Electrical device comprising a cross-linked layer

Abstract

An electrical device includes at least one cross-linked layer obtained from a polymer composition that has: at least one polymer comprising one or more epoxy function(s), and at least one cross-linking agent. The cross-linking agent is selected from: a non-aromatic cyclic amine, an imidazole of formula (I)

##STR00001##

where R.sub.1 and R.sub.2 independently represent a hydrogen atom or a hydrocarbon group, R.sub.3 and R.sub.4 independently represent a hydrogen atom or a hydrocarbon group, or R.sub.3 and R.sub.4 form, together with the carbon atoms of the imidazole ring to which they are attached, a ring, with the imidazole being associated with a cross-linking co-agent having at least one reactive function capable of reacting with the epoxy function of said polymer, and, a mixture thereof.

Claims

1. Electrical device having at least one cross-linked layer obtained from a polymer composition comprising: at least one polymer comprising one or more epoxy function(s), and at least one cross-linking agent, wherein the cross-linking agent is selected from: a non-aromatic cyclic amine, an imidazole of formula (I) ##STR00004## wherein R.sub.1 and R.sub.2 independently represent a hydrogen atom or a hydrocarbon group, R.sub.3 and R.sub.4 independently represent a hydrogen atom or a hydrocarbon group, or R.sub.3 and R.sub.4 form, together with the carbon atoms of the imidazole ring to which they are attached, a ring, said imidazole being associated with a cross-linking co-agent comprising at least one reactive function capable of reacting with the epoxy function of said polymer, and a mixture thereof.

2. Device according to claim 1, wherein the device is an electrical cable comprising at least one elongated electrically conductive element, surrounded by said cross-linked layer.

3. Device according to claim 1, wherein the device is an electrical cable accessory, said accessory comprising at least said cross-linked layer.

4. Device according to claim 3, wherein the accessory is an electrical cable junction or termination.

5. Device according to claim 1, wherein the polymer comprises glycidyl ester groups.

6. Device according to claim 1, wherein the non-aromatic cyclic amine is a non-aromatic cyclic diamine.

7. Device according to claim 1, wherein the polymer composition comprises from 0.01 to 10.0 parts by weight of non-aromatic cyclic amine per 100 parts by weight of polymer(s) in the polymer composition.

8. Device according to claim 1, wherein the imidazole formula (I), R.sub.1 represents an alkyl group having 1 to 20 carbon atoms; R.sub.2 represents an alkyl group having 1 to 20 carbon atoms; and R.sub.3 and R.sub.4 represent hydrogen atoms.

9. Device according to claim 1, wherein the polymer composition comprises from 0.1 to 15.0 parts by weight of imidazole of formula (I) per 100 parts by weight of polymer(s) in the polymer composition.

10. Device according to claim 1, wherein the cross-linking co-agent comprises at least two reactive functions capable of reacting with the epoxy functions of said polymer.

11. Device according to claim 1, wherein the cross-linking co-agent comprises at least one reactive function selected from an anhydride function, a carboxyl function and an amine function.

12. Device according to claim 1, wherein the cross-linking co-agent is selected from an amino acid, a carboxylic acid, an anhydride, and a mixture thereof.

13. Device according to claim 1, wherein the non-aromatic cyclic amine may be associated to at least one cross-linking co-agent comprising at least two reactive functions capable of reacting with the epoxy function of the polymer, said at least one cross-linking co-agent being chosen among an amino acid, a carboxylic diacid, an organic compound in form of a polymer comprising at least two carboxylic functions, and one of their mixtures.

14. Device according to claim 13, wherein the carboxylic diacid is the dodecanedioic acid.

15. Device according to claim 1, wherein the polymer composition comprises from 0.1 to 15.0 parts by weight of cross-linking co-agent per 100 parts by weight of polymer(s) in the polymer composition.

