Bipolar Membrane

Abstract

A bipolar membrane (BPM) comprising a cation exchange layer (CEL) and an anion exchange layer (AEL), wherein the color characteristics of the CEL are visibly different from the color characteristics of the AEL. The CEL and AEL are easily distinguishable, thereby enabling membrane stacks including the BPM to be constructed quickly and without layer ordering errors.

Description

[Technical Field]

[0001] The present invention relates to bipolar ion exchange membranes and methods for their preparation and use. [Background technology]

[0002] Ion exchange membranes are used in electrodialysis, reverse electrodialysis, electrolysis, diffusion dialysis, and several other processes. Typically, ion transport through a membrane occurs under the influence of a driving force, such as an ion concentration gradient or an electric potential gradient. Ion exchange membranes are generally classified according to their charge as cation exchange membranes (CEMs), anion exchange membranes (AEMs), or, if they contain both positively and negatively charged groups, bipolar membranes (BPMs). CEMs contain negatively charged groups that allow cations to pass but reject anions, while AEMs contain positively charged groups that allow anions to pass but reject cations. BPMs contain both positively and negatively charged groups, for example, in the form of cation exchange layers (CELs) and anion exchange layers (AELs).

[0003] Some ion exchange membranes include a porous support that provides mechanical strength. Such membranes are often referred to as "composite membranes" or "pore-filled membranes" because of the presence of both an ionically charged polymer that discriminates between oppositely charged ions and a porous support that provides mechanical strength.

[0004] Ion exchange membranes are often used in the form of stacks containing both AEMs and CEMs, for example, in electrodialysis and electrodeionization, where AEMs and CEMs alternate. In certain applications, BPMs are used, each having a functional layer with anion exchange properties (AEL) and a functional layer with cation exchange properties (CEL). In some applications, the membrane stack includes BPMs and AEMs and / or CEMs.

[0005] In many cases, all membranes used in a stack or device have a similar, usually whitish, appearance, making them difficult to distinguish. In the case of BPMs, the problem arises because of the small visual difference between the AEL and CEL. When assembling stacks, either manually or through an automated process, the small visual difference between the AEL and CEL of a BPM can lead to mistakes, such as a BPM stack in which not all membranes are aligned in the same direction. Such mistakes can lead to severe damage to the membranes and ultimately poor stack performance and should be avoided. Summary of the Invention

[0006] The present invention provides several means for providing a BPM in which the CEL and AEL are readily visually distinguishable, including the color characteristics of the AEL and CEL.

[0007] It is an object of the present invention to provide a BPM that is robust and in which the CEL and AEL are easily distinguishable so that membrane stacks such as BPMs can be constructed quickly and without errors. DETAILED DESCRIPTION OF THE INVENTION

[0008] According to a first aspect of the present invention, there is provided a bipolar membrane (BPM) comprising a cation exchange layer (CEL) and an anion exchange layer (AEL), wherein the color characteristics of the CEL are visibly different from the color characteristics of the AEL.

[0009] In this document (including the claims), the verb "comprise" and its conjugations are used in their open-ended sense to mean that items following the word are included, but items not specifically mentioned are not excluded. Furthermore, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one element is present, unless the context clearly requires that only one element be present. Thus, the indefinite article "a" or "an" normally means "at least one."

[0010] The visible difference in color characteristics between the AEL and CEL of the BPM makes the layers distinguishable by the human eye and by automated sensors or similar recognition systems. For human operation, the visible difference in color characteristics between the AEL and CEL is preferably visible when the AEL and CEL are viewed, for example, in daylight and / or artificial light (e.g., light provided by electrical means, e.g., light used in industrial environments). For automated production of BPM, the visible difference in color characteristics between the AEL and CEL is preferably visible in daylight and / or artificial light. Artificial light is typically generated by electrical means and includes, for example, visible light (e.g., white, red, orange, yellow, green, blue, indigo, and violet light), ultraviolet light, and infrared light.

[0011] In a preferred embodiment, the visible difference in color properties between the AEL and CEL is preferably visible under yellow light, particularly artificial yellow light (e.g., light with a wavelength greater than 490 nm), as this is particularly useful for industrially producing BPMs from AELs and / or CELs that are sensitive (e.g., decompose) in blue light.

[0012] The color characteristics of the CEL and AEL and the visible differences between them can be quantified spectrophotometrically using a spectrophotometer, for example a Konica Minolta CM-3600d spectrophotometer, for example using an 8 mm MAV measurement area.

[0013] Suitable parameters for quantifying the color characteristics of CELs and AELs and the visible differences between them are derived from CIEDE2000, an international standard set out by the International Commission on Illumination, which defines, for example, the Cartesian coordinate system a * , b * CIE L defines cylindrical coordinates C' (chroma, relative saturation) and h' (hue angle) instead of * a * b * The CIELCh color space or the CIELCh color space are used to represent color characteristics and differences. Lightness, L, is the same for both color spaces.

[0014] CIE L * a * b * The three coordinates of the color are the lightness (L * = 0 yields black, L * = 100 indicates diffuse white; specular white is more likely), a position between red / magenta and green (a * , negative values ​​indicate green while positive values ​​indicate magenta), and the position between yellow and blue (b * , negative values ​​indicate blue, positive values ​​indicate yellow).

