Porous membrane composite containing a 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] The present disclosure is in the field of filters and filter membrane composites containing a crosslinked fluorinated ionomer on the surface of a microporous membrane support, and related methods.

Background Art

[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 manufacture of microelectronic circuits, filters made from polymer porous membranes can be used to purify various chemically active liquid or gaseous fluids to remove particulate contamination from the fluids. Useful polymer membranes are chemically resistant to the fluids passing through the membranes.

[0004] Hydrophobic porous filter membranes generally do not wet easily with water. When filtering a liquid that "outgases" (produces gas) during the filtration operation, a certain amount of gas can be released from the liquid in the filter device at the surface of the filter membrane. Hydrophobic membranes have a greater affinity for gases than for liquids. The gas emerging from the liquid can accumulate and form gas pockets that adhere to the hydrophobic porous membrane surface and pores. As these gas pockets increase in size due to continuous liquid-gas evolution, the gas pockets begin to displace the liquid from the pores of the hydrophobic porous membrane, continuously reducing the effective filtration area of the hydrophobic porous membrane. This phenomenon is commonly referred to as the dewetting of the hydrophobic porous membrane, where the fluid-wetted (fluid-filled) portion of the hydrophobic porous membrane is gradually overtaken by the fluid-non-wetted or gas-filled portion. When membrane dewetting 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. Special operating procedures are required to wet a hydrophobic membrane with water or an aqueous fluid. The membrane may first be wetted using a low surface tension organic solvent such as isopropyl alcohol, followed by contacting the membrane with a mixture of water and the organic solvent, and then contacting the membrane with water or an aqueous fluid. This process can generate large amounts of solvent waste and consume large amounts 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 complete penetration of water into a significant portion of the membrane pores.

[0006] In contrast to hydrophobic porous membranes, hydrophilic porous membranes naturally wet upon contact with an aqueous liquid, so no special pre-use treatment of the membrane is required to wet it. Advantageously, hydrophilic membranes can be used to treat aqueous liquids without pre-treatment with an organic solvent or pressure intrusion. SUMMARY OF THE INVENTION

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

[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, the coating comprising 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] The crosslinked fluorinated ionomer may be formed on a microporous membrane support from a coating composition containing various monomers, oligomers, prepolymers, etc. that are reactive to form the fluorinated ionomer, and may contain a fluorinated ionomer precursor derived from the monomer. Monomers ( "monomer units") that can be reacted to produce the fluorinated ionomer include: i) one or more fluorinated monomers having a fluorinated group and a reactive ethylene (unsaturated) group; ii) a fluorinated monomer containing a reactive ethylene (unsaturated) group and a functional group convertible to a hydrophilic group; iii) a bis-olefin crosslinking agent; and iv) a fluorinated monomer 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 a radical initiator is not required.

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

[0011] The exemplary process can be carried out at a non-high temperature, such as room temperature, without the need for the high crosslinking temperatures and the presence of radical initiators required for thermally induced crosslinking systems. Since the temperature requirements of the process are lower 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 the operation 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 containing 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

Figure 2

Figure 3

Figure 4

[0016] All of the figures are not to scale.

[0017] The following description relates to a microporous membrane composite comprising a microporous membrane support and a coating on the surface of the microporous membrane support, the coating comprising 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 may contain a fluorinated ionomer that can be further crosslinked by exposure 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 wet it with a solution containing only methanol and water.

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

[0020] The process includes applying a coating composition to the surface of a microporous membrane support and crosslinking (e.g., further crosslinking) the fluorinated ionomer by exposing the fluorinated ionomer to electromagnetic radiation, and optionally and preferably exposing the fluorinated ionomer to elevated temperature to cause crosslinking of the fluorinated ionomer (the "crosslinking temperature") is not necessary. Past methods of disposing crosslinked fluorinated ionomers on microporous membrane supports have involved crosslinking the fluorinated ionomer by exposing the ionomer to a high crosslinking temperature, which can be at least 100, 120, or 150 degrees Celsius or more, in the presence of a thermally activated radical initiator. In contrast, the systems and methods herein 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 on the surface of the support) by exposing it to electromagnetic radiation, such as ultraviolet light, without the need for a high crosslinking temperature.

[0021] Compared to methods of preparing chemically similar microporous membrane composites by exposing a fluorinated ionomer to a high crosslinking temperature (e.g., a temperature exceeding 100 degrees Celsius) to crosslink the ionomer, the method of the present specification crosslinks the fluorinated ionomer by exposing the ionomer to electromagnetic radiation. The use of electromagnetic radiation to cause crosslinking does not require an increase in crosslinking temperature, which can enable useful differences in methods of preparing microporous membrane composites and methods of forming filter products containing the microporous membrane composites.

[0022] The radiation-induced crosslinking mechanism can avoid the need to expose the coated membrane support to a high crosslinking temperature. Radiation-initiated crosslinking can be carried out at a temperature below 170, 150, 120, or 100 degrees Celsius. The use of a high crosslinking temperature to cause crosslinking of the fluorinated ionomer coated on the surface of the microporous membrane support requires a microporous membrane support that is stable (does not degrade or melt) when exposed to the high crosslinking temperature. The need for stability of the membrane support at high crosslinking temperatures limits the options available for the microporous membrane support and precludes the use of microporous membrane supports that are not thermally stable at high crosslinking temperatures, even if the support would otherwise be useful.

