Note: Descriptions are shown in the official language in which they were submitted.
WO95/33277 '~ 2 ~ ~1737 r~
~ 1
~Tf'~TI~NC: (:A.C: TTTRP! I~pp}~pl~Tus
~In ~ OblllUN FOR USE ~
s
g~R~.R~Nn OF T~ J~VENTIO~
Fi~ld of th~ Tnvent;on
0 This invention relates to gas discharge tube apparatus
for tel~ t;~nR equipment and to compositions for use
in such apparatus.
Tntrodllction to th~ Tnvention
Gas discharge tubes are commonly used to protect
teler ;cations e~uipment and circuits from damage in the
eveLt of electrical interference or high voltage lightning
pulses. Gas tubes used in this way are often oalled gas tube
protectors. The tubes contain a gas which ionizes at high
voltages to allow electrical pulses to be directed to ground,
thus min;m; 7;ng any damage resulting from the pulses. If a
~nt;nn;ng high current overload occurs, e.g. as a result of
an ~cr;~nt~l power line crossover, the tubes ~-;nt~;n a
limited sustained ionization.
To provide protection in the event of failure from
overheating during~sustained over-current conditions, and to
assure protection if the ionizable gas vents from the tube,
gas tube protectors generally incorporate "fail-safe~ and
'~vent-safe" ~h~n;l , respectively. "Fail-safe" refers to
thermal damage protection, which is often provided by a
fusible metal or plastic material If the material is heated
due to the energy from the current overload, it yields to a
3s biased shorting member and provides a pelul~llellL current shunt
around the gas tube_ This may occur by melting a
thermoplastic film positioned between two electrodes, thus
allowing contact between the electrodes and ~hnnt;ng the
WO95/33277 2 1 9 1 737 1~ ..,.,.'C-'~
current to ground. "Vent-safe" refers tQ backup overvoltage
protection that operates when the gas "vents" or is lost to
the atmosphere. Vent-safe protection is often provided by an
air-gap that is part of the external structure of the tube.
s The proportions of the air-gap are selected to re~uire a
firing potential considerably above, e.g. twice, the normal
firing potential of the gas tube itself so that, under normal
circumstances, the gas tube will prevent the air-gap from
firing. This mln;m;7Pq the chances that the air-gap will be
o damaged because although an over-voltage pulse usually fires
harmlessly through a properly fllnrt;~n;ng gas tube, it may
damage the air-gap which is intended as a safety backup.
To improve the reliability of air-gap vent-safe designs,
it is common to enviLl ~ Al ly isolate the air-gap to prevent
r~nt~m;nAtion by moigture, air pollution, insects, or other
~ CnVirl ' Al factors. Sealing materials such as
encapsulants, potting compounds, conformal coatings, and gels,
however, often are of limited utility as they generally cannot
restrict all moisture ingress and may themselves penetrate
into the air-gap, thus rhAng1ng the voltage discharge levels
and/or leading to corrosion. A decrease in the discharge
voltage level will eventually lead to electrical shorts at low
voltage levels; an increase in the discharge voltage level
2s will defeat the purpose of the air-gap backup.
Some of these problems have been addressed by the
r~pl~A~c t of the air-gap by a layer of solid ~t~; Al having
particular non-linear electrical resistivity characteristics.
Such an air-gap is described in co-pending, commonly assigned
U.S. Patent Application No. 08/Og6,059 ~3ebbaut et al, filed
April 10, 1993), the disclosure of which is incorporated
herein by reference. Although envil~~ tAlly stable, the
solid material is subject to a decrease in breakdown voltage
3s on successive impulses, and, in fact, during normal operation
in discharging a high voltage, high energy pulse such as
lightning, will be destructive to itself. Furthermore, not
all such air gaps provide fail-safe protection.
WO 9S5'33277 - ' 2 1 9 1 7 3 7 r~",, ~ ~
. . .
sn~MARy OF T~ TNVEN~ION
e have now found that if an electrically non-linear
s element prepared from an electrically non-linear material
~hich has particular electrical properties when tested for
electrical breakdown is used in place of the solid material
air-gap described in U.S. Patent Application No. 08/046,059, a
gas tube apparatus can be prepared which has both vent-safe
0 and fail-safe propertie~. In addition, because of the nature
af the non-linear material and its physical and electrical
stability during successive electrical events, the apparatus
can be activated repeatedly in typical telecommunication
service conditions without failure of the non-linear element.
