A multi-stage pressing process for producing molded parts such as bipolar plates from highly filled thermosetting materials

Abstract

The present invention discloses a process for producing a molded part (110) using a highly filled thermosetting raw material (106), the process comprising the following steps: introducing the raw material (106) into a pre-pressing tool (102); producing a preform (104) from the raw material (106), the raw material (106) being brought to a pre-pressing temperature by the pre-pressing tool (102) and being compressed using a pre-pressing force to form the preform (104); removing the preform (104) from the pre-pressing tool (102) and introducing the preform (104) into a final pressing tool (108); producing a finished part (110) from the preform (104), the preform (104) being brought to a final pressing temperature by the final pressing tool (108), and being compressed using a final pressing force to form the finished part (110). Here, the pre-pressing temperature is lower than the final pressing temperature, and the final pressing temperature is at least as high as the starting temperature of the curing reaction of the raw material (106).

Description

Technical Field

[0001] The present invention relates to a process for producing molded parts from highly filled thermosetting raw materials. For example, the process can be used to produce graphite-filled bipolar plates, such as those used in fuel cells. The invention also relates to a corresponding pressing device suitable for carrying out the process. Background Art

[0002] Moulded parts made of thermosetting materials can be produced using typical moulding processes used in plastics technology, in which the material is brought into a molten state, introduced into a heated mould and then solidified under pressure and temperature.

[0003] If the molding compound has only low flow properties due to high filler content, standard molding processes such as injection molding, transfer molding, or injection molding may no longer be possible. This is often the case for materials whose properties are primarily determined by the type and volume fraction of fillers, such as sliding materials, friction linings, grinding discs, or polymer binders with good electrical conductivity.

[0004] In these applications, a mixture of powdered or granular fillers, thermosetting polymers, and other additives is typically metered directly into a heated die-casting mold. The mold is then closed, pre-compacting the material, degassing it, and finally compressing and solidifying it. The specific formulation of the pressing program, mold temperature, and force-displacement-time curve used in this process not only determines the cycle time but also, to a large extent, the material properties.

[0005] A specialized form of highly filled thermoset material is used to produce bipolar plates for polymer membrane fuel cells. In these applications, graphite-filled polymers are superior to metals due to their corrosion resistance in acidic and warm, humid conditions. However, achieving the required conductivity requires a filler content of 80-90% by weight, which is only possible through precise adjustment of formulation composition and pressing conditions.

[0006] Typical formulations and process descriptions have been published in scientific publications and patent literature for more than 20 years. A typical example is described in EP3528326A1.

[0007] SUMMARY AND ADVANTAGEOUS EMBODIMENTS

[0008] A process for producing molded parts from highly filled thermoset raw materials may be desired, which allows for economical (high volume) production of molded parts, particularly graphite bipolar plates, from highly filled thermoset molding compounds in relatively short cycle times. A pressing apparatus may be required to perform such a process.

[0009] This need is met by the subject matter of the independent claims. Advantageous embodiments are defined in the dependent claims and in the following description.

[0010] A first aspect of the present invention relates to a process for producing a molded part from a highly filled thermosetting raw material. The process comprises the following steps, preferably performed in a specific order: introducing the raw material into a pre-pressing tool; producing a preform from the raw material, the raw material being brought to a pre-pressing temperature by the pre-pressing tool and being compressed using a pre-pressing force to form the preform; removing the preform from the pre-pressing tool and introducing the preform into a final pressing tool; producing a finished part from the preform, the preform being brought to a final pressing temperature by the final pressing tool and being compressed using a final pressing force to form the finished part. The pre-pressing temperature is lower than the final pressing temperature, which is at least as high as the starting temperature of the curing reaction of the raw material. More specifically, the final pressing temperature may be at least as high as the starting temperature of the curing reaction of the binder in the raw material.

