This invention relates to insulated electrical conductors which can
be used as interconnecting or hookup wire or as components of multiconductor cables.
Many performance criteria are important in an insulated electrical
wire. A number of such criteria that are especially important in the aircraft
industry, include weight and space; arc-track resistance; abrasion and cut-through
resistance; temperature rating; flexibility and stiffness; smoke generation and
flammability; and chemical resistance.
The relative importance of these criteria varies with the particular
application, and it may not be possible to have one insulation system that is the
best in all respects. For example, good abrasion resistance and high cut-through
resistance are usually obtained with high modulus materials, whereas better flexibility
and low-springback generally require low modulus materials. Consequently, insulation
systems offer different balances of properties, excelling in different respects.
In the effort of researchers to find a better balance of properties,
two main approaches have been followed. First, effort has been devoted to the
development of new or modified materials with improved insulating properties. In
this regard, fluoropolymers and polyimides have been widely used. Secondly, combinations
of materials have been evaluated in attempts to realize in the composite the better
properties of the various components. For example, braided fibers have been used
as an external jacketing to improve mechanical properties and protect underlying
Representative of such previous effort is British Patent 1 177 471,
which shows a cable with an inner insulating layer of polycarbonate or polyphenylene
oxide and an outer layer of polyvinylidene fluoride with an optional interposed
braid which preferably is impregnated with a flame retardant, e.g. a paste based
on a highly halogenated wax.
Despite many earlier attempts to develop insulating systems, a need
exists to satisfy the demands of increasingly complex electrical and electronic
systems used in industrial and aerospace applications.
The present invention provides a wire construction that exhibits
an outstanding balance of performance characteristics, including weight and space;
arc-track resistance; abrasion and cut-through resistance; temperature rating;
flexibility and stiffness; smoke generation and flammability; and chemical resistance.
This construction can be used by itself, as the core of a more elaborate single-wire
construction, or in multiconductor cables.
Specifically, the instant invention provides a wire construction
comprising a metallic electrically conductive core, a first insulation layer surrounding
the conductive core, an impregnated fiber braid surrounding the first insulation
layer, and a second insulation layer external to the fiber braid which second insulation
layer is a fluoropolymer, characterized in that the first insulation layer is
a fluoropolymer or a polyimide film having a fluoropolymer on one or both of its
surfaces, the fiber braid consists essentially of at least one polymeric material
selected from the group consisting of polyaramid, PTFE and polyimide, and is impregnated
with fluorocarbon resin, and the first polymeric insulation layer, the resin impregnant
and, thus, the fiber braid and the second polymeric insulation layer are fused.
The electrically conductive core of the present invention can be
prepared from a wide variety of known materials which meet the temperature rating
of the wire or the process temperature requirements for application of the insulation.
Typical of those which can be used are copper, either alone or plated, to prevent
oxidation of the copper, with tin, silver, nickel, silver-nickel or other metals,
depending on end use temperature requirements. The conductive core can be either
solid, i.e., a single strand of metal, or multi-stranded. Multi-strand structures
are preferred in the present invention. While the number of strands will vary
with the specification and conductor size, a strand count of nineteen is common.
The size of the conductive core can vary widely, but is typically
in the range American Wire Gauge (AWG) of about from 30 to 10. For 19-strand conductors,
AWG 30 has a diameter, of about 0.3 mm (0.0124 inch) and AWG 10 has a diameter
of about 2.8 mm (0.111 inch).
The first insulation layer on the conductive core is a fluoropolymer
having electrical insulating characteristics suitable for the application to which
the insulated wire is intended. A wide variety of fluoropolymers can be used in
the present invention, including non-melt-fabricable polymers of tetrafluoroethylene
(TFE) such as polytetrafluoroethylene (PTFE) and polymers of TFE with up to 1%
of a modifying comonomer.
Melt-fabricable fluoropolymers which can be used include PFA (a copolymer of TFE
with one or more perfluoroalkyl vinyl ethers); FEP (copolymer of TFE and hexafluoropropylene);
melt fabricable copolymers of TFE, perfluoroalkyl vinyl ethers (PAVE), and one
or more additional monomers including HFP; ETFE (copolymers of ethylene (E) and
TFE), usually incorporating minor amounts of one or more modifying comonomers
such as hexafluoroacetone, perfluorobutyl ethylene, hexafluoroisobutylene, PAVE,
or HFP; copolymers (ECTFE) of E and chlorotrifluoroethylene (CTRE), also with
modifying comonomers; and polyvinylidenefluoride.
