Electrolytic Capacitor Components and Manufacturing Methods

Abstract

The invention relates to methods for manufacturing an energy storage of an electrolytic capacitor, to a method for manufacturing a foil electrode of an aluminum electrolytic capacitor, to a device for manipulating a component of an aluminum electrolytic capacitor, to specifically designed foil electrodes for an aluminum electrolytic capacitor, to a method and a device for analyzing a quality of a section of paper to be used as separator of an electrolytic capacitor, and to a specifically designed electrolytic capacitor.

Claims

1. Method for manufacturing an energy storage of an electrolytic capacitor, comprising the following steps: a) placing a first component of an energy storage of an electrolytic capacitor onto a transfer area; b) optical measuring the first component to determine its actual position; c) determine a deviation between the actual position and a desired position; d) gripping the first component with a gripper; e) adjusting the actual position of the first component if a deviation between the actual position and the desired position has been determined; f) placing the first component onto a self-adhesive film at a stacking area; g) repeating steps a) to e) with a further component of an energy storage of an electrolytic capacitor and placing the further component onto the first component to form a stack; h) fixing the further component on the stack; i) repeating steps a) to e) with a further component of an energy storage of an electrolytic capacitor and placing the further component onto a topmost component of the stack to enlarge the stack; j) fixing the further component on the stack; k) repeating steps i) and j) a plurality of times yielding a completed stack; l) fixing the completed stack after the last further component has been placed on the completed stack by wrapping the self-adhesive film around at least a section of the completed stack.

2. Method according to claim 1, wherein steps a) to l) are automated executed.

3. Device for manufacturing a stacked capacitor, particularly configured to execute a method according to claim 1, the device comprising: a spring-loaded stacking area, a receptacle configured to receive the spring-loaded area, one or more movable fixation devices being configured to releasably fix the stack of capacitor components in the receptacle, wherein the one or more fixation are movable between an open position and a locked position, a pick-and-place device being configured to pick a capacitor component and place the capacitor component on the spring-loaded stacking area, wherein particularly the pick-and-place device comprise one or more one or more recesses configured to receive the one or more movable fixation devices.

4. Method for manufacturing an energy storage of an electrolytic capacitor, comprising the following steps: a) shaping a first component of an energy storage of an electrolytic capacitor to obtain a desired geometry; b) providing the first component with a marking element; c) optical measuring the marking element of the first component to determine an actual position of the first component; d) determine a deviation between the actual position and a desired position; e) gripping the first component with a gripper; f) adjusting the actual position of the first component if a deviation between the actual position and the desired position has been determined; g) placing the first component onto a stacking area; h) repeating steps a) to f) with a further component of an energy storage of an electrolytic capacitor and placing the further component onto the first component to form a stack; i) repeating steps a) to f) with a further component of an energy storage of an electrolytic capacitor and placing the further component onto a topmost component of the stack to enlarge the stack; j) repeating step i) a plurality of times yielding a completed stack; k) fixing the completed stack after the last further component has been placed on the stack.

5. Method according to claim 4, wherein the adjusted actual position of the first or further component is double-checked by optically measuring the respective marking element after having placed the first component onto the stacking area or after having placed the further component onto the topmost component of the stack.

6. Method for manufacturing a foil electrode of an aluminum electrolytic capacitor, comprising the following steps: a) providing an optionally coated aluminum foil; b) laser-cutting the aluminum foil to obtain a foil electrode in a desired shape.

7. Method according to claim 6, wherein the laser-cutting is done with an ultrashort pulse laser having a pulse duration in the order of 10.sup.−11 seconds or less.

8. Device for manipulating a component, particularly an electrode foil, of an aluminum electrolytic capacitor, comprising a first panel and a second panel, wherein the first panel and the second panel are movable relative to each other around a pivoting axis (A) from a first position to a second position and vice versa, in the first position, a front side of the first panel and a front side of the second panel are arranged beside each other in the same level and face the same direction, in the second position, the front side of the first panel and the front side of the second panel are arranged directly above each other, face each other and are able to contact each other, the front side of the first panel comprises a plurality of first openings through which a vacuum can be applied to a surface of the front side of the first panel, and the front side of the second panel comprises a plurality of second openings through which a vacuum can be applied to a surface of the front side of the second panel.