[0011] The raw material can be a powder and / or granular pre-material. For example, the raw material can include graphite or other mainly carbonaceous compounds as fillers. However, it is also possible to have a raw material with other types of fillers. In this case, "highly filled" can be understood to mean, for example, a filler content of at least 70 mass percent. Specifically, the raw material can have a filler content of at least 80 or even at least 90 mass percent. In addition to the filler, the raw material can include a binder system consisting of an epoxy resin (for example, an epoxidized cresol-linear phenolic type), a hardener (for example, a linear phenolic resin), a curing catalyst (for example, selected from aryl imidazoles or alkyl imidazoles) and an anti-sticking agent (for example, wax).

[0012] For example, a typical formulation may include, for example, approximately 84% graphite, 10% epoxidized cresol novolac as the resin, 5% novolac as the curing agent, 1% wax as the anti-sticking agent, and 0.1% 2-methylimidazole as the curing catalyst.

[0013] Depending on their composition, the raw materials may have a specific onset temperature at which chemical crosslinking, i.e., the curing reaction, begins. In particular, the onset temperature may depend on any curing catalysts present in the raw materials. For example, the onset temperature can be determined experimentally using differential scanning calorimetry.

[0014] A pre-pressing tool or final pressing tool is generally understood to mean a heatable, two- or multi-part die-casting mold used to produce molded parts under the action of pressure and heat. The pre-pressing tool and the final pressing tool can be located in different production stations, i.e., partially separated from one another. Similarly, the pre-pressing tool and the final pressing tool can have different mold volumes and / or mold geometries (see below).

[0015] The raw materials can be formed into a preform using a pre-pressing tool. The pre-pressing temperature should be within the softening range of the binder in order to achieve good compression of the preform. Preferably, a full-surface vacuum gripper can be used to transfer the preform into the final pressing tool, which can, for example, be heatable to prevent cooling during the transfer process or to further increase the temperature of the preform. Depending on the pre-pressing temperature, chemical cross-linking of the raw materials may already begin during the production of the preform. However, the pre-pressing temperature should be selected so that chemical cross-linking during the pre-compression period is at least largely avoided and / or significantly slowed down. Thereafter, the cohesion of the preform is mainly influenced by the physical adhesive forces.

[0016] The introduction of the raw material into the pre-pressing tool can be manual, partially automatic or fully automatic. Likewise, the removal of the preform from the pre-pressing tool and / or the insertion of the preform into the final pressing tool can be manual, partially automatic or fully automatic (see below).

[0017] Pre-pressing parameters, such as the pre-pressing temperature or pre-pressing force, and final pressing parameters, such as the final pressing temperature or final pressing force, can differ significantly, at least in part. In particular, the final pressing temperature should be significantly higher than the pre-pressing temperature to achieve the fastest possible curing in the finished product. At the same time, for the reasons mentioned above, the pre-pressing temperature should not be too high. Similarly, the pre-pressing force and the final pressing force can differ. For example, a different pressing program can be used for preform production than for finished parts. The pressing program can differ, for example, in the force-displacement-time curve.

[0018] For example, molding can be accomplished by pressing at 185°C for 10 seconds or less at a pressure of 37 MPa. After the pressing time, the finished part, such as a plate, can be removed from the mold without deformation. This is followed by a post-curing step, for example, at 150°C to 200°C for a period of time sufficient to adjust the residual reactivity and temperature, to achieve final curing. Following the molding process, additional post-processing steps, such as polishing and / or opening holes, can be performed to reduce contact resistance and / or lower the wetting angle.

[0019] When forming thermosetting materials from powder or granular pre-materials, steps such as preheating, pre-compression and degassing all require a certain amount of time. At the same time, for economical production, especially for the economical production of large quantities of parts, the cycle time should be as short as possible.

[0020] Molding at a temperature of, for example, 150° C., or generally at a temperature just above the curing onset temperature, allows for good degassing and compression. However, the required pressing time may be in the range of several minutes.

[0021] If the curing temperature increases, the time window for preheating, pre-compression, and degassing can become correspondingly narrower. This increases the risk of not meeting certain quality requirements. For example, bubbles or shrinkage cavities may form due to insufficient degassing, or insufficient compression may occur due to spontaneously initiated curing reactions.