[0023] By using the radiation-induced crosslinking mechanism, the need for a high crosslinking temperature is eliminated, and a microporous membrane composite can be prepared using a microporous membrane support that is not necessarily stable at a high crosslinking temperature, such as a temperature of 100, 120, 150, or 170 degrees Celsius or higher. Useful microporous membrane supports for processes using the radiation-induced crosslinking mechanism, which may not be useful for processes by a heat-induced crosslinking mechanism, include polyolefins such as polyethylene (PE) and ultra-high molecular weight polyethylene (UHPE), polyvinylidene fluoride (PVDF), and polyphenylsulfone (PPSU).

[0024] As another useful feature of the described system or process, the described process that uses radiation to cause crosslinking of a fluorinated ionomer coated on a microporous membrane support can include a continuous process step that includes a continuous step of applying a coating composition onto the microporous membrane support and a continuous step of causing crosslinking of the fluorinated monomers in the applied coating composition by continuously exposing the support having the applied coating composition to electromagnetic radiation. The described process can include continuously applying a coating composition onto the surface of a moving sheet of the 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 made using a thermally induced crosslinking technique performs a crosslinking step after the membrane composite is converted and assembled into a filter component, such as a filter cartridge, by heating the filter cartridge.

[0025] The crosslinked fluorinated ionomer can be formed on a microporous membrane support by applying a coating composition containing a fluorinated ionomer component onto the surface of the support. The coating composition contains a fluorinated ionomer component that includes monomers and may include molecules (derived from) previously reacted monomers, such as oligomers or prepolymers derived from the monomers, sometimes referred to as fluorinated ionomer “precursors”. The fluorinated ionomer precursor can be a pre-reacted molecule formed from monomers that are partially crosslinked after the coating composition is applied to the surface of the support, not fully crosslinked, and can be further crosslinked (i.e., “fully crosslinkable”) when exposed to electromagnetic radiation. After applying the coating composition to the membrane 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 scope of the technical fields of chemistry and chemical coatings. Fluorinated compounds include organic chemical compounds, polymers, ionomers, chain transfer agents, crosslinking agents, solvents, etc. that have at least one carbon-bonded hydrogen atom replaced by a carbon-bonded fluorine atom. Fluorinated compounds include perfluorinated compounds. A perfluorinated compound or perfluorocarbon compound is a chemical compound that includes polymers, ionomers, crosslinking groups, chain transfer agents, etc. in which all or essentially all carbon-bonded hydrogen atoms have been replaced by carbon-bonded fluorine atoms. Some residual hydrogen atoms may be present in the perfluorinated composition, for example, less than 2 weight percent of the perfluorinated product, and in some cases less than 0.5 weight percent or less than 0.25 weight percent of the perfluorinated product.

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

[0028] Stated another way, the chemical components of the coating composition include various combinations of the monomers described herein, and any chemical derivatives thereof, which may be completely unreacted (in monomer form), or may form a partially reacted, pre-reacted, i.e., partially polymerized or partially cross-linked fluorinated ionomer “precursor”. Components including monomers (including crosslinking agents) and ionomer precursors may be further reacted (i.e., crosslinked) by exposing the components to electromagnetic radiation to form a “fully polymerized” fluorinated ionomer, which refers to a fluorinated ionomer after crosslinking 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 is applied as part of the coating composition to a microporous membrane support and then crosslinked by exposure to electromagnetic radiation.

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

[0030] The fluorinated monomer (i) having a fluorinated group and an ethylene (unsaturated) group may be a fluorinated or perfluorinated monomer, and examples include the following fluorinated unsaturated monomers: 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 is a C1-C6 (per)fluoroalkyl such as trifluoromethyl, bromodifluoromethyl, pentafluoropropyl); CF2=CFOX perfluoro-oxyalkyl vinyl ether (wherein X is a C1-C 12 perfluoro-oxyalkyl such as perfluoro-2-propoxy-propyl).

[0031] Useful fluorinated monomers (ii) containing an ethylene group and a functional group convertible to a hydrophilic group include -SO2F, -COOR, -COF, and combinations thereof, wherein 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 weight fraction of the fluorinated monomer (ii) as part of the fluorinated ionomer may be fully crosslinked or partially crosslinked, and may be in the range of 380 grams per equivalent (g / eq) to 620 g / eq, for example, in the range of 500-600 g / eq or 550-590 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: TIFF2025522687000002.tif28170wherein j is an integer from 2 to 10, preferably from 4 to 8; R1, R2, R3, and R4 are H, F, or a C1-C5 alkyl or (per)fluoroalkyl group, and may be the same or different from each other. The compound of formula OF-2 is represented as follows: TIFF2025522687000003.tif27170wherein each A is independently selected from F, Cl, and H; each B is independently selected from F, Cl, H, and ORB, and RB is a branched or linear alkyl group that can be partially, substantially, or fully fluorinated or chlorinated; E is a divalent group having 2 to 10 carbon atoms that may be fluorinated and may contain an ether bond. The compound of formula OF-3 is represented as follows: TIFF2025522687000004.tif28170wherein E, A, and B have the same meanings as defined above; each of R5, R6, and R7 is independently H, F, or a C1-5 alkyl or (per)fluoroalkyl group.

[0034] An 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 in the range of 0.1 to 5 weight percent per total weight of the fluorinated ionomer components (including all monomers, precursors, etc.).

