Porous membrane composite containing crosslinked fluorinated ionomer

Abstract

A porous polymer membrane composite containing a crosslinked fluorinated ionomer on the surface of a microporous membrane support and related methods are described.

Description

[Technical Field]

[0001] This disclosure relates to filters and filter membrane composites containing a crosslinked fluorinated ionomer on the surface of a microporous membrane support, as well as related methods. [Background technology]

[0002] Filter membranes made from porous polymer materials are commercially used in a variety of filtration applications, including the filtration of liquids and gases.

[0003] In the fabrication of microelectronic circuits, filters made from porous polymer membranes can be used to purify various chemically active liquids or gases, removing particulate contaminants from the fluid. Useful polymer membranes are chemically resistant to the fluids passing through them.

[0004] Hydrophobic porous filter membranes generally do not wet easily with water. When filtering a liquid that "releases gas" (produces gas) during a filtration operation, a certain amount of gas may be released from the liquid in the filtration device at the surface of the filter membrane. Hydrophobic membranes have a greater affinity for gases than for liquids. The gas released from the liquid can accumulate and form gas pockets that adhere to the surface and pores of the hydrophobic porous membrane. As these gas pockets increase in size due to the continuous release of liquid gas, they begin to move the liquid out of the pores of the hydrophobic porous membrane, continuously reducing the effective filtration area of ​​the hydrophobic porous membrane. This phenomenon is usually called dewetting of a hydrophobic porous membrane, where the fluid-wet (fluid-filled) portion of the hydrophobic porous membrane is gradually overtaken by the fluid-unwet or gas-filled portion. When dewetting of the membrane occurs, filtration stops.

[0005] Fluorine-containing polymers can have good chemical stability, i.e., they can be chemically inert. However, fluorine-containing polymers are typically hydrophobic and difficult to wet. Wetting a hydrophobic membrane with water or an aqueous fluid requires special operating procedures. The membrane may be first wetted using a low-surface-tension organic solvent such as isopropyl alcohol, then brought into contact with a mixture of water and the organic solvent, and then brought into contact with water or an aqueous fluid. This process can generate a large amount of solvent waste and consume a large amount of water. Alternatively, a hydrophobic membrane can be wetted with water under pressure. Techniques using pressure intrusion are time-consuming, expensive, ineffective for membranes with narrow pores, and can cause rupture of thinner membranes. Furthermore, this process does not guarantee that water will completely penetrate a significant portion of the membrane's pores.

[0006] In contrast to hydrophobic porous membranes, hydrophilic porous membranes naturally wet upon contact with aqueous liquids, eliminating the need for special pre-use treatment to wet the membrane. Advantageously, hydrophilic membranes can be used to handle aqueous liquids without pre-use treatment with organic solvents or pressure intrusion. [Overview of the Initiative]

[0007] There is a continuing need for microporous membranes that have improved non-dewetting properties, can be wetted with aqueous solutions, and have good flow characteristics.

[0008] The following relates to a microporous membrane composite comprising a microporous membrane support and a coating on the surface of the microporous membrane support, wherein the coating comprises a fluorinated ionomer. The fluorinated ionomer may be crosslinked, may contain hydrophilic groups, may be non-dewetting, and may be wettable with a solution containing a range of amounts of methanol and water.

[0009] Crosslinked fluorinated ionomers may be formed on a microporous film support from a coating composition containing various monomers, oligomers, prepolymers, etc., that are reactive for forming fluorinated ionomers, and may also contain monomer-derived fluorinated ionomer precursors. Examples of monomers that can be reacted to produce fluorinated ionomers ("monomer units") include: i) one or more fluorinated monomers having a fluorinated group and a reactive ethylene (unsaturated) group; ii) fluorinated monomers containing a reactive ethylene (unsaturated) group and a functional group convertible to a hydrophilic group; iii) bis-olefin crosslinking agents; and iv) fluorinated monomers containing a reactive (e.g., ethylene) group and a terminal iodine atom or terminal bromine atom. The coating composition may contain a radical initiator, but is not required.

[0010] According to an exemplary method, a microporous membrane composite can be prepared by coating a liquid coating composition onto a microporous membrane support and exposing the coating composition to electromagnetic radiation, such as ultraviolet light, to generate a crosslinked fluorinated ionomer on the support. An exemplary process involves coating a film with a coating composition and then crosslinking the fluorinated ionomer by exposing the fluorinated ionomer to electromagnetic radiation.

[0011] The exemplary process can be carried out at non-high temperatures, such as room temperature, without requiring the high crosslinking temperatures and the presence of radical initiators that are necessary for thermally induced crosslinking systems. Because the process has lower temperature requirements compared to thermally induced crosslinking techniques, the microporous membrane support material does not need to withstand exposure to high crosslinking temperatures, and the polymer membrane support can be selected from a wider range of materials, including polymer membrane supports that are unstable at the high crosslinking temperatures required for thermally induced crosslinking.

[0012] The combination of applying a coating composition to a support and exposing the coating composition to electromagnetic radiation can be carried out continuously by continuously applying the coating composition onto a moving sheet or “web” of a microporous membrane support and then continuously exposing the moving sheet or web of the membrane support to electromagnetic radiation.

[0013] In one aspect, the present disclosure relates to a method of preparing a microporous membrane composite comprising a microporous membrane support and a crosslinked fluorinated ionomer coating on the surface of the microporous membrane support. The method includes coating the microporous membrane with a liquid coating composition comprising a fluorinated solvent and a fluorinated ionomer dissolved or dispersed therein. The fluorinated ionomer is derived from copolymerizing (i) a fluorinated monomer containing a fluorinated group and ethylenic unsaturation; (ii) a fluorinated monomer containing ethylenic unsaturation and a functional group convertible to a hydrophilic group; (iii) a fluorinated bisolefin monomer; and (iv) a reactive unit comprising a fluorinated bromoalkyl or iodoalkyl chain transfer agent. The method also includes exposing the coated fluorinated ionomer to electromagnetic radiation to react the reactive units to form a crosslinked fluorinated ionomer.

[0014] In another aspect, the present disclosure relates to a microporous membrane composite comprising a microporous membrane support and a hydrophilic crosslinked fluorinated ionomer coating on the surface of the microporous membrane support. The crosslinked fluorinated ionomer comprises a fluorinated polymer backbone and a hydrophilic group bonded to the fluorinated backbone, and the hydrophilic group comprises a group selected from -SO3H and -COOH. The crosslinked liquid coating composition does not contain a thermally activated radical initiator.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 shows an exemplary system and method for continuously coating the described microporous membrane support. [Figure 2] FIG. 2 shows a schematic block diagram of an exemplary operation of the described method or system. [Figure 3]Figure 3 shows data from NMR analysis of crosslinked fluorinated ionomers prepared with and without a thermally activated free radical initiator. [Figure 4] Figure 4 shows a calibration curve of the absorbance of a methylene blue dye solution used in the dye-binding ability test of the porous membrane composite according to one embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0016] All figures are not to scale.

[0017] The following description relates to a microporous membrane composite including a microporous membrane support and a coating on the surface of the microporous membrane support, the coating including a fluorinated ionomer. This specification also relates to a method for preparing such a microporous membrane composite.

[0018] The microporous membrane composite can be prepared by applying a liquid coating composition onto the microporous membrane support and treating the coating composition to produce a desired crosslinked fluorinated ionomer on the surface of the support. The coating composition applied to the support may be partially crosslinked and contains a fluorinated ionomer that can be further crosslinked by exposing it to electromagnetic radiation (i.e., “fully crosslinked”). After the fluorinated ionomer is fully crosslinked, the ionomer can be further chemically treated to “activate” the crosslinked fluorinated ionomer, add a hydrophilic group to the crosslinked fluorinated ionomer, make the crosslinked fluorinated ionomer non-dewetting, and be wetted with a solution containing only methanol and water.

[0019] Crosslinked polymers include a fluorinated polymer backbone, iodine atoms, bromine atoms, or a combination thereof; and hydrophilic groups bonded to the fluorinated backbone. The iodine or bromine atoms are present within the polymer at positions between the polymer (fluorocarbon) backbones, i.e., the iodine or bromine atoms connect one polymer backbone to another. The hydrophilic groups can be selected from -SO3H PO3H and -COOH groups pendanted from the fluorocarbon backbone and may be present as part of the crosslinked fluorinated ionomer in an equivalent weight ranging from 380 to 620 grams per equivalent of hydrophilic groups.

[0020] This process comprises applying a coating composition to the surface of a microporous membrane support and crosslinking the fluorinated ionomer (e.g., further crosslinking) by exposing the fluorinated ionomer to electromagnetic radiation, and does not require, optionally and preferably, exposure of the fluorinated ionomer to a high temperature to induce crosslinking of the fluorinated ionomer ("crosslinking temperature"). Previous methods for placing crosslinked fluorinated ionomers on a microporous membrane support involve crosslinking the fluorinated ionomer by exposing the ionomer to a high crosslinking temperature, which may be at least 100, 120, or 150 degrees Celsius, in the presence of a thermally activated radical initiator. In contrast, the systems and methods herein can avoid the use of a thermally activated radical initiator and the need to expose the fluorinated ionomer to a high crosslinking temperature by instead inducing a crosslinking reaction in the fluorinated ionomer (applied to the surface of the support) by exposing it to electromagnetic radiation, such as ultraviolet light, without requiring a high crosslinking temperature.

