Sealant for sealing against hydrogen

Abstract

The present invention provides for the use of a composition comprising at least one epoxy-functional silicone-epoxide copolymer (A) as sealant for sealing against hydrogen; a sealing element producible by curing said composition; an apparatus for producing and / or conducting and / or storing and / or converting and / or controlling hydrogen that has at least two joining partners separated from one another by said sealing element; a method of producing said apparatus; and a method of operating said apparatus.

Description

[0001] Sealant for sealing against hydrogen

[0002] The present invention relates to sealants for sealing against hydrogen.

[0003] Hydrogen technology is considered groundbreaking in mobility, energy generation, and chemistry, and is particularly used in fuel cells. The transportation, storage, and conversion of hydrogen require gas-tight containers, pipes, and associated seals, which represent the weak points of many of these systems. Hydrogen molecules can easily diffuse through common sealing materials such as elastomers, especially silicone elastomers. While thermosets generally have a higher barrier effect than elastomers, they are often too hard and brittle to be considered as sealing materials, as is particularly the case with epoxy resins.

[0004] It is well known that seals for hydrogen sealing are made from ethylene-propylene-diene rubber (EPDM; M group) and acrylonitrile-butadiene rubber (AB or NBR). Silicone elastomers are also used.

[0005] DE 11 2008 000 192 B4, for example, discloses a sealing material for a high-pressure hydrogen container, which mainly comprises a silicone rubber consisting of a dimethylsiloxane segment, a methylvinylsiloxane segment and a diphenylsiloxane segment, wherein the sealing material mainly comprises the silicone rubber and contains blended therein at least one element selected from the group consisting of ethylenepropylenediene rubber (EPDM), ethylenepropylene rubber (EPM), natural rubber (NR), isoprene rubber (IR) and nitrileisoprene rubber (NIR).

[0006] As already explained above, elastomeric sealing materials made of silicone have a high degree of flexibility, but have the disadvantage of high hydrogen permeability.

[0007] F. Hübner, M. Hoffmann, N. Sommer, V. Altstadt, A. Scherer, T. Dickhut, H. Ruckdäschel describe in "Temperature-dependent fracture behavior oftenopreg epoxy resins for cryogenic liquid hydrogen composite vessels: The influence of polysiloxane tougheners on the resin yield behavior", Polymer Testing, Volume 113, September 2022, 107678

[0008] (https: / / doi.orci / 10.1016 / i.oolvmertestinci.2022.107678) describes the use of epoxy resin towpregs for cryogenic liquid hydrogen containers. To improve fracture toughness at low temperatures, a polysiloxane core-shell particle is added to the epoxy resin as a toughener. These particles already reduce the brittleness of epoxies and make them ductile, but do not increase flexibility. Cured epoxy resins therefore do not exhibit the flexibility desired for sealing materials, even when modified with tougheners. Accordingly, the use of towpregs as sealing materials is not described. The towpregs are used solely for the production of hydrogen containers.

[0009] J. Balthasar, T. Lubenow, A. Funck, and S. Sprenger describe compositions based on polysiloxane-epoxy copolymers in "Using polysiloxane-epoxy copolymers for flexible electronics," adhesion KLEBEN+DICHTEN, Volume 66, Issue October 2022, pp. 30-33 (https: / / doi.orq / 10.1007 / s35145-022-1118-5) and in "Improving thermal and chemical stabilities of electronic epoxies using polysiloxane copolymers. Part II: block copolymers," Proc. of the 3rd International Conference on Electrical, Communication and Computer Engineering (ICECCE), 12-13 June 2021, Kuala Lumpur, Malaysia. These compositions are intended as adhesives or potting compounds for electronic components. The use of such compositions as sealants for sealing against hydrogen is not described.

[0010] There was therefore still a need for sealing materials whose hydrogen permeability and elasticity or hardness could be specifically adjusted depending on the application, and which preferably also have sufficient elasticity in addition to low hydrogen permeability, especially at very low temperatures.

[0011] The object of the present invention was therefore to provide such sealing materials.

[0012] Surprisingly, it has now been found that the use of a composition containing at least one epoxy-functional silicone-epoxy copolymer (A) as a sealant for sealing against hydrogen solves this problem.

[0013] This composition also has the advantage that it can be formulated either as a liquid or paste. It is therefore easily processed as a sealant. By curing this composition or sealant, sealing elements can be obtained whose hydrogen permeability and elasticity or hardness can be specifically adjusted depending on the application. In particular, sealing elements can be produced that exhibit both low hydrogen permeability and sufficient elasticity, especially at very low temperatures. The use of epoxy-functional silicone-epoxy copolymers (A) surprisingly leads to a combination of the advantageous properties of both polymer classes – epoxy resins and silicones.

[0014] The use of epoxy-functional silicone-epoxy copolymers (A) alone or in combination with epoxy resins offers the following specific advantages: - Under conditions of severe thermal stress and thermal cycling, the use of silicone-epoxy copolymers (A) leads to stress reduction due to its flexibilizing effect and prevents microcracks and fatigue phenomena. The sealing element therefore achieves higher fatigue strength.

[0015] - Compared to conventional silicone seals, chemical resistance is significantly improved.

[0016] - The low-temperature behavior is similar to that of silicone sealants, but mechanically more stable sealing materials with greatly improved barrier properties are obtained.