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

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

[0037] Optionally rather than necessarily, the coating composition may further include 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 generate free radicals in a chemical system and initiate reactions between the reactants of this system, for example, to cause crosslinking or polymerization of reactive monomers, oligomers, prepolymers, crosslinking agents, etc. Various types of free radical initiators (or "radical initiators") are known, and these can generate one or more chemical free radicals by 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] There are different thermally activated free radical initiators known to be useful for causing reactions between chemical components used to form crosslinked fluorinated ionomers. For example, U.S. Patent No. 9,359,480 describes dialkyl peroxide initiators that are activated when heated to a curing temperature in the range of 100 to 300 degrees Celsius to generate radicals. Examples of specific dialkyl peroxide initiators are identified as di-tert-butyl-peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, dicumyl peroxide, dibenzoyl peroxide, di-tert-butyl perbenzoate, di-1,3-dimethyl-3-(tert-butylperoxy)butyl carbonate. According to the present specification, a liquid coating composition need not contain a thermally activated free radical initiator, such as any of the general or specific initiators identified in Patent No. 9,359,480. Instead, useful or preferred liquid coating compositions and derivative crosslinked fluorinated ionomers and coatings may specifically exclude these and other thermally activated free radical initiators, for example, they may contain less than 0.001, 0.0005, or 0.0001 weight percent of these or any other thermally activated free radical initiator and still be acceptable.

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

[0041] Optionally but not necessarily, the described liquid coating compositions may contain a radiation-activated free radical initiator. Examples include compounds of a classification called "type I" photoinitiators, and specific types of radiation-sensitive salts, such as sulfites, for example sodium sulfite (Na2SO3) that generates free radicals in the presence of ultraviolet energy.

[0042] Useful radiation-sensitive initiator compounds include type I free radical initiators and equivalent compounds that are unimolecular free radical generators that decompose in the presence of radiation such as ultraviolet light in the range of 300 to 400 nanometers to form two chemical free radicals. Examples of type I free radical initiators include hydroxyacetophenone (HAP) initiators and phosphine oxide (TPO) initiators. Examples of commercially available type I UV initiators include those 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 essential. In a coating composition containing a radiation-activated free radical initiator, the amount of the radiation-activated free radical initiator in the coating composition can be a useful amount, such as in the range of 0.01 to 10 weight percent, for example 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 or 0.005 or 0.001 weight percent of any type of radical initiator, whether thermally activated or radiation-activated.

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

[0045] Examples of fluorinated solvents include, for example, perfluoropolyethers or mixtures of two or more perfluoropolyethers, for example, those comprising, consisting essentially of, or consisting of them. Perfluoropolyethers have the general formula F3C-O-(CF2CF(CF3)-O) n -(CF2-O) m -CF3 (wherein m and n are integers, n is greater than 0, and m is 0 or more). 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 comprising, consisting essentially of, or consisting of them. Exemplary hydrogenated fluoropolyethers (HFPE) can have the general formula R*-O-R f ’-R*’ wherein 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 of 1 or more and 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 (wherein 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 more, b is 0 or more, c is 0 or more, 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, each occurrence of X is independently selected from -F and -CF3; b, c', and t are integers up to 10, c' is greater than 0, b is 0 or more, and t is an integer of 0 or more; 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 -(wherein, each occurrence of X is independently selected from -F and -CF3; c' and t are integers up to 10, c' is greater than 0, t is 0 or more, 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 are methoxynonafluorobutane compounds, such as (CF3)2CFCF2 - O - CH3 or CF3CF2CF2CF2 - O - CH3, and in some cases are at least 99 weight percent pure.

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

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

[0050] Relatively small ionomer particles tend to remain within the pores and are particles that block the flow of fluid through the pores of the microporous membrane support. When the coating composition is applied to the support, after the crosslinked fluorinated ionomer is formed on the support to form a membrane composite, the appearance of particles that may reduce the flow rate of fluid through the porous membrane support (i.e., cause "flow rate loss") is reduced.

[0051] According to some examples, useful coating compositions contain fluorinated ionomers in the form of suspended particles, and at least 90 weight percent of the fluorinated ionomer particles have a particle size of less than 200 nanometers (nm). For example, at least 90 weight percent 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 the fluorinated ionomer component in the coating composition can be an amount effective to produce a non-dewetting microporous membrane composite when applied to the microporous membrane support and then crosslinked and activated, for example, as measured by an autoclave test. Further, this amount can be effective to produce a microporous membrane composite that can be completely wetted with a solution containing methanol and water, or in some examples, water alone.

[0053] In an exemplary coating composition, the amount of the fluorinated ionomer component (including all non-solvent and solid components such as 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 total weight of the coating composition (e.g., the solid and solvent of the ionomer component). Coating compositions that do not contain a sufficiently high concentration of the fluorinated ionomer component can have uncoated hydrophobic regions and produce incompletely coated microporous membrane supports that are not fully wetted with a solution containing methanol and water. Coating compositions that contain too high a concentration of the fluorinated ionomer component can produce microporous membrane composites in which the amount of fluid flow through the membrane during use is reduced.

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

[0055] Examples of useful microporous membrane supports that can be considered microporous, ultraporous, or nanoporous can have an average pore size that can be 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 can 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) copolymer, copolymer of tetrafluoroethylene and perfluoropropyl vinyl ether (PFA, also called perfluoroalkoxy polymer), copolymer of tetrafluoroethylene and perfluoromethyl vinyl ether (MFA), and polymer compositions containing any of these. The microporous membrane support can be formed, for example, from polytetrafluoroethylene, fluorinated ethylene-propylene copolymer or perfluoroalkoxy polymer, and can include the group of fluoropolymers generally known as fluorocarbons sold by E.I.Dupont 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 can include, but are not limited to, those available from Daikin, such as Neoflon®-PFA and Neoflon®-FEP, or various grades of Hyflon®-PFA and Hyflon®-MFA available from Solvay Solexis. Fluoropolymers have excellent chemical resistance and heat resistance and are generally hydrophobic. Other useful thermoplastic fluoropolymers that can be used can include, inter alia, 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), and may be combined with one or more other non-fluorinated monomers.

