Screen printing device for printing on at least one substrate plate

Abstract

Screen printing device (100) for printing at least one substrate plate, in particular at least one bipolar plate (2), with a printing material (101), wherein the screen printing device (100) comprises a carrier (102) with a carrier surface (102a) configured to accommodate two substrate plates to be printed side by side, a first print head (110) arranged above the carrier surface (102a), comprising a first flood squeegee (111) and a first printing squeegee (112), wherein the first print head (110) is configured and arranged to print one of the two substrate plates to be printed, a printing screen (130) arranged between the carrier surface (102a) and the first print head (110), characterized by a second print head (120) arranged above the carrier surface (102a), comprising a second flood squeegee (121) and a second printing squeegee (122), wherein the second print head (120) is configured and arranged is,to print on a second of the two substrate plates to be printed.

Description

The disclosure relates to a screen printing device for printing at least one substrate plate. The disclosure further relates to a corresponding screen printing method.Known screen printing devices for printing substrate plates typically have a print head comprising a first flow squeegee and a first print squeegee, wherein the first print head is designed and configured to print a substrate plate at least in regions.The substrate plate can be, for example, a bipolar plate or a separator plate of an electrochemical system. Electrochemical systems, for example fuel cell systems or electrochemical compressor systems, redox flow batteries and electrolysers, usually comprise a multiplicity of bipolar plates which are arranged in a stack, such that in each case two adjacent bipolar plates enclose an electrochemical cell. The bipolar plates usually each comprise two separator plates which are connected to one another along their rear sides facing away from the electrochemical cells. The bipolar plates can serve, for example, for the electrical contacting of the electrodes of the individual electrochemical cells (for example fuel cells) and / or for the electrical connection of adjacent cells (series connection of the cells). Single-layer bipolar plates are also common, i.e. consist exactly of a separator plate. In particular, single-layer bipolar plates are used in electrolysers, since here the reaction media themselves act as temperature control agents.The separator plates of the bipolar plates may have channel structures for supplying the cells with one or more media and / or for transporting away media. In the case of fuel cells, the media can be, for example, fuels (e.g. hydrogen or methanol), reaction gases (e.g. air or oxygen) or a coolant as supplied media and reaction products and heated coolant as discharged media. Furthermore, the bipolar plates can serve for conducting away the waste heat generated in the electrochemical cell, as is generated, for example, during the conversion of electrical or chemical energy in a fuel cell, and for sealing the various media or cooling channels from one another and / or from the outside. In fuel cells, the reaction media, i.e. fuel and reaction gases, are usually carried on the mutually remote surfaces of the individual plates, while the coolant is carried between the individual plates. The bipolar plates usually each have at least one or more through openings. The media and / or the reaction products can be conducted through the through openings to the electrochemical cells delimited by adjacent bipolar plates of the stack or into the cavity formed by the separator plates of the bipolar plate or can be discharged from the cells or from the cavity. The electrochemical cells, in particular a fuel cell, can each comprise, for example, a membrane electrode assembly (MEA) with a polymer electrolyte membrane (PEM), electrodes and catalyst layers. Adjacent to the MEA, the MEA system can also have one or more gas diffusion layers (GDL), which are usually oriented toward the separator plates, in particular toward bipolar plates of fuel cell systems and are designed, for example, as a carbon nonwoven. In an exemplary fuel cell, hydrogen carried on an anode side is typically converted to water with oxygen carried on a cathode side. Protons formed during an oxidation of the hydrogen pass from the anode side through the MEA to the cathode side and react there with the oxygen and electrons to form water. The membrane of the fuel cell is electrically insulating and prevents an electrical short circuit between anode and cathode. The electrons are separately supplied from the anode to the cathode, so that the electric current is utilized.In order to seal the through-openings from the interior of the stack and from the environment, the separator plates have, for example, sealing arrangements in the form of sealing beads which are each arranged around the through-openings and which each completely surround the through-openings. A coating is printed on the sealing beads in order to compensate for surface roughness, for example. The coating is typically printed in a screen printing process.The object of the present invention is to propose an improved screen printing device which addresses in particular improvements with regard to printing costs and / or printing times. Additionally or alternatively, it may be the object of the present invention to propose an improved screen printing device which makes it possible to print substrate plates of larger dimensions.At least one of these objects is achieved by a screen printing device according to claim 1.The proposed screen printing device is therefore suitable in particular for printing at least one substrate plate, in particular at least one bipolar plate, with a printing material.The screen printing apparatus includes:a carrier having a carrier surface which is configured to receive two substrate plates to be printed next to one another,a first print head arranged above the carrier surface, comprising a first flow squeegee and a first printing squeegee, wherein the first print head is configured and configured to print a first substrate plate of the two substrate plates to be printed,a print screen disposed between the carrier surface and the first print head,a second print head arranged above the carrier surface, comprising a second flooding squeegee and a second printing squeegee, wherein the second print head is configured and configured to print a second substrate plate of the two substrate plates to be printed.Alternatively or additionally to the fact that the first print head is designed and configured to print a first substrate plate of the two substrate plates to be printed, the first print head can be designed and configured to print a first region of a first substrate plate. Alternatively or additionally to the fact that the second print head is designed and configured to print a second substrate plate of the two substrate plates to be printed, the second print head can be designed and configured to print a second region of the first substrate plate. The screen printing device can therefore be suitable in particular for printing substrate plates of larger dimensions in a comparatively short time, in particular since the first and second print heads can print simultaneously.The term printing here can relate on the one hand only to printing itself, i.e. to the application of the printing composition to the substrate plate, but can also include both flooding and the actual printing.The printing screen is disposed between the second print head and the support surface. Longitudinal axes of the substrate plates can be arranged parallel on the carrier surface. The first and the second substrate plate may have the same dimensions and / or be formed completely identically.The first and / or second substrate plate can / can each have a length I which corresponds to at least 1.4 times