Low and medium voltage cable joint filled with cold thermosetting resin and kit for the deployment thereof

Abstract

A joint for electric power cable, preferably operating at low and medium voltage, filled with a resin obtained in situ by contemporaneously cold setting a composition containing a (meth)acrylate ester of an alkanol having from 6 to 20 carbon atoms with a curing agent acting also as a tackifying agent and selected from the group consisting of a urethaneacrylate and an epoxylacrylate oligomer having a functionality from 1 to 6 in amounts ranging from 0.1 parts to 10 parts by weight per 100 parts by weight of the methacrylate ester. A kit for preparing a cable joint includes the joint and the composition for preparing the cured resin. The resin contained in the joint does not exhibit cold flow and therefore does not flow from the cable joint.

Claims

1. A joint for electric power cable filled with a resin obtained in situ by cold setting a composition comprising (meth)acrylate ester monomer of an alkanol having from 6 to 20 carbon atoms in the presence of a curing agent selected from an aromatic urethane-di-acrylate oligomer, in an amount from 0.3 to 5 parts by weight calculated per 100 parts of said (meth)acrylate ester, wherein said composition is free of further additives that improve adhesion properties of the resin obtained in situ, and wherein the resin obtained in situ does not show cold flow in a cold flow test according to French National Standard NF C33-010, Appendix G (1993).

2. The joint for electric power cable according to claim 1, wherein said (meth)acrylate ester monomer is isodecylmethacrylate ester.

3. The joint for electric power cable according to claim 1, wherein said curing agent oligomer has an average molecular weight from 300 to 8000 Da.

4. The joint for electric power cable according to claim 3, wherein said curing agent oligomer has an average molecular weight from 800 to 6000 Da.

5. The joint for electric power cable according to claim 1, wherein said composition comprises a filler.

6. The joint for electric power cable according to claim 1, wherein said composition comprises a flame retardant agent.

7. The joint for electric power cable according to claim 1, wherein said composition comprises (meth)acrylate ester monomer in an amount lower than 40% by weight with respect to the total weight of the composition.

8. The joint for electric power cable according to claim 1, wherein said composition comprises (meth) acrylate ester monomer in an amount lower than 25% by weight with respect to the total weight of the composition.

Description

DESCRIPTION OF FIGURES

(1) FIG. 1 is a diagrammatic side view of a cable joint in accordance with the invention in course of assembly; and

(2) FIGS. 2 and 3 are top views respectively of upper and lower enclosure halves forming parts of the cable joint of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(3) In the present description and claims as “joint of cable for electric power” it is meant a straight or branched tubular enclosure, which may be made, for example, of acrylonitrile butadiene styrene (ABS) or high impact polystyrene (HIPS). Advantageously, the enclosure may also be made from non halogenated polymers for low smoke zero halogen (LS0H) applications. The material of the enclosure may be opaque or transparent. For all applications, the enclosures may be available on the market already. provided with the connectors to join the cable, or alternatively the connectors may be sold apart.

(4) In FIG. 1 the two enclosure halves 10,11 of a joint 100 are positioned about two lengths of 3-core single-wire-armoured power distribution cable 1 and 2, respectively. The cable ends are cut back and the corresponding cores connected electrically by connectors 3, 4, 5. The armour wires 6 are electrically bonded together, for instance using a copper braid 7 and constant-force spring (clock spring) connecting devices 8, 9. The whole is enclosed using lower and upper plastics enclosure halves 10 and 11, shown respectively in FIGS. 2 and 3, too to provide the enclosure of the cable joint 100. The tapered end-parts 12 and 13 of each enclosure 10,11 may be trimmed, if required, to fit the diameters of the cables. The resin composition of the invention can be poured into the joint through the central opening 14 in the upper enclosure-half 11, and allowed to harden by cold curing.

(5) The joint of the invention are particularly suitable for low and medium voltage cable.

(6) The term low voltage is used to indicate voltages lower than 1 kV.

(7) The term medium voltage is used to indicate voltages of from 1 to 35 kV.

(8) For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

(9) Advantageously, an oligomer according to the invention has an average molecular weight of from 300 to 8000 Da, preferably of from 800 to 6000.

(10) Preferably the composition of the invention contains the monomer (i) in an amount lower than 40% by weight with respect to the total weight of the composition (B), more preferably in an amount lower than 25%, more preferably higher than 10%.

(11) Preferably the composition (B) of the kit according to the invention contains the curing agent (iv) acting also as tackifying agent in amounts of from 0.3 to 5 parts by weight per 100 parts by weight of the component (i).

(12) The urethane acrylate oligomers and epoxyacrylates oligomers as curing agent (iv) according to the invention may be of aromatic and aliphatic type. Preferred urethane acrylate oligomers can be selected from di-, tetra- or hexa-functional aromatic or aliphatic oligomers. Preferred epoxyacrylates oligomers can be selected from di-, tetra- or hexa-functional aromatic or aliphatic oligomers. Examples of commercially available products useful for this aim are marketed by Sartomer under the trademark Craynor.

(13) Examples of (meth)acrylate ester (i) useful for the composition of the invention are 2-ethylhexyl (meth)acrylate, isodecyl(meth)acrylate, isooctyl(meth)acrylate, octyl-decyl-(meth)acrylate, tridecyl(meth)acrylate, stearyl(meth)acrylate. A preferred monomorer (i) is isodecylmethacrylate ester.

(14) For the purpose of the present invention for radicalic catalyst, it is meant a catalyst triggering a polymerization/curing reaction of monomers composition occurring with essentially radical mechanism which therefore may be carried out also in the absence of light.