[0017] - In contrast to the solid sealing materials made of NBR, EPDM or FKM, the sealant can be applied in liquid or pasty form, much like silicone sealants, but has the advantage over silicone sealants that the barrier effect against hydrogen is much higher.

[0018] - Due to the epoxy groups, the sealant also adheres well and permanently to numerous surfaces.

[0019] A first object of the invention is therefore the use of a composition containing at least one epoxy-functional silicone-epoxy copolymer (A) as a sealant for sealing against hydrogen.

[0020] Another object of the invention is a sealing element which can be produced by curing this composition.

[0021] Yet another subject of the invention is a device for generating and / or conducting and / or storing and / or converting and / or controlling hydrogen, comprising at least two joining partners which are separated from one another by the sealing element according to the invention.

[0022] Yet another subject of the invention is a method for producing such a device with the following, non-chronological steps: a) providing a first joining partner; b) providing a second joining partner; c) providing the composition to be used according to the invention; d) applying the composition to the first and / or the second joining partner; e) joining the joining partners such that the composition contacts the first and the second joining partner; f) curing the composition.

[0023] Yet another object of the invention is a method for operating a device according to the invention, comprising the following steps: carrying out the method according to the invention for producing the device;

[0024] Applying hydrogen to the device in such a way that hydrogen contacts both joining partners and the cured composition.

[0025] Advantageous embodiments of the invention are specified in the dependent claims, the examples, and the description. Furthermore, it is expressly pointed out that the disclosure of the subject matter of the present invention includes all combinations of individual features of the present or subsequent description of the invention and the patent claims. In particular, embodiments of one subject matter of the invention also apply mutatis mutandis to the embodiments of the other subject matter of the invention.

[0026] The subject matter of the invention and its preferred embodiments are described below by way of example, without intending to limit the invention to these exemplary embodiments. If ranges, general formulas, or classes of compounds are specified below, these are intended to encompass not only the corresponding ranges or groups of compounds explicitly mentioned, but also all subranges and subgroups of compounds that can be obtained by removing individual values ​​(ranges) or compounds. If documents are cited within the scope of this description, their entire content is intended to be part of the disclosure of the present invention.

[0027] Unless otherwise stated, any measured values, parameters, or material properties specified below that are determined by measurement are measured at 25 °C and preferably at atmospheric pressure. At atmospheric pressure is defined as a pressure of 101325 Pa.

[0028] As already explained above, a first object of the invention is the use of a composition containing at least one epoxy-functional silicone-epoxy copolymer (A) as a sealant for sealing against hydrogen.

[0029] The sealant is preferably a hardening, liquid or pasty material for sealing openings such as joints, gaps, holes, and the like, which may be subject to movement. It is advantageous if the sealant adheres to the edge(s) of the opening. However, the sealant can also initially be used to produce a preferably permanently elastic sealing element, which is subsequently used to seal said openings. Other common names for sealant are joint compound, sealing compound, joint sealant, soft seal, or liquid sealant. According to the invention, the sealant is used to seal against hydrogen. The sealing against hydrogen preferably takes place while the sealant is in its liquid and pasty state, but at the latest as soon as the sealant has hardened.

[0030] Hydrogen here refers to molecular hydrogen (H2). Hydrogen can be in gaseous or liquid form. Hydrogen can exist as a pure substance or in a mixture with other chemical substances, for example, as a component of a gas or as a component of a liquid.

[0031] The epoxy-functional silicone-epoxy copolymer (A) has at least one epoxy group. In the epoxy group, two carbon atoms and one oxygen atom form a three-membered ring structure in the form of a cyclic ether. Carbon atoms can be saturated with hydrogen atoms or other substituents. The epoxy group is preferably part of a glycidyl ether group or a 3,4-epoxycyclohexyl group, but especially a glycidyl ether group.

[0032] It is preferred that the at least one epoxy-functional silicone-epoxy copolymer (A) contains at least one structural unit (I), (II) and (III) wherein: n is an integer from 1 to 1000, preferably from 1 to 100, in particular from 5 to 50;

[0033] L is each independently selected from the divalent radicals sulfonyl, methanediyl, propane-2,2-diyl and 1,1,1,3,3,3-hexafluoro-2,2-propane-2,2-diyl, preferably propane-2,2-diyl; R is each independently selected from the monovalent hydrocarbon radicals having 1 to 16 carbon atoms, preferably from the group consisting of methyl, ethyl, propyl and phenyl, in particular methyl.

[0034] The bonding sites of structural units (I), (II), and (III) are marked with an asterisk (*). Structural units (I) and (II) are therefore divalent, and structural unit (III) is monovalent. In addition to structural units (I), (II), and (III), the epoxy-functional silicone-epoxy copolymer (A) typically contains further atomic groups that link structural units (I), (II), and (III) together. These atomic groups are preferably divalent atomic groups. It is further preferred that the atomic groups consist of carbon, hydrogen, and oxygen atoms and preferably do not exceed 15 non-hydrogen atoms.

[0035] Structural unit (I) essentially serves to make the cured composition elastic or flexible. Structural units (II) and (III) essentially serve to improve the barrier effect against hydrogen. Structural unit (III) also serves to cure the sealant. However, it can also improve adhesion to surfaces, for example, to the edge(s) of the opening to be sealed, provided the sealant is brought into contact with said opening before it cures.