its width b. In particular, the first and / or second substrate plate can / can have a length I which corresponds to at least 1.8 times its width b. In particular, the first and / or second substrate plate can / can have a length I which corresponds to at least 2 times its width b. The first and / or second substrate plate can / can have a length I which corresponds at most to 3.5 times its width b. The first and / or second substrate plate can / can have a length l which corresponds at most to 3 times its width b. The first and / or second substrate plate can / can have a length I which corresponds at most to 2.75 times its width b. With the aforementioned length / width relationships, it is particularly advantageous if flooding and printing is carried out with exactly two print heads.If a substrate plate has a length / width ratio of more than 2.5, in particular of more than 3, it may also be advantageous to provide not only a first and second print head but at least one further, in particular third print head.The first print head can be configured to run along a first region, in particular a first half, of the printing screen. Additionally or alternatively, the second print head can be configured to run along a second region, in particular a second half, of the printing screen. The first region and the second region may be arranged adjacent to each other or spaced apart from each other. In particular, the first region and the second region may be arranged so as not to overlap each other.The first print head can be arranged in a starting position above a first outer edge of the carrier surface. The second print head can be arranged in a starting position above a second outer edge of the carrier surface, in particular opposite the first edge. In the respective starting position, the first and / or the second print head can / can therefore be arranged on the first or second outer edge in a projection onto the carrier surface.The first and / or the second print head can / can be arranged at a distance from the carrier surface along a perpendicular to the carrier surface in the starting position.The home position may be defined as the position that the print head assumes before printing. During printing, the print head can move from the starting position along a printing path into a maximum deflection position. The print head can then move back into the starting position. It is also possible here for the printing squeegee to distribute the printing mass on or in the screen starting from a starting position and to move to a maximum deflection position in the process. On the return path from the maximum deflection position, the printing squeegee can then transfer the printing mass from the screen to the substrate plate and in the process return to the starting position.The first and / or the second print head can / can be designed to be displaceable along a perpendicular relative to the carrier surface. In particular, the first and / or the second print head can / can be designed to reduce a distance perpendicular to the carrier surface relative to the starting position during printing and / or to increase a distance perpendicular to the carrier surface relative to the maximum deflection position after printing.A method along a perpendicular to the carrier surface can correspond to a z-direction in a Cartesian coordinate system. A method in a first direction parallel to the carrier surface can correspond to the x-axis in a Cartesian coordinate system. A method in a second direction parallel to the carrier surface, which direction runs orthogonally to the first direction, can correspond to the y-axis in a Cartesian coordinate system.The longitudinal axis of the first and / or second substrate plate may extend along the x-direction or along the y-direction.In particular, the first and the second print head can both be movable back and forth along the x-axis or can both be movable back and forth along the y-axis. The first and / or the second print head can / can be additionally movable forwards and backwards along the z-axis.In a first embodiment, the first print head can be arranged in its initial position above the first outer edge of the carrier surface and the second print head can be arranged in its initial position above the second outer edge of the carrier surface, wherein the second outer edge is opposite the first edge.In particular in this first exemplary embodiment, the first print head can be configured to move in the direction of the second print head during the printing operation, and the second print head can be configured to move in the direction of the first print head during the printing operation. The first and second print heads can therefore in particular be moved towards one another simultaneously during printing. In particular, the first print head can move in the direction of the second print head during flooding and the second print head can move in the direction of the first print head, while the first print head and the second print head move away from one another again during the actual printing operation. Alternatively, the first print head can move away from the second print head during flooding and the second print head can move away from the first print head during flooding, wherein the two print heads then move towards one another again during the actual printing operation. Their starting positions can lie in particular on two opposite edges, while their maximum deflection positions, i.e. the position after flooding, are arranged in particular substantially centrally above the carrier surface and spaced apart from one another. However, an arrangement which is the reverse of the two phases of the printing process is likewise possible. A distance between the first and second print heads can be maximum in the starting positions and minimum in the maximum deflection positions, or vice versa.In a second exemplary embodiment, the first print head can be arranged in a starting position above the first outer edge of the carrier surface and the second print head can be arranged in a starting position parallel to the first print head and above a central region of the carrier surface running parallel to the first outer edge.The second print head can be arranged in a maximum deflection position above a second outer edge of the carrier surface opposite the first outer edge. The first print head can be arranged in a maximum deflection position parallel to the second print head and above a central region of the carrier surface running parallel to the first outer edge. When both printheads are in the home position, a distance between the printheads may be substantially the same as in the maximum deflection position. Preferably, the distance is substantially constant during the printing process, preferably both during flooding and during actual printing.The first and the second print head can be configured to be simultaneously in their starting position and simultaneously in their maximum deflection position. The first and the second print head can be configured and configured to print substantially simultaneously on the first and the second substrate plates.A distance can be understood as remaining constant in the sense of this application, in particular, if a deviation is not greater than 5%, in particular not greater than 3%, in particular not greater than 1%.A speed can be understood as still constant in the sense of this application in particular if a deviation is not greater than 5%, in particular not greater than 3%, in particular not greater than 1%.The starting position of the second print head can lie in the central region, but in particular not exactly centrally between outer edges of the carrier surface. In particular, in a projection of a travel path of the first and second print heads perpendicularly onto the carrier surface, the region which can be traveled by the first print head can form a first half-field on the carrier surface and the second print head can form a second