Polyimides can also be used for the first insulation layer which
polyimide films have a fluorocarbon polymer such as FEP, PFA, or ETFE on one or
both surfaces as a melt adhesive. Polyimide films which can be used include those
commercially available from the Du Pont Company as "Kapton®" polyimide film.
The thickness of the first insulation layer can vary widely, depending
on the size of the core and the desired degree of insulation. For example, for
AWG 22, a thickness of about from 0.013 to 0.13 mm (0.5 to 5 mils) is typically
If the material used for the first insulation layer is in the form
of thin film tape, a surface treatment can be used to place it in a category known
as cementable film. The choice of the specific material for the first insulation
layer, as for the other components to be described below, will be governed by
the balance of electrical, mechanical, thermal, and chemical properties desired
in the final construction, dimensional and weight constraints considered.
The first insulation layer can be applied by any of several techniques
known to those skilled in wire construction operations. An especially convenient
way to apply a thin layer is to use the resin in the form of thin film tape and
wrap the tape helically around the conductor, with a predetermined amount of overlap.
The first insulation layer can also be formed by extrusion techniques, or by depositing
resin from dispersions and removing the carrier fluid.
A fusion step can be used to achieve sufficient integrity for the
first insulation layer to withstand subsequent processing steps. This can be accomplished
by heating the layer to a temperature above the melting point of the resin.
The next layer of the present constructions, the braid of high strength
fibers, is applied directly over the first insulation layer by braiding techniques
well known in the art. Fibers which can be used for this component include polyaramid,
PTFE and polyimide, for example, high strength fibers of PTFE; and polyaramids,
such as those commercially available from the Du Pont Company as "Kevlar®"
aramid fiber. The braid can be made from fibers of single type, or a mix of fiber
types can be used in the braid construction.
In some cases, it may be desirable to treat the surface of the fibers
to promote the formation of a bond between the fibers and other materials used
in the present construction. For example, PTFE fibers can be treated by sodium
etching or other techniques known to produce a bondable surface. One etchant material
which can be so used is TetraEtch, commercially available form W. L. Gore &
The fiber braid is impregnated with one or more fluoropolymers to
facilitate a void-free construction and the bonding of the layers in the final
construction. The polymer can be applied to the fiber braid in the form of an aqueous
dispersion or organosol of the fluorocarbon polymer resin, or with a polymer solution.
Volatile components of the dispersion or organosol are then removed. Partial fusion
of the fluorocarbon resin particles to each other and/or to the fiber braid can
be accomplished, if desired, by heating the resin particles above their melting
point for a short time. Fluorocarbon polymers which can be used for impregnating
the fiber braid include dispersion forms of the fluorocarbon polymer resins discussed
above as useful for the first insulation layer. Mixtures of certain resin dispersions
might also be useful.
The quantity of the polymer used to impregnate the braid can vary
widely, depending on the thickness and construction of the braid.
In one alternative method of preparing the conductive structures
of the present invention, the braid can be prepared from a high strength fiber
yarn as defined above which has been impregnated with a polymer resin as defined
above prior to braiding over the first insulation layer.
The second insulation layer in the present constructions can be selected
from the same polymers discussed above for the first insulation layer. The second
insulation layer can be the same as or different from the first.
The second insulation layer can be pigmented to achieve a color of
choice or specification, or may incorporate a filler to achieve various purposes.
If the second insulation layer is a polyimide as defined above, a pigmented overcoat
of fluorocarbon polymer dispersion or organosol or of polyimide solution can be
The second insulation layer can be applied over the fiber braid by
wrapping thin film tapes or by extrusion according to the techniques used for the
first insulation layer. The thickness of the second insulation layer will typically
be the same as the first insulation layer.
The composite construction is usually fused by heating the construction
above the melting point of the thermoplastic components used in the construction.