9. Method for manufacturing a foil electrode of an aluminum electrolytic capacitor with a device according to claim 8, the method comprising the following steps: a) placing an optionally coated aluminum foil on a front side of a first panel of the device so that a front side of the aluminum foil faces upwards; b) applying a vacuum to the aluminum foil through openings in the front side of the first panel to keep the aluminum foil in place on the first panel; c) treating the front side of the aluminum foil; d) pivoting the first panel around a pivoting axis (A) so that the front side of the first panel is placed directly above a front side of second panel of the device, wherein the front side of the aluminum foil contacts the front side of the second panel; e) releasing the vacuum applied to the aluminum foil through the openings in the front side of the first panel and applying a vacuum to the aluminum foil through openings in the front side of the second panel so that the aluminum foil is transferred to the second panel and is kept in place on the second panel, wherein a backside of the aluminum foil faces upwards; f) laser-cutting the aluminum foil by applying a laser beam to the backside of the aluminum foil to obtain a foil electrode in a desired shape; g) releasing the vacuum applied to the aluminum foil through the openings in the front side of the second panel and removing the foil electrode from the second panel.

10. Foil electrode for an aluminum electrolytic capacitor, comprising an aluminum foil and a single-layer capacitance-increasing coating applied to at least one of a front side and a backside of the aluminum foil, wherein the single-layer capacitance-increasing coating comprises titanium oxide and titanium nitride, and optionally titanium carbide.

11. Foil electrode for an aluminum electrolytic capacitor, comprising an aluminum foil and a capacitance-increasing coating applied to at least one of a front side and a backside of the aluminum foil, wherein the foil electrode comprises at least one optically detectable marking element formed within the capacitance-increasing coating by a partial removal of the capacitance-increasing coating in a patterned manner.

12. Foil electrode according to claim 11, wherein the capacitance-increasing coating is applied to both the front side and the backside of the aluminum foil, wherein the foil electrode comprises a first marking element on the front side and a second marking element on the backside, wherein the first marking element is a unique identifier of the film electrode and the second marking element enables capturing a position of the foil electrode during a manufacturing process of an electrolytic capacitor.

13. Method for analyzing a quality of a section of paper for using the section of paper as separator of an electrolytic capacitor, the method comprising the following steps: a) unrolling a paper strip from a paper feeding roll and rolling-up the paper strip onto a paper winding roll; b) guiding a section of the paper strip after the unrolling and before the rolling-up between two metallic rollers, wherein a test voltage is applied between the two metallic rollers and wherein each of the metallic rollers contacts the section of the paper strip; c) continuously measuring the test voltage and/or a resulting test current between the two metallic rollers; d) guiding the section of the paper strip after the measuring and before the rolling-up through a tool; e) producing a paper separator from the section of the paper strip only if the test voltage did not fall below a predetermined test voltage threshold and/or if the resulting test current did not exceed a predetermined test current threshold when the section of the paper strip has been positioned between the two metallic rollers.

14. Device for analyzing a quality of a section of paper for using the section of paper as separator of an electrolytic capacitor, comprising: a paper feeding roll carrying a paper strip; a paper winding roll for receiving the paper strip after having unrolled the paper strip from the paper feeding roll; two metallic rollers, wherein each of the metallic rollers serves for contacting a section of the paper strip when the section of the paper strip is guided between the two metallic rollers; a power supply to apply a test voltage to the two metallic rollers; a device for continuously measuring the test voltage and/or a resulting test current between the two metallic rollers; a tool for producing a paper separator from the paper strip, wherein the tool is located downstream the two metallic rollers; a controlling device for allowing the tool to cut a paper separator from the section of the paper strip only if the test voltage did not fall below a predetermined test voltage threshold and/or if the resulting test current did not exceed a predetermined test current threshold, when the section of the paper strip has been positioned between the two metallic rollers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0116] Further details of aspects of the present invention will be explained with respect to embodiments and accompanying Figures. In the Figures:

