layers described above can be used. These layers can be the same or different, but preferably differ in polymer type, thickness, and / or porosity. For example, the first porous polymer layer can be an ultra-thin porous layer, such as an expanded porous PE layer, having a thickness of less than 20 μm. The second porous polymer layer can be a polyolefin layer, such as a porous UHMWPE layer, having a thickness of about 50 μm to about 200 μm.

[0028] In the method of the present disclosure, two or more layers are heated to a lamination temperature, which is a temperature sufficient to bond the layers together without significantly affecting the porosity of either layer. Thus, the lamination temperature depends on the type of porous polymer layers being combined in the laminator. In particular, the lamination temperature can be between 5°C and 20°C below the lowest melting temperature of the two or more layers being laminated. For example, to laminate a first porous polymer layer and a second porous polymer layer, if the first layer has a lower melting temperature than the second layer, the lamination temperature is between 5°C and 20°C below the melting temperature of the first porous polymer layer. Compression is not necessary to form a monolayer composite membrane. However, a minimum compression pressure may be applied, if necessary, as long as the amount of compression does not significantly change (i.e., reduce) the porosity of any of the layers being laminated, as determined by the flow rate, flow time, and / or bubble point values ​​described above. As described above, the use of compression can create compressed regions within the individual layers, preferably near or at the interface. However, this compressed region is still highly porous.

[0029] 3 illustrates an embodiment of a laminator system for forming a monolayer composite membrane according to the method of the present disclosure. As shown, laminator system 300 includes a laminator 330 fed with a first porous polymer layer 310 from a take-off roll 311 and a second porous polymer layer 320 from a take-off roll 321. The laminator 330 is heated to a lamination temperature determined by the relative melting temperatures of the first and second porous polymer layers to form a composite membrane 340. Because this composite membrane is a monolayer composite, the membrane can be easily handled without separation, such as being received on a take-up roll 341 for further processing, such as pleating.

[0030] The features and advantages of the etchant compositions of the present disclosure are illustrated in more detail by the following non-limiting examples. EXAMPLES

[0031] The two porous polymer layers were combined in a laminator and heated to a lamination temperature 15°C below the melting temperature of the polymer layer with the lowest melting temperature. The first porous polymer layer was oriented polyethylene with a thickness of about 4 μm, and the second porous polymer layer was ultra-high molecular weight polyethylene (UHMWPE) with a thickness of about 152 μm. This allowed the lamination of the separate layers without the use of adhesives, followed by cooling to form a monolayer composite membrane. The properties of the porous polymer layers and the resulting composite membrane are shown in Table 1. The flow rate, flow time and bubble point were calculated as described above. The flow rate and flow time values ​​of the monolayer composite membrane were compared to stacking configurations of the same porous polymer layers and used to calculate the flow rate reduction and flow time loss. TIFF2025032133000002.tif46170

[0032] As the data shows, using the method of the present disclosure, a single-layer composite membrane can be formed from different individual porous polymer layers by lamination without adhesives and without significant impact on membrane performance, as shown by minimal changes in flow time, flow rate, and bubble point. For example, the composite membrane has a flow rate of 90% or more of the flow rate of the unlaminated stacked composite of the first porous polymer layer and the second porous polymer layer (i.e., the flow rate decreases by less than 10%), and / or the composite membrane has a flow time of less than 120% of the flow time of the unlaminated stacked composite of the first porous polymer layer and the second porous polymer layer (i.e., the flow time increases by 20% or less), and / or the first porous polymer layer has a first bubble point and the second porous polymer layer has a second bubble point, the first bubble point being higher than the second bubble point, and the composite membrane has a bubble point of 90% or more of the first bubble point of the first porous polymer layer. The overall thickness is slightly less than the sum of the individual layer thicknesses, indicating the presence of compaction. However, this mild compaction does not significantly affect performance. Thus, the resulting single-layer composite film is well suited for the stringent purification requirements of the semiconductor industry.

