Note: Descriptions are shown in the official language in which they were submitted.
92
This invention relates to heat recoverable articles
especially to heat shrinkable articles that may be positioned
~ around a cable, pipe, or connector at a joint or splice and
- then caused to heat recover in place to encapsulate the
joint or splice.
There are many applications where it is desirable to
provide a sealing, insulating or protective encapsulating or
enclosing member for elongate objects for example cables or
, pipes. &ch encapsulation is particularly important where
-I 10 pipes or cables are joined or spliced, particularly when a
joint involving a plurality of pipes or cables is involved.
In many instances, the ends of elongate objects (hereinafter
the term cables will be used, although the invention is, of
course, useful for enclosing or encapsulatingpipes, cables, ducts,
conduits and the like elongate substrates especially junctions
; between them) are not conveniently accessible to allow a
tubular sealing member to be placed thereover. To overcome
thiJ shortcoming, clooure members suitable for wrapping around
the elongate objects have been developed. See for example,
U.S. Patent Nos. 3,379,218, issued 23rd April, 1968, to Conde,
l 3,455,336 issued 15th July, 1969, to Ellis or 3,770,556 issued
jl~ 6th November, 1973, to Evans et al. These oo-called "wrap-
,j,:
around" closures can be installed around an elongate member
without acce~s to a free end thereof. There is nevertheless
a significant need for a closure, hereinafter referred to as
a "splice case", suitable for enclosing electrical cable joints
or splices which provides effective environmental protection,
in particula~, for a splice involving more than two
i incoming cable ends and/or splices
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1~i9192
between different si7es of cables but which may be applied without
accesæ to a free end of the cable~
The present invention is directed to a heat-recoverable,
splice case which can, in variou~ embodiments, accommodate a
plurality of cableæ of differing ~ize6, i.e. out~ide diameter,
which can be removed and in ~ome embodiments reapplied to a
spl~ce and which does not require acces~ to a free end of the
cable. The present design i8 not referred to as a "wrap-
around" ~ince it encapsulates a eplice in a somewhat different
iashion irom the aforementioned "wrap-around" closures. In
alternative embodiments the ~nlice case of the present
invention utilizes either a "clam shell" or separate base
plate and cover member design.
In one embodiment the present invention contemplate~ a
; 15 splice ca6e which will recover and encap~ulate a cable or other
splice when subjected to an external heat source, for example
a propane torch or hot air blower.
Many applications for spli¢e case~ invol~e on ~ite use,
where the ~plice is relatively inaccessible or i8 in a
I 20 potentially haxardous environment, and great care must be
; taken in installing the splice case.
Por example, in the connexion of overhead telephone ¢able~,
or in mine~ and other locations that may contain flammable gases,
the u~e of an open flame torch ior recovery is oiten not only
dangerous, but 60metimes prohibited. Under such circumstancesi
a wrap-around closure, i.e. splice case, that does not require
the applioation of external heat, particularly a flame, would
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~06~192
be particularly advantageouæ.
In a preferred embodiment, therefore, the s~lice case of
the preeent invention has a built-in heating means, i.e. the
splice case contains an integral electrical resist~nce heating
element which, when connected to an appropriate external
electrio power supply, i~ capable of generating suf~icient heat
to cause the splice case to recover and encapsulate the splice.
~his heat recoverable splice case does not require an outside
heating source, but instead may be caused to recover simply
by connectin~ it to an electric power couræe, whether battery
or mains, e.g. a 12 or 24 volt battery, or a 115 vo~t or other
appropriate A.C. eupply, and which, ~hen connected to ~uch
a power source, will recover and may al~o activate an adhesive
or sealant on its inner surface.
.. . .
In formulating the materials which provide the integral
heating element for use in the splice case~ of this invention,
arran~ements and compositions which provide uniform heating
are important. ~n ad~ition, for applications where the heating
element must ca1lse heat activation of an adhesive or sealant,
1 20 a~ well a~ heat recovery of the article, relatively high
; temperatures on the order of 120C to 200C must be obtained,
but careiully controlled. Ii temperatures above that necessary
for heat recovery o~ the splice ¢ase and adhesive activAtion
are reached, then per~anent damage to the sealing article, i.e.
the splice case, and/or to the part to be sealed, e.g. the
substrate cable, may result, such damage frequently not being
apparent by viæu~1 inæpection of the recovered splice ca~e and
.
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1069192 - -
immediately adjoining areas of the cable.
Thermostats and/or other heat control devices may be
employed to control the temperature of the recovering and
recovered a~ticle. But for many applications, this defeats the
object of using a self-containing, i.e., self-heating, closure
system, in that expensive, sensitive and/or bulky external
temperature control devices must be employed in what are
sometimes virtually inaccessible places. Moreover, the tempera-
ture sensed by the control device is only that of its immediate
10 environment, while other areas of the case may be at considerably
lower or higher temperatures.
In recent years a new approach for electrical heating
~!~
appliances has been the use of self-regulating heating systems
~ which utilize plastic materials exhibiting positive temperature
f : :
~5 coefficient of electrical resistance characteristics (herein-
-~ after referred to as PTC characteristics or materials). Such
1 ~
materials generally comprise crystalline thermoplastics with
a conductive particulate filler.
; The distinguishing characteristic of these PTC materials
1 ~ 20 ia that upon reaching a certain temperature a rapid rise in
¦ ~ resistance occurJ. The temperature at which the resistance
¦~ increases sharply i9 often designated the switching temperature
(T8) since the current at that point tends to switch off,
thereby preventing permanent damage through further temperature
increase to the heating article itself or any article being heated
thereby.
Although a number of theories have been propounded for
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1069~
the sharp rise in resistance of the PTC material usually at
about its crystalline melting point, it is generally believed ~ -
that such behaviour is related to the difference in thermal
expansion of the conductive filler and the thermoplastic
matrix material at the melting point. For a more detailed
discussion of a number of alternative mechanisms to explain
the PTC phenomenon, see "Glass Transition Temperatures as a
Guide to the Selection of Polymers Suitable for PTC Materials"
J. Meyers, Polymer Engineering in Science, November, 1973,
13, no. 6.