3ecause the need to replace the element i3 decreased, the
r~l; Ah; 1; ty of the telP ;cations system is increased and
the cost of r~;nt~n~nre is decreased. In a preferred
embodiment, the material comprises a gel which has the ability
to conform to the gas tube protector, decreasing the chance of
moisture ingress, and providing increased manufacturing
tolerances. Furthermore, the gel may be , -t;hle with a gel
encapsulant, thus contributing to the envi~ 1 sealing.
In a first aspect, this invention provides a telecom-
2s munications gas tube apparatus which comprises
(1) a first electrode for electrical crnn~ction to a
first t~r~;n~l on a gas discharge tube;
~2) a second electrode for electrical connection to a
second t~rm;n~1 on the gas tube; and
~ (3) an electrically non-linear resistive element
separating the first and second electrodes, said
'3s element comprising an electrically non-linear
composition which
WosS/33277 2 1 9 1 737 ~ 7
(a) comprises (i) a polymeric component, and (ii~ a
particulate filler,
(b) has an initial resistivity Pi at 25~C of at
s least 109 ohm-cm, and
(c) is such that when a standard device rrnt~in~ng
the composition has an initial breakdown
voltage VSi~ and after the standard device has
lo been exposed to a standard impulse breakdown
test, the device has a final breakdown voltage
Vsf which is from 0.7VSi to 1.3VSi, and the
composition in the device has a final
resistivity pf at 25~C of at least 109 ohm-cm.
In a second aspect, this invention provides a telecom-
munications gas tube apparatus which comprises
(1) a first electrode for electrical rnnn~rtion to a
first terminal on a gas discharge tube;
~2) a second electrode for electrical rrnn~rt;rn to a
second terminal on the gas tube; and
2s (3) an electrically non-linear-resistive element
separating the first and second electrodes, said
element comprising an electrically non-linear
composition which
(a) comprises (i) 30 to 95~ by volume of the total
composition gel, and (ii) 5 to 70~ by volume of
the total composition particulate conductive
filler, and
3s (b) has an initial resistivity p~ at 25~C of at
least 109 ohm-cm.
W095/33277 , ~ 2 1 9 1 7 3 7 . ~
In a third aspect, this invention provides an assembly
which comprises
; (A) a retaining element; and
s
(B) a telecommunications ga3 tube apparatus of the first
aspect of the invention inserted into the rP~;ni
element.
0 In a fourth aspect, this invention provide~ an
electrically non-linear resistive composition of the type
d.isclosed in the first aspect o~ the invention.
RRTR~ D~ 'RTPTI~ N OF T~T~ DRAWING
, , . _ .
Figure 1 is a schematic illustration showing a typical
three-element gas discharge tube incorporated into a one pair
tel~e ;cations line;
Figure 2 is a cross-sectional view of the gas tube of
Figure I;
Figure 3 is an P-~l o~ illustration of a gas tube
a;pparatus of the invention;
2s -- '
Figure 4 is a cross-sectional view of a gas tube
a]?paratus of the invention which is ~nr~rs~lated in a gel;
Figure 5 is an exploded illustration of an assembly of
the invention;
Figure 6 is a cross-sectional view of the assembly of
F:igure 5;
' 35 Figure 7 is a schematic illustration showing a standard
device for testing the compositions of the invention;
.
W095133277 21 91 737 r~ 7
Figure 8 is a graph of impul~e breakdown in volts as a
function of impulse test cycles;
Figures 9 and lo are graphs of impulse breakdown in volts
s as a function of the distance between electrodes for
compositions of the invention; and
Figure 11 is a graph of DC breakdown voltage and impulse
breakdown voltage as a function of the distance between
electrodes for compositions of the invention.
DET~TTTln DE.~rRTPTI~N OF T~ INVENTION
The gas tube apparatus and the assembly of the invention
both comprise an electrically non-linear resistive element
which comprises an electrically non-linear composition. In
this specification the term "non-linear" means that the
composition is substantially electrically nnnrnn~ tive, i.e.
