Method for manufacturing a plate-shaped fuel cell component, in particular a bipolar plate, and a fuel cell component manufactured by this method

Abstract

The present invention relates to a method for producing plate-shaped fuel cell components (6), in particular bipolar plates, from thermoplastic material with additional components having good electrical and thermal conductivity, wherein the plate-shaped fuel cell components are produced by injection molding technology using an injection molding device (1) having at least one injection unit (2) and at least one mold unit (3) with walls surrounding each cavity. Efficient production of plate-shaped fuel cell components is achieved by filling, under pressure, a molten thermoplastic material with the additional components as a molten compound into the hollow spaces of each cavity (31) of the at least one mold unit (3), which permanently correspond to the shape of the fuel cell component, using the at least one injection unit (2), and by adjusting the heat transfer through the walls (30) to the thermal conductivity and heat capacity of the molten compound and the filling speed, so that the molten compound completely fills each cavity (31) as a mold compound (5) before its temperature drops below its melting temperature.

Description

[Technical Field]

[0001] The present invention relates to a method for producing plate-shaped fuel cell components, in particular bipolar plates, from a thermoplastic material having an additional component with good electrical and thermal conductivity, wherein the plate-shaped fuel cell components are produced by injection molding technique using an injection molding apparatus having at least one injection unit and at least one mold unit with walls surrounding each cavity.

[0002] Furthermore, the present invention relates to a plate-shaped fuel cell component manufactured by the above method, and to an apparatus for manufacturing such a plate-shaped fuel cell component.

[0003] This type of method and plate-shaped fuel cell components, particularly bipolar plates, manufactured from modified thermoplastic materials are disclosed as known in WO 94 / 25995. This known method identifies polyethersulfone (PES) as a preferred thermoplastic material, with the additional advantage that this material can be processed by injection molding or extrusion, and thus individual components of the fuel cell made of PES can be joined to each other by plastic welding or adhesive bonding. To achieve the electrical conductivity required for the fuel cell, the thermoplastic material is modified by incorporating conductive particles, such as conductive carbon black, graphite, or the like, which are added to the molten polymer. Details of the injection molding process itself are omitted.

[0004] This type of plate-shaped fuel cell component, particularly a bipolar plate or electrode plate, has a relatively large surface area (e.g., on the order of DIN A4 format) yet is very thin, typically less than 1 mm thick. Therefore, its manufacture by injection molding is difficult, particularly due to rapid cooling in the mold unit during the injection process. To prevent excessively rapid cooling before the thin, large-area cavity of the mold unit is completely filled, it is common to apply heat to the cavity walls during the introduction of the molten compound, followed by a pressing process. In this way, rapid heat dissipation from the molten compound during the injection molding process can be avoided and complete filling of the cavity with the molten compound can be achieved. It should also be noted that molten compounds modified with conductive particles for use in fuel cells have high thermal conductivity, which also leads to rapid heat dissipation. Post-pressing requires additional work steps and a correspondingly complex configuration of the injection molding apparatus. The subsequent need to cool and solidify the molten or molding compound before the molded article is extruded in the form of a plate-like fuel cell component lengthens the injection molding cycle even further. In addition, the heating system and, in variable temperature designs, the cooling system consumes energy.

[0005] U.S. Patent Application Publication No. 2004 / 0115505 describes a method for manufacturing plate-shaped fuel cell components using an injection molding machine. Adjustable mold sections are used to press the injection molding material into the mold cavity, which is already filled or just filling the cavity. The conductive filler material accounts for 60 to 95% by weight of the molding compound. The adjustable mold sections and their operation require additional labor.

[0006] JP 2006-327051 and JP 2009-226641 show further injection molding technology molding devices for plate-shaped moldings, in which adjustable parts of the molding tool are also used for the molding process.

[0007] The object of the present invention is to provide a method for producing plate-shaped fuel cell components, which allows for the efficient production of high-quality plate-shaped fuel cell components, in particular bipolar plates, and also to provide corresponding fuel cell components.

[0008] This problem is solved by a method having the features of claim 1 and a plate-like fuel cell component having the features of claim 5.

[0009] The method according to the invention proposes that a molten thermoplastic material having additional components is filled under pressure as a molten compound using at least one injection unit into the hollow spaces of each cavity of at least one mold unit, which permanently correspond to the shape of the fuel cell component, and that the heat transfer through the walls is adjusted to the thermal conductivity and heat capacity of the molten compound and the filling speed so that the molten compound completely fills each cavity as a molding compound before its temperature drops below its melting temperature.