[0059] The fluoropolymer membrane support is useful for the treatment of the membrane composite at high temperatures including thermally induced crosslinking, but the exemplary methods herein enable a treatment including crosslinking without exposing 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 of the membrane support is not required. Thus, 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 polyolefins such as polyethylene and ultra-high molecular weight polyethylene (UHPE), polyvinylidene fluoride (PVDF), and polyphenylsulfone (PPSU).

[0060] According to a useful method, the microporous membrane composite can be prepared by a process including continuously applying a coating composition to the surface of a moving microporous membrane support to form what is referred to as a "coated microporous membrane support" or "coated support". The coated support can then be exposed to electromagnetic radiation to continuously cause crosslinking of the fluorinated ionomer of the coating composition. The coated support can be subsequently processed after crosslinking to convert the coated support into a filter membrane of a filter product. One or more of the subsequent processing steps may optionally and preferably be performed continuously.

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

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

[0063] In useful and preferred examples, the fully crosslinked fluorinated ionomer of the microporous membrane composite may contain a radiation-activated 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, the fully crosslinked fluorinated ionomer of the microporous membrane may exclude the radiation-activated radical initiator, for example, may contain less than 0.01 or 0.005 or 0.001 weight percent of the radiation-activated radical initiator.

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

[0066] The absence, presence, and amount of either a thermal-activated or radiation-activated radical initiator in the fully crosslinked fluorinated ionomer of the coating of the microporous membrane composite can be determined by quantitative chemical analysis methods. 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 FIG. 1. This exemplary method may be carried out on a continuous coating line 100, and a roll (104) of the continuous length of the microporous membrane support 102 is aligned for unrolling to supply a continuous 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 source 120, various subsequent optional processing devices 130, 140, 150 and 160 may be present.

[0068] In 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 while the support 102 continuously moves through the coater 110. The coater 110 may be of any useful type, such as a spray coater, a dip coater, a curtain coater, etc., and may be equipped with mechanical devices such as rollers or squeegee bars to completely impregnate the pores of the support 102 for a 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 continuously move through and be immersed in a fixed volume of coating composition contained in the bath 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 membrane support 102, the resulting support (the "coated support") can be passed through electromagnetic radiation to crosslink (i.e., "fully crosslink") the fluorinated ionomer of the coating composition by exposure to the 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 includes a coating of fully crosslinked fluorinated ionomer.

[0070] Subsequent steps for treating 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. Thereafter, the solvent can be removed from the remaining coating of the coated support, for example, by using a dryer 140 at a high temperature.

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

[0072] The microporous membrane composite described can be used as a component of a filter device that includes various filter structures such as a support, an outer cylindrical housing or "cage", a frame, an inner cylindrical support or "core", as is known in various configurations of filter devices. The microporous membrane composite can be pleated in a layered configuration having one or more support layers or nets, and the cage, support, and two end cap structures can be potted to form a filter cartridge. The cartridge may be of a type that is replaceable within a filter housing or may be firmly attached to the filter housing.

[0073] Referring further to the exemplary system and method of FIG. 1, during 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, a temperature not exceeding 170, 150, 120, or 100 degrees Celsius.

[0074] In an exemplary method of preparing the composite, the coating composition can be applied to the microporous membrane support by contacting the coating composition to be coated with the "fluid contact surface" (including the outer surface and the internal pore surface) of the membrane support. Preferably, the coating composition can be applied to the support such that the coating composition contacts all or substantially all of the surface of the support to uniformly coat all surfaces of the support.

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

[0076] Coating operation 210, which includes a specific step of applying a coating composition to a film support, can be carried out at any useful conditions and temperatures, typically using a coating composition having a temperature in the normal temperature range, for example, less than 40 degrees Celsius or less than 30 or 25 degrees Celsius. During the continuous coating operation, especially after applying the coating composition 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 not desirable. 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, an increase in the temperature of the coating composition and the support may preferably be avoided. Further, 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 crosslinking operation 214, the coated support can be placed between additional radiation - transmissive films for the 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 continuously passed through a chamber irradiated with electromagnetic radiation, such as ultraviolet light, having a wavelength and amount that cause the desired crosslinking of the fluorinated ionomer contained in the coating composition. Crosslinking operation 214 can be carried out at any useful conditions and temperatures. To avoid thermal degradation of the temperature - sensitive support, when used, the interior of the crosslinking chamber ("UV chamber") can be maintained at a temperature that does not allow the support to reach a temperature exceeding 170, 150, or 120 degrees Celsius.

[0078] After the fluorinated ionomer is exposed to radiation so as to be completely crosslinked, subsequent steps are carried out on the coated support to convert the coated support into a filter membrane (composite) comprising a dry coating having a completely crosslinked fluorinated ionomer, and the fluorinated ionomer contains hydrophilic groups that impart to the membrane composite the desired wetting (by methanol and water) and non-dewetting properties.

[0079] As an example of a useful subsequent step, a coated support having a completely crosslinked fluorinated ionomer on its surface can be treated by one or more chemical extraction steps 220 to remove unreacted excess chemical components from the completely crosslinked coating composition present on the support surface. The extraction can be carried out in a single step using a liquid such as water (e.g., deionized water), an organic solvent (e.g., isopropyl alcohol), or a combination thereof, or in a series of two or more steps each of which can use the same or different liquids (e.g., a solvent or water). The extraction step can be carried out at room temperature, e.g., less than 40, 30, or 25 degrees Celsius. The liquid can be brought into contact with the support by spraying, by immersing the support in the liquid, and by any mechanical agitation such as by the use of pressure from, for example, rollers, squeegees, etc. Effectively, most of the excess components of the coating composition can be removed from the surface of the coated support by one or more extraction steps.

