Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO95/332782 1 9 1 7 4 0 P~./. s c i
Trr.r.~-, , I r~InN~q ~-L~.~ TnFL-r~L ~pp~r~Tus
~n r~MposITIoN FOR USE '~ t~
~ .
s
~ B~t~K~R~LlrNn OF T~ INVENTI~N
Field of thP TnvPntinn
This invention relat~Ls to gas discharge tube apparatus
fior tele, 1cAtions et~ipment and to compositions for use
in such apparatus.
Introduction to t~e TnvPntion
~ :
Gas discharge tubes are commonly used to protect
t.ele~ ;cations et~uipment and circuits from damage in the
eLvent of electrical interference or high voltage lightning
pulses. Gas tubes used in this way are often called gas tube
protectors. The tubes contain a gas which ionizes at high
voltages to allow electrical pulses to be directed to ground,
t:hus min;r;7;ng any damage resulting from the pulses. If a
r-nnt;nn;ng high current overload occurs, e.g. as a result of
an accidental power line crossover, the tubes r-;nt~;n a
2s ].imited sustained ;nn;7A~lnn
To provide protection in the event of failure from
overheating during sustained over-rnrrPnt tnnrl;t;on~, and to
assure protection if the ionizable gas vents from the tube,
qas tube protectors generally incorporate "fail-safe~ and
"vent-safe" mechanisms, respectively. "Fail-safe" refers to
t:hermal damage protection, which is often provided by a
~usible 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 permanent current shunt
around the gas tube. This may occur by melting a
l_hermoplastic film positioned between two electrodes, thus
allowing contact between the electrodes and ~nnt; ng the
W095/33278 2191740 p "., '1!~,
current to ground. "Vent-safe" refers to backup overvoltage
protection that operates when the gas ~vents~ or is lost to
the a ~ re Vent-safe protection is often provided by an
air-gap that i8 part of the external structure of the tube.
The proportions of the air-gap are selected to require 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 m;n;m;7~ the chances that the air-gap will be
o damaged because although an over-voltage pulse usually fires
harmlessly through a properly functioning gas tube, it may
damage the air-gap which is intended as a safety backup.
To improve the reliability of air-gap vent-safe designsl
it is common to environmentally isolate the air-gap to prevent
r~nt~m;n~tion by moisture, air pollution, insects, or other==
enviL~ t~l 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 changlng the volta~e di~scharge 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
will defeat the purpose of the air-gap backup.
Some of these problems have been addressed by the
replacement of the air-gap by a layer of solid material having
particular non-linear electrical resistivity characteristics.
Such an air-gap is described in co-pending, commonly assigned
U.S. Patent Application No. 08/046,059 (Debbaut et al, filed
April 10, 1993), the disclosure of which is incorporated
herein by reference. Although enviL~ t~lly stable, the
solid material is subject to a decrease in breakdown voltage
3~ 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.
W095133278 ' ' 2 1 ~ 1 740
STJI~RY OF T~. T~ TIo~
e have now found that if an electrically non-linear
s element ~LepaIed from an electrically non-linear material
which has particular electrical properties when tested for
electrical breakdown is used in place of the solid material
air-gap described in U.S ~atent Application No. 08/046,059, a
gas tube apparatus can be prepared which has both vent-safe
o i~nd fail-safe properties. In iq~;t;~n, because of the nature
of the non-linear material and its physical and electrical
stability during successive ~lP~tr;c~l events, the apparatus
can be activated repeatedly in typical tPlP~ ~n;cation
service conditions without failure of t~e non-linear element.
:Because the need to replace the element is decreased, the
reliability of the t~le~ ;cations system is increased and
the cost of ~-;nt~n~n~e 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
Imoisture ingress, and providing increased manufacturing
tolerances. Furthermore, the gel may be compatible with a gel
encapsulant, thus contributing to the envi~ ~1 sealing.
In a first aspect, this ;n~rpnt;~n provides a telecom-
2s munications gas tube apparatus which comprises
(1) a first electrode for electrical r~nnPct;on to a
first terminal on a gas discharge tube;
(2) a second electrode for PlPrt~;c~l connection to a
second terminal 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
.
W095/33278 21 91 740 r~
(a) comprises (i) a polymeric cl ~nt, and (ii) a
particulate filler,
(b) has an initial resistivity Pi at 25~C of at
least 109 ohm-cm, and
(c) is such that when a standard device rnnt~;n;ng
the composition has an initial breakdown
voltage VSi, and after the standard device has
0 been exposed to a standard impulse breakdown
test, the device has a final breakdown voltage
Vsf which i5 from 0.7VSi to 1.3VSi, and the
composition in the device has a final
resistivity p~ 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 connection to a
first terminal on a gas discharge tube;
(2) a second electrode for electrical r~nnP~t;~n 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
(b) has an iritial resistivity Pi at 25~C of at
least 109 ohm-cm.