[0015] It is an object of the present invention to provide a BPM comprising a cation exchange layer (CEL) and an anion exchange layer (AEL), wherein the color characteristics of the CEL are visibly different from the color characteristics of the AEL, preferably by incorporating a dye into at least one of the AEL and the CEL. However, an excessive amount of dye is undesirable because it increases manufacturing costs.

[0016] The visible difference in color properties between the AEL and the CEL is preferably expressed according to CIEDE2000 as ΔE 00 The difference is at least 4. In order to make the difference in color properties between the AEL and the CEL easily visible, it is preferable that the color of the AEL and / or the CEL is not too white. Thus, the AEL and / or the CEL preferably have a lightness L' of less than 90, more preferably less than 80, for example less than 70.

[0017] On the other hand, the color of the AEL and / or CEL should not be too dark. Thus, the AEL and / or CEL preferably have a lightness L' of greater than 5, more preferably greater than 8, in particular greater than 10, and even more particularly at least 15, for example at least 20.

[0018] The relative saturation of the AEL and / or CEL, C'(a * and b *(which can be considered as a normalized average of ) is preferably at least 4, more preferably at least 5, especially at least 8.

[0019] The color difference is expressed as ΔE, the well-known formula for CIE DE 2000, also known as CIELab 2000. 00 Further details can be found, for example, in Luo MR (ed.) Encyclopedia of Colour Science and Technology. Springer, New York, NY. https: / / doi.org / 10.1007 / 978-1-4419-8071-7_7, Luo MR (2016) CIEDE2000, History, Use, and Performance, and in ISO standard ISO 11664-6:2014.

[0020] Color difference ΔE between AEL and CEL 00 is preferably at least 4, more preferably at least 8, especially at least 15. Generally, ΔE 00 is less than 95, especially less than 90.

[0021] If the difference in lightness (ΔL') between the AEL and the CEL and the difference in saturation (ΔC') between the AEL and the CEL are very small, a visible difference in color characteristics may still exist, which can be characterized by Δh' > 20 degrees, preferably Δh' > 50 degrees.

[0022] It is preferred that the color characteristics of the AEL and / or CEL are substantially uniform, i.e., the color difference ΔE between different portions of the AEL 00 is preferably less than 5, and / or the color difference ΔE between different parts of the CEL 00 is preferably less than 5.

[0023] In a preferred embodiment, to easily determine which side of the BPM is the CEL and which side is the AEL, one or both of the AEL and CEL contain a dye or combination of dyes such that the color characteristics of the CEL are visibly different from the color characteristics of the AEL, e.g., the AEL and CEL contain different dyes or different combinations of dyes, or the same dye or combination of dyes in different amounts and / or different ratios.

[0024] Preferably, at least one of the AEL and the CEL contains a dye.Optionally, both the AEL and the CEL contain a dye.In one embodiment, the AEL and the CEL each contain different dyes.In another embodiment, the AEL and the CEL contain the same dye, but in different amounts.In a specific embodiment, the AEL and the CEL contain the same dye in the same amount, and are visually different due to the difference in the interaction between the dye and other components of the corresponding layer, which may result in bathochromic shift or hypochromic shift.

[0025] For economic reasons, it is preferred that the CEL and / or AEL contain a dye that has another function in addition to providing a visible color. In a preferred embodiment, the CEL and / or AEL contain a dye that is a photoinitiator. A dye that is also a photoinitiator is preferably a dye that reaches an excited state upon irradiation with light of an appropriate wavelength and intensity, transferring its energy to the co-initiator by abstracting an electron or hydrogen atom, resulting in the co-initiator forming a reactive radical species. Therefore, preferably, the CEL and / or AEL contain a dye that, when in an excited state, can react with the co-initiator to generate radicals. The dye(s) present in the CEL and / or AEL are preferably dyes that do not form ions upon irradiation with light. In other words, preferably, the AEL and CEL do not contain dyes that form ions upon irradiation with light. It is particularly preferred that the dye(s) present in the CEL and / or AEL are dyes that cannot undergo regenerative, reversible light-driven dissociation or association reactions to generate positively and negatively charged ions.

[0026] The dye(s) that may be present in the CEL and / or AEL preferably do not pose a health risk, for example, the dye(s) preferably do not contain transition metal ions. Examples of transition metals include Cr, Co, Cu, Ir, Mn, Ni, Os, Ru, Pd, Pt, and Re.

[0027] Preferably, the dye is not covalently bound to the AEL and / or CEL, at least initially. For example, the dye can be physically trapped within the CEL or AEL. This allows for greater flexibility in dye selection, including cheaper dyes, and may make the BPM easier to manufacture.

[0028] The use of a dye that is also a photoinitiator (instead of using a separate dye and uncolored photoinitiator) provides cost benefits by eliminating the need for a separate dye to achieve a CEL that has color characteristics that are visibly different from the AEL. Therefore, the dye is preferably a colored photoinitiator.

[0029] In some cases, the chemical structure of the dye changes after irradiation. After irradiation, the dye can form reaction products that have a different color than the dye before irradiation, or the dye can lose its color. The latter is undesirable, but unreacted dye can remain and thus contribute color to the formed AEL or CEL.

