Heat recoverable self-heating sealing article and its use

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. Such encapsulation is particularly important where 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 encapsulating pipes, 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 this shortcoming, closure members suitable for wrapping around the elongate objects have been developed. See for example, U.S. Patent Nos. 3,379,218 to Conde, 3,455,336 to Ellis or 3,770,556 to Evans. These so-called wrap-around” closures can be installed around an elongate member without access 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 particular, for a splice involving more than two incoming cable ends and/or splices between different sizes of cables but which may be applied without access to a free end of the cable»

The present invention is directed to a heat-recoverable, splice case which can, in various embodiments, accommodate a plurality of cables of differing sizes, i.e. outside diameter, which can be removed and in some embodiments reapplied to a splice and which does not require access to a free end of the cable» The present design is not referred to as a ^,’wraparound״ since it encapsulates a splice in a somewhat different fashion from the aforementioned “wrap-around” closures. In alternative embodiments the splice case of the present invention utilizes either a clam shell or separate base plate and cover member design.

In one embodiment the present invention contemplates a splice case which will recover and encapsulate a cable or other splice when subjected to an external heat source, for example a propane torch or hot air blower.

Many applications for splice cases involve on site use, where the splice is relatively inaccessible or is in a

20’ potentially hazardous environment, and great care must be taken in installing the splice case.

' ction ־ For example, in the conne«±ert of overhead telephone cables, or in mines and other locations that may contain flammable gases, the use of an open flame torch for recovery is often not only dangerous, but sometimes prohibited. Under such circumstances a wrap-around closure, i.e. splice case, that does not require the application of external heat, particularly,a flame, would be particularly advantageous.

In a preferred embodiment, therefore, the splice case of the present invention has a built-in heating means, i.e. the splice case contains an integral electrical resistance heating element which, when connected to an appropriate external electric power supply, is capable of generating sufficient heat to cause the splice case to recover and encapsulate the splice. This heat recoverable splice case does not require an outside heating source, but instead may be caused to recover simply source by connecting it to an electric power course, whether battery or mains, e.g. a 12 or 24 volt battery, or a 115 volt or other appropriate A.C. supply, and which, when connected to such a power source, will recover and may also activate an adhesive or sealant on its inner surface.

In formulating the materials which provide the integral heating element for use in the splice cases of this invention, arrangements and compositions which provide uniform heating are important. In addition, for applications where the heating element must cause heat activation of an adhesive or sealant, as well as heat recovery of the article, relatively high temperatures on the order of 120°0 to 200°C must be obtained, but carefully controlled. If temperatures above that necessary for heat recovery of the splice case and adhesive activation are reached, then permanent 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 visual inspection of the recovered splice case and

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immediate?.;/ adjoining areas of the cable.

Thermostats and/or other heat control devices may be employed to control the temperature of the recovering and recovered article. But for many applications, this defeats the object of using a self-containing, i.e. self-heating, closiire system, in that expensive, sensitive and/or bulky external temperature control devices must be employed in what are sometimes virtually inaccessible places. Moreover, the temperature sensed by the control device is only that of its immediate 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 coefficient of electrical resistance characteristics (hereinafter referred to as PTC characteristics or materials). Such materials generally comprise crystalline thermoplastics with a conductive particulate filler.

The distinguishing characteristic of these PTC materials is that upon reaching a certain temperature a rapid rise in resistance occurs. The temperature at which the resistance increases sharply is often designated the switching temperature (T ) 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 the sharp rise in resistance of the PTC materia} 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(1) curves at about T_e so that s 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 temperatures, 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 T״, where a rapid increase in resistance occurs, s

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 output.

In general, when a voltage is applied across a PTC heating element, the energy dissipated causes rapid heating of the PTC 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 fuses or thermostats.

Thermoplastic PTC materials contemplated by the prior art are highly crystalline and exhibit a T at about the s crystalline 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 recoverable material to effect recovery thereof, since under such circumstances 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 slightly 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, for example, a carbon black loaded ethylenevinyl acetate polymer. Siich cable jackets are almost always uncrosslinked and therefore, will flow and distort readily if the heater causes 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 results 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 telephone 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 increase in resistance above the 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 most, 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

48181/2 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 German patent specification No. 2,543,346 and by utilizing constructions of the type disclosed in Israel patent specification No. 48180. 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 paner-hased dielectric, it is required that moisture be excluded since, if the moisture content of the wire insulation increases beyond 20 a certain relatively low critical level, the electrical characteristics of the wire are unacceptably 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 amount sufficient to maintain the 25 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.

As might be expected, the desiccant is frequently forgotten or, even if not, the bags (which are customarily 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 15°C 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 case 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 splice case itself ¹so that the relative humidity inside the said splice case may in all normally encountered circumstances be maintained at less than 30% whatever the relative humidity outside, as the following exposition demonstrates.

