Canadian Patents Database / Patent 1266518 Summary

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(12) Patent: (11) CA 1266518
(21) Application Number: 501003
(54) English Title: SELF-HEALING METALLIZED FILM CAPACITOR
(54) French Title: CONDENSATEUR A FILM METALLISE A AUTOREGENERATION
(52) Canadian Patent Classification (CPC):
  • 334/17
(51) International Patent Classification (IPC):
  • H01G 4/32 (2006.01)
  • H01G 4/22 (2006.01)
(72) Inventors :
  • LINZEY, RAYNOR (United States of America)
  • RICE, HERBERT L. (United States of America)
(73) Owners :
  • LINZEY, RAYNOR (Not Available)
  • RICE, HERBERT L. (Not Available)
  • SPRAGUE ELECTRIC COMPANY (United States of America)
(71) Applicants :
(74) Agent: BAKER, HAROLD C.
(74) Associate agent:
(45) Issued: 1990-03-06
(22) Filed Date: 1986-02-03
(30) Availability of licence: N/A
(30) Language of filing: English

(30) Application Priority Data:
Application No. Country/Territory Date
710,834 United States of America 1985-03-12

English Abstract






SELF-HEALING METALLIZED FILM CAPACITOR

Abstract of the Disclosure
A self-healing metallized film capacitor has a
dielectric sheet which is metallized with a high resis-
tivity alloy that is chosen so as to provide a desired
sheet resistivity for a given metallization thickness.
The invention applies to any metallized film capacitor
in which electrode metallization thickness and clear-
ability must be controlled.


Note: Claims are shown in the official language in which they were submitted.



THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for making a self-healing metallized film capacitor
having a dielectric film which is metallized with an alloy to a
thickness which gives reliable end connections, said process
comprising:
selecting a thickness of said alloy to be applied to said film
for termination of the capacitor;
selecting a sheet resistivity for said alloy for self-healing
of the capacitor;
computing a bulk resistivity for said alloy from said
thickness and said sheet resistivity;
selecting a material for said alloy having said computed bulk
resistivity; and
metallizing said film with said material.
2. The process of claim 1 wherein said material is selected from
an alloy of aluminum with a minor portion of copper and having said
desired bulk resistivity.
3. The process of claim 1 wherein said film is selected from the
group of polypropylene, polyester, polyvinylfluoride, and
polycarbonate.
4. The process of claim 1 wherein said alloy on said film is
contacted within said capacitor by a urethane containing unreacted
isocyanate groups.



Note: Descriptions are shown in the official language in which they were submitted.


3~ h ~




SELF-H~ALING METALLI~ED FILM CAPACITOR
This invention relates to a self-healing metal-
lized film capacitor, and more particularly to such a
capacitor in which the metallization material is an alloy
chosen so as to provide both a desired sheet resistivity
and a given metallized electrode thickness. The invention
relates to metallized film capacitors in which electrode
thickness and clearability (self-healing characteristics)
are important considerations, e.g., capacitors subjected
to high electrical stress.
Prior art teaches that improved self-healing of
metallized film capacitors can be obtained by decreasing
the thickness of the metallized layer. However, decreas-
ing the electrode thickness decreases the quality of any
end connection, increases the edge field, and increases
the difficulty in controlling electrode thickness; and,
in the case of an AC capacitor, increases the rate of elec-
trode loss due to corrosion.
It has been proposed in the prior art to use an
aluminum-copper alloy metallization to reduce capacitance
loss in metallized film capacitors. However, with this
prior art alloy, it was deemed necessary to reduce metal-
lization thickness in order to improve the self-healing
characteristics of the capacitor.
Aluminum-copper alloy metallization in normal
thicknesses has been used in the prior art for self-healing
capacitors, but at a high copper content.