; Most self-regulating heating devices utilizing a PTC
material contemplate steep R = f(T) curves at about T8 80 that
above this temperature the device will in effect completely
shut off while, below this temperature, relatively constant
wattage output at a given voltage is achieved. At low tempera-
tures, the resistance is at a relatively low and constant level
and the current is relatively high for any given voltage. The
energy generated is dissipated in the form of heat, thereby
!: '
warming up the material. The resistance stays at the relatively
low level until T8, where a rapid increase in resistance occurs.
With the increase in resistance, there is a decrease in power,
thereby limiting the amount of heat generated and for extremely
steep R = f(T) curves, heating is in effect stopped. Upon a
lowering of the temperature, the resistance drops in turn
increasing the power QUtpUt.
. . .
~ In general, when a voltage is applied across a PTC heating
,~ element, the energy dissipated causes rapid heating of the PTC
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1069192
element up to its switching temperature, after which little
additional temperature rise will occur because of the steep
increase in resistance. Because of the steep resistance rise,
the heating element will theoretically reach a steady state at
about the switching temperature, thereby self-regulating the
heat output without resort to fu~es or thermostats.
Thermoplastic PTC materials contemplated by the prior
art are highly crystalline and exhibit a Ts at about the
cryQtalline melting point. However, most such materials in
fact show a "curl over" effect, i.e. the resistance drops again
at temperatures much above the melting point. This decrease in
resistance above the melting point is generally undesirable,
especially in cases where the PTC material is itself heat
recoverable, or is used in intimate proximity to a heat recover-
able material to effect recovery thereof, since under suchcircumstances it is preferred to heat the heat shrinkable
material as rapidly as possible up to its melting point (i.e.
; by means of high power densities) and thereafter keep the heater
temperature very 91ightly above the melting point of the
thermoplastic constituent(s) of the heater in order to facilitate
rapid and effective shrinkage of the heat recoverable article.
However, heat recoverable articles such as are comprehended by
the instant invention are intended in use to encapsulate and
environmentally seal splices between, for example, telephone cables,
by shrinking down onto and bonding securely, usually by the use
of an adhesive, to the cable jacket, which generally comprises
a low melting, partly crystalline, thermoplastic composition,
1069~92
for example, a carbon black loaded ethylenevinyl acetate polymer.
Such cable jackets are almost always uncrosslinked and
therefore, will flow and distort readily if the heater cau~es
them to reach too high a temperature (i.e. over their melting
points) during the time at such temperature needed to activate
an adhesive. Even more serious re~ults would occur with a
heater which does not very positively "shut off" if, through
omission, the power supply were not disconnected from the heat
shrinkable article. Under such circumstances, it is conceivable
that the PTC heater could remain energized for periods far
in excess of that needed to complete the encapsulation process
which may take only, for example, ten minutes. The above
considerations are even more important if, as often happens, the
individual conductors within teIephone cables are each insulated
with similar thermoplastic compositions. Any distortion of
such conductor jackets is unacceptable, as it causes that
section of the cable to become nonfunctional. Thus, the heater
for the splice case preferably undergoes a steep and extensive
increaJe in resiJtance above the T9 of the heater element and
continues to rise as the temperature of the heater is increased
above the melting point of the thermoplastic constituent, rather
than "curling over" i.e. declining more or less steeply as occurs
with moJt, if not all, prior art heaters. It is believed that
the "curl over" phenomenon and its problems have not previously
been generally recognized.
Furthermore, it has heretofore been generally believed
that conductive polymeric materials exhibiting PTC characteristics
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1069192
did not have sufficient heating capacity to cause recovery
of relatively thick sections of heat recoverable materials
as contemplated for the splice case of this invention, nor
the capacity to activate the high temperature adhesives also
contemplated by this invention.
The shortcomings of the prior art PTC material for
articles such as the splice case of the present invention can
be to a large extent overcome by the use of the compositions
disclosed in our Canadian Application No. 236,456 filed
Sept. 26, 1975 and by utilizing constructions of the type
disclosed in our Canadian Application No. 236,506 filed
Sept. 26, 1975. However? it should be noted that, although
prior art PTC materials are not preferred, they are suitable
for use in the splice case of the present invention under
many circumstances.
During use and operation of telephone cables,
especially when the individual conductors are wrapped with
a paper-based dielectric, it is required that moisture be
excluded since, if the moisture content of the wire insula-
tion increases beyont a certain relatively low critical
level, the electrical characteristics of the wire are un-
acceptably impaired. For this reason it is customary when
cables are spliced to place in the assembly just prior to
closure, a small paper bag of desiccant (usually silica gel)
in an a unt sufficient to maintain the interior humidity of
the splice at a very low level over the lifetime of the
splice, whatever the outside humidity. In a typical
instance, about 50 gram of silica gel might be used.
_ g _
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i069~92
As might be expected, the desiccant is frequently forgotten
or, even if not, the bags (which are customa~ily sealed for
storage) are sometimes left in an unsealed condition for
extended periods of time before emplacement or, in the
extreme, even dropped into water or wet mud and emplaced
nonetheless. A preferred embodiment of this invention offers
an alleviation of this problem.
Excess humidity leads to an unacceptable drop in the
level of paper-insulated cable performance. At 30% relative
humidity (R.H.) and at 15C the insulation resistance of paper
insulated strands of the type often used in telephone cables
decreases to an unacceptable level of about 0.5 giga ohm per
kilometer. Below 30% R.H., performance is acceptable. We
have found that the humidity inside the splice ca9e need not
be maintained at as low a value as possible but should simply
be maintained below 30% whenever possible. Unexpected and
surprising benefits are derived from encapsulating the
desiccant in a container whose water vapour transmission
characteristics have been carefully matched to those of the
9plice case itself 90 that the relative humidity inside the
said splice case may in all normally encountered circumstances
be maintained at less than 30X whatever the relative humidity
outside, as the following exposition demonstrates.