[0030] In one embodiment, the AEL and / or CEL are formed from irradiating a curable composition that includes an excess of a dye that is a photoinitiator (i.e., a "colored photoinitiator"). As a result, there is some unreacted colored photoinitiator in the AEL and / or CEL after irradiation, and therefore the CEL and AEL have a color that corresponds to the color of the unreacted colored photoinitiator used to form them.

[0031] When both the AEL and the CEL are formed by photocuring and both require a photoinitiator, the curable compositions used to form the AEL and the CEL preferably contain different amounts of the same colored photoinitiator and / or different colored photoinitiators. However, due to differences in charge and structure between the monomers in the curable composition used to prepare the AEL and the monomers in the curable composition used to prepare the CEL, surprisingly, in many cases the AEL and the CEL have visibly different color characteristics, even when the same colored photoinitiator is used in the same amount or concentration in each curable composition. This allows for a more efficient manufacturing process, since it is possible to use the same dye as the colored photoinitiator for both the CEL and the AEL and still achieve a CEL with visibly different color characteristics from the AEL.

[0032] Preferably, the AEL and / or CEL can be obtained by irradiating a curable composition comprising a dye that functions as a photoinitiator. Preferably, the curable composition comprises: (a) one or more curable monomers containing at least one anionic or cationic group; (b) dye; (c) optionally, a coinitiator; (d) optionally, a curable monomer that is free of anionic and cationic groups; and (e) optionally, a solvent, which is preferably an inert solvent.

[0033] Preferably, the dye is a colored photoinitiator, especially a Norrish Type II photoinitiator. Preferably, at least one of the CEL and the AEL (e.g., as component (a) in the curable composition) comprises a dye having an absorption maximum at a wavelength longer than 400 nm, more preferably at a wavelength of 400 to 800 nm, for example, 430 to 800 nm, measured in one or more solvents of water, ethanol, and toluene at a temperature of 23°C.

[0034] The absorption maximum is preferably measured at 23°C using a dye (e.g., a colored photoinitiator) at a concentration of 0.01% by weight dissolved in the relevant solvent (i.e., water, ethanol, or toluene) using, for example, a 1 mm path length (e.g., a quartz cuvette with an internal length of 1 mm through which light passes), e.g., a Varian Cary from Agilent Technologies. TM The absorption maximum can be measured using a 100 conc. double beam UV / VIS spectrophotometer.

[0035] The molar extinction coefficient at the dye's absorption maximum (i.e., longer than 400 nm) is preferably at least 7500 M -1 cm -1 (750m 2 mol -1 ), more preferably at least 10,000M -1 cm -1The molar extinction coefficient can be measured using a UV-VIS spectrophotometer, such as the Cary spectrophotometer from Agilent Technologies. TM The chromatographic data can be measured using a UV-visible spectrophotometer.

[0036] Preferably, the dye is a photoinitiator derived from xanthene, flavin, curcumin, porphyrin, anthraquinone, phenoxazine, camphorquinone, phenazine, acridine, phenothiazine, xanthone, thioxanthone, thioxanthene, acridone, flavone, coumarin, fluorenone, quinoline, quinolone, naphthaquinone, quinolinone, arylmethane, azo, benzophenone, carotenoid, cyanine, phthalocyanine, dipyrrine, squarine, stilbene, styryl, triazine or anthocyanin, or a mixture comprising two or more thereof (e.g., 2 to 5 such photoinitiators), provided that the dye has an absorption maximum at a wavelength longer than 400 nm, in each case measured in one or more of the following solvents: water, ethanol and toluene, at a temperature of 23° C.

[0037] Examples of dyes that can function as photoinitiators with the absorption maxima specified above include eosin Y, eosin Y disodium salt, fluorescein, uranine, erythrosin B, rose bengal, phloxine B, 4,5-dibromofluorescein, rhodamine B, riboflavin, flavin mononucleotide, acriflavine, curcumin, resazurin, safranine-O, phenosafranine, neutral red, acridine orange, acid blue 43, 1,4-diamino-anthraquinone, 1,4-dihydroxy-anthraquinone, bromamine acid sodium salt, carminic acid, ethyl violet, patent blue V, methyl orange, naphthol yellow S, methylene blue, and indole. citric acid, citric acid diisopropyl methyl ... Preferred dyes include safranine-O, acridine orange, bromamic acid sodium salt, ethyl violet, methyl orange, curcumin, riboflavin, flavin mononucleotide, methylene blue, zinc phthalocyanine, tetraphenylsulfonic acid porphyrin, quinolone yellow WS, quinaldine red, eosin Y, eosin Y disodium salt, erythrosin B, rose bengal, rhodamine B, phloxine B, and dibromofluorescein.

[0038] The dye preferably comprises a conjugated system having at least 10 (more preferably at least 12) delocalized (π) electrons. A conjugated system is a system of connected p orbitals with delocalized electrons in a molecule, generally with alternating single and multiple bonds.

[0039] For BPMs intended for use in food or pharmaceutical applications, the dye(s) are preferably known to be non-toxic and / or approved (e.g., by the U.S. Food and Drug Administration (FDA)) for food and / or pharmaceutical use, such as erythrosin B, flavin mononucleotide, curcumin, riboflavin, tartrazine, quinolone yellow, azorubine, amaranth, Ponceau 4R, Allura Red AC, patent blue V, indigo carmine, brilliant blue FCF, chlorophyll derivatives, copper complexes of chlorophyll or chlorophyllin derivatives, carotenoids, sunset yellow FCF, carminic acid, green S, xanthophyll derivatives, brilliant black BN, or one or more thereof.

