FR2462775A1 - Dry electrolytic capacitor mfr. - with aluminium anode manganese di:oxide electrolyte and silvered graphite cathode - Google Patents

Abstract

Method of mfg. dry electrolytic capacitors with Al anode of the type in which row elementary capacitors are prepd. simultaneously using an Al lamella fixed to a rod and covered with Al2O3, then with a semiconducting oxide such as MnO2, and finally with a conductive cathode layer such as graphite partly covered with a metallising layer is described. Specifically, a metal strip, pref. of tinned Cu is joined transversely across all the bars of the row of capacitors, these are then sepd. from their supporting bar and stacked before locating the anode and cathode connections which are fixed to the tinned copper strip. The method is used in preparing a stack of capacitors with a common anode connection. The problems associated with the fact that Al does not accept Ag metallisation while Al strip does not lend itself well to folding so that the anodes would become brittle, are avoided.

Description

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

 According to the conventional method, an elementary capacitor is developed comprising an aluminum strip integral with a rod; the coverslip is then covered with aluminum oxide, then with a semiconductor oxide such as manganese dioxide.

Finally, at least one conductive cathode layer is deposited on the manganese dioxide, most of the time a first layer of graphite, partially covered with a 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.

 At present, it is desired to produce capacitors of this type which have a large capacity value.

To this end, it is known to stack a plurality of elementary capacitors obtained by the above method, and to connect together, in a parallel arrangement, their anode and cathode connections, respectively.

 The problem is the establishment of the common anodic connection, since practically pure aluminum does not lend itself to prior metallization, of the type of those based on silver. Furthermore, as will be seen below, strip aluminum accepts bending badly, which weakens the anode of the capacitors, and is moreover hardly compatible with the requirements of mass production.

 The main object of the present invention is to improve this situation.

 According to the proposed method, a metallic strip, advantageously of tinned copper, is welded transversely over all of the rods connected to the lamellae or active parts of the capacitors; the rods are then separated from the support strip after which the elementary capacitors are stacked before the cathode and anode connections are put in place, the latter being fixed to the tinned copper tape.

 In a preferred embodiment of the invention, the tinned copper strip is also cut so that there remains, on each elementary capacitor, a portion of the side ot extending the strip; after stacking, the portions thus obtained are deformed to be joined together. This joint connection is advantageously carried out by welding.

 In a variant of the invention, the copper strip is folded, without being cut, to produce the aforementioned stack of elementary capacitors.

 Advantageously, a conductive adhesive is deposited on the conductive cathode layer, before fixing the anode and cathode connections.

 Preferably, a semi-flexible coating is also interposed between the stacked elementary capacitors.

 The invention finally relates to the product obtained by the above process.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, given with reference to the appended drawings, given to illustrate, without limitation, various embodiments of the present invention, and in which
- Figure I illustrates a set of elementary capacitors with rods and strips, the rods of which are integral with a support strip;
- Figure 2 illustrates the fixing of the tinned copper tape on all the rods of the elementary capacitor
- Figure 3 illustrates an elementary capacitor after cutting a portion of the tinned copper tape
- Figure 4 illustrates a stack of several elementary capacitors, the portions of tinned copper tape are combined
- Figure 5 illustrates reconciliation of a conductive adhesive on the cathode side of the stack of Figure 4
- Figure 6 illustrates the interposition of a semi-flexible coating between the various elementary capacitors equipped with the layer of conductive adhesive obtained in Figure 5
- Figure 7 illustrates a capacitor according to Figure 6, equipped with its anodic and cathodic connections, on which it therefore only remains to do the coating operation; and
- Figure 8 illustrates a variant of Figure 4, in which the copper strip is folded instead of being cut, in order to achieve the stack of elementary capacitors.

The manufacture of dry electrolytic capacitors with aluminum anode can be done as follows - stamping of aluminum foil such as 16, to obtain
(figure 1) a series of capacitor elements in the form of
flags, such as 10, with rods, such as 12, integral
a transverse bar 14; future active games
capacitors, such as 18, generally shaped
square or rectangular, will hereinafter be referred to as "coverslips - cleaning and etching of the coverslips, so that they
give some surface porosity.

- formation of one or preferably several layers of oxide
aluminum on the slats, by electrolytic oxidation to
acidic media, followed by treatment with an acidic salt of
phosphate to prepare aluminum oxide for milking
subsequent thermal elements.

- deposition on the lamellar oxide of a semiconductor oxide, such
than manganese dioxide, by impregnation using a
manganese nitrate solution, followed by pyrolysis, these
two operations being preferably repeated.

