Heat-shrinkable protective element

Abstract

A heat-shrinkable protective element having at least one protective layer is obtained from a polymeric composition having a polymer material, where the polymeric composition additionally has an electrically conducting filler having a BET specific surface of at least 100 m.sup.2/g according to Standard ASTM D 6556.

Claims

1. Heat-shrinkable protective element comprising: at least one protective layer obtained from a polymeric composition having a polymer material, wherein the polymeric composition additionally has an electrically conducting filler having a BET specific surface of at least 100 m.sup.2/g according to Standard ASTM D 6556 (2014), and wherein the protective layer is electrically insulating with an electrical conductivity of at most 1.10.sup.8 S/m, measured at 25 C. in direct current, and wherein the protective layer becomes a semiconducting element with an electrical conductivity greater than 1.10.sup.8 S/m once shrunk.

2. Protective element according to claim 1, wherein the electrically conducting filler has an aspect ratio of at least 10.

3. Protective element according to claim 1, wherein the electrically conductive filler has an aspect ratio of at least 100.

4. Protective element according to claim 1, wherein the electrically conducting filler is a carbon-based filler.

5. Protective element according to claim 1, wherein the electrically conducting filler is selected from the group consisting of carbon blacks, carbon fibers, graphites, graphenes, fullerenes, carbon nanotubes and one of their mixtures.

6. Protective element according to claim 1, wherein the polymeric composition has at most 30.0 parts by weight of electrically conducting filler and preferably at most 10.0 parts by weight of electrically conducting filler, per 100 parts by weight of polymer material.

7. Protective element according to claim 1, wherein the polymer material has at least one olefin polymer.

8. Protective element according to claim 7, wherein the olefin polymer is a copolymer of ethylene and vinyl acetate (EVA).

9. Protective element according to claim 1, wherein said protective element is shrinkable and wherein the protective layer is noncrosslinked.

10. Shrunken protective element obtained from the protective element according to claim 1, wherein the protective layer is semiconducting in the shrunken state with an electrical conductivity greater than 1.10.sup.3 S/m, measured at 25 C. in direct current.

11. Process for the manufacture of a protective element according to claim 1, said protective element being heat-shrinkable, said process comprising the steps of: i. hot drawing the polymeric composition; and ii. cooling, in its drawn state, the polymeric composition drawn in stage i.

12. Cable comprising: a shrunken protective element obtained from a protective element, that is heat shrinkable, defined according to claim 1.

13. Cable according to claim 12, wherein the protective layer is a semiconducting layer.

14. Process for the manufacture of a cable comprising: a shrunken protective element according to claim 12, said method comprising the steps of: a. positioning the protective element that is heat shrinkable around a cable, and b. heat treating the protective element positioned in stage a in order to form the shrunken protective element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention will become apparent in the light of the examples which follow with reference to the annotated figures, the said examples and figures being given by way of illustration and without in any way being limiting.

(2) FIG. 1 represents a diagrammatic view of a heat-shrinkable protective element according to the invention, positioned around electric cables, before and after heat treatment.

(3) FIG. 2 represents a diagrammatic view of a model test specimen for determining the electrical conductivity of a polymeric composition according to the invention as a function of the stages of manufacture of a heat-shrinkable protective element according to the invention.

(4) For reasons of clarity, only the elements essential for the understanding of the invention have been represented diagrammatically, this being done without respecting the scale.

DETAILED DESCRIPTION

(5) FIG. 1 represents a diagrammatic view of a heat-shrinkable protective element 20 according to the invention, positioned around electric cables 10a and 10b, before heat treatment (part a of FIG. 1) and after heat treatment (part b of FIG. 1). The shrinkable protective element 20 is more particularly here a joint surrounding the ends 10a and 10b of the two electric cables 10a and 10b. This joint makes it possible to electrically connect the first cable 10a to the second cable 10b.

(6) The shrinkable protective element 20 comprises a first protective layer 21 according to the invention and a second layer 22 different from the first layer, the first layer 21 surrounding the second layer 22.

(7) In the nonshrunken state (a) (before heat treatment) the first layer and the second layer of the shrinkable protective element 20 are both electrically insulating layers.

(8) When the protective element is shrunk (i.e., shrunken protective element 200) by heat treatment (b), the first protective layer 21 becomes a semiconducting layer and the second layer 22 remains electrically insulating.

(9) In addition, the shrunken protective element 200 substantially matches the shapes of the parts of the electric cables 10a and 10b which it covers.

(10) The first cable 10a and the second cable 10b represented diagrammatically in FIG. 1 respectively comprise an elongated electrical conductor 2a, 2b surrounded by a first semiconducting layer (not represented), an electrically insulating layer 4a, 4b surrounding the first semiconducting layer 3a, 3b and a second semiconducting layer 5a, 5b surrounding the electrically insulating layer 4a, 4b.

(11) Typically, at the said end 10a, 10b of each electric cable 10a, 10b, the second semiconducting layer 5a, 5b is at least partially stripped in order for the electrically insulating layer 4a, 4b to be at least partially positioned inside the protective element 20, 200, without being covered by the second semiconducting layer 5a, 5b of the electric cable.

(12) Conventionally, the electric cables 10a and 10b can be connected to one another by virtue of an electrical connector (not represented).

(13) Finally, the ends of the shrunken protective element 200 can be respectively surrounded by a semiconducting tape 23. Thus, the first protective layer 21 and the second semiconducting layers 5a and 5b are in physical contact via the said semiconducting tape 23.