[0036] The property profile of the composition can be specifically adjusted over a wide range via the mass fraction of the structural units (I), (II) and (III) in the epoxy-functional silicone-epoxy copolymer (A).

[0037] It is preferred that the mass fraction of all structural units (I) based on the total mass of all epoxy-functional silicone-epoxy copolymers (A) is from 10 to 80%, preferably from 20% to 70%, in particular from 30% to 60%.

[0038] It is also preferred that the mass fraction of all structural units (II) and (III) together, based on the total mass of all epoxy-functional silicone-epoxy copolymers (A), is from 20% to 90%, preferably from 30% to 80%, in particular from 40% to 70%.

[0039] The hydrogen permeability and the mechanical properties are also influenced by the crosslinking density of the cured composition. The crosslinking density, in turn, depends on the epoxy equivalent weight of the epoxy-functional silicone-epoxy copolymer (A). The epoxy equivalent weight describes the mass in grams that contains one mole of epoxy groups. It is preferred that the at least one epoxy-functional silicone-epoxy copolymer (A) has an epoxy equivalent weight of 500 g / mol to 1300 g / mol, preferably of 500 g / mol to 1000 g / mol, in particular of 600 g / mol to 900 g / mol. If multiple silicone-epoxy copolymers (A) are used, the epoxy equivalent weight refers to the mixture of these silicone-epoxy copolymers (A). The epoxy equivalent weight is also often given in the unit g / eq, where 1 g / eq = 1 g / mol.The epoxy equivalent weight is preferably determined according to DIN EN ISO 3001 (November 1999) or according to ASTM D 1652 (January 2011), but in particular according to DIN EN ISO 3001 (November 1999).

[0040] A suitable epoxy-functional silicone-epoxy copolymer (A) is commercially available, for example, under the name ALBIFLEX® 297 (Evonik).

[0041] In addition to the at least one epoxy-functional silicone-epoxy copolymer (A), the sealant may contain further components.

[0042] It is preferred that the composition contains at least one hardener (B), preferably selected from the group consisting of amine hardeners, anhydride hardeners, phenolic resins, mercaptan hardeners, polyamide hardeners, isocyanate hardeners, imidazole hardeners, dicyandiamide, and diaminodiphenyl sulfone, in particular selected from the group consisting of amine hardeners and anhydride hardeners. Polyamines are particularly preferred as amine hardeners. Suitable hardeners are commercially available, for example, under the names ANCAMINE® (Evonik) and ANCAMIDE® (Evonik). Particularly suitable hardeners are ANCAMINE® 2167 (Evonik), ANCAMINE® 2719 (Evonik), and ANCAMIDE® 910 (Evonik). In general, however, all customary hardeners known to those skilled in the art for curing epoxy resins can be used.

[0043] It is also preferred that the composition contains at least one silicon-free epoxy resin (C). "Silicon-free" means that the epoxy resin (C) contains no silicon atoms. The epoxy resin (C) is therefore not an epoxy-functional silicone-epoxy copolymer. The epoxy resin (C) is preferably selected from the group consisting of novolak epoxy resins, cycloaliphatic epoxy resins, glycidyl ester epoxy resins, bisphenol diglycidyl ether epoxy resins, in particular selected from bisphenol A diglycidyl ether epoxy resins and bisphenol F diglycidyl ether epoxy resins. Suitable epoxy resins (C) are commercially available, for example, under the name Epilox® (Leuna-Harze). A particularly suitable epoxy resin is Epilox® A 17-01 (Leuna-Harze). As a rule, however, all common epoxy resins known to the expert can be used.

[0044] It is also preferred that the composition contains at least one silicon-free reactive diluent (D). "Silicon-free" here also means that the reactive diluent (D) contains no silicon atoms. The reactive diluent (D) is therefore not an epoxy-functional silicone-epoxy copolymer. The reactive diluent (D) has epoxy groups (oxirane groups) and / or oxetane groups. The reactive diluent (D) preferably contains epoxy groups. It is therefore preferred that the reactive diluent (D) is epoxy-functional. The reactive diluent (D) preferably has a lower viscosity than the epoxy-functional silicone-epoxy copolymer (A) and than the epoxy resin (C), if the latter is present in the composition. The reactive diluent (D) is preferably selected from aliphatic glycidyl ethers, in particular from aliphatic diglycidyl ethers.It is particularly preferred that the reactive diluent (D) is selected from the group consisting of α,α-alkanediol glycidyl ethers and polyalkylene glycol diglycidyl ethers. Suitable reactive diluents (D) include, for example, 1,6-hexanediol diglycidyl ether (HDDGE), also commercially available under the name Grilonit® RV 1812 (Ems-Chemie Holding AG), and polytetramethylene ether glycol diglycidyl ether (polyTHF diglycidyl ether, poly(tetramethylene oxide) diglycidyl ether), also commercially available under the name Ipox® RD 21 (Ipox Chemicals). In general, however, all customary reactive diluents known to the skilled person for diluting epoxy resins can be used.

[0045] The mass fraction of (A), (B), (C) and (D) allows the hydrogen permeability and the elasticity or hardness as well as the curing speed to be specifically adjusted depending on the application.