-- 2 --
A feature of this invention is the provision of
a self-healing metallized film capacitor in which the elec-
trode thickness and shee-t resis-tivities are chosen indepen-
dently of each other.
In accordance with this invention the independent
choices of metal thickness and resistivity are accomplished
through the use of a high resistivity alloy, preferably an
aluminum alloy, as the metallization material.
In a drawing which illustrates embodiments of
this inven~ion,
Figure 1 depicts a partly unwound capacitor
section using alloy metallization of selected thickness
and resistivity,
~ igure 2 depicts a capacitor of Figure 1 with
a fluid urethane additive, and
Figure 3 depicts a capacitor of Figure 1 in
which a urethane is used as a potting compound.
In general, the metallization thickness for a
given capacitor application is determined from the proper-
ties needed for that application, including the thicknessnecessary for good-quality reliable end connections. The
desired sheet resistivity is determined from the electri-
cal stress to which the capacitor will be subjected in
any particular application. Then, the metallization alloy
is selected based on its total resistivity that will pro~
vide the desired sheet resistivity and self-healing charac-
teristics (clearability) at the specified electrode thick-
ness.
As a first approximation, the alloy is selected
by determining the bulk or total resistivity needed by
multiplying the desired electrode thickness in centimeters
times the desired sheet resistivity in ohms/sq. After a
trial metallization, the sheet resistivity measurements
indicate what adjustments must be made, e.g., more or less
alloying metal or a different alloy. As experience is
gained with a particular alloying metal or groups of alloys,
it is possible to select the particular alloy with greater
certainty from the first approximation results.

-- 3
Metalli7ed capacitors of the present invention
find use in a variety of applications such as DC capaci-
tors, energy storage capacitors, and AC capacitors. When
the self-healing al].oy metallized film capacitor of this
invention is to be used for AC application, it is necessary
to incorporate into the capacitor a material which will
prevent capacitance loss and prolong AC life. This is con-
trary to prior art disclosures which teach that the use of
alloy metallization alone will reduce or prevent capaci-
tance loss.
The preferred materials for AC use are urethan~s
containing unreacted i~ocyanate groups as taught by
Dequasie in US 4,317,158 and US 4,317,159 issued February
23, 1982, and by Dequasie and Rice in u.s 4,580,189
issued April 1, 1986 and assiqned to the same assi~nee
of the present invention. The urethane material m~y
be used alone as a liquid or potting compound, or may
be incorporated into the dielectrîc field.

Figure 1 shows a partly unrolled metallized film
capaci~or section 10 having two metallized film electrodes
12 and 14 which have a high resistivity alloy metallization~
Electro~es 12 and 14 are provided with unmetallized margins
13 and 15, respectively, which are oppositely positioned
in the wound section 10, so that the metallized portionof each electrode is available for terminal contact at
only one edge of the winding. The ends of section 10 are
covered with metallic spray or solder 20, and terminal
leads or tabs 16 and 18 are connected thereby to electrodes
12 and 14, respectively.
Figures 2 and 3 show AC capacitors having a
section 10 located within a housing 30. Electrode tab 16
(not shown) and tab 18 are connected to terminals 34 and
36, respectively, located in cover 37. In Figure 2, a
urethane containing unreacted isocyanate groups is pre-
sent in fluid form 31 by itself or dissolved in a dielec-
tric fluid. In Figure 3, the urethane is used as a-pot~
ting compound 32.

