Method for producing partitions by hot pressing

Abstract

A method for producing a separator, wherein a stretchable composite of a thermoplastic polymer and a conductive filler is provided for hot pressing into a separator. The composite is inserted into a compression mold (10), which is heated to a first predetermined temperature in a heating station (23) before being inserted into a press (11) for hot pressing between blocks (15A, 15B), which absorb heat energy during compaction to cool the compression mold (10) and the sheet (14) forming the separator.

Description

Technical Field

[0001] This invention relates to a method for producing partitions by hot pressing, particularly a continuous method. Background Technology

[0002] For example, bipolar plates (BPPs), produced by combining two monopolar plates (MPPs), are key components of fuel cells. They also play a role in providing the required voltage for the stack in the electrical connection.

[0003] EP3041076A1 discloses a method for producing fuel cell separators, wherein a multilayer sheet is preheated prior to compression molding to shorten the required molding time. The polymer composition of the sheet comprises fluorocarbon polymers, particularly FEP, PTFE, PFA, or combinations thereof. The preheating temperature range is specified as 280 to 360°C. The melting points of the three mentioned polymers are 260°C, 327°C, and 315°C, such that the temperature range indicates molding when the polymer is molten; however, this is not optimal. This is discussed in WO2021 / 028000.

[0004] Blue World Technologies Holding's WO2021 / 028000 discloses a continuous production method and apparatus comprising a mixing stage for mixing powders of a thermoplastic polymer material and an conductive filler (ECF), and a subsequent kneading stage for kneading the mixture at a kneading temperature above the glass transition temperature but below the melting temperature of the thermoplastic polymer material, to provide a stretchable but non-melting composite for inducing fibrillation in the thermoplastic polymer material. It also discloses a pre-compression stage following the kneading stage for pre-compressing the stretchable composite into a sheet, and a hot-compression stage for hot-compressing the sheet into a compression mold to form a separator. The compression mold has two opposing forming plates with a sheet between them for hot-compression by the two plates. The plates are made of a material with a thermal conductivity greater than 100 W / (m²). .The material is made of K) to minimize the time for heat absorption from the sheet during compression molding and to rapidly cool the sheet by transferring heat energy to the material in the press plate, thereby inducing rigid solidification in the pressed part in less than two seconds. Rapid compression molding is advantageous because the product can be pressed into its desired and final shape before one or more polymers in the composite reach their glass transition temperature. Additionally, rapid cooling of the sheet during compression molding generally has the advantage of accelerating the production process. To achieve high-speed hot pressing or compression molding, while simultaneously cooling the formed sheet through the press plate in a short time, the material used for the pressed part is configured with high thermal conductivity to carry away heat and thus cool the pressed MPP as quickly as possible. Examples of such materials with high thermal conductivity are molybdenum, tungsten, and some aluminum alloys, such as those with 143, 197, 121, and 130 W / (m²), respectively. . K) Thermal conductivity of 2024-T351, 7075-T651. On the way to the press, the temperature of the stretchable quasi-endless film obtained during the kneading stage is maintained by the heated conveyor surface, so that the film can be inserted into the press and pressed at a temperature in the range of 220°C to 274°C before the temperature drops due to the transfer of heat energy to the press.

[0005] While the method and production equipment disclosed in WO2021 / 028000 do offer some advantages over earlier prior art, further optimization of the method is desired. In particular, better control of the polymer temperature during hot pressing is desired, while still achieving rapid production. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide improvements in the art. In particular, the object of the present invention is to provide an improved method for producing separators, especially BPP. Specifically, the object relative to WO2021 / 028000 is to better control the heating process of the polymer membrane during the hot pressing process. Other objects include high-speed production, simplicity of production equipment and methods, and reduction in the size and cost of production facilities. One or more of these objects are achieved by the method for producing separators for, for example, fuel cells, as explained in the claims and further details below.

[0007] In summary, a method for producing a separator is provided, wherein a stretchable composite of a thermoplastic polymer and a conductive filler is inserted into a compression mold, the compression mold being heated to a first predetermined temperature in a heating station before being inserted into a press for hot pressing between blocks, the blocks absorbing heat energy during compaction to cool the compression mold and the sheet forming the separator.

[0008] For the manufacturing method, an endless strip of a stretchable composite is provided, the composite comprising a mixture of a thermoplastic polymer material and a conductive filler powder. Typically, the filler comprises a carbon material as the main component of the filler. The strip is cut into sheets and shaped for assembly into compression-molded parts. For example, an endless strip is provided similarly to the method disclosed and discussed in WO2021 / 028000, and the endless strip is provided with the components disclosed and discussed in WO2021 / 028000, which is incorporated herein by reference.

[0009] The pressed part includes a bottom pressure plate and a support frame, which together form a hollow section with a lateral dimension and a height H. In the case of a rectangular hollow section, the lateral dimension includes a length L and a width W. However, a rectangular dimension is not mandatory, as the partition can, in principle, be circular or have other flat shapes.