[0021] Compared to methods for preparing chemically similar microporous membrane composites by crosslinking fluorinated ionomers by exposing them to high crosslinking temperatures (e.g., temperatures above 100 degrees Celsius), the method described herein crosslinks fluorinated ionomers by exposing them to electromagnetic radiation. The use of electromagnetic radiation to induce crosslinking does not require an increase in crosslinking temperature, which may enable useful differences in methods for preparing microporous membrane composites and for forming filter products containing microporous membrane composites.

[0022] Radiation-induced crosslinking mechanisms can avoid the need to expose coated membrane supports to high crosslinking temperatures. Radiation-initiated crosslinking can occur at temperatures below 170, 150, 120, or 100 degrees Celsius. The use of high crosslinking temperatures to induce crosslinking of fluorinated ionomers coated on the surface of microporous membrane supports requires microporous membrane supports that are stable (not degraded or melted) when exposed to high crosslinking temperatures. The need for membrane support stability at high crosslinking temperatures limits the available options for microporous membrane supports and discourages the use of microporous membrane supports that are not thermally unstable at high crosslinking temperatures, even if the support is otherwise useful.

[0023] By using radiation-induced crosslinking mechanisms, the need for high crosslinking temperatures is eliminated, and microporous membrane composites can be prepared using microporous membrane supports that are not necessarily stable at high crosslinking temperatures, such as 100, 120, 150, or 170 degrees Celsius or higher. Useful microporous membrane supports that may not be useful for processing by thermal-induced crosslinking mechanisms but are useful for processing using radiation-induced crosslinking mechanisms include polyolefins such as polyethylene (PE) and ultra-high molecular weight polyethylene (UHPE), polyvinylidene fluoride (PVDF), and polyphenylsulfone (PPSU).

[0024] Another useful feature of the described system or process is that the described process, which uses radiation to cause crosslinking of a fluorinated ionomer coated on a microporous membrane support, may include a continuous process step comprising a continuous step of coating a coating composition onto a microporous membrane support, and a continuous step of causing crosslinking of the fluorinated monomer in the coated coating composition by continuously exposing the support having the coated coating composition to electromagnetic radiation. The described process may include a step of continuously coating a coating composition onto the surface of a moving sheet of a microporous membrane support, and subsequently continuously exposing the moving sheet of the microporous membrane support to electromagnetic radiation to crosslink the fluorinated ionomer coated on the surface of the microporous membrane support. In comparison, a typical filter product manufactured using thermal induction crosslinking technology undergoes a crosslinking process after the membrane composite is converted and assembled into filter components, e.g., a filter cartridge, by heating the filter cartridge.

[0025] Crosslinked fluorinated ionomers can be formed on a microporous film support by applying a coating composition containing a fluorinated ionomer component to the surface of the support. The coating composition may contain (or be derived from) a previously reacted monomer, such as an oligomer or prepolymer derived from a monomer, which may be called a fluorinated ionomer “precursor”. The fluorinated ionomer precursor may be a pre-reaction molecule formed from a monomer that is partially crosslinked, not fully crosslinked, and can be further crosslinked (i.e., “fully crosslinkable”) after the coating composition has been applied to the surface of the support. After applying the coating composition to the film support, the coating composition is exposed to electromagnetic radiation to initiate crosslinking of the fluorinated ionomer without the need to expose the coating composition to high temperatures.

[0026] The terms “fluorination” and “perfluorination” are used herein in a manner consistent with their meanings within the field of chemistry and chemical coatings. Fluorinated compounds include organic chemical compounds, polymers, ionomers, chain transfer agents, crosslinking agents, solvents, etc., having at least one carbon-bonded hydrogen atom replaced by a carbon-bonded fluorine atom. Fluorinated compounds also include perfluorinated compounds. Perfluorinated compounds or perfluorocarbon compounds are chemical compounds, including polymers, ionomers, crosslinking groups, chain transfer agents, etc., in which all or essentially all carbon-bonded hydrogen atoms are replaced by carbon-bonded fluorine atoms. Some residual hydrogen atoms may be present in the perfluorinated composition, for example, in amounts less than 2 weight percent of the perfluorinated product, and possibly less than 0.5 weight percent or 0.25 weight percent of the perfluorinated product.

[0027] The coating composition contains chemical components useful for generating fluorinated ionomers, which are suspended, dispersed, or dissolved in a liquid medium containing an organic solvent. The components include reactive units that can react to form fluorinated ionomers, such as monomers, crosslinkers, oligomers, and chain transfer agents, and may be combined with a fluorinated ionomer “precursor” formed from monomers. In some examples, the components may be mainly or completely unreacted, for example, a mainly or completely reactive monomer (including a crosslinker) compound. In other examples, the components may include reactive monomers and crosslinker compounds in combination with a certain amount of partially reacted or partially crosslinked components that react to form a fluorinated ionomer (i.e., “precursor”) that can be further crosslinked (e.g., “fully crosslinked”) by exposing the coating composition containing the precursor to electromagnetic radiation.

[0028] In other words, the chemical components of the coating composition include various combinations of monomers described herein and any chemical derivatives thereof, which may be completely unreacted (in monomer form) or partially reacted and pre-reacted, i.e., partially polymerized or partially crosslinked fluorinated ionomer “precursors.” Components comprising monomers (including crosslinking agents) and ionomer precursors may be further reacted (i.e., crosslinked) by exposure to electromagnetic radiation to form a “fully polymerized” fluorinated ionomer, which refers to a fluorinated ionomer that has been crosslinked by exposure to electromagnetic radiation after being applied to a microporous membrane support. As used herein, the term “fluorinated ionomer” refers to a partially reacted (partially crosslinked) ionomer that may be present in the coating composition, and a fully crosslinked ionomer that has been applied to a microporous membrane support as part of the coating composition and subsequently crosslinked by exposure to electromagnetic radiation.

[0029] The coating composition may contain various monomers (including crosslinking agents), oligomers, prepolymers, etc., that are reactive for forming fluorinated ionomers and may contain fluorinated ionomer precursors derived from monomers. Examples of monomers that can be reacted to produce fluorinated ionomers ("monomer units") include: i) one or more fluorinated monomers having a fluorinated group and a reactive ethylene (unsaturated) group; ii) fluorinated monomers containing a reactive ethylene (unsaturated) group and a functional group convertible to a hydrophilic group; iii) bis-olefin crosslinking agents; and iv) fluorinated monomers containing a reactive (e.g., ethylene) group and a terminal iodine atom or terminal bromine atom.

[0030] Fluorinated monomer (i) having a fluorinated group and an ethylene (unsaturated) group may be a fluorinated or perfluorinated monomer, and examples of fluorinated unsaturated monomers include: fluorinated vinylidene (VDF); C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE); C2-C8 chloro-, bromo- and iodo-fluoroolefins such as chlorotrifluoroethylene (CTFE) and bromotrifluoroethylene; CF2=CFOR f (Per)fluoroalkyl vinyl ether (PAVE) (wherein R f (1) is a C1-C6 (per)fluoroalkyl group, such as trifluoromethyl, bromodifluoromethyl, or pentafluoropropyl. CF2 = CFOX perfluoro-oxyalkyl vinyl ether (wherein X is a C1-C6 group having one or more ether groups). 12 Perfluorooxyalkyl groups, such as perfluoro-2-propoxypropyl.

[0031] Useful fluorinated monomers (ii) containing functional groups convertible to ethylene groups and hydrophilic groups include -SO2F, -COOR, -COF, and combinations thereof, where R is a C1-C20 alkyl radical or a C6-C20 aryl radical. One example is CF2=CF-O-CF2CF2SO2F. After the monomer is formed into a fluorinated ionomer, the functional group may be converted to a hydrophilic group such as -SO3H or -COOH. Other examples are described in U.S. Patent No. 6,354,443.

[0032] The equivalent weight of the fluorinated monomer (ii) as part of the fluorinated ionomer may be fully or partially crosslinked and may range from 380 g / equivalent (g / eq) to 620 g / eq, for example, in the range of 500 to 600 g / eq or 550 to 590 g / eq.

[0033] Examples of useful bis-olefin crosslinking agent molecules (iii) include those having the following formulas OF-1, OF-2, and OF-3. The compound of formula OF-1 is represented as follows: In formula TIFF0007853452000001.tif28170, j is an integer from 2 to 10, preferably from 4 to 8, and R1, R2, R3, and R4 are H, F, or C1-C5 alkyl or (per)fluoroalkyl groups, which may be the same or different from each other. The compound of formula OF-2 is represented as follows: In formula TIFF0007853452000002.tif27170, each A is independently selected from F, Cl, and H; each B is independently selected from F, Cl, H, and ORB, where RB is a branched or linear alkyl group that can be partially, substantially, or completely fluorinated or chlorinated; and E is a divalent group having 2 to 10 carbon atoms, which may contain ether bonds and may be fluorinated. The compound of formula OF-3 is represented as follows: In formula TIFF0007853452000003.tif28170, E, A, and B have the same meanings as defined above; each of R5, R6, and R7 is independently H, F, or C1-5 alkyl or (per)fluoroalkyl group.