[0117] FIG. 1 shows a schematic sketch of a device for manufacturing an energy storage of an electrolytic capacitor;

[0118] FIG. 2 shows an embodiment of a marking element;

[0119] FIG. 3A shows the results of a position determination of the marking element of cathodes with an optical measuring device;

[0120] FIG. 3B shows the results of a position determination of cathodes after having placed them on a stack;

[0121] FIG. 4A shows an X-ray image of a therapeutic aluminum electrolytic capacitor;

[0122] FIG. 4B shows an enlarged view of a section of the therapeutic aluminum electrolytic capacitor of FIG. 4A;

[0123] FIG. 5A shows a scanning electron microscopy image of a punching edge of a thin film;

[0124] FIG. 5B shows a scanning electron microscopy image of a cut edge of a thin film;

[0125] FIG. 5C shows a scanning electron microscopy image of a laser cut edge of a thin film;

[0126] FIG. 6A shows a foil manipulating device in a first position;

[0127] FIG. 6B shows the foil manipulating device of FIG. 6A with an applied coated aluminum foil to be treated;

[0128] FIG. 6C shows the foil manipulating device of FIG. 6A in a transition position;

[0129] FIG. 6D shows the foil manipulating device of FIG. 6A with two laser cut electrodes;

[0130] FIG. 7A shows a front side of a laser cut aluminum cathode;

[0131] FIG. 7B shows a backside of the cathode of FIG. 7A;

[0132] FIG. 7C shows a stack of a plurality of cathodes, anodes and separators;

[0133] FIG. 7D shows the stack of cathodes, anodes and separators and cathodes of FIG. 7C with a shortened connection portion;

[0134] FIG. 8A shows a microscopy image of a metallic particle within a paper;

[0135] FIG. 8B shows a scanning electron microscopy image of a metallic particle within a paper;

[0136] FIG. 9A shows a schematic depiction of a paper testing device;

[0137] FIG. 9B shows a detail of the paper testing device of FIG. 9A;

[0138] FIG. 10A-L shows a device and a mode of operation for manufacturing an energy storage of an electrolytic capacitor according to the present invention; and

[0139] FIG. 11A-C shows cross section of a part of the device of FIG. 10.

DETAILED DESCRIPTION

[0140] FIG. 1 shows a schematic depiction of a device that can be used for manufacturing an energy storage of an electrolytic capacitor. A first component 1, a second component 2, and a third component 3 can be fed by means of a first pick-and-place device 4 to a transfer area 5. The actual position of that component chosen from the first component 1, the second component 2 and the third component 3 that has been transferred to the transfer area is then optically measured by an optical measurement system 6. In doing so, a deviation between the actual position of the respective component on the transfer area 5 and a desired position can be determined. Afterwards, the respective component is gripped by a second pick-and-place device 7 serving as gripper and adjusting the actual position of the component to the desired position if a deviation has been determined. The second pick-and-place device 7 then transfers the component from the transfer area 5 to a stacking area 8.

[0141] This process is repeated for a plurality of times so as to place a plurality of first components 1, second components 2 and third components 3 in a desired sequence one above each other onto the stacking area 8.

[0142] The first components 1 can be, e.g., anodes. The second components 2 can be, e.g., separators. The third components 3 can be, e.g., cathodes. By choosing a desired number of first components 1, second components 2 and third components 3 and by placing them in any desired sequence on the stacking area 8, an energy storage of an electrolytic capacitor may be produced.

[0143] The optical measurement system 6 serves for an exact positioning of the respective component on the piling area 8.

[0144] To avoid an undesired dislocation of any of the components placed onto the already formed stack on the stacking area 8, the individual components are fixed on the already formed stack after having them placed on the topmost layer of the already formed stack. If the stack formed on the stacked area 8 is completed, the completed stack is fixed so that it can be easily transferred to be manipulated in a further process step without risking a dislocation of one or more of the stacked components.