[0040] The dye typically absorbs light with a wavelength longer than 400 nm to generate an excited photoinitiator molecule, which then abstracts an electron, a proton, or both from the co-initiator to produce free radicals. Therefore, the curable composition preferably includes a co-initiator. The free radicals then cure the curable monomer. The co-initiator can be any chemical capable of generating free radicals in a reaction with the dye when the dye is in an electronically excited state, for example, when the curable composition is irradiated with light that matches the absorption spectrum of the dye.

[0041] Preferably, the coinitiator (i.e., component (c)) comprises a tertiary amine, an acrylated amine, an onium salt (e.g., a salt of an iodonium, sulfonium, phosphonium, or diazonium ion), a triazine derivative, an organohalogen compound, an ether group, a ketone, a thiol, a borate, a sulfide (e.g., a thioether), a pyridinium salt, a ferrocenium salt, or two or more thereof.

[0042] Preferred coinitiators include triethylamine, triethanolamine, methyldiethanolamine, dimethylethanolamine, ethylenediamine-tetra(2-propanol), 1,4-dimethylpiperazine, n-phenyldiethanolamine, 4-(dimethylamino)benzaldehyde, 7-diethylamino-4-methylcoumarin, 2-(diethylamino)ethyl methacrylate, carbon tetrabromide, diphenyliodonium chloride, 2-ethylhexyl 4-dimethylaminobenzoate, 4-(dimethylamino)benzonitrile, 4-methyl-2-methyl-1,3-dimethyl-2,4 ... ethyl dimethylaminobenzoate, dimethylaminopropyl acrylamide, dimethylaminoethyl methacrylate, diphenyliodonium nitrate, N-phenylglycine, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, 2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine, hexaethylmelamine, hexamethylenetetramine, piperonyl alcohol, N,N-dimethyl-p-toluidine, L-arginine, and mixtures comprising two or more thereof.

[0043] The curable composition preferably contains 0.002 to 4% by weight, more preferably 0.005 to 2% by weight, and especially 0.005 to 0.9% by weight of the dye (component (b)). The curable composition preferably comprises 0.01 to 40% by weight, more preferably 0.05 to 20% by weight, and even more preferably 0.1 to 5% by weight of the coinitiator (component (c)).

[0044] The molar ratio of dye to coinitiator present in the curable composition is preferably greater than 1:1, more preferably greater than 1:2, especially greater than 1:5, and more especially greater than 1:10.

[0045] The curable composition preferably comprises a curable monomer (component (a)) containing at least one anionic or cationic group, i.e., a cationic group for the AEL and an anionic group for the CEL. Preferred anionic groups that may be present in the curable monomer include acidic groups, such as sulfo, carboxy, and / or phosphato groups, especially sulfo groups. Preferred cationic groups that may be present in the curable monomer include quaternary ammonium and phosphonium groups, especially quaternary ammonium groups.

[0046] Preferably, the curable monomer is a monomer or oligomer rather than a polymer, i.e., the curable monomer preferably has a molecular weight (MW) that satisfies the following formula: MW<(3000+300n) [In formula: MW is the molecular weight of the curable monomer; n has a value of 1 to 6 and is the number of ionic groups present in the curable monomer.

[0047] The curable monomer preferably comprises an anionic or cationic group and one or more ethylenically unsaturated groups, eg, polymerizable ethylenically unsaturated groups. Depending on the pH of the curable composition, the anionic or cationic groups present in the curable monomers can partially or totally form salts with counterions, e.g., sodium, lithium, ammonium, potassium and / or pyridinium in the case of anionic groups, and chloride and / or bromide in the case of cationic groups.

[0048] Preferred ethylenically unsaturated groups that may be present in the curable monomer are in the form of vinyl groups, such as (meth)acrylic groups, allyl groups, or styrene groups. The (meth)acrylic groups are preferably (meth)acrylate or (meth)acrylamide groups, more preferably (meth)acrylamide groups, such as acrylamide or methacrylamide groups.

[0049] Due to environmental and health considerations, the use of perfluorinated polymer backbones such as poly(tetrafluoroethylene) is not preferred. Non-perfluorinated monomers generally have lower costs. For this reason, perfluorinated monomers are not preferred, and therefore, BPM preferably does not contain perfluorinated polymers.

[0050] Examples of preferred curable monomers include compounds of the following formulae (A), (B), (CL), (SM), (MA), (MB-α), (C), (ACL-A), (ACL-B), (ACL-C), and / or (AM-B):

[0051] [ka]

[0052] In formulas (A) and (B), R A1 ~R A3 each independently represents a hydrogen atom or an alkyl group; R B1 ~R B7 each independently represents an alkyl group or an aryl group; Z A1 ~Z A3 each independently represents -O- or -NRa- [wherein Ra represents a hydrogen atom or an alkyl group]; L A1 ~L A3 each independently represents a divalent linking group which is an alkylene group, an arylene group, or a combination thereof; R X represents a divalent linking group that is an alkylene group, an alkenylene group, an alkynylene group, an arylene group, or a combination thereof; and X A1 ~X A3 each independently represents an organic or inorganic anion, preferably a halogen ion or an aliphatic or aromatic carboxylate ion.