has a resistivity of more than 109 ohm-cm, when an applied
voltage is less than the impulse breakdown voltage, but then
becomes electrically conductive, i.e. has a resistivity of=
less than 109 ohm-cm, when the applied voltage is equal to or
greater than the impulse breakdown voltage. The electrically
non-linear composition comprises a polymeric component and a
2s particulate filler. The polymeric ~ Snt may be any
~ ~Liate polymer, e.g. a thermoplastic matçrial such as a
polyolefin or a fluoropolymer, a thermosetting material such
as an epoxy, an elastomer, a grease, or a gel. The polymeric
component is generally present in an amount of 30 to 95~,
preferably 35 to 90~, particularly 40 to 85~ by volume of the
total composition
For many applications it is preferred that the polymeric
, Ant comprise a polymeric gel, i.e. a substantially
3s dilute crosslinked solution which exhibits no flow when in the
steady-state. The crosslinks, which provide a cnntinnnn~
network structure, may be the result of physical or chemical
bonds, crystallites or other junctions, and must remain intact
WO95/33277 ,~ 2 ~ 91 737 r~ 7
under the uae conditions of~the gél~ Most gels comprise a
fluid-extended polymer in which a fluid, e.g. an oil, fills
the interstices of the network. Suitable gels include those
compriaing silicone, e.g. a polyorganosiloxane system,
~ polyurethane, polyurea, styrene-butadiene copolymers, styrene-
-~ isoprene copolymers, styrene-(ethylene/propylene)-styrene
(SEPS) block copolymers (available under the t~Pn~mP Septon~
by Kuraray), styrene-(ethylene-propylene/ethylene-butylene)-
styrene block copolymers (available under the tradename
0 Septon~ by Ruraray), and/or styrene-(ethylene/butylene)-
styrene (SE;3S) block copolymers (available under the tradename
Kraton~ by Shell Oil Co.). Suitable P~tPn~r fluids include
mineral oil, vegetable oil such as paraffinic oil, Eilicone
oil, plasticizer such as trimellitate, or a mixture of these,
generally in an amount o~ 30 to 90% by weight of the total
weight of the gel. The gel may be a thermosetting gel, e.g.
s:ilicone gel, in which the crosslinks are formed through the
u~3e of multifunctional croscl;nk;ng agents, or a thermoplastic
gel, in which microphase separation of domains serves as
~lmction points. Di6closures of gels which may be suitable as
the polymeric ~ , ~nt in the composition are found in U.S.
Patent Nos. 4,600,261 (Debbaut), 4,690,831 (Uken et al),
4,.716,183 (Gamarra et al), 4,777,063 (Dubrow et al), 4,864,725
(I)ebbaut et al), 4,865,905 (Uken et al), 5,079,300 (Dubrow et
2s al), 5,104,930 (Rinde et al), and 5,149,736 (Gamarra); and in
Tn~P~n~t;~n~l Patent Publication Nos. WO86/01634 (Toy et al),
WC)88/00603 (Francis et al), WO90/05166 (Sutherland),
WC)91/05014 (s~thp~lAn~)/ and W093/23472 (~ammond et al). The
di.sclosure of each of these patents and publications is
incorporated herein by reference.
It is preferred that the gel have a Voland hardness of 1
to 50 grams, particularly about 5 to 25 grams, especially 6 to
20 grams, have stress relaxation of 1 to 45~, preferably 15 to
'3~ 4C~, have tack of 5 to 40 grams, preferably 9 to 35 grams, and
. ha.ve an ultimate ~l~ngat;on o~ at least 50~, preferably at
leaat 100~, particularly at least 400~, Pcpec;~lly at least
1000~, most especially at least 1500~. The elongation is
W095/33277 ' 21 91 737 r~ 7
measured according to ~STM 3217, the disclosure of which is
incorporated herein by reference. The Voland hardness, stress
r~ t;nn, and tack are measured using a Voland-Stevens
Texture Analyzer Model ~FRA having a 1000 gram load cell, a 5
gram trigger, and a 0.25 inch (6.35 mm) ball probe, as
described in U.S. Patent No. 5,079,300 (Dubrow et al), the
disclosure of which is incorporated herein by reference. To
measure the hardness of a gel, a 20 ml glass scintillating
vial containing lO grams of gel is placed in the analyzer and
lo the stainless steel ball probe is forced into the gel at a
speed of 0.20 mm/second to a penetration distance of 4.0 mm.
The Voland hardness value is the force in grams re~uired to
force the ball probe at that speed to penetrate or deform the
surface of the gel the specified 4.0 mm. The Voland hardness
of a particular gel may be directly correlated to the ASTM
D217 cone penetration hardness using the procedure described
in U.S. Patent No. 4,852,646 (Dittmer et al), the disclosure
of which is incorporated herein by r~f~r~n~.
