GB2232307A

GB2232307A - A heat-shrinkable repair cover for cables

Info

Publication number: GB2232307A
Application number: GB8916846A
Authority: GB
Inventors: Joseph Gordon Robinson
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-03-03
Filing date: 1989-07-24
Publication date: 1990-12-05
Also published as: KR900015389A; GB8916846D0; GB8904837D0

Abstract

A heat-shrinkable sleeve constituted of at least one cross-linked corrugated layer of a polyolefin intimately sandwiched between two cross-linked layers of a homogeneous plastic material preferably with an elongation at break of at least equal to that of the corrugated polyolefin, has been demonstrated to have a high resistance to creep, to crushing and to punch- through. In addition it has exceptional resistance to splitting during heat-recovery. When the internal surface of the sleeve is coated with a layer of hot melt adhesive the resultant product is suitable for covering and protecting repair joints on distribution telecommunications cables or for protecting repair joints on pressurised telecommunications transmission cables installed either underground or exposed to direct sunlight in temperate climates. The corrugations are triangular, parabolic, part-circular or irregular in shape and preferably run at an angle of 90 DEG to the longitudinal wrap-around sheet edges held together by a C-shaped metal channel. The outer layers are press-laminated, powder, roller or extrusion coated to fill the voids between the corrugations. The sleeve is used with a shaped liner. <IMAGE>

Description

HEAT SE:RINKA3I#E REPAIR COVER FOR PRESSURISED CABLES This invention concerns an improved design of Joint covers for use, particularly on pressurised telecommunications cables.

It is occasionally neceçsary to repair telecommunications cables, and other cables. Since this involves the removal of some of the protective cable sheath it is therefore required to provide the resultant joint with a cover having excellent resistance to moisture ingress and resistance to mechanical damage, ideally for the life of the cable.

It is possible to provide protection against moisture ingress to a telecommunications cable joint by wrapping an adhesive coated wraparound heat-shrinkable sleeve around the joint and extending some way along the entrance and exit cables, as described in British Patent I ,506,242. The longitudinal edges of the sleeve are fastened tightly together by means of a flexible ~shaped metal channel. On heating with a propane flame, for example, the sleeve shrinks and, together with the adhesive, which is on the interior surface, forms a water-tight cover over the joint.The effectiveness of such Joint covers may be assessed by pressurising them to about 6 psi with air and thermally cycling them in water from 50C to 6000. The pressure loss for satisfactory Joints should not exceed 1 pai after 10 cycles, each cycle being of 4 hours duration. This type of test is carried out to evaluate Joint covers used on distribution cables, even though the cables are not normally pressurised.

In the case of telecommunications transmission systems, the cables are usually permanently pressurised to 10 psi to ensure that even in the event of damage water will be kept out. The suitability of the repair Joint covers for use on transmission lines may be assessed by pressurising to 10 psi and then cycling them between -40 C and 60 C in air. No measurable pressure loss should occur after 10 cycles, each cycle of 8 hours duration. Other thermal cycling tests for assessing the air retention effectiveness by these joint covers are used. A further requirement, and a particularly demanding one, is that the pressurised Joint cover should have excellent creep resistance so that it does not move or distort, ideally for the life of the cable.

To meet the exacting requirements for Joint covers to be used on pressurised telecommunications cables many systems have been used. For example iron sections have been bolted together around the joint together with collars and adhesive coated tapes used to seal the outlet and inlet cables. This type of joint cover has the drawback of rigidity, difficulty in assembling and the inconvenience of storing large numbers of different sizes of components needed to cater for the range of cable sizes in use.

I have discovered that the drawbacks with hitherto used joint covers for pressurised telecommunications cables can be overcome by the use of a heat-shrinkable wrap-around sleeve produced from a polyolefin composite.