[0010] The pressed part also includes a cover plate covering the hollow portion. When the cut and trimmed sheet is placed into the hollow portion, the cover plate is placed on top to cover the sheet.

[0011] For example, the cover plate is tightly fitted into the hollow section. The cover plate is still allowed to move smoothly into the hollow section within the support frame, and the tight fit within prevents the sheet material for the partition from being extruded from the pressed part during the hot pressing stage, in which the pressed part is placed in the press and the plates of the part are pressed together.

[0012] Compression-molded parts are used to impart rigidity and flow patterning to baffles, for example, for coolant delivery and / or for the flow of hydrogen or oxygen. For this reason, compression-molded parts include embossing templates in the bottom and / or top plates that form one or more flow patterns for the baffles during compression.

[0013] For example, when the cover plate is positioned within the hollow section and rests on the sheet, a portion of the cover plate extends a distance D above the support frame. During the thermoforming of the sheet into a pressed part, the sheet is pressed into the partition by pressing the cover plate deeper into the hollow section.

[0014] For example, the distance the cover plate is pressed into the hollow section during hot pressing and / or the pressure is measured. In such cases, the depth to which the cover plate moves into the hollow section is determined by the pressure and volume of the sheet material within the hollow section. These parameters can be adjusted to obtain the desired product.

[0015] In some implementations, the press includes a mechanism defined to move the cover platen only a certain distance during hot pressing. An option is a toggle press mechanism, wherein the toggle press cannot push the cover platen further than a certain dead point in the toggle press.

[0016] To adjust the distance by which the cover plate is pushed into the hollow section, this distance may be determined by an adjustment mechanism, for example, by adjustment sheets of different thicknesses, which are selected by thickness according to the distance the cover plate should be pressed into the hollow section and are placed between the press and the cover plate or between the press and the bottom plate.

[0017] For example, the distance by which the cover plate is pressed into the hollow part is less than distance D or at most distance D.

[0018] Another option is to use the support frame of the press-formed part as a stop for compression in the press. For example, during pressing, the cover plate is pushed deeper into the hollow section by a distance D until the cover plate is flush with the upper edge of the support frame, so that the support frame stops further compression of the sheet within the press-formed part. Using the upper edge of the support frame as a stop can be useful because the dimensions of the partition are determined by the hardware in a simple and very precise manner.

[0019] Specifically, when the size of the pressure block extends beyond the support frame of the pressed part, the support frame prevents the pressure blocks from moving towards each other, so pushing is not possible until the cover plate is flush with the upper layer of the support frame. In this case, based on the preset pressure and the volume of the sheet in the hollow section, the cover plate is pushed into the hollow section by no more than a distance D. The distance D defines the maximum compression distance of the sheet during hot pressing.

[0020] A press consists of two opposing metal blocks, typically made of steel, and a drive mechanism, such as an electromechanical actuator system, for pressing the two blocks together. Compared to hydraulic systems, the advantages of using electromechanical actuators are significantly lower energy consumption and less heat generation.

[0021] The press has a pressing zone between the blocks, where the pressed parts are positioned for hot pressing. Furthermore, a conveyor is connected to the pressing zone for moving the pressed parts in and out of the pressing zone. Using such a conveyor, the insertion and removal of pressed parts into and from the pressing zone can be advantageously automated for a smooth and rapid automated production sequence.

[0022] For example, the conveyor includes a ball conveyor table in which the balls are rotatably embedded to facilitate the sliding of the pressed part on the rotating balls onto the table and into the press. Within the pressing area, the balls are spring-loaded to be pressed into the table during the pressing of the pressed part between the pressing blocks. For stability reasons, the platform is advantageously supported by the lower pressing blocks.

[0023] After the sheet is placed in the compression mold, the compression mold and the sheet inside the compression mold are heated to a first predetermined temperature, which is the start temperature of hot pressing.

[0024] This temperature is higher than the glass transition temperature of the thermoplastic polymer material so that the sheet can be molded. If the thermoplastic material in the mixture contains more than one polymer, the temperature higher than the glass transition temperature of the thermoplastic polymer material must be understood as a temperature higher than the glass transition temperature of all the thermoplastic polymers in the mixture, which is higher than the highest glass transition temperature of the thermoplastic in the mixture.

[0025] Advantageously, as discussed in WO2021 / 028000, this temperature is below the melt temperature of the thermoplastic polymer material so that the composite is compacted in a stretchable but non-molten state. If the thermoplastic material in the mixture contains more than one polymer, the temperature below the melt temperature of the thermoplastic polymer material must be understood as a temperature below the melt temperature of all the thermoplastic polymers in the mixture, which is below the lowest melt temperature of the thermoplastic in the mixture.

[0026] Typically, the initial predetermined temperature at the start of hot compression is in the range of 250-350°C, for example, in the range of 300-350°C.