[0010] The plate-like fuel cell components according to the invention are those manufactured using the above method, and in particular those that have sufficient inherent rigidity for their application in fuel cells.

[0011] In this way, the parameters of the injection molding device and the injection molding process, including the state and properties of the injected molten compound, are adjusted to each other during the injection molding process, and the parameters are adjusted to the injected molten compound so that the injected molten compound reliably fills the cavity before solidifying as a molding compound, thereby achieving efficient injection and molding of the plate-shaped fuel cell component in the shortest possible time with the lowest possible energy consumption. The walls around the cavity are exposed to an appropriate temperature precisely adjusted to the injection molding process, and can then be cooled below the solidification temperature in a correspondingly short time before demolding. As a result, the injection molding cycle can be significantly shortened with the lowest possible energy consumption, achieving efficient production of plate-shaped fuel cell components. For example, the walls of each cavity, which have a significantly lower thermal conductivity (unit: W / (k·m)) than the molten compound, can be constructed or insulated with a plastic material with a correspondingly high temperature stability, thereby preventing excessively rapid dissipation of heat from the molten compound, i.e., before the molten compound fills the entire volume of the cavity. Metallic walls and easily open- or closed-loop controllable temperature control elements are also suitable for rapid heat supply and dissipation, and insulating cladding of the walls for temperature control around the cavity is also advantageous for efficient process operation.

[0012] To implement this method, an injection molding apparatus is provided with at least one injection unit for supplying thermoplastic raw material containing an electrically conductive additive, particularly graphite particles, and at least one mold unit. The mold unit has a nozzle-side mold section assigned to the injection nozzle assembly and an ejector-side mold section assigned to the ejector side. The nozzle-side and ejector-side mold sections face each other at a separation plane by their respective separation surfaces. The at least one mold unit includes a portion of each mold section, including a mold insert and a mold core, within a mold section receptacle. The mold insert forms a cavity that can be opened at the separation plane and is closed during the injection process. The cavity is connected to the injection unit via a supply unit with a hot or cold runner system, whereby the molten raw material is injected as a molten compound into the cavity cavity. The shape of the cavity cavity is permanently adapted to the shape of the fuel cell component to be manufactured by the inner surface of the mold insert surrounding the cavity until the at least one mold unit opens during the molding process. There are no post-pressing devices that would change the shape of the cavity during the forming process.

[0013] A plate-like fuel cell component or bipolar plate structure advantageous for the operation of a fuel cell is preferably obtained by adding graphite and optionally additionally carbon black as conductive additives (at most 5, 10 or 25% by weight or at most 5 or 25% by volume of the additive) to a thermoplastic material in a mass ratio of more than 5%, more than 20% or more than 30%, preferably more than 50%, for example 5% to 90% or 95%, in particular 30% to 70% or 87% of the conductive additives, based on the total mass or volume of the raw materials fed to the injection unit. Other additives are also considered as conductive additives, in addition to or in addition thereto.

[0014] Another advantageous measure for efficient injection molding is to use a thermoplastic matrix material with a free π-electron system, particularly a PEEK material, and to use only graphite as the conductive additive. In this configuration, the invention is based on the idea that the graphite in the matrix polymer of the molding compound provides conductive connection via its π-electron system, eliminating the need for conductive carbon black particles, which have traditionally been added for conductive connection. Avoiding the use of conductive carbon black allows for a reduced loading level of the additive, contributing to efficient injection molding. Avoiding post-pressing allows for the orientation of the graphite particles generated during the injection process to be advantageously utilized as a preferred direction for the good conductive properties of the resulting plate-shaped fuel cell component.

[0015] A further advantageous construction feature of the plate-shaped fuel cell component or bipolar plate is that the plate-shaped fuel cell component is manufactured with a thickness (d) perpendicular to its plane, in plan view, of, for example, at most 5 mm, in particular at most 2 mm, at most 1 mm or at most 0.5 mm or 0.2 mm, which has sufficient inherent rigidity for use in a fuel cell.

[0016] A further advantage for the manufacturing process and function of the plate-like fuel cell component is that the graphite particles have an average size D in the range of 5 μm to 50 μm or 100 μm. 50 and / or have an aspect ratio (thickness to the smallest dimension perpendicular to the thickness direction) of less than 5, especially less than 1 or less than 0.5.

[0017] Furthermore, advantageous production of plate-like fuel cell components or bipolar plates is achieved by providing the fuel cell component with at least one connecting, mounting, line and / or sealing element by insert molding and / or integral molding in an injection molding process, which significantly improves the production of the entire fuel cell and even the fuel cell stack and allows for flexible adaptation to different application conditions.

