Method for producing a seal on a substrate

Abstract

The invention relates to a method for producing a seal (1) on a substrate (2), in particular on a layer or layer of an electrochemical cell, by means of stencil printing, comprising the steps of a) applying a sealant and / or adhesive (3) to a stencil (4) lying on the substrate (2) to be printed, b) filling at least one recess (5) of the stencil (4) with the sealant and / or adhesive (3) using a squeegee (6) which is pulled over the stencil (4) in a predetermined squeegee direction so that the squeegee (6) presses the sealant and / or adhesive (3) into the at least one recess (5), and c) Releasing the sealant and / or adhesive (3) from the stencil (4). According to the invention, the squeegeeing process in step b) is recorded using at least one camera (7), and the recording is subjected to image analysis to detect defects, in particular trapped air bubbles (8).

Description

[0001] The invention relates to a method for producing a seal on a substrate. The substrate can be, in particular, a layer or sheet of an electrochemical cell, for example, a monopolar or bipolar plate, a separator plate, and / or a membrane-electrode assembly. Furthermore, the method can be used to produce seals on any substrate. State of the art

[0002] Electrochemical cells, such as fuel cells, electrolysis cells, or battery cells, have a multi-layered structure. This structure requires intermediate seals to separate the media supplied to a cell during operation. To form the seals, a sealant and / or adhesive is applied to a layer or ply of the cell. Dispensing or printing processes are particularly used for this purpose.

[0003] The mass production of electrochemical cells requires high processing speed, meaning short cycle times, as well as high process stability. Stencil printing, in particular, meets these requirements. The stencil printing process is essentially divided into the following three subprocesses: 1. Applying the sealant and / or adhesive to a stencil placed on the substrate to be printed, 2. Filling at least one stencil recess with the sealant and / or adhesive in a squeegee process, 3. Releasing the sealant and / or adhesive from the at least one stencil recess by separating the substrate and stencil.

[0004] The stencil height determines the layer height of the applied structure, with typical layer heights ranging from 100 µm to 300 µm. However, for seals in electrochemical cells, layer heights of up to 1500 µm are required to achieve tolerance compensation and allow for maximum freedom in the design of the applied structures. Depending on the specific sealing concept, the applied structures can be very large and / or complex.

[0005] To achieve the layer heights required for electrochemical cell seals during stencil printing, taller stencils must be used. However, this increases the risk of air bubbles being incorporated during the squeegee process for filling the at least one stencil recess with the applied sealant and / or adhesive, which subsequently lead to defects. This is because the volume of the at least one stencil recess to be filled with the sealant and / or adhesive also increases with the stencil height.

[0006] The present invention is concerned with the object of optimising the production of a seal by means of stencil printing in such a way that defects, in particular those caused by air bubbles, are avoided.

[0007] To achieve this object, the method having the features of claim 1 is proposed. Advantageous further developments of the invention can be found in the subclaims. Disclosure of the invention

[0008] A method for producing a seal on a substrate, in particular on a layer or sheet of an electrochemical cell, by means of stencil printing is proposed. The method comprises the following steps: a) Applying a sealant and / or adhesive to a stencil placed on the substrate to be printed, b) filling at least one recess of the stencil with the sealant and / or adhesive using a squeegee, which is pulled over the stencil in a predetermined squeegee direction so that the squeegee presses the sealant and / or adhesive into the at least one recess, and c) Releasing the sealant and / or adhesive from the template.

[0009] According to the invention, the doctor blade process in step b) is recorded with the aid of at least one camera and the recording is subjected to image analysis to detect defects, in particular trapped air bubbles.

[0010] Using the proposed method, defects or printing errors can be detected and identified, allowing early action to be taken to optimize the process. This reduces the number of rejects and saves material and costs.

[0011] Process optimization measures can include changing the stencil design if the camera recordings show that the current design includes critical areas, such as intersecting recesses, recesses with sharp corners and / or other geometries that lead to venting problems during the squeegee process. Since smearing on the underside can also lead to venting problems, one process optimization measure can also be cleaning the stencil. To make cleaning as efficient as possible, the degree of contamination of the stencil can be identified in advance using the camera. The camera does not record the degree of contamination directly, but indirectly by identifying the formation of bubbles in places where bubbles should not form. By comparing the target state with the actual state, areas with a critical degree of contamination can be detected.Another measure for process optimization can be to adapt the rheology of the sealant and / or adhesive so that the formation of air bubbles is prevented.

[0012] Preferably, a translucent or transparent sealant and / or adhesive is used in the method, so that trapped air bubbles are visible through the sealant and / or adhesive. This allows for the detection of defects that are not located on the surface of the sealant and / or adhesive. Furthermore, air bubbles trapped between the sealant and / or adhesive and the stencil and / or the substrate can be detected.