[0046] It is therefore preferred that the composition contains the following components, based on the total mass of the composition:

[0047] - the at least one epoxy-functional silicone-epoxy copolymer (A) in a mass fraction of 3% to 99%, preferably 5% to 90%, in particular 10% to 80%;

[0048] - the at least one hardener (B) in a mass fraction of 1% to 50%, preferably 3% to 45%, in particular 5% to 40%; and

[0049] - the at least one silicon-free epoxy resin (C) in a mass fraction of 0% to 90%, preferably 5% to 80%, in particular 8% to 80%,

[0050] - the at least one silicon-free reactive diluent (D) in a mass fraction of 0% to 60%, preferably 5% to 50%, in particular 10% to 40%.

[0051] The amounts of (A), (B), (C), and (D) used are preferably adjusted so that, after curing of the composition, complete conversion of the epoxy groups and the epoxy-reactive groups has occurred. Epoxy-reactive groups are understood to be those groups that react with the epoxy groups during the curing of the composition. Epoxy-reactive groups are preferably aminic NH groups.

[0052] In one embodiment of the invention, the epoxy-functional components of the composition, i.e., the at least one epoxy-functional silicone-epoxy copolymer (A), optionally the at least one silicon-free epoxy resin (C), and optionally the at least one silicon-free reactive diluent (D), are stored separately from the at least one hardener (B), and the composition is prepared by mixing said compounds shortly before its use as a sealant. This prevents premature curing of the composition, e.g., during storage.

[0053] It is therefore preferred that the composition is prepared by mixing components of a multi-component composition, wherein the multi-component composition comprises a component (I) containing the at least one epoxy-functional silicone-epoxy copolymer (A) and a component (II) containing the at least one hardener (B).

[0054] It is preferred that component (I) further contains the at least one silicon-free epoxy resin (C), if a silicon-free epoxy resin (C) is used.

[0055] It is also preferred that component (I) further contains the at least one silicon-free reactive diluent (D), provided that a silicon-free reactive diluent (D) is used.

[0056] The multi-component composition is preferably a two-component composition consisting of the aforementioned components (I) and (II).

[0057] It is therefore particularly preferred that the composition is prepared by mixing components of a two-component composition, wherein the two-component composition consists of a component (I) which contains the at least one epoxy-functional silicone-epoxy copolymer (A) and optionally the at least one silicon-free epoxy resin (C) and optionally the at least one silicon-free reactive diluent (D), and a component (II) which contains the at least one hardener (B).

[0058] Alternatively, it is also possible for the multi-component composition to comprise a further component (III) containing the at least one silicon-free epoxy resin (C). In this case, the at least one epoxy-functional silicone-epoxy copolymer (A), the at least one silicon-free epoxy resin (C), and the at least one hardener (B) can be stored separately from one another. Optionally, component (I), which contains the at least one epoxy-functional silicone-epoxy copolymer (A), and / or component (III), which contains the at least one silicon-free epoxy resin (C), can additionally contain the at least one silicon-free reactive diluent (D). Alternatively, it is also possible for the multi-component composition to comprise a further component (IV) containing the at least one silicon-free reactive diluent (D).In this case, the at least one epoxy-functional silicone-epoxy copolymer (A), the at least one silicon-free epoxy resin (C), the at least one silicon-free reactive diluent (D) and the at least one hardener (B) can be stored separately from one another.

[0059] It is preferred that the components of the multi-component composition be stored separately prior to mixing. It is further preferred that the components of the multi-component composition be mixed at the site of use.

[0060] It should be noted, however, that it is not necessary for the components to be stored separately and that the mixing of the components of the multi-component composition only takes place at the place of use.

[0061] In a further alternative embodiment of the invention, the composition is provided as a one-component system, meaning that the composition is not prepared at the site of its use by mixing two or more of its constituents, but rather the composition is prepared at another location and only later transported to the site of use. To prevent premature curing of the composition, in the case of a one-component system, latent hardeners are preferably used as hardeners (B). These hardeners are only activated at the site of use of the composition as a sealant by an external stimulus, such as heat or electromagnetic radiation, and lead to hardening of the composition. Latent hardeners include, for example, imidazole hardeners, dicyandiamide, and diaminodiphenyl sulfone.

[0062] The multi-component composition is preferably stored in a kit. The kit accordingly comprises two or more parts for separate storage of the components.

[0063] It is further preferred that the composition be liquid or pasty. It is particularly preferred that the composition has a viscosity of 0.5 to 100 Pa·s, preferably 1 to 90 Pa·s, in particular 2 to 80 Pa·s, measured at a temperature of 25 °C and a shear rate of 2 s 1 The viscosity is preferably determined according to DIN EN ISO 3219-2 (August 2021)

[0064] J. Balthasar, T. Lubenow, A. Funck, and S. Sprenger describe precisely such compositions that are suitable for the use according to the invention in the publications already cited in the introduction, "Using polysiloxane-epoxy copolymers for flexible electronics," adhesion KLEBEN+DICHTEN, Volume 66, Issue October 2022, pp. 30-33 (https: / / doi.orq / 10.1007 / s35145-022-1118-5) and "Improving thermal and chemical stabilities of electronic epoxies using polysiloxane copolymers. Part II: block copolymers," Proc. of the 3rd International Conference on Electrical, Communication and Computer Engineering (ICECCE), June 12-13, 2021, Kuala Lumpur, Malaysia.

