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Biaxially stretched polypropylene composite film and electrical insulating film made therefrom
| Details |
Inventors: Siefried, Walter; Janocha, Siegfried; Crass, Gunther;
Assignee: Hoechst Aktiengesellschaft (Frankfurt am Main, DE)
Primary Examiner: Robinson; Ellis P.
Assistant Examiner:
Attorney, Agent or Firm: Schwartz, Jeffery, Schwaab, Mack, Blumenthal & Koch
Disclosed is a biaxially stretched, composite polypropylene film suitable for use as an electrical insulating film, comprising a first layer comprising a first propylene polymer and having a maximum roughness height R.sub.z of its exposed surface of about 0.5 .mu.m, and a second layer contiguous to the first layer comprising a second propylene polymer having a composition different from the first propylene polymer and having a roughness height R.sub.z on its exposed surface ranging between about 0.2 .mu.m and 0.4 .mu.m, with the composite film having a modulus of elasticity of at least about 2000 N/mm.sup.2 in all directions of the plane of the film and a DC dielectric strength of at least about 650 V/.mu.m. Also disclosed is a capacitor comprised of a plurality of these composite films having a metal surface layer and being laminated with one another. |
|
DETAILED DESCRIPTION It is therefore an object of the present invention to provide an improved biaxially stretched polypropylene film.
A further object of the invention resides in providing a biaxially stretched polypropylene film which exhibits good electrical properties and extended life test values.
It is a further object of the invention to provide such a film which does not block during processing and which may, therefore, also be used in high-speed capacitor winding machines.
Still another object of the invention is the provision of an improved metallized polypropylene film.
One further object of the invention resides in the provision of an improved capacitor made with the improved polypropylene film of the invention.
In accomplishing these objects, there has been provided in accordance with the present invention a biaxially stretched, composite polypropylene film suitable for use as an electrical insulating film, comprising a first layer comprising a first propylene polymer and having a maximum roughness height R.
sub.
z of its exposed surface of about 0.
15 .
mu.
m, and a second layer contiguous to the first layer comprising a second propylene polymer having a composition different from the first propylene polymer and having a roughness height R.
sub.
z on its exposed surface ranging between about 0.
2 .
mu.
m and 0.
4 .
mu.
m.
The composite film has a modulus of elasticity of at least about 2000 N/mm.
sup.
2 in all directions of the plane of the film and a DC dielectric strength of at least about 650 V/.
mu.
m.
Preferably, the first layer comprises more than about 50% of the total thickness of the composite film.
In accordance with another aspect of the present invention, there is provided a composite polypropylene film as above-defined, further comprising a layer of metal, preferably having a thickness ranging from about 20 nm to 50 nm and a resistivity of from about 1 to 5.
OMEGA.
/.
quadrature.
, on one of its exposed surfaces.
In accordance with yet another aspect of the invention, there has been provided a capacitor comprised of a plurality of the metallized composite polypropylene films laminated with one another
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