[0080] After the extraction step, e.g., 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 the residual solvent, e.g., by passing the coated support through an oven or heating chamber that houses the heating environment. To avoid thermal degradation of the heat-sensitive support, when used, the temperature of the heating environment can be within a range that does not allow the support to reach a temperature at which thermal degradation occurs as the support moves through the heating environment. For example, the environment can be at a temperature not exceeding 170, 150, or 120 degrees Celsius.

[0081] The dried coated membrane can be processed by folding, cutting, pleating, etc. in the conversion and device fabrication step 230. In this step, the coated support contains a fully crosslinked fluorinated ionomer that includes a functional group chemically convertible to a hydrophilic group, e.g., -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 hydrophilic groups as desired. By the conversion operation 230, individual filter membranes may be produced from the coated support, and each individual membrane can be incorporated into a single filter product such as a filter cartridge or a filter housing. The conversion operation may also include assembling the coated support into a filter device such as a filter cartridge or a filter housing.

[0082] By way of example, in method 200, the functional group of the fluorinated ionomer chemically convertible to a hydrophilic group can be converted to a hydrophilic group after the coated support has been first converted to the form of a folded or pleated coated membrane and after the converted (e.g., pleated) coated support has been incorporated into a filter device such as a filter cartridge or a filter housing.

[0083] The first step of chemically converting the 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), water, or both can be passed through the device and, for example, passed through the membrane under ambient conditions.

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

[0085] During all steps of the exemplary method 200, the temperature of the microporous membrane support can be kept below the temperature at which the support can thermally degrade. For example, the temperature of the support can be kept below 170, 150, 120, or 100 degrees Celsius.

[0086] The described membrane composites prepared as presented herein can have properties useful for filter membrane composites of the type considered to be "non-dewetting". The non-dewetting properties of the microporous membrane composite can be determined by heating a sample of the microporous membrane composite wetted by contact with a liquid in an autoclave to a temperature above the boiling point of the liquid. If the sample remains wet and translucent after a specific amount of time in the autoclave treatment at high temperature, the sample can be considered non-dewetting for those autoclave 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 can be considered non-dewetting for those conditions.

[0087] The microporous membrane composite sample for the autoclave test can be prepared by first wetting the sample with a liquid, such as a solution containing methanol and water, and then exchanging the methanol and water solution with water by flushing. The sample exchanged with water can be autoclaved in a sealed container together with water in an oven. If the microporous membrane support is not coated with sufficient crosslinked ionomer, subjecting such an incompletely coated sample to autoclaving in water will cause the incompletely coated sample to dewett and appear opaque after autoclaving. Dewetting resistance is different from the contact angle measurement of the surface energy of the microporous membrane, which is because dewetting resistance refers to the wetting characteristics of the microporous membrane across its thickness and pores, and the liquid contacts not only the outer surface of the microporous membrane but also the filtration surface.

[0088] The different wetting characteristics of the filter membrane composite are the ability of the composite to be wetted (moistened) with a solution of water and methanol. The membrane composite may not be able to be directly wetted with water, but an exemplary microporous membrane composite may be wetted with a solution containing methanol and water, i.e., "wettable".

[0089] The term "wettability" is used to refer to a dry microporous membrane composite that can easily immerse or absorb a solution containing a combination of methanol and water, such as a solution consisting essentially of methanol and water, into substantially all of its coated microporous structure within 5 seconds without using heat, pressure, mechanical energy, surfactant, or other pre-wetting agents.

[0090] The microporous membrane composite herein is such that even when the completely crosslinked fluorinated ionomer coating formed on the surface of the composite has hydrophilic groups and the composite is non-dewetting after autoclaving with water, it is not necessarily directly wettable with water.

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

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

[0093] The described microporous membrane composites that are wettable with these methanol and water-containing solutions can be used for aqueous filtration applications where an aqueous liquid flows through the membrane without the membrane dewetting. An "aqueous liquid" is a liquid that contains some amount of water and includes semiconductor industry known and used aqueous liquids such as SC1 or SC2 cleaning baths; concentrated sulfuric acid with or without an oxidizing agent such as hydrogen peroxide or ozone; other aqueous-based liquids that require filtration such as aqueous solutions of salts (buffered oxide etchants), bases, or acids.

[0094] Considering surface tension, at least approximately, a microporous membrane composite having a surface energy of 25 dynes / cm or more can be wetted with a solution containing 80 weight percent methanol in water; a microporous membrane composite having a surface energy of 40 dynes / cm or more can be wetted with a solution containing 30 weight percent methanol in water; a microporous membrane composite having a surface energy of 50 dynes / cm or more can be wetted with a solution containing 15 weight percent methanol in water. Exemplary microporous membrane composites of the present specification can have a surface energy of at least 25 dynes / centimeter, or at least 27, 30, 32, 35, 37, 40, 45, 50, 55, 60, 65, 70, or 72 dynes / centimeter (the membrane may be wetted 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 of the microporous membrane composite to gases such as air, unless the microporous membrane composite is exposed for a time long enough to dry it. During use in a filtration process, the filter may be exposed to air under a small pressure differential, such as during replacement of the liquid being filtered. Further, versions of the microporous membrane composites of the present disclosure are particularly useful for filtering chemically active aqueous liquids such as acids or bases that can contain oxidizing agents that generate gases or contain high concentrations of dissolved gases. In these instances, both the microporous membrane support and the crosslinked ionomer composition are resistant to chemical degradation, exhibit no excessive flow loss, and provide a microporous membrane composite that is non-dewetting.