[0053] Examples of compounds of formula (A) or (B) include:

[0054] [ka]

[0055] [ka]

[0056] Synthetic methods can be found, for example, in U.S. Patent Publications US2015 / 0353721, US2016 / 0367980, and US2014 / 0378561.

[0057] [ka]

[0058] In formulas (CL) and (SM), L 1 represents an alkylene group or an alkenylene group; R a , R b , R c , and R d each independently represents a linear or branched alkyl group or an aryl group; R a and R b , and / or R c and R d may be bonded to each other to form a ring; R 1 , R 2 , and R 3 each independently represents a linear or branched alkyl group or an aryl group; R 1 and R 2 , or R 1 , R 2 and R 3 may be bonded to each other to form an aliphatic heterocycle; n1, n2, and n3 each independently represent an integer from 1 to 10; and X1 - , X2 - and X3 - each independently represents an organic or inorganic anion.

[0059] Examples of formulas (CL) and (SM) include:

[0060] [ka]

[0061] [ka]

[0062] Methods of synthesis can be found in European Patent EP3184558 and US Patent Publication US2016 / 0001238.

[0063] [ka]

[0064] In formulas (MA) and (MB-α), R A1 represents a hydrogen atom or an alkyl group; Z 1 represents -O- or NRa- [wherein Ra represents a hydrogen atom or an alkyl group]; M + represents an organic or inorganic cation, preferably a hydrogen ion or an alkali metal ion; R A2 represents a hydrogen atom or an alkyl group, R A4 represents an organic group that contains a sulfonic acid group and has no ethylenically unsaturated groups; and Z 2 represents -NRa- [wherein Ra represents a hydrogen atom or an alkyl group, preferably a hydrogen atom].

[0065] Examples of formulas (MA) and (MB-α) include:

[0066] [ka]

[0067] Methods of synthesis can be found, for example, in US Patent Publication US2015 / 0353696.

[0068] [ka]

[0069] Methods of synthesis can be found, for example, in US Patent Publication US2016 / 0369017.

[0070] [ka]

[0071] In formula (C), L 1 represents an alkylene group; n represents an integer of 1 to 3, preferably 1 or 2; m represents an integer of 1 or 2; L 2 represents an n-valent linking group; R 1 represents a hydrogen atom or an alkyl group; R 2 is -SO3 - M + or -SO3R 3- represents R 2 If there are multiple R 2 is independently -SO3 - M + or -SO3R 3- represents; M + represents a hydrogen ion, an inorganic ion, or an organic ion; and R 3represents an alkyl group or an aryl group.

[0072] Examples of formula (C) include:

[0073] [ka]

[0074] The synthesis method can be found in European patent EP3187516.

[0075] [ka]

[0076] In the formulas (ACL-A), (ACL-B), (ACL-C) and (AM-B), each of R and R' independently represents a hydrogen atom or an alkyl group; LL represents a single bond or a divalent linking group; LL 1 , L.L. 1’ , L.L. 2 , and L.L. 2’ each independently represents a single bond or a divalent linking group; each of A and A' independently represents a sulfo group in free acid or salt form; and m represents 1 or 2.

[0077] Examples of formulas (ACL-A), (ACL-B), (ACL-C) and (AM-B) include:

[0078] [ka]

[0079] Methods of synthesis can be found in US Patent Publication US2016 / 0362526. Other examples include:

[0080] [ka]

[0081] Optionally, the curable composition further comprises one or more solvents as component (e). The solvent can be any solvent that does not copolymerize with other components or act as a coinitiator. In one embodiment, the solvent preferably comprises water and optionally an organic solvent, especially when some or all of the organic solvent is water-miscible. Water is useful for dissolving the curable monomer, and the organic solvent is useful for dissolving other organic components of the curable composition. The solvent is useful for reducing the viscosity and / or surface tension of the curable composition.

[0082] In some embodiments, the curable composition preferably comprises 0 to 60 wt. %, more preferably 4 to 50 wt. %, and most preferably 10 to 45 wt. % of a solvent (e.g., as component (e)). In other embodiments, the curable composition comprises 35 to 95 wt. %, preferably 60 to 90 wt. % of a solvent (e.g., as component (e)).

[0083] Preferably, the BPM comprises a porous support, which can reinforce the BPM. The pores of the porous support can be filled with a first curable composition(s) and then cured before applying a second curable composition (comprising a curable monomer(s) comprising at least one ionic group oppositely charged to the curable monomer(s) of the first curable composition), after which the second curable composition can be cured.

[0084] Examples of porous supports include woven and nonwoven synthetic fabrics and extruded films.Examples include wetlaid and drylaid nonwoven materials, spunbond and meltblown fabrics, and nanofiber webs made from polyethylene, polypropylene, polyacrylonitrile, polyvinyl chloride, polyphenylene sulfide, polyester, polyamide, polyaryletherketones such as polyetheretherketone, and copolymers thereof.Porous supports can also be porous membranes, such as polysulfone, polyethersulfone, polyphenylene sulfone, polyphenylene sulfide, polyimide, polyetherimide, polyamide, polyamideimide, polyacrylonitrile, polycarbonate, polyacrylate, cellulose acetate, polypropylene, poly(4-methyl-1-pentene), polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, and polychlorotrifluoroethylene membranes and their derivatives.