This step enhances the sealing of the braided fibers by the resin impregnant and
promotes a melt bond to the first and second insulation layer to achieve an integral
The resulting composite structure is non-wicking to fluids. Fusion
in this step, as in the optional partial fusion of the impregnant resin discussed
above, may be at a temperature above or below the melting point of the fibers used
in the braided layer, depending on the choices of materials. However, if PTFE
fibers are used in the braid and no fusion step after braid impregnation is carried
out at a temperature above the melting point of PTFE, then the fibers are preferably
etched as described above, or otherwise surface treated to facilitate bonding.
The final fusion step should also be carried out under conditions
that will achieve wrap-to-wrap sealing of the second insulation layer, if polymer
film tape is used for this component.
The present constructions can also be treated by irradiation to modify
one or more of the components that may be susceptible to crosslinking. Crosslinking
can improve the high temperature properties of some polymers. If desired, irradiation
can be carried out on either the final construction or at an intermediate stage
of the construction. While the level of radiation will vary with the particular
material used, about from 5 to 25 megarads are typically used for ETFE resin without
Many variations can be used within the concept of the present invention,
as will be recognized those skilled in the art. For example, if a thin film tape
is used for an insulation layer, multiple wraps can be applied. It is not necessary
that the first and second insulation layers be of equal thickness. In larger wire
sizes, thicker insulations are frequently desired and the braid can be present
as two or more layers, optionally separated by layer of film.
The materials for the first insulation layer, the fiber braid, the
impregnating resin, and the second insulation layer can be chosen independently
in any combination. However, it will be recognized that in practice certain combinations
will be preferred depending on performance and cost criteria, and certain combinations
might best be avoided because of interactive considerations. The choice of the
impregnating polymer should be made to achieve melt solidification of the components
to a fused composite. For example, a construction rated at 150°C can be made with
ETFE as the material for the first insulation, polyaramid fiber braid with ETFE
dispersion impregnation, and ETFE as the material for the second insulation. Further,
radiation crosslinking of the ETFE in this construction would increase its temperature
rating to approximately 200°C.
Another illustrative combination of materials, to provide a construction
rated at 180°-200°C, is FEP for the first insulation, polyaramid fiber braid with
FEP dispersion impregnation, and FEP for the second insulation. A construction
rated at 260°C can be obtained with a variety of materials, including the combinations
suggested in Table 1.
The constructions of the present invention provide an outstanding
combination of performance characteristics at a low weight and volume. Specifically,
the constructions of the present invention exhibit excellent cut-through resistance
and arc-propagation performance at surprisingly thin wall thicknesses.
The foregoing description, and the following specific Examples, are
not exhaustive, and a wide variety of other combinations within the scope of this
invention will be readily apparent to those skilled in the art. In these Examples
and Comparative Examples, the following test procedures were used.
Two principal tests were used to evaluate the performance of wire
constructions. These are a cut-through test to assess mechanical performance and
an arc propagation test to assess electrical insulating properties.
Cut-through testing was conducted at room temperature (approximately
23°C) and at 150°C according to the procedures of ASTM D-3032.
The arc propagation test is conducted as follows: Using insulated
wires with AWG 20 or 22 conductor, a seven-wire harness is formed with six wires
around the seventh in a symmetrical bundle and tied with nylon ties. A 400-Hertz
rotary 3-phase converter of 15 KVA capacity is connected to one end of the test
harness according to the following pattern. The 1st and 4th outer wires are connected
to Phase A; the 2nd and 5th outer wires are connected to Phase B; the 3rd and
6th outer wires are connected to Phase C; and the center wire of the harness is
connected to neutral (ground). At the other or test end of the harness, the wires
are cut off evenly in a plane perpendicular to the axis of the harness. The test
end of the harness is dipped in graphite powder, forming a potential short (loose
fault). The harness is hung vertically with the test end at the bottom in an electrically
protective vented chamber. A timer is set for power-on duration of 10 seconds.