[0034] A certain amount of bis-olefin(iii) may be present in any useful amount in the mixture of components used to produce the fluorinated ionomer, for example, in an amount ranging from 0.1 to 5 weight percent per the total weight of the fluorinated ionomer components (including all monomers, precursors, etc.).

[0035] Useful bromine-containing and iodine-containing monomers (iii) include, for example, those of formula R f (I) x (Br) y Examples of fluorinated chain transfer agents include, in the formula, R fx is a fluoroalkyl, (per)fluoroalkyl, or (per)fluorochloroalkyl group having 1 to 10 carbon atoms, where x and y are integers between 0 and 2, and 1 ≤ x + y ≤ 2. Examples include bromine-containing fluoroalkyl compounds and iodo-fluoroalkyl compounds having 1 to 10 carbon atoms, as described in U.S. Patent No. 9,359,480, for example.

[0036] In the exemplary system, bromine or iodine atoms may be present in an amount ranging from 0.1 to 5 weight percent relative to the total weight of the fluorinated ionomer component (including all monomers, precursors, etc.).

[0037] The coating composition may, if not necessary, optionally further contain a radical initiator that can promote crosslinking of the fluorinated ionomer when the fluorinated ionomer is exposed to electromagnetic radiation.

[0038] Various types of free radical initiators are known to be useful in initiating reactions between reactants in a chemical system by generating free radicals, such as those causing crosslinking or polymerization of reactive monomers, oligomers, prepolymers, and crosslinking agents. Various types of free radical initiators (or "radical initiators") are known, and these can generate one or more chemical free radicals through various activation mechanisms. Some radical initiators are activated by exposure to heat to generate free radicals and are called "thermally activated initiators." Other types of radical initiators are activated by exposure to electromagnetic radiation to generate free radicals and are called "radiation activated initiators."

[0039] Different thermally activated free radical initiators are known that are useful for inducing reactions between chemical components used to form crosslinked fluorinated ionomers. For example, U.S. Patent No. 9,359,480 describes dialkylperoxide initiators that can be activated and generate radicals when heated to curing temperatures in the range of 100 to 300 degrees Celsius. Examples of specific dialkylperoxide initiators are identified as di-tert-butyl-peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, dicumylperoxide, dibenzoylperoxide, di-tert-butylperbenzoate, and di-1,3-dimethyl-3-(tert-butylperoxy)butyl carbonate. According to this specification, liquid coating compositions do not need to contain any of the thermally activated free radical initiators, such as the general or specific initiators identified in Patent No. 9,359,480. Alternatively, useful or preferred liquid coating compositions and derivative crosslinked fluorinated ionomers and coatings may be particularly free of these and other thermally activated free radical initiators, and may contain, for example, less than 0.001, 0.0005, or 0.0001 weight percent of these or any other thermally activated free radical initiators.

[0040] To avoid the need for a step of heating the liquid coating composition to cause crosslinking of the coating composition, the liquid coating composition of this specification can be cured by a non-thermal activation method, such as exposure to radiation, for example, ultraviolet light having a wavelength of 300 to 400 nanometers.

[0041] The described liquid coating compositions may, but not necessarily, contain radiation-activated free radical initiators. Examples include compounds of a classification called "Type I" photoinitiators, and certain types of radiation-sensitive salts, such as sulfites, including sodium sulfite (Na2SO3), which generate free radicals in the presence of ultraviolet energy.

[0042] Useful radiosensitive initiator compounds include type I free radical initiators and equivalent compounds that are monomolecule free radical generators that decompose in the presence of radiation, such as ultraviolet light in the 300-400 nanometer range, to form two chemical free radicals. Examples of type I free radical initiators include hydroxyacetophenone (HAP) initiators and phosphine oxide (TPO) initiators. An example of a commercially available type I UV initiator is one sold under the trade name Irgacure (e.g., Irgacure 2959, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone).

[0043] The presence of a radical initiator in the coating composition is optional and not required. In a coating composition containing a radiation-activated free radical initiator, the amount of radiation-activated free radical initiator in the coating composition may be a useful amount, such as 0.01 to 10 weight percent, for example, in the range of 0.1 to 5 weight percent, based on the total weight of the liquid coating composition. In other examples, the coating composition may exclude any radical initiator, for example, the coating composition may contain less than 0.01, 0.005, or 0.001 weight percent of any type of radical initiator, whether thermally activated or radiation-activated.

[0044] A coating composition containing a fluorinated ionomer component also comprises a liquid medium containing an organic solvent, such as a fluorinated solvent, in which the fluorinated ionomer component is dissolved or dispersed. The fluorinated solvent, also referred herein as a liquid fluorocarbon medium, is a fluorinated liquid chemical useful for dissolving or dispersing the chemical components of the coating composition to form a coating composition that wets the surface of the support when applied to the porous surface of a microporous membrane support. The solvent may comprise an effective amount of the fluorinated organic solvent and optionally one or more other fluorinated or non-fluorinated solvents for forming a useful coating composition.

[0045] Examples of fluorinated solvents include, for example, perfluoropolyethers or mixtures of two or more perfluoropolyethers, for example, those containing them, consisting essentially of them, or consisting of them. Perfluoropolyethers have the general formula F3C-O-(CF2CF(CF3)-O) n -(CF2-O) m -CF3 (where m and n are integers, n is greater than 0, and m is 0 or greater). Examples of such perfluoropolyethers can have a molecular weight of 300 to 600 amu and a boiling point of 20 to 150 degrees Celsius.

[0046] Other examples of useful fluorinated solvents include hydrogenated fluoropolyethers, for example, those containing them, consisting essentially of them, or consisting of them. Exemplary hydrogenated fluoropolyethers (HFPE) can have the general formula R*-O-R f ’-R*’, where R* and R*’ are the same or different, and are selected from -C m F 2m+1 and -C n F 2n+1-h H h groups, m and n are integers from 1 to 3, h is an integer greater than or equal to 1, and h is selected such that h is less than or equal to 2n + 1, provided that at least one of R* and R*’ is the -C n F 2n+1-h H h group defined above; -R f’ is (1)-(CF2O) a -(CF2CF2O) b -(CF2-(CF2) z’ -CF2O) c (where a, b, and c are integers up to 10, preferably up to 50, z’ is an integer equal to 1 or 2, a is 0 or greater, b is 0 or greater, c is 0 or greater, and a + b is greater than 0; preferably, each of a and b is greater than 0, and b / a is in the range of 0.1 to 10); and (2)-(C3F6O) c’ -(C2F4O) b -(CFXO) t-(wherein X is independently selected from -F and -CF3 each time it appears; b, c' and t are integers at most 10, c' is greater than 0, b is greater than or equal to 0, and t is a greater than or equal to 0; preferably b and t are greater than 0, c' / b is in the range of 0.2 to 5.0, and (c'+b) / t is in the range of 5 to 50); (3)-(C3F6O) c’ -(CFXO) t -(In the formula, X is independently selected from -F and -CF3 each time it appears; c' and t are integers at most 10, c' is greater than 0, t is greater than or equal to 0, preferably t is greater than 0, and c' / t is in the range of 5 to 50) Selected from.

[0047] Useful types of fluorinated surfactants include methoxynonafluorobutane compounds, such as (CF3)2CFCF2-O-CH3 or CF3CF2CF2CF2-O-CH3, sometimes with a purity of at least 99% by weight.

[0048] Examples of commercially available fluorinated solvents include Novec® HFE-7100 (methoxynononafluorobutane, surface tension 13 dynes / cm, available from 3M Company), Galden® SV90 (perfluoropolyether, surface tension 16 dynes / cm, available from Solvay Solexis), and other similar fluorinated low-surface-tension solvents, combinations thereof, or mixtures containing these solvents.

[0049] The coating composition may be prepared by known methods. Exemplary coating compositions contain components useful for generating fluorinated ionomers, any fluorinated ionomer precursors, etc., which may be in the form of colloidal or gel particles suspended or dispersed in a fluorinated solvent. The particles may preferably have small particle sizes, e.g., less than 600 nanometers (nm), e.g., less than 300 nm, less than 125 nm, less than 40 nm, or an average particle size of less than 15 or 10 nm; for example, fluorinated ionomer particles in the coating composition may have an average particle size in the range of 10 to 600 nanometers, e.g., 10 to 300 nanometers; or 10 to 100 or 10 to 40 nanometers.