[0085] The porous support preferably has an average thickness of 10 to 700 μm, more preferably 20 to 500 μm. Preferably, the porous support has a porosity of 30-95%. The porosity of the support can be measured using a porometer, e.g., Porolux from IB-FT GmbH, Germany. TM It can be determined by 1000.

[0086] The porous support, if present, is one that has been treated, if desired, to modify its surface energy, for example to a value greater than 45 mN / m, preferably greater than 55 mN / m. For example, suitable treatments for improving the wettability and adhesion of polymers to the porous support include corona discharge treatment, plasma glow discharge treatment, flame treatment, ultraviolet radiation treatment, chemical treatment, etc.

[0087] Commercially available porous supports are available from several sources, such as Freudenberg Filtration Technologies (Novatexx materials), Lydall Performance Materials, Celgard LLC, APorous Inc., SWM (Conwed Plastics, DelStar Technologies), Teijin, Hirose, Mitsubishi Paper Mills Ltd, and Sefar AG.

[0088] Preferably, the support is a polymeric support. Aromatic porous supports include porous supports derived from one or more aromatic monomers, such as aromatic polyamide (aramid), (sulfonated) polyphenylene sulfone, poly(phenylene sulfide sulfone), aromatic polyester (e.g., polyethylene terephthalate (PET) or polybutylene terephthalate (PBT)), aromatic polyether ether ketone, polyphenylene sulfide, or a combination of two or more thereof. In one embodiment, the support strongly absorbs UV light (380 nm or less). The support is considered to be strongly absorbing when it has a transmittance of less than 90% at wavelengths longer than 340 nm as measured by a UV spectrometer.

[0089] Examples of commercially available aromatic porous supports include Teijin, Hirose, Mitsubishi Paper Mills Ltd and Sefar AG. According to a second aspect of the invention, there is provided a film stack including a BPM according to the first aspect of the invention.

[0090] According to a third aspect of the present invention, there is provided an electrochemical device comprising a BPM according to the first aspect of the present invention or a membrane stack according to the second aspect of the present invention. According to a fourth aspect of the present invention, there is provided a process for producing a bipolar membrane comprising a cation exchange layer (CEL) and an anion exchange layer (AEL), wherein the color properties of the CEL are visibly different from the color properties of the AEL, the process comprising, in either order or simultaneously, curing a first curable composition to form the AEL and curing a second curable composition to form the CEL.

[0091] Preferably, one or both of the first and second curable compositions comprises a dye, preferably a dye that is a colored photoinitiator. Preferences for the dye and curable composition are as described above in relation to the first aspect of the invention. Thus, for example, it is preferred that the dye does not form ions when irradiated with light.

[0092] In a preferred embodiment, both the first and second curable compositions comprise a dye that is a colored photoinitiator, particularly a photoinitiator that forms radicals upon irradiation with light. Preferably, but not necessarily, the dye present in the first curable composition has a different chemical formula from the dye present in the second curable composition.

[0093] Preferably, the process according to the fourth aspect of the invention further comprises adhering the CEL and AEL together, for example by pressing them together, optionally with heating.

[0094] The AEL and CEL can be prepared independently and then attached together, for example, by a lamination process that involves applying compressive force and / or heat to the AEL and CEL to bond them together, thereby forming a BPM. Alternatively, the BPM can be prepared by a process that involves curing a first curable composition to form an AEL or CEL, then applying a second curable composition to the formed AEL or CEL, and curing the second curable composition to form the other of the AEL and CEL thereon. Optionally, one or both of the AEL and CEL include a porous support.

[0095] In a preferred embodiment, the bipolar membrane manufacturing process involves continuously applying a curable composition (preferably containing a dye) to a moving (porous) support, preferably by a manufacturing unit comprising a curable composition application station (e.g., one for the CEL and another for the AEL), one or more irradiation source(s) for curing the composition, a membrane collection station, and means for moving the support from the curable composition application station(s) to the irradiation source(s) and back to the membrane collection station.

[0096] The curable composition application station can be located upstream relative to the irradiation source(s), which in turn is located upstream relative to the film collection station. Examples of coating techniques suitable for applying the curable composition include slot die coating, slide coating, air knife coating, roller coating, screen printing, and dipping. Depending on the technique used and the desired final specifications, it may be necessary to remove excess coating from the substrate, for example, by roll-to-roll squeeze, roll-to-blade or blade-to-roll squeeze, blade-to-blade squeeze, or removal with a coating bar. Light curing can be achieved at 40-1500 mJ / cm. -2 Preferably, the drying is carried out at a wavelength of 400 nm to 800 nm using a dose of 1000 . ... [Example]

[0097] The invention will now be illustrated by way of non-limiting examples in which all parts and percentages are by weight unless otherwise stated. In the examples, the following properties were measured by the methods described below.

