Method for producing a porous transport layer

Abstract

The present invention relates to a method for making a multi-layer porous transport layer, the method comprising the steps of: (a) providing a first feedstock comprising first metal particles and a first polymer binder, and providing a second feedstock comprising a second metal particles and a second polymer binder, The first and second feedstocks have a metal powder content of 40 to 70 volume percent; and The first feedstock is compared to the second feedstock. (i) metal particles with a smaller average particle size; (ii) A higher metal powder content; or (iii) Both smaller average particle size metal particles and higher metal powder content The process comprising: (b) co-extruding the first and second feedstocks to form a film-shaped green body comprising a first layer and a second layer, the second layer being physically connected to the first layer at a temperature above the melting temperature and / or glass transition temperature of the first and second polymeric binders; (c) optionally smoothing the film-shaped green body by rolling or calendaring; (d) debinding the film-shaped green body to form a brown body; (e) Brownian body in a non-oxidizing atmosphere or 10 -4 sintering under a vacuum of less than mbar and at a temperature of 700-1100°C to form a porous transport layer; Including, The first feedstock and the second feedstock do not contain any solvent.

Description

[Technical field]

[0001] The present invention relates to a method for the production of porous transport layers for electrochemical cells, in particular for electrolysers of the PEM construction type, and specifically for the electrolytic decomposition of water, in particular to oxygen and hydrogen. [Background technology]

[0002] Proton exchange membrane (PEM)-based electrolysis requires a transport layer that is electrochemically stable, electronically conductive, and gas permeable. In the most basic sense, the function of the porous transport layer ("PTL") on the anode side of the electrolyzer is to distribute the reacted water uniformly across the catalyst layer and to efficiently remove and diffuse oxygen evolved at the catalyst / PTL interface away from the PTL towards the bipolar plate. The PTL on the anode side of the electrolyzer must have a large contact area with the electrode's catalyst layer to improve catalyst utilization and therefore electrolysis performance. At the same time, the PTL must have a low pressure drop to facilitate gas and water transport on the anode side. The two parameters of large contact area and low pressure drop are mutually exclusive and are a complex optimization topic to achieve the best overall performance. Various studies have been proposed to overcome this challenge.

[0003] JP2001-279481A discloses a method for producing a sintered body by forming a plurality of sheet-like bodies having different particle sizes of titanium powder and different mixing ratios of titanium powder and binder, and sintering the plurality of sheet-like bodies in a stacked state. According to this method, it is possible to produce a powder sintered body in which powder sintered parts having different porosities are stacked.

[0004] US2006 / 0201800A discloses a method for manufacturing a porous conductor for use in an electrochemical reaction membrane device including an electrochemical reaction membrane, the method including the following steps: providing a sintered body of metal powder having a plate shape; forming a ground surface by a grinding process on the side of the sintered body of metal powder that faces the electrochemical reaction membrane when an electrolytic device is assembled; and removing a deformed portion of the ground surface formed by the grinding process by an etching process after the grinding process, thereby increasing the porosity of the porous conductor on the side facing the electrochemical reaction membrane.

[0005] JP2011-099146A discloses a sintered metal sheet material made of a metal sintered compact prepared by sintering metal powder and having a plurality of pores dispersed therein with a porosity of 10 to 50% by volume. The pores have an average pore diameter of 1 to 30 μm, and some of the pores are open on the surface of the sintered metal sheet material.

[0006] Adv. Eng. Mater. 2019, 21, 1801201 discloses the fabrication of large-scale titanium-based PTL for polymer electrolyte membrane electrolysis by tape casting.

[0007] WO2020 / 20467A1 discloses a method for producing a porous transport layer, which comprises mixing a metal powder with a binder and then forming it into a foil, which is laminated onto a porous metal layer, after which the binder is removed and the remaining brown underlayer is sintered to the porous metal layer, producing a PTL having a porous metal layer with a microporous metal layer applied thereon.

[0008] US2010 / 038809A1 discloses a method for producing multi-layer porous tubular and / or sheet-like filtration membranes. The method includes an apparatus and a method for producing lengths of multi-layer asymmetric membrane by co-extruding different feedstocks, each hopper containing a different mixture, through a die head with multiple exit ports. The mixtures used are based on a binder dissolved in a solvent and subsequently mixed with a powder. The mixtures have different powder / binder ratios and / or different metal powder particle sizes, and the different mixtures contain metal powders with different melting points. After extrusion, the extrudate is immersed in a liquid as it leaves the die head and further processing is carried out, including sintering the multi-layer extrusion in a furnace.

[0009] The current state of the art discusses a two-layer PTL manufacturing method, in which a green part is formed into two separate layers by extrusion, pressing, or any kind of molding, and then placed on top of an already completed metal porous layer or another green part. Placing and aligning two layers on top of each other is not only difficult and adds extra processing steps, but can also induce internal stresses at the interface between the two layers brought together, which can result in reduced mechanical properties and defects in the final sintered PTL (e.g. internal cracks, bumps, or surface warpage). Such defects are well known in the MIM industry and are described, for example, in Hwang, KS Common defects in metal injection molding (MIM), the handbook of metal injection molding, Woodhead, 2012, 235-250. Furthermore, it is known from iScience 23, 101783, December 18, 2020 that stacking two layers on top of each other leads to the formation of a highly porous zone in the center of the PTL, which allows oxygen to merge and form periodic corrugations, which have a negative effect on the water transport properties of the PTL, especially at high current densities.

[0010] According to International Journal of Refractory Metals & Hard Materials 89 (2020) 105214, other processing methods in neighboring technical fields utilizing binder / metal powder mixtures, for example membrane filtration methods, rely on specific binder systems suitable for solvent and / or thermal debinding of the binder system. These not only require high energy consumption and long debinding times, but also do not support good surface flatness for the large dimensions of porous transport layers in electrochemical cell applications. Surface flatness is key to improve contact with the catalyst layer and ensure proper pressure distribution in the electrochemical cell stack. Furthermore, since titanium is preferably used for such applications, it should be noted that the sintering of titanium is extremely sensitive to intervening elements such as carbon, traces of hydrated oxides, chlorine impurities and gases, e.g. water, carbon monoxide, carbon dioxide, oxygen or oxygen-chlorine complexes, which are detrimental to the mechanical properties of the final parts.

[0011] Therefore, removing these shortcomings is beneficial to the performance and quality of PTL. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP2001-279481A [Patent Document 2] US2006 / 0201800A [Patent Document 3] JP2011-099146A [Patent Document 4] WO2020 / 20467A1 [Patent Document 5] US2010 / 038809A1 [Non-patent literature]

[0013] [Non-Patent Document 1] Adv. Eng. Mater. 2019, 21, 1801201 [Non-Patent Document 2] Hwang,KSCommon defects in metal injection molding(MIM),the handbook of metal injection molding,Woodhead,2012,235-250 [Non-Patent Document 3] iScience23,101783,December 18, 2020 [Non-Patent Document 4] International Journal of Refractory Metals&Hard Materials89(2020)105214 Summary of the Invention [Problem to be solved by the invention]

[0014] The objective underlying the present invention is to provide a porous transport layer that exhibits better water and oxygen transport properties, mechanical properties, and fewer defects in the final sintered PTL, in particular reducing internal cracks, bumps, or surface warpage. A further objective of the present invention is to provide a cheaper method for producing a PTL with different porosity throughout the PTL. It is also an objective of the present invention to provide a PTL with at least two layers that does not exhibit any discontinuities such as a highly porous zone in the transition phase between the two layers. [Means for solving the problem]

[0015] A first aspect of the present invention is a method for making a multi-layer porous transport layer, the method comprising the steps of: (a) providing a first feedstock comprising first metal particles and a first polymer binder, and providing a second feedstock comprising a second metal particles and a second polymer binder, The first and second feedstocks have a metal powder content of 40 to 70 volume percent; and The first feedstock is compared to the second feedstock. (i) metal particles with a smaller average particle size; (ii) A higher metal powder content; or (iii) Both smaller average particle size metal particles and higher metal powder content The process comprising: (b) co-extruding the first and second feedstocks to form a film-shaped green body comprising a first layer and a second layer, the second layer being physically connected to the first layer at a temperature above the melting temperature and / or glass transition temperature of the first and second polymeric binders; (c) optionally smoothing the film-shaped green body by rolling or calendaring; (d) catalytically debinding the film-shaped green body to form a Brownian body; (f) Brownian body in a non-oxidizing atmosphere or 10 -4 sintering under a vacuum of less than mbar and at a temperature of 700-1100°C to form a porous transport layer; Including, The first feedstock and the second feedstock do not contain any solvent.

[0016] The PTL produced using the method according to the invention exhibits better water and oxygen transport properties, mechanical properties, and fewer defects in the final sintered PTL. In particular, there is a reduction in internal cracks, bumps, or warping of the PTL surface. Furthermore, the method provides a cheaper way to produce a PTL with two or more layers of different porosity. More specifically, the present invention provides a PTL comprising at least two layers of different porosity without any discontinuity, in particular without any highly porous zone in the transition phase between the two layers of the PTL.

[0017] The method according to the invention can be used to manufacture porous transport layers for electrochemical cells, such as batteries, fuel cells, or electrolyzers.