half-field. At the edge of the second half-array facing the first half-array, the starting position of the second print head can be arranged. At the edge of the first half-field facing the second half-field, the maximum deflection position of the first print head can be arranged. The first print head may be arranged in its maximum deflection position next to the second print head when it is in its home position, such an arrangement not occurring in practice when both print heads are moved substantially parallel to each other. The half-panels can be formed such that they do not overlap.In particular in the second exemplary embodiment, the first print head and the second print head can be configured to move in the same direction during the printing operation, preferably substantially at the same speed.In one embodiment, at least one print head can be formed and configured to have a first alignment in a first printing operation and to have a second alignment in a subsequent second printing operation. The first alignment can preferably be rotated through 90° with respect to the second alignment. The formation of the print head to be rotatable can be applied to both the first and second embodiments. The first and second print heads may also have a different arrangement than described with respect to the first or second embodiment.The configuration and device of the print head such that it has a first alignment in a first printing operation and has a second alignment in a subsequent second printing operation can also be claimed in particular independently of the second print head. For example, the apparatus can have two print heads, of which only one is arranged rotatably and, in the arrangement which is rotated relative to the other print head, flood and print the entire printing screen.Such a screen printing device for printing at least one substrate plate, in particular at least one bipolar plate, with a printing material can comprisea carrier having a carrier surface which is configured to receive two substrate plates to be printed next to one another,a first print head arranged above the carrier surface, comprising a first flow squeegee and a first printing squeegee, wherein the first print head is designed and configured to print at least a first of the two substrate plates to be printed,a print screen disposed between the carrier surface and the first print head,wherein the first print head is designed and configured to have a first orientation in a first printing operation and to have a second orientation in a subsequent second printing operation, in particular wherein the first orientation is rotated through 90° with respect to the second orientation.Such a screen printing device for printing at least one substrate plate, in particular at least one bipolar plate, with a printing material can alternatively or additionally comprise,a carrier having a carrier surface which is configured to receive two substrate plates to be printed next to one another,a first print head arranged above the carrier surface, comprising a first flow squeegee and a first printing squeegee, wherein the first print head is designed and configured to print at least a first of the two substrate plates to be printed,a print screen disposed between the carrier surface and the first print head,wherein the printing screen is designed and configured to have a first orientation during flooding of a first printing operation and to have a second orientation during subsequent flooding of the same printing operation, wherein the first orientation is preferably rotated by 90° with respect to the second orientation.Optionally, these two screen printing devices can each comprise a second print head arranged above the carrier surface, comprising a second flow squeegee and a second print squeegee, wherein the second print head is designed and configured to print a second of the two substrate plates to be printed.In the first and second orientation, the planar surface of the printing screen can preferably be arranged parallel to the carrier surface. If rotation is made between flooding and printing, in the first orientation, i.e. during flooding, in particular only the printing screen can be rotated with respect to the print heads compared with the second orientation. For the actual printing, the printing screen is rotated back into its second orientation and thus reaches its correct position relative to the substrate plates to be printed. Alternatively, it is possible to rotate the print head and in particular the two print heads relative to the overall arrangement of carrier, substrate plates and screen. Here, preferably at least one cycle of flooding and printing in this orientation and a later cycle of flooding and printing in the rotated-back orientation then take place. In principle, it may be advantageous not always to carry out flooding and printing processes in the same relative orientation, in order to regularly supply little screen areas involved in the actual printing process with new printing material and to return printing material present in the screen to the circuit again.Steps of a method for printing a printing material onto a substrate plate, in particular a bipolar plate, are described below. The method can be the subject matter of a further patent application, in particular an international patent application according to the PCT, a European patent application or a German patent application. The method comprises 1. providing a screen printing device as described above 2. laying two substrate plates on the carrier surface, 3. laying the printing screen in a first orientation opposite the print heads, 4. flooding the printing screen with the printing material, wherein the first flooding squeegee distributes the printing material on a first region of the printing screen and the second flooding squeegee distributes the printing material on a second region of the printing screen, 5. simultaneously printing the two substrate plates, wherein the first printing squeegee presses the printing material onto the first substrate plate through open meshes of the printing screen and the second printing squeegee presses the printing material onto the second substrate plate through open meshes of the printing screen.The steps of the method may be carried out in the above order or in a modified order. In particular, steps 2 and 3 can be carried out in interchanged order.The first and second flooding squeegees distribute the printing material in respective areas preferably substantially simultaneously. The first and the second printing squeegee can print the two substrate plates in particular substantially simultaneously. Substantially simultaneously, in the present case, a time offset can be understood which does not exceed 5%, in particular 4%, further in particular 3%.In one embodiment of the method, in particular using a screen printing device according to the first exemplary embodiment, the first flooding squeegee and the second flooding squeegee can move towards one another during flooding of the printing screen.In one embodiment of the method, in particular using a screen printing device according to the first exemplary embodiment, the first printing squeegee and the second printing squeegee can move towards one another during the printing of the substrate plates.In one embodiment of the method, the first flooding squeegee and the second flooding squeegee can move in the same direction spaced apart from one another during flooding of the printing screen. The distance between the first flooding squeegee and the second flooding squeegee can be substantially constant.In one embodiment of the method, the first printing squeegee and the second printing squeegee can move in the same direction at a distance from one another when printing the substrate plates. The distance between the first printing squeegee and the second printing squeegee can be substantially constant.In one embodiment of the method, after the printing of the two substrate