[0018] For an easily controllable injection molding process for efficiently producing plate-shaped fuel cell components such as bipolar plates, a further advantageous configuration of the injection molding apparatus is that a temperature control means is arranged between the mold insert and the mold core in the nozzle-side and / or ejector-side mold section, in particular that the temperature control means comprises a heating means and / or a cooling means, for example that the heating means can be heated inductively via a conductive means by electric current or by a heat transfer fluid guided through a passage, and / or that the cooling means comprises a cooling device that can be operated by a cooling fluid guided through a passage or is electrically operated, and / or that at least the mold insert consists of a material with good thermal conductivity, in particular metal or ceramic, and that the mold part including at least the mold insert and the mold core is surrounded by a heat-insulating insulating member.

[0019] The invention will now be explained in more detail with the aid of examples and with reference to the drawings. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic cross-sectional view of an injection molding apparatus for manufacturing plate-like fuel cell components such as bipolar plates. [Figure 2] 1 is a schematic perspective view of an embodiment of a plate-like fuel cell component. [Figure 3] 1A and 1B are cross-sectional views showing portions of a mold of an injection molding apparatus in partial images a) and b).

[0021] FIG. 1 shows, by way of example, an injection molding apparatus 1 in a schematic longitudinal section, which comprises an injection unit 2 and a mould unit 3 connected thereto.

[0022] The injection unit 2 has a housing 20 with a hopper-like filling portion 21 and a conveying unit 22 with a conveying screw and a drive unit 23 .

[0023] The mould unit 3 comprises a mould part having a cavity 31 formed to correspond to the plate-shaped component to be produced, the cavity 31 being surrounded by a wall 30. In order to remove the component obtained by the injection moulding process, here a plate-shaped fuel cell component 6 (see Figure 2), i.e. a bipolar plate, the mould unit 3 is provided with an opening device (not shown) as well as an ejection or ejection device.

[0024] The injection molding apparatus 1 may also include multiple injection units 2 and / or mold units 3. At least one mold unit is configured for injection via a direct sprue or via a manifold system (cold and / or hot runner system).

[0025] The injection molding apparatus 1 advantageously has a mechanical vent system (not shown) or a vacuum vent system for the mold unit. Furthermore, the injection molding apparatus 1 may advantageously be configured as a two-component or multi-component tool, whereby a sealing system made of a suitable polymer material can be applied circumferentially by injection.

[0026] To carry out the injection molding process, appropriately prepared raw material 4, consisting of a thermoplastic material and additional components, here in particular graphite and possibly carbon black, is placed in the charging section 21 and fed from there by a conveying screw to the conveying unit 22. The raw material 4 is exposed to thermal energy above its melting point by a heating device arranged in the conveying unit 22, and brought to the required temperature of the molten compound to be formed, which is then injected at a defined injection pressure via a correspondingly formed sprue passage on the outlet side of the conveying unit 22 into the cavity 31 of the mould unit 3, after which the cavity 31 is completely filled with a moulding compound 5 corresponding to the plate-shaped component to be produced, here a plate-shaped fuel cell component 6, contained therein.

[0027] The additional components, in particular in the form of graphite and possibly carbon black, introduced into the raw material 4 to modify the thermoplastic material serve to achieve the electrical conductivity required for the operation of the fuel cell or fuel cell stack and also to achieve good thermal conductivity for dissipating the heat generated in the fuel cell. Depending on the requirements, the mass fraction or, as the case may be, the mass or volume fraction of the additional components in the raw material for the production of the plate-shaped fuel cell component 6 may be greater than 5%, greater than 20%, greater than 30%, or even greater than 40%, and may range from 5% to 95%, 20% to 90%, 30% to 80%, or 40% to 80%, and the mass or volume fraction may be suitably varied or adapted depending on the thermoplastic material and the electrical conductivity required during the operation of the fuel cell, as well as depending on the geometrical structure of the plate-shaped fuel cell component 6.