[0096] The present disclosure is further illustrated with respect to the following non-limiting examples.

Example

[0097] Example 1: A porous membrane composite was prepared according to the present specification and tested for filtration, wetness, fluidity, and other performance and physical properties. Examples are listed in Tables 1-4 below. Specifically, the data from Table 1 show UV curing for various polymer membranes including thermally stable membranes (PTFE) and heat-sensitive membranes (UPE and PPSU) without using a radical initiator. 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 show that UV curing also functions 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 only on UV for crosslinking, as opposed to including a radiation-activated radical initiator such as Irgacure or Na2SO3.

[0098] The membrane isopropanol (IPA) flow time reported herein can be determined by measuring the time it takes for 500 ml of isopropyl alcohol (IPA) fluid to pass through a membrane equipped 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 test was determined as follows. The dye binding capacity is measured by the amount or charge of functional groups on the membrane. Methylene blue dye is used to distinguish the negative charges on the surface of the membrane medium. A dried 25 mm disk membrane cut from the modified membrane sheet was pre-wetted 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 membrane disk was immersed for 2 hours while continuously mixing at room temperature. The membrane disk 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 membrane immersion). The dye is essentially cationic and binds to the negatively charged membrane to produce a membrane with the dye binding capacity shown in Tables 1 - 4. In comparison, unmodified membranes typically exhibit a dye binding capacity of less than 0.3 μg / cm2. Using the slope of the calibration curve shown in Figure 4, the absorbance data of the dye solution before and after membrane immersion was converted to weight % of the dye, and then this was converted to the mass of dye bound per unit area of the membrane. Figure 4 shows a calibration curve indicating the absorbance of four known concentration methylene blue dye solutions determined using a Cary spectrophotometer operating at a wavelength of 660 nm (y = 1760.7x).

[0100] As shown in Table 3, the stability (coating loss percentage) was measured as follows: A 47 mm diameter sample of the modified / coated microporous membrane was attached to a stainless steel membrane holder, and the disk area was approximately 17.4 cm 2There was a mixture of hot isopropyl alcohol at a temperature of about 75 °C to about 80 °C containing 2500 ppm of a fluorosurfactant, FC 4432 from 3M (trademark) Novec (trademark), which was recirculated through a modified microporous membrane sample. 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 about 80 ml / min to about 120 ml / min over 5 hours from a volume of the IPA / Fluorosurfactant bath of about 250 milliliters. Some loss of bath volume occurred due to evaporation, which was about 12% in 5 hours. After flowing the hot IPA / fluorosurfactant, the coated microporous membrane sample was washed with IPA and dried. The measurement of the dye-binding ability was completed on samples exposed to hot IPA FS for 5 hours, and the data were compared to a modified / coated control.

[0101] The "wettability" test can be used to characterize the surface energy of the microporous membrane composite. The composition of the liquid used to wet the surface of the microporous membrane composite is related to the surface energy (dynes / cm) of the microporous membrane composite. To conduct the test, liquid solutions of various weight percentages of methanol and water are prepared. Droplets of the liquid solution are applied to a sample of the modified / coated microporous membrane composite. If the membrane of the test sample changes from opaque to translucent within 5 seconds, thereby indicating that the membrane is wetted with the MeOH / aqueous solution, the composite is considered wettable with the solution. If no wetting of the microporous membrane composite sample occurred, a solution containing more MeOH was used. If wetting occurred, a solution containing a smaller amount of MeOH was used. The sample microporous membrane composite was evaluated using various solutions containing methanol and water; the weight percentage of methanol in the solution that wet the sample was reported.

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

[0103] In the test method for the porosity measurement bubble point (the "HFE average BP" in the following table), the pressure required to push air through the wet pores of the porous membrane is measured. The bubble point test is a well-known method for determining the pore size of a membrane.

[0104] This example describes the 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 attaching a 47 mm disk of the dry membrane sample to a holder. The holder is designed to allow the operator to place a small amount of liquid on the upstream side of the membrane. The dry air flow rate of the membrane was first measured by increasing the air pressure on the upstream side of the membrane to 160 psi. The pressure was then released back to atmospheric pressure, and a small amount of ethoxy-nonafluorobutane (available as HFE 7200, 3M Specialty Materials, St. Paul, Minn, USA) was placed on the upstream side of the membrane to wet the membrane. The wet air flux was then measured by increasing the pressure back to 160 psi. The bubble point of the membrane is measured from the pressure required to move the HFE out of the pores of the HFE-wet membrane. This critical pressure point is defined as the pressure at which the first non-linear increase in the wet air flow is detected by the flow meter.

[0106] The HFE average BP of the membranes herein containing the coating of the crosslinked fluorinated ionomer is approximately equal to the HFE average BP of the starting (uncoated) membrane, for example, differing from the starting membrane by 1 or 2 psi or less. Examples of the range of the HFE average bubble point of the membranes created by the process described herein are less than 100 psi, for example, 25 psi to about 90 psi, as shown in Table 1. TIFF2025522687000005.tif66170TIFF2025522687000006.tif81170TIFF2025522687000007.tif49170TIFF2025522687000008.tif59170

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

[0108] In FIG. 3, the top line labeled "Luperox 101" (di-tert-butyl perbenzoate) is the reference line for the Luperox 101 thermally activated free radical initiator. The middle line "This disclosure" is data obtained from a crosslinked fluorinated ionomer prepared from the liquid coating composition disclosed herein that is crosslinked by exposing the liquid coating composition to ultraviolet light to initiate the crosslinking reaction without containing any Luperox 101 or other thermally activated free radical initiator. The bottom line labeled "Comparative Example" is data obtained from a crosslinked fluorinated ionomer prepared from a liquid coating composition that contains Luperox 101 and is crosslinked by exposing the liquid coating composition to high temperature to initiate the crosslinking reaction according to Example 6 of U.S. Patent No. 9,359,480, which is hereby incorporated by reference in its entirety.

