Sealing material and sealing element

Abstract

The present invention relates to a sealing material for a seal, wherein the seal can be, for example, a seal for an electrochemical system. The sealing material comprises a polymer material and an inorganic filler.

Description

[0001] The present invention relates to a sealing material and a sealing element comprising or consisting of the sealing material. The invention further relates to an electrochemical system comprising the sealing element.

[0002] In an electrochemical system such as a fuel cell system or an electrolysis system, chemical reactions occur using or generating electric current. In addition to liquid reactant and / or product streams, gaseous streams are used and / or generated, for example, in hydrogen fuel cell systems or water electrolysis systems. Accordingly, the requirements for the system's sealing elements are high to prevent unwanted leakage.

[0003] Due to the sometimes extreme conditions, many conventional sealing materials are unsuitable for use in such electrochemical systems. For example, sealing elements such as flat gaskets in an alkaline electrolysis system (AEL) must be resistant to a 30% potassium hydroxide solution at a temperature of 95 °C.

[0004] Polytetrafluoroethylene (PTFE) is known to be used as a polymer material for sealing elements, as PTFE is characterized by high chemical resistance and temperature resistance.

[0005] The problem, however, is that the sealing elements should be as durable as possible even under these extreme operating conditions, since replacing the seals is often difficult and / or results in a long downtime.

[0006] Since PTFE exhibits a high tendency to creep under application conditions, it is known to resort to modified PTFE and / or so-called PTFE compounds.

[0007] Modified PTFE is a tetrafluoroethylene copolymer (TFE copolymer) copolymerized with a small amount of perfluoropropyl ether (PPVE). The use of PPVE results in a polymer material characterized by improved mechanical properties and better creep behavior, especially at elevated temperatures.

[0008] A major disadvantage of modified PTFE is that the material is relatively expensive.

[0009] PTFE compounds are mixtures of PTFE and modified PTFE with other materials, which are usually processed using the press sintering process.

[0010] PTFE compounds are also typically found in the high-price segment, making their use rarely economical. Furthermore, the chemical inertness of the sealing material can be reduced by the presence of the compound within the sealing material.

[0011] The object of the present invention is therefore to provide a sealing material with which the aforementioned disadvantages, in particular with regard to creep tendency and economic efficiency, can be avoided.

[0012] The problem is solved by a sealing material for a sealing element according to the independent claim in this respect.

[0013] The term "in particular" is used in this description and the attached claims preferably to describe optional features.

[0014] Unless explicitly stated or required by the context, the use of an indefinite article such as "ein", "eine" or "einen" always means "one or more", "eine or mehr" or "einen or mehr".

[0015] The sealing element can be a sealing element, in particular a flat gasket, for an electrochemical system. The electrochemical system is preferably an electrolysis system, in particular a water electrolysis system, and / or a fuel cell system, in particular a hydrogen polymer electrolyte membrane (PEM) fuel cell system.

[0016] The sealing material comprises a polymer and an inorganic filler. The combination of the polymer and the inorganic filler offers the advantage of a sealing material with beneficial properties in terms of inertness, processability, and durability.

[0017] The sealing material can also comprise two or more polymer materials.

[0018] The polymer material can be a curable (polymerizable) composition. The curable composition can be polymerizable, in particular, by a polycondensation reaction, a polyaddition reaction, or a radical, cationic, or anionic chain polymerization reaction, so that a polymer is formed.

[0019] Preferably, the polymer material is a pre-polymerized composition. The polymer material can therefore already comprise a polymer or consist of the polymer itself.

[0020] The polymer can be a homopolymer or a copolymer.

[0021] Particularly preferred is the use of a polymer with a mean molar mass, in particular a number-average molar mass, of 10 5 up to 10 8 g / mol, preferably 10 6 up to 10 7 g / mol. The mean molar mass can be determined, for example, by light scattering and / or gel permeation chromatography.

[0022] In a preferred embodiment, the polymer material is a fluorinated polymer material. Preferably, the polymer material is a perfluorinated polymer material. (Per)fluorinated polymer materials are characterized in particular by their high chemical inertness.

[0023] It is advantageous if the polymer material consists of a perfluoroalkoxy polymer (PFA), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE) or a mixture of the aforementioned polymers, or comprises at least one of the aforementioned polymers or a mixture thereof.

[0024] The polymer material preferably consists of or comprises PTFE. PTFE has the particular advantage of being relatively inexpensive compared to other (per)fluorinated polymers.

[0025] The polymer material is preferably a solid. This simplifies the production of the sealing material, as the polymer material is easy to store and / or a predetermined quantity of the polymer material can be weighed out.

[0026] In one embodiment, the polymer material comprises 40 to 95 wt.%, preferably 50 to 90 wt.%, and particularly preferably 60 to 80 wt.%, of the sealing material. This can have the advantage that, in particular, the processability and inertness of the sealing material are largely determined by the polymer material.