- deposit of graphite on manganese oxide, then of an argen
ture on graphite, to form the cathode.

- fixing of an anodic connection on the aluminum rod,
as well as a cathodic connection on the external silvering
graphite, separation of the various elementary capacitors
coverings and finishing of the capacitors by molded coating.

 A capacitor is thus obtained which encloses a single strip.

 It is desirable, in order to obtain larger capacities, to manufacture "multiple" capacitors, enclosing several lamellae, the anodic and cathodic connections of which are respectively connected together, in a parallel arrangement.

 If the establishment of a common cathodic connection is relatively simple, it is not the same for the anodic connections, because the practically pure aluminum does not lend itself to a prior metallization, of the type of those based on silver.

 In addition, aluminum strip does not accept bending, which weakens the anode; and such folding makes it difficult to fabricate series of capacitors according to the aforementioned method.

The methods which aim at producing multiple capacitors by folding a series of anodes initially integral do not therefore give complete satisfaction.

 In a practical embodiment of the present invention, the above method is implemented up to the step of fixing the connections (excluded).

 As shown in FIG. 2, a tinned copper ribbon is then welded to the rods such as 12 of the ten or twenty flags carried by the bar 14. Advantageously, the tinned copper ribbon is 1 to 2 mm in width for approximately 0, 05 mm thick, and the welding is electric.

 Then, each flag (rod 12 + strip 18) is separated from the bar 14.

 In a preferred embodiment, the copper strip is cut, so as to leave with each flag a short length 21, on the side where the strip 18 extends. FIG. 3 shows it, in the form of a view in perspective ol there is graphite 26, which constitutes the anode, and its silvering 24, awaiting connection.

 The next step (FIG. 4) consists in stacking several flags according to FIG. 3, so that their portions of ribbon 21 extend on the same side. The free ends of these portions are then slightly deformed so as to join them, after which they are welded, electrically or with a soldering iron.

 On the other side (FIG. 5), which corresponds to the cathode, a conductive adhesive is deposited (arrow 28) which connects the different negative poles (silvering), both electrically and mechanically. The glue can be a suspension of 62% silver in an organic polymer binder.

 This deposited glue is illustrated at 30 in FIG. 6, which is shown diagrammatically to simplify the drawing. In particular, ribbons such as 21 have been shown diagrammatically in the form of simple wires.

 Advantageously, a thin layer of a semi-flexible coating, such as 31, is interposed between the flags, in order to distribute the mechanical stresses over the entire surface of the strips 18. This coating is, for example, a cellulose varnish, or a polyurethane resin, or a silicone resin.

 After that (FIG. 7), an anodic connection 41 is fixed by electrical or iron welding on the strips 21; the cathode connection wire 42 is fixed by cleaning or welding on the lateral metallization 30, or on the conductive adhesive which touches it.

 Finally, the component is placed in a molded case, in a known manner.

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

 FIG. 8 illustrates a variant of the invention and is to be compared with FIG. 4: instead of cutting the copper foil 20 into pieces 21, it is folded so as to stack the strips 18 in superposition. (It is then not necessary to provide for the welding of the foils 21 between them). The rest of the operations are carried out as described with reference to FIGS. 5 to 7.

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

Claims (6)

 1) Process for manufacturing dry electrolytic capacitors with aluminum anode, of the type in which an elementary capacitor is produced comprising an aluminum strip, integral with a rod, the strip being covered with aluminum oxide, then d '' a semiconductor oxide such as manganese dioxide, and finally at least one conductive cathode layer, such as graphite partially covered with a metallization, these operations being carried out at the same time on a series of integral elementary capacitors of a support strip, characterized in that a metal strip is advantageously welded of tinned copper transversely on all of the rods, that these are then separated from the support strip, and that the elementary capacitors are then stacked before the cathode and anode connections are put in place, the latter being fixed to the tinned copper tape.  2) Method according to claim 1, characterized in that the tinned copper strip is also cut, so that there remains on each elementary capacitor a portion of the side where the strip extends, and that after the stacking, these portions thus obtained are deformed to be joined in common.  3) Method according to claim 2, characterized in that the joint connection of said portions of tinned copper tape is produced by welding.  4) Method according to claim 1, characterized in that the tinned copper strip is folded to produce said stack of elementary capacitors.  5) Method according to one of claims 1 to 4, characterized in that a conductive adhesive is deposited on the conductive layer of cathode, before fixing of the anode and cathode connections.  6) Method according to one of claims 1 to 5, characterized in that a semi-flexible coating is interposed between the stacked elementary capacitors.