Stock material or miscellaneous articles – Composite – Of metal
Patent
1998-01-28
2000-10-03
Thibodeau, Paul
Stock material or miscellaneous articles
Composite
Of metal
428500, 3613013, 361311, B32B 1508, H01G 400, H01G 406
Patent
active
061270423
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to capacitors having polypropylene dielectrics. It also relates to films for making such capacitors.
Numerous polypropylene films are already used as dielectric films for capacitors.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel polypropylene film for capacitors, which film offers a better temperature rating than known prior art films, thereby making it possible to improve the reliability of capacitors and to extend their rated temperature range.
The present invention achieves this object by providing a dielectric made of a polypropylene that has a modulus of elasticity in bending higher than 1500 MPa, a sag point under load higher than 110.degree. C., and a Vicat point higher than 150.degree. C.
The modulus of elasticity in bending, the sag point, and the Vicat point are measured in compliance respectively with the following Standards: ASTM D 790; ASTM D 648 (load of 455 MPa--temperature variation of 2.degree. C. per minute); and ASTM D 1525--method A (load of 1 kg--temperature variation of 50.degree. C. per hour).
The invention also provides metallized films for making capacitors of this type.
Other characteristics and advantages of the invention appear from the following description which is given purely by way of non-limiting example and should be read with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic perspective view of a capacitor film of the invention;
FIG. 2 is a comparative graph on which curves are plotted showing modulus of elasticity as a function of temperature for a polypropylene film of the invention and for a prior art capacitor film; and
FIG. 3 is a comparative graph on which curves are plotted showing percentage of shrinkage as a function of temperature for the two films.
DETAILED DESCRIPTION OF THE INVENTION
A capacitor of the invention may be a capacitor in which the polypropylene film and the electrodes are separate, or else, as shown in FIG. 1, it may be made up of metallized polypropylene films.
The capacitor shown in FIG. 1 includes a substrate 1 constituted by a polypropylene film on which one or more layers 2 of a metal such as aluminum and/or zinc or an alloy of aluminum and of zinc are deposited using techniques known per se to a person skilled in the art.
The resulting metallized film is rolled up as shown in FIG. 1. The roll may be covered with a protective covering 3 of a thermosettable resin, of a coating wax, or of a dielectric liquid.
For example, the substrate 1 may be a 6-.mu.m polypropylene film metallized with a layer of pure zinc which has a surface resistance lying in the range 5 .OMEGA. per square to 10 .OMEGA. per square.
The protective covering 3 is constituted by a polyurethane thermosettable resin.
According to the invention, the polypropylene of the substrate 1 is chosen to have the following characteristics: the ASTM D 790 Standard that is higher than 1500 MPa; Standard is higher than 110.degree. C.; and D 1525 Standard is higher than 150.degree. C.
It further offers high dielectric quality.
For example, such a polypropylene may be the polypropylene sold by Himont under the trade name Adstif T 2101 F.
The thermo-mechanical properties of the above-described film are shown in FIGS. 2 and 3 by the curves M1 and R1 (dashed-line curves on which the measured points are marked by * signs).
In the figures, the curves M2 and R2 (solid-line curves on which the measured points are marked by + signs) correspond to the curves of modulus and of shrinkage as a function of temperature of the polypropylene sold by Shell under the name JD6900.
As is understood from reading these figures, the metallized film of the invention has a modulus of elasticity that is significantly higher than those of the prior art films. The modulus of elasticity of the film of the invention (as measured in compliance with the ASTM D 882 Standard) is about 80 daN/mm.sup.2 (800 MPa) at 100.degree. C., and is 50 daN/mm.sup.2 (500 MPa) at 120.
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Bollore Technologies
Kruer Kevin R.
Thibodeau Paul
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