[0065] Another object of the invention is a sealing element which can be produced by curing the composition.

[0066] The sealing element is preferably produced in situ, namely by curing the composition at the intended location of the sealing element.

[0067] It is preferred that the hydrogen permeation coefficient (H2 permeation coefficient) of the sealing element is given in 10' 19 «m 2 / (Pa«s) is from 0 to 9000, preferably from 10 to 7000, in particular from 100 to 5000. The hydrogen permeation coefficient is preferably determined according to DIN 53536 (October 1992).

[0068] It is further preferred that the Shore hardness of the sealing element at 25 °C

[0069] - from 20 A to 150 A, preferably from 50 A to 100 A, in particular from 60 A to 100 A; and / or - from 5 D to 100 D, preferably from 10 D to 90 D, in particular from 15 D to 85 D; The Shore hardness is preferably determined according to DIN ISO 7619-1 (February 2012) at 25 °C.

[0070] The invention further relates to a device for generating and / or conducting and / or storing and / or converting and / or controlling hydrogen, comprising at least two joining partners separated from one another by the sealing element according to the invention. The joining partners are components of the device whose joint is sealed against hydrogen by means of the sealing element.

[0071] Examples of devices within the meaning of the invention are electrolysers for generating hydrogen by electrochemical splitting of water, fuel cells for providing electrical energy by converting hydrogen and oxygen to water, reactors for converting hydrogen to other chemicals, pipelines, hose lines, tanks, valves, buffers and other fittings for conducting, storing and controlling gaseous or liquid hydrogen as well as the associated fittings.

[0072] It is particularly preferred that the device is a hydrogen storage device, a hydrogen line, a valve, a fuel cell, or an electrolyzer for generating hydrogen. It is further particularly preferred that the device or the hydrogen storage device is a cryogenic container, in particular a cryogenic tank. The cryogenic container preferably serves to store liquid (liquefied) hydrogen (LH2), cryogenically compressed hydrogen (CCH2), and / or subcooled liquid hydrogen (sLH2). Suitable cryogenic containers are described, for example, in the following standards:

[0073] EN 1251-1 to -2 and EN ISO 21029-2 for transportable vacuum-insulated containers with a capacity not exceeding 1000 litres,

[0074] EN 13458-1 to -2 and EN ISO 21009-2 for stationary vacuum-insulated vessels,

[0075] EN 13530-1 to -2 and EN ISO 20421-2 for large transportable vacuum-insulated vessels, EN 14197-1 to -3 for stationary non-vacuum-insulated vessels,

[0076] EN 14398-1 to -3 for large transportable non-vacuum insulated containers.

[0077] Cryogenic containers, in particular cryogenic tanks, which are suitable for hydrogen storage, are well known to those skilled in the art.

[0078] In a preferred embodiment, the cryogenic container or cryogenic tank is a vacuum-insulated steel container. The cryogenic containers are preferably constructed as double-walled stainless steel containers, with the spaces between them evacuated for better insulation.

[0079] In an alternative preferred embodiment, the cryogenic container or cryogenic tank consists of carbon fiber-reinforced composite materials, which are preferably manufactured using a winding process. Carbon fiber strands impregnated with an epoxy resin / hardener mixture are wound around a gas-tight hollow body (liner), e.g., made of PA 6 or PA 12, and then thermally cured. A variant of this is the so-called Type V tank, which is constructed without a plastic liner. The particular challenges include particularly high impact strength, even at extremely low temperatures, particularly good fatigue resistance, particularly high pressure resistance, and, of course, good gas impermeability to hydrogen. This property profile can be achieved through the inventive use of a composition based on the epoxy-functional silicone-epoxy copolymer (A).

[0080] The cryogenic container can have one or more supply and discharge lines. The supply line can be different from the discharge line. Or the supply line can also be the discharge line. The cryogenic container can also have one or more closable openings, such as a lid, through which the contents can be accessed. It is further preferred that the device comprises an interior space that is at least partially bounded by both joining partners and the sealing element, wherein the interior space can be pressurized with hydrogen such that the hydrogen contacts both joining partners and the sealing element. The sealing element thus prevents the hydrogen from escaping from the interior space of the device to the outside.

[0081] Alternatively, however, it is also preferred that the interior space be exposed to hydrogen from the outside, such that the hydrogen contacts both joining partners and the sealing element from the outside. In this case, the sealing element prevents hydrogen from penetrating the interior of the device from the outside.

[0082] The sealant is particularly preferably used for bonding, joining, and sealing bipolar plates in fuel cells or electrolyzers. A bipolar plate serves to electrically connect two adjacent electrochemical cells in series. For this purpose, the bipolar plate is placed between the anode of one cell and the cathode of the other cell (or vice versa). Technically designed electrolyzers or fuel cells usually comprise a plurality of electrochemical cells connected in series via bipolar plates. Accordingly, such an electrolyzer or fuel cell comprises a plurality of bipolar plates. The bipolar plates must be sealed gas-tight to prevent mixing of hydrogen gas and oxygen gas, thus preventing the formation of explosive detonating gas. This sealing can be achieved excellently with the sealing element according to the invention because it exhibits a high degree of impermeability to hydrogen gas.In addition, the composition can be easily processed during the assembly of the electrolyzer or fuel cell by applying it in liquid or pasty form to the bipolar plates when stacking the cells and bipolar plates and then curing it in the stack.