In addition to the polymeric component, the composition
also comprises a particulate filler. The ~iller may be
conductive, s~m;cnn~nctive~ nnn~nn~ tive, or a mixture of two
or more types of fillers as long as the resulting composition
has the appropriate electrical non-linearity. It is generally
2s preferred that the filler be conductive or semiconductive.
Conductive fillers generally have a resistivity of at most lO-
3 ohm-cm; semiconductive fillers generally have a resistivity
of at most 103 ohm-cm, although their resistivity is a
function of any dopant material, as well as temperature and
other factors and can be subst~nti~lly higher than 103 ohm-cm.
Suitable fillers include metal powders, e.g. aluminum, nickel,
silver, silver-coated nickel, platinum, copper, tantalum,
tungsten, gold, and cobalt; metal oxide powders, e.g. iron
oxide, doped iron oxide, doped titanium dioxide, and doped
3s zinc oxide; metal carbide powders, e.g. silicon carbide,
titanium carbide, and tantalum carbide; metal nitride powders;
metal boride powders; carbon black or graphite; and alloys,
e.g. bronze and brass. Particularly preferred as fillers ar~e
W09~33277 2 1 ~ 1 7 3 7
~ g
~luminum, iron oxide (Fe304), iron oxide doped with titanium
dioxide, silicon carbide, and 9ilver-coated nickel. If the
polymeric component is a gel, it i8 important that the
~elected filler not interfere with the crosslinking of the
s gel, i.e. not "poison~ it. The filler iB generally present in
an amount of 5 to 70~, preferably 10 to 65~, especially 15 to
~0~ by volume of the total composition.
The volume loading, shape, and size of the filler affect
o 1:he non-linear electrical properties of the composition, in
part because of the spacing between the particles. Any shape
particle may be used, e.g. spherical, flake, fiber, or rod.
17seful compositions can be prepared with particles having an
average size of C.OlO to lO0 microns, preferably O.l to 75
rnicrons, particularly 0.5 to 50 microns, especially l to 20
rnicrons. A mixture of different size, shape, and/or type
particles may be used. The particles may be magnetic or
nonmagnetic.
In addition to the particulate filler, the composition
may comprise other conv~n~inn~l additives, including
tabilizers, pigments, croRRl;nk;ng agents, catalysts, and
i.nhibitors.
2s The compositions of the invention may be prepared by any
Eluitable means, e.g. melt-blending, solvent-blending, or
i.ntensive mixing, and may be shaped by conventional methods
including extrusion, calendaring, casting, and compression
molding. If the polymeric component is a gel, the gel may be
r~lixed with the filler by stirring and the composition may be
poured or cast onto a substrate or into a mold to be cured,
often by the addition of heat.
The compositions of the invention have excellent
3s . stability as measured both by resistivity and breakdown
voltage. The compositions are electrically insulating and
have an initial resistivity Pl at 25~C of at least lO9 ohm-cm,
preferably lClO ohm-cm, particularly l0ll ohm-cm, especially
W095/33277 ' 21 9 1 737 r~ 7
1012 ohm-cm. ~he initial resistivity value Pi is such that
when the composition is formed into a standard device as
described below, the initial insulation resistance Ri is at
least 109 ohms, preferably at least 101~ ohms, particularly at
s least l0ll ohms. An Ri value of at least 109 ohms is
preferred when the compositions of the invention are used in
tel~ ;cations apparatus. After~bein~ exposed to the
standard impulse breakdown test, described below, the final
resistivity pf at 25~C is at least 109 ohm-cm, and the ratio
of p~ to Pi is at most l x 103, preferably at most 5 x 102,
particularly at most 1 x 102, especially at most 5 x 101, most
especially at most 1 x 101. The final insulation resistance
Rf for a standard device after ~o~,e to the standard
impulse breakdown test is at least 109 ohms, preferably at
least 10l~ ohms, particularly at least l0ll ohms.
When the composition of the invention is formed into a
standard device as described below and exposed to a standard
impulse breakdown test, the device has an initial breakdown
voltage VSi and a final breakdown voltage Vsf which is from
0.70Vsi to l.30Vsi~ preferably from 0.80VSi to 1.20VSi,
particularly from 0.85VSi to 1.15VSi, especially from 0.90VSi
to 1.10V~3i. The value of the breakdown voltage is affected~by
the volume fraction of~the particulate filler, by the particle
2s size, and by the distance between the particles among other
factors. In general, as particle size decreases, the
breakdown voltage increases.