The longitudinal edges of the wrap-around sleeve are held together by means of a flexible C-shaped metal channel which runs along a continuous neck on both longitudinal edges, as illustrated in Figures 1 and 2 The polyolefin composite is constructed of a heat-shrinkable conjugated or ridged sheet sandwiched between two plane layers of plastic material hereinafter referred to as the matrix. The corrugations or ridges run essentially parallel to each other and they undulate from the top surface of the sheet to the bottom surface whereby a crest is followed directly by a trough as shown in Figure 3. Alternatively, there may be an interruption in the progress from crest to trough, such as shown in Figure 4 or there may be a definite lateral separation between the ridges or corrugations as shown in Figure 5.The shape of the cross-section at right angles to the longitudinal direction of the corrugations or ridges, tay be triangular, or parabolic, or part-circular, or a combination of two or three of these or even an irregular shape.

The corrugations or ridges preferably cover the entire surface of the interior heat-shrinkable sheet except for the continuous neck, 5 (Figure 1) along each edge, whose surfaces are smooth and when assembled over a joint are held together by means of a C-shaped metal channel, 7, (Figure 2) The direction of the corrugations or ridges is preferably at an angle of 900 to the longitudinal edges of the heat-shrinkable sheet, but, any other angle to the longitudinal edges may be used. The matrix and the corrugated or ridged sheet should preferably have similar chemical and heat-shrinkable properties. Suitable materials are: high density polyethylene for the corrugated or ridged sheet and low density polyethylene for the layer on either side of the corrugated sheet. Other suitable pairs of materials are readily selected by those skilled in the art.

With this construction, comprising a heat-shrinkable corrugated or ridged polymer sheet sandwiched, (except for the continuous neck along each edge of the sheet), between two layers of low density polyethylene it was found, surprisingly, that the resultant composite wrap-around heat-shrinkable sleeve, when adhesive coated and assembled by heatshrinking over a liner around a repair joint in a telecommunications transmission cable it had outstanding resistance to splitting during heating, it could withstand the hoop stresses generated by the high internal pressure without significant creep or distortion and it had excellent pressure retention characteristics. A similar composite construction, but in tubular form, may also be satisfactorily used to cover joints on pressurised transmission cables, providing it can be pushed over the cable leading to the Joint.

The high density polyethylene sheet is extruded with a continuous neck, 5 (Figure 1) along each edge. With the temperature of this extruded strip maintained above that of the crystalline melting point of the polymer the corrugations are made between the necks of the strip.

The resultant corrugated sheet is made heat-shrinkable by stretching it, preferably by 200% to 700% at right angles to its longitudinal edges, at a temperature below the crystalline melting point of the polymer. The corrugated sheet is then cross-linked by exposure to a radiation dose of 2 to 30 Mrad. Alternatively, but less preferably, the extruded strip of high density polyethylene after corrugation at a temperature above the crystalline melting point of the polymer, is exposed to a radiation dose of 2 to 30 Mrad. or more preferably to 5 to 20 Mrad. and then heated above its crystalline melting point and stretched by 200% to 700% at right angles to its longitudinal edges. Then, while still retaining the stretching force the strip is cooled below 80 C to give the required heat-shrinkable sheet.

The heat-shrinkable corrugated sheet of high density polyethylene may, alternatively, be made by stretching the extruded sheet preferably by 200% to 700% at right angles to its longitudinal edges and followed by corrugation indentation of the surface (between the necks on the longitudinal edges). In this case both operations, stretching and corrugation indentation, are carried out below the crystalline melting point of the high density polyethylene. The resultant sheet is exposed to a radiation dose of 2 to 30 Mrad. or more preferably to a dose of 5 to 20 Mrad.

In another preparation process the extruded strip of high density polyethylene with a continuous neck, 5 (Figure 1), along each edge is first cross-linked by exposure to a radiation dose of 2 to 30 Mrad. or more preferably to a dose of 5 to 20 mead. It is then heated above the crystalline melting point of the polyethylene and stretched by 200% to 700%, at right angles to its lingitudinal edges and, with the temperature still held above the crystalline melting point the corrugation indentation of the surface is carried out. Thereafter, while still under the influence of the stretching force, the sheet is cooled to less than about 80 C to give the required heat-shrinkable sheet of high density polyethylene.