The power contactor and timer are energized to initiate an arc at the test end
face of the wire harness. The resulting arc will either self-extinguish after the
initial flash or sustain itself until a portion or all of the harness is consumed
or the power is shut off by the timer or manually. When the arc propagates along
the harness, the power is usually removed manually after approximately 3 seconds
to conserve the sample. After the arc has extinguished, the power switches are
opened, the timer is reset, and after approximately 5 seconds power is reapplied
for a second event. If the arc does not propagate along the harness, or propagates
only a short distance, the harness is cut back approximately 2.54 cm (one inch)
from the original end and another test is run on the same harness. This procedure
is repeated until 10 tests have been run on a sample. Arc propagation either on
initial application of power or on reapplication of power is considered a test
EXAMPLES 1-7 and COMPARATIVE EXAMPLES A-E
In Examples 1-7 and Comparative Examples A-E, wire constructions
with AWG 22 stranded conductor were prepared. The materials and construction procedures
used in Examples 1-7 are summarized in Table 2 and the accompanying notes.
In Comparative Examples A-E, the general construction procedures
of Examples 1-7 were repeated, using the materials summarized in Table 3.
The constructions of Examples 1-7 and Comparative Examples A-E were
tested for cut-through and arc propagation, and the results are summarized in
The data relating to Examples 1-4 show superior cut-through resistance
when compared to the constructions of Comparative Examples A-C at comparable wall
thicknesses, or comparable cut-through resistance at significantly thinner wall
thicknesses, while retaining resistance to arc propagation. Examples 6-7 show
substantially increased cut-through resistance over Comparative Example D while
retaining resistance to arc propagation. Examples 5-7 show cut-through resistance
comparable to the outstanding performance of Comparative Example E, and simultaneously
achieve resistance to arc propagation markedly superior to that of Comparative
Example E. In addition, the constructions of the present invention are more flexible
than those of Comparative Example E, which incorporates a high modulus material.
NOTES FOR TABLE 2Note
(a) The PFA film used was Du Pont's "TEFLON®" PFA-fluorocarbon film grade
100CLP20, thickness 0.03 mm (1.2 mil), width 5.6 and 6.4 mm (7/32 and 8/32 inch)
for the first and second insulation layers, respectively. This film is a cementable
(b) The ETFE film used was Du Pont's "TEFZEL®" fluoropolymer film grade
100CLZ20, thickness 0.025 mm (1.0 mil), width 5.6 and 6.4 mm (7/32 and 8/32 inch)
for the first and second insulation layers, respectively. 100CLZ20 is a cementable
(c) Films were helically wrapped with 50% overlap.
(d) The first insulation layer wraps were fused at 327°C for 1.5 minute for
PFA, 288°C for 1.5 minute for ETFE.
(e) The PTFE fiber used was Du Pont's "TEFLON®" TFE-fluorocarbon fiber
in 444 dtex (400 denier) yarn. For Example 1 only, the fiber yarn was sodium etched
with Gore's TetraEtch following the manufacturer's directions.
(f) The polyaramid fiber used was Du Pont's "KEVLAR®" aramid fiber type
49 in 216.5 dtex (195 denier) yarn.
(g) For Example 4, the PTFE and aramid yarns were supplied on separate bobbins.
(h) The fiber yarns were braided onto the wire with a cross-braiding pattern.
Braid thickness was 0.10 mm (4.0 mil) for PTFE, 0.09 mm (3.5 mil) for aramid, and
0.11 mm (4.5 mil) for the PTFE/aramid combination. The PTFE compressed more than
the aramid during subsequent processing.
(i) The PFA dispersion used was Du Pont's "TEFLON®" PFA-fluorocarbon resin
dispersion grade 335.
(j) The ETFE dispersion used was Hoechst's grade ET6425.
(k) PFA dispersion impregnations were cured at 316°C for 10 minutes for Examples
1 and 3, at 349°C for 0.5 minute for Example 2, and by air drying for Examples
4 and 5.
(l) ETFE dispersion impregnations were cured by air drying.
(m) Following the second insulation layer wrap, final cure was at 327°C for
1.5 minute for PFA, 288°C for 1.5 minute for ETFE.