[0028] 3 shows, in partial images a) and b), also by way of example, two parts of a mould unit 3 of an injection moulding apparatus 1, in particular a nozzle-side mould section 3' and an ejector-side mould section 3'' formed for connection to the injection unit 2, which together form a wall 30 enclosing a cavity 31 required for moulding a plate-shaped fuel cell component. In this case, the wall 30 of the cavity 31 is formed by a mould insert 32 consisting of a first part present in the nozzle-side mould section 3' and a second part arranged in the ejector-side mould section 3''. The first and second parts of the mold insert 32 are also attached to respective mold cores 33, and the mold insert 32 and the mold core 33 as a unit are surrounded by respective insulating members 34 on the outside of this unit facing away from the cavity 31, so that heat radiation from the unit consisting of the mold insert 32 and the mold core 33 is prevented as well as possible, and the cavity is accurately temperature-controlled by the injected molten compound or molding compound, so that the molten compound maintains the temperature required to completely fill the cavity 31 during the injection process, and the best possible temperature control of the cavity 31 by the injected molten compound is achieved.

[0029] The combined unit consisting of both the mold insert 32 and the mold core 33 forms the mold part of the mold unit 3, which is arranged in a mold part receptacle 35, which itself consists of two parts, one of which is arranged in the nozzle-side mold section 3' and the other in the ejector-side mold section 3''. The mold part receptacle 35 is also insulated on its outside by insulating elements 34 or 34' to prevent heat dissipation as well as possible. For accurate positioning, the mold part receptacles 35 each have a centering element 36 on their outside, which is located parallel to the surface extent of the cavity 31.

[0030] In the illustrated embodiment of the mold unit 3, a supply unit 24 equipped with a hot runner system for injecting the molten compound into the cavity 31 is arranged in the mold section 3' on the nozzle side connected to the injection unit 2.

[0031] In the illustrated configuration, the nozzle side mold section has guide pins that protrude from the surface of the nozzle side mold section 3' that is located in the separation plane of the mold unit 3 and cooperate to precisely fit with guide receiving portions (not shown) that are properly positioned on the opposite surface of the ejector side mold section 3'', thereby guiding the mold section 3 to close and guiding it to open following the molding process, and ejecting the molded plate-shaped fuel cell component.

[0032] To appropriately temperature-regulate the cavity 31 during the molding process, temperature-regulating means 7 are arranged between each mold insert 32 and mold core 33 in both the nozzle-side mold section 3′ and the ejector-side mold section 3″. The temperature-regulating means 7 include heating means 70 and, optionally, cooling means 71 for rapidly and appropriately cooling the molding compound. The heating means 70 are formed, for example, as electrically or inductively loaded heating elements in the form of current-carrying heating lines, or as heating channels through which a heat transfer fluid (liquid or gaseous medium) flows. The cooling means 71 are formed as cooling channels or embedded tubes through which a cooling fluid flows, or as electrically operated cooling means. The mold insert 32 is preferably formed from a metal with good thermal conductivity, such as tool steel, or another material with good thermal conductivity, such as ceramic. The mold core 33 may also consist of metal, or alternatively, a heat-resistant plastic material, such as ceramic. Together with the insulation provided by the insulating member 34 surrounding the unit consisting of the mold insert 32 and the mold core 33, an easily controllable and fast-responding temperature regulation in conjunction with the injection process is achieved.

[0033] Advantageously, the present invention further provides a thermoplastic material as a melt compound or molding compound, into which graphite particles with good electrical conductivity are mixed, preferably as the only additional component. The thermoplastic polymer material serves as the matrix material of the resulting plate-shaped fuel cell component, preferably consisting of a matrix material with a free π-electron system, such as a PEEK material with benzene rings. In this case, the conductive connection of the graphite particles is formed via the π-electron system of the matrix material, even without the use of conductive carbon black. As a result, the manufacturing process is advantageously influenced by injection molding, and a relatively low filling level of the conductive additional component can be selected compared to the additional component containing conductive carbon black. As a result, the manufacturing parameters during the injection step, such as the injection pressure, injection molding time, and holding pressure, can be advantageously selected to ensure good flowability within the cavity 31. Additionally, during the injection molding process, two preferred orientations of the graphite layers are generated in the molding compound. In the region close to the wall, the graphite particles are preferably oriented in the flow direction, while in the core zone, they are primarily oriented perpendicular to the flow direction. This has a beneficial effect on the electrical conductivity for the function of plate-like fuel cell components such as bipolar plates.

[0034] Furthermore, the particle size of the additional component or D 50 It is advantageous to select a value in the range of 5 μm to 50 μm or 100 μm, for example 10 μm to 30 μm, and adjustments can also be made to the selected thickness of the plate-shaped fuel cell component. Furthermore, it is advantageous to select graphite particles with a low aspect ratio (thickness to the smallest dimension perpendicular thereto), i.e., plate-shaped graphite particles with as much planar extent as possible, with an aspect ratio of less than 5, in particular less than 1 or less than 0.5. The graphite particle loading level can be in the range of 5% to 95% by volume, for example 20% to 80% by volume, or possibly 5% to 95% by weight, or 20% to 87% or 80% by weight, based on the raw material.