[0109] Two different examples, "This disclosure" and "Comparative Example", were prepared as follows: The surface-modified PTFE membrane using the above liquid composition was immersed in acetone at 25 degrees Celsius for 4 days (about 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 sample is shown in Figure 3. Generally, Figure 3 shows that when molecules are present during 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 Luperox 101 free radical initiator molecules. The second line shows that the two peaks indicating the Luperox 101 molecules at a and b are present in the sample of the "comparative example". The third line shows that the two peaks characteristic of the Luperox 101 molecules at a and b are not present in the sample of the "present disclosure". This data shows that NMR analysis can be used to determine whether a thermally activated radical initiator such as Luperox 101 is present during the crosslinked fluorinated ionomer coating.

[0111] Aspect:

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

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

[0114] In a third aspect according to any of the foregoing aspects, the microporous membrane support includes a polymer selected from ultra-high molecular weight polyethylene, polyvinylidene fluoride, and polyphenyl sulfone.

[0115] In a fourth aspect according to any of the foregoing aspects, the hydrophilic group is present on the crosslinked fluorinated ionomer at an equivalent weight in the range of 380 to 620 grams per hydrophilic group equivalent.

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

[0117] A sixth aspect according to any of the foregoing aspects, having a humidity (of the CH3 / H2O mixture) of less than 92 weight percent CH3.

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

[0119] An eighth aspect according to any of the foregoing aspects, having a flow rate loss of 80 percent or less compared to an uncoated microporous membrane support when measured using 500 milliliters of isopropyl alcohol at a pressure of 14.2 psi.

[0120] A ninth aspect according to any of the foregoing aspects, having a surface energy of at least 25 dynes / cm.

[0121] In a tenth aspect according to any of the foregoing aspects, the microporous membrane comprises a polymer selected from the group consisting of fluoropolymers, polysulfone, nylon, polyacrylonitrile, polyethylene, ultrahigh molecular weight polyethylene, polyvinylidene fluoride, and polyphenyl sulfone.

[0122] In an eleventh aspect, the filter comprises a microporous membrane composite of any of the foregoing aspects.

[0123] In a twelfth aspect, 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 is: a) coating the microporous membrane with a liquid coating composition comprising a fluorinated solvent and a fluorinated ionomer dissolved or dispersed therein, wherein the fluorinated ionomer is derived from copolymerizing a reactive unit comprising: i) a fluorinated monomer comprising a fluorinated group and ethylenic unsaturation; ii) a fluorinated monomer comprising ethylenic unsaturation and a functional group convertible to a 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 to form a crosslinked fluorinated ionomer.

[0124] In a thirteenth aspect according to the twelfth aspect, the fluorinated ionomer further comprises one or more of iodine and bromine atoms at terminal positions, at least 90% by weight of the fluorinated ionomer has a particle size of less than 200 nanometers, and the fluorinated ionomer is: i) a fluorinated monomer comprising a fluorinated group and ethylenic unsaturation; ii) a fluorinated monomer comprising ethylenic unsaturation and a functional group convertible to a hydrophilic group; iii) a bisolefin monomer selected from formulas (OF-1), (OF-2), (OF-3) (wherein (OF-1) is the formula TIFF2025522687000009.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 a C1-C5 alkyl or (per)fluoroalkyl group); (OF-2) is the formula TIFF2025522687000010.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 may be partially, substantially, or fully 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: TIFF2025522687000011.tif21170(wherein E, A, and B have the same meanings as defined above; R5, R6, and R7 are each independently H, F, or a C1-5 alkyl or (per)fluoroalkyl group)); and iv) the reactive unit containing a fluorinated chain transfer agent of the formula R f (I) x (Br) y is derived from copolymerizing (wherein R f is a fluoroalkyl or (per)fluoroalkyl or (per)fluorochloroalkyl group having 1 to 10 carbon atoms, x and y are integers from 0 to 2, and 1 ≤ x + y ≤ 2).

[0125] In a fourteenth aspect according to the twelfth or thirteenth aspect, the microporous membrane comprises a polymer selected from the group consisting of fluoropolymers, polysulfones, nylons, polyacrylonitriles, polyethylenes, ultra-high molecular weight polyethylenes, polyvinylidene fluorides, and polyphenyl sulfones.

[0126] In a fifteenth aspect according to any of the twelfth to fourteenth aspects, the fluorinated monomer containing a fluorinated group and ethylenic unsaturation comprises tetrafluoroethylene.

[0127] In a sixteenth aspect according to any of the twelfth to fifteenth aspects, the functional group convertible to a hydrophilic group is selected from the group consisting of -SO2F, -COOR, -COF, and combinations thereof, wherein R is a C1-C20 alkyl radical or a C6-C20 aryl radical.

[0128] A seventeenth aspect according to any of aspects 12 to 16 further comprises continuously applying a liquid coating composition to a microporous membrane support that is moving, 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 an eighteenth aspect according to any of aspects 12 to 17, the liquid coating composition does not contain a thermally activated radical initiator.

[0130] In a nineteenth aspect according to any of aspects 12 to 18, the liquid coating composition does not contain a radical initiator.

[0131] In a twentieth aspect according to any of aspects 12 to 19, the liquid coating composition contains a radiation-activated radical initiator.