[0018] A further embodiment of the invention is a combination of a first feedstock and a second feedstock, (a) a first feedstock comprising first metal particles and a first polymer binder; (b) the second feedstock comprises second metal particles and a second polymer binder; The first feedstock is compared to the second feedstock. (i) metal particles with a smaller average particle size; (ii) A higher metal powder content; or (iii) Both smaller average particle size metal particles and higher metal powder content and The first and second polymer binders have a melt flow rate MFR of 1 to 5 g / 10 min using 190° C. and 2.16 kg according to ISO 1133-1.

[0019] A further embodiment of the present invention is a film-shaped green body obtainable by carrying out steps (a) to (d) of the method according to the invention.

[0020] A further embodiment of the present invention is a porous transport layer obtainable by the method according to the present invention. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 shows a cross-sectional SEM photograph of the sintered bilayer PTL of Example 2, showing that the interface between the two layers is smooth. [Diagram 2] FIG. 2 shows the final sintered bilayer PTL of Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The method according to the invention is directed to the production of a multi-layer porous transport layer, also referred to herein as a "PTL," which is capable of transporting and uniformly distributing reactants, e.g., water, to the catalyst layer and effectively removing oxygen evolved at the catalyst / PTL interface without impeding the flow of reactants to reach the catalyst layer.

[0023] The feedstock, the metal powders and binders which form the feedstock, and the PTL formation are described in more detail below without limiting the invention.

[0024] Extrusion Feedstock In a first step of the method according to the invention, a first feedstock comprising a first metal particle and a first polymeric binder and a second feedstock comprising a second metal particle and a second polymeric binder are provided, the first feedstock having smaller average particle size metal particles, a higher metal powder content, or both smaller average particle size metal particles and a higher metal powder content compared to the second feedstock.

[0025] The first and second feedstocks (together referred to as "extruded feedstocks" or "feedstocks") comprise or consist of two components, a metal powder and a binder, as described in more detail below. As used herein, feedstock refers to a solid feedstock in the form of granules, pellets, or powder. Most preferably, it is a granule.

[0026] The feedstock comprises 40-70 volume percent of the metal powder described herein and 30-60 volume percent of the binder, based on the total volume of the mixture.

[0027] Preferably, the feedstock comprises or consists essentially of 45-65 volume percent metal powder and 35-55 volume percent binder, based on the total volume of the feedstock.

[0028] Particularly preferably, the feedstock comprises 48-64% by volume of metal powder and 36-52% by volume of binder, based on the total volume of the feedstock.

[0029] Preferably, the feedstock consists essentially of one or more metal powders, one or more binders, and optionally one or more additives, as described in more detail below, the volume percentages of metal powders, binders, and additives adding up to 100%.

[0030] In a preferred embodiment, the first and second feedstocks have an MFR of 50-700g / 10min at 190°C and 21.6kg according to ISO 1133. Most preferably, the first and second feedstocks have the same or at least similar MFR, where similar means that the MFR of the first and second feedstocks differs by 100 or less, preferably 50 or less, most preferably 10 or less.

[0031] Preferably, the first feedstock and the second feedstock do not contain any solvent. As used herein, "solvent" refers to a compound or mixture of compounds that is liquid at room temperature, such as, but not limited to, acetone, n-methylpyrrolidone, water, or formamide.

[0032] metal powder In general, the metal powder can be of any metal that can be used as a PTL.

[0033] Preferably, the metal powder comprises a pulverized metallic material comprising or consisting essentially of titanium.

[0034] As used herein, "essentially" means that there may be trace amounts of unavoidable impurities that do not significantly affect the chemical, mechanical or catalytic properties of other components, particularly the alloy.

[0035] In particular, the method according to the present invention is provided for a porous transport layer formed from titanium or a titanium alloy, although it should be understood that porous transport layers of other materials or metal alloys can be formed by the method according to the present invention.

[0036] Typically, the first and second feedstocks may contain 40-70% by volume of metal powder.

[0037] Beneficial for use in coextrusion are spherical powders with an average particle size, measured by laser diffraction, of 0.1 to 120 μm, preferably 1 to 100 μm, particularly preferably 1 to 63 μm, and most preferably 15 to 63 μm. The average particle size (diameter) of the powder is preferably less than 100 μm, more preferably less than 50 μm, and most preferably less than 35 μm. The powder may be sieved or classified after atomization to reach the desired particle size distribution. Plasma treatment of the powder may be used to improve the sphericity of the powder and to remove contaminants.

[0038] There are two approaches to achieving different pore sizes and porosities in the first and second layers of the final PTL.

[0039] In the first approach, different average particle sizes may be used for the first and second feedstocks. The larger the average particle size of the feedstocks, the higher the pore size and porosity of the final PTL. Thus, in the first embodiment of the invention, the first feedstock has a smaller average particle size of metal particles compared to the second feedstock. Preferably, the first feedstock has an average metal powder particle size of 10-45 μm, more preferably 15-30 μm, which is smaller than the average particle size of the second feedstock.

[0040] Preferably, the first average particle size is from 10 to 45 μm, more preferably from 15 to 35 μm, and most preferably from 15 to 30 μm.

[0041] Preferably, the second average particle size is from 20 to 106 μm, more preferably from 20 to 63 μm, and most preferably from 20 to 45 μm.

[0042] In the second approach, different amounts of metal powder are used in the first and second feedstocks. In this case, the particle size can be the same or different, preferably the same, in the first and second feedstocks. The higher the metal particle content in the feedstocks, the lower the pore size and porosity of the final PTL.

[0043] Preferably, the first feedstock which will form the first layer of the final PTL comprises 54-65% by volume of metal powder, more preferably 56-65% by volume.

[0044] Preferably, the second feedstock forming the second layer of the final PTL comprises 48-56% by volume, more preferably 48-54% by volume, of metal powder.

[0045] Besides commercially available pure milled titanium metal powder, other milled metal powders such as titanium alloys, stainless steel (SS) metal powders are also available for making PTL (anode side or cathode side) in electrolysis. For example, highly corrosion resistant, highly conductive SS grades (e.g. 17-4PH, 316L, Super Duplex) are good candidates for cathode PTL in PEM electrolysis.

[0046] Preferably, the metal powder consists essentially of ground titanium or stainless steel.

[0047] For the preparation of metal powders, it is necessary to grind the inorganic material. Any method known to those skilled in the art may be used to grind the inorganic material. For example, the inorganic material may be ground. Grinding may be carried out, for example, in a classifier mill, a hammer mill or a ball mill.

[0048] The metal powders used in the coextrusion process may be atomized using gas, plasma, or water atomization or hydrogenation. A specific method for producing triangular shaped titanium powder is called hydrogenation-dehydrogenation (HDH) as described in Powder Metall. 2016, 59, 249.

[0049] In certain embodiments, the first metal particles have a particle size.

[0050] binder According to the invention, the feedstock comprises 30-60% by volume of binder. In a preferred embodiment, the mixture comprises 35-55% by volume of binder, and particularly preferably 36-50% by volume of binder, based on the total volume of the feedstock.

[0051] Preferably, the binder comprises or essentially consists of (b1) 40 to 97.5% by weight of at least one polyoxymethylene (POM), (b2) 2 to 35% by weight of at least one polyolefin (PO), (b3) no further polymer (FP) or 0.5 to 20% by weight of at least one further polymer (FP), and (b4) no dispersant or 0 to 5% by weight of at least one dispersant, in each case relative to the total weight of the binder, the weight percentages of (b1), (b2), (b3) and (b4) adding up to 100%.

[0052] In a preferred embodiment, the binder comprises or essentially consists of (b1) 62 to 94.95% by weight of at least one polyoxymethylene (POM), (b2) 3 to 20% by weight of at least one polyolefin (PO), (b3) no or 2 to 15% by weight of at least one further polymer (FP), and (b4) 0.05 to 3% by weight of at least one dispersant, in each case relative to the total weight of the binder, the weight percentages of components (b1), (b2), (b3) and (b4) typically adding up to 100%.

[0053] Particularly preferably, the binder comprises or essentially consists of (b1) 83 to 92.9% by weight of at least one polyoxymethylene (POM), (b2) 4 to 15% by weight of at least one polyolefin (PO), (b3) 3 to 10% by weight of at least one further polymer (FP), and (b4) 0.1 to 2% by weight of at least one dispersant, in each case based on the total weight of the binder (B), the weight percentages of components (b1), (b2), (b3) and (b4) adding up to 100%.

[0054] According to the present invention, POM is different from PO, PO is different from FP, FP is different from dispersant, and dispersant is different from POM, however, POM, PO, FP and dispersant may contain the same building blocks, for example, further building blocks may be different and / or have different molecular weights.

[0055] The binder components (b1) POM, (b2) PE, (b3) FP, and (b4) dispersant are described in more detail below.

[0056] Polyoxymethylene According to the invention, the binder comprises 40-97.5% by weight of polyoxymethylene (also referred to herein as "POM") In a preferred embodiment, the binder comprises 62-94.95% by weight of POM, and particularly preferably 83-92.9% by weight of POM, based on the total amount of binder.

[0057] At least one POM can be used in the binder. "At least one POM" in the present invention means exactly one POM, and also a mixture of two or more POMs.

[0058] For purposes of the present invention, the term "polyoxymethylene" or "POM" includes both POM itself, i.e., polyoxymethylene homopolymer, and polyoxymethylene copolymers and terpolymers.

[0059] POM homopolymers are usually prepared by polymerization of monomers selected from a formaldehyde source.

[0060] The term "formaldehyde source" refers to a substance capable of liberating formaldehyde under the reaction conditions for the preparation of POM.

