Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Patent
1989-03-24
1990-02-20
Griffin, Donald A.
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
29 2542, 428626, H01G 101, H01G 700, B32B 1508
Patent
active
049031651
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process and an apparatus for the production of metallized films for electric capacitors as well as the products thus obtained.
Process for making capacitor's film are known; they foresee the deposit of a double metallic layer on a dielectric means. These double layers aim to make up for the inconvenients of one of the two meals with the qualities of the other. In fact the aluminium has a good conductivity but since it easily ionizes, it produces aluminium oxide that is a bad conductor; on the other hand zinc, having in its oxide a good conductor, requires a considerable thickness for assuring a good conductivity thus increasing the risk of short circuits between the two armatures with consequent overheating that can cause bursts and fires.
The processes for depositing the mentioned layers are complicated; to be carried out they necessitate very expensive equipments; furthermore, the resulting metallized film does not reach an optimized duration and capacitor self-regeneration.
U.S. Pat. No. 3,179,862 foresees the application in a single pass of two layers: one of zinc and one of aluminium.
The magazine "L'ONDE ELECTRIQUE" Vol. 48 No. 493, April 1968, pages 358-365 suggests at 359, third paragraph, to make a preliminary deposit of a very thin metallic layer (for example Ag) on a film of dielectric material.
"THIN SOLID FILMS" Vol. 96 No. 3, October 1982, pages 199-215 describes in a general way the uniform coating of large areas of flat glass, paper and plastic obtained with a single layer of metal.
Main object of this invention is to manufacture in a simple and cheap way metallized films for capacitors having a long service life.
The above mentioned aim has been reached as described in claims 1, 5, 12 and 14.
Other adventageous solutions are described in claims 2-4, 6-11 and 13.
An extremely layer of silver, copper or their alloys, then zinc having an uneven thickness and at least a layer or aluminium or aluminium alloys comprising a percentage of titanium, silicon or cadmium lower than 1% with uniform thickness are deposited on a dielectric film, the latter being placed in a chamber at an absolute pressure of about 10.sup.-4 torr (1,3.10.sup.-2 Pa).
With this process, the possibility is also foreseen of adjusting the thickness of each layer, maintaining the thickness of aluminium or aluminium alloys at a value being from 1/8 to 1/16 of the zinc's thickness.
An apparatus comprising a vacuum chamber divided in at least two sections is provided for carrying out the described process. In a first section an absolute pressure of about 10.sup.-2 -10.sup.-3 torr (1,3-0,13 Pa) is maintained; in a second section an absolute pressure of about 10.sup.-4 torr. (1,3.10.sup.-2 Pa) is maintained. A 10.sup.-4 torr (1,3.10.sup.-2 Pa) pressure is that necessary to obtain the evaporation of aluminium or its alloys at the temperature of 1400.degree..degree.C. Particularly the metal layers deposit takes place in the section at a pressure of about 10.sup.-4 torr(1,3.10.sup.-2 Pa). The section at a pressure of 10.sup.2 -10.sup.-3 torr (1,3-0,13 Pa) acts as a transit chamber for the film. For the deposit of silver, copper or their alloys and zinc a pressure higher than 10.sup.-4 torr (1,3.10.sup.-2 Pa) would be sufficient but, for operational reasons, all the metal deposits are effected at the same pressure i.e. at about 10.sup.-4 torr.(1,3.10.sup.-2 Pa)
The apparatus comprises the means to bring the mentioned metals to the vapour state in separate and different devices, and means to maintain the necessary depression in the apparatus.
The evaporation of silver, copper or their alloys is obtained by putting small quantities of the metal, preferably metal tablets, in housings made in a resistive bar heated at a temperature comprised between 850.degree. and 950.degree. C. The vapour thus obtained reaches the film that runs on a rotating drum; the metal deposited in a thin layer allows a uniform deposit of the following layer. The film with said first layer continues towards the zone where it receiv
REFERENCES:
patent: 2968583 (1961-01-01), Barth
patent: 3179862 (1965-04-01), Dubilier
"Condensateurs a Dielectriques Plastiques Metallises a L'Aluminium et au Zinc", L'Onde Electrique, vol. 48, No. 493, Apr. 1968, by M. Braguier, pp. 358-365.
"Silver Coating by Vacuum Evaporation", Chemical Abstracts, vol. 92, No. 8, Feb. 1980, Abstract 63294u, by S. Horii et al., p. 291.
"Vacuum Coating of Large Areas", Thin Solid Films, vol. 96, No. 3, Oct. 1982, by S. Schiller et al., pp. 199-216.
Griffin Donald A.
Metalvuoto Films S.p.A.
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