[0083] A further subject matter of the invention is a method for producing the device according to the invention with the following, non-chronological steps: a) providing a first joining partner; b) providing a second joining partner; c) providing the composition to be used according to the invention; d) applying the composition to the first and / or the second joining partner; e) joining the joining partners such that the composition contacts the first and the second joining partner; f) curing the composition.

[0084] This process implements the concept of producing the sealing element in situ. Examples of joining partners include adjacent bipolar plates or electrodes in the stack of a fuel cell or electrolyzer. However, components of hydrogen tanks or fittings of hydrogen lines are also considered as joining partners, which can be sealed using the composition according to the invention.

[0085] It is preferred that the composition is provided and / or applied in a liquid or pasty state.

[0086] It is further preferred that the curing takes place after application and before joining; or that the curing takes place after application and after joining; or that the curing takes place after application and during joining.

[0087] If the sealing element not only provides a sealing effect but also an adhesive effect between the joining partners, curing can also be considered part of the joining process. This is the case when the composition, and thus also the subsequent sealing element, adheres to the surfaces of both joining partners. The sealing element then also assumes the function of a connecting element. However, material pairings are also conceivable in which the composition adheres only to one of the two joining partners. In this case, the sealing element also adheres only to one joining partner. Consequently, the joining partners must be joined together using a separate connecting element, such as a screw connection.

[0088] Yet another object of the invention is a method for operating the device according to the invention with the following steps:

[0089] - carrying out the method according to the invention for producing the device;

[0090] - Applying hydrogen to the device in such a way that hydrogen contacts both joining partners and the cured composition.

[0091] In this operating process, the device is first manufactured, sealing the two joining partners. During commissioning, the device is then pressurized with hydrogen.

[0092] The following examples illustrate the present invention by way of example, without the invention, the scope of which is apparent from the entire description and claims, being intended to be limited to the embodiments mentioned in the examples.

[0093] Raw materials / materials: The raw materials and materials used are listed in Table 1.

[0094] Table 1: Raw materials and materials Determination of impact strength (impact flexural strength):

[0095] Preparation of samples:

[0096] Variant 1 (for samples 1 to 8 and a to c): Sheets with a thickness of 2 mm were produced. The components according to Table 2a and 2b were weighed, mixed, and filled into a suitable PTFE mold. The surface was then smoothed with a wooden spatula. The sheets were cured for 24 hours at room temperature and demolded with a painter's spatula.

[0097] Variant 2 (for samples 9 to 11): Plates with a thickness of 2 mm were produced. The components were weighed and mixed according to Table 2a and then poured into a steel casting mold using a wire through a filler neck until the mold was completely filled. The plates were cured for 24 hours at room temperature. After curing, the steel casting mold was unscrewed and the plate removed. The filler neck was removed.

[0098] The samples from the softer plates (samples 1, 2, 3, and 7) were punched out using a punching knife. The resulting specimen was an S2 bar according to DIN 53504 (March 2017). For the harder plates (samples 4, 5, 6, 8, 9, 10, and 11), the specimens had to be milled using a CNC milling machine and diamond cutter. The specimen here was also a standard S2 bar. For EPDM and NBR, standard S2 bars were also punched out of the rubber mats, just as in the case of the softer plates (samples 1, 2, 3, and 7).

[0099] Table 2a: Sample composition a]: according to the invention

[0100] [b]: not according to the invention Table 2b: Sample composition a]: according to the invention

[0101] Test procedure: The determination of the Charpy impact strength was carried out according to DIN EN ISO 179-1 / 1 eU (November 2010).

[0102] To determine impact strength at -196 °C, liquid nitrogen was first filled into a Dewar flask. The specimens were immersed in the liquid nitrogen until no more bubbles appeared, but for at least one minute, and then removed for measurement.

[0103] To determine impact strength at -78.5 °C, the specimens were placed on a metal sheet and covered with a second metal sheet. Dry ice was spread above and below the sheet. The specimens were cooled there for 10 minutes and then removed individually for measurement.

[0104] After cooling to -196 °C or -78.5 °C, the respective specimen was quickly placed on the specimen holder of the Zwick pendulum impact tester, the pendulum was started, and the specimen was struck. The displayed value in joules [J] was noted and then converted to the previously determined specimen dimensions to an absorbed impact energy, based on the initial cross-sectional area of ​​the specimen [kJ / m 2 ] converted. At least five specimens were tested, and a mean value was calculated from these and the standard deviation was calculated.

[0105] Test results:

[0106] The determined values ​​for impact strength at -196 °C and -78.5 °C can be found in Tables 3a and 3b, respectively.

[0107] Determination of Shore hardness:

[0108] Preparation of samples:

[0109] To determine Shore A and D hardnesses, a 6 mm thick specimen was required. The components were weighed and mixed according to Table 2a. The mixture was then poured into an aluminum tray until a thickness of 6 mm was reached. Curing took place for at least 24 hours at room temperature. No samples were prepared for NBR and EBDM; instead, the Shore hardness values ​​specified by the manufacturer were used.

[0110] Experimental procedure:

[0111] The Shore hardness was determined according to DIN ISO 7619-1 (February 2012).