Claims

1. A method for producing a plate-shaped fuel cell component (6), in particular a bipolar plate, from a thermoplastic material having an additional component with good electrical and thermal conductivity, the plate-shaped fuel cell component being produced by injection molding technology using an injection molding device (1) having at least one injection unit (2) and at least one mold unit (3) with walls surrounding each cavity, comprising:

1. A method according to claim 1, wherein the molten thermoplastic material with the additional components is injected under pressure as a molten compound into the hollow spaces of each cavity (31) of the at least one mould unit (3), the hollow spaces corresponding permanently to the shape of the fuel cell component, by means of the at least one injection unit (2), and the heat transfer through the walls (30) is adjusted to the thermal conductivity and heat capacity of the molten compound and to the filling speed, so that the molten compound completely fills each cavity (31) as a moulding compound (5) before its temperature drops below its melting temperature.

2. 2. The method according to claim 1, characterized in that graphite is added to the thermoplastic material as a modifying, conductive additional component, without or with small amounts of carbon black, in a mass fraction of the additional component of more than 5%, more than 20% or more than 30%, advantageously more than 50%, for example 5% to 95%, in particular 30% to 70% or 87%, of the total mass of the raw materials fed to the injection unit (2).

3. a polymer material having a free π-electron system, in particular a PEEK material, is used as a thermoplastic material forming the matrix material of the plate-like fuel cell component, 3. The method according to claim 1, wherein as conductive additive component only graphite particles are used, in particular having an aspect ratio of thickness to smallest dimension of less than 5, in particular less than 1 or 0.

5.

4. 3. The method according to claim 1 or 2, characterized in that the plate-shaped fuel cell component (6) is produced with a thickness (d) perpendicular to its surface extent, in plan view, of at most 2 mm, at most 1 mm, at most 0.5 mm or at most 0.2 mm.

5. The particles of the conductive additional component have a size D in the range of 5 μm to 50 μm or 100 μm. ５０ 5. The method according to claim 1, further comprising:

6. 6. The method according to claim 1, wherein the fuel component (6) is provided with at least one connecting, mounting, line and / or sealing element by insert molding and / or molding in an injection molding process.

7. 7. Plate-shaped fuel cell component (6), in particular a bipolar plate, characterized in that it has been produced using a method according to any one of claims 1 to 6.

8. An injection molding apparatus for carrying out the method according to any one of claims 1 to 6, comprising at least one injection unit (2) for supplying raw material (4) comprising a thermoplastic material and an electrically conductive additive component, in particular graphite particles, and at least one mold unit, the mold unit having a nozzle-side mold section (3') assigned to at least one injection nozzle assembly and an ejector-side mold section (3'') assigned to the ejector side, both mold sections being arranged in a mold section receptacle (35) and facing each other in a parting plane. an injection molding apparatus including a mold section (31) facing each other and each having a mold insert (32) and a mold core (33), each mold insert (32) having a cavity (31) that can be opened at the parting plane and is closed during the injection process, the cavity being connected to the injection unit (2) via a supply unit (24) having a hot runner system or a cold runner system for injecting the molten raw material (4) into the hollow space of the cavity (31) as a molten compound, 1. An injection molding apparatus according to claim 1, wherein the shape of the hollow space of each of said cavities (31) is permanently adapted to the shape of the fuel component to be manufactured by the inner surface of said mold insert (32) surrounding said hollow space until said at least one mold unit (3) opens during the molding process.

9. 9. The injection molding apparatus according to claim 8, characterized in that a temperature control means (7) is arranged between the mold insert (32) and the mold core (33) in the nozzle-side and / or ejector-side mold section (3', 3'').

10. 10. The injection molding apparatus according to claim 9, wherein the temperature control means (7) includes a heating means (70) and / or a cooling means (71).

11. the heating means (70) is heatable by electric current heating, inductively via conductive means, or by a heat transfer fluid conducted through a passage; and / or The cooling means (71) can be cooled by a cooling fluid guided through a passageway or comprises an electrically operated cooling device.

11. The injection molding apparatus according to claim 10.

12. At least the mold insert (32) is made of a material with good thermal conductivity, in particular metal or ceramic, The mold portion including at least the mold insert (32) and the mold core (33) is surrounded by a heat insulating member (34).

12. An injection molding apparatus according to any one of claims 8 to 11, characterized in that it comprises:

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