For 100% R.H. outside and 0% R.H. inside, if a typical
9plice case of the in9tant invention has a moisture vapour
transmission (MVT) of 100 ~g/hr at 15C, the container for the
desiccant must have a MN~ ~100 ~g/hr at 30% R.H. or ~333 ~g/hr
_ 10 --
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'` ' ' ' ' ' ' ~ . ' ', ~ ,. ' ' ' . ' ' '
"''' ' , ~ ' ' ' ' '
"' , '' , ' . '. ~ '"'' ' "
1069192
at 100% R.H. Thus if the desiccant container has a MVT of
500 ~g/hr the requirement is satisfied.
Assume the container holds about 100 g. of desiccant
such as silica gel which is capable of absorbing about 50 g
water. Under shelf storage conditions at 100% R.H. with no
other protective covering the desiccant thus contained will
lose half its absorptive capacity in about six years. Thus, a
container of this type permanently affixed inside the splice
case will suffer no appreciable diminution in effectiveness even
if the splice case is removed from its protective wrapping
during storage and periods of many months elapse before it is
used.
An especially useful feature of certain of the self-
heating splice cases of the present invention is their potential
re-enterability. The case may be re-entered by merely electri-
cally connecting the installed splice case to an electrical power
source, waiting a few minutes to soften the adhesive, removing
the electrical contacts and the side and end clip members (if
they have been left on) snd separating the upper and lower
splice case halves. If desired, after necessary changes to
the individual splices or replacement of any component, the
whole splice case may be reassembled as before and a short
period of reconnexion to an electrical power source will
result in a reforming of the adhesive bonds to yield an assembly
of unimpaired structural integrity. This ease of re-enter-
ability means that if not all the cable folds are required at
the initial installation a plug or plugs may be used, sized
to maintain the redundant folds in an expanded condition
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i069~g2
during initial installation. On subsequent re-entry, additional
cables can be added at any time and any newly added components
sealed as effectively as any of the original components.
Re-entry of the non-self-heating splice cases can also be
effected by u~e of an external heat source to melt the adhesive.
It is an object of this invention to provide a heat
recoverable closure system which is suitable for encapsulating
a plurality of cables of various sizes.
It i8 a further object of this invention to provide
a heat recoverable closure assembly which may be inserted
over or wrapped around cables and which may have the self-
heating capacity to seal such cables without resort to outside
heating sources.
It is another object of this invention to provide a
self-heating closure system which is capable of self-regulating
and not overheating to cause permanent damage to the article
encapsulated, nor on the other hand shut off at a less than
the design temperature.
The present invention provides a heat recoverable
article, e.g. a splice case, preferably having self contained
heating means, said heating means preferably incorporating a
positive temperature coefficient of resistance (prc) material
80 as to regulate the heat output without reso~t to extraneous
temperature control devices. The a~ticle is 80 configured
that it can be positioned around a splice and then caused to
heat recover and seal the splice. The terminology "self-
contained heating means" or "self-heating" signifies that
- 12 -
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- . .
i069igZ
the splice case having such feature incorporates an electric
resistance heating unit which by connexion to an appropriate
electric power source, e.g. a battery or alternating current,
will generate sufficient heat to shrink the shrinkable
portion of the splice case and activate (e.g. melt) any adhesive
present in the splice case. Also provided by the invention
is a splice case not having the self-heating feature (i.e.
it does not incorporate an electric resistance element) and
shrinking and adhesive activation are achieved by use of an
external heat source.
The present invention accordingly provides a heat-
recoverable article capable of being positioned around a
conduit junction to be covered and sealed thereby on recovery
thereof, the article having heating means connectable to and
energizable by an electric power supply, the means including
a material formed of an electric~l}y conductive polymeric
composition which is capable, when connected to an appropriate
el~ctrical supply, of heating the article to a temperature
sufficient to cause recovery thereof.
The material of the conductive polymeric composition
advantageously exhibits a positive temperature coefficient of
resistance and advantageously the material i9 80 shaped that
its length and width are large compared with its thickness, and
: i8 preferable in the form of a layer or sheet, and electrodes
are positioned 80 that current will flow through the thickness
of the material, i.e in the case of the layer or sheet, from
one face thereof to the other.
Advantageously, the heat recoverable portions of the
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lQ69~92
article comprise a polymeric material dimensionally changed
from a heat stable configuration or form to a dimensionally
he~t unstable one, capable of recovering to or toward the
stable form on the application of heat.
Preferably at least a part of the material that forms
the heating means also forms the dimensionally heat unstable
portion of the article.
It will of course be appreciated that the particular
heating means and the properties of the composition and
electrodes will be chosen, in a particular case bearing in
mind the nature of the electric power supply available to the
user.
The composition is advantageously a crystalline polymeric
material, and advantageously has dispersed therein carbon
particles, especially carbon black. The polymeric composi-
tion is advantageously crosslinked, by chemical means or by
irradiation, and the polymer, the conductive particles and
the proportion thereof will be chosen with the end use, and
the power supply available, in mind.
The portions of the surface of the article which will
face the substrate to be covered and those portions which
will contact each other when the article is positioned over
the substrate, advantageously have a coating of heat-act~va-
table sealant or adhesive thereon, which preferably is
activated at about the recovery temperature of the article.
The portions which engage each other are preferably provided
with means to hold them in engagement during recovery. The
central portion of the article may be provided with a heat
_ 14 -
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1069192
stable insert, which will define a cavity for surrounding the
splice, while the end portions are shaped to recover indivi-
dually around each of the cables ~etc. which join at the
splice.