16. Device according to claim 1, wherein the polymer composition further comprises at least one flame-retardant filler.

17. Device according to claim 1, wherein the cross-linked layer is an electrically insulating layer.

18. Device according to claim 1, wherein the cross-linked layer is a semiconductor layer.

19. Device according to claim 1, wherein the device comprises a first semiconductor layer surrounding the elongated electrically conductive element, an electrically insulating layer surrounding the first semiconductor layer, and a second semiconductor layer surrounding the electrically insulating layer, the cross-linked layer being at least one of these three layers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0157] Further features and advantages of the present invention will appear in the light of the description of a non-limiting example of an electrical cable according to the invention made with reference to the figures.

[0158] FIG. 1 shows a schematic cross-sectional view of an electrical cable according to a preferred embodiment in accordance with the invention.

[0159] FIG. 2 shows a schematic view of an electrical device according to the invention, comprising a junction in longitudinal section, this junction surrounding the end of two electrical cables.

[0160] FIG. 3 shows a schematic view of an electrical device according to a first variant of the invention, comprising a termination in longitudinal section, this termination surrounding the end of a single electrical cable.

DETAILED DESCRIPTION

[0161] For the sake of clarity, only the elements essential for the understanding of the invention have been represented schematically, without respect to scale.

[0162] The medium- or high-voltage power cable 1, shown in FIG. 1, consists of an elongated central conductive element 2, in particular made of copper or aluminium. The power cable 1 further comprises several layers arranged successively and coaxially around this conductive element 2, namely: a first semiconductor layer 3 known as the inner semiconductor layer, an electrically insulating layer 4, a second semiconductor layer 5 known as the outer semiconductor layer, a metallic earthing and/or protective shield 6, and an outer protective sheath 7.

[0163] The electrically insulating layer 4 is an extruded and cross-linked layer obtained from the polymer composition according to the invention.

[0164] The semiconductor layers are also extruded and cross-linked layers, which may be obtained from the polymer composition according to the invention.

[0165] The presence of the metal shield 6 and the outer protective sheath 7 is preferred, but not essential, as this cable structure as such is well known to the skilled person.

[0166] FIG. 2 shows a device 101 comprising a junction 20 partially surrounding two electrical cables 10a and 10b.

[0167] More particularly, the electrical cables 10a and 10b include an end 10a and 10b, respectively, intended to be surrounded by the junction 20.

[0168] The body of the junction 20 comprises a first semiconductor element 21 and a second semiconductor element 22, separated by an electrically insulating element 23, said semiconductor elements 21, 22 and said electrically insulating element 23 surround the ends 10a and 10b respectively of the electrical cables 10a and 10b.

[0169] This junction 20 allows the electrical connection of the first cable 10a to the second cable 10b, in particular thanks to an electrical connector 24 arranged in the centre of the junction 20.

[0170] At least one of the elements selected from the first semiconductor element 21, the second semiconductor element 22 and said electrically insulating element 23 may be a cross-linked layer as described in the invention.

[0171] The first electrical cable 10a comprises an electrical conductor 2a surrounded by a first semiconductor layer 3a, an electrically insulating layer 4a surrounding the first semiconductor layer 3a, and a second semiconductor layer 5a surrounding the electrically insulating layer 4a.

[0172] The second electrical cable 10b comprises an electrical conductor 2b surrounded by at least a first semiconductor layer 3b, an electrically insulating layer 4b surrounding the first semiconductor layer 3b, and a second semiconductor layer 5b surrounding the electrically insulating layer 4b.

[0173] These electrical cables 10a and 10b may be those described in the present invention.

[0174] At said end 10a, 10b of each electrical cable 10a, 10b, the second semiconductor layer 5a, 5b is at least partially stripped so that the electrically insulating layer 4a, 4b is at least partially positioned inside the junction 20, without being covered by the second semiconductor layer 5a, 5b of the cable.

[0175] Inside the junction 20, the electrically insulating layers 4a, 4b are in direct physical contact with the electrically insulating element 23 and the first semiconductor element 21 of the junction 20. The second semiconductor layers 5a, 5b are in direct physical contact with the second semiconductor element 22 of the junction 20.