[0145] Thus, the precise alignment of the individual components and the precise piling of the individual components serve for an increase of the energy density of the energy storage.

[0146] FIGS. 10A to 10 illustrate the above described stacking of components in more detail.

[0147] In FIG. 10A, a device for stacking of the capacitor components is shown. The device has a spring-loaded stacking area and a receptable 60 being configured to receive the spring-loaded stacking area 8. The stacking area 8 is elastically movable along direction z. The device further comprises the above mentioned second pick-and-place device 7, which is at least in parts movable along direction z, particularly for placing a picked component on the stacking area 8 in the receptable 60, and along a first plane being perpendicular to direction z, for conveying the picked component 1, 2, 3 between the transfer area 5 and the stacking area 8. The device further comprises six fixations device 61, 62. Each of the fixations devices comprises a tongue 61 being movable between an open position, in which the tongue 61 does not extend into the stacking area 8, and a locked position, in which the tongue 61 at least partly extends into the stacking area 8, and a rail 62, on which the tongue 61 is movable mounted.

[0148] For building the stack, a self-adhesive film 63 is arranged or placed on top of the stacking area 8, wherein the self-adhesive film forms the most bottom layer on the stacking area 8 and is held by suction. The self-adhesive film comprises a plurality of tabs of flaps that are configured to wrapped around the completed stack 64 in order to fix the completed stack 64. The tongues 61 of the fixation devices are in the open position and do not extend into the stacking area 8 (FIG. 10A), particularly in order avoid an adhesion between the tongues 61 and the self-adhesive film 63.

[0149] Next, a first component 1 is placed by the second pick-and-place device 7 on the stacking area 8 and the self-adhesive film 63, respectively FIG. 10B). Here, the first component is held by suction as well, and the tongue 61 remain in the open position, particularly again in order to avoid an adhesion between the self-adhesion film and the tongue in case of the first component is very thin (e.g., 20 μm). In case of thicker first components, the tongues 62 may be move in the locked position in this stage in order to fix the growing stack in the receptacle 60.

[0150] Now the repeating stacking process starts. The stack of capacitor components 64 is fixed between the spring-loaded stacking area 8 and the tongues 61 in the locked position, wherein the stacking area 8 pushes along direction z against the tongues 61 (FIG. 10C).

[0151] Next, the second pick-and-place device 7 places a gripped further component 2 on the tongues 61 in the locked position (FIG. 10D). Here, the second pick-and-place device 7 comprises several recesses 7a to receive the tongues 61 in the locked position in order to avoid physical contact between the tongues 61 and the second pick-and-place device 7. Since the tongues 61 are very thin, the further component 2 can be placed on the tongues 61 without being damaged while nevertheless fixing the stack 64 (FIG. 10E).

[0152] Next, the tongues 61 move from the locked position to the open position, wherein the stack 64 is fixed between the spring-loaded area 8 and the second pick-and-place device 7 (FIG. 10 F). Then, the second pick-and-place device 7 conveys or pushes down the stack 64 below the level of the tongues 61 (FIG. 10 G).

[0153] Next, the tongues 61 move back form the open position to the locked position and engage in the recesses of the second pick-and-place device 7 (FIG. 10H). Then, the second pick-and-place device 7 moves away from the spring-load stacking area, which then urges against the tongues, thereby fixing the stack 64 between the spring-loaded stacking 8 and the tongues 61 (FIG. 10 I).

[0154] After completing the stack 61, the stack is pushed deep down by the second pick-and-place device 7, wherein the receptacle 60 and the spring-loaded stacking area 8 move against each other (FIGS. 10J-L). Thereby, the tabs of flaps of the self-adhesive film 63 are flipped by the edge of the receptacle 60 during the downward movement of the spring-loaded stacking area 8, and thus are wrapped around the completed stack 64.

