Note: Descriptions are shown in the official language in which they were submitted.
~3~ 7
MP0859
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BACXGROUND OF THE INVENTION
Field of_the Invention
This invention relates to fabrics having useful
electrical properties.
Introduction to the Invention
Compositions which have a positive temperature
coefficient of resistance (nPTC compositions") are
known. They can be composed of ceramic material, eg. a
doped barium titanate, or a conductive polymer material
eg. a dispersion of carbon black or other particulate
conductive filler in a crystalline polymer. The term
PTC is generally used (and is so used in this specifi-
cation) to denote a composition whose resistivity pre-
ferably increases by a factor of at least 2.5 over a
temperature range of 14C or by a factor of at least 10
over a temperature range of 100C, and preferabIy both.
The term switching temperature (or Ts) is generally used
~and is so used in this specification) to denote the
temperature at which a sharp increase in resistivity
takes place, as more precisely defined in U.S. Patent
No. 4,237,441. Materials, in particular conductive
polymer compositions, which exhibit zero temperature
coefficient~(ZTC) behavior are also known~ In electri-
cal devices which contain a PTC element and a ZTC ele-
ment, the term ZTC is generally u~ed (and is so used inthis specification) to denote an element which does not
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exhibit PTC behavior at temperature below the Ts of the
PTC element; thus the ZTC eLement can have a resist1vity
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which increases relatively slowly, or which is substan-
tially constant, or which decreases slowly, at tempera-
tures below the Ts of the PTC element. Materials, in
particular conductive polymer compositions, which exhi-
bit negative temperature coef~icient (NTC) behavior are
also known. For further details of conductive polymer
compositions and devices comprising them, reference may
be made for e~ample to U.S. Patents Nos. 2,952,761,
2,978,665, 3,243,753, 3,351,882, 3,571,777, 3,757,086,
3,793,716, 3,823,217, 3,858,144, 3,861,029, 4,017,715,
4,072,848, 4,085,286, 4,117,312, 4,177,376, 4,177,446,
4,188,276, 4,237,441, 4,238,812, 4,242,573, 4,246,468,
4,250,~00, 4,255,698, 4,242,573, 4,271,350, 4,272,471,
4,276,466, 4,304,987, 4,309,596, 4,309,597, 4,314,230,
4,315,237, 4,318,881, 4,330,704, 4,334,351, 4,352,083,
4,361,799, 4,388,607, 4,398,084, 4,413,301, 4,425,397,
4,426,,339, 4,426,633, 4,427,877, 4,435,639, 4,429,216
and 4,442,139, J. Applied Polymer Science 19, 813-815
(1975), ~lason and Xubat; Polymer Engineering and
Science 18, 649-653 (1978), Narkis et al; German OLS
Nos. 2,634,999, 732,792, 2,746,602, and 2,821,799; and
European published patent application Nos. 38,713,
38,714, 38,718, 63,440, 67,679, 68,688, 74,281, 87,8~4,
92,406, 96,492, 84,302,717.8, 84,301,650.2 and the
European application$ corresponding to ~anadian Serial Nos.
~67,265 and 463,796.
SUMMARY OF THE INVENTI N
There are serious limitations in the known tech-
niques for making electrical devices which contain PTC
and/or ZTC elements composed of ceramic or conductive
polymer materials. Ceramic materials are brittle and
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MP0859
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are difficul~ to shape, particularly when large or
complex shapes are needed. Conductive polymers can be
manufactured in a wider variety of shapes, but espe-
cially with PTC materials, close control is needed to
ensure adequate uniformity; it is yet more difficult, if
not impossible, to produce a predetermined variation in
properties in different parts of an article. In addi~
tion, the physical strength of laminar conductive
polymer devices is often less than is desirable. When a
heat-shrinkable PTC conductive polymer article is
required, there is the difficulty that when a PTC con-
ductive polymer sheet is rendered heat-shrinkable (by
stretching the cross-linked sheet above its melting
point and then cooling it in the stretched state), the
PTC of the heat-shrinkable sheet is often substantially
smaller than that of the original sheet; this limits the
stretch ratio that can be employed and, therefore, the
available recovery.
We have now discovered that improved PTC devices
~ can be prepared by incorporating at least one of the
electrodes into a fabric. Thus in one aspect, the
invention provides a fabric which is suitable for use
as an electrical heater and which comprises an
ordered array of interlaced elongate elements, said
fabric comprising (1) a first elongate electrode
which forms at least part of one of said interlaced
elongate elements; (2) a second electrode; and (3) a
PTC element through which current passes when the
first and second electrodes are connected to a source
of electrical power.