[0176] FIG. 3 shows a device 102 with a termination 30 surrounding a single electrical cable 10c.

[0177] More particularly, the electrical cable 10c has an end 10c, intended to be surrounded by the termination 30.

[0178] The body of the termination 30 comprises a semiconductor element 31 and an electrically insulating element 32, said semiconductor element 31 and said electrically insulating element 32 surround the end 10c of the electrical cable 10c.

[0179] At least one of the elements selected from the semiconductor element 31 and the electrically insulating element 32 may be a cross-linked layer as described in the invention.

[0180] The electrical cable 10c comprises an electrical conductor 2c surrounded by a first semiconductor layer 3c, an electrically insulating layer 4c surrounding the first semiconductor layer 3c, and a second semiconductor layer 5c surrounding the electrically insulating layer 4c.

[0181] This electrical cable 10c may be the one described in the present invention.

[0182] At said end 10c of the electrical cable 10c, the second semiconductor layer 5c is at least partially stripped so that the electrically insulating layer 4c is at least partially positioned inside the termination 30, without being covered by the second semiconductor layer 5c of the cable.

[0183] Inside the termination 30, the electrically insulating layer 4c is in direct physical contact with the electrically insulating element 32 of the termination 30. The second semiconductor layer 5c is in direct physical contact with the semiconductor element 31 of the termination 30.

EXAMPLES

[0184] Tables 1 to 3 below list filled polymer compositions intended to be cross-linked, the amounts of which are expressed in parts by weight per hundred parts by weight of polymer(s) in the polymer composition.

[0185] Compositions C1 to C4 are comparative polymer compositions, and compositions 11 to 111 are polymer compositions in accordance with the invention.

[0186] These compositions comprise 100 parts by weight of a polymer P in accordance with the invention.

TABLE-US-00001 TABLE 1 Polymer compositions C1 C2 I1 I2 I3 I4 I5 Polymer P 100 100 100 100 100 100 100 Flame-retardant filler 140 140 140 140 140 140 140 Additives 9 9 9 9 9 9 9 Cross-linking agent 1 0 0 1.00 0 1.00 1.00 1.00 Cross-linking agent 2 0 0.50 0 0.50 0 0.50 0.50 Cross-linking co-agent 1 0.70 0 0 0.70 0.70 0.70 0 ts2 expressed in minutes 11.59 8.33 2.29 3.85 1.98 1.83 2.08 t90 expressed in minutes 42.48 36.10 20.72 23.11 21.38 16.39 14.50 M.sub.H M.sub.L expressed in dN .Math. m 4.84 5.37 5.64 6.44 5.98 6.00 5.73

TABLE-US-00002 TABLE 2 Polymer compositions C2 C3 I6 I7 I8 Polymer P 100 100 100 100 100 Flame-retardant filler 140 140 140 140 140 Additives 9 9 9 9 9 Cross-linking agent 1 0 0 0 1.00 1.00 Cross-linking agent 2 0.50 0 0.50 0 0.50 Cross-linking co-agent 2 0 3.15 3.15 3.15 3.15 ts2 expressed in minutes 8.33 3.26 1.56 1.55 t90 expressed in minutes 36.10 54.14 9.15 6.45 6.20 M.sub.H M.sub.L expressed 5.37 5.64 5.85 6.92 6.64 in dN .Math. m

TABLE-US-00003 TABLE 3 Polymer compositions C2 C4 I9 I10 I11 Polymer P 100 100 100 100 100 Flame-retardant filler 140 140 140 140 140 Additives 9 9 9 9 9 Cross-linking agent 1 0 0 0 1.00 1.00 Cross-linking agent 2 0.50 0 0.50 0 0.50 Cross-linking co-agent 3 0 5.00 5.00 5.00 5.00 ts2 expressed in minutes 8.33 37.79 3.18 2.03 2.06 t90 expressed in minutes 36.10 53.57 16.32 11.75 11.55 M.sub.H M.sub.L expressed 5.37 3.08 8.64 9.82 9.09 in dN .Math. m