[0013] It is further proposed that in step a), the sealant and / or adhesive is applied to the stencil as a bead, preferably with the aid of a dispensing or dosing unit. The sealant and / or adhesive applied as a bead can be evenly distributed and removed using the squeegee. The dispensing or dosing unit can be used to adjust the amount of sealant and / or adhesive, i.e., the width and height of the bead. The dispensing or dosing unit can be moved using a robot arm or a print head. The bead is preferably applied to an edge region of the stencil and then distributed over the surface of the stencil using the squeegee.

[0014] In a further development of the invention, it is proposed that the bead is applied at an angle to the squeegee, so that a longitudinal axis of the bead and a front surface of the squeegee facing the bead enclose an angle that is preferably 5° to 45°. If the squeegee is then placed against the bead and moved in the squeegee direction, initially only one end region of the squeegee comes into contact with the bead. This leaves an air volume that is open on one side between the squeegee and the bead, through which the air can reliably escape. The oblique orientation of the bead to the squeegee thus counteracts the formation of air bubbles when the squeegee is placed against the bead. The squeegee direction runs perpendicular to the longitudinal axis of the squeegee and not perpendicular to the longitudinal axis of the bead. This is because the squeegee direction and the longitudinal axis of the bead enclose an obtuse angle.

[0015] Preferably, in step b), the squeegee is placed behind the sealant and / or adhesive, preferably the bead, in the squeegee direction, and the at least one camera is arranged in front of the sealant and / or adhesive in the squeegee direction. During the squeegee process, the squeegee moves towards the camera, pushing the sealant and / or adhesive in front of it. Should air bubbles form in the sealant and / or adhesive during the squeegee process, these can be detected with the help of the camera. This applies both to air bubbles that form in the area of ​​the at least one recess in the stencil filled with sealant and / or adhesive, and to air bubbles that form in the excess sealant and / or adhesive that is removed with the help of the squeegee. This is because the at least one recess can be followed by at least one further recess in the same stencil or in another stencil, which must be filled with the excess sealant and / or adhesive.If the camera detects an air bubble trapped in the excess sealant and / or adhesive, the sealant and / or adhesive can be replaced.

[0016] In step b), the squeegeeing process can be recorded as a video and / or as a sequence of images using at least one camera. This means that the recording is either a moving image or a sequence of several individual images. In the latter case, the individual images are taken at the shortest possible intervals to ensure that all defects are captured.

[0017] Furthermore, it is preferred to use a stencil with a stencil height of at least 300 µm, preferably at least 500 µm, further preferably at least 1000 µm, for example 1500 µm. Since the risk of bubble formation increases with the height of the stencil, the advantages of the invention are particularly evident when the stencil is particularly high. Furthermore, printed structures with a corresponding layer height can be produced in this way. The method is therefore particularly suitable for the production of seals on a layer or layer of an electrochemical cell, since corresponding layer heights are required here.

[0018] Furthermore, the sealant and / or adhesive is preferably applied to a monopolar or bipolar plate, a separator plate, and / or a membrane-electrode assembly of the electrochemical cell by means of stencil printing. The seal made from the sealant and / or adhesive then serves to separate the media within the electrochemical cell and / or seal it off from the outside.

[0019] The invention and its advantages are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a) to d) each show a longitudinal section through a substrate to be printed during printing in a stencil printing process, Fig. 2 a top view of a stencil with applied sealant and / or adhesive and attached squeegee as well as a camera for recording the squeegee process, Fig. 3 a side view of the arrangement of the Fig. 2 from the camera's perspective, Fig. 4 another side view of the arrangement of the Fig. 2 from the camera's perspective, Fig. 5 a) and b) each show a plan view of a stencil with applied sealant and / or adhesive and attached squeegee, c) and d) each show the corresponding cross-section, and Fig. 6 a top view of another stencil with applied sealant and / or adhesive and attached squeegee. Detailed description of the drawings

[0020] The Fig. 1a) to 1d) show the conventional process for producing a seal 1 on a substrate 2 by means of stencil printing. For this purpose, a stencil 4 is placed on the substrate 2 and a sealant and / or adhesive 3 is applied to the stencil 4. The sealant and / or adhesive 3 is then pressed into a recess 5 of the stencil 4 using a squeegee 6. The squeegee 6 is moved in a predetermined direction, the squeegee direction (see arrow). The sealant and / or adhesive 3 displaces the air present in the recess 5. With increasing stencil height h, the risk of defects due to air bubbles 8 increases (see Fig. 1 c)). Air bubbles 8 can form in the area of ​​the recess 5 of the template 4 as well as outside in the area of ​​the excess sealant and / or adhesive 3 (see Fig. 1d)). If this is used to fill another recess 5, a defect may occur in the printed seal 1 there.