,
Particularly useful devices can be prepared by
making use of an ~longate element which comprises an
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MP0859
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elongate electrode and a resistive element which
electrically surrounds the electrode; this elongate
element is converted into a fabric which can be
incorporated into an electrical system or device. A
wide range of such elongate elements can be easily
produced in a uniform manner, and through the use of
known fabric-manufacturing techniques, such as
weaving, knitting and braiding, they can be converted
into fabrics which are completely uniform or which
vary in a desired predictable way. Other elongate
elements can be included ln the fabric to provide or
enhance desired properties such as strength or heat-
recoverability or other thermally induced response.
In a preferred embodiment, the invention provides
an electrical device which comprises
(1) a first elongate element which comprises
(i) a first elongate electrode and
(ii) a first PTC element, preferably an
elongate PTC conductive polymer element;
~ and
(2) a second electrode which is spaced apart
from the first electrode;
the first and second electrodes being connectable
to a source of electrical power to cause current to
pass through the PTC element; and the first elongate
element forming part of a fabric in which the first
elongate element is interlaced with at least one other
elongate element to form an ordered array of interlaced
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~23~ MPO859
elongate elements. In one preferred embodiment o~ such
devices, the PTC element ~which may be a single elongate
PTC element or a plurality of discrete PTC elements
spaced apart along the length of the electrode) electric-
ally surrounds the first electrode, i.e. the device isso constructed and arranged that, when the electrodes
are connected to a power source, substantially all the
current passing between the electrodes passes through
the PTC element, at least at some temperatures between
room temperature and the equilibrium operating temperature
of the device, and preferably at all temperatures. In
another preferred embodiment, the device comprises a
third electrical element, preferably a ZTC conductive
polymer element, through which current flows when the
electrodes are connected to a power source; preferably
substantially all the current passing between the
electrodes passes through the third electrical element,
at least at some temperatures between room temperature
and the equilibrium operating temperatures of the
device, and preferably at all temperatures.
Particularly useful devices are those which comprise
an element, preferably a non-conductive element, which
is thermally responsive and which is heated when
current is passed through the device. Such devices can
~5 be recoverable, either as a result of passing current
through the device or as a result of some other action.
For example, very useful heat-shrinkable articles
comprise a~woven fabric comprising spaced apart first
and second elongate electrodes running in one direction,
and heat-shrinkable non-conductive elongate elements
running in the other direction, the fabric being
impregnated or coated with a heat-softenable ZTC
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~3~7
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conductive polymer. When the article is powered, the
heat generated by Joule heating causes the ZTC material
to soften and the non-conductive elements to shrink,
thus shrinking the fabric in the direction of the
non-conductive elements and drawing the electrodes
closer together.
The invention also includes processes in which a
recoverable ~abric of the invention as described
above, especiall~ one containing non-conductive heat-
shrinkable filaments in the fabric, is used to cover a
substrate, the process comprising:
~,
(A) placing the fab~ic adjacent the substrate;
(B) recovering ~he fabric against the substrate, and
(C) passing current between the electrodes to effect
a desired change in the non-conductive element.
Step (C) can be carried out before, simultaneously
~lth, or after, step (B), and the recovery of the
faDric can be effected by passing current between the
eiectrodes or by some other means.
In another embodiment, the PTC element is a
substantially continuous laminar element which is com-
posed of a conductive polymer.
BRIEF DESCRIPTION OF THE DRAWING
The invention is illustrated in the accompanying
drawing, in which the Figures are diagrammatic, partlal,
.
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--7--
cross-sectional views of devices of the invention; in
particular,
Figure 1 is a side view of a heat-shrinkable device;
Figure 2 is a side view of the device of Figure 1
after it has been powered to effect shrinkage;
Figure 3 is a plan view of the device of Figure 1,
Figure 4 is a side view of another heat-shrinkable
device;
Figure 5 is a plan view of a device similar to
that shown in Figure 1 and 2, but in which the
electrodes are differently arranged and the ZTC
element coats but does not fill the fabric;
Figure 6 is a side view of ~another device similar
to that shown in Figures 1 and 2 but in which one
lS of the electrodes is woven into one fabric and the
other electrode is woven into another fabric, and
the two fabrics are secured together by the ZTC
element7
Figure 7 i5 a side view of a device similar to
that shown in Figure 1 in which only one of the
electrodes~is coated with a PTC element; and
Figure 8 is a side view of another device of the
invention. : ~ :
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MP0859
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DETAILED DESCRIPTION OF THE INVENTION
The invention will chiefly be described herein
by reference to the preferred devices of the inven-
tion, in which there are two (or more) electrodes, at
least one of the electrodes being an elongate
electrode forming part of an elongate element which
(i) comprises the electrode and a PTC conductive
polymer element electrically surrounding the
electrode and tii) forms part of the fabric.