Some compositions of the invention will "latch", i.e.
remain in a conductive state with a resistivity of less than
106 ohm-cm, after one voltage discharge. If the latched
device is made from a composition comprising a gel, the device
can be "reset" into a high resistivity state, i.e. a
resistivity of at least 109 ohm-cm, by physical deformation,
e.g. flexing, torsion, compression, or tension. The latching
behavior is a function of particle size, interparticle
spacing, and particle 3hape. In gels, generally small
w09~33277 2 T ~ s7
11 -
~ipherical particle~, e.g. 1 to 5;~icrons~, with a Gmall
interparticle spacing, e.g. less than 4 microns, will latch.
Under certain electrical conditions, compositions of the
s invention, particularly compositions comprising aluminum, will
provide fail-safe protection. If exposed to a sufficiently
high energy level, e.g. 30A and 1000 volts for a time of 2
seconds to 30 minutes, the particulate filler ca~L fuse
together and provide a permanent conductive path between the
0 electrodes, giving a final resistance of less than 10 ohms,
e.g. 1 to 10 milliohms. Such behavior is desirable in the
event of crossed power lines and results in a permanent short
circuit.
The invention is illustrated by the drawing in which
Figure 1 is a schematic illustration of a conventional
tele~ ;cations circuit 10 which incorporates a gas tube 12
in a tele~ ;cations line. The gas tube 12, which is shown
in cross-section in Figure 2, has a first terminal 16 and a
second t~rm; n~l 17 for connection to the tip side 13 and the
ring side 14, respectively, of the telP ;cations circuit.
In addition, the gas tube 12 has a center ground terLninal 18.
A ceramic shell 19 encloses an ; ~ni 7~hl e gas 20 which ionizes
to form a discharge plasma at a given voltage.
2s ~
Figure 3 is an exploded view of a gas tube apparatus 40
oE the invention. In this embodiment, the first terminal 16
and the second t~r~;n~l 17 of the gas tube 12 also function as
first and second electrodes, respectively, for the gas tube
apparatus 40. (Although not shown, the gas tube may comprise
a third terminal which may be connected to a third electrode
in the gas tube apparatus. One of the electrodes may be a
grounding electrode.) Electrically non-linear resistive
element 45 is positioned in contact with first t~rm;n~l 16 and
3~ second terminal 17_ Ground electrode 55 is in physical
contact with resistive element 45, and is in electrical
contact with ground t~rm;n~l 18 of gas tube 12. In a
preferred ~- ti--nt, the non-linear compositiorL comprising
wossl33277 2 1 9 1 737 P~"~ c~7
12
the resistive element haa Gufficient flexibility that it
conforms to the shape of gas tube 12.
Figure 4 shows a cross-sectional view of gas tube
s apparatue 40 embedded in a gel encapsulant 50. The
encapsulant, which may be, e.g. a potting compound, a
conformal coating, or a gel, provides enviL~ t~l protection
from moisture and other ~nnt~min~nt~. In addition, the
encapsulant may exclude oxygen from the plasma discharge, and
o act as a heat sink to draw thermal energy away from local hot
spots. It is preferred that the resistive element be
chemically inert to the encapsulant.
Figure 5 is an exploded view of an assembly 70 of the =
invention and Figure 6 is a cross-sectional view of that
assembly. Retaining element 72 i5 designed to contain gas
tube 12, resistive element 45, and a ground electrode 55 ' .
Although the resistive element 45 may be laminar as shown, to
enhance contact with gas tube 12 the resistive element may be
curved or otherwise shaped. Spring leads 76,78 are attached
to gas tube 12 and serve to make electrical contact with
respective insulation displ~r~ t c~nn~t~rs (not shown).
Gas tube 12 is held in the appropriate position with the
resistive element 45 and ground electrode 55 ' by means of
2s retaining element 72, retainer cap 74, and grounding pin 80
which can be inserted into a recess or hole in retainer cap
74. Retainer cap 74 may be ultrasonically welded, glued, or
otherwise fused to retaining element 72. To ~-;n~in the
proper distance between the gas tube 12 and ground electrode
30 55 ', spacer 56 =protrudes from ground electrode 55 ' . The
height of spacer 56 can be eelected to achieve different
levels of voltage breakdown. The retaining element 72 may be
filled with the encapsulant to surround the contents.
The invention is illustrated by the following examples.