Prior to stretching by 200% to 700% the overall thickness of the corrugated high density polyethylene sheet of the present invention, measured from the outside of the crest to the outside of the adjacent trough of the corrugations is preferably between 0.5mum and 15mm and more preferably between 1.5mm and 10mm. The thickness of the material of the corrugated sheet itself is preferably between 0.02mum and Smm and more preferably between 0.2mm and 3.5mm with the separation between the crests of the corrugations or ridges, preferably in the range 0.25mm to 30mm and more preferably in the range 3mm to 15mm, particularly when the crests are followed directly by the troughs without interruption, as shown in Figure 3.In other cases, such as shown in Figures 4 and 5, the optimum separation of the corrugations may be different and will depend on the corrugation profile and on the thickness of the corrugated sheet material.

A suitable separation will readily be determined by those skilled in the art.

A layer of low density polyethylene, is bonded to both top and bottom faces of the corrugated heat-shrinkable sheets of high density polyethylene of the present invention, by press larinations or by powder coating or by roller coating from the melt or by any other suitable technique. The voids and/or channels in the corrugations are thereby filled with the low density polyethylene which preferably, but not essentially, completely covers the corrugations or ridges. The overall thickness of the heat-shrinkable composite is preferably between 0.5sum and 15mm and more preferably between 1.5mm and 1Loam.The heat-shrinkable composite is then further cross-linked by exposure to an electron beam or gL1Ufla radiation to prevent the low density polyethylene sheets from melting, running or dripping during heat-shrinking.

The preferred level of radiation is in the range 1 to 10 Trad. and more preferably in the range 2 to 5 Mrad.

The low density polyethylene is preferably not applied to the continuous neck, 5 (Figure 1), along the edges. The present invention, however, does not exclude covering the necks with the low density polyethylene, it may be more convenient in manufacture to avoid doing so.

The heat-shrinkable polyolefin composite of the present invention can also be prepared in what may be regarded as a semi-continuous process. The high density polyethylene sheet with a continuous neck, 5 (Figure 1) along each edge is extruded through a die using a conventional plastics extruder.

While still at a temperature above the crystalline melting point the corrugations are impressed in the polymer sheet between the neck along either edge and preferably at right angles to the longitudinal axis, but they may be inclined at any angle to the longitudinal axis. The corrugated strip is next cooled below the crystalline melting point of the polymer and preferably to less than 25 C. The low density polyethylene is then applied to both top and bottom faces of the corrugated strip, but preferably not to the neck along each edge, for example by cross-head extrusion or by other means. The voids and channels are thereby filled with low density polyethylene and preferably, but not necessarily, completely covering the corrugations.The resultant polyolefin composite is next exposed to a radiation dose of 2 to 30 mead. or preferably to a dose of 5 to 20 Mrad.

It is then heated above the crystalline melting point of the high density polyethylene and stretched by 200% to 700% at right angles to its longitudinal edges. Then, while retaining the stretching force the sheet is cooled below 80 C to give the required heat-shrinkable wrap-around artefact.

Alternatively, the high density polyethylene sheet after corrugation at a temperature above the crystalline melting point is cooled to room temperature and exposed to a radiation dose of 2 to 20 Mrad. or more preferably to a dose of 5 to 15 Mead. low density polyethylene is then applied by cross-head extrusion or by other means to the top and bottom faces of ,the cross-linked corrugated sheet but preferably not on the neck along each edge. The voids and channels are thereby filled with low density polyethylene preferably, but not necessarily, completely covering the corrugations.The polyolefin composite is then exposed to a radiation dose of 1 to 10 mead. or a more preferred dose of 2 to 5 Mrad. It is then heated above the crystalline melting point of the high density polyethylene and stretched by 200% to 700% at right angles to its longitudinal edges. Then, while retaining the stretching force the strip is cooled below about 800C to give the required heat-shrinkable wrap-around artefact. It is also possible to carry out this stretching of 200% to 700% at right angles to the longitudinal edges at a temperature below rather than at a temperature above the crystalline melting point of the high density polyethylene to obtain the heat-shrinkable wrap-around artefact.

Materials other than low density polyethylene may be used to sandwich the heat-shrinkable corrugated sheet to produce a composite wrap around sleeve and these include, but are not restricted to: ethylene-vinyl acetate co-polymer, ethylene-ethyl acrylate co-polymer, linear low density polyethylene, very low density polyethylene, medium density polyethylene, high density polyethylene, and polyesters. Any of these, or blends thereof, or other polymeric materials may be bonded to the corrugated or ridged sheet, then cross-linked, by exposure to a high energy electron beam or gamma radiation, to prevent melting or flowing during heat shrinking.