`J~
-- 4
The specific urethanes are those taught by
Dequasie as noted above, with the preferred urethane
being a diphenyl methane diisocyanate having a 33.4%
unreacted isocyanate groups. This material improves
capacitance loss of an AC capacitor during its operating
lif~.
It is well known that thinner, and consequently
higher resistance, electrode metallization provides
better self-healing (clearability) characteris-tics in
high stress AC film capacitors. It was not well under-
stood whether this improved self-healing is a function
of electrode metal thickness or of the increased resis-
tivity of the electrode.
It now has been determined that the dominant
factor in self-healing is the sheet resistivity of the
electrode, rather than the thickness of the electrode.
Since it is well known that the addition of a second
metal (creating an alloy) normally will result in a
resistivity which is greater than that of the base metal,
it is possible by proper choice of metals, to tailor a
system in which both the electrode sheet resistance and
thickness are selected independently. This result has
applications not only for DC application but others also,
e.g. energy storage, AC, etc. Clearly, as one skilled
in the art would realize, the alloy system must be chosen
so that it does not result in any deleterious effect on
the performance of the capacitor.
The base metal may be any metal which is use-
ful in capacitors, such as aluminum or zinc, and is pre-
ferably aluminum. Suitable aluminum alloys are those con-
taining chromium, copper, iron, lithium, magnesium,
manganese, nickel silicon, titanium, vanadium, zinc, and
zirconium. Their bulk resistivities at 1% and 5-~% are
(in micro ohm-cm~ respectively: Cu 2.g9, 4.54; ~e 2.84,
3.10; Li 5.96, 16.91; Mg 3.19, 5.62; Mn 5.59, 9.25;
Ni 2.75, 3.02; Si 3.67, 4.67; Ti 5.33, 6.01; ~a 4.58,
5.66; Zn 2.74, 3.17; and Zr 3.17, 3.37.

-- 5
Example 1
This example shows the metallization of a film
dielectric, specifically polypropylene of 8 ~m thickness,
with aluminum and with an aluminum alloy containing 4 wt%
copper in three nominal sheet resistivities of 4, 6 and 8
ohm/sq. (Sheet resistivity is measured on a square piece,
and the result obtained is independent of the size of the
square, hence ohm/sq.) Since the chosen alloy has a resis-
tivity of about twice that of aluminum, some metallized
films were obtained having different resistivities at the
same metallization thickness and some with dif~erent
thicknesses.
In Table la, data are presented to show the
resistivity and metal thickness of the metallized films
used to prepare the test capacitors. Each result is an
avera~e of two lots metallized to -the 4, 6 and 8 ohm/sq.
nominal resistivity; both nominal and measured resisti-
vities are given in ohms/sq., and the approximate aluminum
surface density is given in ~g/cm2 of surface area.
Table la
ResistivitY
Sample MetalNominal Measured Density
1-2 Al-Cu 4 3.45 7.2
3-4 Al-Cu 6 4.45 5.2
5-6 Al-Cu 8 9.25 3.3
7-8 Al 4 3.74 4.3
9-10 Al 6 6.50 3.3
11-12 Al 8 9.95 2.4
Three capacitors made from each of the above
samples were pulse-tested to determine the effect of
electrode thickness on end connection quality. The
ratio of the number of failures to total units are given
for pulses of 0.6, 0.8 and 1 ampere per inch of end
connection.


- 6 -
Table lb
Failures
Sample Resistivity Densit~ 0.6A/in 0.8A/in lA/in
1 3.45 7.7 0/3 0/3 0/3
2 3.~5 6.8 0/3 0/3 0/3
3 4.25 5.5 1/3 1/3 1/3
4 4.25 4.6 0/3 0/3 0/3
9.25 3A2 1/3 1/3 3/3
6 g.25 3.4 2/3 3~3 3/3
7 3.60 4.2 0/3 0/3 0/3
8 3~60 4.4 0/3 0/3 0/3
9 5.51 3.1 0/3 1/3 3/3
5.51 3.5 0/3 1/3 2/3
11 ~.99 2.2 1/3 3/3 3/3
12 8.99 2.6 1/3 3/3 3/3
The data show that good end connections can be made using
electrode thickness greater than about 5 ug/cm2, and parti-
cularly in the range of about 7-8 ~g/cm2. There is no indi-
cation that resistivity has any effect on end connection
quality.
For a self-healing capacitor, the DC breakdown
is a measure of the self-healing qualities of ~he system.
When the DC breakdowns were plotted as a function of resis-
tivity and of thickness, it was found that breakdown, and
hence ability to self-clear, is a unique function of resis
tivity rather than electrode thickness (in the thickness
ranges considered here).
The surface density, surface resistivity, and
breakdowns in volts DC are presented below:
Table lc
Density Resistivity ~reakdowns
Al-Cu 7.2 3.45 1700,1700,1800,1600,1500,1600
5.0 4.25 2200,2300,2100,2300,2000,2200
3.3 9.25 2700,2800,2700,2400,2400,2400
Al 4.3 3.6 1600,1700,1700,1900,1700,1800
3.3 5.51 2500,2600,2400,2400,2600,2700
2.4 8.99 3000,3100,3100,3100,3000,3000