[0022] EP 3528326 A1, mentioned above, describes that pressing times of less than 10 seconds can only be achieved through a combination of several parameters. It also describes the use of graphite with a median particle size d50 of 30 to 100 microns and a rebound property of 20% to 70% when the graphite is pressed dry. It is further stated that higher rebound properties lead to insufficient sheet compression, while lower rebound properties result in low flexural strength. Furthermore, arylimidazoles are assumed to serve as curing catalysts. In this case, the use of more reactive alkylimidazoles, particularly 2-methylimidazole, is explicitly excluded, as their use allegedly makes uniform compression impossible.

[0023] Therefore, one object of the present invention is to enable the economical (mass production) of molded parts, in particular graphite bipolar plates, from highly filled thermosetting molding compounds in relatively short cycle times. Another object of the invention described herein is to enable such production without the aforementioned limitations on the choice of raw materials.

[0024] According to the invention, these objects are achieved by manufacturing the molded component in a plurality of cavities, as will be described in detail below.

[0025] Embodiments of the process described herein offer advantages for the rational production of molded parts from highly filled thermosetting materials, in particular for the production of graphite bipolar plates for fuel cells, for example. One advantage is that the steps of preheating, precompression and degassing of the raw materials can be decoupled from the curing step, at least to a large extent. In other words, the curing temperature can be increased without the time window for preheating, precompression and degassing becoming correspondingly narrower. This can therefore reduce the risk of not meeting certain quality requirements. For example, this can avoid the formation of bubbles or shrinkage cavities due to insufficient degassing, or avoid insufficient compression due to spontaneously initiated curing reactions. In addition, this process allows the production of molded parts from highly filled thermosetting materials without the above-mentioned restrictions on the choice of raw materials. In particular, this can reduce the holding time during curing to 10 seconds or less.

[0026] A second aspect of the present invention relates to a press apparatus for producing a molded component from a highly filled thermosetting raw material using a process according to an embodiment of the first aspect of the present invention. The press apparatus includes a pre-pressing tool for producing a preform from the raw material. The pre-pressing tool is designed to bring the raw material to a pre-pressing temperature and compress it with a pre-pressing force to form the preform. The press apparatus further includes a final press tool for producing a finished component from the preform. The final press tool is configured to bring the preform to a final pressing temperature and compress it with a final pressing force to form the finished component.

[0027] This press allows for efficient mass production of shaped components, such as bipolar plates for fuel cells, and at the same time, achieves a very high production quality.

[0028] Without limiting the scope of the invention in any way, the ideas and possible features relating to the embodiments of the invention may be considered to be based, among other things, on the ideas and findings described below.

[0029] According to one embodiment, the pre-pressing temperature is lower than the starting temperature. For example, the pre-pressing temperature can be at least 5°C, preferably at least 10°C, or even at least 20°C lower than the starting temperature. This allows the raw materials to be compacted without initiating chemical crosslinking. Thus, steps such as preheating, pre-compression, and degassing of the raw materials can occur independently of the curing process of the raw materials.

[0030] According to one embodiment, the final pressing temperature is at least 170°C, preferably at least 190°C. In other words, the final pressing temperature can be significantly higher than the initial pressing temperature. This has the effect of significantly accelerating the curing speed of the finished part without compromising quality. Thus, for example, a press hold time of less than 10 seconds can be achieved.

[0031] According to one embodiment, the pre-pressing temperature is at most 150°C, preferably at most 120°C. This can significantly slow down or even completely prevent solidification during preheating, pre-pressing, and degassing. Thus, good pre-pressing and good degassing can be ensured without excessively extending the cycle time. Depending on the final pressing temperature, the cycle time can even be shortened compared to conventional pressing processes.

[0032] According to one embodiment, the preform is subjected to the final pressing force for at most 10 seconds, preferably at most 5 seconds. This enables a relatively short cycle time to be achieved.

[0033] According to one embodiment, the raw material comprises graphite as filler. This means that the process can be used for efficient (high volume) production of, for example, bipolar plates or similar components.