[0050] Relatively small ionomer particles remain within the pores, blocking the flow of fluid through the pores of the microporous membrane support. This reduces the appearance of particles that, after the crosslinked fluorinated ionomer is formed on the support and forms a membrane composite when the coating composition is applied to the support, can reduce the fluid velocity through the porous membrane support (i.e., cause "flow loss").

[0051] According to some examples, useful coating compositions contain fluorinated ionomers in the form of suspended particles, where at least 90% by weight of the fluorinated ionomer particles have a particle size of less than 200 nanometers (nm), for example, at least 90% by weight of the fluorinated ionomer particles have a particle size of less than 125 nm, or less than 40 nm, or less than 15 nm.

[0052] The amount of fluorinated ionomer component in the coating composition may be sufficient to produce a non-dewetting microporous membrane complex when applied to a microporous membrane support, then crosslinked and activated, as measured, for example, by autoclave testing. Furthermore, this amount may be sufficient to produce a microporous membrane complex that can be completely wetted with a solution containing methanol and water, or in some cases, with water alone.

[0053] In exemplary coating compositions, the amount of fluorinated ionomer components (all non-solvent, solid components, including monomers, ionomer precursors, etc.) can be in the range of 0.1 to 4 weight percent, for example, 0.1 to 3.5 weight percent, per the total weight of the coating composition (e.g., solid and solvent of the ionomer components). Coating compositions that do not contain sufficiently high concentrations of fluorinated ionomer components may produce incompletely coated microporous membrane supports that have uncoated hydrophobic regions and do not completely wet with methanol and water-containing solutions. Coating compositions containing excessively high concentrations of fluorinated ionomer components may produce microporous membrane composites in which the amount of fluid flow through the membrane is reduced during use.

[0054] Microporous membrane supports (i.e., "supports") may be formed from polymers that are chemically inert to the crosslinking and activation steps of the processes described herein. Microporous membrane supports are porous membranes that may also be described in terms such as superporous membranes, nanoporous membranes, and microporous membranes. These microporous membranes are effective in removing undesirable particulate materials such as gel particles, colloids, cells, and polyoligomers that are larger than the pores of the microporous membrane from the liquid feed stream, while components of the liquid smaller than the pores pass through the pores.

[0055] Useful microporous membrane supports that can be considered microporous, superporous, or nanoporous may have average pore sizes of less than 10 microns, less than 5 microns, or less than 1, 0.5, 0.1, 0.05, or 0.01 microns.

[0056] The microporous membrane support may have any useful thickness, for example, about 1 to 100 microns or 5 to 75 microns.

[0057] Exemplary supports may be made from fluorinated or perfluorinated polymers so as to be chemically inert. Examples of fluorinated microporous membrane supports include polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene (FEP) copolymers, copolymers of tetrafluoroethylene and perfluoropropyl vinyl ether (also called perfluoroalkoxy polymers, PFAs), copolymers of tetrafluoroethylene and perfluoromethyl vinyl ether (MFAs), and polymer compositions containing any of these. Microporous membrane supports can be formed, for example, from polytetrafluoroethylene, fluorinated ethylene-propylene copolymers, or perfluoroalkoxy polymers, and may include a group of fluoropolymers commonly known as fluorocarbons, marketed by EIDupont de Nemours and Company, Inc. under the names Teflon® PTFE, Teflon® FEP, and Teflon® PFA, or amorphous forms of Teflon® polymers such as Teflon® AF polymer.

[0058] Other fluorocarbons for microporous membrane supports include, but are not limited to, those available from Daikin, e.g., Neoflon®-PFA and Neoflon®-FEP, or various grades of Hyflon®-PFA and Hyflon®-MFA available from Solvay Solexis. Fluoropolymers have excellent chemical and heat resistance and are generally hydrophobic. Other useful thermoplastic fluoropolymers that can be used may include, among others, homopolymers and copolymers containing monomer units derived from fluorinated monomers such as vinylidene fluoride (VF2), hexafluoropropene (HFP), chlorotrifluoroethylene (CTFE), vinyl fluoride (VF), trifluoroethylene (TrFE), and tetrafluoroethylene (TFE), which may be combined with one or more other non-fluorinated monomers.

[0059] Fluoropolymer membrane supports are useful for processing membrane composites at high temperatures, including thermally induced crosslinking; however, the exemplary method described herein allows for crosslinking without exposure to high crosslinking temperatures. By using a crosslinking process initiated by electromagnetic radiation, the membrane support is not exposed to high crosslinking temperatures, and thermal stability is not required for the membrane support. Therefore, the membrane support may be prepared from polymer materials that are not necessarily stable to high crosslinking temperatures, thereby enabling the use of membrane supports made from polyethylene and polyolefins such as ultra-high molecular weight polyethylene (UHPE), polyvinylidene fluoride (PVDF), and polyphenylsulfone (PPSU).

[0060] According to a useful method, a microporous membrane composite can be prepared by a process that includes continuously coating a coating composition onto the surface of a moving microporous membrane support to form what is called a “coated microporous membrane support” or “coated support.” The coated support can then be continuously exposed to electromagnetic radiation to induce crosslinking of the fluorinated ionomer of the coating composition. After crosslinking, the coated support can be subsequently processed to convert it into a filter film of a filter product. One or more of the subsequent processing steps may be performed optionally and preferably sequentially.

[0061] In exemplary methods, a microporous membrane support may be coated with a coating composition, the coating composition may be exposed to electromagnetic radiation to crosslink (i.e., "fully crosslinked") the fluorinated ionomer, the resulting coated support may be processed to remove excess coating composition, the support may be dried, and the functional groups of the fluorinated monomer may be chemically converted to hydrophilic groups. Specific steps may include, in any useful order: extracting excess (e.g., unreacted) components of the coating composition remaining on the surface after crosslinking to remove excess components from the coated support; drying the fully crosslinked coating after the crosslinking and extraction steps; folding or pleating the coated film with the fully crosslinked fluorinated ionomer to form a pleated filter film from the coated support; assembling a filter product containing the pleated film; and chemically converting the functional groups of the fully crosslinked fluorinated ionomer, which can be converted to hydrophilic groups, to hydrophilic groups.

[0062] The conversion or "activation" of convertible functional groups of fluorinated ionsomers to hydrophilic groups, such as the conversion of a sulfonyl group -SO2F to an acidic sulfone group SO3H, can be carried out by known methods. For example, activation can be carried out by treating a support coated with an intermediate with a fully crosslinked ionomer in a strong basic aqueous solution such as a KOH solution (e.g., at a concentration of about 10 wt percent) at a temperature in the range of about 65 to 85 degrees Celsius for a period of about 4 to 8 hours, then washing the treated coated support with demineralized or deionized water at 80 to 90 degrees Celsius to remove unreacted ionomers for 30 minutes, then treating the coated support in a strong acid aqueous solution such as HCl or nitric acid (e.g., at a concentration of about 20 wt percent) at room temperature for a period of about 2 to 16 hours, and then washing the coated support with demineralized or deionized water. Chemical conversion of -COF and / or -COOR groups can be carried out similarly. A microporous membrane support coated with a coating composition containing a fluorinated ionomer, then completely crosslinked, and then activated as described, is called a microporous membrane composite.

[0063] In a useful and preferred example, the fully crosslinked fluorinated ionomer of the microporous membrane composite may contain a radioactive radical initiator included in the liquid coating composition to promote crosslinking of the fluorinated ionomer component of the liquid coating composition.

[0064] In other useful and preferred examples, fully crosslinked fluorinated ionomers of microporous membranes may be free of radioactive radical initiators, and may contain, for example, less than 0.01, 0.005, or 0.001 weight percent of radioactive radical initiators.

[0065] In these and other useful and preferred examples, fully crosslinked fluorinated ionomers of microporous membranes may be exempt from thermally activated radical initiators, including any of those described in U.S. Patent No. 9,359,480, which include dialkylperoxide initiators that can be activated and generate radicals when heated to a curing temperature in the range of 100 to 300 degrees Celsius. Specific examples include dialkylperoxides such as di-terbutyl (terbutyl)-peroxide and 2,5-dimethyl-2,5-di(tertbutylperoxy)hexane, dicumyl peroxide, dibenzoyl peroxide, di-tert-butylperbenzoate (also known as Luperox 101), and di-1,3-dimethyl-3-(tertbutylperoxy)butyl carbonate. Exemplary fully crosslinked fluorinated ionomers of microporous membranes herein may contain any thermally activated radical initiator in amounts less than 0.01, 0.005, or 0.001 weight percent.

[0066] The presence, absence, and amount of either thermally activated or radiation-activated radical initiators in the fully crosslinked fluorinated ionomers of microporous membrane composite coatings can be determined by quantitative chemical analysis. One such method is nuclear magnetic resonance (NMR) analysis. See Figure 3. Other quantitative chemical analysis methods may also be useful.

[0067] An exemplary method is shown in Figure 1. This exemplary method may be performed on a continuous coating line 100, where a continuous length roll (104) of a microporous film support 102 is aligned for non-rolling to supply a continuously moving web of the support 102 to the coating line 100. Downstream of the roll 104 are a coater 110 and an electromagnetic radiation source 120. Downstream of the supply source 120 are various subsequent optional processing devices 130, 140, 150, and 160.