WogSl33278 ,j~ ' 2 ~ 9 1 7 4 0 ~ 7
In a third aspect, this invention provides an assembly
which comprises
,
~ (A) a r~t~;ning element; and
s
(B) a tel~c ;cations gas tube apparatus of the first
aspect of the invention inserted into the r~t~;n;ng
element.
In a fourth aspect, this invention provides an
e~lectrically non-linear resistive composition of the type
c1isclosed in the first aspect of the invention.
~RT~ DE.~CRTPTION OF T~ DR~WING
Figure 1 is a schematic illustration showing a typical
t:hree-element gas discharge tube incorporated into a one pair
t:elecommunications line;
Figure 2 is a cross-sectional vlew of the gas tube of
Figure 1;
Figure 3 is an exploded illustration of a gas tube
apparatus of the invention;
2s .=
Figure 4 is a cross-sectional view of a gas tube
apparatus of the invention which is ~r~r~n1~ted in a gel;
Figure 5 is an exFloded illustration of an assembly of
the invention;
Figure 6 is a cross-sectional view of the assembly of
Figure 5;
3s Figure 7 is a schematic illustration showing a standard
device for testing the compositions of t~he invention;
~ , . ~ , ,
wogs/33278 2 1 ~ 1 740 P~
Pigure 8 iE a graph of lmpulse breakdown in volts as a
function of impulse test cycles;
Figures 9 and 10 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
o electrodes for compositions of the invention.
DFT~TT,Fn DF..~C~TPTION OF T~T~ lNV~'l'lUN
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 substAnt;A1ly electrically n~nrnn~1nrtive~ 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 erlual to or
greater than the impulse breakdown voltage. The electrically
non-linear composition comprises a polymeric rrmrrnPnt and a
2s particulate filler. The polymeric r~ _r,n~nt may be any
appropriate polymer, e.g. a thermoplastic material such as a
polyolefin or a fluoropolymer, a thermosetting material such
as an epoxy, an elastomer, a grease, or a gel. The polymeric
c ~nt 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
cr~nPnt comprise a polymeric gel, i.e. a substantially
3s dilute croR~1;nk~ solution which exhibits no flow when in the
steady-state. The crosslinks, which provide a continuous
network structure, may be the result of physical or chemical
bonds, crystallites or other junctions, and must remain intact
WO95/33278 21917 4 0 rcl~l ''0~(7
~mder the use conditions of the gel. Most gels compri~ie a
i--luid-PYtpr~pl polymer in which a fluid, e.g. an oil, fills
t:he interstices of the network. Suitable gels include those
~, comprising silicone, e.g. a polyorganosiloxane system,
polyurethane, polyurea, etyrene-butadiene copolymers, styrene-
i.soprene copolymers, styrene-(ethylene/propylene)-styrene
l'SEPS) block copolymers (available under the traderame Septon~
by Kuraray), styrene-(ethylene-propylene/ethylene-butylene)-
tyrene block copolymers (available under the triq~n
0 Septon~ by Kuraray), and/or styrene-(ethylene/butylene)-
styrene (SEBS) block copolymers (available under the tradename
P~raton~ by 5hell Oil Co.). Suitable P~n~Pr fluids include
mineral oil, vegetable oil such as paraffinic oil, silicone
oil, plasticizer such as trimellitate, or a mixture of these,
generally in an amount of 30 to 90~ by weight of the total
weight of the gel. The gel may be a thermosetting gel, e.g.
Elilicone gel, in which the crosslinks are formed through the
use of multifunctional crosslinking agents, or a thermoplastic
gel, in which microphase separation of domains serves as
junction points. Disclosures of gels which may be suitable as
the polymeric c ~nnPnt in the composition are found in U.S.