Wog~/33277 p_"~ "
2 1 9 1 737
13
E ~ ~R 1 to 14 ~~ : ~
The ingredients listed in Table I were mixed with a
tongue depressor to disperse the particulate filler, degassed
s in a vacuum oven for one minute, poured onto a PTFE-coated
release sheet and cured. ~ Standard Device, described below,
W.18 prepared with an electrode spacirLg of 1 mm. Samples were
then subjected to one of three tests, although the Standard
Irnpulse 3reakdown Test was extended for several samples from 5
o to 100 cycles. The results, shown in Figures 8 to 11,
indicated that the compositions based on silicone gel 1 and
thermoplastic gel had excellent stability and reproducibility
over 100 cycles based on impulse breakdown and in~ tion
resistance. The composition based on silicone gel 2 showed a
decrease~in insulation resistance to less than 105 ohms by
~bout 41 cycles. The composition based on a silicone grease
skLowed a similar decrease by four cycles (Figure 8). Example
5, based on an epoxy, shattered under the impulse test
conditions, but showed a decrease in insulation resistance by
15~ cycles under DC breakdown testing. Figures 9 and 10 show
th~e effect of particle size and filler loading on the impulse
breakdown voltage for samples which ranged in thickness from
0.25 to 1.0 mm. Figure 11 8hows that for a given particle
si~e and loading, the impulse breakdown and the DC breakdown
2s voltage were comparable.
St~n~rd Device
A circular sample with a diameter of 11.2 mm (i.e. a
surface area of about 1 cm2) and a thickrLess of 1 mm was cut
from the cured composition and inserted into the test fixture
shown in cross-section in Eigure ~. The test composition
sample 90 was positioned between two circular aluminum
electrodes 91,92, each with a diameter of about 11.2 mm and a
3s surface in contact with the composition 90 of about 100 mm2.
Polycarbonate sleeve 93 with an inner diameter of slightly
more than 11.2 mm waL3 positioned over the assembled electrodes
and composition and the assembly was inserted into fixture 94
2 ~ 9 ~ 737
W095/33277 P~
14
c~nt~;n;ng support elements 95,96 Micrometer 97 was adjusted
until the 9pacing between the electrodes 91,92 was 1 mm. (For
the Modified Impulse Breakdown Test described below, the
micrometer was adjusted to vary the electrode spacing, i.e.
s the sample thickness, from 0.25 to 1_0 mm For gel samples,
the sample had an initial thi~knP~R of 1 mm When the
micrometer was adjusted to decrease the gample th;~knP~5,
excess composition flowed through opening 98 in electrode 94
and between electrodes 91,92 and polycarbonate sleeve 93.)
St~n~rd T 1 ge Rr~k~wn Te~t _ _ _ _
A standard device, with dimensions of 1 cm2 x 1 mm was
inserted into the test apparatus shown in Figure 7. Prior to
testing, the insulation resistance Ri for the device was
mea~ured at 25~C with a biasing voltage of 50 volts using a
Genrad 1863 Megaohm meter; the initial resistivity Pl was
calculated. The device was inserted into a circuit with an
impulse generator and for each cycle a high energy impulse
with a 10 x 1000 ~8 waveform (i.e. a rise time to maximum
voltage of 10 ~s and a hal~-height at lOOQ ~s) and a current
of at most lA was applied The peak voltage measured across
the device at breakdown, i.e. the voltage at which current
begins to flow through the gel, was recorded as the impulse
2s breakdown voltage. For the Standard Impulse Breakdown Test,
five cycles were conducted. The final insulation resistance
Rf after five cycles for the standard test was measured and
the final resistivity pf was calculated.
M~ ied I lse Br~k~wn Test
Samples were prepared with electrode spacing varying from
0.25 to 1 mm and were tested following the procedure of the
Standard Impulse Breakdown Test.
W09~277 2 1 9 1 737 ~ r~7
1~ 15
~ ~ .
OC Rr~kdown Test
A etandard device was inserted into a circuit and was
ubjected to a voltage which increased at a rate of 200
s volts/second (Hipot Model M1000 DC Tester). The DC breakdown
- was recorded as the voltage at which 5 ~;ll;c~s of current
began to flow through the device.