[0027] Heating of the pressed part takes place outside the pressing zone so as not to occupy the pressing zone during the heating phase. This is part of the optimization process. The pressed part is only moved by the conveyor into the pressing zone between the blocks once the pressed part and the sheet therein have been heated to the desired temperature. The main advantage of this external heating is that a first predetermined temperature is controlled before hot pressing begins, in which both the pressed part and the sheet are heated, with the sheet inside the pressed part.

[0028] In the hot pressing stage, the sheet is hot-pressed within the pressed part to transform it into a baffle with a flow field. For this purpose, blocks are pressed together to press against each other for pressing on a cover plate, for example, pressing the cover plate deeper into the hollow portion, so that a flow pattern in the baffle can be formed using an embossing template. High pressure is used, advantageously in the range of 100 to 300 MPa. Due to the high pressure, the pressing time can be advantageously short, while still being sufficiently efficient for forming the flow pattern.

[0029] In this relationship, it should be remembered that during pressing, the temperature is rapidly transferred from the platen material to the press block via thermal conduction, since the block is made of metal, typically steel, while the platen material is advantageously molybdenum, which has high thermal conductivity. Through efficient thermal conduction from the sheet through the platen and into the press block, the temperature of the sheet and the pressed part decreases from a first predetermined temperature to a second predetermined temperature below the glass transition temperature of the polymer in the sheet, causing rigid curing of the formed separator.

[0030] For effective cooling, the briquette has a much larger thickness than the pressure plate, for example, more than ten times the thickness of the pressure plate. This allows the briquette to have sufficient volume to absorb heat from the pressure plate during the pressing action, enabling the pressing process to simultaneously provide the necessary cooling for the pressed part, allowing the partition to cool to its solidified temperature. The advantage of this procedure is that it accelerates the process.

[0031] For example, the cooling process typically lasts less than 5 seconds, optionally within the range of 1-2 seconds.

[0032] Finally, the rigidly cured partition is removed from the pressed part.

[0033] Since the pressed parts are not heated in the pressing area, it is convenient to provide one or more additional pressed parts for a fast production line. During the hot pressing stage, one or more of the additional pressed parts are filled with corresponding additional cut sheets, and after the pressed parts are removed from the pressing area, another of the additional pressed parts is inserted into the pressing area to hot press additional sheets into additional partitions.

[0034] Taking the offset in WO2021 / 028000 as an example, further research on the various materials proposed in WO2021 / 028000 for press plates led to the selection of molybdenum as the press plate material. Although molybdenum does not have the highest thermal conductivity among the four materials proposed in WO2021 / 028000, it has very high hardness, even comparable to steel. This specific choice of molybdenum has been found particularly useful because the press-formed parts are subjected to very high pressures.

[0035] When comparing with WO2021 / 028000, some improvements should be noted as follows, although the above at least partially describes the aspects.

[0036] The first and primary improvement lies in heating the pressed part to the desired hot-pressing temperature in a specially designed heating station while the sheet is already inside the pressed part. This heating station is outside the pressing zone of the press, and it is only inserted into the pressing zone of the press for pressing the sheet once the pressed part has been sufficiently heated to a first predetermined temperature. Such a procedure is not disclosed in WO2021 / 028000, which instead describes the sheet being held at a high temperature by rollers and then inserted into the pressed part for cooling and hot pressing. This implies a risk that hot pressing may not proceed quickly enough relative to the cooling effect of the pressed part on the sheet. Furthermore, WO2021 / 028000 explains cooling the sheet by transferring heat energy to the pressure plate. However, this type of cooling is difficult to control because the temperature change of the sheet begins immediately upon contact with the pressure plate unless the pressure plate is heated to the same temperature as the sheet. Additionally, the pressure plate must be made thick to have the necessary heat capacity to absorb sufficient heat energy from the sheet to reach a temperature below the glass transition temperature. Therefore, compared to WO2021 / 028000, by heating the pressed part, including the sheet, and not just the sheet itself outside the press, complete control of the first predetermined temperature is ensured at the start of the hot pressing process.

[0037] A second improvement over WO2021 / 028000 has been found in that several pressed parts can be in a waiting position to be hot-pressed with corresponding internal sheets at a predetermined first temperature. This allows the hot-pressing process to proceed in a rapid sequence, with one pressed part inserted into the pressing area followed by another, thus optimizing the production process in terms of speed. This means the press itself does not require a heater for the pressed parts. It also means optimized utilization of the press in terms of overall production capacity.

[0038] It has been found that the third improvement over WO2021 / 028000 lies in providing a metal (usually steel) clamping block, and the clamping block is much thicker than the pressure plate, so that the heat absorbed by the pressure plate from the sheet is rapidly transferred from the pressure plate by the heat energy absorbed by the clamping block pressed against the pressure plate. This accelerates the cooling process.