[0021] Whether air bubbles 8 form depends primarily on the stencil geometry, the rheology of the printing material, and other printing parameters, such as the squeegee speed. These parameters may need to be adjusted. However, it is first necessary to recognize that an adjustment is necessary. The proposed method can be used for this purpose.

[0022] As exemplified in the Fig. 2, in the proposed method, the squeegee process is recorded using a camera 7. For this purpose, the camera 7 is arranged in the squeegee direction (see arrow) in front of the sealant and / or adhesive 3, with the squeegee 6 behind it. During the squeegee process, the squeegee 6 moves towards the camera 7. In doing so, it pushes the sealant and / or adhesive 3 in front of it. The sealant and / or adhesive 3 is at least translucent, i.e., transparent to light, so that the camera 7 is able to detect air bubbles 8 trapped in the sealant and / or adhesive 3. If no air bubbles 8 are formed, the recordings from the camera 7 show the Fig. 3. If air bubbles 8 form, the result is the Fig. 4 example image shown.

[0023] The formation of air bubbles 8 may also occur when the squeegee 6 is applied to the sealant and / or adhesive 3 applied to the stencil 4, since an air-filled gap remains between the squeegee 6 and the sealant and / or adhesive 3 (see Fig. 5a) to 5d)). This is because the sealant and / or adhesive 3 does not form a flat surface (see Fig. 5a) and Fig. 5b)). In addition, the doctor blade 6 is usually applied at an angle, so that an air-filled gusset volume 9 remains between the doctor blade 6 and the bead of sealant and / or adhesive 3 (see Fig. 5c)). If the air is not completely expelled when removing the squeegee 6, an air bubble 8 forms (see Fig. 5d)). This can then be inserted into the next recess 5 of the template 4 using the sealant and / or adhesive 3.

[0024] To ensure that the air between the squeegee and the bead is completely expelled during removal, as shown in the example in the Fig. 6 - the bead of sealant and / or adhesive 3 is applied to the stencil 4 at an angle to the squeegee 6. The squeegee 6 and a longitudinal axis A of the bead are therefore not parallel, but together enclose an angle a. This can be 5 to 45°. If the squeegee 6 is now pulled in the squeegee direction (see arrow) over the stencil 4, initially only one end section of the squeegee 6 comes into contact with the bead (in the Fig. 6 the lower end section). As the doctor blade 6 continues to move, the air volume between the doctor blade 6 and the bead decreases, with the air being drawn out via the open side (in the Fig. 6 at the upper end section of the doctor blade 6) can escape reliably.

Claims

[1] Method for producing a seal (1) on a substrate (2), in particular on a layer or layer of an electrochemical cell, by means of stencil printing, comprising the steps of a) applying a sealant and / or adhesive (3) to a stencil (4) lying on the substrate (2) to be printed, b) filling at least one recess (5) of the stencil (4) with the sealant and / or adhesive (3) using a squeegee (6) which is pulled over the stencil (4) in a predetermined squeegee direction so that the squeegee (6) presses the sealant and / or adhesive (3) into the at least one recess (5), and c) releasing the sealant and / or adhesive (3) from the template (4), characterized by that the doctor blade process in step b) is recorded with the aid of at least one camera (7) and the recording is subjected to image analysis to detect defects, in particular trapped air bubbles (8). [2] Method according to claim 1, characterized by that a translucent or transparent sealant and / or adhesive (3) is used, so that trapped air bubbles (8) are visible through the sealant and / or adhesive (3). [3] Method according to claim 1 or 2, characterized by that in step a) the sealant and / or adhesive (3) is applied as a bead onto the stencil (4), preferably with the aid of a dispensing or dosing unit. [4] Method according to claim 3, characterized by that the bead is applied obliquely to the doctor blade (6) so that a longitudinal axis (A) of the bead and an end face of the doctor blade (6) facing the bead enclose an angle (a) which is preferably 5° to 45°. [5] Method according to one of the preceding claims, characterized bythat in step b) the squeegee (6) is placed in the squeegee direction behind the sealing and / or adhesive (3), preferably the bead, and the at least one camera (7) is arranged in the squeegee direction in front of the sealing and / or adhesive (3). [6] Method according to one of the preceding claims, characterized by that in step b) the doctor blade process is recorded as a video and / or as a sequence of images using the at least one camera (7). [7] Method according to one of the preceding claims, characterized by that a stencil (4) is used with a stencil height (h) which is at least 300 µm, preferably at least 500 µm, further preferably at least 1000 µm, for example 1500 µm. [8] Method according to one of the preceding claims, characterized bythat the sealing and / or adhesive (3) is applied by means of stencil printing to a mono- or bipolar plate, a separator plate and / or a membrane-electrode arrangement of the electrochemical cell.

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