[0187] The origin of the compounds in Tables 1 to 3 is as follows: [0188] Polymer P is a copolymer of ethylene, vinyl acetate, glycidyl acrylate and glycidyl methacrylate (GMA), marketed by Denka under the name Denka ER 5300; [0189] Flame-retardant filler is a metal hydroxide of the aluminium trihydroxide type; [0190] Additives are processing agents; [0191] Cross-linking agent 1 is a non-aromatic cyclic amine, in particular 1,4-diazabicyclo[2.2.2]octane, marketed by Merck under the name 1,4-diazabicyclo[2.2.2]octane (CAS No. 280-57-9); [0192] Cross-linking agent 2 is an imidazole, in particular 1,2-dimethylimidazole marketed by Alfa Aesar under the name 1,2-dimethylimidazole (CAS No. 280-57-9); [0193] Cross-linking co-agent 1 is an amino acid, in particular amino-11-undecanoic acid, marketed by SIGMA-ALDRICH under the name amino-11-undecanoic acid (CAS No. 2432-99-7); [0194] Cross-linking co-agent 2 is a dicarboxylic acid in the form of a polymer, in particular polyethylene glycol diacid, marketed by Merck under the name Polyethylene glycol diacid 600; and [0195] Cross-linking co-agent 3 is a dicarboxylic acid, which is not in the form of a polymer, in particular dodecanedioic acid, marketed by SIGMA-ALDRICH under the name dodecanedioic acid (CAS No. 693-23-2).

[0196] The polymer compositions C1 to C4 and I1 to I11 were cross-linked under the same conditions.

[0197] In a first step, the compositions are prepared as follows: a master batch is prepared using an internal mixer with a volume of 1600 cm.sup.3, with preheating to 60 C. and direct incorporation of the polymer P and part of the flame-retardant filler (about one third) to facilitate mixing.

[0198] Then the rest of the flame-retardant filler is added with the additives at a temperature sufficient to ensure homogeneous mixing of the composition (i.e. softening of the polymer P) without reacting the epoxies of the polymer P. By way of example, this temperature may be between 80 and 110 C., and may in particular be 105 C.

[0199] The addition of the cross-linking agent and/or cross-linking co-agent is then carried out at a temperature so as not to trigger cross-linking, such as for example at 40 C., using a roller mixer, then the polymer composition thus obtained is calendered to 3 mm to form a 3 mm-thick plate, and rheometric tests can then be carried out with a rheometer of the MDR2000 type marketed by Alpha Technologies.

[0200] In a second step, the cross-linking of the polymer composition is monitored by the rheometer for 60 min at 180 C. with an oscillation of 0.5.

[0201] Tables 1 to 3 also show the results obtained after cross-linking of polymer compositions C1 to C4 and I1 to I11. These results relate to the onset of cross-linking (ts2) of the compositions, the cross-linking time (t90) of the compositions, and the cross-linking density (M.sub.H-M.sub.L) of the compositions.

[0202] The ts2 corresponds to the time after which, at a given measurement temperature, a value of M.sub.H-M.sub.L=2 dN.Math.m is obtained. It is determined according to the standard ISO 6502 (2018) as described in the present invention. The measurement temperature for the values of the polymer compositions is 180 C.

[0203] The t90 is the time after which 90% of the M.sub.H value measured with the MDR is obtained at a given temperature, this temperature in the examples being 180 C. It is determined according to the standard ISO 6502 (2018) and may advantageously be less than 30 min, preferably not more than 25 min, preferably not more than 20 min, and particularly preferably not more than 15 min.

[0204] The cross-linking density is given by the measured value of M.sub.H-M.sub.L according to the standard ISO 6502 (2018) with a moving die rheometer (MDR). This value is expressed in dN.Math.m and represents the difference in torque measured by the moving die before and after complete formation of the cross-linking network in the polymer composition. The denser the three-dimensional network formed during cross-linking, the higher the M.sub.H-M.sub.L value.