[0068] During use, the web of the support 102 is unwound from the roll 104 and supplied to the coater 110, which applies a coating composition (not shown) to the surface of the support 102 as the support 102 moves continuously through the coater 110. The coater 110 may be any useful type, such as a spray coater, dip coater, or curtain coater, and may be equipped with mechanical devices such as rollers or squeeze bars to completely impregnate the pores of the support 102 with the coating composition for uniform coating of all surfaces of the support 102. A particularly useful type of coater 110 may be a bath containing a fixed volume of coating solution in a vessel. The support 102 may move continuously through a fixed volume of coating composition contained in the bath and be immersed therein in order to impregnate and uniformly coat all surfaces of the porous support. The liquid composition in the coater 110 may be maintained at a temperature in the range of about 19 to about 26 degrees Celsius.

[0069] After the coating composition is applied to the surface of the microporous film support 102, the resulting support ("coated support") can be passed through electromagnetic radiation to crosslink (i.e., "fully crosslinked") the fluorinated ionomer of the coating composition by exposure to radiation. The coated support 102 moves continuously through the coater 110 and then through the electromagnetic radiation 106 emitted by the electromagnetic radiation source 120. The resulting coated support contains a coating of fully crosslinked fluorinated ionomer.

[0070] A subsequent step in processing the coated support may include removing unreacted or excess components from the coating composition remaining on the surface of the support 102 after the crosslinking step, which may be done by an extractor 130 containing a solvent, such as isopropyl alcohol. The solvent can then be removed from the remaining coating on the coated support, for example, by using a dryer 140 at a high temperature.

[0071] After the coating has dried, the coated support can be mechanically transformed to form a filter film, for example, by folding or pleating the dried coated support to form a pleated filter film as shown by the converter 150. The pleated filter can then be incorporated into a filter device and chemically treated to convert the functional groups of the fully crosslinked fluorinated ionomer, which can be converted to hydrophilic groups, as shown to occur using apparatus 160 (which may be a single apparatus or multiple apparatuses).

[0072] The described microporous membrane composites can be used as components of filter devices, including various filter structures such as supports, outer cylindrical housings or "cages," frames, inner cylindrical supports or "cores," as is known in various configurations of filter devices. The microporous membrane composites can be pleated in a layered configuration having one or more support layers or nets, and potted to form a filter cartridge with cages, supports, and two end cap structures. The cartridges may be of a type that is replaceable within the filter housing, or they may be firmly bonded to the filter housing.

[0073] Furthermore, referring to the exemplary system and method in Figure 1, throughout all steps, the temperature of the microporous membrane support 102 can be maintained at a temperature that does not cause degradation of the support, for example, not exceeding 170, 150, 120, or 100 degrees Celsius.

[0074] In an exemplary method for preparing the composite, the coating composition can be applied to a microporous membrane support by bringing the coating composition to be coated into contact with the “fluid contact surfaces” of the membrane support (including the outer and inner pore surfaces). Preferably, the coating composition can be applied to the support in such a way that the coating composition comes into contact with all or substantially all of the surface of the support to uniformly coat all surfaces of the support.

[0075] An exemplary method 200 is schematically shown as a block diagram in Figure 2. As illustrated, a coating operation (210) is used to apply the coating composition described herein to a microporous membrane support. The coating composition can be used to coat the external and internal pore surfaces of the microporous membrane support using any effective method and equipment, e.g., any one or more mechanical coating and impregnation techniques. The coating operation may be carried out in batch or semi-batch manner, but is preferably carried out continuously by applying the coating composition onto a moving web of the microporous membrane support. Effective techniques used alone or in combination may include spraying, roller coating, and dipping by continuously passing the moving web of the membrane support through a bath of the coating composition. In some examples of methods and microporous membrane supports, the support may be patterned by masking such that unmasked portions of the microporous membrane support are coated with the coating composition, while masked portions of the support remain uncoated.

[0076] The coating operation 210, which includes a specific step of applying the coating composition to a film support, can be carried out under any useful conditions and temperatures, typically using a coating composition having a temperature in the range of room temperature, for example, below 40 degrees Celsius or below 30 or 25 degrees Celsius. During a series of coating operations, particularly after the coating composition has been applied to the support in operation 210 and before the subsequent crosslinking operation 214, evaporation of the solvent from the coating composition or drying of the coating composition is undesirable. To prevent evaporation of the solvent from the coating composition present on the support and to prevent drying of the coating composition present on the support, it may be preferable to avoid an increase in the temperature of the coating composition and the support. Furthermore, the solvent of the coating composition may be selected to have a relatively high boiling point, a relatively low vapor pressure, or both.

[0077] In the crosslinking operation 214, the coated support can be placed between radiopaque films for the additional support, and the combination can be passed through electromagnetic radiation that crosslinks, i.e., "fully crosslinks," the fluorinated ionomer component in the coating composition. The coated support can be passed through a chamber irradiated with electromagnetic radiation having a wavelength and amount that causes the desired crosslinking of the fluorinated ionomer contained in the coating composition, such as ultraviolet light. The crosslinking operation 214 can be carried out under any useful conditions and temperatures. To avoid thermal degradation of the temperature-sensitive support, the inside of the crosslinking chamber ("UV chamber") can be maintained at a temperature that does not allow the support to reach temperatures above 170, 150, or 120 degrees Celsius, if used.

[0078] After the fluorinated ionomer is exposed to radiation to completely crosslink, subsequent steps can be performed on the coated support to convert the coated support into a filter film (composite) containing a dry coating having a completely crosslinked fluorinated ionomer, the fluorinated ionomer containing hydrophilic groups that cause the film composite to exhibit desired wetting (with methanol and water) and dewetting properties.

[0079] As an example of a useful subsequent process, a coated support having a fully crosslinked fluorinated ionomer on its surface may be treated by one or more chemical extraction steps 220 to remove unreacted excess chemical components from the fully crosslinked coating composition present on the support surface. The extraction may be carried out in a single step or in a series of two or more steps, each using the same or different liquids (e.g., solvent or water). The extraction steps may be carried out at room temperature, for example, below 40, 30, or 25 degrees Celsius. The liquid can be brought into contact with the support by spraying, by immersion of the support in the liquid, and by any mechanical stirring, such as by using pressure from a roller, squeegee, etc. Effectively, one or more extraction steps can remove most of the excess components of the coating composition from the surface of the coated support.

[0080] After the extraction step, for example 220, the coated support may be dried to remove the solvent from the surface and the crosslinked fluorinated ionomer coating. The drying step (224) can be carried out by exposing the coated support (after extraction) to a high temperature for a time sufficient to remove any residual solvent, for example, by passing the coated support through an oven or heating chamber containing a heating environment. To avoid thermal degradation of the heat-sensitive support, if used, the temperature of the heating environment can be kept within a range that does not allow the support to reach a temperature at which thermal degradation occurs as it moves through the heating environment, for example, the environment may be at a temperature not exceeding 170, 150, or 120 degrees Celsius.

[0081] The dried coated film can be processed in the conversion and apparatus fabrication process 230 by folding, cutting, pleating, etc. In this process, the coated support contains a fully crosslinked fluorinated ionomer containing a functional group that can be chemically converted to a hydrophilic group, for example, -SO2F, -COOR, -COF, or a combination thereof, where R is a C1-C20 alkyl radical or a C6-C20 aryl radical. These groups remain as part of the fluorinated ionomer and can be converted to a hydrophilic group as desired. The conversion operation 230 may produce individual filter films from the coated support, each of which can be incorporated into a single filter product such as a filter cartridge or filter housing. The conversion operation may also include assembling the coated support into a filter device such as a filter cartridge or filter housing.

[0082] By exemplary method 200, the functional groups of a fluorinated ionomer that can be chemically converted to hydrophilic groups can be converted to hydrophilic groups after the coated support has been initially converted into a folded or pleated coated film, and after the converted (e.g., pleated) coated support has been incorporated into a filter device such as a filter cartridge or filter housing.

[0083] The first step, which involves chemically converting functional groups to hydrophilic groups, can wet or "pre-wet" the support coated by the pre-wetting operation 234. To perform the pre-wetting step, a liquid containing a solvent (e.g., IPA) or water or both can be passed through the apparatus and, for example, through the film under ambient conditions.

[0084] In the subsequent hydrolysis step 240, a base such as ammonium hydroxide or potassium hydroxide may be brought into contact with the film and held for a sufficient time, for example at room temperature, to chemically convert the functional groups to include counterions of potassium or -NH4 ions. The apparatus may then be washed with water 224 to remove the ammonium hydroxide or potassium hydroxide. The film is then brought into contact with an acid 250, such as hydrochloric acid (HCl), to convert the functional groups to hydrophilic (acidic) groups. A final warm water rinse 254 is applied to the coated support.

[0085] Throughout all steps of the exemplary method 200, the temperature of the microporous membrane support can be kept below a temperature at which the support can undergo thermal degradation, for example, the temperature of the support may be kept below 170, 150, 120, or 100 degrees Celsius.