However, the invention includes similar devices in
which some other type of PTC element electrically
surrounds the electrode (provided of course that it
permits conversion of the element into the fabric).
In addition~ the invention includes fabrics
comprising at least one elongate element which
comprises (a) an elongate metal element and (b) a
conductive polymer element which substantially
; surrounds the elongate metal element~and which may be
ZTC or NTC element, fox example such a fabric which
further comprises another electrode which is electri-
cally separated from the first electrode not only by
the ZTC or NTC element but also by a PTC element,
preferably a conductive polymer PTC element. It
shouId be understood, therefore, that the following
detailed description also applies, mutatis mutandi~,
to such other embodiments of the invention.
In;the preferred devices of~the invention, at lea~t
one of~the electrodes is an elongate electroder usually
of metal,~e.g. copper or nickel-coated copper, for
exampLe a solid or ~tranded wire, which i~ electriaally
: :
surrounded by~a PTC conductive~polymer element. Usually
the PTC element will~be melt-shaped,~ preferably melt-
extruded, preferably so that it physlcally surrounds
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MP0~59
_g_
the electrode as a uniform coating throughout its
length. However, other methods of formillg the PTC ele-
ment, e.g. dip-coating, and other geometric arrange-
m~nts, are possible. For example the PTC element can
vary in thickness and/or resistivity radially and/or
longitudinally. Alternatively, the PTC element can
alternate radially and/or longitudinally with polymeric
elements which are electrically insulating or which have
a resistance which is much higher than the resistance of
the PTC element at room temperature, so that at least
when the device is at relatively low temperatures,
substantially all the current between the electrodes
passes through the PTC element (it is to be noted that
the broad definition of the devices of the invention
does not exclude the possibility that at temperatures
close to and above the Ts of the PTC element, a substan-
tial part of the current does not pass through the PTC
element). The PTC element can be in direct physical
contact with the electrode or can be separated therefrom
~ by a layer of ZTC material, for example a low resisti-
vity conductive polymer. The dimensions of the PTC ele-
ment and the resistivity and other properties of the PTC
composition should be correlated with the other elements
of the device, but those skilled in the art will have no
~5 difficulty, having regard to their own knowledge ~e.g.
in the documents referenced herein) and the disclosure
herein, in selecting suitable PTC elements. Suitable
polymers include polyethylene and other polyolefins;
copolymers of one or more olefins with one or more polar
comonomers e.g. ethylene/vinyl acetate, ethylene/acrylic
acid and ethylene/ethylacrylate copolymers; fluoropoly-
mers, e.g. polyvinylidene fluoride and ethylene/tetra-
fluoroethylene copolymers; and polyarylene polymers,
~23~5~'7
MP0859
--10--
e.g. poly~ther ketones; and mixtures o~ such polymers
with each other and/or with elastomers to improve their
physical properties.
~The other electrode in the preferred devices is
preferably another elongate electrode which forms
part of the same fabric as the first elongate element
(as is usually preferred) or part of a different
fabric. The second electrode can be the same as or
different from the first electrode. Electrical contact
between the first and second electrodes can be achieved
in any suitable way. For example, the second electrode
can be in contact with the first PTC element; or it can
be electrically surrounded by a second PTC element
which has the same Ts as the first PTC element and
is in physical contact with a third electrical element
as described above; or it can be in direct physical
contact with a third electrical element as described
above. Alternatively the second electrode can be an
elongate electrode which is not interlaced to form part
~ of a fabric, or it can be a laminar electrode, e.g. a
metal foil, apertured metal, or vapor-deposited metal
electrode.
The third electrical element, when present (as
is preferred), preferably comprises a ZTC conductive
polymer. It can be of uniform composition or can
comprise diqcrete sub-elements; for example it may be
desirable to coat an electrode or a PTC element sur-
rounding an electrode with a first ZTC conductive
polymer in order to provide imProved electrical and
physicaI contact to a second ZTC conductive polymer.