More than one layer of corrugated or ridged sheets may be used in the construction of the heat-shrinkable wrap-around composite sleeve. The sheets may be in intimate contact or they may not actually touch but be connected together using, for example, the polymer constituting the matrix or an adhesive.

The surface of the heat-shrinkable wrap-around sleeve which will contact the cable joint is coated with a layer 0.1 to I.Omm thick, of high performance adhesive. The adhesive is preferably a hot melt type and suitable adhesives may for example be based on a polyamide or ethylene-vinyl acetate co-polymer.

During the heat-shrinking process the adhesive flows to form a seal between the heat-shrinkable sleeve and the substrate.

A liner is used in conjunction with the heat-shrinkable wrap-around sleeve. The liner is preferably, but not necessarily, made of rigid cardboard or similar material with creases running lengthwise at lateral separations of about 20mm, to facilitate neat wrapping around the repaired joint in the cable. The ends of the liner have long narrow triangular pieces cut out to form a coronet on either end so that they readily smoothe out the transitions from the maximum joint size to tVe size of the exit and entrance cables, as shown in Figure 1.In order to further enhance the air impermeability of the joint cover system the liner may be coated with a layer, preferably 0.05 to 1.0mm thick, of an air impermeable polymer, preferably but not exclusively, of a co-polymer of vinylidene chloride and acrylonitrile or a co-polymer of vinylidene chloride and vinyl chloride.

In order to pressurise the joint cover an air valve is passed through a hole drilled in the wrap-around sleeve and liner and sealed into position using conventional techniques to form an air-tight seal.

EXAMPLE 1.

100 parts by weight of a high density polyethylene (density O.961g/cc and melt flow index of 16gra/10 minutes at 190 C/2.16kg) were blended on a 2-roll mill with 2.0 parts of Corax P, 2.0 parts of Flectol-H, 0.5 parts of dilaurylthiodipropionate and 5.0 parts of triallyl cya;urate. The resultant blend was granulated and thereafter extruded as a strip of width 48mm and thickness 2.5mum and having a continuous neck running the entire length of each longitudinal edge.

The strip was then stretched at right angles to the longitudinal edges to a width of 170mm with corrugation indentation of the surface being carried out immediately afterwards, both operations carried out at a temperature below the crystalline melting point of the polymer. The corrugation direction was at right angles to the longitudinal edges.

The corrugation profile was triangular as shown in Figure 3, and had a separation of 15mm between each corrugation ridge, and the overall thickness of the sheet was 5.5mm.

The corrugated sheet was cross-linked by exposure to gamma radiation at a dose of 10 Mrad. to give the required heat-shrinkable corrugated sheet.

100 parts of low density polyethylene (density O.916g/cc and melt flow index 20grm/lOmin at 1900C/2.16kg) were blended on a 2-roll mill with 2.0 parts of Corax P, 2.0 parts of Irganox 1010 and 1.0 part of dilaurylthiodipropionate. The resultant blend was granulated and extruded as a sheet of thickness l.Omm.

A sheet of this material, of length 450cm, was pressed between PTFE covered plates in a press at 155 C, into each face of the heat-shrinkable corrugated sheet to completely cover it. The resultant composite was cooled to room temperature in the press and thereafter exposed to a radiation dose of 3 mead. An air valve was then fitted to give a heat-shrinkable wraparound sleeve, the interior surface of which was coated with a 0.4mm thick layer of a polyamide hot melt adhesive.

A joint on a length of polyethylene sheathed telecommunications cable was surrounded by a hard cardboard liner, as illustrated in Figure 1.

The air valve also passed through the liner. The long triangular pieces on the ends 2 (Figure 1) enabled a smooth transition to be achieved from the Joint body to the cable 3. The composite heat-shrinkable sleeve 4 with the necks, 5 running lengthwise, was positioned with the adhesive layer, 6 in contact with the Joint. Figure 2 shows the sleeve 4 after heat shrinking and whose edges are held together by means of the flexible metal channel 7. After assembly, the joint was pressurised to 10 psi through the air valve and cycled between -40 C and +60 C for 120 cycles, each cycle was of 8 hours duration. After this test the covered joint was pressurised to 15 psi and immersed in water and cycled between SOC and 50 C for 100 cycles.The joint pressure was registered on a pressure gauge attached to the cable body. No loss of pressure was observed at the end of these thermal cycling tests, and moreover no creep was detected.