Advantageously, the heating means is self-regulating
and comprises
a first layer of conductive polymeric material having
a positive temperature coefficient of resistance, and in
surface-to-surface contact with at least one face of the layer,
a second layer of conductive polymeric material having
a substantially constant resistance at least up to the recovery
temperature of the article to give a substantially constant
wattage at a given voltage, and at least a pair of electrodes
so positioned that current passing between them will pass
through at least a portion of the constant wattage material
and from one face to the other of the first layer.
Preferably, there is a constant wattage layer in
face-to-face contact with the first layer and the electrodes
are each in contact with a constant wattage layer.
The article preferably contains an insulating layer,
which may also be heat recoverable.
In some instances, the article constructed in accordance
with the invention can be recovered by an external heating
means, and in those cases, of course, the conductive layers
and the electrodes may be omitted.
The invention also provides a method of covering a
junction, by recovering an article constructed in accordance
with the invention, and a junction covered thereby especially
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i069192
a cable splice.
The optional self-contained heating means advantageously
comprises a polymer having dispersed therein an electrically
conductive filler to render it capable of conducting current
at a given voltage (e g. 12 or 24 volts from a battery) while
having sufficient resistance at its operating temperature so
that its heat output is capable of causing a relatively thick
section of heat recoverable materials, on the order of some
millimetres thickness, to heat to its recovery temperature
and recover about the splice to be encapsulated. In
addition, the heating means i9 advantageously capable of
giving sufficient heat output to activate a high temperature
thermoplastic or thermosetting adhesive or sealant.
When a PTC material is in the form of a structure having
two comparatively large dimensions and one comparatively small
dimension, e.g. a layer such as a sheet, passage of current
along the small dimension is preferred for more uniform heat-
ing. When the current flow is along the plane of the PTC layer
localized heating along certain conductive paths may result
causing non-uniform heat output. This in turn can cause an
even greater problem, rendering the entire heating device use-
less for a majority of its heating cycle. If localized heating
causes the material to reach T9 along a line transverse to the
current path, it will prevent the flow of current across the
25 path, in effect causing the heating device to shut down until
the temperature of the thus formed "hot-line" drops below Ts.
In other words, the "hot-line" across the layer between end
electrodes effectively shuts down the heating device even though
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1069i92
~ only a small surface area of the layer has achieved T8. This renders the
- heater so inefficient that it appears to exhibit a very low heating capacity.
The hot-lining problem can be minimized by positioning the PTC material
between the electrodes in a way that minimizes the length of the conductive
paths across which hot-lining can occur. For maximum efficiency with
minimum current path, the length to thickness rationof the layer should
be minimized. This is achieved, for example, with a sheet in which the
electrodes sandwich the PTC material. However, because of the short current
path, and limited surface required for some applications, inadequate heating
for such a configuration may occur at lower power inputs. To remedy this,
a material giving a constant wattage or Joule heat output, at a given volt-
age, i.e. a material not having PTC characteristics, is advantageously
laminated with the PTC layer so that the laminate exhibits good heating
effectiveness yet is self-regulating, without hot-lining. For a more thor-
ough discussion of the advantages of applying a current through the layer,
as opposed to along its length, and fabricating a layered composite, see
our abovementioned Application 236,506.
For a more detailed discussion of suitable PTC compositions which
are preferably employed as layers for use in the present invention, especially ;
for relatively high temperature applications, the reader is referred to our
abovementioned Application 236,456.
17 -
~069192
Such compositions comprise blends of thermoplastic and
elastomeric materials having conductive materials dispersed
therein. As pointed out in the specification, such blends
exhibit a steep rise in resistance at about the melting point
of the thermoplastic component, the resistance continuing to
rise with temperature thereafter. Because of the increased
safety margin given by the further increases of resistance above
the melting point such heaters can be designed to control
("switch off") at temperatures above the theoretical Ts and
have resistances well in excess of that at Ts but yet avoid
the risk of thermal runaway and/or burn out which occurs when
prior art PTC compositions are used in such designs. Such
heaters, especially when the increase in resistance with
temperature above Ts is very steep, are very "demand insensitive"
that i9 the operating temperature of the PTC material varies
very little with thermal load. They can also be designed to
generate very high powers up to Ts when electrically connected
to a power source. Because of their excellent temperature
control, they can be employed to activate adhesives and cause
heat recoverable devices such as the present invention to
recover around substrates such as thermoplastic telephone
cable jackets with reduced risk of melting or deforming the
substrate even if left connected for considerable periods of
time.
It should be noted that a variety of closure means,
including an adhesive as discussed above, for the splice case
can be employed. ~he closure means should be such as to with-
stand the heat recovery forces at the temperature of recovery,
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iO69192
for examples of which see U.S. Patents ~os. 3 379,218 and
3,455,336
The devices and methods of splice encapsulation provided
for in the instant invention differ substantially from and
thereby overcome to some extent or otherwise avoid some of
the deficiencies which characterize prior art devices and
methods. For example, in one of the preferred embodiments
of the invention, the heat recoverable folds when positioned
around the substrate, e.g., the cable, enfold the substrate
in such a manner that the opposing heat recoverable surface
do not come in contact with one another but butt up against
opposing surfaces of, for example, long fingers forming
ridges on the mating surfaces of the non-heat recoverable base
15 member. The forming of closure or splice case from a combina- ~ -
tion of a heat shrinkable and heat stable member as in certain
preferred embodiments so that the areas of the members which
abut to defin~ the cavity containing the cable splice are
not themselves heat shrinkable is another significant departure
from the prior art as will be apparent from the following
more detailed discussion.
It ha~ been long realized that when a heat-recoverable
member is folded or wrapped around a substrate and shrunk down
to region in which the heat recoverable member is brought to-
2S gether and secured with a closure member consitutes an area-of
weakness both mechanically and in its resistance to the environ-
ment, for example, to penetration of water. In the abovementioned
Ellis patent are described ways to solve this problem by the use
19 --
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1069192
of a design with an overlapping flap under'the abutting edges
of the heat recoverable member and secured to the overlying
layer by an adhesive to provide a long leakage path.