[0034] According to one embodiment, the raw materials include a binder and an alkylimidazole as a curing catalyst for the binder. The binder may be, for example, an epoxy resin binder. Raw materials containing an arylimidazole, such as 2-phenylimidazole, as a binder can significantly accelerate curing compared to raw materials without the alkylimidazole.

[0035] According to one embodiment, the raw materials contain 2-methylimidazole as a curing catalyst. This can significantly accelerate curing compared to raw materials without 2-methylimidazole, such as raw materials containing arylimidazoles or other alkylimidazoles as binders. Specifically, curing can be accelerated so that curing is complete before the finished part is removed from the final pressing tool. This eliminates the need for thermal post-treatment of the finished part.

[0036] According to one embodiment, the raw material is introduced into the pre-pressing tool by scraping, which allows a more uniform distribution of the raw material in the pre-pressing tool compared to pouring or other insertion methods.

[0037] For example, a pre-pressing tool can include an upper die and a lower die, each configured with a small offset so that the fill levels on different sub-surfaces, such as edges, seals, flow distributors, and channel areas, correspond to the material requirements of these sub-surfaces. This means that uniform pre-compression can be achieved even on preforms, and undesirable density and / or thickness variations in finished parts, such as in the form of bipolar plates, can be avoided. Furthermore, the required pressing force during production of the finished part can be reduced.

[0038] According to one embodiment, the density of the preform is at least 80% of the density of the finished part, preferably at least 90%. Pre-pressing the preform in this way means that a correspondingly higher final pressing temperature can be selected. In other words, curing in the final pressing tool can occur at a correspondingly higher curing temperature and thus be correspondingly faster.

[0039] According to one embodiment, the raw material is repeatedly compressed and degassed to produce the preform. For this purpose, for example, the upper die of a pre-pressing tool can be placed on the preform with a constant or increasing force and then slightly lifted again.

[0040] According to one embodiment, the pre-pressing force is varied during the production of the preform. For example, the pre-pressing force may be varied according to a predetermined pre-pressing force-displacement-time curve.

[0041] According to one embodiment, the final pressing force can be varied during the production of the finished part. For example, the final pressing force can be varied according to a predetermined final pressing force-displacement-time curve. Preferably, the final pressing force can be initially increased very quickly to a maximum value to achieve plastic flow of the molding compound or preform. After only 1 to 2 seconds, or when the curing reaction of the binder begins, the pressing force can be significantly reduced again.

[0042] According to one embodiment, the pressing apparatus includes a heatable gripper device configured to remove the preform from the pre-pressing tool and insert it into the final pressing tool. The gripper device may be, for example, a gripper robot, a gripper arm, or the like. The gripper device can be used to transfer the preform semi-automatically or fully automatically. The advantage of this automated transfer is that the time spent between pre-pressing and final pressing is relatively short, thereby keeping the overall cycle time as short as possible. With a suitable gripper device, the transfer time can be reduced to, for example, 2 seconds or less.

[0043] According to one embodiment, the pre-pressing tool and the final pressing tool have different tool geometries. For example, the final pressing tool may have a tool geometry that replicates the final geometry of the finished component, while the pre-pressing tool may have a tool geometry that deviates more or less from this final geometry. For example, the final geometry may replicate relatively fine structures, such as channel structures. In contrast, the shape of the pre-pressing tool may generally be more similar, for example, more planar. In other words, the preform and the finished component may have different dimensions. The preform and the finished component may also differ in density.

[0044] It should be noted that the possible features and advantages of the embodiments of the present invention are described in part with reference to a process for producing molded parts from highly filled thermosetting raw materials and in part with reference to a pressing device capable of performing such a process. Those skilled in the art will recognize that the features described for a single embodiment can be transferred, adapted and / or interchanged in a similar and appropriate manner to other embodiments to obtain further embodiments of the present invention and possible synergistic effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Advantageous embodiments of the present invention are further explained below with reference to the accompanying drawings, wherein neither the drawings nor the explanations are to be understood as limiting the present invention in any way.