plates, the printing screen can be rotated into a second orientation. The second orientation can preferably be rotated through 90° with respect to the first orientation.In particular, the printing screen is rotated into the deviating orientation only for the subsequent flooding step and is rotated back into the starting position again after flooding or before the next actual printing step.In one embodiment of the method, after the printing of the two substrate plates, the at least one print head, in particular both print heads, can be rotated into a second orientation. The second orientation can also be rotated here preferably by 90° with respect to the first orientation. Preferably, the next flooding and printing operation is then performed in this rotated position.This process step can be carried out both in a process (as described above) with two print heads and in a process in which a screen printing machine with only one print head is used.The method of this kind for printing a substrate plate, in particular a bipolar plate, with a printing material can comprise the following steps 1. providing a screen printing device as described above, in particular having only exactly one first print head, 2. laying two substrate plates on the carrier surface, 3. laying the printing screen in a first orientation with respect to the first print head, 4. flooding the printing screen with the printing material, wherein the first flooding squeegee distributes the printing material on the printing screen 5. printing the two substrate plates, wherein the first printing squeegee presses the printing material onto the first and the second substrate plates through open meshes of the printing screen.As a sixth step, after printing the two substrate plates, the printing screen can be rotated into a second orientation as described above. The second orientation can preferably be rotated through 90° with respect to the first orientation. As an alternative sixth step, after printing the two substrate plates, the print head may be rotated to a second orientation as described above. Here too, the second alignment can preferably be rotated through 90° with respect to the first alignment. Method steps 2 and 3 can be interchanged in the sequence.The printing material can be a suspension, for example. The printing material can be a sealing paste, in particular based on fluoropolymer or based on silicone or based on EPDM (ethylene-propylene-diene, M-class). In principle, the printing material can comprise microspheres as in DE 10 2021 204 497, but can also be formed without microspheres.The present disclosure further relates to a substrate plate, in particular bipolar plate for an electrochemical system, having an integrally formed sealing element, wherein the substrate plate is printed with a printing material in a method according to the description and the printed printing material forms a microseal of the integrally formed sealing element.The substrate plate may be a bipolar plate, wherein the bipolar plate may comprise two separator plates formed as metallic layers and connected to one another. Alternatively, the substrate plate can be a bipolar plate formed from exactly one separator plate. Each of the bipolar plates may have a plurality of webs and depressions, and in each case a membrane electrode unit arranged between the separator plates.The sealing between the bipolar plates and the membrane electrode unit usually takes place outside the electrochemically active region and usually comprises both at least one port seal, i.e. a sealing of a passage opening for medium, and an outer seal. The bipolar plates are usually constructed from two separator plates, one of which adjoins a membrane electrode unit. In particular in the case of electrolysers, an only single-layer bipolar plate frequently adjoins an analogous membrane electrode unit on both sides. The separator plates can have seals for sealing with respect to the membrane electrode unit, in particular with respect to the frame-shaped seal of the membrane electrode unit. If the separator plates are formed as metallic plates, e.g. from stainless steel or titanium, these can be formed as sealing beads in the separator plates, for example by means of stamping, deep-drawing or hydroforming. To improve microsealing, such sealing beads usually have polymer-based sealing coatings at least on one side.The molded-in sealing element can thus be, in particular, a perimeter bead. This can typically only be macroscopically sealing, in particular resilient. In order to compensate for or at least better compensate for surface roughness and the like, the printed printing material can be applied to the perimeter bead-and preferably at least (partially) crosslinked-which realizes or at least improves a microsealing, for example by the preferably (partially) crosslinked printing material being able to penetrate into small surface depressions.The sealing element, in particular in the form of a perimeter bead, can surround the region with webs and channels. Further sealing elements, which can be designed as port studs, can surround the through openings in each case. One, several or all of these sealing elements can have a coating.The coating may be formed by the above-described printing material. The coating can be printed on one or more of the sealing elements using the above screen printing device and / or according to the above method. The coating can be a microseal, wherein the microseal comprises a foamed material with microspheres, in particular wherein a distribution of the expanded microspheres measured perpendicular to a surface of the metallic layer is inhomogeneous in the microseal.The molded-in sealing element can thus be designed as a metallic layer and the coating can be designed as an elastomeric sealing element. Reference is made to DE 10 2021 204 497 A1, the content of which is hereby incorporated in its entirety into this application.Furthermore, it is possible to monitor a correct application of the printing material, for example, by means of a camera which, after a number of flooding and printing processes to be defined, checks the state of the screen and compares it with a predetermined pattern. This enables, in particular in the case of a printing material which dries only slowly, immediate monitoring without having to wait for the end of the drying process. Technical details can be gathered from DE 69816098 T2, even if the printing of semiconductor components by means of screen printing is described there.Exemplary embodiments of the present invention are illustrated in the figures and are explained in more detail on the basis of the following description. The following are shown: FIG. 1 is a schematic side view of a screen printing device; FIG. 2 schematically shows a plan view of a screen printing device in the manner of the device according to FIG. 1, FIG. 3 schematically shows a top view of an alternative screen printing device in the manner of the device according to FIG. 1, FIG. 4 schematically shows a plan view of a screen printing device in the manner of the device according to FIG. 1, wherein the print heads are shown in their starting position, FIG. 5 schematically shows a plan view of the screen printing device according to FIG. 4, wherein the print heads are shown in their maximum deflection position, FIG. 6 schematically shows a plan view of a screen printing device in the manner of the device according to FIG. 1, wherein only one print head is provided, FIG. 7 schematically shows a plan view of a screen printing device according to FIG. 6, wherein only one print head is provided and this print head is configured to be rotatable, FIG. 8 is a schematic top view of a printing screen, FIG. 9 schematically shows a top view of an exemplary bipolar plate with coated bead roofs; and FIG. 10 schematically shows a section through two bipolar plates arranged one above the other with a membrane electrode unit (MEA) arranged between the bipolar plates, wherein the bipolar