[0061] The formaldehyde source is advantageously selected from the group of cyclic or linear formals, in particular from the group consisting of formaldehyde and 1,3,5-trioxane, 1,3,5-trioxane being particularly preferred.

[0062] POM copolymers are known per se and commercially available. They are usually prepared by polymerization of trioxane as the main monomer. Comonomers are also used concomitantly. The main monomer is preferably selected from trioxane and other cyclic or linear formals or other formaldehyde sources.

[0063] The expression "principal monomers" is intended to indicate that the proportion of these monomers in the total amount of monomers, i.e. the sum of principal monomers and comonomers, is greater than the proportion of the comonomers in the total amount of monomers.

[0064] Very generally, POM according to the invention has at least 50 mol % of repeat units -CH2O- in the main polymer chain. Suitable polyoxymethylene (POM) copolymers are in particular those having the repeat unit -CH2O- and 0.01 to 20 mol %, in particular 0.1 to 10 mol %, and very particularly preferably 0.5 to 6 mol % of the repeat unit -CH2O- of the formula (I) [ka] The repeat unit of During the ceremony, R 1 ~R 4 are each independently selected from the group consisting of H, C1C4 alkyl, and halogen-substituted C1C4 alkyl; R5 is a chemical bond, (-CR 5a R 5b -) group and (-CR 5a R 5b O-) groups, R 5a and R 5b are each independently selected from the group consisting of H and unsubstituted or at least monosubstituted C1C4 alkyl, the substituents being selected from the group consisting of F, Cl, Br, OH and C1C4 alkyl; and n is 0, 1, 2 or 3.

[0065] If n is 0, R 5 R is a chemical bond between adjacent carbon and oxygen atoms. 5 (-CR 5a R 5b In the case of a (-CR 5a R 5b The oxygen atom (O) of the O- group is bonded to another carbon atom (C) of formula (I) and is not bonded to the oxygen atom (O) of formula (I). In other words, formula (I) does not include peroxide compounds. The same is true for formula (II).

[0066] In the context of the present invention, for example, the group R 1 ~R 4 Definitions such as C1C4 alkyl, as defined above for C1C4 alkyl, mean that the substituent (group) is an alkyl group having 1 to 4 carbon atoms. The alkyl group may be linear or branched, and optionally cyclic. Alkyl groups having both cyclic and linear components fall under this definition as well. Examples of alkyl groups are methyl, ethyl, n-propyl, iso-propyl, butyl, isobutyl, sec-butyl, and tert-butyl.

[0067] In the context of the present invention, for example, the group R 1 ~R 4The definition of halogen-substituted C1-C4-alkyl as defined above means that the C1C4 alkyl is substituted with at least one halogen. Halogen is F (fluorine), Cl (chlorine), Br (bromine) and I (iodine).

[0068] The repeating unit of formula (I) can be advantageously introduced into the POM copolymer by ring-opening of a cyclic ether as the first comonomer. [ka] (In the formula, R 1 ~R 5 and n has the meaning defined above for general formula (I). The first comonomer is preferably

[0069] Examples of first comonomers include ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, 1,3-dioxolane and 1,3-dioxepane as cyclic ethers, and linear oligoformals or polyformals, such as polydioxolanes or polydioxepanes. 1,3-dioxolanes and 1,3-dioxepanes are particularly preferred first comonomers, with 1,3-dioxolanes being very particularly preferred as first comonomers.

[0070] Likewise suitable are POM polymers obtainable by reacting a formaldehyde source with a first comonomer and a second comonomer. The addition of the second comonomer makes it possible in particular to prepare POM terpolymers.

[0071] The second comonomer preferably has the formula (III) [ka] and compounds of formula (IV) [ka] is selected from the group consisting of compounds During the ceremony, Z is a chemical bond, a (-O-) group and a (-OR 6 O-) groups, wherein R 6 is selected from the group consisting of unsubstituted C1C8 alkanediyl and C3C8 cycloalkanediyl. The second comonomer may be used, for example as an additional additive, in the first feedstock, the second feedstock, or in both the first and second feedstocks.

[0072] A C1C8 alkanediyl is a hydrocarbon having a free valence of 2 and a carbon number of 1 to 8. A C1C8 alkanediyl according to the present invention can be branched or unbranched.

[0073] A C3C8 cycloalkanediyl is a cyclic hydrocarbon having a free valence of 2 and a number of carbon atoms from 3 to 8. Hydrocarbons having a free valence of 2, cyclic and linear moieties, and a number of carbon atoms from 3 to 8 fall under this definition as well.

[0074] Preferred examples of the second comonomer (b1c) are ethylene diglycidyl, diglycidyl ethers and diethers prepared from a 2:1 molar ratio of a glycidyl compound with formaldehyde, dioxane or trioxane, as well as diethers prepared from 2 moles of a glycidyl compound and 1 mole of an aliphatic diol having 2 to 8 carbon atoms, such as the diglycidyl ethers of ethylene glycol, 1,4 butanediol, 1,3 butanediol, 1,3 cyclobutanediol, 1,2 propanediol and 1,4 cyclohexanediol.

[0075] In a preferred embodiment, component (b1) is a polyoxymethylene (POM) copolymer prepared by polymerization of at least 50 mol % of a formaldehyde source, 0.01-20 mol % of at least one first comonomer and 0-20 mol % of at least one second comonomer (b1c).

[0076] In a particularly preferred embodiment, the POM may be a POM copolymer prepared by polymerization of 80-99.98 mol %, preferably 88-99 mol %, of a formaldehyde source, 0.1-10 mol %, preferably 0.5-6 mol %, of at least one first comonomer, and 0.1-10 mol %, preferably 0.5-6 mol %, of at least one second comonomer.

[0077] In a further preferred embodiment, the POM may be a POM copolymer prepared by polymerization of at least 50 mol % of a formaldehyde source, 0.01-20 mol % of at least one first comonomer of general formula (II), and 0-20 mol % of at least one second comonomer selected from the group consisting of compounds of formula (III) and compounds of formula (IV).

[0078] In a preferred embodiment of the present invention, at least a portion of the OH end groups of the POM are capped. Methods for capping the OH end groups are known to those skilled in the art. For example, the OH end groups can be capped by etherification or esterification.

[0079] Preferred POM copolymers useful for coextrusion have a melting point of at least 150° C., preferably 150-200° C., most preferably 160-180° C. The melting point of the POM is determined on a sample mass of about 8.5 mg according to DIN EN ISO 11357-3 (2013-04) with a heating and cooling rate of 20 K / min.

[0080] Preferred POM copolymers have a weight average molecular weight M in the range from 5000 g / mol to 300 000 g / mol, preferably from 10 000 to 240 000 g / mol, particularly preferably from 80 000 to 220 000 g / mol. w has.

[0081] The preferred POM copolymers have a number average molecular weight M n (determined as described below) preferably in the range of 8000 to 85000 g / mol, preferably in the range of 9000 to 38000 g / mol.

[0082] Preferred POM copolymers useful for coextrusion have a melt flow rate (MFR) of 10 g / 10 min or less, preferably 0.5 to 8 g / 10 min, and most preferably 1 to 5 g / 10 min, according to ISO 1133-1 at 190° C. and 2.16 kg.

[0083] POM copolymers having a polydispersity (Mw / Mn) of 1.4-14 are particularly preferred, with Mw / Mn more preferably in the range of 2.1-14.

[0084] The molecular weights of polymers and POMs were determined by size exclusion chromatography on an SEC apparatus (size exclusion chromatography). The SEC apparatus consisted of a combination of the following separate columns: a preparatory column 5 cm long and 8 mm in diameter, and a second linear column 30 cm long and 7.5 mm in diameter. The separation material for both columns was PLHFIP gel from Polymer Laboratories. The detector used was an Agilent 1100 differential refractometer. A mixture of hexafluoroisopropanol with 0.05% potassium trifluoroacetate was used as the eluent. The flow rate was 1 ml / min and the column temperature was 35°C. 60 microliters of solution were injected at a concentration of 1.5 g analyte per liter of eluent. The analyte solution had been previously filtered through Millipor Millex FG (pore width 0.2 micrometers). For calibration, narrow-dispersity PMMA standards from PSS (Mainz, DE) with molecular weights M ranging from 800 to 2.220.000 g / mol were used. The polydispersity index is defined as the mass average molecular weight divided by the number average molecular weight.

[0085] Mass average molecular weight (M w ) and number average molecular weight (M n The measurement of ) is commonly performed by gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC).

[0086] Methods for preparing POM are known to those skilled in the art.

[0087] Polyolefin The binder typically comprises 2-35% by weight of polyolefin (also referred to herein as "PE") In a preferred embodiment, the binder comprises 3-20% by weight of polyolefin, and particularly preferably 4-15% by weight of polyolefin, based on the total weight of the binder.

[0088] According to the invention, the polyolefin is at least one polyolefin. "At least one polyolefin" in the context of the present invention means exactly one polyolefin and also a mixture of two or more polyolefins.

[0089] Polyolefins are known per se and commercially available. They are usually prepared by polymerization of C2C8 alkene monomers, preferably by polymerization of C2C4 alkene monomers.

[0090] In the context of the present invention, a C2C8 alkene means an unsubstituted or at least monosubstituted hydrocarbon having 2 to 8 carbon atoms and at least one carbon-carbon double bond (C=C double bond). "At least one carbon-carbon double bond" means exactly one carbon-carbon double bond as well as two or more carbon-carbon double bonds.