[0046] Figure 1 shows a schematic representation of a pressing device according to an embodiment of the present invention;

[0047] Figure 2 Shown Figure 1 Schematic representation of the pre-pressing tool of the middle pressing device in the open state;

[0048] Figure 3Shown Figure 2 Schematic representation of the pre-pressing tool in the closed state;

[0049] Figure 4 Shown Figure 1 Schematic representation of the final pressing tool of the middle pressing device in the open state with the preform inserted;

[0050] Figure 5 Shown Figure 4 Schematic representation of the final pressing tool in the closed state during the production of the finished component from the preform;

[0051] Figure 6 Shown Figure 4 A schematic representation of the final pressing tool in an open position and the finished part ready for removal; and

[0052] Figure 7 A flow chart showing a pressing process according to an embodiment of the present invention is shown.

[0053] The figures are schematic and not drawn to scale. Identical reference numerals denote identical or identically acting features in the various figures. DETAILED DESCRIPTION

[0054] Figure 1 A schematic representation of a press apparatus 100 for producing molded parts from highly filled thermoset materials is shown. First, the press apparatus includes a pre-pressing tool 102 for producing a preform 104 from a raw material 106. The pre-pressing tool 102 is configured to bring the raw material 106 to a pre-pressing temperature and compress it with a pre-pressing force to form the preform 104. The press apparatus 100 then includes a final press tool 108 for producing a finished part 100 from the preform 104. The final press tool 108 is configured to bring the preform 104 to a final pressing temperature and compress it with a final pressing force to form a finished part 110. In this process, the pre-pressing temperature is lower than the final pressing temperature. Furthermore, the final pressing temperature is at least as high as the starting temperature of the curing reaction of the raw material 106, more specifically, as high as the starting temperature of the curing reaction of the binder in the raw material 106.

[0055] The transfer of the preform 104 can optionally be carried out by means of a gripping device 112 , which removes the preform 104 from the opened pre-pressing tool 102 and inserts it into the opened final pressing tool 108 .

[0056] Figure 2The pre-pressing tool 102 is shown in an open state. Here, the pre-pressing tool 102 includes a mold frame 200, a pre-pressing lower mold 202, and a pre-pressing upper mold 204 disposed opposite the pre-pressing lower mold 202. When opened, the pre-pressing upper mold 204 moves away from the mold frame 200. The mold frame 200 and the pre-pressing lower mold 202 define a container into which the raw material 106 or the pressing material 106 in the form of granules is filled.

[0057] Figure 3 The pre-pressing tool 102 is shown in a closed state during pre-pressing at, for example, 100°C. During this process, the container is closed by the pre-pressing upper die 204, and the raw material 106 is compressed between the mold frame 200, the pre-pressing lower die 202, and the pre-pressing upper die 204 with an appropriate pre-pressing force to form the preform 104 in the form of a pre-pressed sheet. In order to bring the raw material 106 to the pre-pressing temperature, the pre-pressing lower die 202 and the pre-pressing upper die 204 can be heatable. In addition, the mold frame 200 can be heatable.

[0058] like Figure 2 and Figure 3 As shown, both the pre-pressing lower die 202 and the pre-pressing upper die 204 may have contoured pressing surfaces. For example, the pre-pressing lower die 202 may have a convex portion 300, and the pre-pressing upper die 204 may have a concave portion 302. In this regard, the outer contour of the convex portion 300 may be configured to correspond to the inner contour of the concave portion 302.

[0059] Figures 4 to 6 The final pressing tool 108 is shown in more detail. For example, it can be pressed by a gripping device 112 (see Figure 1 ) automatically removes the preform 104 from the opened pre-pressing tool 102 and inserts it into the opened final pressing tool 108, the gripping device also being heatable.

[0060] Similar to the pre-pressing tool 102, the final pressing tool 108 comprises another die frame 400, a final pressing tool lower die 402 and a final pressing tool upper die 500 (see Figure 5 For example, both the final pressing tool lower die 402 and the final pressing tool upper die 500 may have a pressing surface with a special shape, such as a pressing surface with grooves or grooves, such as Figure 5 The respective pressing surfaces of the final pressing tool lower die 402 and the final pressing tool upper die 500 may be shaped to complement each other, for example.