(14) Of course, the embodiment described in FIG. 1 is not limiting. In another embodiment, the shrinkable protective element 20 can comprise only the first protective layer 21 according to the invention: the shrinkable protective element 20 is thus the protective layer 21 in accordance with the invention. For this reason, the first protective layer 21 of the shrunken protective element 200 substantially matches the shapes of the parts of the electric cables 10a and 10b which it covers. The first protective layer 21 is thus in direct physical contact with the second semiconducting layers 5a and 5b of the electric cables 10a and 10b. In this case, it is not necessary to position the said semiconducting tapes 23.

EXAMPLES

(15) 1. Polymeric Composition According to the Invention

(16) A polymeric composition I1 according to the invention, the amounts of the compounds of which are expressed in parts by weight per 100 parts by weight of polymer material, is described in Table 1 below.

(17) The polymer material in Table 1 is composed solely of EVA.

(18) TABLE-US-00001 TABLE 1 Polymeric composition I1 Polymer material 100 Electrically conducting filler 5.3

(19) The origin of the compounds of Table 1 is as follows: Polymer material is a random copolymer of ethylene and vinyl acetate (EVA) having a melting point of 96 C., sold by ExxonMobil Chemical under the reference Escorene Ultra EVA UL00112, having 12% by weight of vinyl acetate groups; and Electrically conducting filler is multi-walled carbon nanotubes, sold by Arkema under the reference Graphistrength C100, having: a BET specific surface of approximately 250 m.sup.2/g according to Standard ASTM D 6556, a mean external diameter of 10 to 15 nanometers, measured by TEM, a length of 0.1 to 10 micrometers, measured by TEM, and an aspect ratio of the order of 100 to 1000.

(20) 2. Preparation of the Heat-Shrinkable Protective Element

(21) The polymeric composition I1 according to Table 1 is processed as follows.

(22) The polymer material is introduced into an internal mixer at a temperature of 110 C. The carbon nanotubes are added after complete melting of the polymer matrix. The composite obtained after homogenizing for 5 minutes is subsequently passed over a roll mill in order to optimize the dispersion and the distribution of the nanoparticles. The composite can furthermore be obtained by single-screw or also twin-screw extrusion.

(23) The composite is finally processed in the form of plaques with a thickness of 1 mm by hot compression at 130 C. for 10 minutes.

(24) H1-type test specimens with the shape and dimensions shown in FIG. 2 are cut out using a hollow punch, the test specimens having a thickness of 1 mm. The initial elongation LO of the test specimen (before it is drawn) is 15 mm.

(25) These test specimens will be used to evaluate the electrical properties of the polymeric composition of the invention and thus, by extension, the electrical properties of the heat-shrinkable protective element, during its manufacture.

(26) The test specimen will be prepared as follows.

(27) In a first stage i, the test specimen is drawn by 15 mm by virtue of a tensile testing device, under a temperature of 85 C. in a conditioning chamber: the elongation of the test specimen then becomes equal to 30 mm.

(28) As the composite of this example is not crosslinked (i.e., polymeric composition I1), the hot elongation under stress is carried out at 85 C. At this temperature, the material is softened but does not flow since the crystalline phase is not completely molten.

(29) More particularly, the heat treatment stage in i is carried out in an Adamel-Lhomargy conditioning chamber operated using a Eurotherm 808 temperature controller.

(30) The hot drawing stage in i is carried out using an Adamel-Lhomargy DY 32 tensile testing device (coupled to the conditioning chamber) with a pull rate of 3 mm/minute, the maximum elongation supported by the tensile testing device being 20 mm.

(31) Subsequently, in a second stage ii, the test specimen drawn in i is cooled to 25 C. over 60 minutes, in its drawn state.

(32) More particularly, stage ii is carried out in the drawn state of the test specimen in stage i, or in other words under the conditions of mechanical stresses of stage i. In order to do this, the test specimen remains placed between the jaws. In addition, the conditioning chamber of the tensile testing device is removed in order to be able to cool the test specimen to ambient temperature (25 C.).

(33) 3. Shrinking of the Heat-Shrinkable Protective Element

(34) The test specimen cooled in stage ii is subsequently heat treated in order for it to be shrunk into its initial elongation LO of 15 mm, the initial elongation which it had before stage i.

(35) This heat treatment is carried out for 10 minutes using a hot air gun (or paint burner) employed at its maximum power. The temperature obtained at the surface of the protective element by virtue of this heat treatment is greater than the melting point of the EVA making up the polymeric composition of Example I1; namely, it is of the order of 200 C.

(36) 4. Results

(37) The measurements of electrical conductivity at different stages of the manufacture of the test specimen, and also its elongation measurements, are collated in Table 2 below.

(38) The electrical conductivity is measured conventionally via the electrical resistance of the test specimen, according to the formula R=.Math.e/S, in which: R=Measured resistance of the material (), e=Distance between the two measurement points (m), S=Cross section of the test specimen between the two measurement points (m.sup.2), =Resistivity of the material, which is a function of the electrical conductivity according to the well-established formula =1/ ( is expressed in siemens per meter S.Math.m.sup.1 or in (.Math.m).sup.1).

(39) In the present invention, the electrical conductivity is measured according to Standard ISO 3915, in direct current and at 25 C., using a sourcemeter (source of current and voltage measurement) sold under the tradename 2611A by Keithley.

(40) The elongation is measured using a caliper.

(41) TABLE-US-00002 TABLE 2 Electrical Elongation conductivity Test specimen produced of the test of the test from the polymeric specimen, specimen, in composition I1 in mm S .Math. m.sup.1 Initial stage (before 15 <1.10.sup.8 stage i) After the heat treatment 30 <1.10.sup.8 in stage i After the cooling of 30 <1.10.sup.8 stage ii After the stage of 15 approximately shrinking by heat 1.10.sup.1 treatment