[0039] A further improvement over WO2021 / 028000 lies in maintaining the press block at a second predetermined temperature by cooling, where the second predetermined temperature is significantly lower than the first temperature of the pressed part during the start of hot pressing. The second predetermined temperature is in the range of 50-100°C, for example, in the range of 60-80°C. By maintaining the press block at such a predetermined cooling temperature, the cooling process from the first predetermined temperature to the second predetermined temperature is precisely controlled at a high cooling rate. Furthermore, during the time the pressed part is removed from the press, and until the next pressed part is inserted into the press, the heat energy absorbed by the press block can be effectively removed by cooling, allowing the press block to quickly prepare to absorb energy from the next pressed part inserted into the pressing area for hot pressing of the next partition. This principle has also been shown to accelerate the process compared to some prior art, where the pressed part is heated within the press. For example, the press block is effectively cooled by a coolant flowing through cooling channels within the press block.

[0040] In a practical implementation, the press includes a frame having an upper frame portion and a lower frame portion. The lower portion of the frame is fastened to a lower pressure block, and the upper portion of the frame is positioned above the upper block, wherein during hot pressing, an actuator presses the upper block downwards and away from the upper portion of the frame. The force applied to the press-formed part causes the sheet to be compacted within the press-formed part.

[0041] For example, the force applied to the cover plate involves a total force exceeding 1000 tons between the blocks. As an example, for a size of 10cm × 50cm = 500cm... 2 The covering plate, with a pressure of 1000 tons on the plate, results in a pressure of 2 tons / cm. 2 =2000 bar = 200 MPa pressure.

[0042] For actuators, electromechanical solutions are superior to hydraulic systems because the energy consumption for pressing at such high pressures is much lower than that of hydraulic systems. Optionally, the press includes an electromechanical toggle mechanism whose central axis is driven by an electric actuator, which moves a toggle, advantageously a double toggle, which mechanically acts between the upper portion of the frame and the upper block to move the upper block relative to the upper portion of the frame toward the lower block.

[0043] In a particular embodiment where the thermoplastic polymer material comprises at least two thermoplastic polymers, a first predetermined temperature for initiating hot pressing is adjusted to be above the highest of the glass transition temperatures of the at least two thermoplastic polymers but below the lowest melt temperature of the at least two thermoplastic polymers. Thus, all polymers are held at a kneading temperature above their various glass transition temperatures to maintain ductility and below their various melt temperatures. Then, under pressure in the compression mold, the temperature of the formed separator is reduced to a second predetermined temperature below the lowest of the glass transition temperatures of the at least two thermoplastic polymers to induce rigid curing of all at least two thermoplastic polymers before the rigidly cured separator is removed from the compression mold.

[0044] For example, thermoplastic polymer materials include, or consist of, a first group of thermoplastic polymers and a second group of thermoplastic polymers. By selecting polymers from two different groups, physical parameters related to structural stability, toughness, and chemical inertness can be tuned to produce an optimal thermoplastic polymer material for the separator. For example, the thermoplastic polymers of the first group are primarily used to produce structural stability, while the thermoplastic polymers of the second group are primarily used for toughness to prevent fracture. To produce the toughness of the composite, the polymers selected from the second group should be fibrillable by kneading. The ratio between one or more polymers from the first and second groups is adjusted for optimization. In some embodiments, the composite contains a larger amount of polymers from the first group than polymers from the second group.

[0045] For the final separator to be used in an HT-PEM fuel cell, both polymers should have a melting point above 200°C. Furthermore, it is advantageous if the polymer in the first polymer has a flexural strength above 100 MPa to provide good structural stability for the separator.

[0046] Polyphenylene sulfide (PPS) is a very useful candidate as a thermoplastic polymer. However, polyetheretherketone (PEEK), polyetherimide (PEI), and polysulfone (PSU) are useful alternatives. These polymers belong to the first group of polymers, which have high thermal stability, chemical resistance, and high flexural strength. As an example, PPS is an advantageous binder for separators (especially MPP and BPP) because it is insoluble in any solvent at temperatures below 200°C and has a high melting point in the range of 271–292°C, depending on crystallinity and molecular weight. Its melting point is significantly higher than the operating temperature of HT-PEM fuel cells, which is in the range of 120–200°C.

[0047] The second group of polymer candidates includes ETFE, fluorinated ethylene propylene (FEP), polytrifluoroethylene (PCTFE), and polytetrafluoroethylene (PTFE). These polymers exhibit relatively high tensile elongation and can be fibrillated, particularly through kneading.

[0048] The advantageous features of this second group are as follows:

[0049] - Melting temperature above 200℃;

[0050] - Continuous operating temperature of at least 120°C;

[0051] - Elongation at break above 100%, for example, in the range of 100% to 300% or in the range of 200% to 300%;

[0052] - The tendency of fibrillation through kneading.

[0053] In addition, when used in combination, the glass transition temperature of the second group should be lower than the melting temperature of the polymer in the first group.