[0091] In other words, C2C8 alkene means that the hydrocarbon having 2 to 8 carbon atoms is unsaturated. The hydrocarbon may be branched or unbranched. Examples of C2C8 alkenes with one C=C-double bond are ethene, propene, 1-butene, 2-butene, 2-methyl-propene (=isobutylene), 1-pentene, 2-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-hexene, 3-hexene and 4-methyl-1-pentene. Examples of C2C8 alkenes with two or more CC-double bonds are allene, 1,3-butadiene, 1,4-pentadiene, 1,3-pentadiene, 2-methyl-1,3-butadiene (=isoprene).

[0092] When the C2C8 alkene has one C-C double bond, the polyolefins prepared from those monomers are linear. When more than one double bond is present in the C2-C8-alkene, the polyolefins prepared from those monomers can be crosslinked. Linear polyolefins are preferred.

[0093] It is also possible to use polyolefin copolymers prepared by using different C2C8 alkene monomers during the preparation of the polyolefin.

[0094] Preferably, the polyolefin is selected from the group consisting of polymethylpentene, poly-1-butene, polyisobutylene, polyethylene and polypropylene. Particularly preferred are polyethylene and polypropylene and their copolymers, as known to those skilled in the art and commercially available.

[0095] The polyolefins may be prepared by any polymerization process known to those skilled in the art, preferably by free radical polymerization, for example emulsion, bead, solution or bulk polymerization. Possible initiators are free radical initiators such as peroxy compounds and azo compounds, depending on the monomer and type of polymerization, the amount of initiator generally being in the range of 0.001 to 0.5% by weight relative to the monomer.

[0096] Further Polymers The binder may further comprise 1 to 25% by weight of a further polymer. In a preferred embodiment, the binder comprises 2 to 20% by weight of a further polymer, and particularly preferably 4 to 16% by weight of a further polymer, based on the total amount of the binder.

[0097] The further polymer according to the invention is at least one further polymer. "At least one further polymer" in the present invention means exactly one further polymer and also a mixture of two or more further polymers.

[0098] As already mentioned above, the at least one further polymer is different from the polyoxymethylene, the polyolefin and the dispersant described below.

[0099] According to the invention, the at least one further polymer is preferably selected from the group consisting of polyethers, polyurethanes, polyepoxides, polyamides, vinyl aromatic polymers, poly(vinyl esters), poly(vinyl ethers), poly(alkyl(meth)acrylates) and copolymers thereof.

[0100] Preferably, the further polymer is selected from the group consisting of poly(C2-C6-alkylene oxides), aliphatic polyurethanes, aliphatic non-crosslinked epoxides, aliphatic polyamides, vinyl aromatic polymers, poly(vinyl esters) of aliphatic C1-C8 carboxylic acids, poly(vinyl ethers) of C1-C8 alkyl vinyl ethers, poly(alkyl(meth)acrylates) of C1-8 alkyl and copolymers thereof.

[0101] Preferred additional polymers are described in more detail below.

[0102] The polyether has the formula (V) [ka] The repeat unit During the ceremony, R 11 ~R 14 are each independently selected from the group consisting of H, C1C4 alkyl, and halogen-substituted C1C4 alkyl; R 15 is a chemical bond, (-CR 15a R 15b -) group and (-CR 15a R 15b O-) groups, During the ceremony, R 15a and R 15bare each independently selected from the group consisting of H and unsubstituted or at least monosubstituted C1C4 alkyl, the substituents being selected from the group consisting of F, Cl, Br, OH and C1C4 alkyl; and n is 0, 1, 2 or 3.

[0103] If n is 0, R 15 R is a chemical bond between adjacent carbon and oxygen atoms. 15 (-CR 15a R 15b In the case of a (-CR 15a R 15b The oxygen atom (O) of the O- group is bonded to another carbon atom (C) of formula (V), and is not bonded to the oxygen atom (O) of formula (V). In other words, formula (V) does not include a peroxide compound. The same is true for formula (VI).

[0104] Typical polyethers and their preparation are known to those skilled in the art.

[0105] According to the invention, preferred polyethers are, for example, poly(alkylene glycols), also known as poly(alkylene oxides).

[0106] Polyalkylene oxides and their preparation are known to those skilled in the art. They are usually synthesized by the interaction of water and dihydric or polyhydric alcohols with cyclic ethers, i.e., alkylene oxides of general formula (VI). The reaction is catalyzed by acidic or basic catalysts. The reaction is carried out by reacting the alkylene oxides of general formula (VI) with water and dihydric or polyhydric alcohols. [ka] This is the so-called ring-opening polymerization of cyclic ethers of the formula During the ceremony, R 11 ~R 15 has the same meaning as defined above for formula (V).

[0107] According to the present invention, the preferred poly(alkylene oxide) is derived from a monomer of general formula (VI) having 2 to 6 carbon atoms in the ring. In other words, the poly(alkylene oxide) is preferably a poly(C2-C6 alkylene oxide). Particularly preferred is a poly(alkylene oxide) derived from a monomer selected from the group consisting of 1,3 dioxolane, 1,3 dioxepane and tetrahydrofuran (IUPAC name: oxolane). In other words, the poly(alkylene oxide) is particularly preferably selected from the group consisting of poly-1,3 dioxolane, poly-1,3 dioxepane and polytetrahydrofuran.

[0108] In one embodiment, the poly(alkylene oxide) can include OH end groups. In another embodiment, at least a portion of the OH end groups of the poly(alkylene oxide) can be capped. Methods for capping the OH end groups are known to those skilled in the art. For example, the OH end groups can be capped by etherification or esterification.

[0109] The mass average molecular weight of the poly(alkylene oxide) is preferably in the range of 1000 to 100000 g / mol, particularly preferably in the range of 1200 to 80000 g / mol, and more preferably in the range of 1500 to 50000 g / mol.

[0110] Polyurethanes are polymers containing carbamate units. Polyurethanes and their preparation are known to those skilled in the art.

[0111] Aliphatic polyurethanes are preferred in the present invention. They can be prepared, for example, by polyaddition of aliphatic polyisocyanates and aliphatic polyhydroxy compounds. Among the polyisocyanates, those represented by the general formula (VII) OCN-R 7 -NCO (VII) The diisocyanates During the ceremony, R 7 is a substituted or unsubstituted C1-C 20 Alkanediyl or C4-C20 It is a cycloalkanediyl, the substituents being selected from the group consisting of F, Cl, Br and C1C6 alkyl.

[0112] Preferably, R 7 is a substituted or unsubstituted C2C 12 Alkanediyl or C6C 15 It is a cycloalkanediyl.

[0113] C1C 20 Alkanediyl is a hydrocarbon having 2 free valences and 1 to 20 carbon atoms. 20 The alkanediyl can be branched or unbranched.

[0114] In the context of the present invention, C4-C 20 The definition of cycloalkanediyl is C4C 20 It means cycloalkanediyl. C4C 20 Cycloalkanediyl is a cyclic hydrocarbon having two free valences and a carbon number from 4 to 20. Hydrocarbons having two free valences, cyclic and also linear moieties, and a carbon number from 4 to 20 likewise fall under this definition.

[0115] Preferred diisocyanates are selected from the group consisting of hexamethylene diisocyanate, 2,2,4 trimethylhexamethylene diisocyanate, 2,4,4 trimethylhexamethylene diisocyanate, 1,2-diisocyanatomethylcyclohexane, 1,4 diisocyanatomethylcyclohexane and isophorone diisocyanate (IUPAC name: 5-isocyanato 1 (isocyanatomethyl) 1,3,3 trimethyl-cyclohexane).

[0116] The diisocyanates may also be used in oligomeric, e.g. dimeric or trimeric form. Instead of the polyisocyanates it is also possible to use conventional blocked polyisocyanates which are obtained from the mentioned isocyanates, e.g. by addition reaction with phenols or caprolactam.

[0117] Polyhydroxy compounds suitable for the preparation of aliphatic polyurethanes are, for example, polyesters, polyethers, polyesteramides or polyacetals, or mixtures thereof.

[0118] Suitable chain extenders for the preparation of polyurethanes are low molecular weight polyols, especially diols and polyamines, especially diamines, or water.

[0119] The polyurethanes are preferably thermoplastic and therefore essentially uncrosslinked, i.e., they can be repeatedly melted without significant signs of decomposition. Their reduced specific viscosity, measured in dimethylformamide at 30° C., is generally between 0.5 and 3 dl / g, preferably between 1 and 2 dl / g.

[0120] A polyepoxide contains at least two epoxide groups, also known as glycidyl or oxirane groups. "At least two epoxide groups" means exactly two epoxide groups as well as three or more epoxide groups.

[0121] Polyepoxides and their preparation are known to those skilled in the art. For example, polyepoxides are prepared by the reaction of epichlorohydrin (IUPAC name: chloromethyloxirane) and diols, polyols or dicarboxylic acids. The polyepoxides thus prepared are polyethers with epoxide end groups.

[0122] Another possibility for preparing polyepoxides is the reaction of glycidyl (meth)acrylate (IUPAC name: oxiran-2-ylmethyl-2-methylprop-2-enoate) with polyolefins or polyacrylates, which gives polyolefins or polyacrylates with epoxy end groups.

[0123] Preferably, aliphatic uncrosslinked polyepoxides are used. Copolymers of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane (bisphenol A) are particularly preferred.

[0124] Component (b3) (the at least one further polymer (FP)) may also comprise a polyamide. Aliphatic polyamides are preferred.