[0027] If the sealing material comprises more than one polymer material, the aforementioned weight percentage can represent a total weight percentage of the polymer materials in the sealing material.

[0028] Preferably, a polymer material consisting of or comprising PTFE is a main polymer material if the sealing material comprises more than one polymer material. The main polymer material is, in particular, the polymer material that has the largest weight fraction among the polymer materials in the sealing material.

[0029] Inorganic fillers have the advantage over organic fillers that they regularly exhibit higher stability and / or are more cost-effective under extreme, especially corrosive, conditions.

[0030] The inorganic filler can be, for example, a glass, in particular in the form of glass fibers, glass spheres, hollow glass spheres and / or ground glass, a carbon-based filler, in particular in the form of coke coal, electrographitized coal, graphite and / or carbon fibers, molybdenum disulfide (MoS2), a stainless steel powder, a ceramic filler and / or a metal oxide.

[0031] Preferably, the filler is a ceramic filler and / or a metal oxide. The use of a ceramic filler, and in particular a metal oxide, is advantageous because, unlike carbon-based fillers, they are electrically non-conductive and exhibit higher long-term stability compared to glass fillers and / or stainless steel powders.

[0032] Ceramic fillers include, in particular, ceramic fillers comprising a silicate, silicon carbide, silicon dioxide, boron nitride, boron carbide, silicon nitride, aluminum oxide and / or beryllium oxide.

[0033] The metal oxide is particularly preferably used as a filler. The metal oxide can consist of aluminum oxide (Al2O3), in particular α-Al2O3, beryllium oxide (BeO), magnesium oxide (MgO), calcium oxide (CaO), zirconium oxide (ZrO2), titanium oxide (TiO2), or a mixture of the aforementioned metal oxides, or at least comprise one of the aforementioned metal oxides or a mixture thereof.

[0034] Al₂O₃, especially in the form of α-Al₂O₃ (corundum), is particularly favored as a filler material. In addition to the aforementioned advantages, sealing materials containing Al₂O₃, especially corundum, are characterized by high creep resistance and / or surprisingly good processability.

[0035] The creep resistance of the sealing materials can be determined in particular by means of a creep test according to ISO 899-1.

[0036] Preferably, the filler has a weight fraction of 5 to 60 wt.%, preferably 10 to 50 wt.%, particularly preferably 20 to 40 wt.%, and most preferably 25 to 30 wt.%, of the sealing material.

[0037] If the sealing material contains more than one filler, the aforementioned weight percentage can correspond to a total weight percentage of the sealing material.

[0038] Preferably, the ceramic filler and / or the metal oxide is the main filler if the sealing material comprises more than one filler. In particular, the main filler is the filler that has the largest weight fraction among the fillers in the sealing material.

[0039] It can be advantageous if the filler consists of particles with a medium grain size d 50The sealing material consists of particles with a particle size of 0.1 to 200 µm, preferably 1 to 100 µm, and particularly preferably 10 to 50 µm. If the sealing material comprises more than one filler, all fillers preferably consist of particles with the aforementioned average particle size d. 50 The particle size distribution and / or the mean particle size d 50 can be determined in particular by means of laser diffraction. In a preferred embodiment, the filler has a particle size distribution with a d 94 -value of 12 µm, a d 50 -value of 22.8 µm and a d3 value of 40 µm.

[0040] Fillers which have the aforementioned average particle size d 50 These properties can, in particular, result in advantageous mechanical properties of the sealing material.

[0041] The filler particles can have any shape. In particular, the particles can be irregular, elongated, or round. Elongated means that the particle's dimensions in one dimension are significantly larger than in the other two dimensions, for example, at least twice as large.

[0042] In a preferred embodiment, the sealing material is malleable, in particular malleable from a plastic state. This means that the sealing material can be processed into a sealing element, for example, by compression molding, injection molding, extrusion, calendering, and / or drawing.

[0043] It is conceivable that the sealing material contains additional components such as dyes, flame retardants, and antistatic additives. These additional components allow, in particular, the properties of the sealing material to be tailored to the specific application.

[0044] In particular, the sealing material can comprise 0.5 to 4 wt.%, preferably 1 to 3 wt.%, most preferably 2 wt.% of MoS2 as a dry lubricant and dye. This can reduce wear.

[0045] Preferably, the sealing material consists essentially of the polymer material and the filler material. This means that the sealing material may contain further components which, however, do not affect the advantageous material properties, particularly with regard to the parameters described, or only affect them insignificantly. In the context of the present invention, insignificant means that the presence of at least one further component alters a material property by less than ± 5%, preferably less than ± 2%.