plates have a sealing coating on their bead roofs.Here and in the following, recurring features in different figures are each denoted by the same or similar reference numerals.FIG. 1 shows a screen printing device 100 for printing a printing material 101 onto a bipolar plate 2. The printing material 101 is a precursor of an elastomer and, after (partial) crosslinking, forms a coating which in the present case serves as a microseal.The screen printing device 100 comprises a carrier 102 having a carrier surface 102 a. Two bipolar plates 2 to be printed are arranged on the carrier surface 102 a.Above the carrier surface 102a, a first print head 110 comprising a first flooding squeegee 111 and a first printing squeegee 112 is arranged. The first print head 110 is designed and configured to print on the first of the two bipolar plates 2 to be printed on. Above the carrier surface 102 a, a second print head 120 is furthermore arranged, which comprises a second flooding squeegee 121 and a second printing squeegee 122. The second print head 120 is configured and configured to print a second of the two bipolar plates to be printed.The first flow squeegee 111, the second flow squeegee 121, the first printing squeegee 112 and the second printing squeegee 122 are each movable along the x-axis and along the z-axis.A printing screen 130 is arranged between the carrier surface 102 aand the first print head 110 or the second print head 120.The flooding squeegee 121 and the flooding squeegee 111 are each connected via a respective pressure medium line (not shown) to a respective separate pressure medium tank or to a common pressure medium tank (not shown), in which / the pressure medium 101 is mounted.In order to print the first bipolar plate 2, the printing screen 130 is flooded with the printing material 101, wherein the flooding squeegee 111 distributes the printing material 101 on the printing screen 130 in a first region. For this purpose, the flooding squeegee 111 can be moved downward from a starting position along the z-axis in order to come into contact with the printing screen 130 or at least to reduce a distance from it. Furthermore, the flooding squeegee 111 can be moved along the x-axis in order to distribute the printing medium 101 on the printing screen 130. The flooding squeegee can then be moved back into the starting position along the z-axis and / or along the x-axis.The squeegee 112 can be moved from a starting position along the z-axis in such a way that a distance between the printing screen 130 and the squeegee 112 becomes minimum. The printing squeegee can then be moved along the x-axis, so that it prints the printing medium through open mesh of the printing screen 130 onto the first bipolar plate 2. In this case, the printing squeegee 112 can be moved along the x-axis.In order to print the second bipolar plate 2, the printing screen 130 is flooded with the printing material 101, wherein the flooding squeegee 121 distributes the printing material 101 on the printing screen 130 in a second region. For this purpose, the flooding squeegee 121 can be moved downward from a starting position along the z-axis in order to come into contact with the printing screen 130 or at least to reduce a distance from it. Furthermore, the flooding squeegee 121 can be moved along the x-axis in order to distribute the printing medium 101 on the printing screen 130. The flooding squeegee can then be moved back into the starting position along the z-axis and / or along the x-axis.The squeegee 122 can be moved from a starting position along the z-axis in such a way that a distance between the printing screen 130 and the squeegee 122 becomes minimum. The printing squeegee 122 can then be moved along the x-axis, so that it prints the printing medium 101 onto the second bipolar plate 2 through open mesh of the printing screen 130. In this case, the printing squeegee 122 can be moved along the x-axis.The first flooding squeegee 111 and the second flooding squeegee 121 can be configured to flood the first and second region simultaneously with printing medium 101 and to distribute the printing medium simultaneously in the respective region. The first printing squeegee 112 and the second printing squeegee 122 can be configured to print the two bipolar plates 2 with printing medium 101 simultaneously.As an alternative to an independent method of the respective two squeegees, it is also possible to correspondingly method the respective entire print head.The bipolar plates to be printed have a length of at least 120 mm or at least 150 mm or at least 180 mm. The bipolar plates to be printed have a length of at most 800 mm or at most 780 mm or at most 750 mm. The bipolar plates to be printed have a width of at least 60 mm or at least 80 mm or at least 100 mm. The bipolar plates to be printed have a width of at most 300 mm or at most 280 mm or at most 250 mm. In principle, the formats of bipolar plates can range from approximately square to a length / width ratio of 12:1. The bipolar plates to be printed according to the invention preferably have a length / width ratio of at least 1.4, but preferably of at least 1.8 or of at least 2.Figures 2 to 7 are intended to be schematic only for clarity of the relative arrangement of the screen and plate to be printed. The screen is located actually above the substrate plates and below the print heads; in FIGS. 2 to 7, the substrate plates are reproduced above the screen which is not actually transparent (cf. FIG. 8 ) in order to clarify the relative orientation of the respective components in the x-y plane.FIG. 2 schematically shows a plan view of a screen printing device 100 in the manner of the device according to FIG. 1. the first print head 110 in the first exemplary embodiment shown is arranged in its starting position above a first edge of the carrier surface 102 aand the second print head 120 in its starting position in a central region of the carrier surface 102 a. The two print heads 110 and 120 move in the positive direction along the x-axis during printing. Printheads 110 and 120 are aligned in parallel.FIG. 3 schematically shows a plan view of a screen printing device 100 in the manner of the device according to FIG. 1. the first print head 110 is arranged in its starting position above a first edge of the carrier surface 102 ain the second exemplary embodiment shown and the second print head 120 is arranged in its starting position above a second outer edge of the carrier surface 102 awhich is opposite the first outer edge. Printheads 110 and 120 are aligned in parallel. The two print heads 110 and 120 move in opposite directions during printing along the x-axis and move towards one another-preferably during flooding-and preferably away from one another during actual printing. In their maximum deflection positions, the first print head 110 and the second print head 120 are located above a central region of the carrier surface 102 aand are arranged next to one another.In the first and second exemplary embodiments of FIGS. 2 and 3, the first print head 110 is configured to run essentially a first half of the printing screen and the second print head 120 is configured to run essentially a second half of the printing screen.The respective bipolar plate 2 to be printed lies below the printing screen 130. An area of the bipolar plate 2 is typically smaller than one half of the printing screen.The first print head 110 and the second print head 120 are each configured to travel at substantially the same speed. Thus, the first and the second bipolar plate 2 can be printed simultaneously.FIG. 4 shows a variant of the exemplary embodiment of FIG. 2. The difference between the device in FIG. 2 and the device in FIG. 4 lies in the fact that in FIG. 2 the maximum deflection position of the first print head 110 corresponds to the starting position of the second print head 120, or the positions at least overlap. In the device of FIG. 4, on the other hand, the starting position of the second print