[0125] The intrinsic viscosity of suitable polyamides is generally between 150 and 350 ml / g, preferably between 180 and 275 ml / g. The intrinsic viscosity here is determined according to ISO 307 from a solution of 0.5% by weight of polyamide in 96% by weight of sulfuric acid at 25° C.

[0126] Preferred polyamides are semicrystalline or amorphous polyamides.

[0127] Examples of suitable polyamides as component (b3) are those derived from lactams having 7 to 13 ring members. Other suitable polyamides are those obtained by reaction of dicarboxylic acids with diamines.

[0128] Examples that may be mentioned of polyamides derived from lactams are polyamides derived from polycaprolactam, polycaprylolactam and / or polylaurolactam.

[0129] When polyamides obtainable from dicarboxylic acids and diamines are used, the dicarboxylic acids which can be used are alkanedicarboxylic acids having 6 to 14 carbon atoms, preferably 6 to 10 carbon atoms. Aromatic dicarboxylic acids are also suitable.

[0130] Examples which may be mentioned here as dicarboxylic acids are adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and terephthalic acid and / or isophthalic acid.

[0131] Examples of suitable diamines are alkanediamines having 4 to 14 carbon atoms, in particular alkanediamines having 6 to 8 carbon atoms, and aromatic diamines, such as m-xylylenediamine, di(4-aminophenyl)methane, di(4-aminocyclohexyl)methane, 2,2-di(4-aminophenyl)propane, 2,2-di(4-aminocyclohexyl)-propane, and 1,5-diamino-2-methylpentane.

[0132] Other suitable polyamides are those obtainable by copolymerization of two or more of the monomers mentioned above and below, and mixtures of several polyamides in any desired mixing ratio.

[0133] Preferred polyamides are polyhexamethylene adipamide, polyhexamethylene-sebacamide, and polycaprolactam and nylon 6 / 6,6, in particular those having a proportion of caprolactam units of 75 to 95% by weight.

[0134] Mixtures of nylon 6 with other polyamides, in particular nylon 6 / 6,6 (PA6 / 66), are particularly preferred, as are mixtures of 80 to 50% by weight PA6 and 20 to 50% by weight PA6 / 66, the PA6 / 66 containing 75 to 95% by weight of caprolactam units relative to the total weight of PA6 / 66 in the mixture.

[0135] The following non-limiting list includes the polyamides described above, as well as other suitable polyamides and monomers that may be included.

[0136] AB Polymer: PA4 Pyrrolidone PA6 ε-caprolactam PA7 Ethanol Lactam PA8 Caprylolactam PA9 9-Aminopelargonic acid PA11 11-aminoundecanoic acid PA12 Laurolactam.

[0137] AA / BB polymer: PA46 Tetramethylenediamine, Adipic acid PA66 Hexamethylenediamine, Adipic acid PA69 Hexamethylenediamine, Azelaic acid PA610 Hexamethylenediamine, Sebacic acid PA612 Hexamethylenediamine, Decanedicarboxylic acid PA613 Hexamethylenediamine, undecanedicarboxylic acid PA1212 1,12-Dodecanediamine, decanedicarboxylic acid PA1313 1,13-Diaminotridecane, undecanedicarboxylic acid PA6T Hexamethylenediamine, Terephthalic acid PA MXD6 m-Xylylenediamine, Adipic Acid.

[0138] PA6I Hexamethylenediamine, Isophthalic acid PA6-3-T Trimethylhexamethylenediamine, terephthalic acid PA6 / 6T (see PA6 and PA6T) PA6 / 66 (see PA6 and PA66) PA6 / 12 (see PA6 and PA12) PA66 / 6 / 610 (see PA66, PA6 and PA610) PA6I / 6T (see PA6I and PA6T) PA PACM6 Diaminodicyclohexylmethane, Adipic Acid PA PACM12 Diaminodicyclohexylmethane, Laurolactam PA6I / 6T / PACM PA6I / 6T+diaminodicyclohexylmethane PA12 / MACMI Laurolactam, Dimethyldiaminodicyclohexylmethane, Isophthalic Acid PA12 / MACMT Laurolactam, Dimethyldiaminodicyclohexylmethane, Terephthalic Acid PA PDA-T Phenylenediamine, Terephthalic Acid.

[0139] Preferred polyamides are PA6, PA66 and PA PACM6.

[0140] The vinyl aromatic polymer is a polyolefin having unsubstituted or at least monosubstituted styrene as a monomer unit. Suitable substituents are, for example, C1C6 alkyl, F, Cl, Br and OH. The preferred vinyl aromatic polymer is selected from the group consisting of polystyrene, poly-alpha methylstyrene, and copolymers thereof having up to 30% by weight of a comonomer selected from the group consisting of acrylic esters, acrylonitrile and methacrylonitrile.

[0141] Vinyl aromatic polymers are commercially available and known to those skilled in the art, and the preparation of these polymers is also known to those skilled in the art.

[0142] Preferably, the vinyl aromatic polymers are prepared by free radical polymerization, for example by emulsion, bead, solution or bulk polymerization. Possible initiators are free radical initiators such as peroxide compounds and azo compounds, depending on the monomer and type of polymerization, the amount of initiator generally being in the range of 0.001-0.5% by weight relative to the monomer.

[0143] Poly(vinyl ester) and its preparation are known to those skilled in the art. Poly(vinyl ester) is preferably prepared by polymerization of vinyl ester. In a preferred embodiment of the present invention, the vinyl ester is a vinyl ester of an aliphatic C1C6 carboxylic acid. Preferred monomers are vinyl acetate and vinyl propionate. These monomers form poly(vinyl acetate) and poly(vinyl propionate) polymers.

[0144] Poly(vinyl ether) is prepared by polymerization of vinyl ether monomers. Poly(vinyl ether) and its preparation are known to those skilled in the art. In a preferred embodiment, the vinyl ether is an aliphatic C1C8 alkyl ether vinyl ether. Preferred monomers are methyl vinyl ether and ethyl vinyl ether, which form poly(methyl vinyl ether) and poly(ethyl vinyl ether) during polymerization.

[0145] Preferably, the poly(vinyl ether) is prepared by free radical polymerization, for example by emulsion, bead, solution, suspension or bulk polymerization. Possible initiators are free radical initiators such as peroxide compounds and azo compounds, depending on the type of monomer and polymerization, the amount of initiator generally being in the range of 0.001-0.5% by weight relative to the monomer.

[0146] The poly(alkyl(meth)acrylate) in the present invention includes poly(alkyl acrylate), poly(alkyl methacrylate) and copolymers thereof. The poly(alkyl(meth)acrylate) is represented by the formula (VIII): [ka] and a unit derived from the monomer During the ceremony, R 8 is selected from the group consisting of H and C1C8 alkyl, and R 9 is represented by formula (IX) [ka] Based on In the formula, R 10 is C 1 C 14 It is an alkyl.

[0147] Preferably, R 8 is selected from the group consisting of H and C1-C4-alkyl, particularly preferably R 8 is H or methyl. Preferably, R10 is C1-C8-alkyl, particularly preferably, R10 is methyl or ethyl.

[0148] R in formula (VIII) 8 is H and R 9 is a group of formula (IX), and R 10 When is methyl, the monomer of formula (VIII) is methyl acrylate.

[0149] R in formula (VIII) 8 is H and R 9 is a group of formula (IX), and R 10 When is ethyl, the monomer of formula (VIII) is ethyl acrylate.

[0150] R in formula (VIII) 8 is methyl and R 9 When is a group of formula (IX), the monomer of formula (VI) is a methacrylic acid ester.

[0151] The poly(alkyl(meth)acrylate) preferably comprises, as monomers, 40 to 100% by weight of methacrylic acid esters, particularly preferably 70 to 100% by weight of methacrylic acid esters, and more preferably 80 to 100% by weight of methacrylic acid esters, in each case based on the total amount of poly(alkyl(meth)acrylate).

[0152] In another preferred embodiment, the poly(alkyl(meth)acrylate) comprises as monomers 20 to 100% by weight of methyl acrylate, ethyl acrylate or mixtures thereof, preferably 40 to 100% by weight of methyl acrylate, ethyl acrylate or mixtures thereof, and particularly preferably 50 to 100% by weight of methyl acrylate, ethyl acrylate or mixtures thereof, in each case based on the total weight of the poly(alkyl(meth)acrylate).

[0153] Those skilled in the art know that the above monomers for preparing components (b1), (b2) and (b3) may undergo changes in their structure during the polymerization reaction. As a result, the building blocks of the polymer are not the same as the monomers from which they are derived. However, those skilled in the art know which monomers correspond to which building blocks of the polymer.

[0154] Under the conditions of processing by compounding or injection molding, substantially no transacetalization occurs between component (b1), the polyoxymethylene (POM), and component (b3), the at least one further polymer (FP), i.e. substantially no exchange of comonomer units occurs.

[0155] In another embodiment of the invention that is particularly useful for fused filament manufacturing processes, the at least one additional polymer (FP) is selected from the group consisting of polyethers, polyurethanes, polyepoxides, polyamides, vinyl aromatic polymers, poly(vinyl esters), poly(vinyl ethers), poly(alkyl(meth)acrylates), and copolymers thereof.

[0156] Additives In one embodiment of the invention, the feedstock may comprise 0 to 5% by volume of dispersant. In a preferred embodiment, the mixture comprises 0.05 to 3% by volume of dispersant, and particularly preferably 0.1 to 3% by volume of dispersant, in each case relative to the total volume of the mixture.

