GB1558945A - Flat wound electrolytic capacitors - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO FLAT, WOUND ELECTROLYTIC CAPACITORS (71) We, SIEMENS AKTIENGESELLSCHAFT, a German Company, of Berlin and Munich, German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to flat, wound electrolytic capacitors, comprising wound aluminium foils with paper spacers between the winding turns, which paper spacers are saturated with an operating electrolyte, the aluminium foil serving as the anode having the dielectric oxide layer on the faces thereof.

A disadvantage of flat, wound electrolytic capacitors is that they tend to become greatly deformed as a result of internal gas pressure produced during operation. It has therefore not hitherto been possible to exploit fully the advantages pertaining to a flat construction, since this bulging of the capacitor in use had to be taken into account from the outset. For this reason, it has not previously been possible to produce extremely flat capacitors.

Capacitors of the kind in question are usually installed in aluminium housings, the dimensions of which have to take into account the changes occurring in the capacitor in use. Extremely flat capacitors have not been constructed from the outset, since the change in thickness occurring therein in use would have reached at least double the original value of the thickness.

It is an object of the present invention to provide a flat, wound electrolytic capacitor in which the disadvantages referred to above are avoided or at least reduced.

According to the invention, there is provided a flat, wound electrolytic capacitor comprising a flat winding of aluminium foils, the adjacent turns of which are separated by paper spacers saturated with an operating electrolyte and the anode foil having a dielectric oxide layer thereon, and a casing made at least in part of a synthetic resin which has a high permeability towards hydrogen and a low permeability towards water vapour. The casing is preferably made from a foil of polypropylene or polyethylene which may be completely or partially metallised.

An additional outer casing made of a metal foil, or a compound metal-synthetic resin foil, may additionally be provided. In the latter case, a synthetic resin foil, may additionally be provided. In the latter case, a synthetic resin foil and an overall metal foil may be laminated together, or a synthetic resin foil may be laminated to a metal foil having apertures therein, or to a plurality of separate metal segments, so that the metal does not cover the whole area of the additional casing. In all cases, the arrangement must be such that diffusion of hydrogen from the winding to the outer atmosphere is not precluded.

The advantages of the construction of the invention are that the hydrogen which is formed during the operation of the capacitor is discharged to the ambient environment without any build-up of pressure occurring within the capacitor housing, whilst on the other hand, drying out of the capacitor due to too high a diffusion of water vapour therefrom, is prevented.

The invention will now be further described with reference to the drawing, in which: Figures 1 and 2 are respectively similar schematic perspective views, with portions cut away, of the embodiments of the invention.

Referring to Figure 1, the flat, wound capacitor illustrated therein has a wound body 5 formed by winding aluminium anode and cathode foils, with paper spacers between adjacent turns of foil, about a former 4.

The former 4 is left in place with the winding to serve as a mechanical support for it. The paper spacers are saturated with the operat ing electrolyte of the capacitor. The anode foil is provided with a dielectric oxide layer.

The winding 5 is encased within a synthetic resin foil 1 which is welded together at its free edge zones 3 to form a closed bag. The foil 1 consists of a material which is permeable to hydrogen but only difficultly permeable to water vapour. The capacitor is also provided with an additional casing 2 composed of metal-synthetic resin foils 2 which are welded to the foil 1 on each flat face of the capacitor at a peripheral weld zone 11.

The diffusion properties of the capacitor can be adjusted by varying the size of the foil 2. A strip 6 forming part of one of the elec trode foils is connected to an outer terminal 12 via a rivet 7 extending through the casing 1 and carrying an elastic ring 8 and a washer 9 located outside the casing. The other elec trode foil is connected in the same way to an outer terminal 10.

Figure 2 illustrates a second embodiment of the invention in which the casing consists of an aluminium-synthetic resin compound foil 2 which entirely encases the flat winding 5 apart from the region of the outer terminals 10 and 12. The foil 1, which in this embodi ment is provided only in the region of the terminals 10 and 12, is welded to the foil 2 in a weld zone 11. In this embodiment, the dif fusion properties are determined by the size of the foil 1.

As an alternative to the constructions of the embodiments illustrated in the drawing, the foil 1 can be entirely or partially metal- lised, in which case diffusion can be adjusted by varying the area and/or thickness of the metallisation.

When a metal-synthetic resin compound foil is used, this can serve as a lead-through if the casing consists of two separate parts or if the metal foil is in the form of separate seg ments, the synthetic resin foil being cut away below respective parts of the metal foil, so that the electrode foils can be connected through the windows so formed in the synth etic resin foil to the respective parts of the metal foil.

The outer terminals can consist of wires, soldering lugs, or connecting plugs. When a compound foil is used as a lead-through, contacting can also be effected by pressure exerted by spring elements.