[0054] Using two polymers in a blend yields advantages because their individual useful properties can be combined. For example, a blend of PPS and PTFE can be used as a composite binder for conductive fillers. In particular, when combined with PPS, PTFE outperforms other thermoplastic binders due to its high decomposition temperature (410°C), inertness, and other unique properties, including a low coefficient of friction, high strength, toughness, and self-lubricating properties.

[0055] Due to the low resistance, the concentration of ECF should be relatively high, for example, greater than 60% by weight, or greater than 70% by weight.

[0056] After hot pressing, further structuring via the processing of separators is typically unnecessary. For example, the method involves hot pressing sheets into bipolar plates, each having a flow channel pattern on each side. Alternatively, MPPs are produced and typically bonded back-to-back to form a single BPP by gluing.

[0057] Optionally, the separators are arranged in an array, and the fuel cell membrane is located between the separators, separating the hydrogen fuel from the oxygen.

[0058] This production method is not only applicable to BPP, such as BPP provided by combining two MPPs, but also to other separators, such as cathode plates, anode plates, and cooling plates.

[0059] This invention is particularly applicable to fuel cells, especially proton exchange membrane (PEM) fuel cells, such as high-temperature proton exchange membrane (HT-PEM) fuel cells. High-temperature PEM fuel cells offer significant advantages over low-temperature PEM fuel cells, namely, the ability to operate with impure hydrogen (e.g., reformed gas) due to their high tolerance to carbon monoxide. However, the relatively high operating temperature (120-200°C) combined with the concentrated acid medium inside the fuel cell necessitates the use of inert, thermally stable polymers to bind powdered or particulate conductive fillers (ECF).

[0060] However, although the present invention is particularly applicable to fuel cells, especially high-temperature proton exchange membrane (HT-PEM) fuel cells, it can also be used in other electrochemical energy storage and conversion devices, such as batteries, double-layer capacitors or electrolyzers.

[0061] It should be noted that all percentages of concentration and amount mentioned are weight percentages (wt%). Attached Figure Description

[0062] The invention will be explained in more detail with reference to the accompanying drawings, wherein

[0063] Figure 1 An example of a fuel cell stack is shown;

[0064] Figure 2 The method for manufacturing the partition is shown;

[0065] Figure 3A It is a sketch of an exemplary pressed molded part in a front view, and Figure 3B This is a sketch of an exemplary pressed-molded part in a side view;

[0066] Figure 4 An example of a conveyor is shown. Detailed Implementation

[0067] Figure 1 An example of a fuel cell stack is shown. Figure 1The separator, illustrated as a bipolar plate (BPP), is one of the key components of a fuel cell because it separates the membrane electrode assemblies in the fuel cell stack while simultaneously connecting the fuel cells in the stack in series, such that the stack voltage is the sum of the cell voltages. In a fuel cell, hydrogen-containing fuel is supplied through the anode inlet, and oxygen is supplied through the cathode inlet. Hydrogen and oxygen combine to form water, which is distributed through the cathode fuel outlet, while excess hydrogen is removed through the anode fuel outlet, for example, in a burner used in conjunction with a reformer to provide energy for the reforming process. Separators (especially BPPs) typically have flow fields on both sides, acting as flow guides for the gas. Separators are also known to have flow fields for the coolant. For example, two monopolar plate MPPs can be combined back-to-back to form a BPP, with a coolant flow field in the volume between the two MPPs. Flow guides are typically provided in the separator during production by embossing a channel pattern during hot pressing.

[0068] Figure 2 A continuous process for producing partitions (e.g., MPP or BPP) is illustrated.

[0069] In mixing stage 1, raw materials are supplied from dispenser 0 and mixed in mixer. Advantageously, various polymers are combined with conductive filler ECF. For example, the first type of polymer is selected from a first group of polymers with high thermal stability, chemical resistance, and good flexural strength. Examples include polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyetherimide (PEI), and polysulfone (PSU). Another type of polymer is selected from a second group of polymers with relatively high tensile elongation and can also be fibrillated, particularly by kneading. Examples include fluorinated ethylene propylene (FEP), polychlorotrifluoroethylene (PCTFE), and polytetrafluoroethylene (PTFE). Examples of ECF are amorphous carbon, carbon black, carbon fibers, carbon nanotubes, graphene, and / or graphite. For example, the ECF contains a predominantly high concentration of graphite and / or carbon black.

[0070] Optionally, a surfactant is added as a wetting agent and can help the polymer nanoparticles penetrate deeper into the pores and cracks of the ECF. To reduce the water and / or other liquid content in the mixture, the temperature is increased to induce evaporation.