EXAMPLE 2.

The above test was repeated but employing a heat-shrinkable sheet with corrugations as shown in Figure 4 in which the upward corrugations 9 were separated from the downward corrugations 10 by the uncorrugated part 11 No pressure loss was recorded after the thermal cycling tests and only minimal creep was observed.

ExAMPLE 3 The above test was repeated but employing a heat-shrinkable sI.ttt with corrugations as shown in Figure 5 in which the corrugations 12 were separated by the uncorrurated region 13. No pressure losses were recorded after the thermal cycling tests and no creep was detected,# EXAMPLE 4 100 parts by weight of a high density polyethylene (density O.95g/cc and melt flow index of 1.8grm/lOminutes at 1900C/2.16kg) were melt-blended in a 3uss Ko Reader with 0.95 parts of carbon black (Corax P), 1.75 parts of F1ectol-#, 0.4 parts of dilaurylthiodipropionate and 6.0 parts triallyl cyanurate. The resultant blend after granulation was fed into z single screw extruder and extruded as a strip of width of 3. 2mm and thickness 2.0mm and having a continuous neck running the entire length of each longitudinal edge 5, (Figure 1). As the strip emerged from the extruder it was passed through a corrugating system at a temperature above the crystalline melting point. The direction of corrugation was at right angles to the longitudinal edges. The corrugation cross-section was triangular (Figure 3) with a separation of 9mm between each ridge. The external distance from crest to trough was 4.5mm. The resultant corrugated sheet was cooled to about room temperature and then a sheet of low density polyethylene compound was applied to the top and bottom faces, using a cross-head extruder, and sufficient to fill the corrugations and just completely cover them. The average thickness of the resultant composite 5.1mum. The low density polyethylene compound used was made by taking 100 parts of low density polyethylene (density 0.915 and melt flow index 18grm/10minutea at 190 C/2.16kg) together with 2.0 parts of Corax P carbon black, 2.0 parts of Irganox 1010 and 1.0 part of dilaurylthiodipropionate and blending in a Buss Ko Kneaded.

The polyethylene composite was cross-linked by exposure to a gamma radiation dose of 12 Mead. and then heated above the crystalline melting point of the high density polyethylene corrugated sheet. It was then stretched in 1200mm lengths at right angles to its longitudinal edges to a width of 155mm and, while retaining the stretching force cooled to less than 80 C. Each sheet was then fitted with an air valve to give a wrap-around sleeve, the interior surface of which was coated with a 0.55mm thick layer of polyamide hot melt adhesive and the exterior surface with z temperature indicating paint.

The wrap-around sleeve was tested on z joint made on a length of polyethylene sheathed cable as described in Example 1. No pressure losses were observed after the thermal cycling tests and no creep was detected.

EXAMPLE 5 The procedure described in Example 4 was repeated except that after exposure of the composite to a gamma radiation dose of 12 mead. the 1200mum lengths (width 32mm) were stretched at a temperature below the crystalline melting point of the corrugated high density polyethylene to a width of 155or to give the heat-shrinkable wrap-around artefacts.

No pressure loss was observed after the thermal cycling test and no creep was detected.

FXAT#PLE 6 The tests described in Examples 4 and 5 were repeated, but instead of using z hard cardboard liner over the joint in the telecommunications cable a hinged aluminium liner was used whose narrow triangular ends were coated with a layer of PVC. No pressure loss was observed after the thermal cycling tests in either case and no creep was detected.

Flectol-H is an antioxidant available from Monsanto PLC Corax P is a carbon black available from legussa Irganox 1010 is an antioxidant available from Ciba Ceigy PLC

Claims

1. A heat-recoverable wrap-around sleeve comprising a corrugated plastic layer, sandwiched between two layers of a plastic material, and having a grooved protrusion along both longitudinal edges for gripping by a flexible metal channel so as to hold the edges in close proximity during heat recovery of the sleeve.