[0157] As dispersant one or more dispersants may be used.

[0158] Useful dispersants are generally known in the art, examples being oligomeric polyethylene oxides having a low molecular weight of 200 to 600 g / mol, stearic acid, stearamide, hydroxystearic acid, fatty alcohols, fatty alcohol sulfonates and block copolymers of ethylene oxide and propylene oxide, and particularly preferably fatty acid esters.

[0159] In one embodiment of the present invention, the feedstock may contain other additives such as polysorbates.

[0160] PTL formation In accordance with the present invention, a PTL is formed by carrying out the following steps.

[0161] In a first step, a first feedstock comprising a first metal particle and a first polymeric binder, and a second feedstock comprising a second metal particle and a second polymeric binder are provided, where the first and second feedstocks have a metal powder content of 40-70 volume percent, and the first feedstock has either smaller average particle size metal particles or a higher metal powder content, or both smaller average particle size metal particles and a higher metal powder content, compared to the particles in the second feedstock.

[0162] In a second step, the first and second feedstocks are co-extruded to form a film-shaped green body including a first layer and a second layer, wherein the second layer is physically bonded to the first layer at a temperature above the melting temperature and / or glass transition temperature of the first and second binders.

[0163] The second step may be followed by an optional step of further post-processing the film-shaped green body by rolling or calendering.

[0164] Finally, the film-shaped green body is debindered, preferably catalytically debindered, to form a Brown body, and then heated in a non-oxidizing atmosphere or vacuum, preferably for 10 -4 The brown body is sintered at less than mbar and at a temperature of 700-1300° C. to form a porous transport layer.

[0165] One embodiment is a method for making a multi-layer porous transport layer, the method comprising the steps of: (a) providing a first feedstock comprising first metal particles and a first polymer binder, and providing a second feedstock comprising a second metal particles and a second polymer binder, The first and second feedstocks have a metal powder content of 40 to 70 volume percent; and The first feedstock is compared to the second feedstock. (i) metal particles with a smaller average particle size; (ii) A higher metal powder content; or (iii) Both smaller average particle size metal particles and higher metal powder content The process comprising: (b) co-extruding the first and second feedstocks to form a film-shaped green body comprising a first layer and a second layer, the second layer being physically connected to the first layer at a temperature above the melting temperature and / or glass transition temperature of the first polymer binder and the second polymer binder; (c) optionally smoothing the film-shaped green body by rolling or calendaring; (d) debinding the film-shaped green body to form a brown body; (e) sintering the Brownian body in a non-oxidizing atmosphere or in vacuum and at a temperature between 700 and 1100° C. to form a porous transport layer; Includes.

[0166] A particularly preferred embodiment is a method for making a multi-layer porous transport layer, the method comprising the steps of: (a) providing a first feedstock comprising first metal particles and a first polymer binder, and providing a second feedstock comprising a second metal particles and a second polymer binder, The first and second feedstocks have a metal powder content of 40 to 70 volume percent; and The first feedstock is compared to the second feedstock. (i) metal particles with a smaller average particle size; (ii) A higher metal powder content; or (iii) Both smaller average particle size metal particles and higher metal powder content The process comprising: (b) co-extruding the first and second feedstocks to form a film-shaped green body comprising a first layer and a second layer, the second layer being physically connected to the first layer at a temperature above the melting temperature and / or glass transition temperature of the first and second polymeric binders; (c) optionally smoothing the film-shaped green body by rolling or calendaring; (d) debinding the film-shaped green body to form a brown body; (e) sintering the Brownian body in a non-oxidizing atmosphere or in vacuum and at a temperature between 700 and 1100° C. to form a porous transport layer; Including, The first feedstock and the second feedstock are free of any solvent; The first feedstock and the second feedstock have a melt flow rate of 50 to 700 g / 10 min at 190° C. and 21.6 kg according to ISO 1133; and the first polymeric binder, the second polymeric binder, or both the first and second polymeric binders have a melt flow rate of 1 to 5 g / 10 min at 190° C. and 2.16 kg according to ISO 1133-1; and the first polymeric binder, the second polymeric binder, or both the first and second polymeric binders are (i) 35 to 55 volume percent polyoxymethylene; (ii) 2 to 10 volume percent of a polyolefin; (iii) optionally 3 to 10 volume percent of a further polymer, and (iv) optionally 0.5 to 5 volume percent of a dispersant; Includes.

[0167] Feedstock Preparation The feedstock in step (a) may be prepared by any method known to the skilled artisan. Preferably, the feedstock is prepared by melting the binder and mixing it into the metal powder. For example, the binder can be melted in a twin screw extruder, preferably at a temperature of 150-220°C, in particular 170-200°C. The metal powder is then metered in the amount required for the binder melt flow at the same temperature range. Alternatively, the binder may be melted in a Sigma Kneader extruder, preferably at a temperature of 150-220°C, in particular 170-200°C. The metal powder is then metered in the amount required for the binder melt flow at the same temperature range.

[0168] Preferably, the first feedstock and the second feedstock do not contain any solvent.

[0169] Furthermore, the entire compounding line, i.e. hopper, dosing unit, twin screw extruder, granulator, etc., is preferably set up as a closed system that can be washed with inert cases, improving the safe handling of ground titanium or ground metal powders in general.

[0170] The distribution and dispersive mixing of the metal powder within the binder matrix, which determines the pore size distribution, can be influenced by adapting the screw design, which can be designed in a manner known to those skilled in the art.

[0171] During compounding, the binder melts and further mixing / homogenization takes place. Distributive and dispersive mixing can be adjusted based on the process design. Custom screw designs can be implemented using methods known to those skilled in the art. The molten strands are extruded through a die head where they are granulated and further cooled.

[0172] Any compounding method can be used to melt and further homogenize the feedstock, such as, but not limited to, a kneader, a planetary extruder, a twin screw extruder, and the like.

[0173] In a preferred embodiment, a twin screw extruder is used as the primary compounding method, which results in a narrow unimodal or bimodal pore size distribution, thus improving the oxygen transport properties of the PTL and improving water transport through the PTL by reducing pressure drop.

[0174] Co-extrusion According to the invention, the first and second feedstocks are coextruded in step (b) to form a film-shaped green body comprising a first layer and a second layer, the second layer being physically connected to the first layer at a temperature higher than the melting temperature and / or glass transition temperature of the first and second polymer binders.

[0175] Coextrusion simplifies processing and allows the formation of two or more layers of PTL in a one-step process. Coextrusion results in a gradient of porosity and pore size distribution within the bi- or multi-layer PTL, i.e., a continuous and smooth transition from the smaller porosity and pore size of the first layer to the higher porosity and pore size of the second layer without any discontinuities or formation of highly porous regions in the transition phase of the PTL. In addition, the internal stresses at the interfaces between the first, second and any additional layers are reduced. These result in better oxygen-water transport behavior, better mechanical properties and fewer defects in the final sintered PTL (such as, but not limited to, internal cracks, bumps or surface warpage).

[0176] Co-extrusion is typically carried out using conventional cast film (co)extruders known in the art with respective single or twin screw extruders for feeding the respective feedstocks. In one embodiment, the melt is extruded through a flat die with a gap ranging from 0.1 to 2 mm having multiple adjustable heating zones. The extruded melt is fed through a roller system to further reduce the shape and to cool the melt and ultimately reduce the thickness to the target final thickness of the film-shaped green body.

[0177] Optionally, a third, fourth or more layers may be coextruded to obtain a green body followed by a PTL comprising three, four or more layers. Additional layer(s) may be coextruded onto the first or second layer. The layers should be configured in an order such that the layer with the highest porosity and average pore size contacts the bipolar plate, the layer with the lower porosity and average pore size flows through, and finally the layer with the lowest porosity and average pore size contacts the catalyst layer.

[0178] For some POM grades, it may be useful to ensure that the maximum allowable moisture content in the binder is less than 0.2% by weight based on the total binder. If necessary, pre-drying may be performed to reduce the moisture content to less than 0.2% by weight. By way of example, pre-drying may be performed at a temperature of about 100° C. for about 3 hours.

[0179] For co-extrusion, a melt temperature of 175° C. to 220° C. is preferably used. This process produces three-dimensional green bodies.

[0180] It is particularly advantageous to process the feedstock with a three-zone screw having an overall length L of 20-25 D and a constant flight pitch of about 1 D. However, shorter compression screws may also be used.

[0181] Due to temporal and local differences in solidification and cooling of the melt, stresses may arise, especially at low layer thicknesses. These stresses are relieved by a subsequent heat treatment. If high dimensional stability is required, a tempering step may be necessary. Tempering may be carried out in air, liquid wax or oil at temperatures between 100°C and 150°C, preferably between 110°C and 130°C. Usually, a tempering time of 10 minutes per mm of wall thickness is required. This step can be carried out in a debinding oven separately or simultaneously with the debinding.

[0182] In order to minimize material usage, reduce through-surface resistivity, and keep the thickness of the porous transport layer as small as possible, it is advantageous to design the film formed from the metal powder and binder to a thickness of 0.1 mm to 1 mm, preferably 0.1 mm to 0.5 mm, where the minimum layer thickness is determined by the maximum particle size or sieve size of the metal powder fraction, the smaller the maximum particle size, the smaller the layer thickness of the film can be.

[0183] For example, in the case of a PEM electrolyser, it is envisaged that the microporous layer is in contact with a catalyst layer arranged on a polymer electrolyte membrane. In order to ensure a good conductive surface contact, it is now envisaged, according to a further development of the method according to the invention, that the surface of the side of the porous transport layer which is to be supported on the free surface of the catalyst, i.e. the microporous layer, is smoothed by rolling or calendering the film-shaped green body.