[0071] Following mixing stage 1, kneading stage 2 is used for high-temperature kneading in a kneading vessel. The purpose of this kneading operation is to fibrillate the polymer. For this purpose, the temperature is maintained above the glass transition temperature of the fibrillating polymer to achieve fibrillation. The increase in temperature has a positive effect before reaching the melting point of one of the polymers, as the polymer flows too rapidly under molten conditions. Melting one or more polymers has proven less useful, as it leads to an increase in the areal resistivity of the produced BPP. Kneading is carried out for a sufficiently long time to induce significant fibrillation in the polymer. The time depends on the kneading process. Typical kneading times range from 1 to 60 minutes. For the example of PTFE, the temperature must be above 130°C to reach the glass transition temperature of PTFE, where it is in a viscous state. In the case of graphite / PPS / PTFE composites, the temperature should be below the melting temperature of PPS, which is 274°C.

[0072] In the extrusion stage 3, used after kneading stage 2, the composite is extruded from the extruder as a flexible and stretchable material. The composite passes through the extrusion nozzle to form an extruded composite bar, for example, with a rectangular cross-section.

[0073] The extruded bars are transported on a conveyor belt to a first compression stage 4. This first compression stage 4 is exemplified as an inclined top-pressing conveyor with a decreasing height in the transport direction, such that the height of the bars decreases as they pass through the compression stage 4. This single operation can be used to rapidly reduce the height of the bars while increasing the width to produce a quasi-endless belt of the compound.

[0074] Optionally, a calendering stage 5 is added, wherein the calendering station has a reduced gap height in subsequent calendering stations to form a relatively thin sheet with the desired final thickness. Advantageously, when converted into a strip, the thickness of the strip is reduced to less than 2 mm, optionally to less than 1 mm. The final thickness of the strip is optionally less than a few mm and can be made as thin as a tenth of a mm. During this calendering stage 5, nanofiber formation further enhances the material, for example in PTFE. However, the PTFE content is typically low, for example, less than 0.5% by weight. For good conductivity, the carbon content is high, typically above 70% by weight.

[0075] In transport phase 6, the temperature of the composite belt is maintained to keep it ductile, for example by adjusting the temperature of the conveyor surface and ensuring thermal conduction between the conveyor surface and the belt.

[0076] In stage 7 of cutting and trimming, the sheet is typically cut to the desired size using a cutting tool. Optionally, waste is returned to a container in stage 2 for recycling during the manufacturing process.

[0077] Cut and diced sheets are inserted into the pressed part and then heated in a heating station 23 before being inserted into a press 11, which provides hot pressing stage 8. For example, the hot pressing in press 11 of stage 8 begins at a first predetermined temperature, typically in the range of 200°C to 400°C, advantageously in the range of 300°C to 350°C. However, depending on the hot pressing temperature, the useful applied pressure is between 100 and 300 MPa. The advantage of hot compression is a short pressing-compaction time, optionally on the order of 1 second, optionally in the range of 0.5 to 2 seconds. For example, during hot pressing, the density of the pressed material increases by at least 1.5 times, for example in the range of 1.5 to 3 times, such as in the range of 2 to 2.5 times.

[0078] The press 11 used in hot pressing stage 8 is also used to cool the sheet for the separator. In this case, the available time for forming the separator is limited by the sheet cooling rate because forming in the hot pressing stage must be completed before the glass transition temperature of the polymer in the sheet is reached, for example, 85°C for PPS. A rapid hot pressing procedure is advantageous because the product can be pressed into its desired and final shape before one or more polymers in the composite reach their glass transition temperature. Furthermore, rapid cooling of the sheet during hot pressing generally has the advantage of accelerating the production process.

[0079] For example, after hot pressing, the partitions are collected in container 9.

[0080] exist Figure 3A The front view sketch shows an example of a compression molded part 10 for hot pressing in stage 8. A polymer sheet 14, such as MPP, is inserted into the compression molded part 10, between which pressure plates 13A, 13B supported by a support frame 12 are formed. At least one (but typically both) of the pressure plates 13A, 13B has a flow field embossing pattern for transfer to the sheet 14 during the hot compression stage. The compression molded part 10 is positioned in a pressing region 17 between two pressure blocks 15A, 15B, which are pressed together by forces from actuators 16 acting on the first and upper pressure blocks 15A. When the first pressure block 15A is lowered by the force from the actuators 16, it presses against the upper pressure plate 13A, which is arranged to be vertically movable within the support frame 12 to transfer pressure from the upper pressure block 15A to the sheet 14 for compressing and embossing the flow field pattern into the sheet 14.

[0081] The bottom pressing plate 13B and the support frame 12 are combined to form a hollow part with a height of H, and the polymer sheet 14 is inserted into this hollow part. Since the polymer sheet 14 has a thickness T < H, a part of the hollow part can be occupied by the covering pressing plate 13A. The latter is partially inserted into the support frame 12 and extends a distance D above the upper edge of the support frame 12, and thus can be pressed down during hot pressing.