[0112] Test results:

[0113] The Shore hardness values ​​determined or specified by the manufacturer can be found in Table 3a. Determination of the glass transition temperature:

[0114] Preparation of samples:

[0115] To determine the glass transition temperature, sheets with a thickness of 2 mm were prepared. The components were weighed according to Table 2b, mixed, and poured into a suitable PTFE mold. The surface was then smoothed with a wooden spatula. The sheets were cured for 24 hours at room temperature and demolded with a painter's spatula. A test specimen measuring 25 mm in length and 10 mm in width was then cut from the cured sheet using scissors.

[0116] Experimental procedure:

[0117] The glass transition temperature was determined using DMA (dynamic mechanical analysis). The measurement was performed at a frequency of 1 Hz and a heating rate of 3 K / min. The glass transition temperature is the temperature at which the loss factor tan δ reaches a maximum.

[0118] Test results:

[0119] The determined values ​​for the glass transition temperature can be found in Table 3b.

[0120] Table 3a: mechanical properties a]: according to the invention

[0121] [b]: not in accordance with the invention

[0122] [c]: no values ​​or results could be determined because the samples did not break during the measurement

[0123] [d]: Information from the manufacturer (Steinbach AG)

[0124] Table 3b: mechanical properties a]: Determination of hydrogen permeability according to the invention

[0125] Preparation of samples:

[0126] Sheets with a thickness of 2 mm were produced. The components were weighed according to Table 4, mixed, and poured into a suitable PTFE mold. The surface was then smoothed with a wooden spatula. The sheets were cured for 24 hours at room temperature and demolded with a painter's spatula.

[0127] Table 4: Sample composition a]: according to the invention

[0128] Experimental procedure:

[0129] The permeation measurements were carried out at room temperature using a measurement setup analogous to DIN 53536. The measurements were carried out three times for samples 1, 2 and 6, and twice for samples 3, 4 and 5. In contrast to DIN 53536, a gas mixture of 1 bar air and 1 bar hydrogen (absolute pressure 2 bar) was used. a bs, partial pressure H2 = 1 banei) was used and measured discontinuously until equilibrium was reached, rather than continuously. The FL permeation coefficient was determined using the pressure volume flow rate, the sample and measurement chamber geometry, and the FL partial pressure. The results are presented in Table 5. Test results:

[0130] The determined values ​​for the H2 permeation coefficient can be found in Table 5.

[0131] Table 5: Results of the permeation measurements a]: according to the invention

[0132] Discussion of the results

[0133] For samples 1, 2, 3, 4, 5, 6, and 10, the same hardener (B) and the same silicon-free epoxy resin (C) were used. These samples therefore form a useful comparison series. For samples 7, 8, 9, and 11, the same hardener (B) and the same silicon-free epoxy resin (C) were also used. These samples therefore form another useful comparison series. In both test series, the mass fraction of the silicone-epoxy copolymer (A) decreases with increasing sample number.

[0134] The comparison shows (see Table 3a) that the impact strength at -196 °C and -78.5 °C increases with increasing mass fraction of silicone-epoxy copolymer (A), although it should be noted that the standard deviation of the measurement is comparatively high. At a very high mass fraction of silicone-epoxy copolymer (A), the samples do not fracture at all. With increasing mass fraction of silicone-epoxy copolymer (A), the samples show an improvement in their mechanical properties, even at very low temperatures. This makes the compositions ideally suited as sealants for cryogenic containers used for storing liquefied hydrogen. It should be noted that high impact strength at -196 °C is particularly important for cryogenic containers (liquid H2, Type V).

[0135] It is also clear that the Shore hardness D decreases with increasing mass fraction of silicone-epoxy copolymer (A). This is also observed for the Shore hardness A in the first test series (samples 1, 2, 3, 4, 5, 6, 10). In the second test series (samples 7, 8, 9, 11), the Shore hardness A remains virtually unchanged within the expected error range. However, when looking at the Shore hardness values ​​as a whole, it can be seen that the samples become more flexible or elastic as the mass fraction of the silicone-epoxy copolymer (A) increases.

[0136] With a high mass fraction of silicone-epoxy copolymer (A), Shore hardnesses similar to those of EPDM or NBR are achieved. The impact strength at -78.5 °C is comparable to that of EPDM at a high mass fraction of silicone-epoxy copolymer (A), and comparable to that of NBR at low mass fractions. However, the impact strength at -196 °C is higher in the case of the compositions according to the invention than in the case of EPDM and NBR.

[0137] Samples 12, 13, 14, 15, and 16 also used the same hardener (B) and the same silicon-free epoxy resin (C). These samples also represent a useful comparison series. As with the first two test series, the mass fraction of the silicone-epoxy copolymer (A) decreases with increasing sample number. It is clearly evident that the H2 permeation coefficient increases with increasing mass fraction of the silicone-epoxy copolymer (A). This correlates with the silicone content in the composition. However, it should be noted that the hydrogen barrier effect is high for all of these samples.