For 100% R.H. outside and 0% R.H. inside, if a typical splice case of the instant invention has a moisture vapour transmission (M7T) of 100 jig/hr at 15°C, the container for the desiccant must have a MVT >100 )1g/hr at 30% R.H. or ?333 yig/hr at 100% R.H. Thus, if the desiccant container has a MVT of

500 }1g/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 selfheating splice cases of the present invention is their potential re-enterability. The case may be re-entered by merely electrically 15 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) and 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 reconne^i©ft°ⁿto an electrical power source will result in a reforming of the adhesive bonds to yield 321 assembly of unimpaired structural integrity. This ease of re-enterability 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 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 use 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 is 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 (PTC) material so as to regulate the heat output without resort to extraneous temperature control devices. The article is so 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 the splice case having such feature incorporates an electric resistance heating ־unit ction ' which by connerion 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 heatrecoverable 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 electrically condv.ctive nolymeric composition which is capable, when connected to an appropriate electrical 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 is so shaped that its length and width are large compared with its thickness, and is preferable in the form of a layer or sheet, and electrodes are positioned so that current will flow through the thickness

2ל 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 ־ 15 article comprise a polymeric material dimensionally changed from a heat stable configuration or form to a dimensionally heat 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 mears 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 composition 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-activatable 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 stable insert, which will define a cavity for surrounding the splice, while the end portions are shaped to recover individually 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 surfaceto-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 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 5 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 10 heating means is advantageously capable of giving sufficient heat output to activate a high temperature thermoplastic or thermosetting adhesive or sealant.

When a JPTC material is in the form of a structure having two comparatively large dimensions and one comparatively small 15 dimension, e.g. a layer such as a sheet, passage of current along the small dimension is preferred for more xmiform heating. 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 20 greater problem, rendering the entire heating device useless for a majority of its heating cycle. If localized heating causes the material to reach T along a line transverse to the s current path, it will prevent the flow of current across the path, in effect causing the heating device to shut down until the 25 temperature of the thus formed hot-line drops below T . In other words, the hot-line across the layer between end electrodes effectively shuts down the heating device even though t

only a small surface area of the layer has achieved T_s. 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 ratio of 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 voltage, 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 thorough discussion of the advantages of applying a current through the layer, as opposed to along its length, and fabricating a layered composite, see Israel patent specification No. 48180.

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, see German patent specification No. 2,543,346.

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 T and have s resistances well in excess of that at Τθ 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 T is very s steep, are very demand insensitive that is, 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 T when electrically connected to a power source. Because s 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. The closure means should be such as to withstand the heat recovery forces at the temperature of recovery, r for examples of which see U.S. Patents Nos. 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 onl the mating surfaces of the non-heat recoverable base member. The forming of closure or splice case from a combination of a heat shrinkable and heat stable member as in certain preferred embodiments so that the areas of the members which abut to define 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 has been long realized that when a heat-recoverable member is folded or wrapped around a substrate and shrunk down the region in which the heat recoverable member is brought together and secured with a closure member constitutes an area of weakness both, mechanically and in its resistance to the environment, for example, to penetration of water. In the above mentioned Ellisjpatent are described ways to solve this problem by the use of a design with an overlapping flap under the abutting edge's 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 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, does not solve all the problems which the instant invention solves.

These problems are solved in a surprisingly simple and highly effective 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 bead precisely because the heat recoverable member in these regions contains non-heat recoverable segments, facilitates obtaining this highly desirable result.

The invention will now be described in greater detail by way of example only, with reference to the accompanying ' drawings, in which:

Figure 1 is a perspective view of a first embodiment of a heat recoverable article, i.e. a splice case, constructed in accordance with the invention, in which has been positioned and joined a plurality of cables of various dimensions;

Figure 2 is an end view of the article of Figure 1 prior to expansion to its heat unstable, i.e. heat recoverable form;

Figure 3 is an end view of the article after expansion to its heat unstable form;

Figure 4 is an end ־view of the article after it has been caused to heat recover about cables;

Figure 5 is taken along line 5-5 of Figure ל showing in more detail the layered construction of the article;

Figure 6 is a perspective view of the article prior to cable insertion;

Figure ך is a perspective view of an alternative configuration embodiment of an article constructed in accordance with the invention.

It should be noted that, with the exception of Figure 5» and the schematic electric circuit in Figure 6, Figures 1 to 7 are illustrative of a splice case whether or not it incorporates self-heating means. Figure 5 shows a layered construction which exemplifies an embodiment wherein the splice case incorporates 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 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;

Figure 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 constructed in accordance with the invention.

Figure 12 illustrates the formation of the preferred braid electrodes;

Figure 1J shows the positioning of electrodes over and attachment to the bus bars;

Figure 14 shows various layers (cut away to facilitate understanding) of the blank for the heat recoverable member positioned in a jig prior to lamination;

Figure 15 shows the blank being formed into the basic shape for the heat recoverable member;

Figure 16 shows the heat recoverable member in its heat stable configuration after being crosslinked;

Figure 17 shows the construction of the reinforcing flanges for the ends and sides of the heat recoverable member;

Figure 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 shows the upper lower members of the splice case in perspective to show additional details of the interior;

Figure 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. Such 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 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 so 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 unexpanded folds can, of course, take on any configuration, including the general configuration of the cable provided that a sufficient excess of material for expansion is allowed. The folds are expanded by known techniques 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 size onening is recoverable over to seal a wide range of cable sizes. The heat recoverable part 10 is mated with a bottom part of the splice case 12 which is not heat recoverable although as show^, 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 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 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 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, where 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 means of , a bolt 56 and a wingnut 58. The 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 after installation and an adhesive 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 best seen in Figure 6 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 operations.