E'atent Nos. 4,600,261 (Debbaut), 4,69Q,831 (Uken et al),
4,716,183 (Gamarra et al), 4,777,063 (3ubrow et al), 4,864,725
(Debbaut et al), 4,865,905 (Uken et al), 5,079,300 (Dubrow et
al), 5,104,930 (Rinde et al), and 5,149,736 (Gamarra); and in
International Patent Publication Nos. WO86/01634 (Toy et al),
W088/00603 (Francis et al), WO90/05166 (Sutherland),
WO91/05014 (Sutherland), and W093/23472 (Hammond et al). The
disclosure of each of theRe 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, P~pe~ lly 6 to
20 grams, have stress rPlA~iqti~n of 1 to 45~, preferably 15 to
3s 40~, have tack of 5 to 40 grams, preferably 9 to 35 grams, and
have an ultimate elongation of at least 50~, preferably at
least 100~, particularly at least 400~, especially at least
1000~, most especially at least 1500~. The elongation is
W095/33278 2 1 9 1 74o ~ ~'~ '
measured according to ASTM D217, the disclosure of which is
incorporated herein by reference. The Voland hardness, stress
relaxation, and tack are measured using a Voland-Stevens
Texture Analyzer Model LFRA having a 1000 gram load cell, a~5 ~.
s 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 sr;nt;llRting
vial containing 10 grams of gel is placed in the analyzer and
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. 4,852,6~6 (Dittmer et al), the disclosure
of which is incorporated herein by reference.
In addition to the polymeric component, the composition
also comprises a particulate filler. The filler may be
conductive, semiconductive, nnn~nn~lrtive, 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
preferred that the filler be conductive or semiconductive.
Conductive fillers generally have a resistivity of at most 10-
3 ohm-cm; semicnn~llrtive fillers generally have a resistivity
of at most 103 ohm-cm, although their resistivity is a
func~ion of any dopant material, as well as temperature and
other factors and can be substRnt;Rlly 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 are
W095/33278 2 1 9 1 740 ~ otg~7
", i .,,
alluminum, iron oxide (Fe304), iron oxide doped with titanium
dioxide, silicon carbide, and silver-coated nickel. If the
olymeric ~ ~nt is a gel, it is important that the
aielected filler not interfere with the crosslinking of the
s gel, i.e. not "poi80n" it The filler is generally present in
am amount of 5 to 70~, preferably 10 to 65~, especially 15 to
60~ by volume of the total composition.
The volume loading, shape, and size of the filler affect
o t: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.
lJseful compositions can be prepared with particles having an
average size~of 0.010 to 100 microns, preferably 0.1 to 75
microns, particularly 0.5 to 50 microns, especially l to 20
microns A mixture of different size, shape, and/or type
particles may be used. The particles may be magnetic or
n~ gnPtiC.
In aadition to t~e particurate filler, the composition
may comprise other conventional additives, including
stabilizers, pigments, crnRAlink;ng agents, catalysts, and
inhibitors
The compositions of the invention may be prepared by any
f;uitable means, e.g. melt-blending, solvent-blending, or
intensive mixing, and may be shaped by conventional methods
including extrusion, calendaring, casting, and compression
molding If the polymeric com~on,nt is a gel, the gel may be
mixed 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
~itability as measured both by resistivity and breakdown
~roltage The compositions are electrically insulating and
have an initial resistivity Pl at 25~C of at least lC9 ohm-cm,
preferably lolO ohm-cm, particularly lOll ohm-cm, especially
,
WogS/33278 F~ <8~7
2 1 9 1 74~ _
1012 ohm-cm. The initial resistivity value Pi is such that
when the composition i9 formed into a standard device as
described below, the initial insulation resistance Ri is at
least lO9 ohms, preferably at least 101~ ohms, particularly at
least lOl1 ohms. An Ri value of at least 109 ohms is
preferred when the compositions of the invention are used in
telecommunications apparatus. ~fter being 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
o of pf to Pi is at most 1 x 103, preferably at most 5 x 1o2,
particularly at most 1 x 102, especially at most 5 x lOl, most
especially at most l x 101. The final insulation resistance
Rf for a standard device after exposure to the standard
impulse breakdow~ test is at least 109 ohms, preferably at
lS least 10l~ ohms, particularly at least lOll 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 1.30Vsi~ preferably from 0.80VSi to 1.20VSi,
particularly from 0.85Vsi to 1.15VSi, especially from 0.90Vsi
to l.lOVsi. 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. ilexing, torsion, compression, or tension. The latching
behavior is a function of particle size, interparticle
spacing, and particle shape. In gels, generally small
2 1 9 1 74~
W09~33278 r~IJ~ (7
,
spherical particles, e.g. 1 to 5 microns, with a small
interparticle spacing, e.g. less than 4 microns, will latch.