[0033] Although the composite membranes and lamination methods have been variously disclosed herein with reference to exemplary embodiments and features, it will be understood that the above embodiments and features are not intended to limit the scope of the disclosure, and that other variations, modifications, and alternative embodiments will suggest themselves to those skilled in the art based on the disclosure herein. Accordingly, the present disclosure embraces all such variations, modifications, and alternative embodiments within the spirit and scope of the claims set forth below.

[0034] In a first embodiment, the composite membrane includes a first porous polymer layer and a second porous polymer layer laminated with the first porous polymer layer, the composite membrane being adhesive-free.

[0035] In a second aspect of the first aspect, the first porous polymer layer, the second porous polymer layer, or both are selected from the group consisting of polyamides, polysulfones, polyethersulfones, and polyolefins, and the first porous polymer layer and the second porous polymer layer are different.

[0036] In a third aspect according to the first or second aspect, the first porous polymer layer has a thickness of less than 20 μm.

[0037] In a fourth aspect related to the third aspect, the first porous polymer layer is an oriented polyethylene layer.

[0038] In a fifth aspect according to any of the previous aspects, the second porous polymer layer is a polyolefin layer having a thickness of about 50 μm to about 200 μm.

[0039] In a sixth aspect related to the fifth aspect, the polyolefin layer is an ultra-high molecular weight polyethylene (UHMWPE) layer.

[0040] In a seventh aspect according to any of the previous aspects, the composite membrane has a flux that is 90% or greater than a flux of a non-laminated composite of the first porous polymer layer and the second porous polymer layer.

[0041] In an eighth aspect of any of the preceding aspects, the composite membrane has an increased flow time that is 20% or less than the flow time of a non-laminated composite of the first porous polymer layer and the second porous polymer layer.

[0042] In a ninth aspect of any of the preceding aspects, the first porous polymer layer has a first bubble point and the second porous polymer layer has a second bubble point, the first bubble point being higher than the second bubble point, and the composite membrane has a bubble point that is 90% or greater than the first bubble point of the first porous polymer layer.

[0043] In a tenth embodiment, the composite membrane comprises a first region comprising a first porous polymer and having a thickness of less than about 20 μm, and a second region comprising a second porous polymer and having a thickness of about 50 μm to about 200 μm, wherein the second porous polymer is different from the first porous polymer and there is no interlayer region between the first and second regions.

[0044] In an eleventh aspect relating to the tenth aspect, the first region, the second region, or both the first region and the second region comprise a porous compressive region.

[0045] In a twelfth aspect relating to the tenth or eleventh aspect, the first porous polymer is expanded polyethylene.

[0046] In a thirteenth aspect relating to any of the tenth to twelfth aspects, the second porous polymer is a polyolefin.

[0047] In a fourteenth embodiment, a method of forming a composite membrane includes providing a first porous polymer layer and a second porous polymer layer to a laminator, heating the first porous polymer layer and the second porous polymer layer in the laminator to a lamination temperature, and adhesively laminating the heated first porous polymer layer and the heated second polymer layer to form a composite membrane.

[0048] A fifteenth aspect relating to the fourteenth aspect further comprises compressing the composite membrane during or after lamination.

[0049] In a sixteenth aspect related to the fourteenth or fifteenth aspect, the first porous polymer layer is an ultra-thin porous polymer layer having a thickness of less than 20 μm.

[0050] In a seventeenth aspect relating to the sixteenth aspect, the ultra-thin porous polymer layer is an oriented polyethylene layer.

[0051] In an eighteenth aspect relating to the fourteenth to seventeenth aspects, the second porous polymer layer is a polyolefin layer having a thickness of about 50 μm to about 200 μm.

[0052] In a nineteenth aspect relating to the eighteenth aspect, the polyolefin layer is an ultra-high molecular weight polyethylene (UHMWPE) layer.

[0053] In a twentieth aspect relating to any of the fourteenth to nineteenth aspects, the first porous polymer layer has a first melting temperature, and the first porous polymer layer is heated to a temperature between 5°C and 20°C below the first melting temperature.

[0054] In a 21st aspect relating to any of the 14th to 19th aspects, the second porous polymer layer has a second melting temperature, and the second porous polymer layer is heated to a temperature between 5°C and 20°C below the second melting temperature.