[0061] The pre-pressing tool 102 and the final pressing tool 108 may have different tool geometries. In this example, the pre-pressing tool 102 and the final pressing tool 108 differ in the configuration of their respective pressing surfaces.

[0062] In order to bring the preform 104 to the final pressing temperature, the final pressing tool lower die 402 and the final pressing tool upper die 500 may be heatable. The additional mold frame 400 may also be heatable.

[0063] Figure 4 The final pressing tool 108 is shown in an open state with the preform 104 inserted.

[0064] Figure 5 The final pressing tool 108 is shown in a closed position during production of the finished part 110. This process involves compressing the preform 104 to form the finished part 110 at a final pressing temperature (eg, 180°C) and a corresponding final pressing force.

[0065] The finished component 110 may be, for example, a bipolar plate having channel structures on two sides and around the edges in order to conform to the contours of the pressing surface and the selected raw material 106 .

[0066] Finally, if Figure 6 As shown, the finished part 110 is ejected from the final pressing tool 108 .

[0067] Figure 7 It shows that, for example, Figures 1 to 6 FIG. 1 is a flow chart of a pressing process performed by the pressing apparatus 100 shown.

[0068] In step S10 , the raw material 106 is introduced into the pre-pressing tool 102 .

[0069] In step S20 , a preform 104 is produced from the raw material 106 . This involves bringing the raw material 106 to a pre-pressing temperature lower than the final pressing temperature by the pre-pressing tool 102 and compressing it using a pre-pressing force to form the preform 104 .

[0070] In step S30 , the preform 104 is removed from the pre-pressing tool 102 and placed into the final pressing tool 108 .

[0071] In step S40, the finished component 110 is produced from the preform 104. This process includes bringing the preform 104 to a final pressing temperature at least as high as the starting temperature of the binder curing reaction in the raw material 106 by the final pressing tool 108 and compressing it with a final pressing force to form the finished component 110.

[0072] The key to the solution according to the present invention is to divide the pressing process of the press-formed component into two sub-processes in a dual-station interconnected flattener.

[0073] Refer to the following Figures 1 to 6The invention will now be described in a different manner using the example of plate production, such as graphite bipolar plates for fuel cells. However, the invention can also be used to produce non-plate components.

[0074] According to one embodiment, a raw material 106 in the form of a powder or granular mixture, which may include fillers, binder components, and additives, is first loaded into a pre-pressing tool 102 at a pre-pressing station. The pre-pressing tool 102 can be heated to a pre-pressing temperature that is lower than the curing reaction start temperature of the raw material 106. This means that good preheating, degassing, and pre-compression can be achieved without initiating the curing reaction, even when using highly reactive molding materials, such as 2-methylimidazole as a curing catalyst for an epoxy resin binder. However, the pre-pressing temperature can also be approximately the same as, or even higher than, the starting temperature, as long as the raw material cures relatively slowly.

[0075] According to one embodiment, the raw material 106 is scraped into the open pre-press tool 102. This helps ensure that the material is particularly evenly distributed in the pre-press tool, thereby reducing fluctuations in thickness and density. For example, the pre-press tool 102 may include lower and upper tool plates with offsets (see Figure 2 and Figure 3 By combining the tool plates together, the raw material 106 can be formed into a preform 104, that is, pre-compressed into a preform. These offsets can be designed to take into account different surface-related material requirements while still allowing for uniform pre-compression.

[0076] Alternatively, the raw material 106 may also be poured into the pre-pressing tool 102. For example, the raw material 106 may be poured into different zones of the pre-pressing tool 102. The pre-pressing tool 102 may be used to compress the raw material 106 to, for example, approximately 90% of the final compression amount.

[0077] During pre-pressing, the preheating, pre-compression, and / or degassing steps can be repeated several times. In other words, pre-pressing can be performed in two or more consecutive sub-steps with increasing pre-pressing pressure, each of which can include a preheating, pre-compression, and / or degassing step (see above). For example, at a pre-pressing temperature of 100°C, the pre-pressing pressure can be increased in three stages: from 2 MPa to 10 MPa and then to 30 MPa.