[0098] [Table 1]

[0099] [Table 2]

[0100] Step (a) Preparation of the composition for making BPM The AEL compositions used to make the BPMs contained the components shown in Table 3 below, where the photoinitiator was 1173, EL, EB, MB, RZ, or QR:

[0101] [Table 3]

[0102] The CEL compositions used to make the BPMs contained the components shown in Table 4 below, where the photoinitiator was 1173, EL, EB, MB, RZ, or QR:

[0103] [Table 4]

[0104] Step (b) - Preparation of BPM The general method for preparing six BPMs (BPM1 to BPM6 shown in Table 5 below) from the compositions shown in Table 4 (for CEL) and Table 3 (for AEL) was as follows: The composition shown in Table 4 (CEL composition) above was coated onto a PET sheet as a 100 μm layer using a 100 μm Meyer bar. A porous support (2223-10) was placed on the layer of composition, and excess CEL composition was scraped off. The composition present in the porous support was then cured by placing it on a conveyor belt set at 5 m / min using a Heraeus F450 microwave-driven UV curing system equipped with a medium-pressure mercury bulb (240 W / cm, 50%) to obtain the CEL of BPM. Next, the composition shown in Table 3 (AEL composition) above was coated onto the previously formed CEL as a 100 μm layer. A porous support (2223-10) was placed on the layer of composition (i.e., AEL composition), and excess AEL composition was scraped off. The AEL composition present in the porous support was then cured by placing it on a conveyor belt equipped with a Heraeus F450 microwave-driven UV curing system equipped with a medium-pressure mercury bulb (240 W / cm, 100%) and set at 5 m / min to obtain BPMs containing an AEL and a CEL, each containing a porous support.

[0105] BPM color characteristics The AEL and CEL color characteristics of the BPM resulting from step (b) were measured according to CIEDE 2000 using a Konica Minolta CM-3600a spectrophotometer with an 8 mm MAV measurement area on an optical tool sample holder and a white calibration plate (Minolta CM-A139). The AEL and CEL color data are shown in Table 5 below:

[0106] [Table 5]

[0107] The following abbreviations are used in Table 5: Photoinitiator refers to the photoinitiator used to make the AEL (from the composition set forth in Table 3 above) or CEL (from the composition set forth in Table 4 above). L' means lightness according to CIEDE2000 C' means saturation according to CIEDE2000 h' denotes the hue angle according to CIEDE2000. AEL means anion exchange layer. CEL means cation exchange layer. ΔE 00 means the color difference between AEL and CEL according to CIEDE2000. The present invention includes the following aspects. [1] A bipolar membrane (BPM) comprising a cation exchange layer (CEL) and an anion exchange layer (AEL), wherein the color characteristics of the CEL are visibly different from the color characteristics of the AEL. [2] 2. The BPM of 1, wherein at least one of the AEL and the CEL contains a dye. [3] 3. The BPM according to any one of 1 to 2, wherein at least one of the AEL and the CEL contains a dye that is a Norrish Type II photoinitiator having an absorption maximum at a wavelength longer than 400 nm as measured in one or more solvents of water, ethanol, and toluene at a temperature of 23°C. [4] 4. The BPM according to any one of 1 to 3, wherein the AEL and the CEL do not contain a dye that forms ions when irradiated with light. [5] 5. The BPM of any one of 1 to 4, wherein the AEL and the CEL each contain a dye, and the dye present in the AEL is different from the dye present in the CEL. [6] 5. The BPM according to any one of 1 to 4, wherein the AEL and the CEL each contain a dye, and the chemical formula of the dye present in the AEL is the same as the chemical formula of the dye present in the CEL. [7] The visible difference in color characteristics is expressed as ΔE according to CIEDE2000 00 7. The BPM according to any one of 1 to 6, comprising at least 4 differences. [8] 8. The BPM according to any one of 1 to 7, wherein at least one of the AEL and the CEL has a color value expressed by L' according to CIEDE2000 of less than 90. [9] 9. The BPM according to any one of 1 to 8, wherein at least one of the AEL and the CEL has a color value, expressed by L' according to CIEDE2000, of at least 10.

[10] 10. The BPM according to any one of 1 to 9, wherein at least one of the AEL and the CEL has a saturation of at least 5, expressed by the chroma C' according to CIEDE2000.

[11] 11. The BPM according to any one of 1 to 10, wherein the color properties of the AEL and / or CEL are substantially uniform.

[12] 12. The BPM according to any one of 1 to 11, which does not comprise a perfluorinated polymer.

[13] 13. The BPM according to any one of 1 to 12, wherein at least one of the CEL and the AEL comprises a dye having an absorption maximum at a wavelength longer than 400 nm when measured in one or more solvents selected from water, ethanol, and toluene at a temperature of 23°C.

[14] 14. The BPM according to any one of claims 1 to 13, wherein the CEL and / or AEL is obtainable by curing a curable composition comprising a dye that functions as a photoinitiator and a coinitiator that is capable of generating free radicals in a reaction with the dye when the dye is in an electronically excited state.

[15] 15. The BPM of any one of 2 to 14, wherein the dye is not covalently attached to an AEL or a CEL.

[16] 16. A membrane stack comprising the BPM according to any one of 1 to 15.

[17] 17. An electrochemical device comprising the BPM according to any one of 1 to 15 or the membrane stack according to 16.

[18] A process for manufacturing a bipolar membrane comprising a cation exchange layer (CEL) and an anion exchange layer (AEL), wherein the color characteristics of the CEL are visibly different from the color characteristics of the AEL, the process comprising, in either order or simultaneously, curing a first curable composition to form the AEL and curing a second curable composition to form the CEL.

