FR2494891A1 - Dry aluminium anode electrolytic capacitor fabrication process - has single metal pressing which is folded into a multi-leaf structure following chemical treatment - Google Patents

Abstract

The capacitors, opt. of high value, consist of a selectable number of leaf units in a multi-plate construction. The anodes of the capacitor are of rectangular shape with triangular sections linking them to the common bar. They are stamped out of flat aluminium sheet in a single strip of several units. The chemical treatment of the plates to form the electrolyte consists of an initial electrolytic deposition of aluminium oxide followed by deposition of semi-conducting manganese dioxide. This is followed by a coating of graphite with a final metallisation layer which carries the electrical cathode connection. The pressed strip is trimmed longitudinally and transversely before being folded, in concertina fashion, to bring the plates closely adjacent. A deformable insulating coating on the plates allows the even spread of stress during this stage.

Description

 The present invention relates to the manufacture of dry electrolytic capacitors with aluminum anode.

 The conventional method of manufacturing such capacitors consists in developing an elementary capacitor comprising an aluminum strip, this strip then being covered with aluminum dioxide, then with a semiconductor oxide such as manga dioxide, and finally at least one conductive cathode layer, such as graphite partially covered with metallization, for example with silver.

 Industrially, these operations are carried out at the same time on a series of elementary capacitors secured to a support strip. Generally, these strips are connected by a rod to the support bar and take the form of a flag.

 To produce capacitors of this type which have a large capacity value, it is known to stack a plurality of elementary capacitors obtained by the above process, and to connect together, in a parallel arrangement, their anode connections and cathodic, respectively.

 The problem which arises is the establishment of the common anodic connection because practically pure aluminum does not lend itself to a prior metallization, of the type based on that of silver. In addition, the support bar does not accept a folding which is, moreover, hardly compatible with the requirements of mass production.

 The present invention essentially aims to improve this situation.

 According to the essential characteristic of the invention, the strips have a shape symmetrical with respect to their connection to the strip, the strip is cut longitudinally so as to remain a ribbon connecting the strips and this strip is then folded back to stack the elementary capacitors before the installation of cathodic and anodic connection.

The lamellae advantageously have the shape of a rectangle extended on a dimension by US isosceles triangle whose vertex is truncated and constitutes the connection with
the bar.

 It is then possible, after longitudinal cutting of the strip, to cut it transversely to obtain the desired number of elementary capacitors which will then be stacked by folding the ribbon.

 Advantageously, it is possible to deposit, in a manner known per se, a conductive adhesive on the conductive layer of the cathode, before fixing the anode and cathode connections. Preferably, also in a manner known per se, a semi flexible coating between the stacked elementary capacitors.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, made with reference to the appended drawings, given to illustrate without implied limitation a preferred embodiment of the invention, and on which s
. FIG. 1 illustrates a support strip carrying several strips intended to form elementary capacitors
. FIG. 2 illustrates in perspective a strip of FIG. 1, once covered with the above-mentioned different layers;
. Figure 3 is a view similar to that of Figure 1 showing the longitudinal cut of the support strip
. FIG. 4 illustrates a set of four elementary capacitors after longitudinal and transverse cuts of the support strip
. FIG. 5 shows the stacking of the four elementary capacitors of FIG. 4 after folding of the ribbon g and
. FIG. 6 illustrates the affixing of a conductive glue to the cathode side of the stack of FIG. 4 and the interposition of a semiflexible coating between the various elementary capacitors equipped with this layer of conductive glue.

 Reference will now be made to the accompanying drawing to describe the manufacture of the dry electrolytic capacitors with aluminum anode according to the invention.

 First of all, an aluminum foil 10 is stamped in order to obtain, as shown in FIG. 1, a series of identical capacitor elements, such as 12, secured to a transverse support strip 14.

The future active parts of the capacitors have the shape of a rectangle extended on one side by an isosceles triangle, the apex of which is truncated and constitutes the connection 16 with the bar 14. These future active parts will hereinafter be called "strips".

Each slat is then subjected to a series of conventional operations comprising s
- cleaning and chemical attack on the lamellae, so as to give them a certain surface porosity t
- The formation of one or preferably several layers of aluminum oxide on the lamellae, by electrolytic oxidation in an acid medium, followed by a stabilization treatment;
- Despite the oxide on the lamellae of a semiconductor oxide, such as manganese dioxide, by impregnation using a manganese nitrate solution followed by pyrolysis, these two operations being preferably repeated 3
- Despite graphite on manganese oxide and then silvering on graphite, to form the cathode.

 As shown in FIG. 2, each strip 12 constitutes an elementary capacitor comprising a layer of graphite 18, which constitutes the anode, and its silvering 20, awaiting connection.

 According to the invention, the support strip 14 is then cut along along a line 22 along a line 22 shown in dotted lines, so as to leave a ribbon 24 connecting the strips 12 to each other (FIG. 3).

 This strip is then cut transversely to obtain the desired number of elementary capacitors.

FIG. 3 illustrates a set of four elementary capacitors thus obtained.

 The next stamp (FIG. 5) consists in folding the strip 24 so as to stack the strips 12 in superposition, so as to have a parallel arrangement of these elementary capacitors.

 On the side of the strips, opposite their connection with the ribbon, a layer of conductive adhesive 26 is deposited which connects the various negative blades (silvering), both electrically and mechanically (FIG. 6). This adhesive can for example be a suspension containing 62% of silver in an organic polymer binder.

 Advantageously, a thin layer of a semiflexible coating such as 28 is interposed between the elementary capacitors in order to distribute the mechanical stresses over the entire surface of the strips 12. This coating is, for example, a cellulose varnish or a polyurethane resin, or even a silicone resin .

 After this, an anodic connection is fixed by electrical or other welding on the strip 24 and a cathodic connection is fixed by gluing or welding to the metallization layer 26.

 The component thus obtained is placed in a molded case, in a manner known per se.

 Very reliable capacitors are obtained in this way, the capacities of which range between 0.22 and 100 micro-Farada, depending on the dimensions of the elementary strip and the number of stacked strips.

 Of course, the present invention is not limited to the embodiment described and 'extends to any variant in accordance with its spirit.

Claims (3)

 1. Method for manufacturing dry electrolytic capacitors with aluminum anode of the type in which an elementary capacitor is produced comprising an aluminum strip, this strip then being covered with aluminum oxide and then with a semiconductor oxide such as manganese dioxide, and finally at least one conductive cathode layer, such as graphite partially sewn with metallization, these operations being carried out at the same time on a series of elementary capacitors integral with a support strip, characterized by fact that the strips have a symmetrical shape with respect to their connection to the strip, that the strip is cut longitudinally to leave a ribbon connecting the strips and that this ribbon is folded to stack the elementary capacitors before the establishment of cathode connections and anodic.  2. Method according to claim 1, characterized in that the lamellae have the shape of a rectangle extended on one side by an isosceles triangle whose sonnet is truncated and constitutes the connection with the bar.  3. Method according to one of claims 1 and 2, characterized in that, after longitudinal cutting of the strip, it is cut transversely to obtain the desired number of elementary capacitors.