~ nder cer~ain 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 can fuse
together and provide a permanent conductive path between the
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
Th~ invention is illustrated by the drawing in which
Figure 1 is a schematic illustration of a ccnv~nt;on~l
t~ ation8 circuit 10 which incorporates a gas tube 12
in a telecommunications line. The gas tube 12, which is shown
in cross-section in Figure 2, has a first terminal 16 and a
second terminal 17 for ~nnPct;on to the tip side 13 and the
ring side 14, respectively, of the telecl In;~At;~nc circuit.
In addition, the gas tube 12 has a center ground t~m; n~l 18 .
A ceramic shell 19 encloses an i~n;7~hle gas 20 which ionizes
to form a discharge plasma at a given voltage.
2~
Figure 3 is an ~rl o~d view of a gas tube apparatus 40
of the invention. In this 'o~; , the first terminal 16
and the second terminal 17 of the gas tube 12 also function as
first and second electrodes, respectively, for the gas tube
3~ 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~r~;ncl 16 and
3~ second terminar 17. Ground electrode 55 is in physical
cDntact with resistive element 45, and is in electrical
cDntact with ground terminal 18 of gas tube 12 In a
preferred ~mho~;m~nt, the non-linear composition comprising
... ~ .
W095/33278 2 1 9 1 74 0 P~IIU~ S8'7
12
the resistive element ha~ sufficient fl~;h;l;ty that it
conforms to the shape of gas tube 12.
Figure 4 shows a cross-s~t;~n~l view~of gas tube
apparatus 40 embedded in a gel encapsulant 50. The
encapsulant, which may be, e.g. a potting compound, a
conformal coating, or a gel, provides envir~nm~nt~l protection
from moisture and other ~nt~m;n~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. ~t~1n;ng element 72 is 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 ;nq~ t;on displacement connectors (not shown).
Gas tube 12 is held in the appropriate position with the
resistive element 45 and ground electrode S5' by means of
2s ret~;n;nS 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 ret~;n;ng element 72. To --lnt~;n the
proper distance between the gas tube 12 aud ground electrode
55', spacer 56 protrudes from ground~electrode 55'. The
height of spacer 56 can be selected to achieve different
levels of voltage breakdown. The retaining element 72 may be
filled with the encapsulant to surround the contents.
3s The invention is illustrated by the following P~mples
W095/33278 2 ~ 9 ~ 7 4 ~ c ~7
13
E~mrleR 1 to 14
The ingredients li3ted in Table I were mixed with a
t:ongue depres30r to disperse the particulate filler, degassed
in a vacuum oven for one minute, poured onto a PTFE-coated
release sheet and cured. A Standard Device, described below,
~as prepared with an electrode spacing of 1 mm. Samples were
t:hen subjected to one of three test3, although the Standard
Impulse 3reakdown Te3t wa3 extended for several samples from 5
o t:o 100 cycle6. The results, shown in Eigure3 8 to 11,
indicated that the compositions based om 3ilicone gel 1 and
t:hermoplastic gel had excellent stability and reproducibility
c~ver 100 cycles based on impulse breakdown and insulation
resistance. The compositio~L based on silicone gel 2 showed a
clecrease in insulation resi3tance to le33 than 105 ohm3 by
about 41 cycles. The composition based on a silicone grease
Elhowed a similar decrease by four cycles (Figure 8). Example
5, based on an epoxy, shattered under the impulse test
c:onditions, but showed a decrea3e in in3ulation resistance by
15 cycles under DC breakdown te3ting. Figures 9 and 10 show
t:he 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 shows that for a given particlé
E;ize and loading, the impuIse breakdown and the DC breakdown
voltage were comparabIe.
':t~n~d Device
A circular sample with a diameter of 11.2 mm ~i.e. a
surface area of about 1 cm2) and a th; ekn~ of 1 mm was cut
from the cured composition and inserted i~Lto the test fixture
Elhown in cross-section in Figure 7. The test composition
ample 90 was positioned between two circular ~lnm;nllm
e.lectrode3 91,92, each with a diameter of about 11.2 mm and a
Elurface in contact with tELe composition 90 of about 100 mm2.
E'olycarbonate sleeve 93 with an inner diameter of slightly
more than 11.2 mm was positioned over the assembled electrodes
aLnd composition and the assembly was inserted into fixture 94
W095/33278 21 9174 r~ 7
14
nrnt~;n;ng support elements 95,96. Micrometer 97 was adjusted
until the spacing between the electrodes 91,92 was 1 mm. (For
the Modified Impulse Breakdown Test described below, the
mi~,~ trr 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 th;rkn~ of l mm. When the
micrometer was adjusted to decreaae the sample thickness,
excess composition flowed through opening 98 in electrode 94
and between electrodes 91,92 and polycarbonate sleeve 93.)