[0138] In summary, it can be stated that the silicone-epoxy copolymer (A) improves the mechanical properties (high impact strength), ensures high flexibility / elasticity (reduction in Shore hardness), and also provides a high barrier effect (reduction in the H2 permeation coefficient). The corresponding sealants are liquid or pasty and, compared to conventional rubber seals made of EPDM and NBR, have the advantage of being easier, more versatile, and more precisely fitting, for example, by dispensing or screen printing. The H2 permeation coefficient is lower than that of seals made of silicone sealants (approx. 50,000'10- 19 «m 2 / (Pa«s)) is lower. With a high mass fraction of the silicone-epoxy copolymer (A), the H2 permeation coefficient is comparable to that of conventional rubber seals made of EPDM (approx. 200010- 19 «m 2 / (Pa«s) up to 5,000'10-19 «m 2 / (Pa«s)). However, it can be further reduced by increasing the epoxy content.

[0139] The comparison of samples a and b with sample c demonstrates the influence of a reactive diluent (D) on the material properties. It can be seen that the glass transition temperature can be reduced to below -30 °C by using a reactive diluent (D). A glass transition temperature below -30 °C is particularly relevant for fuel cell seals and Type IV tanks (with inner liners).

Claims

Patent claims 1. Use of a composition containing at least one epoxy-functional silicone-epoxy copolymer (A) as a sealant for sealing against hydrogen.

2. Use according to claim 1, characterized in that the at least one epoxy-functional silicone-epoxide copolymer (A) comprises at least one structural unit (I), (II) and (Hl) wherein: n is an integer from 1 to 1000, preferably from 1 to 100, in particular from 5 to 50; L is each independently selected from the divalent radicals sulfonyl, methanediyl, propane-2,2-diyl and 1,1,1,3,3,3-hexafluoro-2,2-propane-2,2-diyl, preferably propane-2,2-diyl; R is each independently selected from monovalent hydrocarbon radicals having 1 to 16 carbon atoms, preferably from the group consisting of methyl, ethyl, propyl and phenyl, in particular methyl.

3. Use according to claim 1 or 2, characterized in that - the mass fraction of all structural units (I) based on the total mass of all epoxy-functional silicone-epoxy copolymers (A) is from 10 to 80%, preferably from 20% to 70%, in particular from 30% to 60%; and / or - the mass fraction of all structural units (II) and (III) together based on the total mass of all epoxy-functional silicone-epoxy copolymers (A) is from 20% to 90%, preferably from 30% to 80%, in particular from 40% to 70%.

4. Use according to one of claims 1 to 3, characterized in that - that the composition further contains at least one hardener (B), preferably selected from the group consisting of amine hardeners, anhydride hardeners, phenolic resins, mercaptan hardeners, polyamide hardeners, isocyanate hardeners, imidazole hardeners, dicyandiamide and diaminodiphenyl sulfone, in particular selected from the group consisting of amine hardeners and anhydride hardeners; and / or - that the composition contains at least one silicon-free epoxy resin (C), preferably selected from the group consisting of novolak epoxy resins, cycloaliphatic epoxy resins, glycidyl ester epoxy resins, bisphenol diglycidyl ether epoxy resins, in particular selected from the group consisting of bisphenol A diglycidyl ether epoxy resins and bisphenol F diglycidyl ether epoxy resins; and / or - that the composition contains at least one silicon-free reactive diluent (D), preferably selected from aliphatic glycidyl ethers, in particular from aliphatic diglycidyl ethers.

5. Use according to claim 4, comprising preparing the composition by mixing components of a multi-component composition, wherein the multi-component composition comprises a component (I) containing the at least one epoxy-functional silicone-epoxy copolymer (A) and a component (II) containing the at least one hardener (B).

6. Use according to claim 5, characterized in that component (I) further contains the at least one silicon-free epoxy resin (C).

7. Sealing element, producible by curing the composition according to the specifications of any one of claims 1 to 6.

8. Sealing element according to claim 7, characterized in that its hydrogen permeation coefficient is given in 1019 «m 2 / (Pa«s) is from 0 to 9000, preferably from 10 to 7000, in particular from 100 to 5000.

9. Device for generating and / or conducting and / or storing and / or converting and / or controlling hydrogen, comprising at least two joining partners which are separated from one another by the sealing element according to one of claims 7 to 8.

10. Device according to claim 9, which is a hydrogen storage device, a hydrogen line, a fitting, a fuel cell or an electrolyzer for producing hydrogen.

11. Device according to claim 9 or 10, which is a cryogenic container.

12. Device according to one of claims 9 to 11, comprising an interior space which is at least partially delimited by both joining partners and the sealing element, wherein the interior space can be supplied with hydrogen in such a way that the hydrogen contacts both joining partners and the sealing element.

13. A method for producing a device according to one of claims 9 to 12, comprising the following non-chronological steps: a) providing a first joining partner; b) providing a second joining partner; c) providing a composition according to the specifications of one of claims 1 to 6; d) applying the composition to the first and / or the second joining partner; e) joining the joining partners such that the composition contacts the first and the second joining partner; f) curing the composition.

14. The method according to claim 13, characterized in that the composition is provided and / or applied in a liquid or pasty state.

15. A method according to claim 13 or 14, characterized in that the curing takes place after application and before joining; or that the curing takes place after application and after joining; or that the curing takes place after application and during joining.

16. A method for operating a device according to any one of claims 9 to 12, comprising the following steps: - carrying out a method according to one of claims 13 to 15 for the purpose of producing the device; - Applying hydrogen to the device in such a way that hydrogen contacts both joining partners and the cured composition.

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