[0046] In particular, the sealing material can consist of the polymer material, especially PTFE, and the filler, preferably Al₂O₃, especially α-Al₂O₃, and optionally 0.5 to 4 wt.%, preferably 1 to 3 wt.%, particularly preferably 2 wt.% of MoS₂, i.e., it contains no other components. This enables simple and, above all, economical production of the sealing material.

[0047] The problem is further solved by a sealing element according to the independent claim in this respect.

[0048] The sealing element can, in particular, be a sealing element for an electrochemical system. The electrochemical system is preferably an electrolysis system, more preferably a water electrolysis system, particularly preferably an AEL system, and / or a fuel cell system, in particular a hydrogen PEM fuel cell system.

[0049] In a preferred embodiment, the sealing element is a flat gasket.

[0050] The flat gasket is preferably a static gasket and / or can be a gasket for a flange connection of the electrochemical system.

[0051] The sealing element comprises a sealing material as described herein.

[0052] Alternatively, the sealing element consists entirely of the sealing material. This means that the sealing element is formed completely from the sealing material. This has the advantage that no different materials need to be joined together, as a joint can represent a potential weak point in the sealing element.

[0053] In one embodiment, the sealing element comprises an insert. The sealing material can be applied to and / or bonded with the insert.

[0054] The insert can be, for example, a metal, ceramic, or plastic insert. The insert is preferably a flat material. The flat material is particularly suitable for forming the flat gasket.

[0055] In accordance with the present invention, a flat material has a dimension many times greater in at least one dimension, such as length, preferably in two dimensions, such as length and width, than in another dimension, such as in particular the thickness of the flat material.

[0056] In one embodiment, the sealing element, in particular the flat gasket, can have an average thickness of 0.5 to 10 mm, preferably 1 to 5 mm. The insert can, for example, have a thickness of 0.5 to 5 mm, preferably 1 to 3 mm.

[0057] A connection between the sealing material and the insert can be achieved in particular by form-fitting and / or material-fitting means.

[0058] A positive fit can be achieved, for example, by partial reshaping, particularly in an area that fulfills a sealing function in an application, or by complete reshaping of the insert.

[0059] A material bond can be formed, in particular, by means of an adhesion promoter, which is applied, for example, to a contact area between the sealing material and the insert. The choice of adhesion promoter can be based, in particular, on the materials to be bonded.

[0060] In a preferred embodiment, the at least one adhesion promoter is a silane, in particular an aminosilane, preferably 3-aminopropyl-triethoxysilane with the structure and / or 3-aminopropyl-trimethoxysilane; an epoxysilane such as for example and / or a derivative of the aforementioned silanes. Vinyl, methacrylic acid, urea, or thiol silanes can also be used additionally or alternatively.

[0061] Oligomers of such silanes, in particular di-, tri-, tetra-, penta-, and hexamers, can also be used as at least one adhesion promoter. A siloxane network can be formed from the silanes by cleavage of the alcohol residues, such as the methoxy and / or ethoxy groups, which improves adhesion.

[0062] Additionally or alternatively, the adhesion promoter can comprise a modified polyolefin, in particular a polyolefin soluble in organic solvents. Polyolefins can be modified, for example, with chlorine and maleic anhydride (CPO). The polyolefin can be, for example, polypropylene and / or polyethylene.

[0063] In a preferred embodiment, the adhesion promoter is applied to the insert as an aqueous emulsion of a polyolefin that has been converted into a liquid state with an anhydride of an unsaturated carboxylic acid and modified with methacrylic acid ester copolymers, particularly by spraying. The anhydride can be, in particular, maleic anhydride. The polyolefin can be, for example, polypropylene and / or polyethylene.

[0064] The present invention also relates to an electrochemical system according to the independent claim in this respect.

[0065] The electrochemical system is preferably an electrolysis system, in particular a water electrolysis system, and / or a fuel cell system, in particular a hydrogen PEM fuel cell system.

[0066] The electrochemical system can be designed in any known way and using common materials. For example, the electrolysis system can have a polymeric membrane permeable to hydroxide ions and two electrodes on opposite sides of the membrane. The membrane and electrodes can be arranged in a chamber in which an aqueous electrolyte, such as a KOH solution, can be supplied to an oxygen-producing side, or anode side. The hydrogen-producing side, opposite the membrane separating the chamber, can optionally also be supplied with an electrolyte.

[0067] The electrochemical system preferably comprises at least one sealing element, wherein the sealing element can be configured in any manner described herein. The use of the sealing element according to the invention can, in particular, enable more economical production of the electrochemical system and / or an extension of the system's service life.

[0068] In a preferred embodiment, the sealing element is a flat gasket, which serves in particular as a sealing element for a flange connection of the electrochemical system.

[0069] The invention further relates to a method for manufacturing a sealing element according to the independent claim in this respect.

[0070] The sealing element can be any sealing element described herein.