However, this solution fails if the substrate does not
S provide a firm foundation against which the heat recoverable
enclosure can press the flap so as to cause the adhesive to
flow and wet the faying surfaces. When to this factor is
added the difficulty of constructing a multiple entry splice
case having overlapping heat recoverable regions it can be
seen that an article constructed in accordance with the
Ellis patent, while extremely useful in most instances,
doe~ not solve all the problems which the instant invention
solves.
, ,
.~ . .
These problems are solved in
a surprisingly simple and highly e~fective manner by the preferred
approach of the present invention. The optional provision of
an intervening ridge or finger on the non-heat recoverable base
member in combination with the clips and flanges on the heat
recoverable member, which flanges can be used precisely because
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1069192
the heat recoverable member in these regions contains non-heat
recoverable eeg~ents, iacilitates obtaining this highly desirable
re~ult.
~he invention will now be described in greater detall
by way oi e~ample only, with reierence to the aocompanying
dxawings, in which:
Figure 1 i~ a per~pective view of a first embodiment
oi a heat recoverable article, i.e. a splioe
case, con6tructed in accordance with the
invention, in which has been positioned and
~oined a plurality of cables of varloue dimensions;
Figure 2 i8 an end view of the article of Figure 1 prior
to expaneion to its heat unstable, i.e. heat
recoverable form;
Figure 3 iB an end view o~ the article aiter expansion to
its heat un~table form;
Figure 4 i~ an end view of the article after it has been
caused to heat recover about cables;
Fi~ure 5 is taken along line 5-5 o~ Figure 3 ~howing in
more detail the layered construction oi the article;
Fi~ure 6 i~ a perspective view oi the article prior to
cable in~ertion;
Flgure 7 i~ a per6pective view of an alternative con-
iiguration embodiment of an article constructed
in accordance with the invention.
It should be noted that, with the e~ception of Figure 5,
and the schematic electric circuit in Figure 6, Figures 1 to 7
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1069192
are illustrated of a splice case whether or not it incorporates
self-heating means. Figure S shows a layered construction
which exemplifies an embodiment wherein the splice case in-
corporates self-heating means. Figures 8 to 11 show the
structure of a second preferred embodiment of a splice case
constructed in accordance with the invention.
Figure 8 on the third sheet of drawings, is a cross
section through one end of the splice case;
Figure 9 is a perspective view of one end cut away to
show the details of the structure;
Pigure 10 is a perspective view of the splice case
from below the non-heat recoverable base member;
Figure 11 is a longitudinal section through the splice
case showing details of the internal cavity;
Figures 12 to 19 show details of the preferred method
of construction of a third preferred form of splice case con-
structet in accordance with the invention.
Figure 12 illustrates the formation of the preferred
braid electrodes;
Pigure 13 shows the positioning of electrodes over and
attachment to the bus bars;
Pigure 14 shows vsrious layers (cut away to facilitate
understanding) of the blank for the heat
recoverable member positioned in a jig
prior to lamination;
Pigure 15 shows the blank being formed into the basic
shape for the heat recoverable member;
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~)69192
Figure 16 shows the heat recoverable member in its
heat stable configuration after cross-
linked;
Figure 17 shows the construction of the reinforcing
flanges for the ends and sides of the heat
recoverable member;
Pigure 18 shows the flanges being applied to the heat
recoverable member positioned in a jig prior
to expansion;
Figure 19 shows the heat recoverable member at the end
of the expansion step;
Figure-20 on the last sheet of drawings, shows the
upper lower members of the splice case in per-
spective to show additional details of the
interior;
Pigure 21 shows the especially preferred embodiment
after installation around a cable splice.
Referring now to the drawings, Figure 1 shows a heat
recoverable closure apparatus constructed in accordance with
this invention, adapted for receiving a plurality of cables
and having an enlarged central section for accommodating a
splice between the cables. &ch a configuration is particularly
suited for low voltage telephone cables wherein a plurality of
cables are to be joined quickly and efficiently at minimum cost.
The apparatus shown in Figure 1 may be entirely made of
a heat recoverable material, preferably having layered therein
a self-heating composition, as shown in Figure 5, which will be
discussed in more detail hereafter. Alternatively, only that
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portion of each end of the splice case comprising the folds,
i.e. that portion of the splice case between the ends thereof
and dashed lines 18, can be made heat recoverable with the
center portion being non-heat recoverable. The layer or
layers of heat recoverable material are crosslinked as, for
example, by irradiation 80 as to render them heat recoverable.
A heat recoverable part comprising a layer 10 is positioned
in its stable, unexpanded state with folds 11 as shown in
Figure 2. The unexpa~ded folds can, of course, take on any
configuration,1ncluding the general configuration of the
cable provided that a sufficient excess of material for
expansion i8 allowed. The folds are expanded by known tech-
niques to a dimension greater than the diameter of the cables
to be sealed, as shown in Figure 3. The material is sufficiently
resilient and flexible that the cable may be snapped into
the opening of the fold. As best seen in Figures 3 and 4,
the openings may be of varying dimensions depending upon the
~; size of the cable which is to be inserted, although it should
be kept in mind that one ~ize opening is recoverabIe over to
seal a wide range of cable ~izes. The heat recoverable part
10 is mated with a bottom part of the splice case 12 which
is not heat recoverable although as shown, for example, in
Figure 7, it may be heat recoverable in some embodiments.
The bottom part 12 may serve as a permanent mounting for the
cable splice, giving rigidity to the system. Alternatively,
the parts 10 and 12 may have a cooperating hinge at one edge
14 (Figure 4) with a closure means at the opposite edge 6.
Alternatively, where parts 10 and 12 are formed from the same
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106919Z
material, they may be integral at the edge 14, utilizing a
closure at the edge 6, or the parts 10 and 12 may be separate
parts separated at both edges 14 and 6 in which case the heat
shrinkable part 10 is merely lifted from the part 12 for
5 insertion of the cables. If desired, the parts 10 and 12
may have reinforcing strips embedded therein along the long
axis thereof, preferably adjacent the edges 14 and 6. Such
strips can also 'serve as bus bars.