[19] 19. The process of claim 18, wherein one or both of the first and second curable compositions comprises a dye that is a colored photoinitiator and a coinitiator that is capable of generating free radicals in a reaction with the dye when the dye is in an electronically excited state.

[20] 20. The process of claim 18 or 19, wherein the first curable composition and / or the second curable composition comprises a dye, which provides color to the CEL and / or AEL and does not form ions when irradiated with light.

[21] 21. The process of any one of paragraphs 18-20, wherein both the first curable composition and the second curable composition comprise a colored photoinitiator and a coinitiator capable of reacting with the colored photoinitiator to generate free radicals when the colored photoinitiator is in an electronically excited state.

[22] 22. The process of any one of claims 18 to 21, wherein both the first curable composition and the second curable composition comprise a dye, and the dye present in the first curable composition has a different chemical formula than the dye present in the second curable composition.

[23] 23. The process of any one of 18 to 22, comprising attaching a CEL and an AEL together.

[24] 24. The process of any one of claims 18 to 23, comprising curing a first curable composition to form an AEL or CEL, applying a second curable composition to the formed AEL or CEL, and curing the second curable composition, thereby forming the CEL or AEL.

Claims

1. A bipolar membrane (BPM) comprising a cation exchange layer (CEL) and an anion exchange layer (AEL), wherein at least one of the AEL and the CEL contains a dye, and the dye has a viscosity of at least 7500 M. －１ cm －１ wherein the color characteristics of the CEL are visibly different from the color characteristics of the AEL, the AEL and the CEL do not contain a dye that forms ions when irradiated with light, the BPM does not contain a perfluorinated polymer, and the BPM comprises a coated cation exchange layer (CEL) and / or a coated anion exchange layer (AEL) on and / or in a porous support.

2. 2. The BPM of claim 1, wherein the dye is a Norrish Type II photoinitiator having an absorption maximum at wavelengths greater than 400 nm when measured in one or more of the following solvents at a temperature of 23°C: water, ethanol, and toluene.

3. 3. The BPM of claim 1 or 2, wherein the dye does not contain transition metal ions.

4. The BPM of any one of claims 1 to 3, wherein the dye comprises a conjugated system having at least 10 delocalized electrons.

5. 5. The BPM of any one of claims 1 to 4, wherein the AEL and the CEL each contain a dye, and the dye present in the AEL is different from or the same as the dye present in the CEL.

6. The visible difference in color properties is expressed as ΔE according to CIEDE 2000. ００ The BPM according to any one of claims 1 to 5, comprising a difference of at least 4.

7. 7. The BPM according to any one of claims 1 to 6, wherein at least one of the AEL and the CEL has a color value of less than 90 and a color value of at least 10, expressed by L' according to CIEDE2000.

8. 8. The BPM according to any one of claims 1 to 7, wherein at least one of the AEL and the CEL has a saturation of at least 5, expressed by a chroma C' according to CIEDE2000.

9. The BPM according to any one of claims 1 to 8, wherein the color characteristics of the AEL and / or CEL are substantially uniform.

10. 10. The BPM according to any one of claims 1 to 9, wherein the CEL and / or AEL is obtainable by curing a curable composition comprising a dye that functions as a photoinitiator and a coinitiator that is capable of generating free radicals in a reaction with the dye when the dye is in an electronically excited state.

11. The BPM according to any one of claims 1 to 10, wherein the dye is a photoinitiator derived from xanthene, flavin, curcumin, porphyrin, anthraquinone, phenoxazine, camphorquinone, phenazine, acridine, phenothiazine, xanthone, thioxanthone, thioxanthene, acridone, flavone, coumarin, fluorenone, quinoline, quinolone, naphthaquinone, quinolinone, arylmethane, azo, benzophenone, carotenoid, cyanine, phthalocyanine, dipyrrin, squarine, stilbene, styryl, triazine, or anthocyanin.

12. The BPM of any one of claims 1 to 11, wherein the dye is not covalently attached to an AEL or a CEL.

13. The BPM according to any one of claims 1 to 12, (a) the dye does not contain a transition metal ion; (b) the visible difference in color characteristics between the AEL and the CEL makes the layers distinguishable by the human eye and by automated sensors or similar recognition systems; (c) the dye comprises a conjugated system having at least 10 delocalized electrons; BPM.

14. An electrochemical device comprising the BPM of any one of claims 1 to 13.

15. 1. A process for manufacturing a bipolar membrane (BPM) comprising a cation exchange layer (CEL) and an anion exchange layer (AEL), wherein the color characteristics of the CEL are visibly different from the color characteristics of the AEL, the process comprising, in either order or simultaneously, curing a first curable composition to form the AEL and curing a second curable composition to form the CEL, wherein at least one of the first and second curable compositions contains a dye, and the dye has a viscosity of at least 7500 M. －１ cm －１ wherein the AEL and CEL do not contain a dye that forms ions when irradiated with light; the BPM does not contain a perfluorinated polymer; and the BPM comprises a coated cation exchange layer (CEL) and / or a coated anion exchange layer (AEL) on and / or in a porous support.

16. one or both of the first curable composition and the second curable composition comprises: (a) one or more curable monomers containing at least one anionic or cationic group; (b) a photoinitiator dye; (c) optionally, a coinitiator; (d) optionally, a curable monomer that is free of anionic and cationic groups; and (e) optionally, a solvent 16. The process of claim 15, comprising:

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