[0184] In a preferred embodiment, the film-shaped green body has a thickness of 0.1 to 1 mm, preferably 0.1 to 0.5 mm.

[0185] In one embodiment of the present invention, the meter-long film-shaped green bodies are preferably wound on spools for ease of handling, storage and transportation.

[0186] Debinding The co-extrusion step is followed by a debinding step in which at least a portion of the binder is removed from the three-dimensional green body. The binder is removed thermally or catalytically. Catalytic debinding is preferred.

[0187] To remove at least a portion of the binder, the three-dimensional green body is preferably treated in an atmosphere containing a gaseous acid. Suitable processes are described, for example, in US 2009 / 0288739 and US 5145900. This process step is preferably carried out according to the invention at a temperature below the melting temperature of the binder. In general, debinding is carried out at a temperature in the range of 20 to 150° C., and particularly preferably 100 to 140° C. Preferably, the debinding step is carried out for a period of 0.1 to 24 hours, particularly preferably 0.5 to 12 hours, and most preferably 0.5 to 4 hours.

[0188] The required treatment time varies depending on the treatment temperature and the concentration of the acid in the treatment atmosphere, as well as the dimensions and thickness of the three-dimensional object.

[0189] Catalytic debinding provides the necessary tempering effect for the coextruded green bodies, which further flatten the large green PTLs due to temperature and gravity. This is especially important for film-shaped green bodies with a thickness of less than 1 mm. In addition, this process helps to flatten film-shaped green bodies that have previously been rolled on spools, for example during transportation, storage, etc.

[0190] Catalytic debinding offers the possibility of slowing down the debinding reaction kinetics, which is favorable to relieve the inevitable internal stresses within the PTL resulting from the bypass of the highly loaded polymer melt through a thin flat die with a gap of 0.1 mm to 2 mm, a roller system to adjust the final film thickness, and / or thin flat coextrusion followed by subsequent calendering, in addition to stresses due to differences in the thermal properties of the feedstock mixtures utilized.

[0191] Suitable acids for debinding are, for example, inorganic acids that are gaseous at room temperature or can be vaporized below the processing temperature. Examples include hydrogen halides and nitric acid. Hydrogen halides include hydrogen fluoride, hydrogen chloride, hydrogen bromide and hydrogen iodide. Suitable organic acids are those that have a boiling point below 130°C at atmospheric pressure, such as formic acid, acetic acid or trifluoroacetic acid and mixtures thereof. Acids with a boiling point above 130°C, such as methanesulfonic acid, can be utilized in the debinding step when introduced as a mixture with a lower boiling acid and / or water. Preferred acids for process step (III) are nitric acid, a 10% by weight aqueous solution of oxalic acid, or a mixture of 50% by volume of methanesulfonic acid in water.

[0192] Additionally, BF3 and its adducts with inorganic ethers can be used as acids.

[0193] When using carrier gas, carrier gas is generally passed through acid and preloaded with acid.The carrier gas thus loaded with acid is then brought to the temperature at which debinding is carried out.This temperature is advantageously higher than the loading temperature in order to avoid condensation of acid.Preferably, the temperature at which debinding is carried out is at least 1°C higher than the loading temperature, particularly preferably at least 5°C, and most preferably at least 10°C higher.

[0194] Preferably, the acid is mixed into the carrier gas by a metering device and the gas mixture is heated to a temperature at which the acid can no longer condense. Preferably, the temperature is at least 1° C., particularly preferably at least 5° C., and most preferably at least 10° C. higher than the sublimation and / or vaporization temperature of the acid and / or the carrier gas.

[0195] The carrier gas is generally any gas that is inert under the reaction conditions of the catalytic debinding step. According to the present invention, the preferred carrier gas is nitrogen or argon, most preferably nitrogen. The binder removal may be carried out under reduced pressure.

[0196] The catalytic debinding is preferably continued until at least 80% by weight, preferably at least 90% by weight, particularly preferably at least 95% by weight, of the polyoxymethylene (POM) binder, based on the total weight of the POM, has been removed, which can be seen, for example, by the magnitude of the mass loss.

[0197] It is known to those skilled in the art that at the temperatures of the catalytic debinding process, the metal powder contained in the three-dimensional green body may undergo chemical and / or physical reactions, in particular, the particles of the metal powder may fuse together, undergo solid-state phase transitions, and / or chemical reactions with the acidic atmosphere or carrier gas.

[0198] The same is true for the binder: during the catalytic debinding process the composition of the binder may change.

[0199] Sintering Debinding of the green body is followed by a sintering step (f) in which the three-dimensional brown body is sintered.

[0200] After sintering, the three-dimensional object is a three-dimensional sintered body, which comprises an agglomerate of the initial metal powder and is essentially free of binder.

[0201] "Essentially free of binder" according to the present invention means that the three-dimensional sintered body contains less than 5% by volume, preferably less than 2% by volume, particularly preferably less than 0.5% by volume, and most preferably less than 0.01% by volume of binder.

[0202] It is known to those skilled in the art that metal powders are sintered together during the sintering process to produce sintered inorganic powders. Furthermore, during the sintering process, the metal powders may undergo chemical and / or physical reactions. As a result, the metal powders contained in the three-dimensional Brownian body are usually different from the sintered inorganic powders contained in the three-dimensional sintered body.

[0203] Sintering may generally be carried out by heating the brown body to a temperature of from 700 to 1300° C. for a time sufficient to sinter the particles.

[0204] In a preferred embodiment of pure titanium particles, sintering temperatures of 700-1100°C, preferably 800-980°C, and most preferably 850-950°C are used. For example, by sintering the PTL at 870°C instead of 940°C with the same sintering hold time, the porosity can be increased by about 15%. Furthermore, the average pore size increases by 2-4 μm. The entire PTL (two- or three-layer PTL) is sintered at the same temperature for the same time.

[0205] In one embodiment of the present invention, sintering is performed according to the following temperature profile: i. heating at a rate of 2-7°C / min to a temperature of 550-650°C; ii. Holding at a temperature of 550-650°C for 0.5-1.5 hours; iii. heating at a rate of 2-7°C / min to a temperature of 700-1000°C; iv. Holding at a temperature of 700-1000°C for 0.5-2 hours; and v. Cool to ambient temperature at a rate of 5-15°C / min.

[0206] In another embodiment of the invention, sintering is carried out according to the following temperature profile: i. heating at a rate of 2-7°C / min to a temperature of 550-650°C; ii. Holding at a temperature of 550-650°C for 0.5-1.5 hours; iii. heating at a rate of 2-7°C / min to a temperature of 650-800°C; iv. heating at a rate of 2-7°C / min to a temperature of 800-1100°C; v. Holding at a temperature of 800-1100°C for 2-5 hours; and vi. Cool to ambient temperature at a rate of 5-15°C / min.

[0207] The sintering step is preferably carried out at normal pressure using an atmosphere of argon, nitrogen, hydrogen, partial pressure variants or mixtures thereof. The use of reduced pressure or vacuum is also possible. When sintering titanium powder in a vacuum, 10 -4 Pressures below mbar are preferred.

[0208] In one embodiment of the present invention, after debinding and before sintering, the three-dimensional brown body obtained in step (e) is heated for preferably 0.1 to 12 hours, particularly preferably 0.3 to 6 hours, preferably at a temperature of 250 to 700°C, particularly preferably 250 to 600°C, in order to completely remove the residual binder.

[0209] Alternatively or additionally to smoothing, it is advantageous to chemically roughen the surface, preferably by etching. In particular, the porosity of the surface region and the intimate, electrically conductive contact when the surface contacts the catalyst layer are ensured by this method. For porous transport layers made of titanium, such pickling procedures are effected, for example, by treatment with sulfuric acid.

[0210] Alternatively or additionally, the final PTL may be surface treated, e.g., by post-treatment with hydrochloric acid, as described in Journal of Applied Electrochemistry (2018) 48:713-723. In this case, HCl can reduce the TiO2 content, which improves the electrical conductivity of the PTL, which is positively reflected in the efficiency and durability of the PTL.

[0211] PTL The method according to the invention provides a PTL comprising at least two layers of different porosity without any discontinuities, in particular without any highly porous zones in the transition phase between the two layers of the PTL.The method according to the invention can be used for the manufacture of porous transport layers for electrochemical cells, such as batteries, fuel cells or electrolysers.

[0212] The porosity of the layer(s) of the final PTL can be varied by changing the metal powder loading (loading) and / or the sintering temperature. In general, higher sintering temperatures result in a decrease in porosity and average pore size as the embodiments sinter to higher densities. Porosity can be measured by volumetric mercury intrusion porosimetry, pressure difference method, fluid saturation, or optical methods. Preferably, porosity is measured by volumetric mercury intrusion porosimetry according to DIN66133.

[0213] As already mentioned above, the pore size is mainly controlled by varying the powder particle size and / or the binder / powder ratio.

[0214] The pore size and pore size distribution can be measured by mercury volumetric intrusion porosimetry according to DIN 66133 or by bubble point measurements according to ISO 4003 and ASTM E1294, respectively, preferably by the capillary flow porometry technique which measures the pore diameter and size distribution of the through pores of the PTL according to ASTM standard F316.