In sealing cable splices in accordance with the process
10 of the invention, the parts 10 and 12 are separated and cables
20, 22 and-24 are placed therein. Referring more'specifically
to Figures 2, 3 and 6, ~iere the parts 10 and 12 are neither
integral nor hinged, a clamping device, for example, hinged
clamps 52 and 54 are utilized, such clamps being tightened by
15 means of a bolt 56 and a wingnut 58. Iihe clamps may serve to
maintain the parts 10 and 12 together during expansion (Figure
2) as well as during'insertion of the cables and recovery
thereover (Figure 4). Although such clamps could form a
permanent part of the installation; they are preferably removed
20 after installation and' an adhe'sive such as, for example, that
described in U.S. Patent 3,770,556 is used to seal the edges
permanently.
Also, at the ends, proper spacing between cables is most
suitably assured by a clamping'device. As bes~t seen in Figure 6
25 this may be a plate separator 62 having openings therein to
accommodate the folds 11 (Figure 2), such plate tightly sealing
the parts 10 and 12 by clamps 64 and 66 during the expansion
and sealing opera~ions.
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To add strength and further to protect the system, and
where necessary to provide moisture vapour transmission protection
or radio frequency shielding, the cable splice itself can
optionally be encapsulated within a rigid can with the case,
having an outline defined by dashed lines 18 and 18a located
beneath the central portion of the heat recoverable member
generally designated 26 in Figure 1. Where the central portion
26 is heat recoverable it will conform to the shape of the can
which can suitably be fabricated of any rigid material including
metal or moulding plastic. The end openings 19, 21 and 23 are
adapted to receive individual cables of varying dimensions. The
other end of the heat recoverable member will generally contain
openings of similar dimensions to accommodate the cables to be
joined, although all of the openings may be confined to one side.
Where a rigid can i8 employed for covering the splice,
;~ sealing at the central portion by the heat recoverable member
may not be necessary. Therefore, as heretofore indicated, the
heat recoverable portion of the article of this invention can be
limited to the end portions 80 that it will seal the individual
incoming cables up to the can. In this case, the cent~al portion
26 can be of non-recoverable material or, if recoverable, need
not be caused to recover. Alternatively, the material need not
extend across the can so that the can is allowed to remain
exposéd, or only an insulation layer, for example the layers 30
or 31 of Figure 5, need extend across the can with remaining
layers being confined to the ends.
Referring now more specifically to Figure 5, the heat
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~0691~2
recoverable closure preferably comprises a self-heating laminate having
electrodes embedded therein, the electrodes being connectable to an ap-
propriate power source. A suitable laminate is more fully described in
the abovementioned Application No. 236,506. Briefly, the laminate consists
of an outer insulating layer 30, which is heat recoverable. A layer 34
comprises a polymer or polymer blend, for example a blend of a highly
crystalline polyolefin and ethylene-propylene rubber, having dispersed
therein conductive carbon black. The layer 34 preferably exhibits positive
temperature coefficient of resistance properties to control the heating.
The layer 34 is preferably interleaved between layers 32 and 36 which may
also be polymer blends having carbon black dispersed therein, these layers
preferably yielding constant wattage outputs at a given voltage over a wide
temperature range and not exhibiting significant positive temperature
coefficient of resistance properties. An inner insulating layer 31 may
also be provided. The layers 31, 32, 34 and 36 are preferably also heat
recoverable. The inner layer can advantageously contain an adhesive coating
(not shown~ on its free surface for bonding and sealing to the cable.
Embedded in the constant wattage layers 32 and 36 are electrode
grids 38 and 40, which are capable of being connected to a suitable power
source for example a battery as schematically shown in Figure 6. This
configuration causes the current to pass through the PTC layer 34 from
electrode 38 to electrode 40. A preferred type of electrode design and
configuration is more fully described below.
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10691~2
Referring now more especially to Figure 7, an alternative con-
figuration of the present invention is shown. Such a configuration may
be formed and expanded out of a single sheet of material, generally having
the layered configuration of Figure 51 After inserting the cables as
previously described through openings 44, 46 and 48 the apparatus is closed
by bringing together the opposite edge 50 of the sheet by a suitable closure
means 51. Such apparatus may, of course, be made to conform to various
cable diameters and shapes as shown. It can be a "clam shell" design having
a closure means at 50 and self-hinging at 47.
An especially preferred embodiment of the invention is illustrated
in c~toss-section in Figure 8. It comprises upper and lower members 96 and
80. The upper member 96 comprises an outer splice case shell 67 affixed
irmly to a heater which consists of outer and inner layers of constant
wattage material 68 and 70 and a core layer of PTC material 69. To the
inside surface of the inner constant wattage layer 70 is affixed an adhesive
layer 71. The heater PTC core 69 preferably constructed as described in
the abovementioned Application No. 236,456 is combined with constant wattage
outer layers 68 and 70 of compositions whose thermoplastic polymer ingredi-
ents, if any, have a lower melting point than that of the thermoplastic
polymer component of the PTC composition. The constant wattage layers, if
comprising thermoplastic polymers, may be made heat recoverable and pre~
ferably an additional outer shell 68 comprising a layer of a heat recover-
able polymer composition
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having a recovery temperature less than the melting point of
the thermoplastic component of the PTC composition is also
provided. An additional layer 71 of a hot melt adhesive or
mastic may also be provided, the hot melt, if used, having a
melting point similar to that of the heat recoverable member
and an activation temperature less than the melting point
of the thermoplastic component of the PTC composition. Such
an embodiment has been found to be particularly advantageous
where the substrate is heat sensitive, i.e. where if warmed
above its melting point it will deform or flow.