[0086] The membrane composites described herein, prepared as presented herein, may possess properties useful for filter membrane composites of a type considered "non-dewetting." The non-dewetting properties of a microporous membrane composite can be determined by heating a microporous membrane composite sample, moistened by contact with a liquid in an autoclave, to a temperature above the boiling point of the liquid. If the sample remains moist and translucent after a certain amount of time in high-temperature autoclaving, the sample may be considered non-dewetting for those autoclaving conditions. For example, a microporous membrane composite that does not dewet when autoclaved in water at a temperature of 135 degrees Celsius or higher for 40 to 60 minutes or about 60 minutes may be considered non-dewetting for those conditions.

[0087] Microporous membrane composite samples can be prepared for autoclaving by first wetting the sample with a liquid, such as a solution containing methanol and water, and then flushing to replace the methanol-water solution with water. The sample replaced with water can be autoclaved in a sealed container with water in an oven. If the microporous membrane support is not sufficiently coated with crosslinked ionomer, subjecting such an incompletely coated sample to autoclaving in water will cause the incompletely coated sample to dewet and appear opaque after autoclaving. Non-dewetting differs from the contact angle measurement of the surface energy of the microporous membrane, because non-dewetting refers to the wetting properties of the microporous membrane across its thickness and pores, and because the liquid comes into contact with the filtration surface as well as the outer surface of the microporous membrane.

[0088] The different wetting properties of filter membrane composites are their ability to be wetted (or have been wetted) with solutions of water and methanol. While membrane composites may not be able to be wetted directly with water, exemplary microporous membrane composites may be wetted with solutions containing methanol and water, i.e., "wettingable".

[0089] The term "wetting" is used to refer to a dry microporous membrane composite that readily immerses or absorbs, within 5 seconds, a solution containing a combination of methanol and water, for example, a solution essentially consisting of methanol and water, to substantially all of its coated microporous structure without the use of heat, pressure, mechanical energy, surfactants, or other pre-wetting agents.

[0090] The microporous membrane composites described herein are not necessarily directly wettable with water, even if the fully crosslinked fluorinated ionomer coating formed on the surface of the composite has hydrophilic groups and the composite is non-dewetting after autoclaving with water.

[0091] Wetting can be measured by placing a single droplet of methanol-water solution directly onto a portion of the microporous membrane composite sample from a height of approximately 5 centimeters or less. The time it takes for the droplet to penetrate the pores of the sample is measured. If the droplet penetrates the pores of the sample within 5 seconds and the sample appears transparent, the sample is considered wettingable with a droplet of methanol-water solution. If the droplet does not penetrate the microporous membrane composite sample, the sample is retested using a methanol-water solution containing a higher weight percentage of methanol.

[0092] The exemplary microporous membrane composites described herein are wettable with methanol-water solutions containing 95% by weight or less methanol, for example, methanol-water solutions containing 95, 92, 90, 87, 85, 82, 80, 77, 75, 72, 50, 30, or 20% by weight methanol (the remainder being water). Microporous membrane composites wettable with solutions containing the lower end of these amounts of methanol, i.e., solutions containing a lower relative amount of methanol, have relatively high surface energy and are more resistant to dewetting. In some examples, the described microporous membrane composites may be wettable with methanol-water aqueous solutions containing less than 10 or 5% by weight methanol in water, or with pure water (99 or 100 percent water).

[0093] These described microporous membrane composites, which can be wetted with methanol and water-containing solutions, can be used in aqueous filtration applications where aqueous liquids flow through the membrane without the membrane dewetting. “Aqueous liquid” is a liquid containing a certain amount of water and includes aqueous liquids known and used in the semiconductor industry, such as SC1 or SC2 washing baths; concentrated sulfuric acid with or without an oxidizing agent such as hydrogen peroxide or ozone; and other aqueous-based liquids requiring filtration, such as aqueous solutions of salts (buffer oxide etching), bases, or acids.

[0094] With respect to surface tension, a microporous membrane composite having a surface energy of at least approximately 25 dynes / cm may be wettable in a solution containing 80 wt% methanol in water; a microporous membrane composite having a surface energy of 40 dynes / cm may be wettable in a solution containing 30 wt% methanol in water; and a microporous membrane composite having a surface energy of 50 dynes / cm may be wettable in a solution containing 15 wt% methanol in water. Exemplary microporous membrane composites herein may have a surface energy of at least 25 dynes / cm, or at least 27, 30, 32, 35, 37, 40, 45, 50, 55, 60, 65, 70, or 72 dynes / cm (the membrane may be wettable in 100 percent deionized water and 0 percent methanol).

[0095] A fully crosslinked fluorinated ionomer coating on a microporous membrane support prevents dewetting of the membrane during exposure to gases such as air, provided that the microporous membrane composite is not exposed for a sufficiently long time to dry out. During use in filtration processes, filters may be exposed to air under small pressure differences passing through them, such as during replacement of the liquid being filtered. Furthermore, the microporous membrane composites of the versions of the present disclosure are particularly useful for filtering chemically active aqueous liquids such as acids or bases, which may contain oxidizing agents that generate gases or contain high concentrations of dissolved gases. In these cases, the microporous membrane composites provided are resistant to chemical degradation, do not exhibit excessive flow loss, and are non-dewetting, with both the microporous membrane support and the crosslinked ionomer composition being resistant to chemical degradation.

[0096] This disclosure further illustrates the following non-limiting examples. [Examples]

[0097] Example 1: Porous membrane composites were prepared according to this specification and tested for filtration, wetting, flowability, and other performance and physical properties. Examples are listed in Tables 1-4 below. Specifically, the data from Table 1 shows UV curing performed on various polymer membranes, including thermally stable membranes (PTFE) and heat-sensitive membranes (UPE and PPSU), without the use of radical initiators. This also shows that the crosslinked coating increased the surface hydrophilicity of the membrane, as evidenced by the lower methanol concentration required to wet the membrane surface. The data from Table 2 shows that UV curing also works when a radiation-activated radical initiator such as Irgacure is included. This also shows that the crosslinked coating increased the surface hydrophilicity of the membrane, as evidenced by the lower methanol concentration required to wet the membrane surface. The data from Tables 3 and 4 show that there was no coating loss when relying solely on UV for crosslinking, compared to when a radiation-activated radical initiator such as Irgacure or Na2SO3 was included.

[0098] The membrane isopropanol (IPA) flow times reported herein can be determined by measuring the time it takes for 500 ml of isopropyl alcohol (IPA) fluid to pass through a membrane with a 47 mm membrane disk having an effective surface area of ​​17.35 cm² at a temperature of 14.2 psi and 21 °C.

[0099] The dye-binding capacity was determined as follows: Dye-binding capacity is measured by the amount of functional groups or charge on the film. Methylene blue dye is used to distinguish the negative charge on the surface of the film medium. A dried 25 mm disc film, cut from a modified film sheet, was pre-moistened with isopropyl alcohol, washed with DI water, and placed in a 50 ml vial containing 0.00075 wt% methylene blue dye (Sigma) in DI water. The film disc was immersed at room temperature for 2 hours with continuous mixing. The film disc was then removed, and the absorbance of the dye solution was measured using a Cary spectrophotometer (Agilent Technologies) operating at 606 nm and compared to the absorbance of the starting solution (before film immersion). The dye is inherently cationic and binds to negatively charged films to produce films with the dye-binding capacity shown in Tables 1-4. In comparison, unmodified films typically exhibit a dye-binding capacity of less than 0.3 ug / cm2. Using the slope of the calibration curve shown in Figure 4, the absorption data of the dye solution before and after immersion of the film is converted to weight percentage of the dye, and then to the mass of dye bound per unit area of ​​the film. Figure 4 shows the calibration curves for four methylene blue dye solutions of known concentrations, determined using a Cary spectrophotometer operating at a wavelength of 660 nm (y=1760.7x).

[0100] As shown in Table 3, stability (coating loss percentage) was measured as follows: a 47 mm diameter sample of modified / coated microporous film was mounted in a stainless steel film holder, with a disk area of ​​approximately 17.4 cm². 2A mixture of hot isopropyl alcohol at a temperature of approximately 75°C to approximately 80°C, containing a fluorosurfactant, FC 4432 from 3M™ Novec™, at a concentration of 2500 parts per million, was recirculated through the modified microporous membrane samples. The surfactant-containing mixture was recirculated at a flow rate of at least 80 ml / min, and depending on the pore size, this flow could range from approximately 80 ml / min to approximately 120 ml / min over 5 hours from a volume of approximately 250 ml in the IPA / Fluorosurfactant bath. Some bath volume loss occurred due to evaporation, approximately 12% over 5 hours. After circulating the hot IPA / fluorosurfactant, the coated microporous membrane samples were washed with IPA and dried. Dye binding ability was measured on samples exposed to hot IPA FS for 5 hours, and the data were compared to the modified / coated controls.