[0082] Optionally, the upper edge of the support frame 12 serves as a movement stopper for the upper pressing block 15B. This means that the covering pressing plate 13A is pressed into the hollow part by a distance D for compressing the sheet 14 and forming the separator. Alternatively, the distance that the covering pressing plate 13A is pressed into the hollow part is less than the distance D. For example, the pressure applied by the press in combination with the adjustment of the volume of the sheet in the hollow part determines the distance that the covering pressing plate 13A is pressed downward into the hollow part. Another option is to use a toggle press, which applies a strong force until its dead point, at which point no further reduction in the distance between the pressing blocks 15A and 15B is achieved. However, in principle, the upper pressing block 15A with the lower side assembled into the hollow part can press the covering pressing plate even deeper into the hollow part than the distance D. There are various options for such a press configuration.

[0083] The rapid hot compression process is to form the sheet 14 into a separator, MPP or BPP, with a flow field for gas and optionally for coolant. As described above, the pressing plates 13A and 13B need to be highly rigid and stable so that the separator 14 obtains the correct dimensions and shape. For this reason, the pressing plates 13A and 13B must be made of hard materials.

[0084] To prevent the material from escaping from the press molding 10, the pressing plates 13A and 13B need to closely abut against the inner wall of the support frame 12. In addition, the shrinkage of the pressing plates during cooling should not be different from the shrinkage of the sheet 14 during cooling.

[0085] To achieve high-speed hot pressing while cooling the formed sheet in a short time, the material for the press molding in the press 11 has a high thermal conductivity in order to take away the heat and thus cool the pressed MPP as quickly as possible.

[0086] Examples of such materials are molybdenum, tungsten, and some aluminum alloys, such as 2024-T351 and 7075-T651 with thermal conductivities of 143, 197, 121, and 130 W / (m . K), respectively. However, in particular, it has been found that molybdenum has advantages due to its high strength comparable to steel and its high thermal conductivity. According to the Brinell method, molybdenum has a high hardness of 225. In addition, during cooling, molybdenum has a low degree of thermal shrinkage.

[0087] The press 11 includes a press frame 20. The press frame 20 has an upper portion 20A, a side portion 20B, and a lower portion 20C. The lower portion 20C is connected to a lower pressure block 15. The side portion 20B connects the lower portion 20C to the upper portion 20A of the press frame 20. When the actuator 16 acts on the upper pressure block 15B, the force applied to the upper pressure block 15B is transferred to the upper pressure plate 13A.

[0088] Figure 3B This is a schematic side view of the press 11 and shows a heating station 23 that heats the pressed part 10 to a predetermined first temperature, such as 300°C or higher, suitable for initiating hot pressing before inserting the pressed part 10 into the press 11. Once heated, the pressed part 10 is moved into the press 11 by a conveyor 21A, as indicated by arrow 22. Once inside the press 11, hot pressing is performed by pressure between two pressing blocks 15A, 15B. The metal pressing blocks 15A, 15B are held at a pressing temperature much lower than the temperature of the pressed part. For example, the pressing blocks 15A, 15B are held at 70°C by controlled cooling. Due to the temperature difference and the fact that the pressing blocks 15A, 15B have a much larger volume than the pressing plates 13A, 13B, the pressed part 10 is effectively cooled from both sides by the pressing blocks 15A, 15B during hot pressing. After hot pressing, the pressed part 10A is removed again from the press 11 on conveyors 21A or 21B. At this stage, the sheet 14 has hardened into a rigid baffle with an embossed flow pattern. The illustrated procedure is fast and smooth and can be used in an efficient production line.

[0089] If the separator is produced as an MPP, the MPP can be used to assemble a BPP in pairs if the BPP is intended as the final product. Typical assembly methods involve periphery bonding around two MPPs that are back-to-back. The requirements for the adhesive used in the PEM BPP are very similar to those for the polymer used in the MPP composite, namely, mechanical, thermal, and chemical stability within the operating temperature range of the high-temperature PEM fuel cell. It should be mentioned that forming the BPP by the methods described herein also allows for the creation of gas flow channels and pores during the process, eliminating the need for additional operations such as grinding.

[0090] Figure 4 An optional conveyor 21A is shown, which in this embodiment is exemplified as a ball conveyor table 25. Balls 24 are supported to roll in bearings, allowing the pressed part 10 to easily slide into and out of the press on the table 25. Reference Figure 3A and Figure 3B Once the pressed part 10 is inside the press 11 and subjected to the pressure of the upper pressure block 15A, the pressed part 10 will... Figure 4The spring-loaded balls 24 of the shown 26 and 27 are pressed into the platform 25, causing the pressed part 10 to rest on the upper side of the platform. The lower side of the platform 25 is supported by the lower pressure block 15B.