As shown in greater detail in Figure 9, embedded in the
constant wattage layers are flexible and compliant electrodes
72 whiah may be advantageously formed from braided wires. Each
heat shrinkable end fold contains six electrodes 72, three being
connected together for connexion to one terminal and three to
; another, oppos-d to each other in pairs and running transverse
to the longitudinal axis of the case. Electrodes of the first
polarity are connected (as by welding, soldering, or glueing
with a conductive adhesive at the areas of intersection)
to bus electrodes 73 and 73a, and of the second polarity to
bus electrodes 74 and 74a, running the length of each side
of the case. The electrodes 73, 73a, 74 and 74a may be
constructed from wire braid or thin metallic strip, optionally
perforated. To the mid portion of electrode 73 on one side and
to the mid portion of electrode 74a on the other side are
affixed tabs 75 and 76 adapted for easy connexion to an
electrical power source. On the top of the primary heat
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1~69192
shrinkable layer (see also Figure 8) along each side and
between the heat recoverable end fold structures are
attached (by glueing or otherwise adhering) reinforcing
flanges 77, 78 and 79, fabricated from any suitably rigid
material. Especially suitable materials include metals, and
engineering thermoplastics, for example, polycarbonates,
acrylonitrile butadiene styrene or SAN resins and filled
polymers for example polyamides or polyolefins. Especially
preferred is a glass filled polyamide (nylon). The lower
member 80, which is not heat recoverable, preferably has
external ribs 81 for increased rigidity and, optionally,
internal ridges 82 corresponding to and adapted to be mated
with the open sides of the heat recoverable folds as also
shown in Figure 10. The splice case may be assembled by
bringing the upper and lower members together and securing
with spring clips 83, 84 and 85 suitably constructed of
similar materials to flanges 77, 78 and 79.
Turning now to Fiqure 11 there is shown a section along
the longitudinal axis of the case. A central cavity 86 serves
to contain the individual spliced wire~ from the cables.
Optionally and advantageously, there i8 present a small con-
tainer 95 (filled with a desiccant) whose walls permit water
to diffuse through at a rate in excess of the diffusion rate
into the splice case internal cavity, as previously explained
in greater detail. A valve may be provided to afford access
to cavity 86 enabling pressure testing of the installed
splice case.
The preferred method of fabrication of a splice case will
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be illuQtrated, with particular reference to the embodiment
of Figure~ 8 to 11, with reference to Figures 12 to 21.
The electrode material, preferably a metallic braid,
which may be, for example, formed from sixteen carriers each
of four strands of 38 AWG (about 0.010 cm diameter) tinned
copper wire braided at as high a braid angle aQ possible
(to achieve a high degree of compliability) is formed around
a thin conductive or nonconductive thermoplastic tube.
Excellent results have been obtained with a braid angle of
75 around a 6.25 mm outside diameter 0.25 mm wall tubing of
the same composition as the constant wattage material. The
braided tube is then heated to or above the softening tempera-
ture of the thermoplastic tube and flattened, care being taken
to pre~ent stretching of the braid. These steps are shown
in Figure 12.
The next stage in the process is the construction of the
electrode/bus system comprising the steps of affixing the
tab 75 to the side electrode 73a, followed by attachment of
the end electrodes 72. Suitable affixing methods include
spot welding,; soldering and glueing. When the electrode
comprises wire braid around a conductive core of the aame
material as the constant wattage layer it has been found that
excellent results are obtained by hot bonding using the con-
ductive thermoplastic core to bond the electrodes together.
Attachment of the electrodes to one another to form the basic
configuration is facilitated by the use of a jig as shown in
Figure 14. The material used for the end electrodes,~ in
addition to the flattened braid referred to hereinabove, may
include knitted or woven or plated metal wires, conductive
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1069~ 92
fibres or metal plated polymer fibres or polymeric fibres
containing conductive particles which have been so treated as
to render them highly conductive in the fibre direction.
It is preferred'in all these embodiments that the
resultant electrode be highly extensible and compllant so as
not to offer any appreciable resistance to expansion or
recovery of the heat recoverable portions of the splice case
as occurs during manufacture and installation in service of
the splice case.
Similar materials may be used for the side or bus
electrode~. As these electrodes are not required to undergo
any significant deformation during manufacture and installation
they may additionally be formed out of such relatively non-
extensible and noncompliant materials as flat metal or other-
~ 15 wise highly conductive strips, preferably perforated and single
; or multiple stranded wires.
The construction of"the blank for the splicé case is shown
in Figures 13 and 14. The various heater layers, prepared by,
for example, extrusion, coextrusion or hot calendering, are
conveniently assembled in a ~lg frame. In the particular
embodiment illustrated, a skin layer 67 i8 placed in the frame
and ~uccessively a constant wattage layer 68a, the first set of
electrodes 73/73a (with the tab 75 pointing to the right as
shown in the drawing), another constant wattage layer 68b, the
PTC control layer 69, another constant wattage layer 70a, the
second set of electrodes 74/74a (with the tab 76 pointing to the
left), and a final constant wattage layer 70b laid over. The
whole structure is sandwiched between polytetrafluoroethylene
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1069~92
protective layers 97 and laminated together by heating under
pressure. A jig is used to hold the various layers and the
electrodes in fixed relation to one another during lamination,
the minimum pressure being applied. After lamination and removal
of the polytetrafluoroethylene layers, the assembled splice
case blank is preferably sandwiched between foam rubber ~heets
100 and annealed for example, at about 185C, for a sufficient
period of time with minimum applied pressure to allow the
constituent layers to relax thoroughly. ~epending on the materials
involved annealing periods of as little as two minutes to over
one hour are suitable, five minutes to fifteen minutes being
preferred. The blank is removed while still at the annealing
temperatures and conformed over a male mould as in Figure 15
using pressure as indicated by the arrows so as to form the
unexpanded splice case configuration 87 shown in Figure 16.
In this operation, as previously, care should be taken to ensure
that the heater is not stretched during the forming operation.
If desired a plurality of ridges, preferably wedge shaped, may
be present on the upper surface of flanges 77, 78 and 79 which
ridges serve to direct the compressive forces exerted by clamps
83 and 89.