[0055] In a 22nd aspect relating to any of the 14th to 19th aspects, the composite membrane has a flow rate that is 90% or more of a flow rate of a non-laminated composite of the first porous polymer layer and the second porous polymer layer.

[0056] In a twenty-third embodiment, a filter comprises the composite membrane of any of the first to thirteenth embodiments.

Claims

1. a first porous polymer layer; a second porous polymer layer laminated with the first porous polymer layer; Including, Adhesive-free composite membrane.

2. 10. The composite membrane of claim 1, wherein the first porous polymer layer, the second porous polymer layer, or both are selected from the group consisting of polyamides, polysulfones, polyethersulfones, and polyolefins, and the first porous polymer layer and the second porous polymer layer are different.

3. 3. The composite membrane of claim 1 or 2, wherein the first porous polymer layer has a thickness of less than 20 μm.

4. 4. The composite membrane of claim 3, wherein the first porous polymer layer is an oriented polyethylene layer.

5. The composite membrane of any of claims 1 to 4, wherein the second porous polymer layer is a polyolefin layer having a thickness of about 50 μm to about 200 μm.

6. 6. The composite membrane of claim 5, wherein the polyolefin layer is an ultra-high molecular weight polyethylene (UHMWPE) layer.

7. 7. The composite membrane of claim 1, wherein the composite membrane has a flux that is 90% or greater than the flux of a non-laminated composite of the first porous polymer layer and the second porous polymer layer.

8. 8. The composite membrane of claim 1, wherein the composite membrane has an increase in flow time of no more than 20% over the flow time of a non-laminated composite of the first and second porous polymer layers.

9. 9. The composite membrane of claim 1, wherein the first porous polymer layer has a first bubble point and the second porous polymer layer has a second bubble point, the first bubble point being higher than the second bubble point, and the composite membrane has a bubble point that is 90% or greater than the first bubble point of the first porous polymer layer.

10. a first region comprising a first porous polymer and having a thickness of less than about 20 μm; a second region comprising a second porous polymer and having a thickness of about 50 μm to about 200 μm; Including, the second porous polymer is different from the first porous polymer; A composite membrane, wherein there is no interlaminar region between the first region and the second region.

11. 11. The composite membrane of claim 10, wherein the first region, the second region, or both the first region and the second region comprise a porous compressed region.

12. 12. The composite membrane of claim 10 or 11, wherein the first porous polymer is expanded polyethylene.

13. The composite membrane of any one of claims 10 to 12, wherein the second porous polymer is a polyolefin.

14. 1. A method of forming a composite membrane, comprising: i) providing a first porous polymer layer and a second porous polymer layer to a laminator; ii) heating the first porous polymer layer and the second porous polymer layer to a lamination temperature in a laminator; iii) laminating the heated first porous polymer layer and the heated second polymer layer without the use of an adhesive to form a composite membrane; A method comprising:

15. The method of claim 14 further comprising compressing the composite membrane during or after lamination.

16. 16. The method of claim 14 or 15, wherein the first porous polymer layer is an ultra-thin porous polymer layer having a thickness of less than 20 μm.

17. 17. The method of claim 16, wherein the ultra-thin porous polymer layer is an oriented polyethylene layer.

18. The method of any of claims 14 to 17, wherein the second porous polymer layer is a polyolefin layer having a thickness of about 50 μm to about 200 μm.

19. 20. The method of claim 18, wherein the polyolefin layer is an ultra-high molecular weight polyethylene (UHMWPE) layer.

20. 20. The method of any of claims 14 to 19, wherein the first porous polymer layer has a first melting temperature, and the first porous polymer layer is heated to a temperature between 5°C and 20°C below the first melting temperature.

21. The method of any of claims 14 to 20, wherein the second porous polymer layer has a second melting temperature, and the second porous polymer layer is heated to a temperature between 5°C and 20°C below the second melting temperature.

22. The method of any of claims 14 to 21, wherein the composite membrane has a flux that is at least 90% of the flux of a non-laminated composite of the first porous polymer layer and the second porous polymer layer.

23. A filter comprising the composite membrane according to any one of claims 1 to 13.

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