[0155] FIGS. 11A to C illustrate the above process step in more detail. In FIG. 11A, the starting situation is shown, in which the self-adhesive film 63 is placed on the spring-loaded stacking area. Here, the tabs or flaps 63a of the self-adhesive film 63 rest on a circumferential edge of the receptacle 60, until stacking of the capacitor components is completed (FIG. 11B).

[0156] For final fixation of the completed stack 64 with the self-adhesive film 63, the stack 64 together with the spring-loaded stacking area 8 is pushed down (along direction z) by the second pick-and-place device 7), and tabs or flaps 63a of the self-adhesive film 63 are flipped upwards by the circumferential edge of the receptacle 60 and wrapped around the completed stack 64 (FIG. 11C).

[0157] FIG. 2 shows a capacitor cathode 3 bearing a marker 9 in its lower right corner. In this and in all following Figures similar elements will be marked with the same numeral reference. The marker 9 serves as marking element and has a circular shape. It has been applied into a coating of the cathode 3 by laser ablating a part of the coating. In doing so, a patterned shape, namely the circular shape of the marker 9, has been introduced into the coating of the cathode 3.

[0158] The cathode 3 carries two such markers 9 in two different positions. The position and rotation of the cathode 3 can be easily determined by optically capturing the two markers 9.

[0159] FIG. 3A shows the results of a position determination of such markers of cathodes. For this purpose, an optical measurement device has been used.

[0160] A first group 10 of measuring points is located in a narrow spatial distribution. To test whether a dislocation of a few micrometers can be detected by this method, the marking has been displaced from its original position by +20 μm in x and y direction. A second group 11 of measuring points was obtained that can be clearly distinguished from the first group 10 of measuring points. Thus, a dislocation of +20 μm is easily detectable. Furthermore, the marking has been dislocated by −10 μm in x and y direction. Also here, a clearly distinguishable third group 12 could be detected by checking the position of the marking element. Thus, even deviations of as small as 10 μm of the marker can be detected by the applied optical measuring method.

[0161] The marking element was also used to determine the position of the cathodes after having placed them on a stack. The results are depicted in FIG. 3B. Three clearly distinguishable populations (highlighted with frames) were detectable. The first population 10 corresponds to cathodes bearing the marker in its original position. The second population 11 corresponds to cathodes bearing the marking element dislocated by +20 μm in x and y direction. The third population 12 corresponds to cathodes bearing the marking element dislocated by −10 μm.

[0162] The following measuring results were obtained:

[0163] First population 10 (original position of the marking element):

TABLE-US-00001 Average value 923149.26 Standard deviation 4.3943154 Standard error of the average value 1.0081251 95% confidence interval above the average value 923151.38 95% confidence interval below the average value 923147.15 Number of samples 19

[0164] Second population 11 (+20 μm dislocation of the marking element):

TABLE-US-00002 Average value 923169.47 Standard deviation 2.8268651 Standard error of the average value 0.6168725 95% confidence interval above the average value 923170.76 95% confidence interval below the average value 923168.19 Number of samples 21

[0165] Third population 12 (−10 μm dislocation of the marking elements):

TABLE-US-00003 Average value 923138.08 Standard deviation 4.3028442 Standard error of the average value 0.9173695 95% confidence interval above the average value 923139.98 95% confidence interval below the average value 923136.17 Number of samples 22

[0166] Thus, the variance is smaller than 5 μm, i.e., the position of the marking element and thus the exact position of the cathodes can be optically determined in a very precise manner.

[0167] FIG. 4A shows an X-ray image of a therapeutic aluminum electrolytic capacitor 13. A plurality of stacked anodes 14 and intermediately arranged cathodes 15 can be seen. For sake of clarity, only an individual anode 14 and only a single cathode 15 is marked with the respective numeral reference.

[0168] Each anode 14 is made up of a plurality of individual anode films 140, as can be seen from the enlarged view of FIG. 4B. Furthermore, a separator 16 is placed between each anode 14 and the adjacent cathode 15.