Claims

1. A method for producing a partition, the method comprising: - A pressed molded part (10) is provided, the pressed molded part including a bottom pressure plate (13B) and a support frame (12) and a hollow portion formed by the bottom pressure plate (13B) and the support frame (12), the hollow portion having a height H, the pressed molded part (10) further including a cover pressure plate (13A) covering the hollow portion; wherein at least one of the bottom pressure plate (13B) and the cover pressure plate (13A) includes a template for embossing a fluid flow pattern in a partition (14) formed in the pressed molded part (10); - Provides an endless band of stretchable composites comprising a mixture of thermoplastic polymer materials and conductive filler powders. - Cut and trim sheet material (14) from the strip, the sheet material (14) having a constant thickness T less than H for assembly into the hollow portion, place the cut and trimmed sheet material (14) into the hollow portion, and place the covering plate (13A) above the sheet material (14) to cover the hollow portion. - A press (11) is provided having a pressing region (17) for receiving the pressed part (10) so as to heat-press the sheet (14) inside the pressed part (10) in the pressing region (17). - In the hot pressing molding stage (8), the sheet (14) in the pressed part (10) is hot-pressed into a partition by pressing the pressure plates (13A, 13B) toward each other and shaping the flow pattern in the sheet (14) with the template. - While under pressure in the compression molded part (10), the temperature of the sheet (14) is reduced below the glass transition temperature of the thermoplastic polymer material to induce rigid curing, and then the sheet (14) is removed from the compression molded part (10) as a rigid curing separator. Its features are, The press (11) is provided with two metal blocks (15A, 15B) positioned opposite each other and a drive mechanism (16) for pressing the two blocks (15A, 15B) toward each other, and wherein conveyors (21A, 21B) are connected to the pressing area (17) to move the pressed part (10) into and out of the pressing area (17). The method includes, - After the sheet (14) is placed in the compression molded part (10), while the sheet (14) is inside the compression molded part (10), the compression molded part (10) and the sheet (14) are heated to a first predetermined temperature in a heating station (23) outside the compression area (17), the first predetermined temperature being higher than the glass transition temperature of the thermoplastic polymer material but lower than the melting temperature of the thermoplastic polymer material, so as to compress the composite into a stretchable but non-melting state; - Only after heating the pressed part (10), the pressed part (10) is moved by the conveyors (21A, 21B) into the pressing area (17) between the pressing blocks (15A, 15B), and then pressure is applied to the pressed part (10) by the pressing blocks (15A, 15B). At the same time, during the hot pressing, the temperature of the pressed part (10) is reduced from the first predetermined temperature to a second predetermined temperature below the glass transition temperature by transferring heat energy from the pressed part (10) to both the pressing blocks (15A, 15B). The pressed part (10) is then removed from the pressing area (17) by the conveyors (21A, 21B).

2. The method according to claim 1, wherein the method includes providing additional pressed parts during the repetition process, and during the hot pressing of the sheet in the pressed parts (10), filling the additional pressed parts with corresponding additional cut sheets (14), and after the pressed parts (10) are removed from the pressing area (17) by the conveyors (21A, 21B), inserting the additional pressed parts into the pressing area (17) by the conveyors (21A, 21B) to hot press the additional sheet into additional partitions.

3. The method according to any of the preceding claims, wherein the cover plate (13A) is tightly fitted into the hollow portion, and wherein the method comprises positioning the cover plate (13A) within the hollow portion and placing the cover plate (13A) on the sheet (14), a portion of the cover plate (13) extending a distance D above the support frame (12), and by pressing the pressure blocks (15A, 15B) toward each other and pushing the cover plate (13A) deeper into the hollow portion by the pressure blocks (15A, 15B) until the cover plate (13A) is flush with the upper edge of the support frame (12) so that the support frame (12) stops the pressure blocks (15A, 15B) from moving toward each other, thereby hot-pressing the sheet (14) in the pressed molded part (10) into a partition.

4. The method according to any one of the preceding claims, wherein the method comprises providing the pressing block (15A, 15B) with a thickness not less than ten times the thickness of the pressing plates (13A, 13B) such that the pressing block (15A, 15B) has a volume sufficient to absorb heat from the pressing plates (13A, 13B) during simultaneous cooling and hot pressing.

5. The method according to any one of the preceding claims, wherein the method comprises providing a cooling system for the compact (15A, 15B) and maintaining the compact (15A, 15B) at a second predetermined temperature by cooling, wherein the second temperature is below the glass transition temperature of the thermoplastic polymer.

6. The method according to any of the preceding claims, wherein the method comprises maintaining the pressing blocks (15A, 15B) at a second predetermined temperature in the range of 50-100°C.

7. The method according to any of the preceding claims, wherein the conveyors (21A, 21B) include a ball conveying table (25), a rotating ball (24) being embedded in the ball conveying table for sliding the pressed part (10) on the rotating ball (24) onto the table (25) into the press (11), wherein the ball (25) within the pressing area (17) is spring-loaded (26, 27) for being pressed into the table (25) during pressing of the pressed part (10) between the pressing blocks (15A, 15B).

8. The method according to any of the preceding claims, wherein the method comprises providing a base plate (13B) and a cover plate (13A) in molybdenum.

9. The method according to claim 6, wherein the method includes maintaining the pressing blocks (15A, 15B) at a second predetermined temperature in the range of 60-80°C.

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