The third electrical elemen~ can ~ill or bridge the
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MPO859
interstices of the fabric(s), thus providing a con-
tinuous laminar element. Alternatively, the third
electrical element can be coated onto the fabric(s)
so that apertures remain in the fabric. In another
embodiment, part tor all) of the third electrical
element is provided by an elongate element which is
interlaced with at least one other elongate element
to form part of the fabric(s), with the remainder (if
any) of the third element being coated on or other-
wise united to the fabric to provide desired electri-
cal contact between the elongate elements. The third
electrical element can be thermally responsive, e.g.
heat-shrinkable. The dimensions of the third
electrical element and the resistivity and other pro-
perties of the ZTC conductive polymers preferablyused for it should be correlated with the other ele-
ments of the device, but those skilled in the art
will have no difficulty, having regard to their own
knowledge (e.g. in the documents referenced herein)
and the disclosure herein, in selecting suitable ZTC
elements. When the device is recoverable, the ZTC
element preferably has low viscosity at the recovery
temperature so that it impedes recovery as little as
possible. Suitable polymers for the ZTC material
include copolymers of ethylene with one or more polar
copolymers, e.g. ethyl acrylate and vinyl acetate.
The first elongate element (and the other elongate
elements) can be ormed into a fabric by any method
which results in an ordered array of interlaced elongate
elements. Weaving is the preferred method, but
knitting, braiding etc. can be used in suitable cases.
The density of the weave (or other form of interlacing)
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~3~ 7 MPo85 9
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can be selected in order to provide the desired power
output or shrinkability (when the fabric incorporates
shrinkable elements as described below) or other pro-
perty. Similarly, the density of the weave can be
varied from one area to another to provide a desired
variation, egO of at least 10~ or at least 25~, in one
or more properties from one discrete area (which may be,
for example, at least 5~ or at least 15% of the total
area) to another. Triaxial weaving can he employed.
In order to pass current through the device, the
electrodes must of course be connected to a power
source, which may be DC or AC, e.g. relatively low
voltage, e.g. 12, 24 or 48 volts. The various com-
ponents of the device must be selected with a view to
the power source to be employed. When the electrodes
are elongate electrodes, they may be powered from one
end or from a number of points along their lengths; the
former is easier to provide, but the latter results in
more uniform power generation.
2~ The device may include, at least in selected areas
thereof, a non-conductive element which provides desired
properties, particularly a non-conductive element which
is thermally responsive and which is heated when current
is passed between the electrodes~ or a non-conductive
element, e.g. of glass fibers, which provide stiffness
or other desired physical properties. The non-
conductive element can be, for example, a heat-
recoverable, e.g. heat-shrinkable, element. Such
heat-recoverable elements can for example be composed of
an organic polymer (which can be cross-linked) or a
memory metal alloy. Other useful thermally responsive
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MPO859
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members include a layer of a hot melt adhesive or a
mastic; a thermochromic paint; or a component which
foams when heated. The non-conductive element can be an
elongate element which forms part of the fabric(s)
incorporating the elongate electrode(s), e.g. a con-
tinuous monofilament or multifilament yarn or a staple
~iber yarn. Suitable heat-shrinkable elements can be
composed of, for example, a polyolefin, e.g. high,
medium or low density polyethylene; a fluoropolymer,
e.g. polyvinylidene fluoride; a polyester, e.g. poly-
ethylene terephthalate or poly butylene terephthalate;
or a polyamide, e.g. Nylon 6, Nylon 6~6, Nylon 6, 12,
Nylon 11 or Nylon 12. The element is preferably capable
of unrestrained recovery to less than 50%, preferably
less than 35~, especially less than 25% of its stretched
dimension.
An especially preferred embodiment of the invention
is a heat-shrinkable device which is useful, for
example, for protecting ~oints between elongate sub-
strates such as telephone cables, and which comprises:
(1) a first elongate electrode which comprises
(i) a first elongate electrode composed of
metal and
(ii) a PTC element composed of a PTC
conductive polymer composition;
(2) a second elongate element which comprises
a second elongate electrode composed of
a metal;
MPO859
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(3) a heat-shrinkable elongate element which
shrinks when heated to a temperature TShrink
and which is composed of an electrically
insulating polymeric composition;
said first, second and heat-shrinkable elongate elements
having been woven together to form a fabric; and
~4) a ZTC electrical element which is composed
of a ZTC conductive polymer composition;
the first and second electrodes being connectable to a
source of electrical power to cause current to flow
through the ZTC element and to cause shrinkage of
the heat-shrinkable element, and the PTC element
being positioned so that, when the electrodes are
connected to a power source, suhstantially all the
current passing between the electrodes passes through
the PTC element.