St~n~rd I~nlse Bre~k~nwn Te~t
A standard device, with dimensions of 1 cm2 x l mm was
inserted into the test apparatus shown in Figure 7. Prior tP
testing, the insulation resistance Ri for the device was
measured 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 ~s waveform (i.e. a rise time to maximum
voltage of 10 ~8 and a hal~-height at 1000 ~s) and a current
of at most 1~ 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 rnn~ct~d~ The final insulation resistance
Rf after five cycles for the standard test was measured and
the final resistivity P~ was calculated.
3~ ~r,~;fied T~Ul ge ~re~kdown Te~t
Samples were prepared with electrode spacing varying from
0.25 to 1 mm and were tested following the procedure o~ the
Standard Impulse Breakdown Test.
WO95/33278 2 ~ 9 1 7 4 ~
~ 15
DC ~rG~k~nwn Test
A standard device was inserted into a circuit and was
subjected to a voltage which increased at a rate of 200
volts/second (~ipot Model M1000 DC Tester). The DC breakdown
Wcl8 recorded as the voltage at which 5 milliamps of current
began to flow through the device.
TABLE I
Al F ller
Polymer ~iZ~ Vol. 1~9~ f I~
t~m) % (Q~ tQ) ~Y~
1 Silicone gel 1 20 40 0 I1 1012 1012100
2 Thermoplastic gel 20 35 1 I1 1012 1012100
3 Silicone grease 20 26.4 I1 1012 ~105 4
4 Silicone gel 2 20 40.0 I1 101~ ~105 46
Fpoxy 20 26.4 D* 101~ ~105 15
6 Silicone gel 1 1-5 45.6 I2,D
7 Silicone gel 1 1-5 40.0 I2
8 Silicone 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**
Nc)tes to Table:
Silicone gel 1 was a mixture of 0.8 parts of a first
composition composed of 26% ~y weight Nusil Ply~ 7520 CS 170
divinyl t~rmln~t~ polydimethylsiloxane (available from
McGhan-Nusil), 73 88~ Carbide L45/50 CS polydimethylsiloxane
silicone fluid diluent (available from Union Carbide), 0.1%
Nusil Cat~ 50 catalyst (3 to 4% platinum in silicone oil,
available from McGhan-Nusil), and 0.02% T2160 inhibitor
(1,3,5,7-tetravinyltetramethylcyclotetr~R;ln~n~, available
WO95/33278 2 1 9 1 7 4 0 F~l/~ 5'~-~C7
16
from Huls~ and 1.0 parts of a second composition composed of
26~ by weight Nusil Ply~ 7520 CS 170 polydimethyl~ Y~nP,
73.91~ Carbide L45/50 CS s;l;cnn~ iluid diluent, and 0.9
T1915 tetrakisdimethylsiloxysilane crosslinking agent
(available ~rom Huls).
Thermoplastic gel ~ntA;nP~ lO~ by weight Septon~ 4055
styrene-(ethylene/propylene)-styrene block copolymer having
an ethylene/propylene midblock and a molecular weight of
308,000 (available from ~uraray), 87.5~ Witco~ 380 extender
oil (available from Witco), and 1~ Irganox~ BgO0 ~nt;~ nt
(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 ~nder its own weight.
Silicone gel 2 was SylGard~ Q3-6636 silicone dielectric
gel (available from Dow Corning).
Epoxy was ACE~ 1861~ 5-minute epoxy (available from Ace
Hardware Stores).
Aluminum powder with an average particle size of 20
microns and a subst~nt;~lly spherical shape was product type
26651, available from Aldrich Chemicals.
Aluminum powder with an average particle size of 1 to 5
microns (pasaed 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.
~ les 15 to 18
To determine whether compositions of the invention would
remain in a conducting 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 oi the type
described in the Standard Impulse Breakdown Test above. After
the discharge the fi~al resistance was meaAured. A device was
deemed to have latched i~ the final resistance was less than
W09~33278 , 2 1 9 1 740
~ 17
105 ohms. The approximate spacing between particleu was
calculated using the formula ~ = 4(1-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 ~hether the composition latched was a function of both the
E~article size and lQading of the particles. The 20 micron
aluminum 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~ntl~lly
lo ~pherical.
TABLE II
~1 F:ller Interp~rticle
~l~m~ ~iZ~ Y~ Sk~ Spac~ng
(~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
., ,