(15) The radicalic catalyst (ii) present in the composition (B) of the invention may be any radical catalyst of conventional type. Preferably, organic peroxides can be used as radical catalyst (ii), for example benzoylperoxide.

(16) The filler (iii) may be of various types as a function of the specific application of the cable joint. Mineral fillers such as chalk and sand can be used, and solid or hollow glass beads and some grades of fly ash. Solid or, preferably, hollow mineral microspheres can be used alone or in combination with chalk and/or sand or other mineral fillers adapted to reduce the density of the fillers and therefore increasing the maximum volume of the resin to be supplied.

(17) Barium titanate can be used as high permittivity filler. Other fillers may include antimony trioxide, zinc borate, gypsum, wollastonite, clays, mica, quartz, silicon carbide, zirconium silicate, carbon black, synthetic zeolites and oxides e.g. of aluminium, magnesium, zinc and titanium oxides.

(18) The composition (B) can be loaded with a high amounts of filler, for example up to 85% by weight based on the total composition (B) weight (650 parts by weight per 100 parts by weight of the monomer (i)).

(19) The cable joints and the kit for preparing the same can be advantageously used for LS0H applications. In fact further to the advantages exposed above, the cable joint of the invention also solves another technical problem of the joint cable of the prior art. The known resin compositions containing flame retardant agent adapted for LS0H application have little or no adhesive performance. The use of urethane acrylate oligomers and epoxyacrylates oligomers as curing agent (iv) allows to incorporate flame retardant agent and have enhanced sealing capability (connected with a suitable adhesion of the composition to the cable joint parts.

(20) Flame retardant agent adapted for the composition of the invention can be selected from inorganic oxides and hydroxide, for example magnesium or aluminium oxides or hydroxides. A preferred zero halogen flame retardant agent according to the invention is alumina trihydrate. The composition of the inventions can be loaded zero halogen with a high amounts of flame retardant agent, for example up to 75% by weight based on the total composition (B) weight as in the case of alumina trihydrated as LS0H filler (corresponding to about 350 parts by weight per 100 parts of the monomer (i)).

(21) In the case a more rapid cure is desired, a catalyst accelerator may be further used. These kinds of additives are generally products of condensation, for example, between p-toluidine and ethylene oxide, also defined as PTE.

(22) Preferably the composition (B) of the invention is in a two-pack composition, a first pack containing the (meth)acrylate ester monomer (i), the curing agent (iv) and the optional curing accelerator, the second pack containing the filler and the radical catalyst, in order to avoid a premature polymerisation, before the composition is completely poured.

(23) The curing by polymerization of the composition of the invention can take place irrespective from the presence of light (including UV and IR irradiation). In view of the technical field of the invention where the composition should polymerize in a substantially closed environment—the joint box—a photocuring could not or could hardly be carried out even in the case of a transparent box, because the box material could anyway hinder the effect of the actinic radiation.

(24) The conventional compositions exhibit poor or absent adhesive property. The use of the curing additive according to the present invention in place of the acrylates taught by the prior art, for example PEG200 dimethacrylate, increases the adhesive properties, thus rendering not necessary the use of additional sealing mastics which are indeed indispensable, when using the conventional cross-linker to ensure adequate property and therefore insulation resistance.

(25) The following examples of the composition (B) of the kit of the invention are provided for illustrative but not limiting purposes.

COMPARATIVE EXAMPLE

Composition A

(26) The standard composition (in parts by weight) disclosed in EP 1070730 is as follows:

(27) TABLE-US-00001 IDMA (isodecylmethacrylate) 100 PTE (p-toluidine-thylene oxide) 1.2 PEG200DMA (polyethyleglycol200 dimethacrylate) 0.3 Silica Sand 400 Calcium Carbonate 150 Benzoyl Peroxide (20%) 20

(28) The liquid components (IDMA, PTE and PEG200DMA) are supplied by either Cognis or Evonik

(29) Silica sand is a C30 grade supplied by WBB Minerals and the calcium carbonate is Calmote AD from OMYA.

EXAMPLE 1-4

(30) In the following composition according to the invention, PEG200DMA was eliminated and replaced by Craynor CN976, supplied by Cray Valley (Sartomer Corporation; aromatic urethane diacrylate, mean molecular weight 5800) and the following compositions were prepared CN976 concentrations of 0.3, 3 and 5 parts per hundred parts IDMA.

(31) Compositions (parts by weight) according to the invention were prepared as from Table 1.

(32) TABLE-US-00002 TABLE 1 Composition Composition 1 Composition 2 Composition 3 4 IDMA 100 100 100 PTE 1.2 1.2 1.2 Craynor CN976 0.3 3.0 5.0 Silica Sand 400 400 400 Calcium Carbonate 150 150 150 Benzoyl Peroxide (20%) 20 20 20
Cold Flow Test:

(33) This test was carried out on Composition (A) and on Composition 1 of the invention according to the operating conditions described in French National Standard NF C33-010, Appendix G (1993).

(34) In order to meet the requirements of the above specification, there should be no evidence of material flow after heating at 100° C. Flow was detected with Composition A, but not in Composition 1 (the former containing 0.3 parts by weight of PEG200-dimethacrylate and the latter containing 0.3 parts by weight of urethane acrylate).

(35) The results obtained demonstrate the improvement in inhibiting cold flow of the new formulation even when containing low amounts of curing agent, if compared to that of the prior art.

(36) Compositions A, B and C in Table 1 of GB 2433511 (which advocates the use of reactive polybutadienes as tackifying additives) were evaluated by the cold flow test, too. All of these compositions showed evidence of flow.