The first and second elements generally run in one
direction in the fabric (which may be the warp or the
weft, depending on the ease of weaving), with the heat-
shrinkable element running at right angles thereto. Thisenables the first and second elements to accommodate to
shrinkage of the heat-shrinkable element by moving
closer together, without longitudinal shrinkage.
The first and second elements can be powered from
one end, in which case they will normally have a
serpentine shape. Alternatively the fabric can be
woven so that the electrode is or can be exposed at
regular inter~a1s along th~ fabric, g each time it
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MPO859
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changes direction, thus permitting the exposed ends to
be bussed together by some bussing means which
permits the desired shrinkage to take place. Generally,
the exposed ends of the first electrodes will be ioined
5 together along one edge of the fabric and the exposed
ends of the second electrode will be joined together
along the opposite edge of the fabric.
In these devices, it is important that the heat
generated in the conductive polymer elements is sufficient
to raise the heat-shrinkable elements to their shrinkage
temperature. In order to ensure that there is adequate
heating of the ZTC element before the PTC element shuts
off, it is preferred that the resistance of the ZTC
element is greater than, preferably at least 1.2 times,
the resistance of the PTC elementts~ at all temperatures
between 0C and TShrink. When the ZTC element forms
a continuous laminar element (as is usually preferred
in order to protect the substrate against which the
device is to be recovered), this usually means that the
resistivitv of the ZTC composition is greater than,
preferably at least twice, the resistivity of the PTC
composition at all temperatures between 0C and
Tshrink.
In these devices, it is preferred that the PTC con-
ductive polymer composition has a first resistivity
and comprises a first polymeric component which con-
tains at least 50~ by volume of a crystalline polymer
having a fi~st melting point Tl, the ZTC conductive
polymer composition comprises a polymeric component
which contains at least 50% by vblume of a thermoplastic
polymer having a softening point T2 and a resistivity
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~3~5~
MPO859
-16-
e2; wherein
Tl > Tshrink > T2,
and
~2 ~ el at all temperatures between
0C and Tshrink-
It is also preferred that (Tl-T2) is at least
30C, particularly at least 50C, and that (Tl~Tshrink)
is at least 10C, preferably at least 20C. We have
obtained good results when the polymer in the PTC com-
position is polyvinylidene fluoride, the polymer in theZTC composition is a copolymer of ethylene, eg. an
ethylene/ethyl acryIate polymer, and the heat-
shrinkable element comprises polyethylene.
.
The thermal properties of the device and of the
surroundings are important in determining the behavior
of the device. Thus the device can comprise, or be used
in conjunction with, a thermal element which helps to
spread heat uniformly over the device, eg. a metal foil
layer, or which reduces the rate at which heat is removed
from the device, eg. a layer of tbermal insulation such
as a foamed polymer layer.
Referring now to the drawingl Figure 1 is a partial
cross-sectional side view of a device of the invention,
showing electrodes l of one polarity, each surrounded by
a PTC conductive polymer element 11, and parallel
electrodes 2 0f~opposite polsrity, each surrounded by a
PTC conductive polymer elsment 21. The electrodes are
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woven into a fabric with heat-shrinkable non-conductive
filaments 4 at right angles to the electrodes, and the
fabric is impregnated or coated with ZTC conductive
polymer element 3.
Figure 2 is a partial cross-sectional side view of
the device of Figure 1 after it has been powered to cause
sbrinkage of the filaments 4 and softening of the ZTC
element 3.
Figure 3 is a partial cross-sectional plan view of
a device as shown in Figure 1. The electrodes 1 are
connected at one end to a bus bar connector 12 which
runs along one edge of the fabric and does not prevent
shrinkage of ~he filaments 4 when they are heated.
Similarly the electrodes 2 are connected at one end to
a bus bar connector 22 which runs along the opposite
edge of the fabric and does not prevent shrinkage of
the filaments 4 when they are heated. The ZTC element
3 completely fills the interstices of the fabric.