[0169] FIGS. 5A and 5 B show the drawbacks of prior art techniques for shaping a thin foil to produce an electrode. When punching a foil 17, a burr 18 results that is clearly visible against a background 19 in a scanning electron microscopy image, as illustrated in FIG. 5A. The same holds true in case of cutting a thin foil with a pair of scissors, as illustrated in the microscopy image of FIG. 5B.

[0170] In contrast, laser cutting results in a burr-free cutting edge of a thin foil 17, as illustrated in FIG. 5C. For carrying out such laser cutting, the desired contour is repeatedly followed with a laser beam of a cutting laser. For a 20 μm thin aluminum foil coated with a capacitance-increasing coating made of titanium oxide and titanium carbide, such cutting requires 6 seconds. The burr-free cutting edge of the thin foil 17 allows a closer stacking of individual thin foil layers above each other.

[0171] FIG. 6A shows a foil manipulating device 20 having a first panel 21 and a second panel 22. The first panel 21 can be pivoted around a pivoting axis A so as to be placed directly above the second panel 22. The first panel 21 comprises a plurality of small openings 23 through which a vacuum can be applied to a surface of the first panel 21. Similar openings 24 are also present in the second panel 22 to apply a vacuum to a surface of the second panel 22.

[0172] FIG. 6B shows the same foil manipulating device 20 as FIG. 6A in the same position. However, here, a coated foil 17 has been placed onto the front side of the first panel 22. Furthermore, a suction force is applied by a vacuum through the openings 23 within the first panel 21 (cf. FIG. 6A). Due to the suction force, the foil 17 is kept flatly in place on the first panel 21. The front side of the foil 17 which faces upwards in the depiction of FIG. 6B can then be manipulated as desired. To give an example, the coating of the foil 17 can be partially abraded by laser abrading. In doing so, a pattern can be introduced into the coating of the foil 17.

[0173] As shown in FIG. 6C, the first panel 21 can be pivoted around the pivoting axis A by moving a handle 25. In this context, FIG. 6C shows an intermediate position in which the first panel 21 is about to be moved onto the second panel 22. By such a movement, it is possible to turn the foil 17 (cf. FIG. 6B) upside down so that its backside faces upwards. Then, the foil 17 is positioned on the front side of the second panel 22. For illustrating purposes, the foil 17 is not shown in FIG. 6C.

[0174] FIG. 6D shows the final result of a process for manufacturing electrodes for an electrolytic capacitor. Individual cathodes 3 have been laser cut out of the foil 17 (cf. FIG. 6B). In the illustration of FIG. 6D, only two of the cut-out cathodes 3 are displayed. The surface of the second panel 22 can have virtually any desired shape so that differently shaped cathodes 3 can be produced. The foil 17 from which the cathodes 3 are cut is kept in place on the surface of the second panel 22 by applying a suction through the corresponding openings 24 (cf. FIG. 6A).

[0175] The device 20 shown in FIGS. 6A to 6D is particularly appropriate to first introduce a marking on the front side of the foil 17, to then turn the foil 17 upside down by pivoting the first panel 21 of the device 20 around the pivoting axis A, to then apply further markings onto a backside of the foil 17 and to finally cut out individual cathodes 3 from the foil 17.

[0176] FIG. 7A shows a front side of a cathode 3 that has been produced with a device as shown in FIGS. 6A to 6D by laser cutting. The front side of the cathode 3 comprises a black capacitance-increasing coating and a matrix code 30 serving as unique identifier. This matrix code 30 has been introduced into the coating of the cathode 3 by partially ablating the coating in a patterned manner. The removed part of the coating (white parts) and the remaining parts of the coating (black parts) from together the matrix code 30.

[0177] Furthermore, the capacitance-increasing coating is also removed from a connecting portion 31 of the cathode 3. This removal has also been done by laser ablation. Removal of the capacitance-increasing coating in the area of the connecting portion 31 facilitates subsequent cold welding of the connecting portions of individual cathodes.

[0178] FIG. 7B shows the backside of the cathode 3 of FIG. 7A. Here, two circular markings 9 can be seen that allow for precise positioning of the cathode 3 during a stacking process upon manufacturing an energy storage of an electrolytic capacitor. Reference is made in this circumstance to the explanations given with respect to FIG. 2.