[0078] For example, the pre-pressing temperature may be between 70°C and 140°C, preferably between 90°C and 120°C.

[0079] Pre-pressing ensures that the plastic compression of the raw material 106 takes place without any competing solidification reaction, or at most only with a very slow solidification reaction. In this way, it is possible to achieve well-structured grain boundaries between the powders or particles, which is a prerequisite for good mechanical properties and low permeability of the finished component 110 in the form of a finished stamped sheet.

[0080] After the pre-pressing, the final pressing is carried out in a final pressing station using a final pressing tool 108 that is separate from the pre-pressing tool 102. To this end, the preform 104, i.e. the pre-pressed, preheated sheet, is transferred from the pre-pressing station to the final pressing tool station, more precisely, by means of a heated gripping device 112, for example.

[0081] For example, the gripping device 112 can be heated to a temperature similar to the pre-pressing temperature and / or the starting temperature and / or the temperature of the final pressing tool 108, which means that the gripping surface of the gripping device 112 can be adjusted to one of the above temperatures plus or minus 20° C. or plus or minus 10° C. The transfer should be performed relatively quickly. In particular, the transfer should take less than 2 seconds.

[0082] The final pressing tool 108 produces the final geometry of the finished part 110. The final pressing tool 108 and the pre-pressing tool 102 may have different shapes. For example, the pre-pressing tool 102 may only replicate an approximate version of the final geometry of the finished part 110.

[0083] The final pressing tool 108 is heated to a final pressing temperature that produces a very fast curing reaction, for example, to at least 170° C., preferably, to at least 190° C. Final pressing temperatures of 200° C. and higher are also conceivable. Generally, the final pressing temperature should be significantly higher than the starting temperature of the curing reaction of the raw material 106, because an increase in the curing temperature will correspondingly shorten the curing time.

[0084] Due to the high precompression of the preform 104 , the final pressing tool 108 can be closed relatively quickly and the pressure can be built up correspondingly quickly.

[0085] For example, when 2-methylimidazole is used as a curing catalyst for epoxy resin and a final pressing temperature of 170° C. is used, demoulding can be performed after a pressure holding time of only 8 to 10 seconds. With a final pressing temperature of, for example, approximately 190° C., a pressure holding time of less than 5 seconds can be achieved.

[0086] In the same manner as pre-pressing, parameters of final pressing, such as final pressing temperature, final pressing force or pressure dwell time, may be varied during the final pressing process.

[0087] After final pressing, the final pressing tool 108 can be opened and the finished component 110 in the form of a finished pressed sheet can be removed from the final pressing tool 108. This can again be done by means of the gripping device 112, by means of another suitable gripping device or manually.

[0088] This can be followed by an additional heat treatment. Depending on the reactivity of the binder system used, this post-curing can be significantly shortened by the process described herein. In the case of very high reactivity, such as when using 2-methylimidazole, post-curing can even be completely omitted, since in this case curing is already largely complete after the final pressing.

[0089] This two-stage pressing process eliminates or overcomes limitations, such as those found in the prior art, in raw material selection for producing airtight separator plates with high flexural strength and short cycle times. Specifically, using graphite with a springback of less than 20% or greater than 70% can achieve flexural strengths exceeding 60 MPa. Furthermore, the process described herein can also utilize 2-methylimidazole as a curing catalyst without adversely affecting the properties of the finished component. The resulting extremely rapid curing reaction enables a high degree of crosslinking to be achieved even within very short processing times.

[0090] Flat and structured test molds on various automated presses demonstrate the potential for significantly reducing cycle times. Rather than a continuous production process, the pelletized sheets to be pressed are pre-pressed in a separate step, and the pre-pressed sheets are then final-pressed at a higher mold temperature. Compared to conventional processes, the pressed sheets exhibit significantly better mechanical properties and more uniform compression.

[0091] Finally, it is worth noting that terms such as "comprising" and "including" do not exclude other elements or steps, and terms such as "a" and "single" do not exclude a plurality. It is also worth noting that features or steps described with reference to any one of the above embodiments can also be used in combination with other features and steps of other embodiments described above. Reference numerals in the claims are not to be considered as limitations.