head 120 lies next to the maximum deflection position of the first print head 110, in particular no overlap between the positions is provided. In Figure 4, printheads 110 and 120 are shown in their home positions. In Figure 5, printheads 110 and 120 are shown in their maximum deflected positions.FIG. 6 shows a plan view of a screen printing device 100' for printing a printing material 101 onto a bipolar plate 2. The screen printing device 100' corresponds to the screen printing device 100 according to FIG. 1, wherein the screen printing device 100' does not have a second print head 120 or is at least shown without a second print head 120, but such a print head can be arranged in a plane different from the plane of the print head 110. The printing material 101 is an elastomer precursor and forms a coating which in the present case serves as a microseal.The screen printing apparatus 100' includes a support 102 having a support surface 102a. Two bipolar plates 2 to be printed are arranged on the carrier surface 102 a.Above the carrier surface 102a, a first print head 110 comprising a first flooding squeegee 111 and a first printing squeegee 112 is arranged. The first print head 110 is designed and configured to print on the first and the second of the two bipolar plates 2 to be printed on. In contrast to the preceding screen printing devices, the first print head 110 is connected here to a rotary frame 114 or mounted on such a rotary frame.The first flow squeegee 111 and the first printing squeegee 112 are movable along the x-axis and along the z-axis, respectively.A printing screen 130 is arranged between the carrier surface 102 aand the first print head 110.The flooding squeegee 111 is connected via a pressure medium line (not shown) to a pressure medium tank (not shown), in which pressure medium 101 is stored.In order to print on the bipolar plates 2, the printing screen 130 is flooded with the printing material 101, wherein the flooding squeegee 111 distributes the printing material 101 over the entire printing screen 130. For this purpose, the flooding squeegee 111 can be moved downward from a starting position along the z-axis in order to come into contact with the printing screen 130 or at least to reduce a distance from it. Furthermore, the flooding squeegee 111 can be moved along the x-axis in order to distribute the printing medium 101 on the printing screen 130. The flooding squeegee can then be moved back into the starting position along the z-axis and / or along the x-axis. However, advantageously, flooding and printing squeegees are combined in a print head in such a way that the print head as such is moved along the x-axis. In particular, during flooding, the print head reaches a maximum deflection position, which represents its maximum deflection in the x direction.The squeegee 112 can move from a starting position along the z-axis in such a way that a distance between the printing screen 130 and the squeegee 112 becomes minimum. This starting position can be, in particular, the aforementioned maximum deflection position of the print head with respect to the print head or the x-axis. The printing squeegee can then be moved along the x-axis, so that it prints the printing medium through open mesh of the printing screen 130 onto the first bipolar plate 2 and subsequently onto the second bipolar plate 2. In this case, the printing squeegee 112 can be moved along the x-axis. Advantageously, the entire print head is moved along the x-axis, namely in the direction of the original starting position.In this first printing operation, the first print head 110 has a first orientation (as shown in Fig. 6). In a subsequent printing operation, the print head 110 may have a second orientation (as shown in FIG. 7 ). The second orientation is rotated through 90° with respect to the first orientation. Advantageously, the first print head 110 is mounted on a rotating device 114, in particular a rotary frame, and rotated therewith in the x-y direction. The printing direction then runs along the y-axis.In a or for a subsequent printing operation, the print head 110 can be rotated back into the original position.In screen printing, it is typical--especially in the case of printing material with elastomer precursors--that the printing material 101 can dry on the screen in certain areas, especially in the area of the edges and in dead points, and ages there. This can lead to the formation of propulsing and clogging of meshes of the printing screen 130 and thus to a reduced print quality. Rotating the orientation of the printing screen 130 relative to the print head may be advantageous because the printing screen is flooded in another direction in this way. Thus, printing material 101 can be better distributed and there are less dead areas where printing material 101 can age. Thus, an improved print quality can be ensured, in particular for many printing processes.In an embodiment in which the print heads 110 and 120 are designed to be rotatable, a rotating device 114 can be provided, which automatically performs a rotation of the print heads 110 and 120. The rotating device 114 may include a motor (not shown) that performs the rotation, and a controller unit (not shown) connected to the motor and configured and configured to instruct the motor to perform the rotation. The controller unit may be configured and configured to automatically cause rotation of the print heads 110 and 120 after a certain number of printing operations.Alternatively, it is also possible to rotate the printing screen 130 by 90° only for individual flooding processes and to move it back into the starting position again for the immediately following printing process. A motor and, if appropriate, a controller unit can also be provided for this purpose.FIG. 8 shows a plan view of a printing screen 130 which is designed for printing the sealing regions of two separator plates 2. It has permeable regions 51 a- dand also closed regions 52. The permeable areas 51 a- cin this case correspond to the clearances for printing porticks 11 a- c,the permeable areas 51 dare the clearances for printing a perimeter bead 11 d. The shapes of the beads are only shown schematically here and do not correspond to those of the following FIG. 9.FIG. 9 shows a printed bipolar plate 2 which is formed from two separator plates joined together in a materially bonded manner, of which only the first separator plate facing the observer is visible in FIG. 9, which covers the second separator plate. The bipolar plate was printed using the method described above and using an apparatus according to one of FIGS. 1 to 7 or using a printing screen according to FIG. 8. The separator plates can each be manufactured from a metal sheet, e.g. from a stainless steel sheet. Each metallic separator plate has a thickness of about 75 μm, for example. The separator plates may be welded together, for example, by laser welds. The separator plates have through-openings aligned with one another, which form the through-openings 11 a- cof the bipolar plate 2. When stacking a plurality of bipolar plates of the bipolar plate 2 type, the through-holes 11 a- cform lines that extend through a stack in a stacking direction. Typically, each of the conduits formed by the through openings 11a-c is each in fluid communication with a port in an end plate of the system. By way of the lines formed by the through openings 11 a, for example, coolant can be introduced into the stack or discharged from the stack. The lines formed by the through openings 11 b, 11 c, on the other hand, can be designed to supply electrochemical cells of the fuel cell stack, for example, with fuel and with reaction gas and to discharge the reaction products from the stack. The medium-carrying through-openings 11 a- 11 care formed substantially parallel to the plate plane. In order to seal the through-openings 11 a- cto the interior of the stack 6 and to the environment, the first separator plates usually each have sealing arrangements