[0071] The procedure includes, in particular, the following steps: i) Providing a sealing material; and ii) at least one shaping step for the formation of the sealing element.

[0072] The sealing material can be any sealing material described herein. Providing the sealing material can involve mixing a polymer material and an inorganic filler. Mixing can, in particular, produce a homogeneous mixture. The polymer material can, in particular, be in the form of granules.

[0073] The mixing process can include grinding the polymer material and the inorganic filler to obtain a mixture with a favorable particle size distribution.

[0074] Additionally or alternatively, the sealing material can be granulated. A binder can be added for this purpose.

[0075] In a preferred embodiment of the method, the at least one shaping step comprises injection molding of the sealing material, press sintering of the sealing material, forming a flat material from the sealing material and / or forming a hollow cylinder from the sealing material.

[0076] A press-sintering process is particularly preferred. Specifically, pressure is first applied to the sealing material, followed by an increase in temperature. A hollow cylinder formed in this way is then machined, and the resulting individual sealing elements are subsequently hot-pressed.

[0077] The at least one shaping step preferably takes place at elevated temperature and / or elevated pressure. In particular, the shaping step can take place at a temperature of 340 to 380 °C, preferably 355 to 375 °C, and / or a pressure of 100 to 700 bar abs., preferably 150 to 400 bar abs. Under the aforementioned conditions, the sealing materials according to the invention are readily processable.

[0078] It can be advantageous if the formation of the sealing element includes at least two shaping steps and / or at least one post-processing step.

[0079] The sealing element can, for example, be punched and / or cut out of the flat material. It is also conceivable that the sealing element could be cut off from the end face of the hollow cylinder.

[0080] At least one post-processing step can, for example, involve adjusting the thickness and / or shape of the sealing element in sections. For instance, sealing material can be removed by machining.

[0081] Further features of the sealing material according to the invention will become clear with reference to the example composition listed in the following table, whereby the invention is not intended to be limited to this exemplary sealing material. Table 1: Sealing material according to the invention ingredient Percentage by weight PTFE 73 corundum 25 MoS2 2

[0082] The sealing material with the composition listed in Table 1 and sealing elements comprising or consisting of the sealing material are characterized by particularly high durability, high chemical resistance and temperature resistance, combined with advantageous creep behavior and low raw material and manufacturing costs.

Claims

Sealing material for a sealing element, which may be, for example, a sealing element for an electrochemical system, wherein the sealing material comprises a polymer material and an inorganic filler. Sealing material according to claim 1, characterized in that the polymer material is a fluorinated, in particular perfluorinated, polymer material, which preferably consists of a perfluoroalkoxy polymer (PFA), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE) or a mixture of the aforementioned polymers, or comprises at least one of the aforementioned polymers. Sealing material according to claim 1 or 2, characterized in that the polymer material has a weight fraction of 40 to 95 wt.%, preferably 50 to 90 wt.%, particularly preferably 60 to 80 wt.%, in the sealing material. Sealing material according to one of claims 1 to 3, characterized in that the filler is a ceramic filler and / or a metal oxide, wherein the metal oxide preferably consists of aluminum oxide, in particular α-Al2O3, magnesium oxide, beryllium oxide, zirconium oxide, titanium oxide or a mixture of the aforementioned compounds or comprises at least one of the aforementioned compounds. Sealing material according to one of the preceding claims, characterized in that the filler has a weight fraction of 5 to 60 wt.%, preferably 10 to 50 wt.%, particularly preferably 20 to 40 wt.%, most preferably 25 to 30 wt.%, in the sealing material. Sealing material according to one of the preceding claims, characterized in that the filler has a grain size d50 of 0.1 to 200 µm, preferably of 1 to 100 µm, particularly preferably of 10 to 50 µm. Sealing material according to one of the preceding claims, characterized in that the sealing material is plastically deformable. Sealing material according to one of the preceding claims, characterized in that the sealing material consists essentially of the polymer material and the filler. Sealing element, which may be, for example, a flat gasket, for an electrochemical system, wherein the sealing element comprises or consists of a sealing material according to any one of claims 1 to 8. Sealing element according to claim 9, characterized in that the sealing element comprises an insert, wherein the sealing material is applied to the insert and / or connected to the insert, preferably by material and / or form-fitting means. Electrochemical system, in particular an electrolysis system, comprising at least one seal according to claim 9 or 10. Method for manufacturing a sealing element according to claim 9 or 10, wherein the method comprises the following steps: i) providing a sealing material according to any one of claims 1 to 8; and ii) at least one shaping step for forming the sealing element. The method according to claim 12, characterized in that the provision of the sealing material comprises a mixing of a polymer material and an inorganic filler. Method according to claim 12 or 13, characterized in that the at least one shaping step comprises injection molding of the sealing material, press sintering of the sealing material, forming a flat material from the sealing material and / or forming a hollow cylinder from the sealing material.