[0101] The surface energy of a microporous membrane complex can be characterized using the "wetting degree" test. The composition of the liquid used to wet the surface of the microporous membrane complex is related to the surface energy (dynes / cm) of the microporous membrane complex. To perform the test, liquid solutions of various weight percent of methanol and water are prepared. Drops of the liquid solution are applied to a sample of a modified / coated microporous membrane complex. If the film on the test sample changes from opaque to translucent within 5 seconds, indicating that the film has been wetted with MeOH / aqueous solution, the complex is considered wettable with the solution. If wetting of the microporous membrane complex sample did not occur, a solution containing more MeOH was used. If wetting occurred, a solution containing less MeOH was used. Sample microporous membrane complexes were evaluated using various solutions containing methanol and water; the weight percent of methanol in the solution that wetted the sample was reported.

[0102] Porosity measurement bubble point ("HFE average BP")

[0103] The bubble point test (HFE average BP in the table below) measures the pressure required to push air through the moist pores of a porous membrane. The bubble point test is a well-known method for determining the pore size of a membrane.

[0104] This embodiment describes a porosity measurement bubble point test method used to measure the pressure required to push air through the wet pores of a membrane.

[0105] The test was performed by mounting a 47 mm disc of dry film sample in a holder. The holder is designed to allow the operator to place a small amount of liquid upstream of the film. The dry air flow velocity of the film is first measured by increasing the air pressure upstream of the film to 160 psi. Then, the pressure is released back to atmospheric pressure, and a small amount of ethoxy-nonafluorobutane (available as HFE 7200, 3M Specialty Materials, St. Paul, Minn, USA) is placed upstream of the film to wet it. The humid air flux is then measured by increasing the pressure again to 160 psi. The bubble point of the film is measured from the pressure required to move the HFE out of the pores of the HFE-wet film. This critical pressure point is defined as the pressure at which the first nonlinear increase in the humid air flow is detected by the flowmeter.

[0106] The HFE mean BP of the films described herein containing a cross-linked fluorinated ionomer coating is approximately equal to the HFE mean BP of the starting (uncoated) film, differing from, for example, the starting film by 1 or 2 psi or less. Examples of the range of HFE mean bubble points for films produced by the processes described herein are less than 100 psi, e.g., 25 psi to about 90 psi, as shown in Table 1. TIFF0007853452000004.tif66170TIFF0007853452000005.tif81170TIFF0007853452000006.tif49170TIFF0007853452000007.tif59170

[0107] Example 2: Referring to Figure 3, nuclear magnetic resonance data obtained from three different crosslinked fluorinated ionomers prepared from different liquid coating compositions are shown.

[0108] In Figure 3, the top line labeled "Luperox 101" (di-tert-butyl perbenzoate) is the baseline for the Luperox 101 thermally activated free radical initiator. The middle line, "Disclosure," represents data obtained from crosslinked fluorinated ionomers prepared from the liquid coating compositions disclosed herein, which contain no Luperox 101 or other thermally activated free radical initiators and are crosslinked by exposing the liquid coating composition to ultraviolet light to initiate the crosslinking reaction. The bottom line, labeled "Comparative Example," represents data obtained from crosslinked fluorinated ionomers prepared from liquid coating compositions containing Luperox 101 according to Example 6 of U.S. Patent No. 9,359,480, which is incorporated herein by reference in its entirety, and which are crosslinked by exposing the liquid coating composition to high temperature to initiate the crosslinking reaction.

[0109] Two different examples, “This Disclosure” and “Comparative Example,” were prepared as follows: The surface-modified PTFE film using the above liquid composition was immersed in acetone at 25 degrees Celsius for 4 days (approximately 5% by weight); and The extracted acetone was evaporated, the residue was redissolved in acetone (D6), and the sample was tested by NMR.

[0110] The data from the samples are shown in Figure 3. In general, Figure 3 shows that if molecules are present in the crosslinked fluorinated ionomer coating, free radical molecules such as Luperox 101 can be detected by using NMR analysis. The top line shows peaks a and b characteristic of the Luperox 101 free radical initiator molecule. The second line shows that the two peaks indicating the Luperox 101 molecule in a and b are present in the "Comparative Example" sample. The third line shows that the two peaks characteristic of the Luperox 101 molecule in a and b are absent in the "Present Disclosure" sample. This data shows that NMR analysis can be used to determine whether thermally activated radical initiators such as Luperox 101 are present in the crosslinked fluorinated ionomer coating.

[0111] Pattern:

[0112] In the first embodiment, the microporous membrane composite comprises a microporous membrane support; and a hydrophilic crosslinked fluorinated ionomer coating on the surface of the microporous membrane support, wherein the crosslinked fluorinated ionomer comprises a fluorinated polymer backbone and hydrophilic groups bonded to the fluorinated backbone, the hydrophilic groups comprising groups selected from -SO3H, -COOH, and PO3H, and the crosslinked coating does not contain a thermally activated radical initiator.

[0113] In the second embodiment according to the first embodiment, the crosslinked coating contains a UV-activated radical initiator.

[0114] In a third embodiment according to any of the aforementioned embodiments, the microporous membrane support comprises a polymer selected from ultra-high molecular weight polyethylene, polyvinylidene fluoride, and polyphenylsulfone.

[0115] In a fourth embodiment according to any of the aforementioned embodiments, the hydrophilic groups are present on the crosslinked fluorinated ionomer in an equivalent weight in the range of 380 to 620 grams per hydrophilic group equivalent.

[0116] A fifth embodiment according to any of the aforementioned embodiments, having a dye-binding capacity of at least 5 micrograms / cm².

[0117] A sixth embodiment according to any of the aforementioned embodiments, having a wettability of less than 92 weight percent of CH3 (of the CH3 / H2O mixture).

[0118] At room temperature: 14.2 psi / 500 ml / 17.35 cm 2 A seventh embodiment according to any of the aforementioned embodiments, having an isopropyl alcohol flow time of less than 4092 seconds.

[0119] An eighth embodiment, in any of the aforementioned embodiments, having a flow loss of 80 percent or less compared to an uncoated microporous membrane support, as measured using 500 milliliters of isopropyl alcohol at a pressure of 14.2 psi.

[0120] A ninth embodiment according to any of the aforementioned embodiments, having a surface energy of at least 25 dynes / cm.

[0121] In a tenth embodiment according to any of the aforementioned embodiments, the microporous membrane comprises a polymer selected from the group consisting of fluoropolymers, polysulfones, nylons, polyacrylonitriles, polyethylenes, ultra-high molecular weight polyethylenes, polyvinylidene fluoride, and polyphenylsulfones.

[0122] In the eleventh embodiment, the filter includes a microporous membrane composite of any of the aforementioned embodiments.

[0123] In a twelfth aspect, a method for preparing a microporous membrane composite comprising a microporous membrane support and a crosslinked fluorinated ionomer coating on the surface of the microporous membrane support comprises: a) coating a microporous membrane with a liquid coating composition comprising a fluorinating solvent and a fluorinated ionomer dissolved or dispersed therein, wherein the fluorinated ionomer is derived from copolymerizing reactive units comprising i) a fluorinated monomer containing a fluorinated group and an ethylenically unsaturated group; ii) a fluorinated monomer containing a functional group convertible to an ethylenically unsaturated and hydrophilic group; iii) a fluorinated bisolefin monomer; and iv) a fluorinated bromoalkyl or iodoalkyl chain transfer agent; and b) exposing the coated fluorinated ionomer to electromagnetic radiation to react the reactive units and form a crosslinked fluorinated ionomer.

[0124] In the 13th aspect according to the 12th aspect, the fluorinated ionomer further comprises one or more iodine and bromine atoms at terminal positions, and at least 90% by weight of the fluorinated ionomer has a particle size of less than 200 nanometers, and the fluorinated ionomer comprises i) a fluorinated monomer containing a fluorinated group and an ethylenically unsaturated group; ii) a fluorinated monomer containing a functional group convertible to an ethylenically unsaturated and hydrophilic group; and iii) a bisolefin monomer selected from formulas (OF-1), (OF-2), and (OF-3) (wherein (OF-1) is). TIFF0007853452000008.tif22170 (wherein j is an integer from 2 to 10, preferably from 4 to 8, and R1, R2, R3, R4 are equal to or different from each other and are H, F, or C1-C5 alkyl or (per)fluoroalkyl groups); (OF-2) is a formula TIFF0007853452000009.tif20170 (wherein each A is independently selected from F, Cl, and H; each B is independently selected from F, Cl, H, and ORB, where RB is a branched or linear alkyl radical that can be partially, substantially, or completely fluorinated or chlorinated; E is a divalent group having 2 to 10 carbon atoms, which may be fluorinated and may contain an ether bond); (OF-3) is of the formula: TIFF0007853452000010.tif21170 (wherein E, A and B have the same meanings as defined above; R5, R6 and R7 are each independently H, F or C1-5 alkyl or (per)fluoroalkyl); and iv) Formula R f (I) x (Br) y Fluorinated chain transfer agent (wherein R f It is derived from copolymerizing reactive units (where x and y are integers from 0 to 2, and 1 ≤ x + y ≤ 2) that are fluoroalkyl or (per)fluoroalkyl or (per)fluorochloroalkyl groups having 1 to 10 carbon atoms.