in the form of sealing beads 12 a- c, which are arranged in each case around the through-openings 11 a- cand which in each case completely surround the through-openings 11 a- c. The second separator plates 2 bhave corresponding sealing beads (not shown) on the rear side of the bipolar plates 2 facing away from the observer of FIG. 9 for sealing the through-openings 11 a- c.In an electrochemically active region 18, the first separator plates have, on their front side facing the observer of FIG. 9, a flow field 17 with structures for guiding a reaction medium along the front side of the separator plate. These structures are provided in FIG. 9 by a plurality of webs and channels running between the webs and bounded by the webs. On the front side of the bipolar plates 2 facing the observer of FIG. 9, the first separator plates additionally each have a distribution or collection region 20. The distribution or collection region 20 comprises structures which are configured to distribute a medium introduced into the distribution or collection region 20 starting from a first of the two passage openings 11 bvia the active region 18 and / or to collect or bundle a medium flowing from the active region 18 towards the second of the passage openings 11 b. The distribution structures of the distribution or collection region 20 are likewise provided in FIG. 9 by webs and channels running between the webs and bounded by the webs.The sealing beads generally have feedthroughs 13 a- 13 c, which are designed here at least partially as local elevations of the bead, of which the feedthroughs 13 afor conducting coolant are designed both on the underside of the upper separator plate and on the upper side of the lower separator plate, while the feedthroughs 13 bin the upper separator plate are designed, for example, for conducting hydrogen and the feedthroughs 13 cin the lower separator plate 2 bare designed, for example, for conducting oxygen.The first separator plates typically also each have a further sealing arrangement in the form of a perimeter bead 12 d, which circulates around the flow field 17 of the active region 18, the distribution or collection region 20 and the through-openings 11 b, 11 cand seals them with respect to the through-opening 11 a, i.e. with respect to the coolant circuit, and with respect to the environment of the system 1. The second separator plates each comprise corresponding perimeter beads. The structures of the active region 18, the distribution structures of the distribution or collecting region 20 and the sealing beads 12 a- dare each formed integrally with the separator plates 2 aand are formed into the separator plates 2 a, for example in an embossing process, deep-drawing process and / or by means of hydroforming. The same applies to the corresponding distribution structures and sealing beads of the second separator plates. Roofs of the beads 12 a- dare coated with the printing material 101 (compare FIGS. 1 to 7 ) which forms an elastomeric sealing element 52 (see FIG. 10 ). This coating can be applied with a screen printing device as described above, in particular according to FIGS. 1 to 7.FIG. 10 schematically shows a section through a section of a plate stack of an electrochemical system. The electrochemical system has a plurality of identically constructed metallic bipolar plates 2 in the manner of the bipolar plate 2 described in FIG. 9, which are arranged in a stack and stacked along a z-direction. The bipolar plates 2 of the stack are clamped between two end plates. It can be a fuel cell stack, for example. Each two adjacent bipolar plates 2 or the mutually facing separator plates of each of these bipolar plates 2 of the stack thus delimit an electrochemical cell 70, which serves, for example, for converting chemical energy into electrical energy. To form the electrochemical cells of the system, a membrane electrode unit (MEA) 10 is arranged in each case between adjacent bipolar plates 2 of the stack. The MEA 10 typically includes at least one membrane 14, e.g., an electrolyte membrane. Further, a gas diffusion layer (GDL) 16 may be disposed on one or both surfaces of the MEA.In FIG. 10, the section was selected such that it runs through two mutually adjacent bipolar plates 2. In this case, FIG. 10 shows a section which visualizes a sealing bead 12 bcirculating a through opening 11 b. For space reasons, the section is shown broken away to both outer sides of the beads 12b surrounding the through-opening 11b. A first sealing arrangement 50' comprises a separator plate 2b, which is designed as a metallic layer 60 and is provided with an elastomeric sealing element 52' on its bead roof 68, i.e. on its convex side. The second sealing arrangement 50" comprises a separator plate 2a which is designed as a metallic layer 60 and which is likewise provided on its bead roof with an elastomeric sealing element 52". The sealing elements 52' and 52" may be made of the same elastomeric material or of different elastomeric materials. The first sealing arrangement 50' faces the second sealing arrangement 50". On their concave sides, the sealing arrangements 50', 50" are each designed without a surface structuring and without an elastomer coating. The first sealing arrangement 50' and the second sealing arrangement 50" abut on both sides of a sealing edge region of the membrane electrode unit, sealing them circumferentially around the port bead 12b.The disclosure further includes the following aspects. 1. screen printing device for printing at least one substrate plate, in particular at least one bipolar plate, with a printing material, wherein the screen printing device comprises a carrier having a carrier surface which is designed to accommodate two substrate plates to be printed next to one another, a first print head arranged above the carrier surface, comprising a first flow squeegee and a first print squeegee, wherein the first print head is designed and designed to print a first substrate plate, a print screen arranged between the carrier surface and the first print head, characterized by a second print head arranged above the carrier surface, comprising a second flow squeegee and a second print squeegee, wherein the second print head is designed and designed to print a second substrate plate. 2. screen printing device according to aspect 1, wherein the first print head is configured to run off a first half of the printing screen and the second print head is configured to run off a second half of the printing screen. 3. screen printing device according to aspect 1 or 2, wherein the first print head is arranged in a starting position above a first outer edge of the carrier surface and the second print head is arranged in a starting position above a second outer edge of the carrier surface opposite the first edge. 4. The screen printing apparatus according to Aspect 1, 2 or 3, wherein the first print head is configured to move toward the second print head in the printing operation, and the second print head is configured to move toward the first print head in the printing operation. 5. screen printing apparatus according to aspect 1 or 2, wherein the first print head is arranged in a starting position above a first outer edge of the carrier surface and the second print head is arranged in a starting position parallel to the first print head and above a central region of the carrier surface running parallel to the first outer edge. 6.The screen printing device according to aspect 5, wherein the first print head and the second print head are configured to move in the same direction during the printing operation, preferably at the same speed. 7. screen printing device according to one of the preceding aspects, wherein at least the first print head is configured and configured to have a first orientation in a first printing operation and to have a second orientation in a subsequent second printing operation, wherein the first orientation is preferably rotated by 90° with respect to the second orientation. 