Figure 4 is similar to Figure 1 and shows the same
elements 1, ~, 3, 4, 11 and 21, and in addition shows
elongate elements 6 which are woven into the fabric
parallel to the PTC elements and are composed of a hot
melt adhesive 15 which melts at the shrinkage tempera-
ture of the filaments 4. Also shown in Figure 4 is an
electrically insulating polymeric backing 7 which
softens at the shrinkage temperature of the filaments 4.
Figure 5 is a partial cross-sectional plan view of
another device of the invention which is similar to
that shown in~Figures l and 3, but in which the electrodes
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~:34~97
-18-
follow a serpentine path and are powered from one end,
and the ZTC element 4 coats the fabric but does not
fill its interstices r leaving a plurality of voids 41.
Figure 6 is a partial cross-sectional side view
of another device of the invention which is similar to
that shown in Figures 1 and 2 except that the electrodes
1 are woven into one fabric with half of the heat-shrink-
able filaments 4, while the electrodes 2 are woven into
a second fabric with the other half of the heat-shrinkable
filaments 4. The fabrics are secured to each other by
the ZTC conductive polymer element.
Figure 7 is a partial cross-sectional side view of
another device of the invention which is very similar
to that shown in Figure 1 but in which there is no
lS PTC coating around the electrodes 2.
Figure 8 is a partial cross-sectional side view of
another device of the invention which comprises electrodes
1 and 2 embedded in a PTC element 11 to form a self-
limiting strip heater preferably having an outer
insulating jacket (not shown). The strip heater is
woven into a fabric with heat-shrinkable Eilaments 4.
For further details of techniques for preparing fabrics
and for using heat-shrinkable ~abric materials, and of
heat-responsive materials which can be incorporated into
or form part of fabrics, reference may be made to Canadian
Patent Application Nos. 444,701; 444,695; 444,700; 444,698;
444,691; 444,697; 444,696 and 461,077 (Case Nos. RK 167, 176,
177, 178, 179, 181 and 205, and MPO790) filed by Raychem
Limited on
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January 6, l983 and August 16, 1983 and Application No.
~48,547 filed by N.V. Raychem S.A. on March 1, 1983,
Case No. BO89.
The invention is illustrated by the following
Example.
EXAMPLE
A satin weave fabric was prepared using the
following elongate elements:-
1. a 24 AWG (diameter 0.064 cm) nickel-coated copper
stranded wire conductor having a uniform melt-extruded
coating thereon, about 0.008 inch (0.02 cm) thick, of a PTC
conductive polymer composition which had a resistivity of
about 40 ohm.cm at 25C and over 500 ohm.cm at 130C, and
which comprised carbon black dispersed in polyvinylidene
fluoride,
2. a monofilament which is about 0.01 inch (0.025 cm) in
diameter and which is composed of a polyamide hot melt
adhesive; and
3. a high density polyethylene about 5 grams per denier
monofilament which had been drawn down about 20 to 30 times
immediately after extrusion, and which was therefore
heat-shrinkable, with a TShrink Of about L28C~
The weft of the fabric was~composed of elements (1) and
(2), there being three elements (2) between each of the
elements (1), and the elements ~1) being 0.3 inch (0.76 cm)
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-20- ~ ~34597 MPO859
apart (center-to-center). The warp of the fabric was com-
posed of elements (3) at a frequency of 72 filaments per
inch.
The fabric was then irradiated to a dosage of 12-17
Mrad; thus cross-linking PTC conductive polymer and the
polyethylene.
The irradiated fabric was laminated under heat and
pressure to a 0.03 inch (0.076 cm) thick sheet of a conduc-
tive polymer composition which had a resistivity of about
80 ohm.cm at 25C and about 200 ohm.cm ak 140C [i.e. it
was ZTC compared to the PTC composition of element (1)],
and which comprised carbon black dispersed in a very low
crystallinity ethylene/ethyl acrylate copolymer. At the
same time, the opposite face of the fabric was laminated to
lS a 0.011 inch (0.028) thick layer of an insulating polymeric
composition.
The resulting product had a cross-section similar to
that shown in Figure 4. The electrodes followed a
serpentine pattern similar to that shown in Figure 5.
When the electrodes were connected to a 36 volt DC
power source, the fabric heated to a temperature of about
130C, at which temperature the polyethylene filaments had
reached their shrinkage temperature, and the hot-melt adhe-
sive filaments and ZTC layer had softened; the fabric
therefore shrank in the transverse direction to about 33%
of the original transverse dimension.
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