2. An article according to claim 1, wherein the corrugated plastic layer is a polyolefin.

3. An article according to claim 2, wherein the separation between the tops of the corrugations is in the range of 0.25 mm to 30 mm.

4. An article according to claim 2, wherein the corrugations run parallel to each other.

5. An article according to claim 2, wherein the corrugations runs at an angle of 900 to the longitudinal edges of the corrugated polyolefin sheet.

6. An article according to claim 2, wherein the corrugations are at any angle to the longitudinal edges of the corrugated polyolefin sheet.

7. An article according to claim 2, wherein the corrugations extend across the entire surface of the corrugated polyolefin sheet to the grooved protrusions along both longitudinal edges described in claim 1.

8. An article according to claim 2, wherein the corrugations undulate from the top to the bottom surface of the polyolefin sheet whereby a crest is followed directly by a trough.

9. An article according to claim 2, wherein there is an interruption in the progress from crest to trough of the corrugations.

10. An article according to claim 2, wherein there is a lateral separation between some of the corrugations.

11. An article according to claim 2, wherein there is a lateral separation between all of the corrugations.

12. An article according to claim 2, wherein the corrugations are triangular shape in the cross-section at right angles to the longitudinal direction of corrugation.

13. An article according to claim 2, wherein the corrugations are parabolic shape in the cross-section at right angles to the longitudinal direction of corrugation.

14. An article according to claim 2, wherein the corrugations are part circular shape in the crosssection at right angles to the longitudinal direction of corrugation.

15. An article according to claim 2, wherein the shape of the corrugations in the cross-section at right angles to the longitudinal direction of corrugation is a combination of two or more of the shapes according to claims 12 to 14.

16. An article according to claim 2, wherein the corrugations have an irregular shape in the crosssection at right angles to the longitudinal direction of corrugation.

17. An article according to claims 1 to 16, wherein the corrugated polyolefin layer is crosslinked.

18. An article according to claims 1 to 17, wherein the corrugated polyolefin layer is heatrecoverable.

19. An article according to claim 2, wherein the corrugations of the polyolefin layer are completely filled with a homogeneous polymeric material to form a laminate.

20. An article according to claim 2, wherein the corrugations of the polyolefin layer are partly filled with a homogeneous polymeric material to form a laminate.

21. An article according to claims 19 and 20 wherein the homogeneous polymeric material used to fill or partly fill the corrugations of the sandwiched layer of corrugated polyolefin has an elongation at break at least equal to that of the corrugated polyolefin.

22. An article according to claims 19 to 21, wherein the homogeneous polymeric material used to fill or partly fill the corrugations in the sandwiched layer of the corrugated polyolefin is cross-linked after deposition within the corrugations.

23. An article according to claim 22, is heatrecoverable.

24. An article according to claim 23, is a wraparound sleeve.

25. An article according to claim 1, and claim 24, in which the heat-recoverable wrap-around sleeve has a layer of heat-reactivated adhesive on the internal surface.

26. An article according to claim 1, and claims 24 and 25 in which the heat-recoverable wrap-around sleeve has a temperature indicating paint on the external surface which changes colour during heating indicating recovery of the sleeve and activation of an internal coating of heat-reactivatible adhesive.

27. A junction between elongated substrates when enclosed by a wrap-around sleeve according to claim 2, and claims 24 to 26.

28. A junction according to claim 27, in which the substrates are electrical cables.

29. A junction according to claim 27, in which the substrates are telecommunications cables.

30. A junction according to claim 27, in which the cables are pressurised cables.

31. A method of protecting an elongate substrate using a heat-shrinkable wrap-around sleeve according to claim 1, and claims 24 to 26, and heat-shrinking the sleeve over the substrate.

32. A method of protection according to claim 31, wherein the heat-shrinkable sleeve is wrapped around a liner which is positioned around the substrate and is so constructed as to enable a gradual transition to be made from the maximum joint diameter to the smaller diameter cables entering or emerging from the joint.

33. A method of protection according to claim 31, wherein the substrate is a cable branch out having a plurality of cable portions entering or emerging from the joint.