[0132] A twenty-first aspect according to any of aspects 12 to 20 further comprises exposing the coated fluorinated ionomer to electromagnetic radiation to react reactive units to form a crosslinked fluorinated ionomer, and then contacting the membrane with a solvent to remove unreacted reactive units from the crosslinked fluorinated ionomer.

[0133] A twenty-second aspect according to any of aspects 12 to 21 further comprises converting -SO2F, -COOR, or -COF groups to hydrophilic groups by sequentially contacting the crosslinked fluorinated ionomer with a base and then an acid.

[0134] A twenty-third aspect is a microporous membrane composite prepared according to any of aspects 12 to 22.

Claims

1. A microporous membrane composite, comprising: 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 The hydrophilic group is attached to a fluorinated backbone, the hydrophilic group being -SO ３ H, -COOH, and PO ３ H; the crosslinked coating does not contain a thermally activated radical initiator, the 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 or 2, wherein the microporous membrane support comprises a polymer selected from ultra-high molecular weight polyethylene, polyvinylidene fluoride, and polyphenyl sulfone.

4. The microporous membrane composite according to any one of claims 1 to 3, wherein the hydrophilic groups are present on the crosslinked fluorinated ionomer with an equivalent weight in the range of 380 to 620 grams per hydrophilic group equivalent.

5. At least 5 micrograms / cm ２ The microporous membrane composite according to any one of claims 1 to 4, having a dye-binding ability of

6. CH less than 92 weight percent ３ of (CH ３ / H ２ O mixture), the microporous membrane composite according to any one of claims 1 to 5.

7. At room temperature, 14.2 psi / 500 ml / 17.35 cm ２ The microporous membrane composite according to any one of claims 1 to 6, having an isopropyl alcohol flow time of less than 4092 seconds at ２ .

8. The microporous membrane composite according to any one of claims 1 to 7, having a flow rate loss of 80 percent or less when measured using 500 milliliters of isopropyl alcohol at a pressure of 14.2 psi as compared to the uncoated microporous membrane support.

9. The microporous membrane composite according to any one of claims 1 to 8, having a surface energy of at least 25 dynes / cm.

10. The microporous membrane composite according to any one of claims 1 to 9, wherein the microporous membrane comprises a polymer selected from the group consisting of fluoropolymers, polysulfones, nylons, polyacrylonitriles, polyethylenes, ultra-high molecular weight polyethylenes, polyvinylidene fluorides, and polyphenyl sulfones.

11. A filter comprising the 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, the method comprising: a) coating the microporous membrane with a liquid coating composition comprising a fluorinated solvent and a fluorinated ionomer dissolved or dispersed therein, wherein the fluorinated ionomer comprises 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 fluorinated bromoalkyl or iodoalkyl chain transfer agent coating, which is derived from copolymerizing reactive units comprising; b) exposing the coated fluorinated ionomer to electromagnetic radiation to react the reactive units to form a crosslinked fluorinated ionomer A method comprising.

13. The fluorinated ionomer further comprises one or more of iodine atoms and bromine atoms at terminal positions, at least 90% by weight of the fluorinated ionomer has a particle size of less than 200 nanometers, The fluorinated ionomer is 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 bisolefin monomer selected from the formulas (OF-1), (OF-2), (OF-3) [wherein, (OF-1) is the formula (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 a C1-C5 alkyl or (per)fluoroalkyl group); (OF-2) is the formula (wherein each A is independently selected from F, Cl, and H; each B is independently selected from F, Cl, H and ORB, and 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 the formula: (wherein E, A and B have the same meaning as defined above; R5, R6, R7 are each independently H, F or a 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, which is derived from copolymerizing reactive units comprising.

14. The method according to claim 12 or 13, wherein the microporous membrane comprises a polymer selected from the group consisting of fluoropolymers, polysulfones, nylons, polyacrylonitriles, polyethylenes, ultra-high molecular weight polyethylenes, polyvinylidene fluorides, and polyphenyl sulfones.

15. The method according to any one of claims 12 to 14, wherein the fluorinated monomer containing a fluorinated group and ethylenic unsaturation comprises tetrafluoroethylene.

16. The functional group convertible to a hydrophilic group is -SO ２ F, -COOR, -COF, and combinations thereof, wherein R is a C1-C20 alkyl radical or a C6-C20 aryl radical, the method according to any one of claims 12 to 15.

17. continuously applying a liquid coating composition to a microporous membrane support moving Continuously curing a liquid coating composition applied to a microporous membrane support by passing the moving microporous membrane support and the applied liquid coating composition through electromagnetic radiation The method according to any one of claims 12 to 16, further comprising **Claim 18** The method according to any one of claims 12 to 17, wherein the liquid coating composition does not contain a thermally activated radical initiator. **Claim 19** The method according to any one of claims 12 to 18, wherein the liquid coating composition does not contain a radical initiator. **Claim 20** The method according to any one of claims 12 to 18, wherein the liquid coating composition contains a radiation-activated radical initiator. **Claim 21** The method according to any one of claims 12 to 19, further comprising exposing the coated fluorinated ionomer to electromagnetic radiation to react reactive units to form a crosslinked fluorinated ionomer, and then contacting the membrane with a solvent to remove unreacted reactive units from the crosslinked fluorinated ionomer. **Claim 22** By sequentially contacting the crosslinked fluorinated ionomer with a base and then an acid, further comprising converting a —SO ２ F, —COOR, or —COF group to a hydrophilic group, the method according to any one of claims 12 to 21. **Claim 23** The microporous membrane composite prepared according to any one of claims 12 to 22.

Images