Ein Drahtaufbau, umfassend einen metallenen elektrisch leitenden Kern, eine
erste, den leitenden Kern umgebende Isolationsschicht, ein die erste Isolationsschicht
umgebendes, imprägniertes Fasergeflecht und eine zweite Isolationsschicht außerhalb
des Fasergeflechts, wobei die zweite Isolationsschicht ein Fluorpolymer ist, dadurch
gekennzeichnet, daß die erste Isolationsschicht ein Fluorpolymer oder eine Polyimidschicht
mit einem Fluorpolymer auf einer ihrer oder beiden ihren Oberflächen ist, daß das
Fasergeflecht im wesentlichen aus mindestens einem polymeren Material besteht,
ausgewählt aus der Gruppe, bestehend aus Polyaramid, PTFE und Polyimid, und mit
Fluorkohlenstoffharz imprägniert ist, und daß die erste polymere Isolationsschicht,
das Harzimprägniermittel und daher das Fasergeflecht und die zweite polymere Isolationsschicht
miteinander verschmolzen sind.
Ein Drahtaufbau nach Anspruch 1, worin das erste polymere Isolationsmaterial
im wesentlichen aus einem Fluorpolymer, ausgewählt aus PFA (Copolymer aus TFE und
einem oder mehreren Perfluoralkylvinylethern), PTFE und E/TFE besteht.
Ein Drahtaufbau nach Anspruch 1, worin das Geflecht im wesentlichen aus Polyaramid
Ein Drahtaufbau nach Anspruch 1, worin das Geflecht im wesentlichen aus PTFE
Ein Drahtaufbau nach Anspruch 1, worin das zweite polymere Isolationsmaterial
im wesentlichen aus einem Fluorpolymer, ausgewählt aus PFA, PTFE und E/TFE, besteht.
A wire construction comprising a metallic electrically conductive core, a first
insulation layer surrounding the conductive core, an impregnated fiber braid surrounding
the first insulation layer, and a second insulation layer external to the fibre
braid which second insulation layer is a fluoropolymer, characterized in that
the first insulation layer is a fluoropolymer or a polyimide film having a fluoropolymer
on one or both of its surfaces, the fiber braid consists essentially of at least
one polymeric material selected from the group consisting of polyaramid, PTFE
and polyimide, and is impregnated with fluorocarbon resin, and the first polymeric
insulation layer, the resin impregnant and, thus, the fiber braid and the second
polymeric insulation layer are fused.
A wire construction of Claim 1 wherein the first polymeric insulation consists
essentially of a fluoropolymer selected from PFA, PTFE and ETFE.
A wire construction of Claim 1 wherein the braid consists essentially of polyaramid.
A wire construction of Claim 1 wherein the braid consists essentially of PTFE.
A wire construction of Claim 1 wherein the second polymeric insulation consists
essentially of a fluoropolymer selected from PFA, PTFE and ETFE.
Un agencement de fil métallique comprenant une âme métallique électriquement
conductrice, une première couche d'isolant entourant l'âme conductrice, un guipage
de fibre imprégné entourant la première couche d'isolant, et une deuxième couche
d'isolant externe par rapport au guipage de fibre, l'isolant de ladite deuxième
couche étant un polymère fluoré, caractérisé en ce que la première couche d'isolant
est en un polymère fluoré ou en un film de polyimide portant un polymère fluoré
sur l'une ou chacune de ses deux faces, en ce que le guipage de fibre est essentiellement
constitué d'au moins une matière polymère choisie dans le groupe formé par les
polyaramides, le polytétrafluoréthylène et les polyimides et est imprégné de résine
fluorée, et en ce que la première couche d'isolant polymère, la résine d'imprégnation
et, par conséquent, le guipage de fibre et la deuxième couche d'isolant polymère
Un agencement de fil selon la revendication 1 dans lequel le premier isolant
polymère est essentiellement constitué d'un polymère fluoré choisi parmi un PFA
(copolymère de tétrafluoréthylène avec un ou plusieurs éthers de perfluoroakyle
et de vinyle), le polytétrafluoréthylène, et les copolymères d'éthylène et de tétrafluoréthylène.
Un agencement de fil selon la revendication 1 dans lequel le guipage est essentiellement
constitué de polyaramide.
Un agencement de fil selon la revendication 1 dans lequel le guipage est essentiellement
constitué de polytétrafluoréthylène.
Un agencement de fil selon la revendication 1 dans lequel le deuxième isolant
polymère est essentiellement constitué d'un polymère fluoré choisi parmi le PFA,
le polytétrafluoréthylène et les copolymères d'éthylène et de tétrafluoréthylène.