TA3LE I
1 0 ' ~
Al F ll~r
Ex~m~l~ Polymer SiZ~ Vol~ I~9~ f Test
(~m~ ~ (Q)
1 Silicone gel 1 20 40.0 I1 1012 1012100
2 Thermoplastic gel20 35.1 I1 1012 1012100
3 Silicone grease 20 26.4 I1 1012 <105 4
4 Silicone gel 2 20 40.0 I1 101~ c105 46
Epoxy 20 26.4 D* 101~ c105 15
6 Silicone gel l 1-5 45.6 I2,D
7 Silicone gel 1 1-5 40.0 I2
8 Siiicone gel 1 1-5 35.1 I2
9 Silicone gel 1 1-5 26.4 I2
Silicone gel 1 20 45.6 I2,D
11 Silicone gel 1 20 35.1 I2
12 Silicone gel 1 20 26.4 I2
13 Silicone gel 1 20 19.3 I2
14 Silicone gel 1 20 13.3 I2~*
Notes to Table:
Silicone gel 1 was a mixture of 0.8 parts of a first
composition composed of 26~ by weight Nusil~PlyW 7520 CS 170
divinyl terminated polydimethylsiloxane (available from
McGhan-Nusil), 73.88~ Carbide L45/50 CS polydimethylsiloxane
S; 1; cnn~ fluid diluent (available from Union Carbide), 0.1
Nusil Cat~ 50 catalyst (3 to 4~ plati~um in silicone oil,
available from McGhan-Nusil), and 0.02~ T2160 inhibitor
(l~3~5~7-tetravinyltetramethylcyclotetr~c;l n~n~, available
2 1 9 1 737
WO95/33277 '- Ic~ ,5.~'7
16 : '
from Huls) and 1.0 pa~ts of a second composition composed of
26~ by weight Nusil Bly~ 7520 CS 170 polydimethylsiloxane,
73.91~ Carbide B~5/5Q CS silicone fluid diluent, and 0.9
T1915 tetr~ki~' thylsiloxysilane cro~l;nk;ng agent
tavailable from ~uls).
Thermoplastic gel c~nt~;r~ 10~ by weight Septon~ 4055
styrene-(ethylene/propylene)-styrene block~copolymer having
an ethylene/propylene midblock and a molecular weight of
308,000 (available from Kuraray), 87.5~ Witco~ 380 extender
oil (available from Witco), and 1~ Irganox~ B900 antioxidant
(available from Ciba-Geigy).
Silicone grease was a mixture of silicon dioxide and 50
cst silicone oil with the SiO2 added until the silicone oil
would no longer flow under its own welght.
Silicone gel 2 was SylGard~ Q3-6636 silicone dielectric
gel (available from Dow Corning).
Epoxy was A OE~ 18612 5-minute epoxy (available from Ace
~ardware Stores).
Aluminum powder with an average particle size of 20
microns and a sub3tantially spherical shape was product type
26651, available from Aldrich Chemicals.
Aluminum powder with an average particle size of 1 to~ 5
microns (passed 325 mesh) and a substantially spherical
shape was product type 11067, available from Johnson Mathey.
2s I1 is the Standard Impulse Breakdown Test.
I2 is the Modified Impulse Breakdown Test.
D is the DC Breakdown Test.
~ 15 to 18
To determine whether compositions of the invention would
remain in a c~n~n~t;ng condition after a voltage discharge,
standard devices with the compositions shown in Table II were
prepared. The initial resistance was measured prior~:to
3s exposing the device to one voltage discharge of the type
described in the Standard Impulse Breakdown ~est above. After
the discharge the final resistance was measured. A device was
deemed to have latched if the final resistance was less than
: ~ - ' 21 91 737
W095/33277 1 ll~ ,r~ 7
17
105 ohms. The approximate spacing between particles was
calculated using the formuIa ~ = 4(l-f)r/(3f)~ where A is the
mean free path (i.e. the interparticle spacing), f is the
volume fraction of particles, and r is the particle radius.
s Whether the composition latched was a function of both the
- particle size and loading of the particles. ~The 20 micron
a.luminum latched at a higher interparticle spacing, apparently
i.n part because not all the particles were completely
~pherical although the particles on average were subst~nt;~lly
o spherical.
T~3LE II
Al F ller Tnterp~rticle
E8~mpl~ Polymer Siz~ Vol. I~h~ SpSclnc
(~m~ m~
Silicone gel 1-5 26.4 No 5.6
16 Silicone gel 1-5 35.1 Yes 3.7
17 Silicone gel 20 35.1 No 24.6
18 Silicone gel 20 45.6 Yes 15.9