8th Screen printing device according to one of aspects 1 to 6, wherein the printing screen is configured and configured to have a first orientation during flooding of a first printing operation and to have a second orientation during subsequent flooding of the same printing operation, wherein the first orientation is preferably rotated through 90° with respect to the second orientation. 9. screen printing device according to one of the two preceding aspects, comprising a rotating device which is designed and configured to move the printing screen and / or at least one of the print heads, in particular driven by motor, from a first orientation into a second orientation and back. 10. method for printing a substrate plate, in particular a bipolar plate, with a printing material, wherein the method comprises (1) providing a screen printing device according to one of the preceding aspects, (2) inserting two substrate plates onto the carrier surface, (3) inserting the printing screen in a first orientation with respect to the print heads, (4) flooding the printing screen with the printing material, wherein the first flooding squeegee distributes the printing material on a first region of the printing screen and the second flooding squeegee distributes the printing material on a second region of the printing screen, (5) simultaneously printing the two substrate plates, wherein the first squeegee presses the printing material onto the first substrate plate through open meshes of the printing screen and the second squeegee presses the printing material onto the second substrate plate through open meshes of the printing screen. 11 The method according to aspect 10, wherein the first flooding squeegee and the second flooding squeegee move towards one another during flooding of the printing screen. 12th Method according to aspect 10 or 11, wherein the first printing squeegee and the second printing squeegee move towards one another during the printing of the substrate plates. 13.The method according to aspect 10, wherein the first flooding squeegee and the second flooding squeegee move in the same direction spaced apart from one another during flooding of the printing screen. 14. The method according to aspect 10 or 13, wherein the first printing squeegee and the second printing squeegee move in the same direction in a manner spaced apart from one another during printing of the substrate plates. 15. The method according to any one of aspects 10 to 14, wherein after the printing of the two substrate plates the printing screen is rotated into a second orientation, wherein the second orientation is preferably rotated through 90° with respect to the first orientation. 16. Method according to one of aspects 10 to 15, wherein the printing material is a sealing paste, in particular based on fluoropolymer or based on silicone. 17. substrate plate, in particular bipolar plate for an electrochemical system, having a sealing element formed in it, wherein the substrate plate is printed in a method according to one of aspects 10 to 16 and the printed printing material forms a microseal of the sealing element formed in it. 18. substrate plate, in particular according to aspect 17, whereinthe substrate plate is a bipolar plate, the bipolar plate comprises two separator plates formed as metallic layers and connected to one another, each of the separator plates having a multiplicity of webs and depressions, and a membrane electrode unit arranged between the separator plates,wherein the sealing element has at least one one single-sided coating.19. Substrate plate according to aspect 17 or 18, wherein the microseal comprises a foamed material with microspheres, in particular wherein a distribution of the expanded microspheres measured perpendicular to a surface of the metallic layer is inhomogeneous in the microseal.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2021 204 497 [0051, 0058]DE 69816098 T2

[0059]

Claims

Screen printing device (100) for printing at least one substrate plate, in particular at least one bipolar plate (2), with a printing material (101), wherein the screen printing device (100) comprises a carrier (102) having a carrier surface (102a) which is configured to accommodate two substrate plates to be printed next to one another, a first print head (110) arranged above the carrier surface (012a), comprising a first flow squeegee (111) and a first print squeegee (112), wherein the first print head (110) is configured and configured to print a first of the two substrate plates to be printed, a print screen (130) arranged between the carrier surface (102a) and the first print head (110), characterized a second print head (120) arranged above the carrier surface (102a), comprising a second flooding squeegee (121) and a second printing squeegee (122), wherein the second print head (120) is configured and configured to print a second of the two substrate plates to be printed.The screen printing apparatus of claim 1, wherein the first print head (110) is configured to traverse a first half of the print screen (130) and the second print head (120) is configured to traverse a second half of the print screen (130).The screen printing device according to claim 1 or 2, wherein the first print head (110) is arranged in a starting position above a first outer edge of the carrier surface (102a), and the second print head (120) is arranged in a starting position above a second outer edge of the carrier surface (102a) opposite the first edge.The screen printing apparatus according to claim 1, 2 or 3, wherein the first print head (110) is configured to move toward the second print head (120) during the printing operation, and the second print head (120) is configured to move toward the first print head (110) during the printing operation.The screen printing apparatus according to claim 1 or 2, wherein the first print head (110) is arranged in a starting position above a first outer edge of the carrier surface (102a), and the second print head (120) is arranged in a starting position parallel to the first print head (110) and above a central region of the carrier surface (102a) running parallel to the first outer edge.Screen printing device according to claim 5, wherein the first print head (110) and the second print head (120) are configured to move in the same direction during the printing operation, preferably at the same speed.Screen printing device according to one of the preceding claims, wherein at least the first print head (110) is formed and configured to have a first orientation in a first printing operation and to have a second orientation in a subsequent second printing operation, wherein the first orientation is preferably rotated through 90° with respect to the second orientation.Screen printing device according to one of the preceding claims, wherein the printing screen (130) is designed and configured to have a first orientation during flooding of a first printing operation and to have a second orientation during the subsequent flooding of the next printing operation, wherein the first orientation is preferably rotated through 90° with respect to the second orientation.Screen printing device according to one of the two preceding claims, comprising a rotating device which is designed and configured to move the printing screen (130) and / or at least one of the print heads (110, 120), in particular driven by motor, from a first orientation into a second orientation and back.Screen printing device according to one of the preceding claims, wherein the printing material (101) is a sealing paste, in particular based on fluoropolymer or based on silicone.Substrate plate, in particular bipolar plate (2) for an electrochemical system, produced by means of a device according to one of Claims 1 to 9, having a sealing element which is formed in a mold and on which a printing material (101) is printed, the printed printing material (101) forming a microseal of the sealing element which is formed in a mold.

Images