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 2J 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 maj־׳ be confined to one side.

Where a rigid can is employed for covering the eplice, 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 so that it will seal the individual incoming cables up to the can־ In this case, the central 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 exposed, or only an insulation layer, for example the layers JO 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

48181/2 recoverable closure preferably comprises a selfheating laminate having electrodes embedded therein, the electrodes being connectable to an appropriate power source. A suitable laminate is more fully described in Israel patent specifidation No. 48180.

Briefly, the laminate consists of an outer insulating layer JO, 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

0ן conductive carbon black. The layer 34 preferably exhibits י positive temperature coefficient of resistance properties to control the heating. The layer 34 is preferably interleaved between layers 32 and J6 which may also be polymer blends having carbon black dispersed therein, these layers preferably yielding י

ן 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.

&lt; 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 3θ to electrode 40. A preferred type of electrode design and configuration is more

48181/2 fully described below.

Referring now more especially to Figure 7, an alternative configuration 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 5, 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 cross-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 firmly 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 German patent specification No. 2,543,345 is combined with constant wattage outer layers 68 and 70 of compositions whose thermoplastic polymer ingredients, 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 preferably an additional outer shell \68 comprising a layer of a heat recoverable polymer composition

ר .1 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 which may be advantageously formed from braided wires. Each heat shrinkable end fold contains six electrodes 72, three being cation connected together for connexion to one terminal and three to another, opposed 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 fran 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 ction י adapted for easy conneRi©» to an electrical power source. On the top of the primary heat shrinkable layer (see also Figure 8)

סו 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 SAIT 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.

’j (Burning now to Figure 11 there is shown a section along

I i the longitudinal axis of the case. A central cavity 86 serves

I to contain the individual spliced wires from the cables. Optionally and advantageously, there is present a small container 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 be illustrated, with particular reference to the embodiment of

Figures 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 0.010cm diameter) tinned copper wire braided at as high a braid angle as possible (to achieve a high . 5 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 ram outside diameter 0.25 mm wall tubing of the same composition as the constant wattage material. The braided tube is then heated to 10 or above the softening temperature of the thermoplastic tube and flattened, care being taken to prevent 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 15 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 same material as the constant wattage layer it has been found that excellent results are obtained by 20 hot bonding using the conductive 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 25 hereinabove, may include knitted or woven or plated metal wires, conductive fibres or nj#tal plated polymer fibres or polymeric fibres containing conductive particles which have been so treated

־ 31 48181/2 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 compliant 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 electrodes. As these electrodes are not required to undergo 0ן any significant deformation during manufacture and installation י they may additionally be formed out of such relatively non-extenBible and noncompliant materials as flat metal or otherwise highly conductive strips, preferably perforated and single or multiple stranded wires.

ן The construction of the blank for the splice 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 jig frame. In the particular embodiment illustrated, a skin layer 67 is placed in the frame and successivley a constant wattage layer 68a, the first set of electrodes 72/73a (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 wat.tage 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 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 sheets 100 and annealed, for example, at about 185°C, for a sufficient period of time with minimum applied pressure to allow the constituent layers to relax thoroughly. Depending 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 85.

The basic splice case 87 is then irradiated with ionizing radiation using techniques well known to those skilled in the art to ensure uniform irradiation. 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 crystalline melting point of any of its polymeric constituents but not sufficiently high as adversely to affect

־ the elongation behavior 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 J?see Fig. 19) 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 flange 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 lips 98 at their outer edges to serve to contain and protect the edges of the heater from mechanical damage. The side flanges 77 and 7.9 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.

r

In this operation care should be taken to prevent longitudinal compression of the folds when a mandrel is used. Suitable m^ans 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 longitudinal insertion forces exerted bjr 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?

/ (see Fig. 20) removed from the jig and an adhesive layer 93/affixed to the surfaces 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 centra], cavity 94 as shown in Figure 20 which is a view of the completed upper heat recoverable member 96 !where the relation of the folds, and central cavity can be seen, ׳ t Alternatively, the desiccant can be affixed to the base plate as 20 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 (see Fig. 21).

clips 84a and 84b/ The heater is then electrically connected to a power source.

Because of the disposition of the electrodes in the splice 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 acid battery, heating to cause recovery 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 to a 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 preferred PTC compositions of the type hereinabove referenced, it has been found that the heater in the fold area typically heats to 115 - 120°C 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 instance 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, allowing 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

I 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 mechanical 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 restraining means to inhibit the complete recovery of the recoverable member when 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» &amp; tongue having the »«יק« 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 means. This means may be left in position during use, if desired.