[0215] In one embodiment, the (first) mesoporous layer has a smaller pore size of about 5 μm to about 14 μm on the catalyst layer side, and the (second) metallic porous layer (substrate) has a pore size of about 15 μm to about 40 μm on the bipolar plate side.

[0216] In a preferred embodiment, the PTL exhibits an overall porosity between 30-65% by volume. Preferably, a specific porosity of 30-50% by volume in the first layer and 40-65% by volume in the second layer is achieved.

[0217] In another preferred embodiment, the PTL exhibits an overall pore size of 5 to 40 μm. Preferably, the specific first layer is 5 to 14 μm, and the second layer is 14 to 40 μm.

[0218] According to the present invention, a bilayer or multilayer film is coextruded, as follows: A gradient of porosity across the interface between at least two coextruded layers a gradient in average pore size across the interface between at least two coextruded layers; and Bimodal distribution with two sharp peaks A PTL exhibiting the following is produced.

[0219] The main advantages of the PTL production according to the present invention are: Better overall water (reactant) transport Better oxygen transport Better interfacial contact with the catalyst and therefore better catalyst utilization Better mechanical properties Higher efficiency Lower overall capital expenditures due to lower catalyst loading It is.

[0220] All percentages, ppm, or equivalent values ​​refer to weight relative to the total weight of the respective composition unless otherwise indicated. All cited documents are incorporated herein by reference.

[0221] The following examples further illustrate the invention without limiting its scope. EXAMPLES

[0222] Melt flow rates (MFR) were measured according to ISO 1133-1 at 190° C. and 2.16 kg (for binder) or 21.6 kg (for feedstock).

[0223] The particle size of the metal powders was determined by static light scattering measurements performed on a Beckman Coulter LS13320.

[0224] The porosity was measured by volumetric mercury intrusion porosimetry according to DIN66133.

[0225] The pore diameter and pore size distribution were determined by means of mercury volumetric intrusion porosimetry according to DIN66133.

[0226] Example 1 Spherical Ti metal powder with a powder particle size D50 = 33 μm was procured.

[0227] The powder was converted into feedstocks by mixing / blending with liquid additives and binders using a co-rotating twin screw extruder. The first and second feedstocks are shown in Tables 1 and 2, respectively.

[0228] [Table 1]

[0229] [Table 2]

[0230] Feedstocks 1 and 2 were coextruded using a flat die coextruder at a nozzle temperature of about 190° C. and a screw speed of 20-40 m / min to produce a film green body having a thickness of 500 μm.

[0231] Two different feedstocks with the same powder particle size of D50=33 μm but with two different recipes shown in Tables 1 and 2 were coextruded to produce a bilayer film.

[0232] This "green" PTL was further shaped by rolling and calendaring to obtain the final PTL shape, surface finish and thickness.

[0233] The produced two-layer PTL (green part) was directly debindered by catalytic debinding and sintered as a whole part to obtain a brown body with a robust and defect-free structure.

[0234] These green bodies were sintered in a molybdenum furnace under argon, vacuum or hydrogen atmosphere using the following temperature profile: i. heating at a rate of 2-7°C / min to a temperature of 550-650°C; ii. Holding at a temperature of 550-650°C for 0.5-1.5 hours; iii. heating at a rate of 2-7°C / min to a temperature of 720-940°C; iv. Holding at a temperature of 720-940°C for 0.5-2 hours; and v. Cool to ambient temperature at a rate of 5-15°C / min.

[0235] The results are shown in Table 3.

[0236] [Table 3]

[0237] Example 2 Ti metal powder with powder particle size D50=33 μm and D50=70 μm was procured for the first and second feedstocks, respectively.

[0238] The powder was converted into feedstocks by mixing / compounding with liquid additives and binders using a co-rotating twin screw extruder. The first and second feedstocks are shown in Tables 4 and 5, respectively.

[0239] [Table 4]

[0240] [Table 5]

[0241] Feedstocks 1 and 2 were coextruded in a flat die coextruder, with a nozzle temperature of about 210° C. and a screw speed of 10-40 m / min to produce a film green body with a thickness of 400 μm.

[0242] D 50 = 33 μm and D 50Two different feedstocks with different powder particle sizes of 0.1 μm to 0.5 μm and two different recipes shown in Tables 3 and 4 were coextruded to produce bilayer films.

[0243] These green bodies were further shaped by rolling and calendaring to obtain the final PTL shape, surface finish and thickness.

[0244] The two-layered green bodies produced were directly debindered by catalytic debinding and sintered as whole parts to obtain brown bodies with a robust and defect-free structure.

[0245] These green bodies were heated in a molybdenum furnace under vacuum for 10 -4 Sintering was performed at a pressure of 1000 psi and 1000 psi. The following temperature profile was used: i. heating at a rate of 2-7°C / min to 550-650°C; ii. Holding at a temperature of 550-650°C for 0.5-1.5 hours; iii. heating at a rate of 2-7°C / min to a temperature of 875-1000°C; iv. Holding at a temperature of 875-1000°C for 1-4 hours; and v. Cool to ambient temperature at a rate of 5-15°C / min.

[0246] The obtained PTL is shown in Figure 1. It shows a cross-sectional SEM picture of the sintered two-layer PTL, showing that the interface between the two layers is smooth. The first layer (in contact with the catalyst layer) is based on a feedstock with titanium powder of D50 = 33 μm and a layer thickness of 100 μm, the second layer on top is based on a feedstock with titanium powder of D50 = 70 μm and a layer thickness of 380 μm. The total thickness of the two-layer PTL was 480 μm ± 25 μm. The smooth transition phase is highlighted with a dashed line.

[0247] FIG. 2 shows the final sintered two-layer PTL with a smooth surface and a thickness tolerance of less than ±25 μm, and without defects.

Claims

1. 1. A method for making a multi-layer porous transport layer comprising the steps of: (a) providing a first feedstock comprising first metal particles and a first polymeric binder, and providing a second feedstock comprising a second metal particles and a second polymeric binder, the first and second feedstocks have a metal powder content of 40 to 70 volume percent; and The first feedstock is more efficient than the second feedstock. (i) metal particles having a smaller average particle size; (ii) a higher metal powder content, or (iii) Both smaller average particle size metal particles and higher metal powder content. The process comprising: (b) co-extruding the first and second feedstocks to form a film-shaped green body comprising a first layer and a second layer, the second layer being physically connected to the first layer at a temperature above the melting temperature and / or glass transition temperature of the first polymer binder and the second polymer binder; (c) optionally smoothing the film-shaped green body by rolling or calendering; (d) debinding the film-shaped green body to form a brown body; (e) subjecting the Brownian body to a non-oxidizing atmosphere or －４ sintering under vacuum up to mbar and at a temperature of 700-1100°C to form a porous transport layer; Including, The method, wherein the first feedstock and the second feedstock are free of any solvent.

2. The method of claim 2, wherein the first average particle size is from 15 to 35 μm and the second average particle size is from 25 to 45 μm.

3. 3. The method of claim 1 or 2, wherein the amount of the first metal powder in the first feedstock is 54-65 vol. % and the amount of the second metal powder in the second feedstock is 48-56 vol. %.

4. The method of claim 1 or 2, wherein the first and second metal particles are comprised of titanium or stainless steel.

5. 3. The method of claim 1 or 2, wherein the first feedstock and the second feedstock have a melt flow rate of 50 to 700 g / 10 min at 190° C. and 21.6 kg according to ISO 1133.

6. 3. The method of claim 1 or 2, wherein the first polymeric binder, the second polymeric binder, or both the first and second polymeric binders have a melt flow rate of 1 to 5 g / 10 min according to ISO 1133-1 using 190° C. and 2.16 kg.

7. the first polymeric binder, the second polymeric binder, or both the first and second polymeric binders are (i) 35 to 55 volume percent polyoxymethylene; (ii) 2 to 10 volume percent of a polyolefin; (iii) optionally 2 to 20 volume percent of a further polymer, and (iv) optionally 0.5 to 5 volume percent of a dispersant; The method of claim 1 or 2, comprising:

8. The process according to claim 1 or 2, wherein the coextrusion is carried out at a melt temperature of from 175 to 220°C.

9. 3. The method of claim 1 or 2, wherein in the coextrusion step (c), a third layer is coextruded onto the first or second layer.

10. 3. The method according to claim 1 or 2, wherein the smoothing is carried out by rolling, calendering, or both rolling and calendering.

11. 3. The method according to claim 1 or 2, wherein the debinding step (d) is carried out in an atmosphere comprising a gaseous acid.

12. 3. The process according to claim 1 or 2, wherein the debinding step (d) comprises catalytic debinding at a temperature of from 100 to 140°C.

13. The method according to claim 1 or 2, wherein the sintering step (e) is carried out at a temperature of from 700 to 1000°C, preferably from 720 to 920°C.

14. A combination of a first feedstock and a second feedstock, (a) the first feedstock comprises first metal particles and a first polymer binder; (b) the second feedstock comprises second metal particles and a second polymeric binder; The first feedstock is more efficient than the second feedstock. (i) metal particles having a smaller average particle size; (ii) a higher metal powder content, or (iii) Both smaller average particle size metal particles and higher metal powder content. and The first and second polymer binders have a melt flow rate MFR of 1 to 5 g / 10 min at 190° C. and 2.16 kg according to ISO 1133-1; Combining the first feedstock with the second feedstock.

15. A film-shaped green body obtainable by carrying out steps (a) to (d) of the method according to claim 1 or 2.

16. A porous transport layer obtainable by the method according to claim 1 or 2.

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