[0179] FIG. 7C shows a stack were the outer cathode 3 is provided a data matrix code 30 for individually identifying the respective capacitor stack. The connective portions 31 still have their original length.

[0180] In the depiction of FIG. 7D, the connective portions 31 have been shortened and mechanical welded with a connecting sheet.

[0181] FIG. 8A shows a microscopy image of a metallic particle 40 within a sheet of paper 41. The particle 40 shown in FIG. 8A is pushed into the paper. However, there exist also metallic particles that are enclosed by paper fibers and are thus embedded into the paper.

[0182] Since the paper 41 will be wetted with electrolyte solution when used as separator paper in an electrolytic capacitor, it will swell. Therefore, the position of the metallic particle 40 is not fixed within the paper 41. Rather, there is a risk that the particle 40 moves within the paper 41 and thus finds its way through the paper 41 during the lifetime of an electrolytic capacitor. Thus, the electrical properties of such an electrolytic capacitor can change over its lifetime so that an undesired short-circuit can occur at any time after having used the electrolytic capacitor for the first time.

[0183] FIG. 8B shows another scanning electron microscopy image of a metallic particle 40 pushed into paper 41 in a larger magnification.

[0184] FIG. 9A shows a schematic depiction of device for testing the electrical properties of paper to be used as separator paper for an electrolytic capacitor. This device comprises a paper feeding roll 50 and a paper winding roll 51. A strip of paper 52 is unrolled from the paper feeding roll 50 and rolled up onto the paper winding roll 51. For better illustration purposes only, only a short portion of the paper strip 52 is depicted in FIG. 9A. It should be understood that the paper strip 52 is a continuous paper strip that is not interrupted between the paper feeding roll 50 and the paper winding roll 51.

[0185] When the paper strip 52 is unrolled from the paper feeding roll 50, it is first guided through an impedance testing appliance 53. In this impedance testing appliance 53, the impedance of the paper strip 52 is tested. In doing so, it is possible to detect an inclusion of metallic particles within the paper strip 52. Afterwards, the paper strip 52 is guided towards a die cutter 54. This die cutter 54 serves for die-cutting a paper separator 55 out of the paper strip 52.

[0186] However, the die-cutting of the paper separator 55 is only done if the impedance of the section of the paper strip 52, from which the paper separator 55 is to be punched out was above a predetermined threshold.

[0187] The functioning of the impedance measuring appliance 53 will be explained with reference to FIG. 9B. For this purpose, FIG. 9B shows an enlarged view onto the impedance measuring appliance 53 from a backside of the device shown in FIG. 9A. Here, an upper metallic roller 56 and a lower metallic roller 57 can be seen through which the paper strip 52 is fed. A test voltage of 360 V for a 10 μm thin paper is applied between the upper metallic roller 56 and the lower metallic roller 57. If there is a sudden decrease of voltage (or, likewise, a sudden increase in the resulting test current), this is a clear indication for the presence of a metallic particle within the paper strip 52. Then, this section of the paper strip 52 will not be used for die-cutting a paper separator 55 from it. Rather, this section of the paper will pass the die cutter 54 untreated and will be simply wound up by the paper winding roll 51.

[0188] If, however, the test voltage did not decrease below a predetermined threshold (or, alternatively, if the test current did not exceed a predetermined threshold), the tested section of the paper strip 52 is considered to be appropriate for die-cutting a paper separator 55 out of it. Thus, the die cutter 54 will then punch out the paper separator 55.

[0189] The test voltage is applied to the upper metallic roller 56 by means of a sliding contact 58. The lower metallic role 57 is set to ground.

[0190] The other rollers depicted in FIG. 9B serve for giving a sufficiently high tension to the paper strip 52 when being fed through the device.

[0191] The device for testing the electric properties of the paper strip 52 enhances the overall quality of the die-cut paper separators 55 and thus serves for less waste of electrolytic capacitors being produced with the help of the tested paper separators 55.

[0192] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points.