[0125] In a 14th embodiment according to the 12th or 13th embodiment, the microporous membrane comprises a polymer selected from the group consisting of fluoropolymers, polysulfones, nylons, polyacrylonitriles, polyethylenes, ultra-high molecular weight polyethylenes, polyvinylidene fluoride, and polyphenylsulfones.

[0126] In the 15th embodiment according to any of the 12th to 14th embodiments, the fluorinated monomer containing a fluorinated group and an ethylenically unsaturated group includes tetrafluoroethylene.

[0127] In the 16th embodiment according to any of the 12th to 15th embodiments, the functional group convertible to a hydrophilic group is selected from the group consisting of -SO2F, -COOR, -COF, and combinations thereof, where R is a C1-C20 alkyl radical or a C6-C20 aryl radical.

[0128] A 17th aspect according to any of the 12th to 16th aspects further comprises continuously applying a liquid coating composition to a moving microporous membrane support, and continuously curing the liquid coating composition applied to the microporous membrane support by passing the moving microporous membrane support and the applied liquid coating composition through electromagnetic radiation.

[0129] In the 18th embodiment according to any of the 12th to 17th embodiments, the liquid coating composition does not contain a thermally activated radical initiator.

[0130] In the 19th embodiment according to any of the 12th to 18th embodiments, the liquid coating composition does not contain a radical initiator.

[0131] In the 20th embodiment according to any of the 12th to 19th embodiments, the liquid coating composition contains a radiation-activated radical initiator.

[0132] A 21st embodiment according to any of the 12th to 20th embodiments further includes exposing the coated fluorinated ionomer to electromagnetic radiation to react reactive units and form a crosslinked fluorinated ionomer, and then bringing the film into contact with a solvent to remove unreacted reactive units from the crosslinked fluorinated ionomer.

[0133] A 22nd embodiment according to any of the 12th to 21st embodiments further comprises converting the -SO2F, -COOR, or -COF group of a crosslinked fluorinated ionomer into a hydrophilic group by sequentially contacting it with a base, and then with an acid.

[0134] The 23rd embodiment is a microporous membrane composite prepared according to any of the 12th to 22nd embodiments.

Claims

1. It is a microporous membrane complex, With a microporous membrane support; The microporous membrane support includes a hydrophilic crosslinked fluorinated ionomer coating on its surface, wherein the crosslinked fluorinated ionomer is Fluorinated polymer skeleton, and It contains a hydrophilic group bonded to a fluorinated skeleton, and the hydrophilic group is -SO ３ H, -COOH, and PO ３ Includes a group selected from H, The cross-linked coating does not contain a thermally activated radical initiator. Crosslinked fluorinated ionomers i) Fluorinated monomers containing a fluorinating group and ethylenically unsaturated compounds; ii) Fluorinated monomers containing functional groups that can be converted to ethylenically unsaturated and hydrophilic groups; iii) Fluorinated bisolefin monomers, and iv) Fluorinated bromoalkyl or iodoalkyl chain transfer agents This is derived from copolymerizing reactive units that include Microporous membrane composite.

2. The microporous membrane composite according to claim 1, wherein the crosslinked coating contains a UV-activated radical initiator.

3. The microporous membrane composite according to claim 1, wherein the microporous membrane support comprises a polymer selected from ultra-high molecular weight polyethylene, polyvinylidene fluoride, and polyphenylsulfone.

4. The microporous membrane composite according to claim 1, wherein hydrophilic groups are present on the crosslinked fluorinated ionomer in an equivalent weight range of 380 to 620 grams per equivalent amount of hydrophilic groups.

5. At least 5 micrograms / cm³ ２ A microporous membrane complex according to claim 1, having the ability to bind dyes.

6. Less than 92% by weight of CH ３ (CH ３ / H ２ A microporous membrane composite according to claim 1, having a degree of wetness of the mixture.

7. 14.2 psi / 500 ml / 17.35 cm at room temperature ２ The microporous membrane composite according to claim 1, having an isopropyl alcohol flow time of less than 4092 seconds.

8. The microporous membrane composite according to claim 1, having a flow loss of 80 percent or less compared to an uncoated microporous membrane support when measured using 500 ml of isopropyl alcohol at a pressure of 14.2 psi.

9. The microporous membrane composite according to claim 1, having a surface energy of at least 25 dynes / cm.

10. The microporous membrane composite according to claim 1, wherein the microporous membrane support comprises a polymer selected from the group consisting of fluoropolymers, polysulfones, nylons, polyacrylonitriles, polyethylenes, ultra-high molecular weight polyethylenes, polyvinylidene fluoride, and polyphenylsulfones.

11. A filter comprising a microporous membrane composite according to any one of claims 1 to 10.

12. A method for preparing a microporous membrane composite comprising a microporous membrane support and a crosslinked fluorinated ionomer coating on the surface of the microporous membrane support, a) Coating a microporous membrane support with a liquid coating composition comprising a fluorinated solvent and a fluorinated ionomer dissolved or dispersed therein, wherein the fluorinated ionomer is i) Fluorinated monomers containing a fluorinating group and ethylenically unsaturated compounds; ii) Fluorinated monomers containing functional groups that can be converted to ethylenically unsaturated and hydrophilic groups; iii) Fluorinated bisolefin monomers, and iv) Fluorinated bromoalkyl or iodoalkyl chain transfer agents Coating is derived from copolymerizing reactive units containing; b) Exposing the coated fluorinated ionomer to electromagnetic radiation to react the reactive units and form a crosslinked fluorinated ionomer. Methods that include...

13. The fluorinated ionomer further contains one or more iodine and bromine atoms at its terminal positions. At least 90% by weight of the fluorinated ionomer has a particle size of less than 200 nanometers. Fluorinated ionomers, i) Fluorinated monomers containing a fluorinating group and ethylenically unsaturated compounds; ii) Fluorinated monomers containing functional groups that can be converted to ethylenically unsaturated and hydrophilic groups; iii) Bisolefin monomers selected from formulas (OF-1), (OF-2), and (OF-3) [wherein (OF-1) is formula: (wherein j is an integer from 2 to 10, and R1, R2, R3, R4 are equal to or different from each other and are H, F, or C1-C5 alkyl or (per)fluoroalkyl groups); (OF-2) is given by the formula: (wherein each A is independently selected from F, Cl, and H; each B is independently selected from F, Cl, H, and ORB, where RB is a branched or linear alkyl radical that can be partially, substantially, or completely fluorinated or chlorinated; E is a divalent group having 2 to 10 carbon atoms, which may be fluorinated and may contain an ether bond); (OF-3) is given by the formula: (wherein E, A, and B have the same meanings as defined above; R5, R6, and R7 each independently have H, F, or C1-5 alkyl or (per)fluoroalkyl group)); and iv) a fluorinated chain transfer agent of formula R ｆ (I) ｘ (Br) ｙ [wherein, R ｆ is a fluoroalkyl or (per)fluoroalkyl or (per)fluorochloroalkyl group having 1 to 10 carbon atoms, x and y are integers of 0 to 2, and 1 ≦ x + y ≦ 2] The method according to claim 12, derived from copolymerizing reactive units containing the reactive units.

14. The method according to claim 12, wherein the microporous membrane support comprises a polymer selected from the group consisting of fluoropolymers, polysulfones, nylons, polyacrylonitriles, polyethylenes, ultra-high molecular weight polyethylenes, polyvinylidene fluoride, and polyphenylsulfones.

15. The method according to claim 12, wherein the fluorinated monomer containing a fluorinated group and ethylenically unsaturated material includes tetrafluoroethylene.

16. Functional groups that can be converted to hydrophilic groups are -SO ２ The method according to claim 12, wherein R is selected from the group consisting of F, -COOR, -COF, and combinations thereof, and in the formula R is a C1-C20 alkyl radical or a C6-C20 aryl radical.

17. The liquid coating composition is continuously applied to a moving microporous film support, The liquid coating composition applied to a microporous membrane support is continuously cured by passing the moving microporous membrane support and the applied liquid coating composition through electromagnetic radiation. The method according to claim 12, further comprising:

18. The method according to claim 12, wherein the liquid coating composition does not contain a thermally activated radical initiator.

19. The method according to claim 12, wherein the liquid coating composition does not contain a radical initiator.

20. The method according to claim 12, wherein the liquid coating composition contains a radiation-activated radical initiator.

21. The method according to claim 12, further comprising exposing a coated fluorinated ionomer to electromagnetic radiation to react reactive units and form a crosslinked fluorinated ionomer, and then contacting the film with a solvent to remove unreacted reactive units from the crosslinked fluorinated ionomer.

22. By sequentially contacting the cross-linked fluorinated ionomer with a base and then an acid, -SO ２ The method according to claim 12, further comprising converting an F, -COOR, or -COF group into a hydrophilic group.

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