The basic splice case 87 is then irradiated with ionizlng
radiation using techniques well known to those skilled in the
art to ensure uniform irrad~ation. Suitable ionizing radiations
include gamma rays, X-rays, and accelerated elections. The
dose required should be sufficient to ensure integrity of the
configuration above the arystalline melting point of any of its
polymeric constituents but not sufficiently high as adversely
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to effect the elongation behaviour during the expansion operation
to form it into the heat recoverable configuration. A suitable
irradiation dose range has been found to be 2 to 50 megarads,
5 to 20 megarads being preferred.
The blank which following irradiation may be considered
to be in a "heat stable" configuration is then formed into the
"heat recoverable" configuration 88 in the sequence of operations
shown in Figures 17 to 19. After a preheat sufficient to warm
the article 87 to about the melting point of its crystalline
polymeric constituents the formed blanks are inserted into a
jig 89 as shown in Figure 18. The reinforcing flanges 77 78
and 79~which have their contacting surfaces coated with an
adhesive 90 as shown in Figure 17 are placed on the sides and
ends of the formed blank 87. The end flanges 78 (and the
corresponding flange at the other end of the splice case) is
made with a~long "break off" tab 91 having locating holes 92 for
mounting in the jig 89 as shown in Figures 17 and 18. All the
flanges have turned down lip8 98 at their outer edges to serve
to contain and protect the edges of the heater from mechanical
damage. The side flanges 77 and 79 have a small shroud 99 in
the middle outside edge surrounding the electrode tabs 75 and
76 and sized to accept a standard "quick disconnect" connector
6.3 x 0.8 mm such as are supplied by the Arc-Less Company.
Pressure is applied to the side and end flanges and the
splice case folds and central cavity formed by suitable expansion
means. Such expansion techniques are well known to the prior art
and include mandrel expansion and pneumatic or vacuum forming.
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1069192 ,
In this operation care should be taken to prevent longitudinal
compression of the folds when a mandrel is used. Suitable means
for minimizing such compression include provision of a radially
expansible or circumferentially segmented sleeve member between
the mandrel and the fold which serves to decouple the longi-
tudinal insertion forces exerted by the mandrel from the folds.
Alternatively pneumatic or hydraulic expansion of an elastomeric
tube longitudinally constrained may be used. The central
splice case cavity is preferably formed pneumatically. The
expanded blank is then cooled while under constraint as in
Figure 19, removed from the jig and an adhesive layer 93 affixed
to the surface~ that will butt on to the lower member and on
to the interior surfaces of the folds. An adhesive layer can
also be affixed to the abutting surface of member 80. At this
stage if desired, a container 95 filled with a desiccant may
be fixed to the inner wall of the central cavity 94 as shown
in Figure 20 which is a view of the completed upper heat recover-
able member 96 where the relation of the folds and central
cavity can be seen. Alternatively, the desiccant can be
affixed to the base plate as shown in Figure 11.
In use, after completion of the splices and incorporation
into the splice case the complete splice case is assembled, as
above described, by bringing the upper and lower members 96
and 80 together and securing with the side clips 83 and 85
and end clips 84a and 84b. The heater is then electrically
connected to a power source.
Because of the disposition of the electrodes in the splice
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9~
case upper member and the relative resistances of the constant
wattage and PTC layers on connexion to a power source for
example a 12 or 24 volt lead ac~d battery heating to cause
reaovery and/or activation of the adhesive occurs predominantly
at the folds and in the flange regions. Thus, the central cavity
does not develop enough power to warm toa significant extent.
As has been mentioned hereinabove the compositions used
in the heater layers may be chosen so as to provide extremely
quick heating of the splice case. For example, using the
10 preferred PTC compositions of the type hereinabove referenced,
it has been found that the heater in the fold area typically
heats to 115 - 120C in less than one minute. On reaching such
temperature the fold regions start to recover. In about two
minutes the fold regions have shrunk around the substrate, e.g.
cable and after a further eight to thirteen minutes the
adhesive layers have been thoroughly activated and have wet
- and sealed to the cable jacket and to the non-heat recoverable
base member. Thus, in a typical instànce the heater is
appropriately connected to a power source for from about ten
to fifteen minutes during which time the assembly may be safely
left unattended, ailowing the assembler to proceed with other
operations. Those skilled in the art will realize that the
period of time the heater is under power will vary according
to the temperature demands of the adhesive, the thermal
load and other factors. Surprisingly it has been found that
the period of time required is relatively insensitive to
the ambient temperature. It is believed that this may
be due to the extremely sharp PTC cut off made possible
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-` ~069192
by the particular advantageous design combination of the
instant invention.
After an appropriate period of time the electrical power
source is removed and the splice case allowed to cool to
ambient temperatures. At this time the side and end clips
may be removed or left in place to provide additional mechani-
cal protection if desired.
A particularly advantageous result of the combination of
elements in the instant invention is that because the heater
is capable of maintaining itself in a particularly limited
range of temperatures whatever the environmental thermal load
even if this temperature range is very close to the melting
points of commonly used thermoplastic cable jacketing or
individual wire insulating materials, the splice case may be
left electrically connected to a power source for periods
(e.g. of several hours) after the joint has been made and
damage to the telephone wires or cables may be avoided.
In order to facilitate re-entry, the article may be
provided with restrain-ng means to inhibit the complete recovery
of the reaoverable member ~hen the installed member is re-heated
to soften it and any adhesive. The restraining means may
comprise rigid, e.g., metal, tongues which will underlie the
portions which are to surround the cable. Referring to Fig. 9,
a tongue having the same width as the flat portion 78 between
the cable entries is positioned on the surface of the flat
portion, with a portion extending axially outwardly therefrom.
Similar tongues may be positioned on the outer flat surfaces
77 and 79, and all the axially extending portions joined
together by appropriately shaped connecting links to form an
integral restraining mean~. Thi~ means may be left in position
during use, if desired.
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