s;~L~
-- 7
Comparing DC breakdown for 3.45 and 3.6 ohm/sq resistivi-
ties and for both 3.3 ~g/cm2 densities~ it can be seen
that DC breakdown is determined by resistivi~y rather than
electrode thickness.
Example 2
This example shows the use of the alloy metal-
lization in AC capacitor applications. As has been shown
by Dequasie, noted above, the loss of capacitance of a
metallized polypropylene capacitor on AC voltage due to
corrosion can be controlled by the addition of unreacted
isocyanate to the dielectric fluid. Normally, 8~ thick
polypropylene i.s used for AC capacitors to be operated at
370 VAC, and 10~ polypropylene for those to be opera~ed in
the 440 to 480 VAC range. Since such limitation is pre-
dominately determined by the loss of capacitance due tocorrosion, it is to be expected that the addition of iso-
cyanate to the dielectric fluid would allow 6~ polypropy-
lene to be operated at 370 VAC, and 8~ polypropylene to
be operated in the 440 to 480 VAC range. However, when
aluminum metallized capacitors manufactured in this manner
were tested under accelerated conditions using standard
industry requirements, the results showed a high and
unacceptable number of failures due to poor self-healing.
Capacitors were constructed from polypropylene
dielectric with electrodes made with aluminum containing
from 5 to 6% copper and with a surface resistivity from
6.5 to 8 ohms/sq. Diphenyl methane diisocyanate (8g) was
added to the dielectric fluid. The units were tested
according to industry standards with the following results.
Table 2
Dielectric Test No. of Test No. of
Cap. Thickness Conditions Units Hrs. Failures
40~f 8u 600VAC/25C 60 120 0
40~f 8~ 585VAC/80C 12 500 0
45~f 6~ 500VAC/25C 60 120
45~f 6~ 466VAC/80C 12 500 0

1;~6~5~8
-- 8
These results are well within industry requirements, are
unattainable using the standard aluminum metallizing, but
are attainable with the alloy metallization and show that
a thinner dielectric film may be used with the alloy
metallization.
Although the specific example cited here is for
metallized polypropylene, it should be recognized that this
invention can be used with any other dielectric suitable
for use in a metallized capacitor such as polyester, poly-
vinylfluoride, polycarbonate, kraft, etc.
It should also be recognized that the metalliza-
tion in the application is not limited to DC use but it
can be used anywhere a metallized dielectric is suitable,
e.g., DC, AC, energy storage, etc.
The particular dielectric film thickness used
will depend on the capacitor application. For example,
for energy storage capacitors, the thickness may be 10
to 12~; while ~or DC applications, the thickness will most
likely be 6 to 8~ or less.


A single figure which represents the drawing illustrating the invention.

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Admin Status

Title Date
Forecasted Issue Date 1990-03-06
(22) Filed 1986-02-03
(45) Issued 1990-03-06
Lapsed 1992-09-08

Abandonment History

There is no abandonment history.

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Application Fee $0.00 1986-02-03
Registration of a document - section 124 $0.00 1986-04-24
Current owners on record shown in alphabetical order.
Current Owners on Record
LINZEY, RAYNOR
RICE, HERBERT L.
SPRAGUE ELECTRIC COMPANY
Past owners on record shown in alphabetical order.
Past Owners on Record
None
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.

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Representative Drawing 2001-05-09 1 12
Drawings 1993-09-18 1 27
Claims 1993-09-18 1 29
Abstract 1993-09-18 1 12
Cover Page 1993-09-18 1 15
Description 1993-09-18 8 315