A particularly important field of use of capacitors in accordance with the invention is as electrolytic photographic flash capacitors, in particular in flash devices incorporated in cameras.

WHAT WE CLAIM IS: 1. A flat, wound electrolytic capacitor comprising a flat winding of aluminium foils, the adajcent turns of which are separated by paper spacers saturated with an operating electrolyte and the anode foil having a dielectric oxide layer thereon, and a casing made at least in part of a synthetic resin which has a high permeability towards hydrogen and a low permeability towards water vapour.

2. A capacitor as claimed in Claim 1, wherein said casing consists of a foil of poly- propylene or polyethylene.

3. A capacitor as claimed in Claim 1 or Claim 2, wherein said casing is at least partially metallised, thickness of the metallisation in the case where the casing is completely metallised being insufficient to preclude the diffusion of hydrogen therethrough.

4. A capacitor as claimed in Claim 1 or Claim 2, wherein the capacitor is additionally encased in a metal foil, or a metal-synthetic resin compound foil, in such manner that diffusion of hydrogen from said winding to the ambient atmosphere is not precluded.

5. A capacitor as claimed in Claim 4, wherein said additional casing consists of a partially laminated metal-synthetic resin compound foil.

6. A flat, wound electrolytic capacitor substantially as hereinbefore described with reference to and as illustrated in Figure 1, and Figure 2, of the drawing.

7. A photographic flash device including a flat, wound electrolytic capacitor as claimed in any one of Claims 1 to 6.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. paper spacers are saturated with the operat ing electrolyte of the capacitor. The anode foil is provided with a dielectric oxide layer. The winding 5 is encased within a synthetic resin foil 1 which is welded together at its free edge zones 3 to form a closed bag. The foil 1 consists of a material which is permeable to hydrogen but only difficultly permeable to water vapour. The capacitor is also provided with an additional casing 2 composed of metal-synthetic resin foils 2 which are welded to the foil 1 on each flat face of the capacitor at a peripheral weld zone 11. The diffusion properties of the capacitor can be adjusted by varying the size of the foil 2. A strip 6 forming part of one of the elec trode foils is connected to an outer terminal 12 via a rivet 7 extending through the casing 1 and carrying an elastic ring 8 and a washer 9 located outside the casing. The other elec trode foil is connected in the same way to an outer terminal 10. Figure 2 illustrates a second embodiment of the invention in which the casing consists of an aluminium-synthetic resin compound foil 2 which entirely encases the flat winding 5 apart from the region of the outer terminals 10 and 12. The foil 1, which in this embodi ment is provided only in the region of the terminals 10 and 12, is welded to the foil 2 in a weld zone 11. In this embodiment, the dif fusion properties are determined by the size of the foil 1. As an alternative to the constructions of the embodiments illustrated in the drawing, the foil 1 can be entirely or partially metal- lised, in which case diffusion can be adjusted by varying the area and/or thickness of the metallisation. When a metal-synthetic resin compound foil is used, this can serve as a lead-through if the casing consists of two separate parts or if the metal foil is in the form of separate seg ments, the synthetic resin foil being cut away below respective parts of the metal foil, so that the electrode foils can be connected through the windows so formed in the synth etic resin foil to the respective parts of the metal foil. The outer terminals can consist of wires, soldering lugs, or connecting plugs. When a compound foil is used as a lead-through, contacting can also be effected by pressure exerted by spring elements. A particularly important field of use of capacitors in accordance with the invention is as electrolytic photographic flash capacitors, in particular in flash devices incorporated in cameras. WHAT WE CLAIM IS:

1. A flat, wound electrolytic capacitor comprising a flat winding of aluminium foils, the adajcent turns of which are separated by paper spacers saturated with an operating electrolyte and the anode foil having a dielectric oxide layer thereon, and a casing made at least in part of a synthetic resin which has a high permeability towards hydrogen and a low permeability towards water vapour.

2. A capacitor as claimed in Claim 1, wherein said casing consists of a foil of poly- propylene or polyethylene.

3. A capacitor as claimed in Claim 1 or Claim 2, wherein said casing is at least partially metallised, thickness of the metallisation in the case where the casing is completely metallised being insufficient to preclude the diffusion of hydrogen therethrough.

4. A capacitor as claimed in Claim 1 or Claim 2, wherein the capacitor is additionally encased in a metal foil, or a metal-synthetic resin compound foil, in such manner that diffusion of hydrogen from said winding to the ambient atmosphere is not precluded.

5. A capacitor as claimed in Claim 4, wherein said additional casing consists of a partially laminated metal-synthetic resin compound foil.

6. A flat, wound electrolytic capacitor substantially as hereinbefore described with reference to and as illustrated in Figure 1, and Figure 2, of the drawing.

7. A photographic flash device including a flat, wound electrolytic capacitor as claimed in any one of Claims 1 to 6.