[0092] Reference Signs List

[0093] 100 Pressing device

[0094] 102 Pre-pressing tools

[0095] 104 Prefabricated Parts

[0096] 106 raw materials

[0097] 108 Final Suppression Tool

[0098] 110 Finished or molded parts

[0099] 112 Grabbing device

[0100] 200 mold frame

[0101] 202 Pre-pressing lower die

[0102] 204 Pre-pressing upper die

[0103] 300 raised part

[0104] 302 recessed part

[0105] 400 Additional mold frame

[0106] 402 Final pressing tool lower die

[0107] 500 Final pressing tool upper die

Claims

1. A process for producing a molded component (110) for a fuel cell bipolar plate from a highly filled thermosetting raw material (106), characterized in that: The process comprises: introducing the raw material (106) into a pre-pressing tool (102), wherein the highly filled thermosetting raw material (106) includes at least one of graphite and other major carbon-containing compounds as a filler in the raw material, wherein the filler content is at least 70 mass percent, wherein the raw material (106) includes 2-methylimidazole as a curing catalyst; producing a preform (104) from the raw material (106), wherein the raw material (106) is brought to a pre-pressing temperature by passing through a pre-pressing tool (102) and compressed using a pre-pressing force to form the preform (104), the pre-pressing tool (102) comprising a pre-pressing lower die (202) having a contoured pressing surface and a pre-pressing upper die (204) having a contoured pressing surface; removing the preform (104) from the pre-pressing tool (102) and introducing the preform (104) into a final pressing tool (108); and producing a finished component (110) from the preform (104), wherein the preform (104) is brought to a final pressing temperature by the final pressing tool (108) and compressed using a final pressing force to form the finished component (110); wherein the pre-pressing temperature is lower than the final pressing temperature; The final pressing temperature is at least as high as the starting temperature of the curing reaction of the raw material (106).

2. The process according to claim 1, wherein The pre-pressing temperature is lower than the starting temperature.

3. The process according to claim 1, wherein The final pressing temperature is at least 170°C.

4. The process according to claim 1, wherein The pre-pressing temperature is at most 150°C.

5. The process according to claim 1, wherein The preform (104) is subjected to the final pressing force for a period of at most 10 seconds.

6. The process according to claim 1, wherein The raw material (106) contains graphite as a filler.

7. The process according to claim 1, wherein The raw material (106) is introduced into the pre-pressing tool (102) by scraping.

8. The process according to claim 1, wherein The density of the preform (104) is at least 80% of the density of the finished part (110).

9. The process according to claim 1, wherein The raw material (106) is repeatedly compressed and degassed to produce the preform (104).

10. The process according to claim 1, wherein The pre-pressing force is varied during production of the preform (104).

11. The process according to claim 1, wherein The final pressing force is varied during production of the finished component (110).

12. A pressing device (100) for producing a molded part (110) for forming a bipolar plate for a fuel cell from a highly filled thermosetting raw material (106) by the process of claim 1, wherein the pressing device (100) comprises: a pre-pressing tool (102) for producing the preform (104) from the raw material (106), the pre-pressing tool (102) comprising a pre-pressing lower die (202) having a contoured pressing surface and a pre-pressing upper die (204) having a contoured pressing surface, and configured to bring the raw material (106) to a pre-pressing temperature and compress it using the pre-pressing force to form the preform (104); and A final pressing tool (108) for producing the molded part (110) from the preform (104), the final pressing tool (108) being configured to bring the preform (104) to the final pressing temperature and to compress it using the final pressing force to form the finished part (110), wherein the final pressing tool (108) has a tool geometry that replicates the final geometry of the finished part having a channel structure.

13. The pressing device (100) according to claim 12, further comprising: A heatable gripping device (112) is configured to remove the preform (104) from the pre-pressing tool (102) and insert it into the final pressing tool (108).

14. The pressing device (100) according to claim 12 or 13, wherein: The pre-pressing tool (102) and the final pressing tool (108) have different tool geometries.

Images